4- M/P DNA & PROTEIN SYSNYHESIS QP Flashcards
A mutation of a tumour suppressor gene can result in the formation of a tumour.
Explain how.
(2)
- (Tumour suppressor) gene inactivated / not able to control / slow down
cell division;
Ignore: references to growth - Rate of cell division too fast / out of control.
1 and 2 Accept: mitosis
1 and 2 Reject: meiosis
Not all mutations result in a change to the amino acid sequence of the
encoded polypeptide.
Explain why.
(Genetic) code degenerate;
Accept: codon for triplet
Accept description of degenerate code, e.g. another triplet
codes for the same amino acid
The table below shows the base triplets that code for two amino acids.
Aspartic acid GAC, GAU
Proline CCA, CCG, CCC, CCU
Aspartic acid and proline are both amino acids. Describe how two amino acids differ
from one another. You may use a diagram to help your description. (1)
Describe how two amino acids differ
from one another. You may use a diagram to help your description.
Have different R group.
AUGCCGUACCGACU
Deletion of the sixth base (G) in the sequence shown in the diagram above would
change the nature of the protein produced but substitution of the same base would
not. Use the information in the table and your own knowledge to explain why.
- Substitution would result in CCA / CCC / CCU;
- (All) code for same amino acid / proline;
- Deletion would cause frame shift / change in all following codons /
change next codon from UAC to ACC.
Messenger RNA (mRNA) is used during translation to form polypeptides. Describe how mRNA is produced in the nucleus of a cell. (6)
- Helicase;
- Breaks hydrogen bonds;
- Only one DNA strand acts as template;
- RNA nucleotides attracted to exposed bases;
- (Attraction) according to base pairing rule;
- RNA polymerase joins (RNA) nucleotides together;
- Pre-mRNA spliced to remove introns.
Describe the structure of proteins.
- Polymer of amino acids;
- Joined by peptide bonds;
- Formed by condensation;
- Primary structure is order of amino acids;
- Secondary structure is folding of polypeptide chain due to hydrogen
bonding;
Accept alpha helix / pleated sheet - Tertiary structure is 3-D folding due to hydrogen bonding and ionic /
disulfide bonds; - Quaternary structure is two or more polypeptide chains.
Describe how proteins are digested in the human gut.
- Hydrolysis of peptide bonds;
- Endopeptidases break polypeptides into smaller peptide chains;
- Exopeptidases remove terminal amino acids;
- Dipeptidases hydrolyse / break down dipeptides into amino acids.
how would enough DNA be obtained for sequencing?
how would sequencing allow the identification of a mutation?
- Enough DNA using PCR;
2. Compare DNA sequence with ‘normal’ DNA
Compare DNA replication and transcription by describing the similarities and differences between the two processes (6)
- DNA unwinds and upzips
- Helicase enzymes
- Template DNA
- Complementary base pairing
- Hydrogenbonds
- Free activated nucloetides
- Polymerase enzymes
. Only small section of DNA unzips during transciption
. Both strands act as templates during replication
.Different Helicase enzymes
. Products are two new daughter strands of DNA in replication and one mRNA strand in transcription
Some cancer cells have a receptor protein in their cell-surface membrane that binds
to a hormone called growth factor. This stimulates the cancer cells to divide.
Scientists have produced a monoclonal antibody that stops this stimulation.
Use your knowledge of monoclonal antibodies to suggest how this antibody stops
the growth of a tumour.
(3)
- Antibody has specific tertiary structure / binding site / variable region;
Do not accept explanations involving undefined antigen - Complementary (shape / fit) to receptor protein / GF / binds to receptor
protein / to GF;
Ignore: same shape as receptor protein / GF - Prevents GF binding (to receptor).
In the diagram above, the first codon is AUG.
```
Give the base sequence of:
the complementary DNA base sequence
……
the missing anticod
on
2
~~~
TAC
UAC
Read the following passage carefully.
A large and growing number of disorders are now known to be due to types of
mitochondrial disease (MD). MD often affects skeletal muscles, causing
muscle weakness.
We get our mitochondria from our mothers, via the fertilised egg cell. Fathers
do not pass on mitochondria via their sperm. Some mitochondrial diseases
are caused by mutations of mitochondrial genes inside the mitochondria.
Most mitochondrial diseases are caused by mutations of genes in the cell
nucleus that are involved in the functioning of mitochondria. These mutations
of nuclear DNA produce recessive alleles.
5
One form of mitochondrial disease is caused by a mutation of a mitochondrial
gene that codes for a tRNA. The mutation involves substitution of guanine for
adenine in the DNA base sequence. This changes the anticodon on the tRNA.
This results in the formation of a non-functional protein in the mitochondrion.
There are a number of ways to try to diagnose whether someone has a
mitochondrial disease. One test involves measuring the concentration of
lactate in a person’s blood after exercise. In someone with MD, the
concentration is usually much higher than normal. If the lactate test suggests
MD, a small amount of DNA can be extracted from mitochondria and DNA
sequencing used to try to find a mutation.
15
Use information in the passage and your own knowledge to answer the following
questions
Mitochondrial disease (MD) often causes muscle weakness (lines 1–3). Use your
knowledge of respiration and muscle contraction to suggest explanations for this
effect of MD. (3)
- Reduction in ATP production by aerobic respiration;
- Less force generated because fewer actin and myosin interactions in
muscle; - Fatigue caused by lactate from anaerobic respiration.
Two couples, couple A and couple B, had one or more children affected by a
mitochondrial disease. The type of mitochondrial disease was different for each
couple.
None of the parents showed signs or symptoms of MD.
• Couple A had four children who were all affected by an MD.
• Couple B had four children and only one was affected by an MD.
(b) Use the information in lines 5–9 and your knowledge of inheritance to suggest why:
• all of couple A’s children had an MD
• only one of couple B’s children had an MD.
Couple A
COUPLE b (4)
Couple A,
1. Mutation in mitochondrial DNA / DNA of mitochondrion affected;
2. All children got affected mitochondria from mother;
3. (Probably mutation) during formation of mother’s ovary / eggs;
Couple B,
4. Mutation in nuclear gene / DNA in nucleus affected;
5. Parents heterozygous;
6. Expect 1 in 4 homozygous affected
Suggest how the change in the anticodon of a tRNA leads to MD (lines 10–13). (3)
- Change to tRNA leads to wrong amino acid being incorporated into
protein; - Tertiary structure (of protein) changed;
- Protein required for oxidative phosphorylation / the Krebs cycle, so less /
no ATP made.
If someone has MD, the concentration of lactate in their blood after exercise is
usually much higher than normal (lines 15–17). Suggest why.
(3)
- Mitochondria / aerobic respiration not producing much / any ATP;
- (With MD) increased use of ATP supplied by increase in anaerobic
respiration; - More lactate produced and leaves muscle by (facilitated) diffusion.
