6.1 Cellular Control Flashcards
(47 cards)
What is a mutation?
a change in the base sequence of DNA
What causes a mutation?
They occur randomly, yet can be caused by:
1. UV light
2. Ionising radiation e.g. x-rays
3. Chemicals - carcinogens
What is a Deletion mutation?
A base has been deleted / removed from the code.
Effects of a deletion mutation?
Frameshift - all the bases move down.
Now all the subsequent codons will code for different amino acids, changing the overall shape of the protein
What is degenerate code?
Code where multiple codons code for the same amino acid
What is an Insertion mutation?
When a nucleotide is randomly inserted into the DNA sequence
Effects of insertion mutations?
Changing the triplets (groups of three bases) further on in the DNA sequence
This is sometimes known as a frameshift mutation
This may change the amino acid sequence produced and the ability of the polypeptide to function
What is a substitution mutation?
Where one base is substituted for another
Effects of a substitution mutation?
Will not have a knock-on effect
Will only change the amino acid which the triplet codes for
What are 3 types of substitution mutation?
Silence - the mutation does not alter the amino acid sequence (due to degenerate code)
Missense - mutation alters a single amino acid
Nonsense - mutation creates a premature stop codon
What is a stop codon?
A signal for the cell to stop translation of the mRNA molecule into an amino acid sequence
Beneficial mutations
A significantly altered polypeptide shape, yet the mutation causes an altered characteristic which has beneficial effects for the organism
—> e.g. Pale skin synthesising vitamin D from decreased melanin production
Harmful mutations
Causes an altered characteristic which has harmful effects for the organism
—> e.g. cystic fibrosis
Neutral mutations
No selective advantage or disadvantage
- A mutation does not alter the polypeptide
- A mutation only alters the polypeptide slightly so that its structure or function is not changed
- A mutation alters the structure or function of the polypeptide but the resulting difference in the characteristic of the organism provides no particular advantage or disadvantage to the organism
What are regulatory mechanisms?
They make sure the correct genes are expressed in the correct cell at the correct time
3 main types of regulatory mechanism?
- Transcriptional level
- Post-transcription
- Post-translation
What does a structural gene do?
codes for a protein that has a function within a cell e.g. enzymes
What do regulatory genes do?
code for proteins that control the expression of structural genes
What is the lac operon an example of?
a regulatory mechanism at the transcriptional level
What is an ‘operon’?
a group or a cluster of genes that are controlled by the same promoter
Where is the lac operon found, and what does it control?
Bacteria
It controls the production of lactase.
Lactase can be used to break down lactose which can be used as an energy source for the cell
Why is lactase referred to as an inducible enzyme?
it is only synthesized when lactose is present
What happens when lactose is absent?
- Regulatory gene is transcribed and translated to produce lac repressor protein
- lac repressor binds to operator region
- RNA polymerase cannot bind to promoter region
- transcription of structural genes does not take place
- no lactase is synthesised
(obvs, when there is no lactose, no lactase is needed to break it down)
What happens when lactose is present?
- uptake of lactose by bacteria
- lactose binds to 2nd binding site on repressor protein and distorts its shape
- Repressor protein cannot bind to operator region
- RNA polymerase binds to promoter region
- transcription takes place
- lactase enzyme is produced
- Lactase breaks lactose down into galactose and glucose which can be used as a substrate.
