Cells and Chemicals

Question 1

Cell Theory and Exceptions

Answer 1

Cell Theory:

1. All living things composed of cells (or cell products)
2. The cell is the smallest unit of life
3. Cells only arise from pre-existing cells

Exceptions:

1. Striated Muscle Fibres: Type of tissue used to change position of our body. Form very long fibres with multiple nuclei surrounded by single, elongated plasma membrane.
2. Fungi may have thread-like structures (hyphae), separated into cells by internal walls (septa). Aseptate hyphae have no cell partitions, so have continuous cytoplasm along hyphae.
3. Giant Algae: Very large unicellular algae with one nucleus, but can be extremely large.

Question 2

Microscopes and Magnification

Answer 2

1. Magnification = Image / Object (x = I/O)
2. Resolution: Ability of microscope to distinguish between two different points.
3. Transmission electron microscopes (TEM):
   Generate high res. cross-sections of objects
4. Scanning electron microscopes (SEM): Display enhanced depth to map surface of objects in 3D.

Question 3

SA : Volume Ratio

Answer 3

1. Cells produce chem. energy (via metabolism) to survive, which requires material exchange.
2. Rate of metabolic reactions ∝ vol. of cell.
3. Rate of substances crossing cell memb. ∝ SA.
4. As cell grows, vol. inc. faster than SA
   → SA : Vol dec.
5. If SA:Vol too small → supply < demand;
   & waste not removed → waste + heat
   accumulate in cell builds → death.
6. Hence growing cells divide & stay small to maintain high SA:Vol ratio suitable for survival.

Question 4

MR SHENG and Unicellular organisms

Answer 4

Functions of Life

1. Metabolism – Undertake essential chemical reactions
2. Reproduction – Producing offspring, either sexually or asexually
3. Sensitivity – Responding to int. & ext. stimuli
4. Homeostasis – Maintain a stable int. env.
5. Excretion – Removal of waste products
6. Nutrition – Exchanging materials & (g) with env.
7. Growth – Moving & changing shape or size

Question 5

Multicellular Organisms Advantages

Answer 5

1. Emergent properties arise from interaction of the component parts of complex structure.
   
   1. Cells
   2. Tissues
   3. Organs
   4. Systems
   5. Organism
2. Different cells also perform different functions and so become specialised, via differentiation.
3. Differentiation: Expression of some genes, but not others in a cell’s genome.

Question 6

Stem Cells

Answer 6

1. Stem Cells differ from most cells because they:
   
   1. Are unspecialised.
   2. Divide repeatedly to make many cells.
   3. Can differentiate into different cell types.
2. 4 different types of stem cell:
   
   1. Totipotent: Form any cell type, as well as placental tissue (e.g. zygote)
   2. Pluripotent: Form any cell type
      (e.g. embryonic stem cells)
   3. Multipotent – Differentiate into some,
      closely related cell types
      (e.g. haematopoeitic adult stem cells)
   4. Unipotent – Can’t differentiate, but can
      self renew (e.g. adult & muscle stem cells)
3. Taken from embryos, umbilical cords, or rarely from adult tissue.
4. Used therapeutically to replace/repair
5. Used non-therapeutically (e.g. prevent cattle killing by making meat from stem cells).
6. 2 main therapeutic uses (table)

Question 7

Compartmentalization Advantages

Answer 7

1. Enzymes and substrates for a particular process can be much more concentrated than if they were spread throughout the cytoplasm.
2. Substances that could damage cell kept inside membrane of an organelle.
3. Conditions like pH can be maintained at an ideal level for particular process, which may be different to levels needed for other processes in cell.
4. Organelles with their contents can be moved around within cell.

Question 8

Prokaryote Structure

Answer 8

Question 9

Eukaryote Structure

Answer 9

Question 10

Draw Eukaryote & Prokaryote

Answer 10

Question 11

Differences between Eukaryotes and Prokaryotes

Answer 11

Question 12

Membrane Structure + Properties

Answer 12

1. Hydrophilic Tail: Attracted to water, face out.
2. Hydrophobic Head: Repelled by water, face in.
3. Amphipathic: Membrane therefore part hydrophilic and part hydrophobic.
4. Phospholipids thus, spontaneously arrange into bilayer in water (such as in cells).
5. Tails face in & are shielded from surrounding polar fluids, whilst heads face outwards.
6. Structural Properties:
   
