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Transcript
Year 12 AS Level Past Paper Genetic Control Mark Scheme 1. (a) (i) U - phosphate / PO4; R phosphoric acid / phosphorus / P W - deoxyribose; R pentose X - cytosine; R nitrogenous base / pyrimidine / C 3 (ii) Z - hydrogen; R H 1 (b) Assume answer is about polypeptide unless indicated otherwise. A comparison is not required. Information given below is for either polypeptide or DNA features. A ideas from either column. Do not penalise if points are not corresponding on one line /sentence. Mark all points on line. Only R if biologically incorrect. polypeptide DNA, amino acids nucleotides ; one / single strand / chain two / double strand / chains ; peptide bonds phosphodiester ; R between peptides /polypeptides 20 monomers / sub units only 4 monomers / sub units ; A > 4 monomers / sub units R 4 bases no phosphate / PO4 has phosphate / PO4 ; 2o / 3o structure double helix ; 3 max [Total: 7] 2. a) W cytosine; X deoxyribose; Y nucleotide (triphosphate); [3] (b) base pairing/A-T and C-G; A purine - pyrimidine ref to complementary/explained with ref to H bonds; R complementary in wrong context (free) nucleotides pair with both, strands/each strand/polynucleotides/sides; both strands act as templates; to produce two DNA molecules that are identical to one another; [max 3] (c) (all nuclei/cells) are genetically identical; A genetic stability, same genetic information, exact genetic material, genetic material does not vary, same genotype; no mutation; any consequence of mutation; e.g. cells not recognised, cells divide uncontrollably, substitution of 1 amino acid results in disease e.g. sickle cell anaemia, enzyme’s active site altered, forms different protein with different function. [max 2] [Total: 8] 3. (a) one mark per row [5] (b) CAG; [1] (c) tRNA, combines with amino acid / carries amino acid to ribosome; idea of specificity; e.g. each type of tRNA is specific to an amino acid anticodon matches amino acid idea; example from Fig. 3.1; codon on messenger RNA pairs with anticodon on tRNA; example from Fig. 3.1; two sites on ribosome; further detail; e.g. P and A site (and E) leave ribosome after amino acid joins polypeptide; continually reused; [max 5] (d) variable region; binding region to antigen; shape is specific to, choleragen / antigen; complementary; ref to R groups on amino acids (in polypeptide / protein); different, sequences of amino acids / primary structures; ref to, folding of the molecule / secondary structure / tertiary structure; [max 3] (e) poor sanitation / no treatment of faecal waste; contamination of (drinking) water supply; poverty / poor living conditions / poor hygiene / poor (health) education; ref to natural disasters; e.g. assistance / aid / medical help / AW, cannot arrive in time no rehydration therapy available (at time when needed); no (effective) vaccine; further detail; (bacteria live in gut, where immune system is not effective) [max 3] [Total: 17] 4. (a) (i) tertiary (structure) ; A 3o [1] (ii) secondary (structure) ; A 2o , alpha / α, helix [1] (b) active site ; A catalytic site [1] (c) (i) mRNA CGU ; UGC / UGU GAA; DNA GCA ACG / ACA CTT ; [3] (ii) many / several / more than one, triplet for each amino acid ; A codon an e.g. from Table 3.1 ; degenerate code / description e.g. 64 possible triplets for 20 amino acids ; A codons AVP ; e.g. may be an intron in this region, different nucleotides at the beginning (signal sequence) [2 max] (d) (i) reject references to time e.g. rapid, slowly as the concentration of, enzyme / lysozyme, increases the percentage of bacteria surviving decreases / AW ; R if only 1 named steep, decline / decrease, 0 to 10 / first two concentrations, for E. coli ; A large percentage difference in E.coli surviving at 0 to 10 / first two concentrations less steep / more gradual, decline / decrease, from 10 to 150 for E. coli ; decline / decrease, shallower / less steep from 0 – ,40 / 60 / 70 / 80, for S. aureus ; A small percentage difference in S. aureus surviving from 0 – , 60 / 70 / 80 decline / decrease, more significant / steeper / more abrupt, from 60 / 70 / 80, up to 150 for S. aureus ; A large percentage difference in S.aureus surviving from 60 / 70 / 80, up to 150 always more S. aureus than E. coli ; ora all bacteria survive with no lysozyme ; lysozyme is more effective, at killing / against, E. coli / AW ; A ora all E. coli killed, at 150 pmol dm-3 (of lysozyme) / at highest concentration ; comparative data quote ; both axes, both curves comparative data quote ; penalise once for lack of units in both [4 max] (ii) different, polysaccharides / peptidoglycans, in cell walls ; S. aureus, does not have / has less, polysaccharides / peptidoglycans, in cell wall ; ref to shape of active site ; ref to shape of, polysaccharide / peptidoglycan (to fit into active site) ; S. aureus has a capsule / ora ; A protective lipids AVP ; e.g. S. aureus produces inhibitor [2 max] [Total: 14]