BiM Biochemistry and Cells

Question 1

1. What are radioisotopes and what is their medical use?
2. Name 2 types of radioisotopes and their role

Answer 1

1. Isotopes with unstable nuclei that emit radiation (energy). Used as tracers
2. Cobalt-60 - radiotherapy. Technecium-99 - locate brain tumours. Iodine-131 - locate brain tumours

Question 2

1. Describe covalent bonding
2. Describe ionic bonding
3. Describe hydrogen bonding
4. Describe van der Waals forces

Answer 2

1. Sharing of electrons in outer shell to form electron pairs. Stable balance of attraction and repulsion. Can be polar (hydrophilic), where electrons are shared unequally due to differences in electronegativity (pull due to different number of protons) or non-polar (hydrophobic), where electrons are shared equally
2. Electrostatic force of attraction between positively charged (metal) ion and negatively charged (non-metal ion).
3. Weak bonding between hydrogen atom and negatively charged ion
4. Weak interaction between nucleus of atom and electrons of nearby atom

Question 3

1. Define pH
2. Define acid and base
3. What is the normal pH range for the body
4. Define acidosis and alkalosis
5. Define and provide an example of a buffer

Answer 3

1. Measure of acidity/alkalinity of a substance/solution
2. Acid - substance capable of donating hydrogen ion to another substance (low pH).
   Base - molecule able to accept hydrogen ion from acid
3. 70-7.7 (7.4 ideal)
4. Acidosis - when blood becomes too acidic.
   Alkalosis - when blood becomes to alkaline
5. Substance which minimises changes in pH. Bicarbonate/carbonic acid

Question 4

1. Define diffusion
2. Give 3 things that effect the rate of diffusion
3. Define osmosis
4. Define simple diffusion

Answer 4

1. Random, passive movement of molecules from area of high to area of low concentration, until equally distributed
2. Steepness of concentration gradient, molecular size, temperature
3. Diffusion of water molecules from area of high to area of low concentration, until equilibrium achieved
4. Diffusion across lipid bilayer membrane

Question 5

1. Define tonicity
2. What happens to cells in a hypertonic solution?
3. What happens to cells in a hypotonic solution?
4. What happens to cells in an isotonic solution?

Answer 5

1. Ability of extracellular solution to move water into or out of cell by osmosis
2. Higher concentration (more solute) outside cell. Water concentration higher inside cell, so net flow of water out of cell, in attempt to achieve equilibrium. Cells shrivel/shrink (crenation)
3. Higher concentration (more solute) inside cell. Water concentration higher outside cell, so net flow of water into cell, in attempt to achieve equilibrium. Cells swell/expand (leading to lysis)
4. Equal concentration of solute and water inside and outside of cell. Equilibrium already achieved, no net flow of water, no effect on cell

Question 6

1. Describe dehydration reactions
2. Describe hydrolysis reactions
3. Give 3 examples of simple carbohydrates
4. Give 3 examples of complex carbohydrates
5. What is the name of the functional group in a lipid
6. What defines whether lipids are mono, di or triglycerides
7. Give 3 types of lipids

Answer 6

1. Synthesis reaction that links subunits into larger molecules and releases water
2. Degradation reaction that breaks down large molecules into smaller subunits by adding water
3. Glucose, fructose, galactose
4. Glycogen, starch, cellulose
5. Carboxyl (-COOH) group
6. Number of fatty acid chains
7. Steroids, phospholipids, eicosanoids (signalling molecules)

Question 7

1. What is an essential amino acid and how many are there
2. What is the difference between an oligopeptide, polypeptide and proteins
3. Describe the level of organisation within a protein and what each structure is involved in
4. What 3 amino acids are must be present/not substituted for sickle cell disease to be absent
5. What is the function of nucleotides

Answer 7

1. Cannot be synthesised and must be derived from diet. There are 9
2. Oligopeptides (2-9 amino acids). Polypeptides (10-100 amino acids). Proteins (>100 amino acids)
3. Primary structure - sequence/number of amino acids. Determines function
   Secondary structure - shape/spatial arrangement (a-helix or b-pleated sheets). Determines stability and shape.
   Tertiary structure - 3D shape (globular/fibrous). Determines specificity.
   Quaternary structure - number of subunits (dimer, trimer, tetramer, ring/chain, helix). Formation of functional protein
4. Glutamic acid, histidine, proline
5. Transmit and store genetic information

