a. 1 mark for correctly linking sugar, phosphate, and base to form at least one nucleotide

b. 1 mark for labeling deoxyribose, phosphate, and base/named base at least once

c. 1 mark for showing adenine paired with thymine and cytosine paired with guanine

d. 1 mark for drawing two antiparallel chains of nucleotides linked by hydrogen bonds, with all sugar-phosphate bonds in the correct position

$$\text{Sugar} - \text{Phosphate} - \text{Base}$$ - Ignore labeling 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. - For (c), full names of all four bases are required, but not relative sizes of the purine and pyrimidine bases. - For (d), 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.

1. A1 Translation occurs on ribosomes
2. A1 tRNA-activating enzymes attach amino acids to tRNAs
3. A1 Small and large ribosome units assemble on mRNA OR translation/polypeptide synthesis starts at a start codon
4. A1 Each tRNA arriving at the ribosome binds to the A site
5. A1 Anticodon «on tRNA» binds to codon «on mRNA»
6. A1 According to complementary base pairing/A with U and G with C
7. A1 Ribosome moves along the mRNA / mRNA moves over ribosome
8. A1 tRNA shifts from the A site to P site/from the P to the E site
9. A1 Peptide bond between amino acids «on tRNAs at A and P sites»
10. A1 tRNA released from ribosome at E site
11. A1 Cycle repeats with other tRNAs / polypeptide grows as tRNAs bring more amino acids
12. A1 Until stop codon on mRNA is reached
13. A1 Components are disassembled / polypeptide leaves the ribosome

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

a. 1 mark linear/not circular DNA molecule OR one chromosome is one molecule of DNA/one chromosome is two DNA molecules «after replication»

b. 1 mark associated with histone proteins/nucleosomes

c. 1 mark centromere joins sister chromatids «after DNA replication»

d. 1 mark telomeres at the end «of the chromosome/chromatid»

e. 1 mark carries a sequence of genes / each gene occupies a specific locus

f. 1 mark alternative alleles of genes / homologous chromosomes carry same sequence of genes

g. 1 mark chromosomes in pairs / two «homologous chromosomes» of each type «in a diploid cell»

h. 1 mark non-coding sequences/example of a non-coding sequence

i. 1 mark supercoiled/condensed «during mitosis/meiosis»

Do not accept 'sequence of bases' for mpe. Do not allow mph if the response states that chromosomes are always condensed.

6