   1. Bilayer held together in bilayer by hydrophobic interactions between tails.
   2. Hydrophilic / hydrophobic layers thus restrict passage of many substances
   3. Individual phospholipids move within
      bilayer → membrane fluidity & flexibility
   4. Fuidity allows spontaneous breaking &
      reforming of membranes (end/exocytosis)

Question 13

Membrane Proteins (TRACIE)

Answer 13

Types:

1. Integral Proteins: Permanently attached to membrane & are typically transmembrane (span across bilayer)
2. Peripheral Proteins: Temporarily attached by non-covalent interactions & associate with
   surface of membrane

Structure: AA polarity leads to function of protein:

1. Non-polar (hydrophobic) AA’s associate directly with lipid bilayer → Peripheral.
2. Polar (hydrophilic) AA’s located internally & face aqueous solutions → Internal.
3. Amphipathic AA’s → transmembrane.

Functions (TRACIE):

1. Transport: Pump (Na⁺/K⁺ pump = AT) & channel (K⁺ or Na⁺ channels or aquaporin = FD)
2. Receptors: Function as receptors for peptide hormones (e.g. Insulin).
3. Anchorage: Attachment points for cytoskeleton & extracellular matrix.
4. Cell Recognition: May function as markers for cellular ID. (e.g. self-antigens)
5. Intercellular Joinings: Serve to connect & join 2 cells together (e.g. Plasmodesmata)
6. Enzymatic Activity: Fixing to memb. localises metabolic pathways (e.g. e¯ transport chain)

Question 14

Cholesterol

Answer 14

1. Cholesterol: Amphipathic steroid positioned between phospholipids.
2. ​The higher the conc, the less rigid, permeable & flexible membrane becomes.
3. Chol. immobilises outer surface of membrane, reducing fluidity
4. Makes memb. less permeable to hydrophilic molecules that usually cross (e.g. Na⁺).
5. Separates tails → prevents memb. crystallisation.
6. Helps secure peripheral proteins by forming high dens lipid rafts that anchor protein.

Question 15

Membrane Models and Structure

Answer 15

1. Membranes viewed under TEM exhibit 2 dark outer layers & lighter inner region.
2. Danielli & Davson first proposed model whereby 2 protein layers flanked central phospholipid bilayer — ‘lipo-protein sandwich’.
3. There were a number of problems with the lipo-protein sandwich model proposed by Davson and Danielli:
   
   1. Dark segments seen under TEM were identified (wrongly) as representing the 2 protein layers
   2. Assumed all memb. had uniform thickness & had constant lipid-protein ratios.
   3. Assumed all membranes had symmetrical int. & ext. surfaces.
   4. Temps at which membranes solidified did not correlate with those expected under the proposed model
   5. Membrane proteins were discovered to be amphipathic & insoluble in water (indicating hydrophobic surfaces)
   6. Model suggests memb. proteins exposed to hydrophilic surfaces on all sides, so when proteins found to be amphipathic →
      Protein’s outer hydrophobic part would face hydrophilic surfaces, which isn’t a stable configuration.
4. Singer-Nicolson Model showed proteins embedded within lipid bilayer rather than existing as separate layers:
   1. Fluid: Phospholipid bilayer is viscous &
      single phospholipids can move position
   2. Mosaic: Phospholipid bilayer embedded with proteins, resulting in mosaic of parts.

Question 16

Forms of Transport

Answer 16

Diffusion: Net movement of molecules from
region of high conc. to region of low conc. until molecules become evenly dispersed (equilib.)

1. Small & non-polar molecules freely diffuse across cell memb, (e.g. O₂, CO₂, glycerol)
2. Rate of diffusion can be influenced by a number of factors, including:
   
   1. Temp: Affects KE of particles in solution
   2. Molecular size: Fluid medium resists larger particles more (moves slower).
   3. Steepness of gradient

​​​Osmosis: Net movement of H₂O across semi-perm. memb. from region of low [solute] to region of high [solute] until equilibrium is reached.

1. H₂O associates with, & dissolves, polar or charged molecules (solutes) so acts as solvent.
2. As solutes can’t cross cell memb. unaided, H₂O moves to equalise solutions
3. At higher [solute], less free H₂O molecules in solution as H₂O associated with solute.

