Option B: Human Biochemistry

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How is energy made available?
Respiration - oxidation reactions
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What is energy provided by?
Fats, carbohydrates + proteins - converted into glucose + intermediates
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What is the function of proteins?
Structure of body (hair, fingernails, tendons, contractile structures in muscles) + tools (catalysts, enzymes, hormones)
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What is the structure of proteins?
Polymers - monomers are amino acids
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What are some of the properties of proteins?
Exist as zwitterions (dipolar ions), amphoteric (contain acidic and basic group), buffers (important in maintaining pH levels in cells)
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How do amino acids link?
Condensation reactions, releasing water, forming peptide bonds
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What is name of a chain of amino acids?
Two = dipeptide / Chain = polypeptide
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What is the primary structure of proteins?
Sequence of amino acids in chain - covalent backbone of molecule
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What is the secondary structure of proteins?
Regular hydrogen bonding between peptide groups (C=O and N-H), resulting in folding of polypeptide chain
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What is the alpha-helix structure like?
regular, coiled configuration - hydrogen bonds form 4 amino acid units apart - flexible + elastic, as hydrogen bonds break easily and reform
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What is a beta-pleated sheet like?
'side by side' polypeptides - pelted sheets, cross-linked by inter-chain hydrogen bonds - flexible - inelastic
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What are proteins with well-defined secondary structures called?
Fibrous proteins - physically tough + insoluble in water
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What is the tertiary structure of proteins like?
Result of interactions between R groups / side chains - causes further twisting, folding + coiling
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What is the conformation of a protein?
The most stable arrangement of the protein
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What happens when the protein loses its specific tertiary structure?
Denatured - upset by temperature or pH
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What is the quaternary structure of proteins like?
Where there is an association between different polypeptides (e.g. collagen + haemoglobin)
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How are proteins analysed?
First chemically separate amino acids through hydrolysis reactions using acid - then mixture separated through chromatography or electrophoresis
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What is chromatography useful for?
Coloured mixtures - amino acids = colourless in solution, but take on colour when treated with locating agent (ninhydrin)
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How is the position of an amino acid expressed?
Rf Value / Retention Factor = distance moved by amino acid, divided by the distance moved by the solvent
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What is electrophoresis based on?
movement of charged particles in electric field - amino acids placed in buffered solution - they carry different charges depending on pH
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What is the medium used in electrophoresis?
Polyacrylamide gel
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What are carbohydrates?
Composed of carbon, hydrogen + oxygen
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What are the two types of carbohydrates?
Simple sugars = monosaccharides (eg. glucose, fructose) + condensation polymers = polysaccharides
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What are the qualities of monosaccharides?
Readily soluble in water (taken up by cells rapidly), release energy in respiration, are precursors in metabolic reactions (eg. synthesis of fats, nucleic acids + amino acids)
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What are the qualities of polysaccharides?
Insoluble, used in storage - mostly as glycogen in liver + muscles, cellulose in plants, dietary fibre
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What is the structure of monosaccharides?
Empirical formula = CH2O - Contain carbonyl group (C=O) + at least two -OH groups - exist in chain forms, which in aqueous solution undergo internal reactions to make ring structure
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What is the structure of disaccharides?
Two monosaccharides linked together through glycosidic linkage (carbon 1-4) - -OH group eliminated by each sugar in condensation reaction
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What is lactose made from?
Beta-glucose + beta-galactose (milk)
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Whats is maltose made from?
alpha-glucose + alpha-glucose (product from starch digestion)
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What is sucrose made from?
alpha-glucose + beta-fructose (cane sugar)
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What are the three common glucose-based polysaccharides?
Starch, glycogen + cellulose
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What are the two types of starch?
Amylose + amylopectin
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What is the structure of amylose like?
Carbon 1-4 linkages, soluble in water, polymer of alpha-glucose
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What is the structure of amylopectin like?
Branched polymer, carbon 1-4 and 1-6 linkages, polymer of alpha-glucose
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What is the structure of glycogen like?
Polymer of alpha-glucose, similar to amylopectin but more 1-6 branches, 'animal starch' main storage carbohydrate in animals
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What is the structure of cellulose like?
Linear polymer of beta-glucose, structural material in plant cell walls, alternate monomers 'upside down' with respect to each other - hydroxyl groups form hydrogen bonds with parallel cellulose molecules - forms cables = microfibrils
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Digestion of polysaccharides
Insoluble so cannot be transported by blood, broken down through hydrolysis reactions controlled by enzymes, producing soluble monosaccharides
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Dietary fibre
