M6, C19 Genetics Of Living Systems Flashcards
define mutation
changes (amount or arrangement) to the base (nucleotide) sequence of DNA
define chromosome mutation
changes to parts of or whole chromosomes
define DNA mutation
changes to genes due to changes in nucleotide base sequence
what are the things called which cause mutations
mutagens
what are the 6 types of gene mutations
point or substitution - only one nucleotide is affected
insertion - inserting a base which shifts nucleotides to the right
deletion - base or triplet removed
nonsense - stop codon being coded for due to substitution
missense - different amino acid being coded for, which will alter primary structure of polypeptide and probably change its tertiary structure
silent/neutral - same amino acid being coded for, as genetic code is degenerate, therefore polypeptide will be unaltered
what are the different ways mutations can affect an organism (both beneficially and harmfully)
Beneficial - mutation produces an advantage to the organism, so increase chance of survival
- these are passed onto offspring, by the process of natural selection
Harmful - mutation produces a disadvantage, so decrease chance of survival
- organism may not survive or mate
what is a conservative mutation
when the amino acid change leads to an amino acid being coded for which has similar properties to the original, this means the effect of the mutation is less severe
what is non-conservative mutation
when the new amino acid coded for has different properties to the original
what are frameshift mutations
adding or deleting a base causes a sift in bases that follow
the base sequence is read differently
the earlier the frameshift, the greater the effect on the protein
(it is NOT a frameshift if a triplet is added)
what are the 4 types of chromosome mutations
Deletion - a section of chromosome breaks off and is lost within the cell
Duplication - sections get duplicated on a chromosome
Translocation - a section of chromosome breaks off and joins another non-homologous chromosome
Inversion - a section of chromosome breaks off, is reversed and then joins back onto the chromosomes
give 3 ways in which a mutation gives a neutral effect on the protein
If the mutation changes a base sequence in a triplet, but the amino acid the triplet codes for doesn’t change
If the mutation produces a triplet that codes for a different amino acid, but the amino acid is chemically similar to the original so it functions like the original amino acid.
If the mutated triplet codes for an amino acid not involved in the proteins function.
Give one example of how a mutation can lead to a protein not being produced
A mutation at the start of a gene could result in RNA polymerase not being able to bind to the gene, which would mean that the protein coded for by the gene wouldn’t be produced.
Outline why the majority of mutations do not have an influence on phenotype
Mutations are random.
Mutations are more likely to occur in non-coding regions.
Majority of DNA is non-coding.
But a mutation on a non-coding region doesn’t affect the phenotype.
define operon
a section of DNA that contains a cluster of structural genes that are transcribed together
what are factors that start transcription called?
what are factors that stop transcription called?
start - activators
stop -repressors
The image for lac operon in E.coli is represented with the letter IPOZYA
what do they all stand for
I - lacI produces lac repressor, which is the transcription factor
P - promoter - RNA polymerase binds here to start transcription of structural genes
O - repressor binds here, switch structural genes on and off
Z - lacZ - beta-galactosidase - hydrolyse lactose to glucose and galactose
Y - lacY - lactose permease - allows cell to take up lactose
(A - lacA - enzyme that transfers an acetyl group from acetyl-CoA to beta-galactosides, precise function not known)
in the lac operon in E. coli, what happens when lactose is NOT present
- lacI produces the lac repressor which is the transcription factor
- it binds to the operator site
- this also covers the promoter which blocks transcription because the RNA polymerase can’t bind to the promoter
in the lac operon in E. coli, what happens when lactose is present
- the lactose binds to the repressor which is on the operator site
- this changes the shape of the repressor meaning it can no longer bind to the operator site
- RNA polymerase can now begin transcription of the structural genes
at what stages can gene expression be controlled
- transcriptional - genes can be turned on/off
- post-transcription - mRNA can be modified which regulates translation and the types of protein produced
- translational - translation can be stopped/started
- post-translation - proteins can be modified after synthesis which changes their function
how is protein production controlled at the post-transcriptional level
After transcription
- mRNA is edited because it contains sections that don’t code for amino acids (introns)
- the primary mRNA transcript has introns in it so they have to be removed by the process of splicing
- exons (bits that do code for amino acids) and joined together to make mature mRNA
define introns and exons
introns - genes in eukaryotic DNA that don’t code for amino acids
exons - bits that do code for amino acids
how is protein production controlled at the post-translational level
-some proteins aren’t functional straight away (they need to be activated to become functional)
-protein activation is controlled by molecules (hormones and sugars)
-the molecules bind to the cell surface membrane and trigger the production of cAMP (cyclic-AMP) inside the cell
-cAMP activates proteins inside the cell by altering their 3D structure
(-by altering the 3D structure the active site changes shape making it more or less active)
give some details about fruit flies
what was first found in them
Genes that control body development first found in fruit flies
Very small (2mm), easy to keep, short life cycle
Reproduce quickly
Cheap
Feed on rotting fruit
define homeobox
define homeobox genes
The homeobox:
Is a section of DNA, 180 base pairs long coding for a part of the protein, 60 amino acids long that is very similar in plants, animals and fungi
Homeobox genes:
Group of genes that contain a homeobox
direct the formation of many body structures during early embryonic development
define homeobox domain
Homeobox domain:
The part of the protein that binds to DNA and switches other genes on or off
what type of genes are homeobox genes
regulatory genes
what are gene clusters
homeobox genes are found in clusters
why do humans have lots of Hox genes
Humans have 39 Hox genes, due to duplication and accumulated mutations
what does it mean when it’s said that homeobox sequences are highly conserved
they haven’t changed much during evolution of different organism
how do homeobox sequences work
- They code for a part of the protein called the homeobox domain
- The homeobox domain binds to specific sites on DNA, enabling the protein to work as a transcription factor
- The proteins bind to DNA at the start of developmental genes, activating or repressing transcription, so altering the production of proteins involved in the development of body plans
what types of symmetry can be seen in organisms
Radial symmetry – in diploblastic animals like jellyfish – they have no right/left sides, only a top and bottom
Bilateral symmetry – seen in most animals, have left/right symmetry and a head/tail rather than top/bottom
Asymmetry – seen in sponges – no lines of symmetry
define apoptosis
programmed cell death
what type of genes regulate mitosis and apoptosis
hox genes
how does apoptosis shape us when we’re developing
Removing unwanted cells and tissues can cause different body parts to be shaped
Cells undergoing apoptosis can release chemical signals which stimulate mitosis and cell proliferation, causing the remodelling of tissues.
what is the step-by-step process of apoptosis
1) Cell shrinks, enzymes break down cytoskeleton
2) Cell membrane changes, blebs form
3) Chromatin condenses, nuclear envelope breaks and the DNA breaks into fragments
4) The cell breaks up into vesicles
5) Phagocytes engulf the vesicles
6) The cellular debris is either disposed of or reused.
what internal factors can affect regulatory genes
Psychological stress
Release of hormones, growth factors
Cytokines
what external factors can affect regulatory genes
temperature change
light intensity
give an example of a drug which affects regulatory genes and prevented mitosis and apoptosis from working
thalidomide
prevented the expression of a particular Hox gene
resulted in shortened limbs in babies
