IB BIO Test 3

D2.1.1 + D2.1.12

Cell division 

• New cells (daughter cells) are produced by division of preexisting cells 

• Nucleosome:structural unit made up of DNA wound around a center of histone proteins 

• Sister chromatids:identical copies of chromatids  are held together by cohesin

• Kinetochore: connects chromosomes to microtubules

• Mersitam: cells that can divide and grow (roots/shoots)

• Chromatids: one copy of chromosomes

• Chromatins: decondensed chromosomes 

Purpose

1. Growth: increase size of the body (ex. Lengthening roots)

2. Cell replacement: production of cells to replace those with a limited lifespan (ex. Replacing skin cells that get damaged)

3. Tissue repair: healing after loss or damaged tissues (ex. Wounds need healing)

D2.1.13 Phases of the cell cycle 

• Cells need time to move through the cycle so that it moves from one phase to the next; cancer results when cells divide when they shouldn't

• Interphase

  • G1: The phase after mitosis and before DNA replication where each chromosome is a single DNA molecule; active growth phase

  • S: All DNA in the nucleus is replicated; two identical pairs of DNA; synthesis of new DNA

  • G2: growth may resume during this phase while the cell is preparing for mitosis; such as synthesis of proteins 

  • G0: a nondividing state; cell here are alive and perform their role but wont divide again

    • Differentiated bone cells (osteocytes)

    • Skeletal muscle fibre cells

    • Neurons

Cell division:

• Mitosis: division of the nucleus

  • Early Prophase: Microtubules are growing from the centriole; chromosomes become shorter

  • Late Prophase: Spindle microtubules extend; each chromosomes consists of two identical sister chromatids each with a centromere and kinetochore 

  • Metaphase: chromosomes move to equator; spindle microtubules attached to kinetochore with sister chromatids attached to opposite poles

  • Anaphase: sister chromatids separated so each is now a separate chromosome; kinetochores shorten spindle microtubules

  • Early Telophase: all chromosomes reach poles and membrane forms; spindle microtubules break down

  • Late Telophase: chromosomes uncoil

• Cytokinesis: division of cytoplasm and organelles;Mitochondria and chloroplasts also grow and divide here

D2.1.15

 Control of the cell using cyclins

• Cell cycle checkpoints (G1, M, G2)

  • Checks for errors or defects before proceeding to the next stage of the cell cycle

    • Ex. correct amount of chromosomes 

    • If it doesn't repair it may be killed, fixed, or sent to G0

  • G1: Checks if the cell is the correct size and checks for DNA damage ( if it doesn't pass it moves to G0)

  • G2: Checks DNA  has be correctly replicated

  • M: Checks that all sister chromatids are all attached to the spindle microtubules

• Cyclins + Cyclin dependent kinase 

  • Proteins that control the cell cycle’s progression through the checkpoints (regulatory proteins)

  • concentration cycle moves up and down as the cell progresses through the cell cycle 

    • 4 different types of cyclins (D E, A, and B)

  • Cyclins bind to kinase enzymes or cyclin dependent kinases (CDKs), activating them, the kinases phosphorylate other proteins in the cell activating them, these proteins then perform tasks specific to the phase of the cell cycle it is in. 

    • Low concentration cyclin the CDk will not be active and the cell cycle will freeze 

D2.1.16 

Consequence of mutations in genes that control the cell cycle

• Initiation of Tumor formation

  • Cause a mutation to the DNA in a gene that control the cell’s progression through the cell cycle

    • 1) random errors in DNA replication

    • 2) mutagen 

  • Tumors originate from a single cell that loses control of it cell cycle which is inherited by its daughter cells

• Mutagens

  • Are anything that permanently changes genetic material 

    • 1) Radiation: high energy (UV, X-ray)

    • 2) Chemicals: carcinogens that interact directly with DNA or produce mutagenic compounds (Cigarettes, Benzoyl peroxide, nitrates)

    • 3) Infectious agents: virus or bacteria cause DNA damage or reduce efficiency of DNA repair systems  (HPV and Helicobacter Pylori) 