Question 8

1. Define protein ligand
2. Define binding site
3. Define protein specificity
4. Define protein affinity
5. Define isoformers

Answer 8

1. Molecule which produces a signal by binding to a site on a target protein
2. Region that binds to another molecule with specificity
3. Ability of binding site to bind specific ligands
4. Attraction to a ligand - strength of binding reaction between protein and ligand
5. Proteins like another that have similar roles within cells (similar function, affinity differ)

Question 9

1. Briefly describe the induced-fit model of protein binding and what causes this
2. Describe 4 factors affecting protein affinity
3. Give 4 factors affecting protein binding
4. Describe saturation in relation to a protein reaction, and how this can be overcome

Answer 9

1. Protein binding sites change conformation as ligand approaches. Caused by interaction between hydrogen, ionic and van der Waals bonding
2. Cofactors (any non-protein substance required for a protein to be catalytically active), competitive inhibition (blocks ligand at binding site. Can be overcome by increasing concentration of ligand), allosteric modulation (activation/inhibition - modulator binds to protein away from binding site activating/inactivating protein), temperature (denaturation), pH (denaturation)
3. Cofactors, proteolytic activation, competitive inhibitors, irreversible inhibitors, allosteric modulators, covalent modulators, pH and temperature
4. Maximum rate of reaction reached. Reaction rate increases until ligand (or protein) concentration increases, whilst other remains constant. Can be overcome by increasing the constant

Question 10

1. Give 4 functions of the cell membrane
2. Brief describe what is meant by the fluid mosaic model
3. How thick is the cell membrane

Answer 10

1. Physical barrier, gateway for exchange, communication, cell structure
2. Bilayer arrangement of phospholipids, with hydrophobic tails inside and hydrophilic heads facing out, with embedded proteins
3. 8nm thick

Question 11

1. Define cytosol
2. What are inclusions and what are their function
3. Give one example of an inclusion
4. Define organelles
5. What are the function of cytoplasmic protein fibres. Give 2 examples

Answer 11

1. Fluid portion of cytoplasm
2. Insoluble particles within cytoplasm with no membrane. Involved in energy storage and protein synthesis
3. Ribosomes
4. Membrane-bound structures in cytoplasm
5. Structural support and movement. actin, myosin, keratin, neurofilament, tubulin

Question 12

1. What are microtubules and what 3 things do they form
2. Where are microtubules formed
3. What are cilia and flagella, what do they do and what is the difference between them

Answer 12

1. Hollow, rigid structures. Key component of cytoskeleton. Help cells maintain shape. Form centrioles, cilia and flagella
2. Centrosome
3. Tiny, hair-like organelles that protrude from the surface of many types of cells in the body. Help cells move themselves forward or sweep substances along outer surface of cell. Cilia are shorter and more numerous than flagella. Cilia are present in organisms, while flagella can be found in bacteria and sperm cells

Question 13

1. Give 4 functions of the cytoskeleton
2. What is the function of motor proteins
3. Give 3 types of motor proteins

Answer 13

1. Cell shape (mechanical strength), internal organisation, intracellular transport, movement
2. Convert stored energy to movement
3. Myosins, kinesics, dyneins

Question 14

1. What is the function of the nucleus
2. What is the structure of the nucleus
3. What are 2 components of the nucleus

Answer 14

1. Control centre, contain/store genetic material
2. Envelope - double membrane with pores
3. Chromatin (genetic material), nucleolus (where rRNA produced)

Question 15

1. What is the endoplasmic reticulum
2. What are 2 types of ER
3. What are the functions of different types of ER

Answer 15

1. Folded membrane attached to nuclear membrane that extends into cell
2. Rough ER, smooth ER
3. Rough ER - protein synthesis
   Smooth ER - lipid synthesis (included phospholipids), involved in hormone production and drug detoxification

Question 16

1. What is the role of mitochondria
2. Describe the key feature of mitochondria shape/structure

Answer 16

1. ATP generation - powerhouse of cell
2. Double membrane (inner membrane folded into cristae)

Question 17

1. What is the Golgi apparatus and what is its function
2. Describe the process of protein release
3. What is the difference between secretory and storage cytoplasmic vesicles

