Cells and Chemicals Flashcards
Cell Theory and Exceptions
Cell Theory:
- All living things composed of cells (or cell products)
- The cell is the smallest unit of life
- Cells only arise from pre-existing cells
Exceptions:
- 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.
- 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.
- Giant Algae: Very large unicellular algae with one nucleus, but can be extremely large.
Microscopes and Magnification
- Magnification = Image / Object (x = I/O)
- Resolution: Ability of microscope to distinguish between two different points.
-
Transmission electron microscopes (TEM):
Generate high res. cross-sections of objects - Scanning electron microscopes (SEM): Display enhanced depth to map surface of objects in 3D.

SA : Volume Ratio
- Cells produce chem. energy (via metabolism) to survive, which requires material exchange.
- Rate of metabolic reactions ∝ vol. of cell.
- Rate of substances crossing cell memb. ∝ SA.
- As cell grows, vol. inc. faster than SA
→ SA : Vol dec. - If SA:Vol too small → supply < demand;
& waste not removed → waste + heat
accumulate in cell builds → death. - Hence growing cells divide & stay small to maintain high SA:Vol ratio suitable for survival.
MR SHENG and Unicellular organisms
Functions of Life
- Metabolism – Undertake essential chemical reactions
- Reproduction – Producing offspring, either sexually or asexually
- Sensitivity – Responding to int. & ext. stimuli
- Homeostasis – Maintain a stable int. env.
- Excretion – Removal of waste products
- Nutrition – Exchanging materials & (g) with env.
- Growth – Moving & changing shape or size

Multicellular Organisms Advantages
- Emergent properties arise from interaction of the component parts of complex structure.
- Cells
- Tissues
- Organs
- Systems
- Organism
- Different cells also perform different functions and so become specialised, via differentiation.
- Differentiation: Expression of some genes, but not others in a cell’s genome.
Stem Cells
- Stem Cells differ from most cells because they:
- Are unspecialised.
- Divide repeatedly to make many cells.
- Can differentiate into different cell types.
- 4 different types of stem cell:
- Totipotent: Form any cell type, as well as placental tissue (e.g. zygote)
-
Pluripotent: Form any cell type
(e.g. embryonic stem cells) -
Multipotent – Differentiate into some,
closely related cell types
(e.g. haematopoeitic adult stem cells) -
Unipotent – Can’t differentiate, but can
self renew (e.g. adult & muscle stem cells)
- Taken from embryos, umbilical cords, or rarely from adult tissue.
- Used therapeutically to replace/repair
- Used non-therapeutically (e.g. prevent cattle killing by making meat from stem cells).
- 2 main therapeutic uses (table)

Compartmentalization Advantages
- Enzymes and substrates for a particular process can be much more concentrated than if they were spread throughout the cytoplasm.
- Substances that could damage cell kept inside membrane of an organelle.
- 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.
- Organelles with their contents can be moved around within cell.
Prokaryote Structure

