fundementals questions

describe the structure and function of carbohydrates including starch, cellulose and glycogen.

carbohydrates are formed of carbon hydrogen and oxygen. they can be polymers or monomers.

carbohydrates are used as feul to produce ATP, as building material suppling carbin for the synthesis of DNA and as structure forming glycoproteins and glycolipids

1 unit=monosaccheride, 2=di, 3-10=oligo, 10+=poly.

monosacherides include glucose and fructose.

polysaccherides include starch, cellulose and glycogen which are all polymers of glucose.

starch has alpha 1-4 glycosidic bonds and is used as storage in plants

cellulose has beta 1-4 glycosidic bonds, this makes every other molecules flipped and means it can only be digested by ruminants (fibre for non-ruminants), it is used as storage in plants.

glycogen has both alpha 1-4 and 1-6 glycosidic bonds that give it a branched structure that makes it easier to break down, it is used as storage in animals.

describe the structure and function of lipids, including triglyerides, phospholipids, sterols and glycolipids and the importance of fatty acids.

lipids are high energy yeilding compounds containing mainly carbon, hydrogen and oxygen that are insoluble in water.

they are used as an energy source, are the main componant of cellular membranes , act as insulation and are used in the synthesis of hormones and vitamins

triglycerides are formed of a glycerol molecule and 3 fatty acids, they are the main form found in the body and diet. their structure means they are hydrophobic so are insoluble in water.

phospholipids are formed of glycerol, 2 fatty acids and a modified phosphate group. they are ampiphatic as they have both hydrophobic(fatty acid tail) and hydrophilic(phosphate) sections. phospholipids are the main componant of cellular membranes, they also act as emulsifiers during digestion and are a component of bile.

sterols such as cholestrol add structuure to cell membranes and are used for the synthesis of sex hormones, vitamin D and bile salts. they are made of interlinked rings of carbon with side chains of carbon, hydrogen and oxygen.

glycolipids are lipids with a carbohydrate group attached they are involved in protection, immunity, transplant compatibility and cell adhesion.

fatty acids are formed of a long carbon chain with a carboxyl group on one end this makes the ampiphatic. the chain can be saturated meaning it has no double bonds or unsaturtaed meaning double bonds are present this effects the properties of the molecule with a higher degree of saturation increasing mb/bp and intermoleular forces, length of the chain also effects this. fatty acids are essential for the function of body systems and can be essential (non synthisisable) or non essential (synthesisable). fatty acids are never found in a free state in nature

describe the structure and function of nucleic acids and the structure of DNA

nucleic acids are formed of a sugar (ribose or deoxyribose) a phosphate group and a base.

ribose is the sugar in RNA, deoxyribose is the sugar in DNA and lacks an oxygen on the 2nd carbon.

purine bases are A and G, pyrimidine bases ate T, U and C. purine bases always bind to pyrimidine bases via hydrogen bonds and vis ver a, G,C is a tripple bond A,T is a double bond.

the sugar phosphate backbone is formed by phosphodiester bonds between C5 (phosphate group) and C3 (OH). this forms the 5’ and 3’ ends.

the 2 strands are linked between bases by hydrogen bonds and form a double helix shape. this is then wrapped around histone octomers in approx 200 base fragments to form nucleosomes that are compacted into chromatin to form chromosomes

describe the structure and function of proteins

proteins are polymers of amino acids joined by peptide bonds.

amino acids have an amine NH2, Carboxyl (COOH) and R-group that determines the properties of the amino acid the R groups of the amino acids in a protein determine its structure and function.

amino acids an be a source of energy by forming ketone bodies or as a substrate of gluconeogenesis.

the primary structure of a protein is the sequencee of amino acids as coded by the gene. the secondary structure isformed by hydrogen bonding between the backbone to form alpha helixs and beta pleated sheets. tertiary structure is the final folxing held together by intermolecular forces, quaternary structure is the interaction between subunits in multi-subunit proteins.

functions of proteins include, enzymes, receptors, transport, hormones, structure, immune system and synthesis of other molecules.