Answer 17

1. Stack of curved membranous saccules. Transport and protein secretion (processing, sorting, packaging)
2. Synthesis - in ER
   Transport - proteins transported from ER to Golgi apparatus for processing (addition/modification if required) and maturation
   Packaging - into transport vesicles
   Release/secretion - transport vesicles move through cytoplasm and fuse with cell surface, releasing proteins into extracellular space
3. Secretory - contain proteins for outside cell
   Storage - store contents which don’t leave cytoplasm

Question 18

1. What are lysosomes and what do they do
2. How are they activated
3. Faulty lysosomes are implicated in which two disorders
4. What are peroxisomes and what do they do

Answer 18

1. Storage vesicles which act as cell digestive system (breakdown and recycle cellular materials) and encourage cell apoptosis
2. Normally inactive at pH 7-7.3. Lysosomes sit in cytoplasm and acquire H ion. ph drops to 4.8-5.0, activating enzymes which break down cellular material
3. RA and Tay-Sachs
4. Storage vesicles, similar to lysosomes, that contain different enzymes. Breakdown long-chain fatty acids and foreign molecules, generating H2O2, which is converted into H2O and O2 by catalase

Question 19

1. Describe the difference between cell necrosis and cell apoptosis
2. Describe the process of cell necrosis
3. Describe the process of apoptosis

Answer 19

1. Necrosis - due to trauma/toxins/lack of oxygen. Apoptosis - programmed cell death
2. Damage occurs, necrotic cell swells, organelles deteriorate and cells rupture. Digestive enzymes leach out and damage adjacent cells, triggering inflammatory response
3. Chromatin in nucleus condenses, cell shrinks and breaks up. Cell eaten by neighbouring cells or phagocytes. No damage to adjacent cells

Question 20

1. Name 5 ways cells can communicate with each other and briefly describe each method
2. Name four categories of membrane receptors and briefly describe how binding of extracellular signal molecules works

Answer 20

1. Gap junctions - form direct cytoplasmic connection between adjacent cells
   Contact-dependent signals - require interaction between membrane molecules on two cells
   Paracrine and autocrine signals - chemical signals that diffuse through interstitial fluid to reach target cells
   Hormones - long distance communication
   Neurotransmitters - chemicals secreted by neurons
2. Ligand-gated channel - ligand binding opens/closes channel
   Receptor-enzyme - ligand binding activates intracellular enzyme
   G protein-coupled receptor - ligand binding opens ion channel/alters enzyme activity
   Integrin - ligand binding alters cytoskeleton

Question 21

1. Briefly describe the concept of the cascade effect/second messenger in intracellular signalling in relation to adenylyl cyclase-cAMP

Answer 21

1. Signal molecule binds to G protein-linked receptor, activating G protein.
   G protein activates adenylyl cyclase (amplifier enzyme)
   Adenylyl cyclase converts ATP to cAMP, which activates protein kinase A.
   Protein kinase A phosphorylates other proteins, leading to a cellular response

Question 22

1. What is the function of a cell junction
2. What are the 3 types of cell junctions

Answer 22

1. Provide contact or adhesion between cells or between cell and ECM
2. Gap junctions, tight junctions, anchoring junctions

Question 23

1. What are gap junctions and what is their function
2. List 3 places gap junctions are found
3. What are gap junction channels formed by
4. What are gap junctions held together by

Answer 23

1. Communicating junctions. Membrane channels between adjacent cells. Allow the direct exchange of cytoplasmic substances (small molecules, substrates, and metabolites) between cells (cytoplasmic communication bridges)
2. Muscles, neurons, liver, pancreas, thyroid gland, ovary
3. Connexins
4. Connexons

Question 24

1. What are tight junctions and what is their function
2. List 2 places tight junctions are found
3. How are tight junctions formed

Answer 24

1. Occluding junctions. Block movement of material between cells and regulate the movement of water and solutes between epithelial layers
2. GI tract, kidney
3. Proteins, Claudia and occludin (transmembrane proteins) allow cell membrane of adjacent cells to fuse together, providing connection between membrane proteins

