6.1.1 Cellular Control Flashcards
1
Q
What is a mutation?
A
- a random change to the DNA
- they may occur spontaneously during DNA replication before cell division
- some chemicals may be mutagenic and increase chances of mutation
2
Q
What is somatic mutations?
A
- mutation associated with mitotic division
- are not passed down to offspring
- may be associated with the development of cancerous tumours
3
Q
How might mutations be inherited by offspring?
A
- mutations associated with meiosis and gamete formation
4
Q
What are the two main classes of DNA mutation?
A
- point mutation: one base pair substitutes another
- insertion or deletion (indel) mutation: one or more nucleotides are inserted or deleted from a length of DNA
- these may cause a frameshift
5
Q
Where do point mutations occur?
A
- the mRNA as codons, that was transcribed
- complementary to the base triplets on the template strand of the length of DNA
6
Q
What are the three types of point mutation?
A
- silent
- missense
- nonsense
7
Q
Describe silent mutations
A
- a silent mutation is a point mutation involving a change to the base triplet, where the triplet still codes for the same amino acid
- this is because all amino acids, apart from methionine, have more than one base triplet code
- this reduces the effect of point mutations
- the primary structure of the protein, and so the secondary and tertiary structure is not altered
8
Q
Describe missense mutations
A
- a change to the base triplet sequence that leads to a change in the amino acid sequence in a protein
- this may have a significant effect on the protein produced
- the change to primary structure changes the secondary etc
- this prevents it from carrying out its usual function
- sickle cell anaemia results from a missense mutation
9
Q
Describe nonsense mutations
A
- a point mutation may alter a base triplet so that it becomes a termination triplet
- this results in a truncated protein that will not function
- it will most likely be degraded within the cell
- Duchenne muscular dystrophy is the result of a nonsense mutation
10
Q
How do insertions and deletions cause frameshifts?
A
- if nucleotide base pairs, not in multiples of three, are inserted in the gene or deleted from the gene, all the subsequent base triplets are altered
- this is a frameshift
- this is because the code is non-overlapping and read in groups of three bases
- when the mRNA is translated, the amino acid sequence is severely disrupted
- hence the primary structure and the tertiary structure is much altered
- protein cannot carry out its normal function
- if it is very abnormal, it will be rapidly degraded within the cell
- some forms of thalassaemia are caused by frameshifts
11
Q
Why are insertions or deletions of a triplet of base pairs not cause a frameshift?
A
- since it is a triplet, it will either result in the addition or loss of an amino acid
12
Q
What are expanding triplet nucleotide repeats?
A
- some genes contain a repeating triplet such as CAG CAG CAG
- in an expanding triple nucleotide repeat, the number of CAG triplets increase at meiosis and again from generation to generation
- Huntingdon disease results from this
- they will develop symptoms if the number of repeating sequences go above a certain number
13
Q
Why are not all mutations harmful?
A
- many mutations are beneficial and have helped to drive evolution through natural selection
- different alleles of a particular gene are produced via mutation
14
Q
Give some examples of beneficial and neutral human mutations
A
- blue eyes arose 6000-8000 years ago
- allows people to see better is less bright light
- paler skin allows better vitamin D absorption in lower light
Neutral mutations:
- inability to smell certain flowers
- differently shaped ear lobes
15
Q
Describe how E.coli uses respiratory substrates
A
- the bacterium E.coli normally metabolises glucose as repiratory substrate
- however, if glucose is absent and the disaccharide lactose is present, lactose induces the production of two enzymes:
- lactose permease: allows lactose to enter the bacterial cell
- ß-galactosidase: hydrolyses lactose to glucose and galactose
17
Q
Describe how the lac operon works
A
- lactose molecules bind to the LacI repressor protein molecules
- this alters the shape of the LacI repressor protein, preventing it from binding to the operator
- the RNA polymerase enzymes then binds to the promoter regions and begins transcribing the structural genes into mRNA that will then be translated into the two enzymes
22
Q
Describe how introns and exons work
A
- all the DNA of a gene, both introns and exons, is transcribed
- the resulting mRNA is primary mRNA
- it is then edited and the RNA introns are removed
- the remaining mRNA exons, corresponding to DNA exons, are joined together
- endonuclease enzyme may be involved in the editing and splicing processes
- some introns may themselves encode proteins
- some become short non-coding lengths of RNA involved in gene regulation
23
Q
How does post-translational level of gene regulation occur?
A
- post-translational regulation of gene expression involves the activation of proteins
- many enzymes are activated by being phosphorylated
29
Q
How are Hox genes arranged in clusters?
A
- they are arranged in clusters and each cluster may contain up to 10 genes
- in tetrapods, there are four clusters
- at some point during evolution, the Hox clusters have been duplicated
34
Q
Describe the process of apoptosis
A
- enzymes break down the cell cytoskeleton
- cytoplasm becomes dense with tightly packed organelles
- cell surface membrane changes and small protrusion called blebs form
- chromatin condenses, the nuclear envelope break and DNA breaks into fragments
- the cell breaks into vesicles that are ingested by phagocytic cells so that cell debris does not damage any other cells or tissues. the process happens quickly