Describe the structure and function of the nucleus

the nucleus contains DNA and is the site of DNA replication and transcription and rRNA synthesis. it is formed of the nuclear membrane which has pores to allow for the transport of molecules in and out of the nucleus. the nucleoplasm that contains genetic information and the nucleosis which is the site of rRNA synthesis

describe the structure and function of ribosomes.

ribosomes are a complex of rRNA and proteins formed of 2 subunits, one small and one large. they are the site of protein synthesis and can either be free (in cytosplam) or bound (attached to ER)

describe the structure and function of the endoplasmic reticulm

membrane tubules continues with the nucleus, it is formed of cisternae (flatened membrane bound sacs). it consists of smooth ER which as no ribsomes attcahed and is the site of lipid synthesis and rough ER which has ribosomes attched and is the site of secretory and membrane protein synthesis. when these polypeptides are synthesised the enter the lumen which is the hollow space in the middle of the tubules before it is packaged into vesicles and transported to the golgi apparatus

describe the structure and function of the golgi apperatus

the golgi apperatus is formed of cisternae and is the site of post-translational modification of proteins. the cis face of the golgi apparatus faces the ER and recives vesicles, the trans face fcaes the plasma membranes and exports vesicles, these can be secretory vesicles that then exit the cell via exocytosis.

proteins pass through the golgi from cis to trans and undergo post translational modifications such as, addition of disulfide bonds, addition and processing of carbohydrate groups, specific proteolytic cleavages(not all are activated as this could cause damage) and assemebly of quaternary structure. it also ensure the proteins are correctly folded with any incorrectly folded proteins being retained by the golgi.

describe the structure and function of mitochondria

mitochondria are the site of metabolic reactions such as, oxidative phosphorylation (formation of ATP after electon transport chain), the electron transport chain and krebs cycle (citric acid cycle). it has an inner(site of electron transport chain) and outer membrane with space inbetween (site of krebs cycle).

the mitochondria also has a small circular genome mtDNA that contains approx 37 genes.

describe the structure and function of lysosomes and peroxisomes

lysossomes are membrane bound orgenelle formed of a lipid bilayer containing hydrolase enzymes to degrade proteins, nuclaic acids, carbohydrates an lipids. they have an acidic pH for the enzymes to work.

peroxisomes are formed of a single lipid layer and contain oxidases and catalase enzymes. they break down fatty acids and harmful substances via beta oxidation, this process produces hydrogen peroxide which is then broken down by catalase.

describe the structure and function of the cytoplasm and cytoskeleton

the cytosplams is everything within the cell

the cytosol is the fluid in the cytoplasm, it is the site of metabolic reactions.

the cytoskeleton provides structure and support to the cell, anchors orgenelles and allows for movement is is formed of, microfiliments made of actin that give the cell flexablility and can be modified buring cell movement for migration and endo/exo cytosis (the are easily polymersied). microtubules formed of tublin that give shape and strucute to the cell and attach to chromosomes during mitosis. and intermediate filements that are mainly structural

describe the structure of the plasma membrane.

the plasma membrane is formed of phospholipids and proteins in an approximately 50/50 ratio. other cellular membranes have a different protein to phospholipid ratio such as the mitochondrial membrane that has more proteins to allow for ATP synthesis. the lipids in the membrane are predominately phospholipids with some cholesterol and glycolipids.

the phospholipis form a bilayer with the hydrophillic heads facing outwards and the hydrophillic tails facing inwards, this creates a selectively permeable barrier across the membrane.

proteins within the membrane can be intergral, have hydrophobic and phillic sections and are embedded in membrane so hard to remove or peripheral, hydrophillic interact with the surface of the membrane and are easier to remove.

comment on the dynamic nature of the plamsa membrane and factors that effect its rigidity

membranes are dynamic and constantly moving factors effecting membrane rigidity include length of fatty acid chain, longer chain means a more rigid membrane, saturation of fatty acids, saturated fatty acids give a more rigid membrane and cholestrol content, more cholestrol gives a more rigid membrane.

phospholipids move within the membrane, they can bob up and down, rotate on the spot and move within their plane of the bilayer (lateral diffusion) movement to the other side of the bilayer (flip flop) is very rare and only occurs with the aid of enzymes.