Question 25

1. What are anchoring junctions and what is their function
2. Give 3 types of anchoring junction and describe their specific functions
3. What are cadherins
4. Give 3 conditions that may result due to cell junction malfunction

Answer 25

1. Attach/anchor cells to one another and attach to components of ECM
2. Adherens junctions - attach cells to other cells/ECM. Anchored to actin filaments (cytoskeleton anchor)and use cadherin/integrin/nectins as transmembrane linker.
   Desmosomes - attach cells to other cells. Anchored to intermediate filaments and use cadherin as transmembrane linker.
   Hemidesmosomes - attach cell to ECM. Anchored to intermediate filaments, and use integrins as transmembrane linker.
3. Cell adhesion molecules important in forming adherens junctions
4. Pemphigus (damaged cell junctions - desmosomes)
   Metastasis

Question 26

1. Name the 4 primary tissue types and their roles
2. List the types of epithelia and give one example of where each type may be found
3. What lines epithelium
4. What are microvilli and where are they found
5. What are cilia and where are they found
6. What are goblet cells and where are they found
7. What do goblet cells look like histologically

Answer 26

1. Epithelial - protection, secretion, absorption, excretion, filtration
   Connective - binds and supports body parts
   Muscle - movement
   Nerve - conduct nerve impulses (send and receive messages) and glial cells for neuronal support
2. Simple squamous - lung alveoli, endothelium
   Simple cuboidal - kidney, glands
   Simple columnar - intestine
   Stratified squamous - oesophagus, mouth
   Stratified cuboidal - salivary gland’s
   Stratified columnar - male urethra
   Ciliated pseudo stratified columnar - respiratory tract (trachea)
3. Basement membrane
4. Microscopic, hair-like protrusions on membrane Increase surface area for diffusion, involved in absolution, secretion, adhesion. Intestines, plasma surface of eggs
5. Microscopic heir-like projections, involved in mucociliary clearance (motile cilia) and sensory organelles (non-motile cilia). Respiratory epithelial cells (motile cilia)
6. Simple columnar epithelial cells that secrete mucins. Found in respiratory, reproductive and lower GI tract
7. Clear bubbles

Question 27

1. What is ground substance
2. Name 4 fibres found within connective tissue ground substance
3. Name 6 types of connective tissue and their functions. What are they composed of and where are they found

Answer 27

1. Extracellular Matrix
2. Collagen, elastin, fibrillar, fibronectin
3. Loose fibrous CT - areolar tissue. Supports epithelium and internal organs. Fibroblasts. Skin, under epithelia
   Dense regular CT - tensile strength to ligaments and tendons. Fibroblasts. Tendons and ligaments
   Dense irregular CT - strength in multiple directions. Fibroblasts. Muscle and nerve sheaths
   Adipose tissue - adipocytes. Fat (energy) storage, cushioning, insulation. Around organs, subcutaneous
   Cartilage - flexible support and cushioning. Chondrocytes. Hyaline, elastic, fibro. Joints, ear, nose
   Bone - supports and protects structures, movement. Osteocytes. Compact/spongy bone. Bones
   Blood - carry oxygen and nutrients to tissue, remove waste, maintain homeostasis. RBCs, WBCs, PLTs. In blood vessels
   Lymph - absorb/redistribute fluid, fight infection. WBCs. In lymph vessels

Question 28

Briefly describe the inflammatory process involved in connective tissue injury, relating the process to the cardinal signs of inflammation

Answer 28

Injury due to stimulus
Mast cell activation - release chemicals (pro-inflammatory markers)
Blood vessel dilation, increased blood flow (redness and heat)
Capillary walls increase in permeability, plasma diffuses into injured tissue (swelling)
Abnormal conditions in tissue and chemicals released stimulate nerve endings (pain)
May contribute to loss of function

Question 29

1. What is muscular tissue composed of
2. Name 2 key proteins found within muscles
3. Name the 3 types of muscular tissue and briefly describe the differences between them (contraction and fibres) and where they are found

