short answers

biology saq's

name the key anatommical parts of the nephron involved in filtration, reabsorption, and secretion and name the events that occur within each region

1. glomerulus — filters small solutes from the blood

2. PCT — reabsorbs ions, water, and nutrients; removes toxins and adjusts filtrate pH

3. descending loop of Henle — aquaporins allow water to pass from the filtrate into the interstitial fluid

4. ascending loop of Henle — reabsorbs Na+ and Cl- from the filtrate into the interstitial fluid

5. DCT — selectively secretes and absorbs different ions to maintain blood pH and electrolyte balance

6. collecting duct — reabsorbs solutes and water from the filtrate

describe the process of filtration, reabsorption, and secretion in the kidney

glomerular filtration: water and solutes smaller than proteins are forced at high pressure through the glomerular capillary walls and pores of the glomerular capsule into the renal tubule.

tubular reabsorption: water, glucose, amino acids, and ions are transported out of the filtrate into the tubule cells and then into the capillaries.

tubular secretion: H+, K+, creatine and drugs are removed from the peritubular capillaries and secreted back into the filtrate within the renal tubular lumen.

describe the CCM

1. due to glomerular filtration, ions, water, and nutrients enter the nephron

2. they are reabsorbed in the PCT

3. this creates higher osmolarity within the ECF and so more water leaves the descending limb via osmosis

4. this increases the concentration of ions in the descending limb as it goes further into the medulla

5. ions are pumped out of the ascending limb to ensure more water is reabsorbed in the descending limb

6. this ensures concentrated urine is formed

describe the function of ADH after dehydration

1. water loss is detected by the hypothalamus due to increased plasma osmolarity

2. the posterior pituitary releases ADH into the bloodstream

3. ADH binds to the V2 receptor on the basolateral membrane on the DCT which increases the number of aquaporins that are inserted into the membrane (signal transduction)

4. this increases the amount of water that is reabsorbed into the bloodstream, thereby diluting blood

5. plasma osmolarity is returned to its normal level

6. this is detected by the hypothalamus and as a result ADH secretion is reduced

describe the effect of temperature on enzyme activity

at low temperature, enzyme activity is low.

molecules have low speeds with reduction in frequency of collision, molecules do not have sufficient energy to overcome activation energy

between 0-40 degrees enzyme activity increases with increasing temperature

molecules move faster and collide more frequently and successfully

enzyme activity peaks at optimum body temperature

above 40 degrees, most enzymes denature as intra/intermolecular bonds are broken and tertiary structure is damaged no longer forming ESC

describe the 3 meningeal layers and their function

the meninges cover the brain and spinal cord & protect the neural tissue from bruising against the bones of the skeleton

dura matter — outermost layer and adheres the skull, thickest layer, and is associated with veins that drain blood to the venous sinuses

arachnoid layer — loosely connected to the inner membrane (forms subarachnoid space)

pia matter — innermost layer, adheres to brain surface, many tiny blood vessels

compare and contrast the main features of skeletal and cardiac muscle tissue

skeletal — attach and help move bone, voluntary, composed of muscle fibre with a striated appearance, multi-nucleated

cardiac — shorter, thicker, branched, involuntary, striated, uni-nucleated, found in the heart only

describe the function of the troponin complex

tropomyosin — prevents myosin and actin from binding at rest

troponin I — blocks myosin-binding sites

troponin C — binds to calcium to initiate muscle contraction

troponin T — facilitates the binding of tropomyosin to troponin

describe what is excitation-contraction coupling

refers to the mechanism that converts action potentials to muscle fibre contraction

1. ACh releases binds to nicotinic receptor found on motor endplate

2. Na+ released into T-tubule depolarising it and initiating an action potential

3. DHP receptor at end of T-tubule undergoes conformational change

4. RyRs receptor (mechanically attached to DHPR) on sarcoplasmic reticulum opens up and releases Ca2+

5. increased intracellular Ca2+ attaches to troponin C and allows cross-bridge cycle to initiate

what constitutes the upper and lower respiratory tracts?

nose, nasal cavity, pharynx, larynx, trachea, bronchi, terminal bronchioles, respiratory bronchioles, alveolar ducts, alveoli

explain the stages of inspiration during pulmonary ventilation

the diaphragm and external intercoastals contract, diaphragm descends and rib cage rises, thoracic cavity volume increases decreasing its pressure, alveolar volume increases (decreasing pressure) and alveolar pressure becomes less than atmospheric pressure, a pressure gradient is formed between the atmosphere and lungs, air flows from the atmosphere into the alveoli and gas exchange occurs

describe the second line of defence

innate/non-specific

1. phagocytes / macrophages

2. natural killer cells

3. inflammation

4. complement system

5. interferons

6. fever

describe the difference between active and passive immunity

active — our own immune system is responsible for protecting us against a pathogen and producing antibodies (uses APC, T-helper, T-killer, T-memory, T-suppressor cells & memory B cells and plasma cells)

passive — antibodies artificially produced outside the body and injected into the body (no contact with antigen)

describe the general structure of a virion?

