STRUCTURE OF DNA & RNA A1. D A2. D J WERBA – IB BIOLOGY 1

STRUCTURE OF DNA & RNA A3. four nucleotides shown in diagram with one nucleotide clearly labeled; base, phosphate and deoxyribose (shown as pentagon) connected between the correct carbons and labeled at least once; backbone labeled as covalent bond between nucleotides correctly shown as 3′ to 5′ bond; two base pairs linked by hydrogen bonds drawn as dotted lines and labeled; two H bonds between A and T and three H bonds between C and G; adenine to thymine and cytosine to guanine; (do not accept initials of bases) antiparallel orientation shown; J WERBA – IB BIOLOGY 2

DNA REPLICATION, TRANSCRIPTION & TRANSLATION N15 isotope has a greater mass than the N14 isotope Generation 0 contained DNA with only N15 isotopes (giving it a greater density) With each generation, the proportion of N14 isotopes would increase After four generations, most strands contain only N14 isotopes J WERBA – IB BIOLOGY 3

DNA REPLICATION, TRANSCRIPTION & TRANSLATION The N15 isotope band = 1.730g cm-3 The N14 isotope band = 1.700 g cm-3 After one generation, the DNA would be 50/50 N15/N14 Average mass = 1.715 g cm-3 conservative replication would be falsified if conservative replication had occurred, all generations after generation 0 should have had the two distinct bands. J WERBA – IB BIOLOGY 4

DNA REPLICATION, TRANSCRIPTION & TRANSLATION Results = 2 bands One band with a mixture of N15 & N14 – semi-conservative replication means that some DNA strands would still contain the N15 isotopes One band contains only N14 – N14 strand from generation 1 would become parent strand for generation 2, forming DNA with two N14 strands This would falsify the theory of dispersive replication Results = 3 bands One band contains only N15 – no replication has occurred yet in generation 0 One band with a mixture of N15 & N14 – from generation 2 One band contains only N14 – from generation 2 J WERBA – IB BIOLOGY 5

DNA REPLICATION, TRANSCRIPTION & TRANSLATION DNA replication is semi-conservative; DNA is split into two single/template strands; nucleotides are assembled on/attached to each single/template strand; by complementary base pairing; adenine with thymine and cytosine with guanine / A with T and C with G; strand newly formed on each template strand is identical to other template strand; DNA polymerase used; Marks may be awarded for any of the above points if clearly presented in a well-annotated diagram. J WERBA – IB BIOLOGY 6

DNA REPLICATION, TRANSCRIPTION & TRANSLATION A3. D A4. A-T and C-G in DNA; A-U and C-G in RNA; complementary base pairing in replication ensures identical nucleotide sequence of new complementary strands; semi-conservative replication; transcription produces RNA sequence complementary to the DNA sequence (of the gene); triplets of nucleotides on mRNA are codons; translation converts mRNA sequence of information into a specific amino acid chain (polypeptide); (each class of) tRNA carries a specific triplet of (three) bases called an anticodon; anticodons bind to codons by complementary base pairing; (each class of) tRNA with specific complementary anticodons carry specific amino acids; sequence of mRNA codons translates into specific amino acid sequence; enables conservation of information transfer from DNA to RNA to polypeptide; J WERBA – IB BIOLOGY 7

DNA REPLICATION, TRANSCRIPTION & TRANSLATION A5. GAU, GAC A6. Leu, Thr, Lys, Arg, Ser, Gly. GAC TGA TCC AGG CCT A7. ACT AAC J WERBA – IB BIOLOGY 8

CELL RESPIRATION A1. C A2. C A3. B J WERBA – IB BIOLOGY 9

CELL RESPIRATION A4. aerobic cell respiration if oxygen available and anaerobic if unavailable; pyruvate enters mitochondrion for aerobic respiration; whereas pyruvate stays in the cytoplasm for processing under anaerobic conditions; pyruvate converted aerobically into carbon dioxide and water; whereas pyruvate converted anaerobically to lactate; large ATP yield when oxygen available/from aerobic cell respiration; no (further) ATP yield without oxygen; J WERBA – IB BIOLOGY 10

PHOTOSYNTHESIS A1. B A2. D A3. chlorophyll is the (main) photosynthetic pigment; absorbs (mainly) red and blue light; green light is reflected; light energy absorbed is converted into chemical energy; ATP produced; water split; to form oxygen and hydrogen; ATP and hydrogen used to fix carbon dioxide to make organic molecules; J WERBA – IB BIOLOGY 11