explain the diffrent ways molecules can travel across the plasma membrane

molecules can move across the membrane via diffusion, a passive process that can be facilitated with specific transmembrane proteins. this can be regulated via gated channels. active transport which uses ATP to move molecules against their concentration gradient using specific transporter proteins. endo/exocytosis that inolve the remodelling of the membrane to engulf or expel molecules.

describe the different types of cells in terms of proliferate ability

not all cells divide all the time.

labile tissues are cells that are continuously dividing, these include skin and intestinal epithelium cells.

stable tissue can divide in response to stimulus, they exist in quiescence a temporary state of cell arrest (G0). these include liver cells

permanent tissues are non-dividing and are terminally differentiated, they are highly specialised cells that can never divide again. these include neurons, skeletal and cardiac muscle.

briefly describe the stages of the cell cycle

G1 is a growth phase where the cell prepares for DNA replication, S phase is where DNA replication occurs, G2 is a growth phase where the cell prepares for mitosis, M phase is where mitosis and cytokenesis occurs. G1, S and G2 phases are collectively known as interohase.

G0 is a non-dividing state enterd into from G1, this can be temporary (quiescence) or permanent.

describe the role of mitogens in control of the cell cycle

mitogens are growth factors that trigger the start of the cell cycle by stimulating the synthesis of cyclin D. cells only respond to mitogens during G1, if no mitogens are present the cell will enter G0.

describe the role of cyclins and CDKs in the control of the cell cycle.

different cyclins are produced and degraded throughout the cell cycle in a phased manner. CKDs are always present but can only be activated when there complementary cyclin is present.

cyclins form a complex with CDKs activating them and allowing for the phosphorylation of proteins involved in cell cycle progression.

state the roles of p16 and p21

p16 and p21 are CDK inhibitors that prevent the progression of the cell cycle by preventing phosphorylation of proteins in G1

state the importance of G1 checkpoints

prevent cells with mutated or damaged DNA from dividing.

describe the G1 restriction point

pRb is assocaited with E2F transcription factor. when cyclin D is synthesised (due to presence of mitogens) and activates CDK 4 the complex phosphorlates pRb, this causes a change in conformation that causes E2F to dissocaite. E2F then binds to DNA stimulating the transcription of genes involved in DNA replication.

describe the G1 DNA damage checkpoint

DNA damage is recognised my sensor cells, this cause p53 to stabalise within the cell. this will then trigger cell death via apoptosis, or cell arrest (entry to G0) so that DNA can be repaired. Entry into G0 is caused by p53 triggering p21 whihc inhibits CDKs

state the role and properties of p53

p53 is a tumour suppressor that has a very short half life in normal cells but stabilises under genotoxic stress.

describe the state of senescence including the senescent associate secretory phenotype

senescence is an intrinsically programmed limit to cell proliferation, when senescence is reached cell will not divide again but is still metabolically active.

senescent cells, resist apoptosis, become larger and express p16 a CDK inhibitor that prevents the cell cycle form occurring.

when a cell enters senescence its secretosome changes, the cell starts to secrete inflammatory substances. these can be tumour suppressant or tumourgenic.

describe the structure of telomers and their role in the regulation of cell senescence and how stem cells are able to divide indefinatly.

telomers are non-coding, single stranded sections at the end of DNA strands that protect the ends and prevent them from sticking together. telomers are formed of TTAGGG repeated many times, these fold over to cap the DNA strand.

when DNA is replicated the prescence of primers on the lagging stand cause a section of the telomere to be lost, when telomers are degraded to a critical level, this stimulates p53 and the persistent response maintains senescence.

stem cells express the enzyme telomerase that rebuilds telomers preventing them from degrading and meaning the cell can divide indefintly

describe the process of apotosis

apoptosis is the process of controlled cell death used in development and to maintain homeostasis, it is triggered when the balance between survival and death signals tips to death.

during apoptosis DNA is cut by DNAases that cuts DNA its fragments of histones. the cytoplasm contracts and the membrane blebs, all organelles are packaged into vesicles known as apoptotic bodies with phosphatidylserine on the surface, these are then recognised and engulfed and digested by phagocytes.

caspase are a class of enzymes that trigger morphological changes in apoptotic cells by activating digestive enzymes such as protases and nucleases

describe the process of necrosis

necrosis is an unorganised form of cell death triggered by cell injury.