• Cell cycle control genes

  • Proto-oncogenes:

    • Concerned with control of the cell cycle, such as the genes that code for cyclin proteins

    • Normally help cells grow

  • Tumor suppressor genes:

    • Code for proteins that prevent uncontrolled cell division 

    • Are normal genes that slow down cell division, repair DNA mistakes, or tells cells when to die (apoptosis)

• Oncogene

  • When a proto-oncogenes mutate it creates this cancer causing allele

  • Permanently activated even when they aren't supposed to be ; Cells grows out of control and causes cancer 

• Mutated Tumor suppressor gene

  • Cells grows out of control and causes cancer; losses that defense  

• Cancer correlates with age

  • Results from the accumulation of multiple mutations to a cell’s genes that control the cell cycle 

    • Multiple hit hypothesis: cells must acquire a series of mutations leading to unrestrained cell growth and division

  • Elephants like humans have lots of cells and live a long time yet don't die as frequently to cancer; this is because they have a zombie genes that causes cell apoptosis do cells die before they become cancerous

D2.1.17 Tumors and rates of growth

• Benign Tumor: cells in the tumor adhere to each other and remain in a single mass; do not cause cancer

• Malignant tumors: cells in the tumor can detach and invade neighboring tissues, lymph vessels or blood vessels; cause cancer

• Cancer symptoms:

  • Fatigue, Lump, Skin changes, Weight changes 

• Cancer developed in four stages

  • 1) Initiation: normal cell transformed into cancerous cell as a result of mutations 

  • 2) Promotions: the cancerous cell divides, making a large # of daughter cells containing the mutations (primary tumor)

  • 3) Progression: cancerous cells become aneuploid (have the wrong # of chromosomes) and begin to invade surrounding tissues 

  • 4) Metastasis: cancer cells break away from the primary tumor (First Formed), travel through blood/ lymph system, from new tumors (secondary tumors) in other parts of the body

• Mitotic Index (MI)

  • Ratio of percentage of cells in a sample undergoing mitosis relative to the total number of cells in the sample

    • Larger the MI, higher rate of division by cells in the simple

MI = # of cells in mitosistotal # of cells100

• Uses of MI: predicts how rapidly the tumor will grow 

  • Diagnosis: higher MI relative to a tissue specific standard more likely a tissue is cancerous

  • Treatment: stop cell division, so if cancer treatment is working means fewer cells in mitosis and MI would decrease; predicts how rapidly the tumor will grow 

B2.1.1 + B.1.12

Phospholipid bilayer 

• Lipid Bilayers : membrane barrier (sheet-like bilayers) separating the interior from its surrounding 

• Lipids

  •  hydroxyl groups, fourlinked hydrocarbon rings, a hydrocarbon tail

  • Unique structure (bent shape) 

  • Amphipathic

    • Hydrophilic head composed of polar hydroxyl groups and charged parts of lipids

    • Hydrophobic tails composed of nonpolar parts/ hydrocarbon chains and other amphipathic lipids

• Membrane Cholesterol ( Animals)

  • Acts to modulate membrane fluidity and permeability to some solutes

    • Plants have (Sterols) 

• Cholesterol interests into the bilayer of phospholipids

  • Amphipathic (contains both hydrophilic and hydrophobic parts) 

B2.1.11 

Membrane fluidity

• Greater the temperature:greater the fluidity/ lower viscosity/ less densely packed/ won't hold shape/ too permeable   

• Lower temperature: high viscosity/ densely packed/ more rigid/ may break/ not permeable 

• Importance of Membrane Fluidity 

  • Enables molecules to diffuse through the membrane

  • Facilitate the interactions between proteins (for cell signaling)

  • Enable membranes to fuse with each other during vesicle formation (endocytosis and exocytosis)

  • Ensure an even distribution of membrane molecules between daughter cells during cytokinesis

• Phospholipids structure affects membrane fluidity

  • Phospholipids molecules can vary in their tail length and degree of tail saturation

• Fatty acids and membrane fluidity 

  • Satuaturared: fatty acids do not have double bonds between adjacent carbon atoms; straight tail 