Answer 29

1. Myocytes
2. Actin and myosin
3. Skeletal - voluntary contraction/ Attached to bone by tendons. Fibres are cylindrical and long (multiple nuclei, pushed to sides of cells). Striated
   Cardiac - involuntary contraction. Striated. Cells bound end-to-end by intercalated discs.
   Smooth muscle - non-striated, spindle nucleus. Involuntary contraction. Located in viscera

Question 30

1. What is the law of mass balance
2. What is the definition of clearance
3. What does it mean when ICF and ECF are maintained in dynamic disequilibrium, in relation to osmotic, chemical and electrical equilibria
4. Provide the relative concentrations (ECF and ICF) for the following molecules: Na, K, Cl, Ca, HCO3

Answer 30

1. Total mass of a system remains constant over time as long as no matter is transferred into or out of the system - any gain must be offset by equal loss
2. Rate at which a molecule disappears (is cleared) from the body
3. Stability in composition, but not in equilibrium
   Osmotic - equilibrium (water moves freely between ICF and ECF until equal)
   Chemical - solutes more concentrated in ECF or ICF.
   Electrical - ICF negatively charged, ECF positively charged. Body electrically neutral
4. Na, Cl, Ca, HCO3 - ECF > ICF
   K ICF > ECF

Question 31

1. What is Fick’s law
2. What is membrane permeability dependent on
3. What is the definition of flux
4. What is the formula for Fick’s law (rate)

Answer 31

1. Rate of diffusion is proportional to the surface area and concentration difference (gradient), and inversely proportional to the thickness of the membrane
2. Lipid solubility and molecular size
3. Diffusion rate per unit of surface area of membrane (concentration gradient x membrane permeability)
4. Rate = (Surface area x concentration gradient x membrane permeability) / membrane thickness

Question 32

1. What is passive transport
2. What is facilitated diffusion
3. Describe how gated channels work
4. Give 3 examples of a gated channel
5. What is the name for water channels
6. Describe how carrier proteins facilitated protein-mediated transport

Answer 32

1. Type of membrane transport in which substances follow Fick’s law, and move from an area of high concentration to an area of low concentration because this movement increases the entropy of the overall system
2. Type of passive transport that moves molecules or ions across a cell membrane with the help of specialised proteins
3. Small polar molecules are transported by proteins in the form of gated channels that open and close (on cytoplasm side). They are normally closed and open in response to signal (electrical, chemical, ligand), and thus deregulate the flow of ions or small polar molecules across membranes, sometimes against the osmotic gradient
4. Voltage-gated sodium channels, ligand-gated sodium channels, voltage-gated potassium channel, calcium-gated potassium channel
5. Aquaporins
6. Bind specific substrate and move substrate across membrane by changing configuration (similar to canal lock - close one side before opening the other). They are selective and can be uniport (single molecule) or cotransporters (multiple molecules)

Question 33

1. What is active transport
2. What is the difference between primary and secondary active transport. Give an example of each type
3. Describe the processes of primary active transport
4. Describe the process of secondary active transport
5. What is the difference between uniporters, symporters and antiporters
6. Briefly describe how SGLTs work in terms of active transport

Answer 33

1. Movement of molecules from area of low to area of high concentration (against gradient), requires energy
2. Primary - uses energy directly from ATP. Na/K ATPase
   Secondary - uses energy stored in concentration gradient of one molecule to push other molecules against concentration gradient. Energy sourced from electrochemical gradient of molecule. Sodium glucose transporter
3. ATP molecule and 3 Na ions bind pump.
   ATP phosphorylates pump (attaches phosphate group), giving the pump energy to change shape.
   Pump opens towards outside of the cell, releasing Na ions.
   2 K ions bind pump from outside cell.
   Phosphate group released, pump returns to original shape
   K ions released inside the cell
4. Known as cotransport or coupled transport, energy is used to transport molecules across a membrane; however, in contrast to primary active transport, there is no direct coupling of ATP.
5. Uniporter - transport one molecule across a membrane independently of other molecules.
   Symporter - transport two molecules in the same direction across a membrane (cotransport).
   Antiporter - transport two molecules in opposite directions across a membrane.
6. SGLTs bind to an extracellular glucose molecule and two sodium ions (Na+). The Na+ moves into the cell, releasing energy that the SGLT uses to move the glucose inside the cell.