during necrosis chromatin clumps together, the cytoplasm expands and the cell undergoes lysis (membrane bursts) normally triggering an immune response. no caspases aree involved in the process

describe the structure of a nueron

the cell body of a neuron contains the nucleus and is where information is integrated and metabolic activity occurs, coming off of the cell body are dendrites and an axon. dendrites are how the cell receives information, the axon is how the cell transfers information. the axon hillock is where the axon meets the cell body and is the origin of action potentials, these then travel down the axon to terminals where information is transferred between cells via synapses. axons can be mylinated or non-mylinated mylinated neurons are wrapped in insulating proteins that allow for faster transmission over long distances.

describe breifly how a neural communication system is structured

a receptor senses a change in the environment, this sends a signal to the integrating centre which then sends out an action signal to the effector generating a response.

explain the differnce between volentary and involentary controls

voluntary controls are ones we are aware of eg. writing. involuntary controls are used to achieve homeostasis, they are achieved via reflexes which are involuntary, unpremeditated unlearned responses.

describe the central and periferal nervous systems

the central nervous system is made up of the brain and the spinal chord, it contains internuerons and is where information is processed.

the peripheral nrevous system consists of afferent neurons that are connected to receptors and feed information into the CNS and efferent neurons which are connected to effectors and transfer info out of the CNS.

the responses produced by effectors can be somatic (conscious) or autonomic (unconscious).

not all neural pathways contain an interneuron eg. mono-synaptic reflexes.

describe the membrane potential and how it is maintained

the membrane potential exists due to there being different concentrations of ions and other charged particles inside and outside the cell. the membrane potential stores electrical energy across the membrane allowing for electrical transmission in excitable cells

outside the cell there are higher concentrations of Na⁺, Ca²⁺ and Cl⁺ and inside the cell there is a high concentration of K⁺ these concentrations are maintained by the sodium potassium pump and membrane permeability for different ions. changes in membrane permeability cause changes in the membrane potential

state and explain the values of the resting membrane potential and equilibrium potentials of Na and K

the resting membrane potential is -70mV, this means the inside of the cell is more negative than the outside, this is due to there being more ‘leaky’ K⁺ channels.

the equilibrium membrane potential is the membrane potential reached when the chemical (concentration) and electrical gradients of an ion are balanced. for Na⁺ ions it is at +60mV and for K⁺ ions it is -90mV.

describe the different types of ions channels in cells

sodium potassium pump- maintains a steep sodium potassium gradient via active transport and the hydrolysis of ATP.

channel proteins, allow the passive movement of ions down there concentration gradeints.

‘leaky’ channels are always open and set the base permeability of an ion.

regulated channels open and close in response to specific stimuli, voltage gated, in response to changes in ion concentrations, ligand gated, in response to the binding if a signalling molecule, mechanically gated, in response to changes in pressure. regulated channels can be used by excitable cells to modify their membrane potential

describe a graded potential

a graded potential is a small change in membrane potential bellow the threshold potential. it occurs when regulated channels (ligand or mechanical) open for a short period of time allowing ions to enter/exit the cell but not for long enough to trigger voltage gated channels. is Na⁺ channels are open the membrane will depolarise is K⁺ channels open the membrane will hyperpolarise, these ions will then disperse through ‘leaky’ channels restoring the resting potential. as not many ions enter/exit the cell graded potentials have decremental transfer and do not influence neighbouring areas of the membrane.

a larger stimulus will cause a larger graded potential (it is a graded potential until it goes over threshold, graded potentials can also accumulate to form an action potential)

describe an action potential

an action potential occurs when a graded potential goes over the threshold. this triggers the opening of voltage gated Na⁺ (fast opening) and K⁺ (slow opening) channels. the fast opening Na⁺ channels cause an influx of Na⁺ ions into the cell depolarising the membrane, these channels then inactivate (via a internal protein) and the slow opening K⁺ channels open causing K⁺ ions to exit the cell repolarising the membrane. when the resting membrane is reached the channels close but the slow response time of the K⁺ channels causes the membrane to hyperpolarise. the resting membrane potential is then restored by the sodium potassium pump.