    • Press closely together making a dense and viscous membrane

    • Stronger intermolecular forces causing them to have higher melting points

    • Ex. Arabidopsis plant grows at higher temps has an increase in saturation of fatty acids 

  • Unsaturated: fatty acids have one or more double bonds. Leads to a bend in the molecule

    • Have kinks in their tails preventing close packing; keeping space between them; Helps increase fluidity of the membrane 

    • Weaker intermolecular forces causing them to have lower melting points 

    • Ex. Plants (Chickpea) increase in fatty acids at low temperatures 

• The saturation of membrane lipids can vary within the body of a single organisms 

  • Caribou have high amounts of unsaturated fatty acids in their hooves than the tissue in their upper leg (hooves are in snow means lower temp)

,

B2.1.12 Cholesterol and membrane fluidity 

• Membrane Cholesterol ( Animals)

  • Acts to modulate membrane fluidity and permeability to some solutes

• Function of Cholesterol

  • At high temperatures cholesterol physically restrains the movement of phospholipids =  increases viscosity (membrane fluidity) , reducing its permeability to small molecules  

  • At lower temperatures cholesterol prevents stiffening of the phospholipids by lowering freezing point and increasing boiling point 

B2.1.13 membrane fluidity and fusion and formation of vesicles 

• Temperature

  • Affects viscosity (measure of a fluid’s resistance to flow)

  • Higher temp means lower viscosity

  • Lower temp means higher viscosity 

• Fatty acids length

  • Longer fatty acids tails allow for more interaction between phospholipids leading to less fluidity

• Fatty acid saturation 

  • Unsaturated fatty acids have one or more double bond in the fatty acid tails, double bond lead to a bend pushing the adjacent phospholipids further apart increasing spacing increases fluidity 

• Presence of cholesterol

  • The presence of cholesterol affects the fluidity depending on the temp

    • High temperature; cholesterol decreases fluidity

    • Lower temperature: cholesterol increases fluidity 

• Vesicles: move materials around the inside cell 

  • Proteins synthesized by ribosomes on the rough ER are carried to golgi apparatus; protein process by golgi are carried to plasma membrane

• Endocytosis: formation of vesicles in the cytoplasm by pinching off a piece of plasma membrane ; goes into the cell

  • Contain water and solutes; may contain larger molecules 

  • Ex. Macrophages (white blood cell)- engulfs pathogens when fighting infection

  • Ex. Foetal cells in the placenta; absorb proteins from mothers blood (antibodies)

• Exocytosis: fusion of vesicles with the plasma membrane expelling the contents of the vesicles from a cell

  • Release of neurotransmitters from a presynaptic membrane

  • Secretion of hormones from endocrine glands from the pancreas (ex. insulin)

  • Removal of excess water from contractile vacuole 

B2.1.10 Fluid Mosaic Model

• Fluid mosaic model: describes the structure of the cell membrane as a dynamic, flexible structure made up of different components

  • The main component of the cell membrane are phospholipids, cholesterol and proteins 

B2.1.4 Membrane proteins 

• Integral and Peripheral proteins

• Membrane proteins are synthesized by bound ribosomes (Found on Rough ER) and then brought to the cell membrane via exocytosis 

• Peripheral proteins

  • Are associated with membrane surfaces and do not fully span the membrane; temporary

  • Attachment to the lipid bilayer is achieved by binding to one side of the bilayer or to an integral membrane protein

• Integral protein

  • Are embedded and may span the lipid bilayer; mostly transmembrane

  •  They are able to establish hydrophobic interactions with the tails of the phospholipids

• Function of membrane bound proteins

  • Enzymatic activity

    • Process substrates of various metabolic pathways

      • Ex. ATP Synthase (enzyme that catalyze chemical reactions)

  • Receptors

    • Identification of cell type for communication between cells

    • Proteins that are embedded in the cellular membrane to which specific chemical signals from outside the cell attach; when the chemical signal binds,s the membrane protein triggers a response by the cell