viral genome

nucleic acid core

capsid/protein coat

nucleocapsid

glycoprotein envelope

surface protein

describe the general structure of prokaryotes

DNA in nucleoid

peptidoglycan cell wall

plasma membrane

70s ribosomes

cytoplasm

glycocalyx gel-coating

appendages (flagellum, fimbriae, conjugation pilus)

define bacterial conjugation and describe this process

conjugation is the process where one bacterium transfers genetic material to another through direct contact

1. a pilus forms between 2 bacteria

2. donor passes DNA to recipient through pilus

3. requires F plasmid (fertility factor)

4. F+ has F plasmid and donates to F- cells

what is an energy profile and how do energy profiles of exothermic reactions differ from endothermic ones?

energy profiles show the energy of reactants and products

exothermic — products have less energy than reactants, releases energy to surroundings

endothermic — products have more energy than reactants, absorbs energy from surroundings

transition state point on graph with highest energy

activation energy is energy barrier between converting substrate to product

reversibe competitive vs. non-competitive inhibition

competitive — bind to same site as substrate, can be displaced by increasing substrate concentration, do not effect Vmax but Km increases

non-competitive — bind to allosteric site, not displaced, Vmax reduced, Km stays the same

what are two models that explain how enzymes and substrates interact and how do they differ?

lock & key model — proposes that the enzyme and substrate fit together like a lock and key and hence only the substrate fits the active site forming an ESC

induced fit model — suggests that the active site detects the substrate and molds around it and therefore make it more accurate

what are cofactors and coenzymes? give an example of each

cofactor — non-protein inorganic substance that binds to enzymes to enhance their activity, e.g. Fe2+, magneisum, zinc, cobalt

coenzyme — an organic substrate that is necessary for the functioning of an enzyme, e.g. vitamin derivatives such as CoA, NAD, FAD

what are the factors that affect enzyme activity and which of these factors can cause denaturation?

the concentration of the enzyme, the concentration of the substrate, temperature, pH, presence of an inhibitor

temperature & pH can cause denaturation by breaking the weak intermolecular bonds within the 3D tertiary structure

what are the key functions of saliva?

1. protects the oral cavity by coating it with a proline-rich protein (pellicle)

2. to ease swallowing

3. to moisten and lubricate the mouth

4. to dissolve food molecules so they react with taste receptors

5. chemical digestion of polysaccharides with amylase

what are the main functions of the stomach?

1. mechanical and chemical digestion

2. temporary storage of food

3. secrete intrinsic factor to absorb vitamin B12

4. regulate the release of chyme into the duodenum

describe the cells of the stomach and what they secrete

parietal cells — gastric acid (HCl)

chief cells — pepsinogen (pepsin precursor)

goblet cells — mucus

D cells — somatostatin (inhibits gastric acid release)

G cells — gastrin (induces gastric acid release)

direct vs. indirect pathway

acid secretion is stimulated by acetylcholine (neural), histamine (paracrine), and gastrin (endocrine)

direct pathway — ACh binds directly to M3 receptor, histamine binds to H2 receptor, gastrin binds to CKK2 receptor on parietal cells

indirect pathway — ACh and gastrin bind to ECL cell and stimulate histamine release that then binds to parietal cells

both pathways end up in the secretion of H+ into the lumen via a K+ co-transporter

how is the structure of the small intestine adapted for its function?

1. rich blood supply

2. lacteals

3. intestinal crypts

4. single-layer epithelial cells

5. microvili

6. several membrane proteins

7. chyme forced into a circular motion aiding digestion and absorption

describe the differences between DNA and RNA

DNA — double stranded, thymine base, found in the nucleus and mitochondria, more stable (long-term storage), deoxyribose sugar, converted to mRNA during transcription

RNA — single stranded, uracil base, found in the cytoplasm, nucleus, and ribosomes, less stable ribose sugar, translated into a protein

what is a codon and why are they considered degenerate?