during depolarisation and repolarisation no new action potentials can be produced this is the absolute refractory period. after the channels close and the membrane is hyperpolarised a new action potential can be triggered but it requires more energy this is the relative refractory period.

action potentials are an all or nothing response and are all the same size so information is coded based on frequency, Action potentials are fired for as long as the graded potential is over threshold. A larger stimulus = higher frequency, this is because a larger stimulus produces a larger graded potential so can overcome hyperolarisation more quickly

explain how action potentials move

the entering Na+ ions create current loops to to adjacent areas of the membrane as there are many ions entering this brings the adjacent area of membrane up to threshold triggering an action potential, creating more current loops and so forth. the action potential will move out in all areas from the point of stimulation (normally the axon hillock) over the cell body where it has little effect and along the axon to the terminal and does not degrade over time as it is an all or nothing response. the previous area of membrane is not re-stimulated as it is in the absolute refractory period.

explain the structure of myelinated nerve cells and how they allow for quicker transfer of action potentials and the other way transfer can be increased.

the axons of myelinated nerve cells are wrapped in sections of fibres. the fibres prevent adjacent areas of the membrane from being polarised so instead the action potential jumps to the next gap between fibres (node of Ranvier). this means that less action potentials have to be produced making transfer significantly quicker and more energy effeicent.

the speed of transfer can also be increased by increasing the diameter of the axon, but this has a much smaller effect.

sate the different types of neural system

convergent system, this is where many cells influence the activity of 1/few.

divergent system, this is where 1 cell influences the activity of many

describe how information is transferred at an electrical synapse

electrical synapses are formed of channels that connect 2 cells and allow for the direct transfer of ions and there for current flow between cells. this means an action potential can be transferred directly between 2 cells information can be transferred both ways, these types of cells are found in brain and muscle tissue.

describe how information is transferred at chemical synapses.

the action potential travels along the axon the to synapse of the pre-synaptic cell and causes the opening of Ca²⁺ channels causing Ca²⁺ ions to enter the cell this causes the migration of neurotransmitter containing vesicles to the cell membrane causing the release of neurotransmitters into the cleft between the pre and post synaptic cells. the neurotransmitters then bind to ligand gated ion channels or other receptors on the post-synaptic cell causing a graded potential to be produced.

an action potential in the pre-synaptic cell does not cause and action potential in the post synaptic cell, to produce one the post synaptic cell must be repeatedly stimulated.

in order for tranfer of new information the neurotransmitters must be cleared from the cleft, this can be done via, degradation by enzymes, re-absorption into the pre-synaptic cell or via diffusion away from the receptor

state the ways that transfer of information between excitable cells can be effected by disease or drugs

the pre-synaptic cell can be effected by Ca²⁺ concentrations, the availability of neurotransmitters and the availability of enzymes, they can also be externally regulated.

the post-synaptic cell can be effected by the concentration of neurotransmitters in the cleft, receptor concentration and function, neurotransmitter agonist and antagonists.

local anaesthetic disrupts neurotransmitter binding preventing signals from passing between cells.

explain how disparate information is intergrated by a single excitable cell

signals coming into a cell can be excitory (depolarising Na) or inhibitory (hyperpolarising K). In order for a response to occur multiple excitory signals must be recieved (summation), inhibitory signals increase the number of excitory signals needed by increasing the graded potential needed to reach threshold.

temporal summation is when many signals come from the same cell. spacial summation is when signals come from different cells at the same time. spacial and temporal summation can combine to create a greater response.

the closer a signal is to the axon hillock the greater effect it will have on the cell.

describe the role of receptors and state the different types

receptors measure signals and convert them into action potentials, they are specialised but not exclusive. receptors are very sensitive systems a small increase in stimulation gives a large change in membrane potential.

mechanoreceptor, senses pressure. thermoreceptor senses temperature, these can be internal or external, electromagnetic receptor senses light, nociceptor senses pian/damaged tissue, chemoreceptors measure chemicals.

describe how the pacium corpsical mechanoreceptor produces an AP.

the receptor is surrounded by a series of membranes with fluid in between, when pressure is applied it distorts the membranes causing mechanically gated ion channels on the receptor to open generating an receptor potential which brings the fist node up to AP.

define adaptation and state the different forms.