Question 34

1. How do endocytosis and exocytosis work and what is their function
2. Describe the difference between endocytosis and exocytosis
3. Briefly describe the transepithelial transport of glucose
4. Briefly describe transcytosis across the capillary endothelium

Answer 34

1. Endocytosis and exocytosis allow cells to take in nutrients and remove waste. Both are examples of active transport as they move substances against concentration gradients and require energy
2. Endocytosis - cell membrane engulfs a substance/particle from outside cell, forming a vesicle that moves substance into the cell.
   Exocytosis - vesicle containing a substance fuses with the cell membrane, releasing its contents outside the cell
3. Glucose enters the epithelial cells, catalysed by SGLT-1 cotransporter.
   Intracellular cAMP activates the transport.
   Glucose accumulates intracellularly.
   Glucose diffuses out of the cells by facilitated diffusion through GLUT2.
4. Process by which large molecules are transported across the capillary endothelium.
   Endocytosis: The cargo is taken up by vesicles on one side of the cell.
   Intracellular trafficking: The cargo is moved through the cell within the vesicles.
   Exocytosis: The vesicles fuse with the other side of the cell, releasing the cargo.

Question 35

1. What type of energy is used to perform cellular work
2. What type of energy is stored in cells and converted to perform cellular work. In what way is some energy lost during this conversion
3. Define activation energy
4. Define free energy
5. What is the net free energy change of a reaction
6. What is the difference between exergonic and endergonic reactions
7. Where do cells trap and store energy from exergonic reactions

Answer 35

1. Kinetic
2. Potential. When converted, some energy lost as heat
3. Energy required to intimated a chemical reaction
4. Potential energy stored in chemical bonds. free to do work after accounting for loss
5. Difference in free energy between reactants and products
6. Exergonic - reaction that releases energy (free energy reactants > products)
   Endergonic - reaction that traps energy (free energy products > reactants)
7. In cofactors such as NADH, FADH2, NADPH

Question 36

1. Give 2 functions of enzymes
2. Define isozyme
3. Give 4 factors that influence reaction rate
4. What is the law of mass action

Answer 36

1. Increase rate of reaction, lower activation energy
2. Enzyme isomers. Structurally similar (not identical) and catalyse same reaction under different conditions/tissues
3. How quickly products are synthesised
   How quickly substrates are consumed
   Temperature, pH, amount/concentration of substrate and enzyme
4. When reaction is at equilibrium, ratio of products and substrates will remain constant (no net change in amount of substrate or product)

Question 37

1. What are oxidation-reduction (redox) reactions. Give an example of an enzyme involved in these reactions
2. What are hydrolysis-dehydration reactions. Give an example of an enzyme involved in these reactions
3. What is an addition reaction. Give an example of an enzyme involved in this reaction
4. What is a subtraction reaction. Give an example of an enzyme involved in this reaction
5. What is an exchange reaction. Give an example of an enzyme involved in this reaction
6. What is a ligation reaction. Give an example of an enzyme involved in this reaction

Answer 37

1. Chemical reaction involving transfer of electrons between two species
   Oxidation - loss of electrons, gain of oxygen or loss of hydrogen. Oxidase
   Reduction - gain of electrons, loss of oxygen or gain of hydrogen. Reductase
2. Hydrolysis - breakdown of polymer into monomer by adding water (releases energy). Protease, lipase
   Dehydration - synthesis of polymer from monomer by removing water (requires energy). Enolase
3. Addition - functional group added to substrate. Kinase
4. Subtraction - functional group removed from substrate. Deaminase
5. Exchange - function groups exchanged between substrates. Transaminase
6. Ligation - two molecules joined together. Synthetase

Question 38

1. Define catabolism
2. Define anabolism
3. What are reaction intermediates. Give 2 examples
4. List 4 ways cell regulation/metabolism occurs

Answer 38

1. Breakdown of large polymers, producing energy
2. Synthesis of large polymers which requires energy
3. Molecules of metabolic pathways - products of one reaction which become substrate for the next. Acetyl CoA, glucose
4. Controlling enzyme concentration
   Producing modulators (feedback inhibition)
   Using different enzymes
   Isolating enzymes
   Maintaining ratio of ATP to ADP

