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 cause mutations
DNA replication due to change of sequence of bases. Rate of mutation is increased by mutagens (chemical, physical or biological agent such as viruses which insert its dna into a genome changing the base sequence)
Free radicals also can disrupt base pairing during DNA replication
what are the 3 types of gene mutations
substitution - only one nucleotide is affected
insertion - inserting a base which shifts nucleotides to the right
deletion - base or triplet removed
3 effects of the 3 mutation
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
(Eg ability to digest lactose, development of antibiotics resistance in bacteria)
Harmful - mutation produces a disadvantage, so decrease chance of survival
- organism may not survive or mate
(Eg albinism, sickle cell anemia (shape of rbc))
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
Promoter
Operator
Structural genes
a section of DNA that contains a cluster of structural genes that are transcribed together
Where rna polymerase binds
Repressor protein binds here
Cluster of genes regulated by the same mechanism
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 (REGULATORY GENES)
P - promoter - RNA polymerase binds here to start transcription of structural genes
O - operator- 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)
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
1) splicing
- 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
2) capping
- methyl group added to 5- end of transcribed RNA which provides protection against degradation and helps bind to ribosome
3) polyadenylation
- addition of long chain of adenine nucleotides to end of 3- transcript increasing stability of RNA transcript
4) RNA editing
- base addition, deletion or substitution resulting in synthesis of different proteins W differnt functions, increasing range of proteins produced from a single mRNA gene which are catalaysed by enzymes.
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
Involves modifications to proteins that have been synthesised including:
- addition of non protein groups such as carbs
- modifying amino acids and formation of bonds such as disulphide bridges
- folding or shortening of proteins
- modification by cAMP Eg in lac operon cAMP binds to CAP increasing rate of transcription of structural genes.
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
Group of genes all contains a honeobox (highly conserved sequence of dna)
Homeobox genes:
Group of genes that contain a homeobox, regulatory genes w 180 base pairs coding for 60 a.a (homeodomain prptein)
direct the formation of many body structures during early embryonic developmen
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 hox genes
One group of homeobox genes only present in animals responsible for correct positioning of body parts, In animals these genes are found in gene 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) proteins and nucleus are catabolised
3) mitochondria catabolised
4) blebs develop on cell surface
5) Phagocytes engulf the blebs
6) phagocytes release signals to inhibit inflammation
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
Allele
Genotype
Phenotype
The version of the gene
The alleles an organism has inherited (Eg Bb)
Characteristics displayed by an organism as a result of its genotype
Dominant
Recessive
Homozygous
Version of gene that’ll always be expressed if present
Version of gene that will only be expressed if two copies present
Two identical alleles for a characteristic
Heterozygous
Locus
Homologous
Two different alleles for a characteristic
Position of a gene
Matching pair of chromosomes, one inherited from each parent
Gene regulation
- Genes that code for enzymes that are necessary for reactions present in metabolic pathways are called housekeeping genes
- whole genome present in nuclear cells including genes not required by the cell so expression of genes need regulated by being turned on and off and rate of product synthesis increased or decreased depending on demand.
- expressing genes only when products needed also prevents vital resources being wasted.
Transcriptional control - chromatin remodelling
-heterochromatin is tight,y wound dna causing dna to be visible during cell division whereas euchromatin is loosely wound dna present during interphase.
Transcription of genes not possible when tightly bound bc rna polymerase can’t get to the gene. However genes in euchromatin can b freely transcribed. Thus protein synthesis only occurs in interphase not cell division (type of transcriptional control)
Transcriptional control - histone modification
1) dna coils around histones bc they’re positively charged and dna is negatively charged. Thus his tones can b modified to increase/ decrease condensation of dna.
- acetylation/ phosphorylation reduces the positive charge on histones causing less tight coiling of DNA which allows certain genes to b transcribed
- methylation makes histones more hydrophobic so bind more tightly to each other = dna coil more preventing transcription of genes
What occurs when repressor binds to operator
What occurs when activator binds to regulatory gene sequence
Prevents transcription as blocks rna polymerase transcribing gene. Corepressors are molecules that can bind to change proteins shape enabling more binding or less binding
Increases transcription. Inducers can be added to the protein activator to turn the activator on and binds to the promoter and vice versa to turn activator off.
Lac repressor protein and down regulation in presence of glucose
1) acts as lactose sensor and utilised when lactose not present
- regulatory gene (LacI) codes for a repressor protein. When lactose absent the lac repressor binds to operator and blocks rna polymerase inhibiting transcription of lac operon
2) lac repressor protein always present but only binds to operator in absense of lactose
- if lactose present, lactose (allolactose) binds to repressor protein and looses the shape and ability to bind to operator. Repressor floats off and rna polymerase can transcribe operon
Lac operon low glucose and high glucose
Low glucose - when glucose low, cAMP is produced which attaches to CAP allowing it to bind to the CAP site. Thus helping rna polymerase bind to the promoter.
High glucose - when glucose levels are high, no cAMP is made. CAP can’t bind to CAP site without cAMP so transcription occurs at low level.
Translational control
- degradation of mRNA
- binding of inhibitory proteins to mRNA which prevents binding to ribosome and no translation
- activation of initiation factors which aid binding of mRNA to ribosomes
Protein kinases
-enzymes that catalyse the addition of a phosphate groups to proteins which changes the tertiary structure and the function of the protein. Many enzymes are activated by phosphorylation.
Continuous variation
Discontinuous variation
1)Polygenic (controlled by number of genes)
Characteristic that can have any value within a range (quantitative) Eg height
2)controlled by one or two genes
Characteristic only appears as a qualitative value Eg blood group
Layout of living organisms
Animals common feature is that they’re segmented. These segments have multiplied over time and are specialised to perform a fifer to function. Eg hox genes in head control mouthparts development
The individual vertebrae and associated structures have all developed from somites(segments in embryo) which r directed by hox genes to develop in a particular way depending on their .position in sequence