Fac. Diff.: Passive movement of molecules across cell membrane via aid of memb. protein

1. Utilised by molecules that can’t freely cross bilayer (e.g. large, polar molecules & ions)
2. Mediated by 2 distinct types of interal proteins:
   
   1. Carriers: Bind to spec. solute & change structurally to translocate solute across membrane. May move molecules against [gradients] in presence of ATP
   2. Channels: Contain pore via which ions may cross entire membrane. Ion-selective and may be gated to regulate passage of ions in response to certain stimuli. Only move molecules along [gradient].

AT: Uses energy to move molecules against [grad.] along carrier proteins (protein pumps).

1. This energy may either be generated by:
   
   1. Direct hydrolysis of ATP.
   2. Indirectly coupling transport with another molecule that is moving along its gradient.
2. Specific solute binds to protein pump on 1 side of memb.
3. Hydrolysis of ATP (to ADP + P) causes structure
   change in protein pump
4. Solute molecule translocated across memb.
   (against [gradient]) & released.
5. K+ channels:
   1. Axons of nerve cells transmit elec.
      impulses by translocating ions to create a voltage diff. across membrane
   2. At rest, Na/K pump expels Na⁺ from nerve cell, whilst K⁺ ions accumulate within.
   3. When neuron fires, ions swap locations via fac. diff. via Na⁺ & K⁺ channels
   4. K+ Channels: Integral proteins with
      hydrophilic inner pore via which K⁺ may be transported. Usually voltage-gated &
      open & close depending on transmemb V.

Question 17

Na and K Transport in Nerve Cells

Answer 17

1. Axons transmit electrical impulses by translocating ions to create V diff. across memb
2. At rest, the Na/K pump expels Na⁺ from neuron
   whilst K⁺ accumulate within.
3. When neuron fires, these ions swap locations via facilitated diffusion via Na⁺ & K⁺ channels

Sodium-Potassium Pump: Integral protein that exchanges 3 sodium ions (moves out of cell) with two potassium ions (moves into cell)

1. Process of ion exchange against [grad.] is energy-dependent & involves steps:
   
   1. 3Na⁺ ions bind to intracellular sites on Na/K pump
   2. Phosphate group transferred to pump via ATP Hydrolysis.
   3. Pump undergoes structure change, translocating Na⁺ across membrane
   4. Structure change exposes 2K⁺ binding sites on extracellular surface of pump.
   5. Phosphate group released → pump return to original conformation
   6. Translocates K⁺ across membrane, completing ion exchange.
2. K⁺ Channel: Integral proteins with hydrophilic inner pore via which K⁺ may be transported
   1. Channel comprised of 4 transmembrane subunits.
   2. Inner pore has filter at its narrowest region that stops alt. ions passing.
   3. K channels typically V-gated & open & close depending on the transmemb. V.

Question 18

Osmolarity in Cells

Answer 18

1. Osmolarity: Total concentration of osmotically active solutes in a solution.
2. Hypertonic: Higher osmolarity than tissue.
   
   • Hypertonic solutions cause H₂O to leave cells by osmosis, so cytoplasm shrinks in volume
3. Hypotonic: Lower osmolarity than tissue.
   
   • Hypotonic solutions causes H₂O to enter cells by osmosis, which make cell swell.
   • Cell wall prevents plant cells bursting.
4. Isotonic: Has same osmolarity as a tissue.
   
   • H₂O to entry/levels = same
   • For this reason:
     
     • Human tissue bathed in isotonic solution in medic procedures.
     • Used to rinse wounds & abrasions.
     • Used to keep areas of damaged skin moistened prior to skin grafts.
     • Used as basis for eye drops.

Question 19

Protein Transport

Answer 19

1. Proteins produced by euk. initially synth. by free ribosomes found within cytosol.
2. If protein targeted for intracellular use within cytosol, ribosome remains free and unattached
3. If protein targeted for secretion, memb fixation or use in lysosomes, ribosome binds to ER.
4. Presence of signal seq. results in addition of signal recogn. particle (SRP), which stops transl
5. SRP-ribosome complex binds to receptor located on ER membrane (forming rough ER).
6. Transl. restarts & polypep. chain continues to grow via transport channel into ER lumen.
7. Signal seq. then cleaved & SRP recycled once polypep. completely synth. within ER.
8. Vesicle with polypeptide (made by memb.
   budding) moves & binds to Golgi cis-face.
9. Polypeptide moves (via vesicle) from cis face to trans face, may be modified along the way.
10. Synth. protein transported via vesicle to:
    
    1. Golgi complex (for secretion)
    2. Lysosome
    3. Embedded into ER memb (for memb. fix.)
    4. Plasma memb, where it’s released by exocytosis either:
       1. Constitutive Secretion: Released immediately into extracellular fluid.
       2. Regulatory Secretion: Stored within
          intracellular vesicle for delayed release in response to cellular signal.