adaptation is the decrease in a neural response despite continued application of a stimulus. it makes responses more effective by decreasing noise.

fast and complete adaptation, there is a peak at the initial stimulation then response quickly goes back to 0 and there is another peak if the stimulation changes, used for things like the paciunium corpsical when sitting down.

slow and complete adaptation, there is a large spike at the initial stimulus then the response slowly deceases to 0 and there is another long spike when the stimulus changes, an example is balance after spinning round.

fats and incomplete, there is a spike at the initial stimulus and the response decreases quickly but dosen’t return to 0 and will spike again is the stimulus changes, it is used in muscle spindles.

slow and incomplete, there is a wide spike at the initial stimulation and the response slowly decrease but doesn’t go to 0 and will slowly increase again if there is a change in stimulus, used by cold and pain receptors.

incomplete adaptation is used to monitor a stimulus.

slow adaptation is used to give information on the strength of a stimulus. fast adapting is used to give information on the rate of change of a stimulus

describe methods of adaptation including how it is achieved by the pcium corpsical

in the parciuiuj corpus constant stimulation results in the redistribution of the fluid between the membranes to relieve the pressure on the receptor causing mechanically gated channels to close. when the stimulus is removed it causes the membrane to deform in the opposite direction causing the generation of an AP.

another method is the opening of Ca²⁺ channels, resulting in the opening of K⁺ channels that hyperpolarise the membrane making it harder to bring up to threshold.

iris changes the amount of light entering the eye by contracting.

describe a monosynaptic reflex.

a monosynaptic reflex consists of 2 neurons and 1 synapse, it is the fastest way to transfer information and are used for spinal reflexes. the receptor transfers information directly to the motor neuron in the CNS which triggers a response. the synaptic transfer of a signal is the slowest part so only having one makes this much faster. monosynaptic reflexes do not involve the brain but they can be overridden by it.

describe a polysynaptic reflex and how they are connected to monosynaptic arcs.

polysynaptic reflexes have one or more interneurons in the CNS that integrate information, the presence of multiple synapses between these neurons makes these slower responses.

monosynaptic reflexes can have polysynaptic collateral branch to inhibit (relax) the antagonistic muscle of a reflex and allow the target muscle you contract. this is done via an inhibitory interneuron which converts the receptors excitatory signal into a inhibitory signal and passes this on to a motor neuron that inhibits the antagonistic muscle. the inhibitory interneuron is needed as neurons can only fire one kind of signal.

state the functions of, epithelial, connective tissue, muscle and nerve.

epithelia, lines tissues including the skin and surface or organs

connective tissue - plays a supportive role includes, general connective tissue, adipose, bone, tendons and blood.

muscle, allows for movement, includes skeletal cardaic and smooth

nerve, allows for neural communication between brain/spinal cord and tissues.

describe the structures of the different types of epithia

epithilia is formed of cohesive sheets of cells that perform specialised functions, these cells are joined at junctional complexes that determine what can pass between the cells. simple epithelia is one layer and stratified epithelia is multiple layers. the tyep of stratified epithiula is determined by teh type of cells on the surface.

types of epithiala include, squamous, which has flat irregular shaped cells. simple squamous tissue is used where mechanical protection is not required (blood vessels) and stratified where varying degrees of protection are required (oesophagus). cuboidal has square shape is used on surfaces involved in absorption or secretion, stratified is associated with ducts. columnar, has a rectangular shape, is used on surfaces involved in absorption. transitional epithilia allows for stretching and is used on organs such as the bladder, pseudostratified appears stratified as nuclei are not aligned but is only one layer, is found on surfaces involved in moistening and cleansing.

cells may have surface modification such as keritinisation which is a layer of dead cells that provides protection. microvillia or cillia.

describe the different types of glandular cells

goblet cells retain conneection with surafce epithelia and stain light in colour.

glandular exocrine and endocrine cells are grouped into clusters in connective tissue. exocrine cells have a duct to the surface where as endocrine cells have no duct. these cells can produce 2 different types of secretion, serous which stains dark or mucus which stains light.

describe the basic structure of connective tissue and its role

connective tissue consists of cells that produce specific fibres, fibres and ground substance. the cells present can be resitent or transeint.