    • ex.Acetylcholine receptor, chemoreceptors, hormone receptors(glucagon, insulin), thermoreceptors, electromagnetic receptors, mechanoreceptors, baroreceptors 

      • Insulin: lowers your blood sugar

      • Glucagon: raises your blood sugar

  • Recognition 

    • Chemical messengers interact with receptor binding sites to transduce signals into cells

      • Proteins that are embedded in the cellular membrane that allow cells to identify each other and interact

    • Glycoproteins and glycolipids: components of plasma membranes 

      • short chains of sugars (oligosaccharides) attached to the membrane and the carbohydrate is attached to proteins or the lipid; Interactions between the sugar and carbohydrate binding proteins allows cell-cell recognition 

      • ABO blood grouping is based on differences in type of glycoprotein present on the surface of red blood cells

      • Helps in development of tissues and organs

  • Adhesion

    • Connect neighboring cells to form a tissue

    • Is the process by which cells from tissues by adhering to neighboring cells through specialized adhesion proteins 

    • Glycoproteins and glycolipids form a layer called glycocalyx; which helps bind cells  

    • Cell to cell adhesion molecules (CAMs) link adjacent cells in animal cells (integral protein) 

      • Cells of the same type have same CAMs; different cells have different CAMs

  • Transport

    • Move molecules and ions across the membrane 

      • Passive transport: do not require energy (high to low concentration)

        • Simple diffusion: movement of small nonpolar molecules (O2, CO2)

        • Osmosis: net movement of water (low solute concentration to high)

          • Aquaporan: moves water molecules through membrane

        • Facilitated diffusion: passive movement with membrane proteins for large polar molecules/ions

          • Channel and carrier proteins (integral) and potassium channels

      • Active transport: moves against the gradient; uses ATP

        • Carrier proteins: protein pumps and sodium potassium pumps (3Na out and 2 K in)

  • Anchorage

    • Anchor the cell to the extracellular matrix to hold cells in place 

    • Extracellular matrix (ECM), provide support, segregating tissues from one another, and regulating intercellular communication

      • Cells use membrane bound proteins called integrins to anchor the cell to the extracellular matrix

C2.1.1 

Receptors and Signals

• Chemical signaling 

  • Cells are able to receive and process chemical signals in order to respond to their environment

• Ligand

  • Is a chemical that binds to another specific molecules (receptor molecule) 

1) Ligand approaches binding site

2) Binding causes changes within the receptor

3) Signal is passed on to the cell

4) Ligand dissociates from the binding site

• Hormones, neurotransmitters, cytokines, and calcium ions 

C2.1.3 

Types of signaling molecules

• Hormones

  • Are the chemical signals secreted from cells in endocrine glands that travel through the bloodstream to target any cell which has a receptor for the hormones; long distances signals

    • Ex. Insulin, thyroxine, testosterone 

• Neurotransmitters

  • Chemicals that transmit signals across a synapse, the junction between two neurons 

    • Dopamine, acetylcholine, norepinephrine

• Cytokines

  • Small signaling proteins

  • May affect same cell it was secreted from, other cells or act in more systematic manner (affects nearby cells)

    • interferon

• Calcium Ions

  • Used for signaling with in muscle fibers + neurons

  • Attach to proteins of sarcomere, muscle contraction

  • Diffuse into cells through voltage-gated channels in plasma membrane 

C2.1.4 Chemical diversity of hormones and neurotransmitters

Hormones

• Hormones are used to integrate organ systems and can affect cells at a distance from where they were released

  • Three classes: Amines, Peptides /proteins, Steroids

    • Amine Hormones: small molecules synthesized by modification of amino acids

      • Melatonin and Epinephrine

    • Peptide and protein Hormones

      • Peptide: Antidiuretic hormone, Oxytocin

      • Protein: Insulin and Glucagon

      • Glycoprotein: Follicle stimulating hormone 

    • Steroid Hormones: Lipids derived from cholesterol

      • Oestradiol, progesterone, testosterone

Neurotransmitters

• Are chemicals that transmit signals across the junction between two neurons 

  • Classes of hormones: 

