Draw the structure of a section of DNA showing all possible bases.

Outline the structural and genetic characteristics of eukaryotic chromosomes.

Explain how a polypeptide chain is synthesized in a eukaryotic cell.

a. sugar, phosphate and base linked correctly to form at least one nucleotide ✔ For mpa, ignore labelling of the subunits of the nucleotide. Carbon atoms in deoxyribose do not have to be numbered but the phosphate should be linked to C5 and the base to C1. Shapes other than circles and rectangles could be used for the phosphate and base.

b. deoxyribose, phosphate and base/named base labelled at least once ✔

c. adenine paired with thymine and cytosine paired with guanine ✔ For mpc, full names of all four bases are required, but not relative sizes of the purine and pyrimidine bases.

d. two antiparallel chains of nucleotides linked by hydrogen bonds with all sugar-phosphate bonds in correct position ✔ For mpd, a bond should connect the C3 of deoxyribose on one nucleotide to the phosphate on the adjacent nucleotide. Two nucleotides in each strand is sufficient.

a. linear/not circular DNA molecule
OR
one chromosome is one molecule of DNA/one chromosome is two DNA molecules «after replication» ✔

b. associated with histone proteins/nucleosomes ✔

c. centromere joins sister chromatids «after DNA replication» ✔

d. telomeres at the end «of the chromosome/chromatid» ✔

e. carries a sequence of genes / each gene occupies a specific locus ✔ Do not accept ‘sequence of bases’ for mpe.

f. alternative alleles of genes / homologous chromosomes carry same sequence of genes ✔

g. chromosomes in pairs / two «homologous chromosomes» of each type «in a diploid cell» ✔

h. non-coding sequences/example of a non-coding sequence ✔ Do not allow mph if the response states that chromosomes are always condensed.

i. supercoiled/condensed «during mitosis/meiosis» ✔

a. translation occurs on ribosomes ✔

b. tRNA-activating enzymes attach amino acids to tRNAs ✔

c. small and large ribosome units assemble on mRNA
OR
translation/polypeptide synthesis starts at a start codon ✔

d. each tRNA arriving at the ribosome binds to the A site ✔

e. anticodon «on tRNA» binds to codon «on mRNA» ✔

f. according to complementary base pairing/A with U and G with C ✔

g. ribosome moves along the mRNA / mRNA moves over ribosome ✔

h. t-RNA shifts from the A site to P site/from the P to the E site ✔

i. peptide bond between amino acids «on tRNAs at A and P sites» ✔

j. tRNA released from ribosome at E site ✔

k. cycle repeats with other tRNAs / polypeptide grows as tRNAs bring more amino acids ✔

l. until stop codon on mRNA is reached ✔

m. components are disassembled / polypeptide leaves the ribosome ✔

Accept these points in an annotated diagram.
Do not award any marks for events in transcription.