Eukaryote Structure

Draw Eukaryote & Prokaryote

Differences between Eukaryotes and Prokaryotes

Membrane Structure + Properties
- Hydrophilic Tail: Attracted to water, face out.
- Hydrophobic Head: Repelled by water, face in.
- Amphipathic: Membrane therefore part hydrophilic and part hydrophobic.
- Phospholipids thus, spontaneously arrange into bilayer in water (such as in cells).
- Tails face in & are shielded from surrounding polar fluids, whilst heads face outwards.
-
Structural Properties:
- Bilayer held together in bilayer by hydrophobic interactions between tails.
- Hydrophilic / hydrophobic layers thus restrict passage of many substances
- Individual phospholipids move within
bilayer → membrane fluidity & flexibility - Fuidity allows spontaneous breaking &
reforming of membranes (end/exocytosis)
Membrane Proteins (TRACIE)
Types:
- Integral Proteins: Permanently attached to membrane & are typically transmembrane (span across bilayer)
-
Peripheral Proteins: Temporarily attached by non-covalent interactions & associate with
surface of membrane
Structure: AA polarity leads to function of protein:
- Non-polar (hydrophobic) AA’s associate directly with lipid bilayer → Peripheral.
- Polar (hydrophilic) AA’s located internally & face aqueous solutions → Internal.
- Amphipathic AA’s → transmembrane.
Functions (TRACIE):
- Transport: Pump (Na+/K+ pump = AT) & channel (K+ or Na+ channels or aquaporin = FD)
- Receptors: Function as receptors for peptide hormones (e.g. Insulin).
- Anchorage: Attachment points for cytoskeleton & extracellular matrix.
- Cell Recognition: May function as markers for cellular ID. (e.g. self-antigens)
- Intercellular Joinings: Serve to connect & join 2 cells together (e.g. Plasmodesmata)
- Enzymatic Activity: Fixing to memb. localises metabolic pathways (e.g. e¯ transport chain)
Cholesterol
- Cholesterol: Amphipathic steroid positioned between phospholipids.
- The higher the conc, the less rigid, permeable & flexible membrane becomes.
- Chol. immobilises outer surface of membrane, reducing fluidity
- Makes memb. less permeable to hydrophilic molecules that usually cross (e.g. Na+).
- Separates tails → prevents memb. crystallisation.
- Helps secure peripheral proteins by forming high dens lipid rafts that anchor protein.
Membrane Models and Structure
- Membranes viewed under TEM exhibit 2 dark outer layers & lighter inner region.
- Danielli & Davson first proposed model whereby 2 protein layers flanked central phospholipid bilayer — ‘lipo-protein sandwich’.
- There were a number of problems with the lipo-protein sandwich model proposed by Davson and Danielli:
- Dark segments seen under TEM were identified (wrongly) as representing the 2 protein layers
- Assumed all memb. had uniform thickness & had constant lipid-protein ratios.
- Assumed all membranes had symmetrical int. & ext. surfaces.
- Temps at which membranes solidified did not correlate with those expected under the proposed model
- Membrane proteins were discovered to be amphipathic & insoluble in water (indicating hydrophobic surfaces)
- 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.
- Singer-Nicolson Model showed proteins embedded within lipid bilayer rather than existing as separate layers:
-
Fluid: Phospholipid bilayer is viscous &
single phospholipids can move position - Mosaic: Phospholipid bilayer embedded with proteins, resulting in mosaic of parts.
-
Fluid: Phospholipid bilayer is viscous &
Forms of Transport
Diffusion: Net movement of molecules from
region of high conc. to region of low conc. until molecules become evenly dispersed (equilib.)
- Small & non-polar molecules freely diffuse across cell memb, (e.g. O2, CO2, glycerol)
- Rate of diffusion can be influenced by a number of factors, including:
- Temp: Affects KE of particles in solution
- Molecular size: Fluid medium resists larger particles more (moves slower).
- 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.
- H2O associates with, & dissolves, polar or charged molecules (solutes) so acts as solvent.
- As solutes can’t cross cell memb. unaided, H2O moves to equalise solutions
- 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
- Utilised by molecules that can’t freely cross bilayer (e.g. large, polar molecules & ions)
- Mediated by 2 distinct types of interal proteins:
- Carriers: Bind to spec. solute & change structurally to translocate solute across membrane. May move molecules against [gradients] in presence of ATP
- 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).
- This energy may either be generated by:
- Direct hydrolysis of ATP.
- Indirectly coupling transport with another molecule that is moving along its gradient.
- Specific solute binds to protein pump on 1 side of memb.
- Hydrolysis of ATP (to ADP + P) causes structure
change in protein pump - Solute molecule translocated across memb.