Question 39

1. Briefly describe the process of aerobic cellular respiration
2. How many ATP does 1 cycle of aerobic respiration produce from 1 glucose molecule
3. Briefly describe the process of anaerobic cellular respiration

Answer 39

1. 3 stages
   Stage 1 - glycolysis. Glucose converted into pyruvate and 2 ATP. Occurs in cytosol
   Stage 2 - citric acid cycle. CO2 removed from pyruvate, leading to formation of acetyl CoA. Combines with oxaloaecetate to form citrate. Produces 3 NADH, 1 FADH2 and 1 ATP as intermediates, which gradually reverses reaction, resulting in cycle. Happens in mitochondria
   Stage 3 - electron transport chain. NADH release H ions and electrons into transport chain. Electron pairs transfer energy to membrane proteins, providing energy to pump H ions across inner mitochondrial membrane, creating H ion concentration gradient. Flow of ions back out synthesise ATP (via ATP synthase) and oxygen combines with H ions and electrons to form water. 36ATP produced (via oxidative phosphorylation)
2. 38 ATP (2 in glycolysis, 36 in electron transport chain)
3. Glycolysis - glucose converted into pyruvate and 2 ATP. CO2 removed from pyruvate. Lack of oxygen causes pyruvate to convert into lactate

Question 40

1. What is the difference between autocrine and paracrine signals
2. What is signal transduction

Answer 40

1. Autocrine - act on cell that secretes signals
   Paracrine - signal secreted by one cell and diffuses to adjacent cells
2. Transducers convert extracellular signals into intracellular messages which create a response

Question 41

1. Define homeostasis
2. What are Cannon’s 4 postulates

Answer 41

1. Continuous process that uses a physiological control system to monitor regulated variables - the tendency towards a relatively stable equilibrium between interdependent elements
2. 1 - all living organisms demonstrate constancy and have a relatively stable and consistent internal environment within an open system.
   2 - any change must be countered with a resistance to change
   3 - homeostatic state is determined by a regulating system composed of multiple cooperative mechanisms that work to maintain homeostasis through simultaneous or sequential acts
   4 - homeostasis is the end result of an organised self-government of an organism

Question 42

1. Briefly describe local control of blood vessel oxygenation
2. Briefly describe a generic reflex pathway
3. Describe the afferent pathways, integrating centres, efferent pathways and effectors in the nervous system and endocrine system

Answer 42

1. Controlled by paracrine and autocrine signals.
   Fall in oxygen concentration sensed by endothelium. Cells secrete paracrine signal causing smooth muscle to relax, leading to vasodilation and an increase in oxygen via blood.
2. Response and feedback loop
   Input signal - stimulus, sensor/receptor, afferent pathway
   Integration of signal, efferent pathway (integrating centre)
   Output signal (target/effector, response)
3. Nervous system - electrical and chemical signals sent through neuron (afferent pathway)
   Integrating centre - CNS
   Efferent pathway - efferent neuron
   Effectors - cells/tissues that carry out response

Endocrine - no afferent pathway. Endocrine cell acts as sensor (afferent pathway) and integrating centre
Efferent pathway - blood stream
Effectors - any cell with specific receptor for secreted hormone

Question 43

1. Give an example of a positive feedback loop and describe it
2. Describe the stages involved in a generic feedback loop
3. What are the difference between neural and endocrine control systems relating to:
   Specificity
   Nature of signal
   Speed
   Duration of action
   Coding for intensity stimulus

Answer 43

1. Uterine contraction during child birth
   Foetus travels to uterus, putting pressure on cervix. Sensory receptors send afferent signal to brain, causing oxytocin release. Oxytocin causes contractions, and foetus pushes further against cervix. Process repeats until delivery (removing stimulus)
2. Initiation event or stimulus
   Variable –> receptor –> control centre –> effector –> variable (feedback loop, leading to change in conditions when required)
3. Specificity: neural - very specific. Endocrine - generalised
   Nature of signal: neural - electrochemical. Endocrine - chemical
   Speed: neural - rapid. Endocrine - slow
   Duration: neural - rapid, termination mechanism. Endocrine - longer, ongoing
   Coding for intensity stimulus: neural - increased frequency. Endocrine - amount of hormone released