Mutations And Gene Expression Flashcards
Mutation
Random change in base sequence of DNA
The order of DNA bases in gene determines
The sequence of amino acids in a particular polypeptide
If a mutation occurs in the gene
The sequence of amino in the polypeptide that it codes for could be changed
Substitution mutation
One or more bases are swapped for one another
Deletion mutation
One or more bases are removed
Addition mutation
One or more bases are added/ inserted
Duplication mutation
One or more bases are repeated
Inversion mutation
A sequence of bases is reserved
Translocation mutation
A sequence of baes is moved from one location in th genome to another
This could be movement within the same chromosome or movement to a different chromosome
Silent mutation
2
If a mutation doesn’t cause a change in the sequence of amino acids
As the genetic code is degenerate, some amino acids are coded for by more than one triplet code
Which three mutations almost always cause a change in the amin acid sequence of a polypeptide
Addition
Duplication
Deletions
Frame shift
A shift in the base triplets that follow the mutation so that the triplet code is read in a different way
The base triplets that follow on from the mutation are said to be downstream
What in a mutation would bring transcription to a permanent halt
If. Stop codon is introduced
Mutagenic agents
Increase the rate of mutations
Examples of mutagenic agents
4
Ultraviolet radiation
Ionising radiation
Some chemicals
Some viruses
Mutagenic agents
Acting as a base
Chemicals called base analogs can substitute for a base during DNA replication, changing the base sequence in the new DNA
Mutagenic agents
Acting as a base
Example
4
5- bromouracil
Substitutes for thymine
Incorporates with the DNA and is most likely to pair with adenine however can spontaneously shift into another isomer which pairs with guanine
If thi happens during DNA replication, a guanine will be inserted as the opposite base analog, and so in the next DNA replication , the guanine will pair with a cytosine
Mutagenic agents
Altering bases
Some chemicals can delete or alter bases
Mutagenic agents
Altering bases
Example
Alkylating agents
Add an alkyl group to guanine
Changes its structure so that it pairs with thymine instead of cytosine
Mutagenic agents
Changing the structure of DNA
Some types of radiation can change the structure of DNA, which causes problems during DNA replication
Mutagenic agents
Changing the structure of DNA
Example
5
UV radiation
Cause adjacent thymine bases to pair up together
This alters the structure of DNA and consequently inhibit polymerases and stop replication
Unprepared dimers are usage in
Pyramiding dimers awe the primary cause of melanomas in humans
Stem cells
Unspecialised cells that have not differentiated and so may specialise to become any cell type and can undergo mitosis
Summary of how cells become specialised through gene expression
4+2
Genes expresses -> mRNA transcribed and translated into proteins -> proteins modify the cell -> cell becomes specialised for a particular function
Genes switched off -> mRNA not transcribed or translates -> proteins not produced
4 types of stem cells
Totipotent
Pluripotent
Multi potent
Unipotent
Totipotent stem cells
3
Found in the early embryo and can differentiate into any type of cell
Since all body cells are formed from a zygote, the zygote is totipotent
As the zygote divides and matures, its cells develop into slightly more specialised cells called pluripotent stem cells
Pluripotent stem cells
2
Found in embryos and can differentiate i to almost any type of cell
Examples= embryonic stem stem cels and foetal stem cells
Multi potent stem cells
4
Found in adults and can differentiate into a limited number of specialised cells
They usually develop into cells of a particular type
Eg stem cells inn the bone marrow can produce any type of blood cells
Examples= adult stem cells, umbilical cord, blood stem cells
Unipotent stem cells
2
Can only differentiate into a single type of cell
Derived from multi potent stem cells and are made in adult tissue
Cells used for treating human disorder
Pluripotent
Uses of pluripotent cells
Cells can be used to regrow tissues that have been damaged in some way either by accident or s a result of disease