Question 20

Endocytosis and Exocytosis

Answer 20

1. Endocytosis: Process by which large materials
   enter cell without crossing plasma membrane
   
   • Memb invagination forms flask-like depression that envelopes extracell material.
   • Invagination sealed off by surrounding memb. to form intracellular vesicle with material + H₂O.
2. Exocytosis: Process by which large substances
   exit cell without crossing plasma memb
   
   • Vesicles fuse with plasma memb, expelling their contents out of cell.
   • Exocytosis adds vesicular phospholipids to cell memb as well, replacing those lost by vesicles formed in endo.
3. Both processes carried out by membrane proteins, using energy from ATP.
4. Both processes also rely on the fluidity and flexibility of membrane.

Question 21

Miller-Urey Experiment

Answer 21

Miller and Urey demonstrated the non-living synthesis of simple organic molecules.

1. Recreated postulated conditions of pre-biotic Earth using closed system of flasks & tubes
2. H₂O boiled to vapour to reflect high temps common to Earth’s original conditions
3. Vapour mixed with variety of gases (including H₂, CH₄, NH₃) to create reducing atm (no O₂)
4. Mixture then exposed to electrical discharge
   (simulates lightning, which supplied E for
   reactions)
5. Mixture then allowed to cool (concentrating components) & left for a period of time.
6. Condensed mixture then analysed & found to contain traces of simple organic molecules.

Question 22

Endosymbiosis

Answer 22

1. Mitochondria were once free-living prokaryotes that developed aerobic cell resp.
2. Larger prokaryotes that could only respire anaerobically took them in by endocytosis.
3. Instead of killing + digesting smaller cell, they were allowed to live in their cytoplasm.
4. Smaller cell grew & divided as fast as larger cell, so persisted indefinitely inside larger cells.
5. Mutualistic relationship arose as smaller cell supplied with food by larger one, whereas smaller cell supplied energy efficiently to larger cell through aerobic respiration.
6. Natural selection therefore favoured cells that had developed this endosymbiotic relationship
7. Supported by fact that mitochondria and chloroplasts have:
   
   • Their own genes, on a circular DNA molecule like prokaryotes.
   • 70S ribosomes of size & shape typical of prokaryotes.
   • Transcribe DNA and use mRNA to synthesise their own proteins.
   • Only produced by binary fission of pre-existing mitochondria and chloroplasts

Question 23

Louis Pasteur’s Experiments

Answer 23

1. Nutrient broth made by boiling H₂O containing yeast + sugar & placed in short, vertical-necked flasks and swan-necked flasks.
2. Broth in both types of flasks in contact with air (“needed” for spont. gen.) yet none occurred in swan-necked flask.
3. Mould only made when swan-neck snapped, which allowed bacteria to enter flask.
4. Different liquids experimented, including milk and urine, which gave similar results.
5. Demonstrated that cells only made by other cells, which falsified spont. gen. theory.

Question 24

Cell Cycle

Answer 24

1. Interphase: Stage in cell dev. between 2 succ. cell divisions. Most metabolic reactions occur in this stage. Continuum of 3 distinct stages:
   
   • G₁: Cell growth, organelle replication, transcription/lation & respiration for ATP.
   • S: DNA/Chromosome replication
   • G₂: Copied DNA checked for mutations & final metabolic reactions occur before replication.
   • Sometimes cells leave cell cycle & enter G₀, whereby it no longer divides.
2. Mitosis: Nucleus divides into 2 genetically identical daughter cells. Each chromatid made in S phase goes to each daughter cell:
   
   • Prophase
   • Metaphase
   • Anaphase
   • Telophase
3. Cytokinesis: Cytoplasm divides. Separation occurs from outside & moves to centre in animals and vice-versa in plants.
   
