6.1 Cellular control Flashcards
What is a mutation?
Change to the genetic material.
What do muations include?
Changes to the structure or number of chromosomes.
When do most mutations occur?
Before cell division/ interphase.
What can cause mutations?
- Tar in tobaocco smoke
- Ionising radiation such as UV light, xrays and gamma rays.
-> These may contain chemicals that are mutagenic.
What are somatic mutations?
Mutations associated with mitotic divsions.
What are the charateristics of miotic divisions?
They’re not passed onto their offspring and can be associated with cancerouks tumours.
What are he characteristics of a mutation associates with mieosis?
Mutaion in gamete formation and will be inherited by offspring.
What are the main 2 classes of DNA mutation?
- Point mutation
- Insersion or deletion
What is a point mutation?
One base replaces another.
What is a insersion or deletion mutation?
One or more nucleotides are inserted or deleted from a length of DNA. These may cause a frameshift.
What are rhe 3 types of point mutation?
- Silent
- Missence
- Nonsence
What does it mean that DNA is degenerate?
t
There are many instances in which different codons specify the same amino acid.
What characteristic of DNA means a mutation does always lead to a change of the sequence of amino acids in a protein?
DNA is degenerate
What is a silent mutation?
A type of point mutation involving a change to the base triplet where that triplet still codes for the same amino acid.
What is a missense mutation?
A point mutation which leads to a change to the base triplet sequence that leads to a change in the amino acid sequence in a protein.
What is the effect of a missence mutation?
THere can have a significant effect on the protein being produced as it is altering the primary structure leading to a change on the teritary structure and its function.
Hiwever, the change to it’s tertiary structure may be in an area that does effect it’s function so could be insignificant.
What condition is caused by a missence mutation?
Sickle cell amaenia results from a missence mutation on thr 6th base triplet of the gene B-polypeptide chains for haemoglobin.
What is a nonsence mutaion?
A point mutation that alters a base triplet so that it becomes a termination triplet.
What is the result of a nonsence mutation?
It results in a truncated protein that will not function. This abnormal protein will most likely be degraded within the cell.
What is an indel mutation?
Insertion and deletion mutations
What is the result of an indel mutation (not in multiples of 3)?
Because the cose is non-overlapping, all the subsequent base triplets are altered. This is a frameshift. THis will sevely alter the primary structure, the tertiary structure and therfore, it will not be able to carry out it’s function. The protein will be degraded within the cell.
What condition is a result of an indel mutation?
Thalassaemia, a haemoglobin disorder, results from a frame shift due to deletions of nucleotide bases.
When would indel muations not be very dissruptive?
With insertions or deletions of a triplet of base pairs result in the addition or loss of an amino acid- this is not a frameshift.
What happens is an expanding triple nuceotide repeat?
This is a type of indel mutation, the number of CAG triplets increases at meiosis and again from generation from generation.
What condition is a result from an expanding triple nuceotide repeat?
Huntington disease. If the number of CAG sequences goes above a certain critiacl number then the person with that genotype will develop the sympotoms of Huntingtons disease later on in life.
When have mutations been benificial?
They’ve helped drive evolution through natural selection.
What a some examples of mutations that appear to be neutral, neither benificial or negative?
- Inability to smell certain flowers
- Differently shaped earlobes.
What is an exon?
The coding, or expressed, reigon of DNA
What is an intron?
The nonb-coding region of DNA.
What is operon?
A group of genes that function as a single transcription unit; first identified in prokaryote cells.
What is a transcription factor?
Protein or non-coding RNA that can combine with a specific site on the length of DNA and inhbit or activate trascription of the gene.
What does E.coli normally respire?
Glucose
What will E.coli respire if glucose isnt available?
Lacose
What enzymes does the presence of lactose in E.coli produce?
- Lactose permease
- B-galactosidase
What is the lac operon? What does it contain?
A length of DNA, about 6000 base pairs long, containing lacO next to structural genes lacZ and lacY that cose for the enzymes lactose permease and B-galactosidase.
What does lactose permease do?
Make the bacteria E.coli nore permeable to lactose.
What does B-galactosidase do?
Hydrolyses lacose to glucose and galactose.
Which reigion does RNA polymerase bind to on the lac operon to allow the trascription of the structural genes lacZ and lacY?
The promoter region.
What does the regulatory gene on the lac operon code for?
A repressor protein (lacI)
What occurs in the lac operon in E.coli in the presence of glucose?
- The regulatory gene codes for a repressor protein.
- When this protein is expressed, it will bind to the operator, preventing RNA from binding to the promoter reigion.
- The repressor reigion therefore prevents the genes lacZ and lacY.
What are the control sites on the lac operon?
- Promotor reigion
- Operator
What are the structural genes o the lac operon?
- LacZ
- lacY
What is the advantage to E.coli having a lac operon system to induce the formation of enzymes to metabolise lactose?
The presence of a lac operon system means energy and amino cids aren’t wasted on producing enzymes when they’re not needed.
What occurs in the lac operon in E.coli in the presence of lacose?
- The regulatory gene expressed the repressor protein, however, lactose will act as an inducer and lacose will will bind to the repressor protein.
- This alters the shape of the repressor protein, preventing it from binding to the operator.
- The RNA polymerase can then binf to the promoter reigion and begin transcribing the structural genes into MRNA that will then be translated into lactse permease and B-galactoside.
In the lac-operon system, which molecule is the inducer?
Lacose- lacose induces the enzymes needed to break it down.