a codon is a series of triplet nucleotides that corresponds to an amino acid

there are 64 different codons (61 of which code for amino acids) — 1 stop AUG (methionine), 3 stop UAA UAG UGA

the genetic code is considered degenerate as more than one codon can code for a specific amino acid

describe the structure of transfer RNA involved in eukaryotic gene expression

tRNA has distinct three hairpin loops (T loop, D loop, and anti-codon loop) that form a three-leafed clover

anti-codon loop recognises mRNA codon

aminoacyl-tRNA is covalently bonded to an amino acid

describe the difference in gene expression in eukaryotes and prokaryotes

eukaryotes — controlled at multiple levels: epigenetics, transciption, post-transcriptional modification, translation, and post-translation, 60s and 40s subunits, occurs in the nucleus (transcription) and cytoplasm (translation)

prokaryotes — controlled at transcription, 50s and 30s subunits, transcription and translation occurs in the cytoplasm

what are post-transcriptional modifications, and why do they occur?

before modifications, mRNA is called pre-mRNA

a 5’ cap is added to the beginning of the chain to prevent degradation

a 3’ poly-A tail is added to the end to prevent degradation and to help move the mRNA to the ribosomes

introns (non-coding bits) are spliced and removed while exons (coding bits) are ‘glued’ together using ligases — this is known as gene splicing

mRNA is now considered mature

what nutrients are absorbed in the small intestine?

glucose, amino acids, lipids, electrolytes, water, vitamins, minerals

how are carbohydrates digested and absorbed?

first digested by amylases in saliva

enzymes released by brush border (lactase, sucrase, maltase) breaks down disaccharides to monosaccharides — glucose, galactose, fructose

monosaccharides transported into bloodstream by means of a cotransporter with Na+ (SGLT) set up by Na+/K+ ATPase

monosaccharides then leave the basolateral membrane by simple/facilitated diffusion down its concentration gradient

where and how are proteins broken down and absorbed?

broken down into polypeptides in the stomach by pepsin

these polypeptides are further broken down into oligopeptides in the small intestine by proteases secreted by the pancreas (trypsin & chymotrypsin)

oligopeptides broken down into amino acids by pancreatic enzyme carboxypeptidase and converted into free amino acids by aminopeptidase

these free a.a. are transported into epithelial cells by secondary active transport coupled with the movement of Na+

these a.a. are then moved into the bloodstream by transport proteins and ATP

where and how are fats digested and absorbed?

occurs mainly in the small intestine

pancreatic enzyme lipase which breaks down fats into monoglycerides and free fatty acids

emulsification of larger fat droplets into smaller ones by bile increases surface area for lipase to act on

small fat droplets bound to bile salts (makes micelles) then lose the bile salts and enter the cell passively

these fats binds to proteins in the golgi complex to form chylomicrons which are then removed from the cell via lacteals

what do pancreatic juices include and what is their function?

amylase — breaks down carbohydrates into monosaccharides

lipase — breaks down fats into glycerol and fatty acids

ribonuclease & deoxyribonuclease — breakdown of nucleic acids into mononucleotides

proteolytic enzymes (trypsin, chymotrypsin, carboxypeptidase, elastase) — proteins into small peptides into a.a.

+ water, bicarbonate ions (neutralise gastric acid)

what are the key functions of the liver?

1. metabolism

2. storage of vitamins and minerals

3. production of bile

4. production of alkaline fluids

5. breakdown of waste products

6. detoxification

what are the key functions of bile, where is it secreted from, and where is it stored?

• made and released by the liver into the duodenum

• stored in the gallbladder

• provides an alkaline fluid to neutralize stomach acid

• bile salts aid in digestion of fats (emulsification)

• increases surface area of lipids allowing absorption of fat-soluble vitamins

what is the key function of the large intestine and how does it perform it?

to absorb water and electrolytes:

• movements of the large intestine are slow and sluggish to allow for absorption

• chyme that enters is isotonic so requires energy (Na+/K+ ATPase)

• water enters chyme by osmosis

alveolar type i vs. ii cells

type 1 — involved in gas exchange, cover 95% of alveolar surface area, thin structure allows for shorter diffusion distances, susceptible to damage by emphysema

type 2 — cuboidal cells, secrete surfactant which prevents collapse of alveoli and reduces tension, repair alveolar epithelium, more resistant to damage

spinal nerve pairs

31 spinal nerve pairs in total:

8 (cervical) C1-C8

12 (thoracic) T1-T12

5 (lumbar) L1-L5

5 (sacral) S1-S5

1 (coccygeal) C0

lung volumes?