   1. In animal cells:
      
      • After anaphase, contractile microtubule filaments form ring around cell equator.
      • Microfilaments constrict to form
        cleavage furrow, which deepens from periphery towards centre
      • Furrow meets in centre → cell pinched off & 2 daughter cells form.
   2. In plant cells:
      
      • After anaphase, cellulose-rich vesicles fuse to form tubular structures across equator.
      • Tubular structures fuse together &
        cell plate forms along cell equator.
      • Cell plate extends outwards & fuses with cell wall, dividing cell into 2
        distinct daughter cells

Question 25

Purposes of Mitosis (GATE)

Answer 25

• Growth: Multicellular organisms inc. their size by inc. their number of cells through mitosis
• Asexual reproduction: Certain eukaryotic organisms may reproduce asexually by mitosis (e.g. vegetative reproduction)
• Tissue Repair: Damaged tissue can recover by replacing dead or damaged cells
• Embryonic development: Zygotes undergo mitosis & differentiation to develop into embryo.

Question 26

Mitotic Index

Answer 26

1. Mitotic Index: Ratio between no. of cells in mitosis in a tissue and total no. of observed cells.
2. Used to predict:
   
   1. Whether a cell is a cancer cell
   2. Response of cancer cells to chemotherapy.

Question 27

Cyclins

Answer 27

1. Cyclins: Group of proteins that control
   progression of cell cycle.
2. 4 types of cyclins in human cells, that bind to bind to, & activate, different classes of CDK.
3. CDK’s phosphorylate proteins responsible for tasks in each cell cycle stage.
4. Thus [Cyclin] regulated to ensure correct progression of cell cycle.
5. Cyclins peak when target protein needed & degrade after task completed, so CDK is rendered inactive again & [cyclin] low again.
6. Richard Hunt found cyclins by accident when working on haemoglobin synthesis in sea urchin eggs. He noticed chemicals in different conc. during mitosis & interphase.

Question 28

Tumours + Cancers

Answer 28

1. Tumours: Abnormal cell growths resulting from uncontrolled cell division, can occur in any tissue or organ.
2. Metastasis: Cell movement from 1º tumour to set up 2º tumours in other parts of body.
3. Benign: Tumours that adhere to each other & don’t invade nearby tissues or move to other parts of body (usually harmless).
4. Malignant: 1º tumours with cells that can detach & move elsewhere in body, developing into 2º tumours = carcinomas (usually lethal).
5. Cancers: Diseases caused by carcinomas.
6. Carcinogens: Cancer-causing mutagens:
   
   • Physical: Ionising radiation (X-rays, UV, Gamma) transmit lots of energy, may cause mutations.
   • Chemical: (e.g. reactive O₂ species) Interact with DNA, thus inc. mutation risk.
   • Biological: Viruses, Bacteria, etc.
7. Mutations: Random changes to base sequences of genes.
8. Oncogenes: Genes involved in control of cell cycle + division.
   
   • Mutation to oncogenes causes uncontrolled cell division (cancer).

Question 29

Smoke and Cancer

Answer 29

1. Positive correlation exists between cigarette smoking and death rate due to cancer.
2. Also higher DR among those who smoked at one time but had stopped.
3. Huge inc. in DR due to cancers of mouth, pharynx, larynx & lung; & smaller inc. in cancers to other areas of body.
4. Although + correlations don’t mean causation, causal links established as cigarette smoke contains many different chemical mutagens.

Question 30

Chemical Drawings

Answer 30

Question 31

Urea + Vitalism

Answer 31

1. Vitalism: Doctrine that dictated that “vital element” needed to make organic molecules.
2. Urea: N-compound made by cycle of reactions in liver to break down excess AA’s in body.
3. Vitalism falsified by Woehler who produced urea artificially, using similar reactions (and without body enzymes):
4. NH₃ + CO₂→ NH₄(Carbamate) → Urea + H₂O
5. Falsifies Vitalism.
6. Used as fertilizer to provide N to plants.

Question 32

Anabolism and Catabolism

Answer 32

1. Metabolism: Describes totality of all enzyme-catalysed reactions in a cell or organism.
2. Two main types of metabolic pathways:
3. Anabolism: Condensation reactions that involve synthesis of complex polymers + H₂O from simpler monomers (using ATP).
   