(against [gradient]) & released. -
K+ channels:
- Axons of nerve cells transmit elec.
impulses by translocating ions to create a voltage diff. across membrane - At rest, Na/K pump expels Na+ from nerve cell, whilst K+ ions accumulate within.
- When neuron fires, ions swap locations via fac. diff. via Na+ & K+ channels
-
K+ Channels: Integral proteins with
hydrophilic inner pore via which K+ may be transported. Usually voltage-gated &
open & close depending on transmemb V.
- Axons of nerve cells transmit elec.
Na and K Transport in Nerve Cells
- Axons transmit electrical impulses by translocating ions to create V diff. across memb
- At rest, the Na/K pump expels Na+ from neuron
whilst K+ accumulate within. - 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)
- Process of ion exchange against [grad.] is energy-dependent & involves steps:
- 3Na+ ions bind to intracellular sites on Na/K pump
- Phosphate group transferred to pump via ATP Hydrolysis.
- Pump undergoes structure change, translocating Na+ across membrane
- Structure change exposes 2K+ binding sites on extracellular surface of pump.
- Phosphate group released → pump return to original conformation
- Translocates K+ across membrane, completing ion exchange.
-
K+ Channel: Integral proteins with hydrophilic inner pore via which K+ may be transported
- Channel comprised of 4 transmembrane subunits.
- Inner pore has filter at its narrowest region that stops alt. ions passing.
- K channels typically V-gated & open & close depending on the transmemb. V.
Osmolarity in Cells
- Osmolarity: Total concentration of osmotically active solutes in a solution.
-
Hypertonic: Higher osmolarity than tissue.
- Hypertonic solutions cause H2O to leave cells by osmosis, so cytoplasm shrinks in volume
-
Hypotonic: Lower osmolarity than tissue.
- Hypotonic solutions causes H2O to enter cells by osmosis, which make cell swell.
- Cell wall prevents plant cells bursting.
-
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.
Protein Transport
- Proteins produced by euk. initially synth. by free ribosomes found within cytosol.
- If protein targeted for intracellular use within cytosol, ribosome remains free and unattached
- If protein targeted for secretion, memb fixation or use in lysosomes, ribosome binds to ER.
- Presence of signal seq. results in addition of signal recogn. particle (SRP), which stops transl
- SRP-ribosome complex binds to receptor located on ER membrane (forming rough ER).
- Transl. restarts & polypep. chain continues to grow via transport channel into ER lumen.
- Signal seq. then cleaved & SRP recycled once polypep. completely synth. within ER.
- Vesicle with polypeptide (made by memb.
budding) moves & binds to Golgi cis-face. - Polypeptide moves (via vesicle) from cis face to trans face, may be modified along the way.
- Synth. protein transported via vesicle to:
- Golgi complex (for secretion)
- Lysosome
- Embedded into ER memb (for memb. fix.)
- Plasma memb, where it’s released by exocytosis either:
- Constitutive Secretion: Released immediately into extracellular fluid.
-
Regulatory Secretion: Stored within
intracellular vesicle for delayed release in response to cellular signal.
Endocytosis and Exocytosis
-
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.
-
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.
- Both processes carried out by membrane proteins, using energy from ATP.
- Both processes also rely on the fluidity and flexibility of membrane.
Miller-Urey Experiment
Miller and Urey demonstrated the non-living synthesis of simple organic molecules.
- Recreated postulated conditions of pre-biotic Earth using closed system of flasks & tubes
- H2O boiled to vapour to reflect high temps common to Earth’s original conditions
- Vapour mixed with variety of gases (including H2, CH4, NH3) to create reducing atm (no O2)
- Mixture then exposed to electrical discharge
(simulates lightning, which supplied E for
reactions) - Mixture then allowed to cool (concentrating components) & left for a period of time.
- Condensed mixture then analysed & found to contain traces of simple organic molecules.
Endosymbiosis
- Mitochondria were once free-living prokaryotes that developed aerobic cell resp.
- Larger prokaryotes that could only respire anaerobically took them in by endocytosis.
- Instead of killing + digesting smaller cell, they were allowed to live in their cytoplasm.
- Smaller cell grew & divided as fast as larger cell, so persisted indefinitely inside larger cells.
- Mutualistic relationship arose as smaller cell supplied with food by larger one, whereas smaller cell supplied energy efficiently to larger cell through aerobic respiration.
- Natural selection therefore favoured cells that had developed this endosymbiotic relationship
- 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