→ tidal volume (TV)

‘quiet breathing’ rate, average resting value of 500ml

→ inspiratory reserve volume (IRV)

amount of air that can be maximally inspired above TV, average value of 3000ml

→ inspiratory capacity (IC)

tidal volume + inspiratory volume, TV + IRV

→ expiratory reserve volume (ERV)

extra volume of air that can be expired after TV, average of 1000ml

→ residual volume (RV)

volume of air remaining in lungs to prevent deflation, average of 1200ml

→ functional residual capacity (FRC)

expiratory reserve volume + residual volume, ERV + RV

→ vital capacity (VC)

maximum volume of air that can be moved in and out in a single breath, all the values minus residual volume

→ total lung capacity (TLC)

the maximum volume of air the lungs can hold, IRV + TV + ERV + RV

how is oxygen transported in the body?

dissolved in plasma & combined with haemoglobin

oxygen binding is cooperative, binding affinity increases as more oxygen is binded

how is CO2 transported in the body?

dissolved in plasma (5%), carbaminohaemoglobin (10%), bicarbonate (85%)

what controls the rate of breathing?

• medullary respiratory centre

dorsal respiratory group at the back of the medulla spontaneously fire off neurons

• pons respiratory centre

pneumotaxic area sends inhibitory signals to dorsal group

sometimes we need to breathe in deeper, the medulla mainly (as well as chemoreceptors, carotid & aortic bodies) send signals to intercostal muscles to increase ventilation

describe the main functions of the skeletal system

• facilitates movement

• stores and releases minerals

• supports the body

• protects internal organs

• stores and releases fats

• produces red blood cells

what are the components of the muscoskeletal system?

muscles, bone, tendons (bone to muscle), ligaments (bone to bone), cartilage, joints

describe cartilage and it’s key function

cartilage is a tough flexible connective tissue that protects bones and joints

• acts as a shock absorber

• prevents friction between bones

  • synovial fluid found in the cavities of synovial joints (viscous solution)

different layers of bone

1. periosteum

2. compact bone

3. spongy bone

4. bone marrow (yellow/red)

   bone is richly vascularised and has a hydroxyapatite bone (calcified matrix)

bone cells

1. osteoblasts — build up bone

2. osteoclasts — break down bone

3. osteocytes — trapped osteoblasts within the calcified matrix

4. osteogenic cells — undifferentiated bone cells (stem cells)

what are prostaglandins?

local mediators that are stimulated when the mucosa is irritated and increase the thickness of the mucosa (as well as increase bicarbonate production)

describe the structure of skeletal muscle fibres

• Each fibre is a long, cylindrical cell arranged in parallel and contain multiple nuclei.

• The membrane of the muscle fibre is the sarcolemma.

• The cytoplasm is the sarcoplasm, that contains many mitochondria.

• Composed of myofibrils that are responsible for the striated appearance.

• The sarcoplasmic reticulum is a form of endoplasmic reticulum (stores Ca2+ required for muscle contraction).

• Each myofibril contains contractile proteins, which are arranged into units called sarcomeres

• The main unit of the thick filament is the large motor protein myosin.

• Each myosin molecule contains two identical protein chains, each with one large heavy and two light chains.

• The other contractile filament in myofibrils is the thin filament, mainly composed of three proteins: actin, tropomyosin, and troponin.

describe the key stages of the cross-bridge cycle

1. myosin bound to actin, no adenosine triphosphate (ATP); rigor state

2. ATP binds to myosin head resulting in a conformational change decreasing affinity to actin

3. ATP bound to myosin hydrolyses to ADP + Pi which remain linked to myosin

4. myosin binds weakly to actin, tropomyosin moves off the binding site and power stroke begins

5. myosin releases ADP at the end of the power stroke and the rigor state begins again

describe the organisation of the nervous system

• CNS

  • brain

  • spinal cord

• PNS

  • sensory neurons (afferent)

  • motor neurons (efferent)

    • somatic nervous system (voluntary)

    • autonomic nervous system (involuntary: fight or flight + rest and digest)

describe the main catergories of neurons

1. afferent — carry information about temperature, pressure, light, and other stimuli from sensory receptors to the CNS

2. efferent — both somatic motor and autonomic have enlarged endings called axon terminals and carry signals from the CNS to muscles and glands

3. mixed — nerves that carry signals in both directions

4. interneurons — neurons that lie entirely within the CNS and often have quite complex branching processes that allow them to communicate with many other neurons

name the differeny types of glial cells and their function

• CNS

  • microglia — act as scavengers

  • oligodendrocytes — form myelin sheath and associated with more than 1 axon

  • ependymal — create a selectively permeable barrier separating fluids of the CNS

