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 things called that increase the chance of a mutation happening (non-genetic)
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,
resulting in all amino acids being coded for downstream to change
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 2 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, as the genetic code is degenerate
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.
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
Majority of DNA is non-coding regions
So a mutation is most likely to occur in non-coding regions of DNA
This will have no effect on the proteins coded for and the organism’s phenotype as introns are removed from mRNA when it is spliced
define operon
a section of DNA that contains a cluster of genes that are transcribed together as well as control elements and a regulatory gene.
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 - lac- regulatory gene that 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- lac A codes for acetyl transferase
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
What are the 3 stages gene expression can be controlled
- transcriptional - genes can be turned on/off
- post-transcription - mRNA can be modified which regulates translation and the types of protein produced
- post-translation - proteins can be modified after synthesis which changes their function- role of cAMP
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 and reordered to make mature mRNA
The different order of mature mRNA changes the sequence of amino acids it codes for resulting in a different protein being produced.
A cap is added to the 5’ end of the mRNA strand and a tail is added to the 3’ end of the mRNA strand.
This prevents degradation of the mRNa stand in the cytoplasm so it stays in the cytoplasm for longer
This means more of it can be translated resulting the production of more protein
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)
what was first found in fruit flies
Why are fruit flies used in scientific research rather than another organism
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 sequence
define homeobox genes
The homeobox sequence :
Is a 180 bp long sequence which codes for 60 amino acid long homeodomain and is involved in regulating the development and body plan of plant animals and fungi.
The homeobox sequence is highly conserved within the plants animal and fungi kingdoms
Homeobox genes:
Group of regulatory genes that contain a homeobox sequence which codes for a homeodomain which acts as a transcription factor by controlling gene expression of an organism’s body plan.
homeodomain proteins
proteins that acts as transcription factors by binding to DNA and activating or repressing genes that regulate the cell cycle, mitosis and apoptosis.
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) Enzymes break down the cytoskeleton causing the cell to shrink
2) Cell begins to bleb and nucleus disintegrates
3) Small fragments are produced with the cell membrane intact and containing organelles
4) Phagocytes engulf the fragments by phagocytosis
5) Hydrolytic enzymes break down cell fragments
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
Define Hox genes
Hox genes are a subset of homeobox genes found only in animals. They are involved in the formation of anatomical features in correct location of an animal’s body plan. They code for homeodomain proteins.
What internal factors affect rate of appoptosis
Release of Hormones
Mutations
What external factors affect the rate of apoptosis
Physiological Stress- People lose hair and weight
Drugs
Lack of nutrients/food
Infection
Light- In plants, leaf fall occurs during winter due to lower light intensities
Give examples of mutagens
Carcinogens
X-rays
UV Light
