NCEA Level 3 Science (90729) 2012 — page 1 of 3
Assessment Schedule – 2012
Science: Describe genetic processes (90729)
Evidence Statement
Q
ONE
Achievement
Structure of mRNA.
• Single stranded.
• Bases identified OR implied.
Diagram or description given.
Achievement with Merit
Achievement with Excellence
Explanation of how transcription
occurs.
The DNA unwind to expose one
side and the bases, nucleotides
match (A=U; G=C) and copy the
code to mRNA molecule.
Discussion of how transcription
occurs.
DNA unwinds due to enzymes
(helicase).
RNA polymerase starts the process.
Free RNA nucleotides are matched
to the exposed DNA nucleotides.
A=U and G=C.
Occurs for the length of a gene
only needed to make a protein.
DNA winds up again and remains
in the nucleus.
Either explanation of HOW or
WHY of transcription.
BOTH ideas needed with link to
specific amino acids coded for and
why the DNA cannot leave the
nucleus.
Function of mRNA.
• Carry code for the making of
proteins from DNA in nucleus
to ribosomes for protein
synthesis.
Description of how transcription
occurs.
The code is copied from the DNA
molecule to mRNA / make a
mRNA molecule that carries the
code from the DNA molecule.
Need description of structure
and function of mRNA AND
either how or why of
transcription.
NCEA Level 3 Science (90729) 2012 — page 2 of 3
TWO
Substitution is when one base is
replaced by another.
(Or clear diagram.)
A substitution effects one triplet
only and therefore only one amino
acid (coded for by this triplet).
AAA TTT AAA becomes
ACA TTT AAA
There is still the same number of
triplet / codons overall and only
one amino acid may change.
A is replaced by C
Deletion is the removal of one
base pair on the DNA molecule.
(Or clear diagram.)
AAA TTT AAA becomes
AA- TTT AAA
A is removed
These mutations change the order
of bases (triplet codes) from the
point of the mutation onwards
causing a frame shift (moving of
the bases in the triplet code)
causing different amino acids to be
coded for from the point of the
mutation onwards.
A frame shift mutation results in
different triplet / codons from the
point of the mutation onwards.
Therefore different amino acids are
coded for in the sequence of the
polypeptide chain. This affects the
overall functioning of the protein as
the order of the amino acids
determines how the protein folds /
shape of the protein (active site) to
make a functional protein.
Insertion is adding one base into
the DNA sequence.
(Or clear diagram.)
AAA TTT AAA becomes
AAA GTT TAA A
G is added into second codon.
Descrition of all three mutations
OR description of how one
mutation affects the overall
codon / amino acid / protein.
This mutation may have no or little
effect on the protein due to
• The degeneracy of the code.
Each amino acid may be coded
for by more than one codon. A
substitution mutation may change
one codon but it may still code
for the same amino acid; hence
no effect (silent mutation).
• A change in the codon may result
in a different amino acid with
similar properties, and it does not
affect the overall function of the
protein.
• The mutation may be at the end
of the polypeptide chain and have
little effect on the overall folding
and shape of the protein.
Effect of all three mutations on
the codon / amino acid / protein
OR explanation of the effect of
frame shift (from deletion /
insertion) on the overall protein.
Discussion of effect of substitution
due to degeneracy of the code
AND discussion of the effect of
the frame shift on the sequence of
amino acids and therefore the
final structure of the protein.
NCEA Level 3 Science (90729) 2012 — page 3 of 3
THREE
Description of how recombinant
DNA Is created.
• Use of restriction enzymes to
cut a specific sequence /
recognition site of DNA /
desired gene and the same
restriction enzyme is used to
cut the viral DNA
• Ligase “glues” the desired gene
and the viral vector together as
they have the same recognition
site.
• Use of PCR to amply the
desired gene / DNA to give
sufficient copies to work with.
Need 2 out of 3 processes linked
to the context given.
Explanation of why a viral vector is
used.
• Simple DNA (plasmid) and easy
to add the target DNA by using
the same restriction enzymes /
ligase to form recombinant DNA
• Easily infect the host cells
without altering the recombinant
DNA thus delivering the gene of
interest
• Once in the human cells, the
virus uses the human cells to
make more copies of itself
(including the recombinant
DNA).
Description of why a viral vector
is used.
Easy to add the target / desired
gene / DNA into the viral DNA
plasmid.
Easily infect the host cells / good
uptake by the host cells.
Fast replication within host cells.
Explanation of the risks or
implications of gene therapy.
• The new gene could be inserted
incorrectly disrupting the virus
DNA OR cause a mutation,
which could harm the patient
when it is inserted OR it could
have a detrimental effect on the
human cells.
• The virus can infect more than
one type of cell thus healthy cells
could be harmed.
• The virus could affect the
reproductive cells and the altered
gene / mutation can be passed on
to offspring.
• The virus is specific to cancer
cells and is an effective treatment
when the drugs are used to kill
the cells with the recombinant
DNA only.
One reason needed.
Description of the risks or
implications of gene therapy
• The new gene may be inserted
incorrectly.
• The new gene inserted may
disrupt or cause mutation in the
viral DNA.
• The virus may infect more than
the target / one type of cell
• The virus may affect the
reproductive cells.
• The virus may target cancer
cells only.
One risk or implication
described.
Description of gene therapy
AND EITHER one reason why
virus used OR one implication /
risk.
Two ideas from either “why virus”
is used OR implications of gene
therapy (or one idea from each)
explained.
Implications and risks of using a
viral vector– discussion of three
ideas in total.
Judgement Statement
Criterion
Achievement
Achievement with Merit
Achievement with Excellence
2A
2M
2E