substances that cannot be digested (e.g. cellulose - enzyme cellulase not found in human body)
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Why is cellulose beneficial to the health of the large intestine?
Fibrils abrade wall of digestive tract + stimulate lining to produce mucus = smooth passage of undigested food - prevents constipation, haemorrhoids, irritable bowel syndrome
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What are lipids?
Made of carbon, hydrogen + oxygen - hydrophobic / insoluble in water - soluble in non-polar solvents - (e.g. fats, phospholipids, steroids, oils)
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Properties of lipids
Contain stored energy - 1 gram of lipid releases almost twice as much energy as 1 gram of carbohydrate - but, lipids not as readily available due to insolubility and more reactions required for breakdown
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Functions of lipids
Ideal storage molecules (fat stores = adipose tissue), hormones (lipids in form of steroids = testosterone + oestrogen), bile acids
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What are the functions of phospholipids?
major component in membrane of cells, nerve cells, cholesterol (important in plasma membrane structure), essential fatty acids, help absorb fat-soluble vitamins
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What are the negative effects of lipids?
Due to low solubility of lipids - some deposited in walls of main blood vessels (restrict blood flow), obesity (converting excess fats into adipose tissue for storage), cholesterol (cardiovascular disease)
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What are triglycerides?
Fats + oils - esters made through condensation reactions between glycerol + 3 fatty acids
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Fatty acids
In most natural oils and fats 3 fatty acids not same - differ in length of hydrocarbon chain, number + position of of C-C double bonds in hydrocarbon chain
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What does the number of C-C double bonds do to the saturation of fatty acids
No double bonds = saturated, One double bond = mono-saturates, several double bonds = polyunsaturated
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What does the nature of fatty acids affect in triglycerides?
Melting point
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Saturated fatty acids
Tetrahedral bond angles (109.5) - molecules pack close together - significant Van der Waal's forces - form saturated trilycerides = solid at room temperature (high M.P.) - FATS
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Unsaturated fatty acids
120 bond angles - kinks in chains - make it difficult to pack molecules close together - form unsaturated triglycerides - weaker intermolecular forces - liquids at room temperature (low M.P) - OILS
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Essential fatty acids
linoleic acid / omega-6-fatty acid + linolenic acid / omega-3-fatty acid
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Where are 'omega fatty acids' obtained from
plants + fish
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Why are some fatty acids essential?
Involved in synthesis of prostaglandins (lipids) - involved in lower blood pressure - lower LDL cholesterol, protecting against heart disease
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How is the degree of unsaturation in a fat determined?
Using iodine - unsaturated fatty acids undergo addition reactions with iodine - 1 mole of iodine will react with each mole of double bonds in fat
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Iodine number
Number of grams of iodine which reacts with 100g of fat
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'Partially hydrogenated fat'
Oils which have been chemically modified by addition reactions, using hydrogen to add across double bonds + decrease degree of unsaturation
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What is the outcome of 'partially hydrogenated fat'?
Fat is more saturated, with higher melting point - solid/semi-solid - breaks down less easily under conditions of high temperatures
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What is the issue with 'partially hydrogenated fat'?
Chemical modifications involve heat + pressure - affects positions of groups around double bonds - -cis to -trans - LDL increased + HDL decreased
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Digestion of fats
fats + oils = insoluble - broken down in gut through hydrolysis reactions into fatty acids + glycerol
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Similar to triglycerides, but only 2 fatty acids condensed onto glycerol molecule - (e.g. lecithin)
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What does the structure of phospholipids look like?
Have polar hydrophilic 'head' + two non-polar hydrophobic 'tails'
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What do phospholipids do?
Spontaneously form phospholipid bilayer - maximises interactions between polar groups and water, while creating non-polar hydrophobic interior - provides basis of membrane structure
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Have 4 fused rings - (eg. cholesterol - used in body in synthesis of other steroids like sex hormones)
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Molecules required in diet for absorption + use in body
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How do we classify nutrients?
According to amounts in which they are needed / recommended daily intake
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Needed in extremely small amounts - enable body to produce enzymes + hormones - (e.g. vitamins + trace minerals)
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Needed in relatively large amounts - provide energy, build + maintain structure of body - (e.g. macromolecules = carbohydrates, proteins, lipids - other minerals)
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Organic micronutrients not synthesised in body
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Water-soluble vitamins
Transported directly in blood - excess filtered out by kidneys + excreted - polar bonds
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Fat-soluble vitamins
Slower to be absorbed - excess stored in fat tissues - can produce serious side effects - non-polar - long hydrocarbon chains / rings
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Vitamin A / Retinol
Fat soluble - hydrocarbon chain + ring = non-polar - involved in visual cycle in eye + important for vision at low intensity
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Vitamin C / Ascorbic acid