Louis Pasteur’s Experiments
- Nutrient broth made by boiling H2O containing yeast + sugar & placed in short, vertical-necked flasks and swan-necked flasks.
- Broth in both types of flasks in contact with air (“needed” for spont. gen.) yet none occurred in swan-necked flask.
- Mould only made when swan-neck snapped, which allowed bacteria to enter flask.
- Different liquids experimented, including milk and urine, which gave similar results.
- Demonstrated that cells only made by other cells, which falsified spont. gen. theory.
Cell Cycle
-
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.
-
Mitosis: Nucleus divides into 2 genetically identical daughter cells. Each chromatid made in S phase goes to each daughter cell:
- Prophase
- Metaphase
- Anaphase
- Telophase
-
Cytokinesis: Cytoplasm divides. Separation occurs from outside & moves to centre in animals and vice-versa in plants.
-
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.
-
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
-
In animal cells:

Purposes of Mitosis (GATE)
- 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.
Mitotic Index
- Mitotic Index: Ratio between no. of cells in mitosis in a tissue and total no. of observed cells.
- Used to predict:
- Whether a cell is a cancer cell
- Response of cancer cells to chemotherapy.
Cyclins
-
Cyclins: Group of proteins that control
progression of cell cycle. - 4 types of cyclins in human cells, that bind to bind to, & activate, different classes of CDK.
- CDK’s phosphorylate proteins responsible for tasks in each cell cycle stage.
- Thus [Cyclin] regulated to ensure correct progression of cell cycle.
- Cyclins peak when target protein needed & degrade after task completed, so CDK is rendered inactive again & [cyclin] low again.
- Richard Hunt found cyclins by accident when working on haemoglobin synthesis in sea urchin eggs. He noticed chemicals in different conc. during mitosis & interphase.
Tumours + Cancers
- Tumours: Abnormal cell growths resulting from uncontrolled cell division, can occur in any tissue or organ.
- Metastasis: Cell movement from 1º tumour to set up 2º tumours in other parts of body.
- Benign: Tumours that adhere to each other & don’t invade nearby tissues or move to other parts of body (usually harmless).
- Malignant: 1º tumours with cells that can detach & move elsewhere in body, developing into 2º tumours = carcinomas (usually lethal).
- Cancers: Diseases caused by carcinomas.
-
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.
- Mutations: Random changes to base sequences of genes.
-
Oncogenes: Genes involved in control of cell cycle + division.
- Mutation to oncogenes causes uncontrolled cell division (cancer).
Smoke and Cancer
- Positive correlation exists between cigarette smoking and death rate due to cancer.
- Also higher DR among those who smoked at one time but had stopped.
- Huge inc. in DR due to cancers of mouth, pharynx, larynx & lung; & smaller inc. in cancers to other areas of body.
- Although + correlations don’t mean causation, causal links established as cigarette smoke contains many different chemical mutagens.
Chemical Drawings

Urea + Vitalism
- Vitalism: Doctrine that dictated that “vital element” needed to make organic molecules.
- Urea: N-compound made by cycle of reactions in liver to break down excess AA’s in body.
- Vitalism falsified by Woehler who produced urea artificially, using similar reactions (and without body enzymes):
- NH3 + CO2→ NH4(Carbamate) → Urea + H2O
- Falsifies Vitalism.
- Used as fertilizer to provide N to plants.
Anabolism and Catabolism
- Metabolism: Describes totality of all enzyme-catalysed reactions in a cell or organism.
- Two main types of metabolic pathways:
-
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
-
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.
Water Properties
Heat Capacity: High, as lots of nrg needed to break extensive H-bonding & change H2O’s temp:
- Env’s are thermally stable as they tend to remain at same temp.
- Blood or other fluids can carry heat around their bodies.
BPt: High as many H-bonds need a lot of nrg to be broken:
- H2O is (l) at most temps, making it a suitable habitat for aquatic organisms.
-
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).
- Sweating & transp. enable orgs to lose heat as they involve evaporation, which releases heat required to evaporate H2O in sweat.
- H2O acts as a coolant.
Cohesion: Binding of 2 molecules of same type (like 2 H2O molecules due to H-bonding).
- H2O sucked through xylem vessels at low press, without being separated by suction forces (as they stick to themselves).
-
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.
- 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.
- 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;

Molecules transported by blood
- 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.
Cellulose, Starch, Glycogen

Lipid Functions (SHIPS) & comparision with carbohydrates for storage
- Structure: Phospholipids are main component of cell membranes
- Hormonal Signalling: Steroids involved in hormonal signalling (e.g. oestrogen, progesterone, testosterone)
- Insulation: Fats in animals can serve as heat insulators in sub-cutaneous adipose tissue.
- Protection: Triglycerides form adipose tissue around organs & are shock absorbers.
-
Storage of energy: Triglycerides used as LT energy storage because:
- Can’t break down as easily as glycogen.
- Triglycerides insoluble, whereas mono-disacc’s are soluble so more easily moved
- Can’t be used for anaerobic respiration
- Lipids store more E/gram, so release more energy when broken than glycogen.
- Lipids also have smaller effect on cell osmotic pressure than glycogen.
BMI differences and effects in rich/poor countries
- BMI = Mass (kg) ÷ (Height (m))2
- Obesity: Too much fat in adipose tissue from lack of exercise & excessive food taken
- Obesity inc. risk of CHD and Type 2 diabetes. Also reduces LE significantly & inc. costs of healthcare in countries where it’s rising.
- In poor countries, Mal/undernutrition more common and reduces BMI in these countries.
- in richer countries it’s anorexia nervosa, a psychological condition involving voluntary starvation and loss of body mass as a result).
- Cis-fatty acids: Unsaturated fatty acids with H atoms on same side of double bond.
- Bend in hydrocarbon chain at double bond present → less good at packing together in regular arrays than saturated fatty acids → dec. mpt → usually (l).
- Trans-fatty acids: Unsaturated fatty acids with H atoms on opposite sides of double bond.
- Trans don’t have bend → pack together in regular arrays better → inc. mpt → usually (s).
- Trans-fatty acids produced artificially through partial hydrogenation of vegetable or fish oils.
Health Risks of Fats + Cholesterol
Protein Structure
-
1º Structure: Sequence & no. of AAs in polypeptide:
- 20 diff. AA’s naturally synthesised by rib.
- Ribosomes can make pep bonds between any AA pair, so any AA seq. possible.
- For a polypeptide of n AA’s, there are 20n possible sequences.
-
2º Structure: Formation of alpha helices and ß-pleated sheets stabilised by H-bonding.
- 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.
- This results in formation of patterns within polypeptide called 2º structures.
-
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:
- Oppositely charged R-groups interact with each other.
- Hydrophobic AAs orientate themselves towards polypeptide centre to avoid contact with H2O, whilst hydrophilic AAs orientate themselves outwards.
- Polar R-groups form H-bonds with other polar R-groups.
- R-group of cysteine can form disulphide bridges with R-group of another cysteine.
-
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.
-
Haemoglobin: Composed of 4 polypep.
Globular vs. Fibrous Proteins