   • Protein synthesis using ribosomes.
   • Triglyceride synthesis.
   • DNA synthesis during replication.
   • Polysacc. synthesis + Photosynthesis
4. Catabolism: Hydrolysis reactions that breakdown complex polymers using H₂O into simpler monomers, releasing energy.
   
   • Food digestion in mouth, stomach and small intestine.
   • Cell respiration where glucose or lipids are oxidised to CO₂ and H₂O.
   • Digestion of complex carbon compounds in dead organic matter by decomposers.

Question 33

Water Properties

Answer 33

Heat Capacity: High, as lots of nrg needed to break extensive H-bonding & change H₂O’s temp:

1. Env’s are thermally stable as they tend to remain at same temp.
2. Blood or other fluids can carry heat around their bodies.

BPt: High as many H-bonds need a lot of nrg to be broken:

1. H₂O is (l) at most temps, making it a suitable habitat for aquatic organisms.
2. ​H₂O has wide range of temps where it’s (l)
   (0-100ºC), which are found in most habitats on Earth.

LHV: High as evaporating H₂O requires H-bond breaking, which requires absorbing lots of heat
(to break bond).

1. Sweating & transp. enable orgs to lose heat as they involve evaporation, which releases heat required to evaporate H₂O in sweat.
2. H₂O acts as a coolant.

​Cohesion: Binding of 2 molecules of same type (like 2 H₂O molecules due to H-bonding).

1. H₂O sucked through xylem vessels at low press, without being separated by suction forces (as they stick to themselves).
2. Surface Tension: H-bonding between H₂O
   molecules makes H₂O dense enough for some small organisms to move along its surface.

Adhesion: Binding of 2 molecules of diff types (e.g.
H₂O + Cellulose) due to their polarities/H-bonding.

1. Capillary Action: H₂O & cellulose adhere, so if H₂O evaps from cell walls & is lost from leaf, adhesive forces cause H₂O to be drawn out of nearest xylem vessel → Keeps walls moist to absorb CO₂ needed for photosynthesi

Universal Solvent: H₂O solvates polar/charged molecules due to polarity of lots of H₂O, which weaken IM forces & cause ion dissociation.

1. Cytoplasm mainly composed of H₂O containing complex mixture of dissolved substances in which metabolism occurs.

Transparency: H₂O is transparent so it allows photosynth & capture of prey; so aquatic food chains can exist;

Density: Ice less dense than H₂O, so ice forms at surface, providing insulation to H₂O below, in which living orgs can survive in;

Question 34

Molecules transported by blood

Answer 34

• NaCl: Ionic, water-soluble compound; dissolves to form Na⁺ & Cl¯ ions; carried in blood plasma.
• Amino Acids: Polar due to δ⁺ amine & δ¯
  carboxyl, so dissolve & carried in blood plasma.
• Glucose: Polar molecule due to hydroxyl groups, so dissolves & carried in blood plasma.
• Oxygen: Non-polar, but small so low [O2]
  dissolve in H₂O. Haemoglobin in RBCs has binding sites for O₂ & greatly inc capacity of blood for O₂ transport despite high temp.
• Fats: Non-polar & hydrophobic, so insoluble. Carried in blood inside lipoprotein complexes (groups of molecules with single layer of phospholipid on outside and fats inside).
• Cholesterol: Mostly hydrophobic so insoluble, it’s transported with fats in lipoprotein complexes.

Question 35

Cellulose, Starch, Glycogen

Answer 35

Question 36

Lipid Functions (SHIPS) & comparision with carbohydrates for storage

Answer 36

1. Structure: Phospholipids are main component of cell membranes
2. Hormonal Signalling: Steroids involved in hormonal signalling (e.g. oestrogen, progesterone, testosterone)
3. Insulation: Fats in animals can serve as heat insulators in sub-cutaneous adipose tissue.
4. Protection: Triglycerides form adipose tissue around organs & are shock absorbers.
5. Storage of energy: Triglycerides used as LT energy storage because:
   
   1. Can’t break down as easily as glycogen.
   2. Triglycerides insoluble, whereas mono-disacc’s are soluble so more easily moved
   3. Can’t be used for anaerobic respiration
   4. Lipids store more E/gram, so release more energy when broken than glycogen.
   5. Lipids also have smaller effect on cell osmotic pressure than glycogen.