Water soluble - OH groups enable hydrogen bonds - cofactor in some enzymic reactions - important in tissue - helps give resistance to some diseases
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Vitamin D / Calciferol
Fat soluble - chemically similar to cholesterol - stimulates uptake of calcium ions by cells, so important in health of bones + teeth
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Result of deficiencies or imbalance in diet
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Iodine Deficiency
needed to synthesise hormone thyroxine (regulates metabolic rate) - present in seafood + some vegetables - lack = swelling of thyroid gland / goitre - in children deficiency considered largest cause of mental retardation
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What is the way of controlling iodine deficiency?
Adding it to salt
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Vitamin A deficiency
needed for healthy skin, good eyesight + protection against some damaging effects of toxins - orange / yellow fruits and vegetables, spinach + egg yolks - deficiency = xerophthalmia (dry eyes + night blindness)
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What is the way of controlling Vitamin A deficiency?
Adding it to margarine via 'Vitamin A fortification' or possibly using rice as a vehicle
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Iron Deficiency
essential part of haemoglobin - deficiency = anaemia (fatigue, brittle nails, poor endurance, lowered immunity) - found in read meats, green leafy vegetables, nuts + seeds
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What is the way of controlling iron deficiency?
Iron fortification with Vitamin C to cereal flours + milk products
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Vitamin B3 / Niacin Deficiency
pellagra = dermatitis, diarrhoea + dementia
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Vitamin B1 / Thiamin Deficiency
beriberi = weight loss, fatigue + swelling
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Vitamin C / Ascorbic acid
scurvy = bleeding gums, lowered resistance to infection + dark spots on skin
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Vitamin D / Calciferol
rickets = softened + deformed bones
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Selenium Deficiency
Kashin-Beck disease = atrophy + degeneration of cartilage
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Protein deficiency
life threatening - marasmus = failure to gain weight, weight loss + emaciation - kwashiorkor = affects young children whose diet in high in starch + low in protein
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What are some of the causes of malnutrition?
lack of distribution of global resources, depletion of nutrients in soil + water cultures, lack of education about importance of balanced diet, over-processing of food, chemical treatments in food production
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chemical messengers - endocrine system
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Where are hormones produced?
Endocrine glands - secrete hormone directly into blood - circulate until reach target cells, with correct receptors
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Pituitary gland
Anti-diuretic hormone (ADH) - short peptide - kidney tubules - increases uptake of water, raising concentration of urine
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Thyroid gland
thyroxine - modified amino acid - all cells - regulation of basal metabolic rate, growth + development
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Adrenal cortex
Aldosterone - steroid - kidney tubules - increases uptake of Na+ and K+ ratios in fluids, raises blood pressure
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Adrenal medulla
Adrenaline - modified amino acid - muscles, brain, circulatory + digestive systems - raises blood glucose levels, increases rate of heartbeat + increases blood supply to heart and skeletal muscles
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Insulin - protein - all cells - decreases blood glucose level by increasing uptake + utilisation by cells - increases glucose to glycogen conversion in liver
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oestrogen + progesterone - steroids - uterus lining - development of secondary female characteristics, control of menstrual cycle, growth + development of placenta + fetus
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Testosterone - steroid - many parts of body - development of male secondary sexual characteristics
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Steroid-based hormones
All have common structure (eg. sex hormones) - testosterone, oestrogen / estradiol, progesterone
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Oral contraceptives
Prevents ovulation (release of unfertilised ovum) - contains progesterone + oestrogen - suppress secretion of other hormones
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Female steroid hormones
Uses = contraceptive pill, medications prescribed to women at menopause (HRT - hormone replacement therapy)
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Male steroid hormones
Androgens - testosterone = treatment of testes + breast cancer - promote tissue growth of muscles - synthetic forms used to help gain weight after debilitating diseases / Anabolic steroids = build up muscles + endurance in athletes
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Effects of anabolic steroids
can cause many changes in secondary sexual characteristics from systemic hormone imbalances - changes in hair distribution, sexual desire + fertility - hormones are toxic to liver = liver cancer
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Proteins - tertiary structure / globular - some have quaternary structure - soluble in water (exists in solution in cytoplasm of cells) - some require binding of non-protein molecules for activity (co-factors / coenzymes if organic)
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What do enzymes do?
Are biological catalysts (reactant catalysed in reaction = substrate) - control all biochemical reactions - lower activation energy
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How do enzymes work?
Able to form temporary binding to substrate - weak forces of attraction, forming enzyme substrate complex - occurs in active site (pocket/groove on surface of protein) - enzymes highly specific for reactions they catalyse
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Enzyme substrate complex
Formation of complex depends on 'chemical fit' between substrate + R groups of amino acids at active site - involves hydrophobic interactions, dipole-dipole, hydrogen bonds + ionic reactions
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What happens when the substrate has reacted?