Gene and Polypeptide Relationship
- Gene: DNA seq. that encodes a polypep. seq.
- Gene seq. converted into polypep. seq. via:
- Transcription: Synthesising mRNA from DNA template (occurs within nucleus)
- Translation: Synthesising polypep’s using mRNA (occurs at ribosome)
- Typically, 1 gene will code for 1 polypep. But:
- Genetic code is degenerate, so more than one amino acid coded for by each codon.
- Genes may be alt. spliced to make
multiple polypep. variants - Genes encoding tRNA seq. transcribed but never translated
- Genes may be mutated & so produce an alt. polypep. seq.
Proteome and Genome
-
Proteome: All of proteins produced by a cell, tissue or organism.
- Found by extracting protein mix’s from sample & separating by gel electroph.
- Fluoresce-marked antibodies specific to each protein fluoresce if protein present.
-
Genome: All of genes in cell/tissue/organism.
- Proteome varies between cells as diff. cells make different proteins.
- Proteome varies over time; depending on cell’s activity.
- Genome is fixed between cells & indiv.
- Proteome larger than genome because:
- Gene seq. may be alt. spliced following transcription to generate multiple protein variants from a single gene
- Proteins may be modified following translation to promote further variations
Protein Functions (SHIT AF MEDS)
-
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).
-
Hormones:
-
Insulin: Hormone produced by pancreas,
triggers ↓ blood [glucose] - Glucagon: Hormone produced by pancreas. triggers ↑ [glucose]
-
Insulin: Hormone produced by pancreas,
-
Immunity:
- Immunoglobulins: Antibodies produced by plasma cells, target specific antigens.
- Antigens: Distinguishes between body cells and foreign bodies (e.g. pathogens).
-
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.
-
Adhesion:
- Interactions between proteins allow adhesion → greater cell packing.
-
Factors:
- Clotting Factors cause blood to turn from (l) → gel in wounds by starting cascade of enzyme-controlled reactions.
-
Movement:
-
Actin: Thin filaments involved in
contraction of muscle fibres -
Myosin: Thick filaments involved in
contraction of muscle fibres
-
Actin: Thin filaments involved in
-
Enzymes:
- Rubisco: Enzyme involved in carbon fixation in LIR during photosynthesis.
- Catalase: Enzyme that catalyses breakdown of H2O2 into H2O + O2.
-
DNA Packing:
- Histones: Associate with eukaryotic DNA & help chrom’s condense during mitosis.
-
Sensitivity:
- Rhodopsin: A pigment in photoreceptor cells of retina, detects light
- NT Receptors: Acetylcholine receptors.
Factors that affect enzyme activity
-
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.
- Particles move faster when temp inc. as more KE given to them. Thus, enzyme
-
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.
- [H+] changes, which changes charge of
-
[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.

Enzyme Immobilisation
- Immobilisation: Attachment of enzymes to another material, or into aggregations, to restrict their movement.
- Immobilisation done by:
- Attaching enzymes to glass surface.
- Trapping them in alginate gel.
- Bonding them together to form enzyme aggregates.
- 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.
Lactose-free milk adv. and method
Method:
- Lactose is sugar naturally present in milk.
- Lactose → glucose + galactose
- Yeast cultured; lactase extracted & purified.
- Milk repeatedly passed over immobilised lactase, until lactose-free.
- 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:
- Allows lactose intolerants to consume milk (products);
- Galactose + glucose sweeter than lactose → ↓ need for additional sweetener (in flavoured milk products like fruit youghurts, shakes);
- Galactose + glucose more soluble than lactose, so don’t crystallise during ice-cream prod.
→ gives smoother texture; - Bacteria ferment glucose + galactose more rapidly than lactose → ↓ prod. time of yoghurt;