Question 37

BMI differences and effects in rich/poor countries

Answer 37

1. BMI = Mass (kg) ÷ (Height (m))²
2. Obesity: Too much fat in adipose tissue from lack of exercise & excessive food taken
3. Obesity inc. risk of CHD and Type 2 diabetes. Also reduces LE significantly & inc. costs of healthcare in countries where it’s rising.
4. In poor countries, Mal/undernutrition more common and reduces BMI in these countries.
5. in richer countries it’s anorexia nervosa, a psychological condition involving voluntary starvation and loss of body mass as a result).

Answer 38

1. Cis-fatty acids: Unsaturated fatty acids with H atoms on same side of double bond.
2. Bend in hydrocarbon chain at double bond present → less good at packing together in regular arrays than saturated fatty acids → dec. mpt → usually (l).
3. Trans-fatty acids: Unsaturated fatty acids with H atoms on opposite sides of double bond.
4. Trans don’t have bend → pack together in regular arrays better → inc. mpt → usually (s).
5. Trans-fatty acids produced artificially through partial hydrogenation of vegetable or fish oils.

Question 39

Health Risks of Fats + Cholesterol

Question 40

Protein Structure

Answer 40

1. 1º Structure: Sequence & no. of AAs in polypeptide:
   
   1. 20 diff. AA’s naturally synthesised by rib.
   2. Ribosomes can make pep bonds between any AA pair, so any AA seq. possible.
   3. For a polypeptide of n AA’s, there are 20ⁿ possible sequences.
2. 2º Structure: Formation of alpha helices and ß-pleated sheets stabilised by H-bonding.
   
   1. H-bonds form between COOH group of 1 AA & NH₂ of AA in another part of chain due to folding caused by polar covalent bonds between AAs.
   2. This results in formation of patterns within polypeptide called 2º structures.
3. 3º Structure: Refers to overall 3-D shape of polypeptide caused by further folding of polypeptide stabilised by interactions between R-groups. Several different types of interaction:
   
   1. Oppositely charged R-groups interact with each other.
   2. Hydrophobic AAs orientate themselves towards polypeptide centre to avoid contact with H₂O, whilst hydrophilic AAs orientate themselves outwards.
   3. Polar R-groups form H-bonds with other polar R-groups.
   4. R-group of cysteine can form disulphide bridges with R-group of another cysteine.
4. 4º Structure: Interactions between >1
   polypeptide chain and/or prosthetic groups.
   
   • Haemoglobin: Composed of 4 polypep.
     chains (2 alpha chains & 2 beta chains)
   • Also contains Fe-containing haeme groups, which binds to O₂.

Question 41

Globular vs. Fibrous Proteins

Answer 41

Question 42

Gene and Polypeptide Relationship

Answer 42

1. Gene: DNA seq. that encodes a polypep. seq.
2. Gene seq. converted into polypep. seq. via:
   
   1. Transcription: Synthesising mRNA from DNA template (occurs within nucleus)
   2. Translation: Synthesising polypep’s using mRNA (occurs at ribosome)
3. Typically, 1 gene will code for 1 polypep. But:
   
   1. Genetic code is degenerate, so more than one amino acid coded for by each codon.
   2. Genes may be alt. spliced to make
      multiple polypep. variants
   3. Genes encoding tRNA seq. transcribed but never translated
   4. Genes may be mutated & so produce an alt. polypep. seq.

Question 43

Proteome and Genome

Answer 43

1. Proteome: All of proteins produced by a cell, tissue or organism.
   
   1. Found by extracting protein mix’s from sample & separating by gel electroph.
   2. Fluoresce-marked antibodies specific to each protein fluoresce if protein present.
2. Genome: All of genes in cell/tissue/organism.
   
   1. Proteome varies between cells as diff. cells make different proteins.
   2. Proteome varies over time; depending on cell’s activity.
   3. Genome is fixed between cells & indiv.
3. Proteome larger than genome because:
   
   1. Gene seq. may be alt. spliced following transcription to generate multiple protein variants from a single gene
   2. Proteins may be modified following translation to promote further variations

Question 44

Protein Functions (SHIT AF MEDS)

Answer 44

1. Structure:
   
   • Collagen: Component of connective tissue of animals (especially mammals)
   • Tubulin: Microtubule subunit, used in cytoskeletons & pull chromosomes in mitosis.
   • Spider Silk: Fiber spun by spiders & used to make webs (by weight, stronger than kevlar & steel).
2. Hormones:
   