resident cells include fibrobasts that produce fibres and fibrocysts that maintain fibres. transeint cells include immune cells.

connective tissue supports epithelium blood vessels and glandular cells

describe adult/general connective tissue

this tissue can be dense or loose. dense tissue has more fibres than cells and stains dark, loose tissue has more cells than fibres and stains lighter.

dense tissue can either bee regular, meaning all the fibres are in alignment giving strength in 1 direction or irregular meaning the fibres are arranged in multiple directions giving strength in all directions.

describe adipose tissue

adipose tissue (fat) is used as an energy source (white) and for heat production (brown). it appears light on staining with the nucleus at the edge of the cell due to a large lipid droplet in the middle of the cell.

describe how you would identify each type of muscle

skeletal muscle is multinucleiated with the nuclei on the peripheral of the cell, it forms long thin strands thta all run in parallel and are striated. it is attached to bones and has limited connective tissue between cells.

smooth muscle has a single nuclei in the centre of the cell the cells are short spindle shaped and non-striated. there is limited connective tissue between the cells and the cells overlap so when viewed in transverse not all cells are teh same size and not all nuclei are visible. smooth muscle is found in organs

cardiac muscle has a single nuclei in the centre of the cell and is branching and striated, it contains more connective tissue and inter-calculated disks between the cells. it is found in the heart

describe how nerve cells look in a histological section

they stain light and look like fibre optics when viewed in transverse, they are surrounded by connective tissue

describe the structure and appearance of skeletal muscle cells

long thin cells that are help in parallel. the cells are multi-nucleated (makes them hard to produce so number mainly set at birth) and the presence of myofibrils in the centre of the cells means the nuclei are pushed to the peripheral. the cells are striated with very little connective tissue between the. they are attached to bone and give support and movement to the skeleton. the cells have a large number of mitochondria. the cell membrane of muscle cells is called the sarcolema and is formed of an inner plasma membrane and an outer basement membrane

describe the general structure of thick filaments

formed of myosin, they consist of 6 proteins, 2 long proteins wrapped together to form the tail and 4 globular proteins that form 2 heads. myosin is arranged with the tails in parallel and the head sticking out at right angles. it is anchored in to a structural protein.

describe the general structure of thin filaments.

formed of 2 strands of actin wrapped around each other with tropomyosin wrapped around the actin and troponin mlecuels held in place across the filament. they are anchored to a structural protein

explain the structure of a sacromere including the arrangement of thin and thick filaments and the names of the different lines, zones and bands and how they change during contraction.

the structural proteins that anchor thick and thin filaments have filaments on both sides, thick filaments this protein is known as the M plate and formed the M line and for thin filaments the Z plate which formed the Z line. M and Z lines are arranged in an alternating fashion with an overlap between the thick and thin filaments. the area between 2 Z lines is known as a scaromere.

the H zone is the area that only contains thick filaments it shortens during contraction. the I band is the area that only contains thin filaments, it shortens during contraction. the A band is the entire length of the thick filaments including the bit that overlaps with thin, its length remains constant.

thin and thick filaments are arranged in a honeycomb fashion with each thick surrounded by 3 thin

describe how contraction occurs in skeletal muscle

ATP binds to myosin causing a conformational change that allows myosin to bind actin and ADP is released, this causes a conformational change that causes the fibres to slide past each other, ATP thin binds to myosin and it reverts back to its original conformation, ADP is released, this cycle happens many times during each contraction.

this is regulated by tropomyosin on the actin fibres. tropomyosin blocks the myosin binding site on actin preventing cross bridge formation. it is bound to troponin which has a Ca²⁺ binding site.

when Ca²⁺ is released from the sarcoplasmic reticulum it binds to troponin causing a change in conformation that moves tropomyosin unblocking the myosin binding site and allowing for cross bridge formation

describe the structure of the scarcoplasmic reticulum

the sarcoplasmic reticulum is a network of membrane bound tubules that overlays the fibre structure. it is formed of transverse tubules that run through the to transfer the AP to the centre and lateral sacs that store interacellular calcium.

explain how the sarcolplasmic reticulum allows fro contraction of skeletal muscle cells.