Product no longer hits in active site, so detaches - enzyme released unchanged, so able to catalyse further reaction
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What effects enzyme activity?
Temperature, pH + presence of heavy-metal ions
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How does temperature effect enzyme activity?
rise in temp. = increased rate of reaction - BUT up to certain temp. (+/- 40C) - enzyme becomes denatured - increase in kinetic energy changes conformation of protein, disrupting bonds + forces - enzyme no longer able to bind to substrate
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NOT digestion - irreversible - why maintaining body temperature is so important
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How does pH affect enzyme activity?
Effects equilibrium of ionisation reactions - change in ionic charge alters attractive forces in molecule - changes shape + ability to bind to substrate - optimum pH depends on pKa + pKb values of R groups of amino acids in enzyme
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How do heavy-metal ions affect enzyme activity?
eg. lead, copper, mercury, silver - poisonous - react with sulfhydryl (-SH) groups in side chains of cysteine residues in protein - form covalent bond w/ sulphur atom, displacing H atom - disrupts folding of protein, changing shape of active site
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Chemical inhibitors
Affect activity of enzymes by binding to them
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Competitive inhibitors
Bind reversibly at active site, competing w/ substrate - do not react to form products - increasing concentration of substrate reduces extent of inhibition - Vmax no altered - Km increased
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Non-competitive inhibitors
Bind reversibly away from active site - causes conformational change in protein structure, altering active site - increased substrate concentration does not reduce extent of inhibition - Vmax decreases + cannot be restored - Km unchanged
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deoxyribonucleic acid
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ribonucleic acid
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What is the role of DNA?
store information that controls genetic characteristics of organism
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What is the role of RNA?
enable information to be expressed
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What must DNA do?
Be very stable - able to retain precise chemical structure in cell conditions - contain some 'code' that stores genetic info - be able to replicate / produce an exact copy of itself
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What is the structure of nucleic acids like?
Polymers = polynucleotides (monomers = nucleotides)
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What are nucleotides made up of?
Pentose (DNA = deoxyribose / RNA = ribose) , Phosphate group + organic nitrogenous base (purines + pyridines)
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What are the purine bases?
Adenine + Guanine
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What are the pyridine bases?
Cytosine, thymine, uracil
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What is DNA composed of?
A, G, C, T
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What is RNA composed of?
A, G, C, U
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How do nucleotides form?
Condensation reactions, releasing water
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What is DNA?
Double helix of two polynucleotides - sugar-phospahte backbone on outside - nitrogenous base on inside - held together by hydrogen bonds between bases
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How do the bases bond?
A - T + G - C
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What are some of the properties of DNA?
Stability achieved by maximising hydrophobic interactions between stacked bases - sequence of bases in strand = digital code - base pairing between strands provides means for replication of code
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What is RNA?
Simple-stranded polynucleotide - less stable than DNA - more short-lived in cells - able to cross nuclear membrane
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What are the 3 types of RNA?
messenger RNA (mRNA), transfer RNA (tRNA) + ribosomal RNA (rRNA)
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How is information in DNA expressed?
Through control of protein synthesis - four letter code of bases in DNA translated into code to account for 20 amino acids found in proteins
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What are the two steps in protein synthesis?
Transcription + translation
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How does transcription work?
2 strands of DNA separate by breaking H-bonds between paired bases (unzipping) - nucleotides assemble to form mRNA strand using DNA strand as template - mRNA detaches + leaves nucleus for ribosome
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How does translation work?
Assembly of protein from code - tRNA molecule recognises specific triplet of bases in mRNA = codon - successive tRNA molecules bring appropriate amino acids into position, linking together by peptide bods to form polypeptide
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Genetic code
Specific relationship between bases + amino acids - code = universal in all organisms
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DNA replication
Occurs during cell division - molecule of DNA makes exact copy of itself - new molecules contain one strand from original parent molecule + one newly synthesised strand = semi-conservative replicaiton
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What can DNA profiling be used for?
identify victims whose bodies are not recovered from scene of accident / crime, forensic cases to identify subject, confirm biological relationships of individuals, determine relationships between populations in study of evolution + ecology
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Card 2


Fats, carbohydrates + proteins - converted into glucose + intermediates


What is energy provided by?

Card 3


Structure of body (hair, fingernails, tendons, contractile structures in muscles) + tools (catalysts, enzymes, hormones)


Preview of the back of card 3

Card 4


Polymers - monomers are amino acids


Preview of the back of card 4

Card 5


Exist as zwitterions (dipolar ions), amphoteric (contain acidic and basic group), buffers (important in maintaining pH levels in cells)


Preview of the back of card 5
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