   • Insulin: Hormone produced by pancreas,
     triggers ↓ blood [glucose]
   • Glucagon: Hormone produced by pancreas. triggers ↑ [glucose]
3. Immunity:
   
   • Immunoglobulins: Antibodies produced by plasma cells, target specific antigens.
   • Antigens: Distinguishes between body cells and foreign bodies (e.g. pathogens).
4. Transport:
   
   • Haemoglobin: A protein found in red blood cells that is responsible for the transport of oxygen
   • Channels/Carriers: Carry substances across cell membrane by fac. diffusion.
   • Protein Pumps: Carry substances across cell membrane by AT.
5. Adhesion:
   
   • ​Interactions between proteins allow adhesion → greater cell packing.
6. Factors:
   
   • Clotting Factors cause blood to turn from (l) → gel in wounds by starting cascade of enzyme-controlled reactions.
7. Movement:
   
   • Actin: Thin filaments involved in
     contraction of muscle fibres
   • Myosin: Thick filaments involved in
     contraction of muscle fibres
8. Enzymes:
   
   • Rubisco: Enzyme involved in carbon fixation in LIR during photosynthesis.
   • Catalase: Enzyme that catalyses breakdown of H₂O₂ into H₂O + O₂.
9. DNA Packing:
   
   1. ​Histones: Associate with eukaryotic DNA & help chrom’s condense during mitosis.
10. Sensitivity:
    
    • Rhodopsin: A pigment in photoreceptor cells of retina, detects light
    • NT Receptors: Acetylcholine receptors.

Question 45

Factors that affect enzyme activity

Answer 45

1. Temperature:
   
   • Particles move faster when temp inc. as more KE given to them. Thus, enzyme
     & sub. move faster; & chance of collision between AS & substrate occurring inc.
   • However, bonds in enzyme vibrate more with temp, so chance of peptide bonds breaking inc. → shape change in AS = denaturation = permanent → Can’t
     catalyse as substrate can’t fit in AS
   • Dec. in activity steeper than inc. in activity for temp.
2. pH:
   
   • [H+] changes, which changes charge of
     AA’s and/or R-groups → alters enzyme’s
     3º structure → denaturation on either end
   • Different enzymes have different optimums pH’s. E.g. Protease = pH 2 / Amylase = pH 7
   • Bacillus Licheniformis used for its basic properties in laundry detergents.
3. [Substrate]:
   
   • Inc. [sub] inc. freq. collisions & rate at which enzyme catalyses reaction inc.
   • However, AS occupied & unavailable to other sub when a sub bound to AS until products formed & released from AS.
   • As [sub] rises, inc. more AS occupied at any moment → Inc. prop. of collisions blocked → inc. in catalysis rate is inc. smaller as [sub] rises.

Question 46

Enzyme Immobilisation

Answer 46

1. Immobilisation: Attachment of enzymes to another material, or into aggregations, to restrict their movement.
2. Immobilisation done by:
   
   • Attaching enzymes to glass surface.
   • Trapping them in alginate gel.
   • Bonding them together to form enzyme aggregates.
3. Enzymes used in industry usually immobilised; several advantages:
   
   • Easy to separate enzyme + product (prevents contamination).
   • Enzyme reusable → ↑ economic viability of process (as enzymes expensive)
   • Production time can be extended.
   • Enzymes can be kept in stable, opt. temp. / pH → ↑ productivity.

Question 47

Lactose-free milk adv. and method

Answer 47

Method:

1. Lactose is sugar naturally present in milk.
2. Lactose → glucose + galactose
3. Yeast cultured; lactase extracted & purified.
4. Milk repeatedly passed over immobilised lactase, until lactose-free.
5. Scientists now trying to create trasngenic cows that produce lactose-free milk by splicing
   lactase gene into cow’s genome so that
   lactose is broken down prior to milking.

Advantages:

1. Allows lactose intolerants to consume milk (products);
2. Galactose + glucose sweeter than lactose → ↓ need for additional sweetener (in flavoured milk products like fruit youghurts, shakes);
3. Galactose + glucose more soluble than lactose, so don’t crystallise during ice-cream prod.
   → gives smoother texture;
4. Bacteria ferment glucose + galactose more rapidly than lactose → ↓ prod. time of yoghurt;