Question X.
The Nature of the Genetic Code.
Evidence for
Achieved
Question
Evidence for
Achieved with Merit
Evidence for
Achieved with
Excellence


a.
Phosphate
Sugar/deoxyribose sugar/pentose
sugar
 Nitrogenous / nitrogen containing base
(not just base)
All 3 required
No. of bases
b.
A
T
G
C
Strand A
6
4
5
2
Strand B
4
6
2
5
All 5 correct
c.
3 features described:
 Replicate itself accurately/semi
conservative replication
 Stable molecule
 Variation in instructions/no
restrictions on sequence of
nucleotides
 Specific base pairing
 Large molecule / with unlimited
potential for variation in the
sequence of bases.
3 Features described and 2 explained.
e.g.
 Can replicate itself accurately - DNA
code can pass through generations.
Semi-conservative replication/
parent strands form templates for new
strands - leads to more precise
copying mechanism
 Stable molecule - doesn’t disintegrate
in cell. Histones and repair enzymes
protect molecular structure.
 Variation in codons/nucleotide
sequence leads to variation in
proteins formed. Unlimited variations
in sequence possible.
 Specific base pairing – more
accuracy in transcription and
translation of code to proteins
 Large molecule – to enable all the
necessary instructions for complete
organism
Transcription
 DNA, mRNA, RNA polymerase /
enzymes, transcription factors /
enhancers, nucleotides etc
d. i.
Translation
 mRNA, tRNA, ribosomes / rRNA,
enzymes, amino acids etc
3 for each process identified
Description of transcription factors as
proteins / enzymes that assist
transcription (not RNA polymerase)
d. ii.
Explanation of function of factors
 bind to RNA polymerase
and/or DNA strand
 enhances mRNA production
 detach from RNA
polymerase/DNA strand when
stop codon reached
Any two explanations.
Similarities:
 Enzymes involved in both
processes
 Three bases/codons is the
code
 Base pairing rule followed
 mRNA produced in
transcription is then used in
translation
Differences:
 Location in cell: Transcription
occurs in nucleus, translation
occurs in cytoplasm
 Transcription precedes
translation
 Template molecule: DNA in
transcription, mRNA in
translation
 Additional factors/transcription
factors present in transcription
 Ribosomes present in
translation, not in transcription.
 Translation involves joining of
codon with anticodon.
d. iii.
Introns – non protein-coding
sections of DNA
 Exons – Protein-coding sections of
DNA

e.
Both must be described
Total
6
Two similarities
and two
differences
discussed in
answer showing
linking of ideas.
e.g. Transcription
precedes
translation in the
process of protein
synthesis, mRNA
produced in
transcription is
then used in
translation as the
template
molecule.
One similarity and one
difference explained fully
Explanation of fate of both
introns and exons:
 Exon mRNA is translated into
protein molecules
 Intron mRNA is spliced/cut out
by enzymes and broken
down/recycled/has regulatory
role
4
1