    • Esters: Acetylcholine

    • Gasses: Nitrous oxide

    • Amino acids: Glutamine

    • Amines: Dopamine 

C2.1.9 Transmembrane receptors that activate G proteins

•  Chemical signaling 

  • A signaling pathway is the process in which binding of an extracellular chemical to a receptor is translate into changes in the cell

  • Three main steps

    • 1) Reception: the process by which a cell detects a signal in the environment

    • 2) Transduction: The process of activating a change within the cell

    • 3) Response: the change that occurs in the cell as a result of the signal 

• Signal Transduction (Ex. activating G-protein inside the cell)

  • when the binding of signaling molecule to the receptor induces a change in the shape of the receptor, the activated receptor can then initiate changes in the cell

1. Transmembrane receptors: binding of signaling molecule causes reversible changes to its structure 

2. Intracellular receptors:Binding of molecules results in formation of active ligand receptor 

• G proteins receptors (GPCRs) 

  • Transmembrane receptors  (Consists of single polypeptide and embedded in a cell’s plasma membrane)

  • In the absence of a chemical signal the Gprotein coupled receptor is inactive 

  • Activation can happened by opening ion channels, altering metabolism, activating gene expression or changing cell shape 

• G-protein coupled receptors (medicine)

  • Antihistamines, opioid agonists, depression medications, chemotherapy drugs, diabetes medicine

  • Ozempic and Wegovy are being used to treat diabetes and obesity 

C3.1.12 Epinephrine (adrenaline) secretion by the adrenal glands to prepare the body for vigorous activity

• Chemical signaling

  • Epinephrine binds to cells with a transmembrane receptor called adrenergic receptor which is a type of G-protein coupled receptor

  • Epinephrine triggers a signaling pathway ( a process in which binding of an extracellular chemical to a receptor is translated into changes in the cell)

• Effects of epinephrine

  • Causes liver and muscle cells to break down glycogen into glucose which can be used for anaerobic or aerobic respiration (helps make ATP)

  • Bronchi and bronchioles dilate to relaxation of smooth muscle, widening the airway for increased airflow during ventilation

  • Ventilation rate increases, so a larger total volume of air is moved per minute 

  • Speeds up firing of the sinoatrial node increasing the heart rate, which moves blood to the tissue faster

  • Increases strength of the cardiac contraction increasing volume of blood

  • Arterioles that carry blood to the skeletal muscles dilate, widening so more blood flows to them, redirects blood flow to the areas of the body most crucial for the immediate threat

  • Blood carried to the gut, kidney, and skin constrict narrow so less blood flows to them, not vital for dealing with immediate threat 

C2.1.11

• Circadian Rhythms 

  • Physiological and behavioral changes of an organism over a 24 hour cycle 

  • Dictate multiple processes including alertness, sleepiness, appetite, and body temperature  

    • Exist in both unicellular and multicellular organisms  

  • Can be synchronized by light and darkness; can continue even if place in continuous light/dark

• Suprachiasmatic Nucleus (SCN)

  • Pacemaker of the circadian rhythm; neurons here produce a circadian rhythm of neuron firing frequency which allows them to synchronize other cells throughout the body

  • Visible light (blue) synchronizes the rhythm of the SCN

• Melatonin (Amine hormone )

  • The SCN releases melatonin from the pineal gland

  • Dark: SCN promotes secretion of melatonin from the pineal gland

    • During night it is high

  • Light: SCN inhibits secretion of melatonin from the pineal gland

    • During the day it is low 

  • For nocturnal animals melatonin promotes activity for diurnal animals it promotes sleep

• Melatonin Effects

  • Reduce blood pressure

  • Reduce kidney production of urine

  • Drops core body temperature when sleeping

  • Cause drowsiness and promote sleep

  • Reduce inflammation response/ enhance immune response 

• Insulin

  • Protein hormone; secreted by the pancreas by beta cells when glucose levels are high

  • Causes cells to uptake glucose from the blood to be used in cellular respiration or converted to glycogen  

  • Goes directly to skeletal muscles, livers, and adipose tissue (fat)