Long Answer Questions Topic 3 and 7 – Biochemistry

question

Outline the positions and functions of proteins in membranes (8)
answer

Integral proteins are embedded in the phospholipid bilayer Peripheral proteins are on the surface membrane Some integral proteins extend from on side of the membrane to the other Act as: Hormone binding sites (eg insulin) Enzymes (eg Sucrase) Cell adhesion Cell to cell communication (antigenic markers) Glycoproteins Channels for passive transport / facilitated diffusion Pumps for active transport Receptors for neurotransmitters (Such as acetylcholine) Electron carriers Pigments (in rods and cones)
question

Explain how polar and non-polar amino acids help channel proteins and enzyme proteins carry out their function (5)
answer

Non-polar amino acids cause channel proteins to embed in a membrane Polar amino acids at either ends cause channel proteins to be transmembrane Polar amino acids lining in a pore allow polar molecules to pass through Polar amino acids in surface of enzyme allow it to dissolve in water Polar and non-polar amino acids contribute to the specificity of an enzyme Non-polar amino acids on surface of enzyme allow it to embed into a membrane Polar amino acids at active site of enzyme attract polar substrate Positively charged amino acids attract neg. charged substrate and vice versa
question

Compare competitive and non-competitive inhibition of enzymes (5)
answer

Both types reduce enzyme activity Both bind to the enzyme Both prevent the substrate from binding to active site Comp – Substrate and inhibitor are same shape, whereas for non-comp. – substrate and inhibitor are not similar shape For comp. Inhibitor binds to active site. from non-comp – inhibitor binds to an allosteric site (away from active site) Comp – inhibitor does not change shape of active site, non-comp – inhibitor changes the shape of the active site Comp- increases in substrate concentration reduces inhibition, non-comp. Increase in substrate conc. do not affect inhibition Example of comp. Succinate dehydrogenase is inhibited by malonate, non-comp – pyruvate kinase inhibited by alanine
question

Explain how translation is carried out from the initiation stage onwards (9)
answer

Translation involves initiation, elongation and termination mRNA binds to the small sub-unit of the ribosome Ribosomes slide along mRNA to start codon Anticodon of tRNA pairs with codon on mRNA COMPLEMENTARY BASE PAIRING between codon and anticodon AUG is the start codon Second tRNA pairs with next codon Peptide bond forms between amino acids Ribosomes moves along mRNA by one codon Movement in 5′ to 3′ direction rRNA that has lost its amino acid detached another tRNA pairs with next codon tRNA activating enzymes Link amino acids to specific tRNA Stop codon eventually reached
question

Distinguish between unique and highly repetitive sequences in nuclear DNA (5)
answer

Unique Highly repetitive Occur once in genome Occur many times Long base sequence Short sequence (5-300) May be genes Not genes May be translated Never translated Small difference in individuals Can vary greatly Exons (are unique seq) Introns (repetitive) Smaller proportion of genome Higher proportion of gen Satallite DNA is repetitive Repetitive used for DNA profiling Prokaryotes do not contain repetitive sequences
question

Draw a labeled diagram to show four DNA nucleotides (5)
answer

diagram should include: Four nucleotides Base, Phosphate, DEOXYRIBOSE (as a pentagon), connected between the correct carbons and labelled at least once Backone labelled as covalent bonds between nucleotides correctly shows as 3′ to 5′ Two base pairs linked by hydrogen bonds drawn as dotte lines and labelled Two H bonds between AT and three between C and G Adenin to thymine, and cytosine to guanine
question

Explain the methods and aims of DNA profiling (8)
answer

Methods: DNA sample obtained From hair/blood/semen Quantity of DNA increased by PCR polymerase chain reaction Satellite DNA are used (highly repetitive sequences) DNA cut into fragments Using restriction enzyme endonuclease gel eletrophoresis used to separate DNA fragments Using electric field, fragments are separated by size Number of repeats varies between individuals, patterns of bands therefore unique to individual Aims: Forensic use for crime scenes Eg DNA used from the scene/victim Compared to DNA of suspect Paternity testing e.g DNA obtained from parents in paternity case Biological father if one half of all bands in the child are found in father Genetic screening Presence of particular bands correlates with probability of certain phenotype
question

Outline the structure of a ribosome (4)
answer

Small and large subunit mRNA binding site on small subunit Three tRNA binding sites (A, P and E) made of Protein AND RNA composition 70s in prokaryotes, 80s in Eukaryotes Can be free or bound to the RER
question

Distinguish between fibrous and globular proteins with reference to one example of each protein type (6)
answer

Fibrous proteins are strands whereas globular proteins are rounded Fibrous proteins (usually) insoluble whereas globular proteins are (usually) soluble Globular more sensitive to changes in pH/temp than fibr. Glob. used for catalyst/transport Named fibrous protein – keratin, actin, collagen Named globular – insulin, hemoglobin
question

State four functions of proteins, giving a named example of each (4)
answer

Structure – collagen Transport – hemoglobin Enzyme – lysozyme Movement – actin Hormones – insulin Antibodies – immunoglobin Storage – albumin Pumps – sodium potassium pump
question

Distinguish between RNA and DNA (3)
answer

DNA RNA Double stranded Single stranded Deoxyribose Ribose Base – thymine Base – Uracil One form of DNA (helix) Many of RNA (tRNA, mRNA)
question

Explain the process of DNA replication (8)
answer

DNA replication occurs during S phase f interphase, in preparation of mitosis Cell division occurs DNA replication is semi-conservative Unwinding of double helix by Helicase Hydrogen bonds between strands are broken Each strand of parent DNA used as a template for synthesis Synthesis continuous on leading strand, but staggered on lagging strand Leading to the formation of Okazaki fragments on lagging strand Synthesis occurs in a 5′ to 3′ direction RNA primer synthesized on parent DNA using RNA primese, puts in primer DNA polymerase III puts adds nucleotides Added according to complimentary base pairing Adenine with Thymine, Cytosine with Guanine DNA Polymerase ! removes RNA primers and replace them with DNA DNA ligase joins okazaki fragments
question

Outline how enzymes catalyse reactions (7)
answer

Enzymes increase the rate of reaction Enzymes remain unchanged at the end of reaction They lower activation energy required Activation energy is required to overcome the energy barrier that prevents reaction Substrate joins with enzyme at active site To form an enzyme-substrate complex Active site specific for a particular substrate Enzyme binding with substrate brings reactants closer to facilitate chemical reactions Induced fit model – change in enzyme conformation, making substrate more reactive
question

Distinguish between Prokaryotic and Eukaryotic DNA
answer

question

Outline the thermal, cohesive and solvent properties of water (5)
answer

Water has high specific heat capacity A large amount heat causes a small increase in temperature Water has a high latent heat of vaporisation A large amount of heat energy is needed to vaporize/evaporate water Good for sweating, meaning sweat largely cools the body Hydrogen bonds between water molecules make them cohesive (stick to each other) This gives water high surface tension/ explains how water rises of the xylem Water molecules are polar This makes them a good solvent
question

Distinguis between fibrous and globular
answer

Get instant access to
all materials

Become a Member