the action potential travels along the sacroplasmic reticulum causing the opening of voltage gated Ca²⁺ channels releasing Ca²⁺ and allowing for cross bridge formation. the transverse tubles transfer the AP to the centre of the cell allowing contraction of these fibres.

after stimulation reuptake of Ca²⁺ into the sarcoplasmic reticulum allows it to be stored for the next contraction

describe the structure of a motor end plate and how this allows for nerve transmission into skeletal muscle

the muscle cell is folded and wrapped around the end of the motor neuron creating a large surface area.

when an AP travels down the neuron Ca²⁺ chanels are opened and the neurotransmitter acetylchlorine released into the cleft, binding to receptors on the muscle cell. the large surface area of the muscle cell means there are lots of receptors so many graded potentials are produced and an AP is always generated.

describe a motor unit

each neuron innervates multiple muscle cells, connecting to them in the centre of the cell

describe isometric contraction

isometric contraction is when the load increases with contraction but more stimulation of the muscle does not create a change in length due to a high external load. it is used to create tension

descibe isotonic contraction

isotonic contraction is when contration causes a chhange in length but the load remains constant. it is used to provide movement.

define a twitch and how they can be summed together.

a twitch is the mechanical response as a result of a single action potential.

the duration of a twitch is longer than that of an AP so if multiple APs occur in quick succession then a larger twitch will be generated as more Ca²⁺ is released from the SR. very high frequencies of APs result in saturation of cross bridges so the muscle cannot contract more, this is known as titanic contraction.

define hormones

hormones are signalling molecules that are secreted by endocrine glands that travel in the bloodstream (making the endocrine system universal) to innate a response in target tissues that have specific receptors, the responses in each target tissue may be different for the same hormone.

state the 2 types of hydrophillic hormone and their action on target cells

protein and catecholamine hormones are hydrophilic hormones. they cannot diffuse through the cell membrane so bind to transmembrane receptors that transcuce the signal. they are involved in cellular signalling. these receptors can be enzyme linked or G protein linked

state the 2 types of hydrophobic hormones and their action on target cells

steriod and thyroid hormones are hydrophobic. they diffuse through the cell membrane and bind to cytosolic or nuclear receptors which are transcription factors, they are involved in the regulation of gene expression.

state and define the 2 processes hormone signals can go through

amplification, this results in the activation/reaction of many molecules via a cascade.

divergance, this results in the alteration of many cellular pathways simultaneously

describe the action of enzyme linked receptors

binding of the hormone causes a conformational change that activates the enzyme in the receptor. this can then go on to activate other enzymes such as kinases triggering a cascade

describe the structure of a G protein

G proteins are formed of 3 units α, β and γ. the α subunit has a GDP group attached this can be phosphorylation into GTP to activate the protein.

describe the structure of trans membrane receptors

they span the width of the membrane a have extracellular, transmembrane and intracellular domains.

enzyme linked receptors have intrinsic enzyme activity within their intracellular domain.

G protein linked receptors have 7 transmembrane helixes

describe how binding of a hormone leads to g protein activation

the binding of the hormone causes a conformational change to the intacellular domain of the receptor, this causes the phosphorylation of the α subunit of the G protein causing it to dissociate and activate other enzymes

describe the phosphotase C G protein pathway

G protein activates phosphotase C, this causes the cleavage of specific phospholipids in the plasma membrane into IP₃ which opens Ca²⁺ channels in the ER and DAG which activates the protein kinases C. these actions trigger a cascade

describe the Adenylasse cyclase G protein pathway.

G protein activates Adenylasse cyclase which converts ATP into cyclic AMP. this activates protein kinase A which activates glycogen phosphoylase causing the breakdown of glycogen into glucose

describe how steriod and thyroid hormones cause a cellular response.

these hormones diffuse through the phospholipid bilayer into the cell and bind to cytosolic or nuclear receptors. most steroid hormones bind to cytosolic receptors (apart from oestrogen) and most thyroid hormones to nuclear.

the resulting complex binds to specific gene promoters that regulate the transcription of genes. they can them stimulate the transcription of these genes by recruiting RNA polymerase. the genes targeted can differ between cell types for the same hormone.

this is a much slower pathway than extracellular signalling as the proteins need to be synthesised.