DNA and Protein Synthesis ( Genetic Diversity Via Mutation ) Flashcards
A mutation of a tumour suppressor gene can result in the formation of a tumour.
Explain how.
- Tumour suppressor gene is inactivated
- Rate of cell division is too fast
Not all mutations result in a change to the amino acid sequence of the encoded polypeptide.
Explain why.
- Genetic code is degenerate
- Mutation in intron
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.
- Antibody has a specific tertiary structure
- Complementary to receptor protein
- Prevents growth factor binding to receptor
Messenger RNA (mRNA) is used during translation to form polypeptides. Describe how mRNA is produced in the nucleus of a cell.
- Helicase ( DNA )
- Breaks H bonds
- Only one strand is used as a template strand
- RNA nucleotides are attracted to exposed bases
- RNA polymerase joins nucleotides together
- Pre - mRNA is spliced to remove introns
Describe the structure of proteins.
- Polymer of amino acids
- Joined by peptide bonds
- Formed by condensation
- Primary structure is the order of amino acids
- Secondary structure is the folding of polypeptide chain due to hydrogen bonding
Describe how proteins are digested in the human gut.
- Hydrolysis of peptide bonds
- Endopeptidases breaks polypeptides into smaller peptide chains
- Exopeptidases removes terminal amino acids
- Dipeptidases hydrolyses dipeptides into amino acids
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.
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.
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.
- Reduction in ATP production by aerobic respiration
- Less force generated because fewer actin and myosin interactions in the muscles
- Fatigue is 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.
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: Mutation in mitochondrial DNA
- All children got affected mitochondria from the mother
- Couple B: Mutation in nuclear gene
- Parents are heterozygous
Suggest how the change in the anticodon of a tRNA leads to MD (lines 10–13).
- Change to tRNA leads to the wrong amino acid being put into the protein
- Tertiary structure changes
- Protein is required for the krebs cycle, so less ATP is 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.
- Mitochondria isn’t producing much ATP
- With MD, increased use of ATP is supplied by increase in anaerobic respiration
- More lactate produced, which leaves muscles by diffusion
A small amount of DNA can be extracted from mitochondria and DNA sequencing
used to try to find a mutation (lines 18–19).
From this sample:
- how would enough DNA be obtained for sequencing?
- how would sequencing allow the identification of a mutation?
- Enough DNA is obtained using PCR
- Compare DNA sequence with normal DNA