  • astrocytes — take up water, K+, neurotransmitters and help form the BBB

• PNS

  • schwann — form myelin sheath around 1 axon

  • satellite — support cell bodies

arrangement of the lower spinal column

→ the L2 vertebral level tapers off forming the conus medullaris

→ at the end of the spinal cord the subarachnoid space expands forming the lumbar cistern

→ this space is accessed during a standard lumbar puncture procedure

→ the filum terminale is a fibre that extends from the conus medullaris to the coccyx and it helps fixate the spinal cord

→ the spinal nerves that arise from the end of the spinal cord are known as the cauda equina

what is the blood-brain barrier

⇒ high selectively permeable brain capillaries protects brain from harmful substances

⇒ endothelial cells form tight junctions that prevent solute movement

⇒ these tight junctions form a functional blood brain barrier

describe how the brain and spinal cord are protected by bone

→ The brain is encased in a bony skull, or cranium, and the spinal cord runs through a canal in the vertebral column

→ The bony vertebrae are stacked on top of one another and separated by disks of connective tissue

→ Nerves of the PNS enter and leave the spinal cord by passing through notches between the stacked vertebrae

explain how neurotransmitters are released and removed from axon terminals

• depolarisation at axon terminal opens voltage-gated Ca²⁺ channels

• Ca²⁺ enters cell due to electrochemical gradient and triggers exocytosis

• neurotransmitters diffuses across synaptic cleft and binds to receptor on postsynaptic cell

• neurotransmitter binding initiates a response in postsynaptic cell

  REMOVED:

• diffuse away from the synapse separating from receptors

• inactivated by enzymes, e.g. ACh broken down into acetyl CoA and choline by the enzyme acetylcholinesterase and choline can be reused at the presynaptic axon terminal

• transport into adjacent glia or neurons and can be recycled to refill empty vesicles

describe the different stages of neural action potentials

• action potential initiates when Na⁺ channels open and enter the neuron

• this causes depolarisation and opens more adjacent Na⁺ channels

• continuous entry of Na⁺ opens along the axon so that the signal does not diminish

• K⁺ channels open and K⁺ leaves cell; repolarisation

• additional K⁺ leaves hyperpolarising the cell

• voltage-gated K⁺ channels close and cell returns to resting membrane potential

name all the functions of an astrocyte

• glial cell in the CNS

• highly branched

• provide neurons with metabolic substances for ATP production

• maintain homeostasis by taking up K+ and water

• forms the BBB

• source of neural stem cells

• secrete neurotrophic factors

what are conditions that arise from nondisjunction?

1. down syndrome (trisomy 21)

2. edwards syndrome (trisomy 18)

3. turners syndrome (monosomy X)

4. klinefelter syndrome (XXY)

5. patau’s syndrome (trisomy 13)

what factors can cause nondisjunction?

• failure of homologues to separate in anaphase I

• failure of sister chromatids to separate in anaphase II

• the resulting gamete will either possess either an extra or missing copy

• the resulting offspring will have an incorrect chromosome number in every cell of the body

what is a zymogen? give an example

an inactive substance which is converted into an enzyme when activated by another enzyme, e.g. pepsinogen

anterior pituitary hormones

1. FSH & LH

2. ACTH

3. GH

4. endorphins

5. TSH

6. prolactin

what are the 3 laws of inheritence?

1. law of dominance

in a heterozygote, one trait will conceal the presence of another trait for the same characteristic; the dominant allele will be expressed in the phenotype

1. independent assortment

the alleles of two or more different genes get sorted into gametes independently of another; the allele a gamete receives for one gene doesn’t influence the allele received for another

1. law of segregation

during gamete formation, each gene separates from each other so that each gamete only carries only one allele for each gene

explain the process of deamination

Intake of proteins produces excess amino acid in the gastrointestinal tract, which needs to be excreted.

In the liver, the amino acid is converted to ammonia soluble in water to form alkaline fluid, which is toxic through deamination.

This toxic substance is converted to urea for safe excretion.

The protease enzyme breaks down the digested protein into amino acids in the small intestine and stomach.

After the conversion of excessive amino acid into urea, it is transported to the kidney via the bloodstream, where the blood is filtered, and urea is excreted through urine

explain how vitamin B12 is absorbed

• B12 comes from animal proteins

• HCl in the stomach releases B12 from proteins

• free B12 binds to R-proteins (glycoproteins) secreted by the salivary glands and stomach

• pancreatic enzymes in the duodenum break apart B12 and R-protein

• free B12 binds to intrinsic factor

• B12-IF is absorbed in the ileum by receptor-mediated endocytosis