Genetics of living systems Flashcards
mutation
a random change is the sequence of DNA bases within a gene or in the structure of a chromosome
ionising radiation - factor increasing the probability of a gene mutation
can break DNA strands and mutation occurs during the repair process
- deaminating chemicals - converts one base to another
- alkylating agents - add methyl or ethyl groups to a base resulting in incorrect pairings
- base analogs
deaminating chemicals - factor increasing the probability of a gene mutation
converts one base to another
alkylating agents - factor increasing the probability of a gene mutation
add methyl or ethyl groups to a base resulting in incorrect base pairing
base analogs - factor increasing the probability of a gene mutation
derivatives of original bases which are incorporated into DNA instead of them
viruses - factor increasing the probability of a gene mutation
viral DNA inserted into a host genome and is replicated instead of DNA
effects of mutations
- no effect - due to degenerate nature of genetic code - doesn’t offer selection advantage or disadvantage
- damaging - phenotype affected as non-functional proteins synthesized or proteins not synthesised at all
- beneficial - proteins synthesised that offer an adaptive trait
types of mutations
insertion or deletion - causes a frameshift as DNA is read in a non-overlapping way
- substitution - no frameshift, may still code for the same amino acid
missense mutation
changes the amino acids that are incorporated into the polypeptide
nonsense mutation
introduces a stop codon into the genetic code so protein does not finished being synthesised
types of chromosome mutations
- deletion - sections of chromosome break off and are lost
- duplication - sections are repeated
- translocation - a section of a chromosome breaks off and joins another non-homologous chromosome
- inversion - a section of a chromosome breaks off, reversed then reattaches
- whole chromosome - entire chromosome is lost or replicated eg. Down’s syndrome due to extra chromosome 21
heterochromatin
- EUKARYOTES
- DNA very tightly wrapped around histones
- DNA not accessible for transcription so this section of DNA is not needed for the protein
euchromatin
- EUKARYOTES
- DNA loosely wrapped around histones
- DNA accessible to enzymes for transcription so this section of DNA is needed for the protein
acetylation
- EUKARYOTES
- acetyl group added, neutralises the charge on the histone tails causing DNA to wrap loosely around histones so the gene can be transcribed
- causes gene expression
methylation
- EUKARYOTES
- methyl group added, maintains positive charge on histone tails causing DNA to wrap tightly around histones
- causes gene silencing
what is epigenetics?
- our environment can change gene expression without the DNA code itself being changed
- acetyl or methyl groups can be altered by enzymes
- this is reversible
- changes can be inherited or acquired throughout life
structural gene
- PROKARYOTES
- codes for enzymes
- Z - gene that codes for Beta-galactosidase
- Y - gene that codes for lactose permease
regulatory gene
- PROKARYOTES
- codes for a repressor protein that prevents transcription of structural genes (Z and Y) - switches them on/off
when is the lac operon switched on?
- PROKARYOTES
- when glucose is in short supply but lactose is present, lactose can be used as a respiratory substrate
enzymes coded for by the lac operon
- PROKARYOTES
- lactose permease - makes membrane more permeable to lactose - transported into cell (transmembrane symport protein)
- galactosidase - hydrolyses lactose into glucose and galactose
operator region
- PROKARYOTES
- switches Z and Y genes on/off
promoter region
- PROKARYOTES
- binding site of RNA polymerase for transcription of Z and Y
- can be blocked or not
lac operon if glucose is present and lactose is absent
- PROKARYOTES
1. regulatory gene is expressed and synthesis of repressor protein occurs
2. repressor protein binds to operator region
3. repressor protein partially covers promoter region
4. RNA polymerase can’t bind - Z and Y genes can’t be transcribed - no enzymes produced
lac operon is glucose is absent and lactose is present
- PROKARYOTES
1. inducer molecule (lactose) binds to repressor protein after it’s translated
2. repressor protein dissociates from operator region
3. promoter region is exposed and RNA polymerase can bind to promoter region
4. Z and Y genes can be transcribed - mRNA produced and galactosidase and lactose permease are synthesised
role of cAMP in the lac operon
- PROKARYOTES
1. it is produced by the bacterial cell when glucose levels are low
2. cAMP binds to CAP, causing a conformational change of shape, activating CAP
3. CAP can now bind to a region of DNA just before the promoter region
4. RNA polymerase can now bind to the DNA, increasing transcription levels - as glucose levels increase, production of cAMP decreases, reducing transcription of enzymes responsible to lactose metabolism
transcription factors
- EUKARYOTES
- proteins that bind to the promotor sequence to allow RNA polymerase to bind control transcription of the target gene
post-transcriptional modification - splicing
- EUKARYOTES
- both the introns and exons are transcribed to produce pre-mRNA (primary mRNA)
- splicing - exons are fused together to form mature mRNA ready to be translated
- ensures only the coding sections of DNA are used to form proteins
intron
non-coding sequences that won’t be translated
exon
coding sequences of DNA that will be translated into polypeptides
RNA editing
- changing the sequence of nucleotides through base insertion, deletion or substitution
- results in different proteins being synthesised
- increases range of proteins produced from one mRNA molecule
post-translational modifications
- addition of non-protein groups - carbohydrates, lipids, phosphates etc.
- modifying amino acids and formation of bonds
- folding/shortening of proteins
- modification of cAMP for second messenger systems
morphogenesis
- development of an organism from eg. an egg or seed
- it’s controlled by homeoboxes
homeobox
- a DNA sequence that is part of a regulatory gene involved the regulation of development of animals
- around 180 base pairs long
- codes for homeodomain - transcription factor causing DNA to be transcribed
how are homeobox genes highly conserved?
- they are found in all organisms and are all similar
- they have not evolved much and were found before the origin of animals
- this is because many mutations to homoebox genes resulted in disrupted development making them less likely to survive
transcription factor
- bind to nearby DNA to switch genes on or off
- activators - increase a gene’s transcription
- repressors/inhibitors - decrease a gene’s transcription
- eg. could switch on genes that code for a leg
hox gene
- a group of homeobox genes unique to animals
- they control the body plan - which body parts grow where on the body
- almost identical in all animals - highly conserved
- most are linked together in a cluster in a chromosome
- they are in order of their placement on the organism
effects of mutations of hox genes
- body plan is disrupted
- eg. leg growing where an antennae should be
apoptosis steps
- programmed cell death
1. cytoskeleton, DNA, mitochondria and proteins broken down by enzymes
2. membrane blebs start forming
4. nucleus condenses and fragments form
3. cell breaks up into small fragments wrapped in membrane called apoptotic bodies
4. phagocytes engulf apoptotic bodies
apoptosis examples
- tadpole tail falls off when it changes into a frog
- shedding of lining of uterus
- removal of skin between finger or toes
metamorphosis
a major change in structure of an organism as it changes from one stage of its life cycle to the next
proto-oncogenes
stimulate cell division
- too much of this results sin tumor
tumor-supressor genes
reduce cell division
- can stimulate apoptosis in cells with damaged DNA that cannot be repaired
factors affecting the expression of regulatory genes for the cell cycle and apoptosis
- stress - homeostatic balance is disrupted
- external factors eg. temperature, light
- internal factors eg. hormones
- drugs eg. thalidomide (resulted in shorter limbs of babies in pregnant women)
- inside the cell biochemical stress eg. damaged DNA
