Genetics of living systems Flashcards
1
Q
mutation
A
a random change is the sequence of bases in DNA
2
Q
ionising radiation - physical mutagen increasing the probability of a gene mutation
A
can break DNA strands and mutation occurs during the repair process
eg. X-rays
3
Q
deaminating chemicals - chemical mutagen increasing the probability of a gene mutation
A
converts one base to another
4
Q
alkylating agents - biological agent increasing the probability of a gene mutation
A
add methyl or ethyl groups to a base resulting in incorrect base pairing
5
Q
base analogs - biological agent increasing the probability of a gene mutation
A
derivatives of original bases which are incorporated into DNA instead of them
6
Q
viruses - biological agent increasing the probability of a gene mutation
A
viral DNA inserted into a host genome and is replicated instead of DNA
7
Q
effects of mutations
A
- 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
8
Q
types of mutations
A
insertion or deletion - changes no. of bases in a sequence which causes a frameshift, multiple triplet codes will be affected, changing the amino acids it codes for
- substitution - same no. of bases, no frameshift, may still code for the same amino acid
9
Q
missense mutation
A
changes the amino acids that are incorporated into the polypeptide - changes primary structure
10
Q
nonsense mutation
A
introduces a stop codon into the genetic code so protein does not finished being synthesised - shorter protein
11
Q
example of beneficial mutation
A
- ability to digest lactose
- found more in european populations who are more likely to farm cattle
- prevented people starving during famines
12
Q
types of chromosome mutations
A
- 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
13
Q
heterochromatin
A
- EUKARYOTES
- DNA very tightly wrapped around histones
- DNA not accessible for transcription so this section of DNA is not needed for the protein
14
Q
euchromatin
A
- EUKARYOTES
- DNA loosely wrapped around histones
- DNA accessible to enzymes for transcription so this section of DNA is needed for the protein
15
Q
why does DNA coil around histones?
A
histones are positively charged, DNA is negatively charged
16
Q
acetylation
A
- EUKARYOTES
- acetyl group added, reduces positive charge on the histones causing DNA to wrap loosely around histones so the gene can be transcribed
- causes gene expression
17
Q
methylation
A
- EUKARYOTES
- methyl group added, maintains positive charge on histones, makes the histones more hydrophobic causing DNA to wrap tightly around histones
- prevents transcription
18
Q
what is epigenetics?
A
- 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
19
Q
structural genes on lac operon
A
- PROKARYOTES
- codes for enzymes
- Z - gene that codes for Beta-galactosidase
- Y - gene that codes for lactose permease
20
Q
regulatory gene
A
- PROKARYOTES
- codes for a repressor protein that prevents transcription of structural genes (Z and Y) - switches them on/off
21
Q
when is the lac operon switched on and why?
A
- PROKARYOTES
- glucose is the preferred respiratory substrate but when glucose is in short supply and lactose is present, lactose can be used as a respiratory substrate
- saves resources bc if certain gene products aren’t needed, all genes involved in their production can be switched off
22
Q
enzymes coded for by the lac operon and their role
A
- PROKARYOTES
- lactose permease - makes membrane more permeable to lactose - transported into cell (transmembrane symport protein)
- beta galactosidase - hydrolyses lactose into glucose and galactose
23
Q
operator region
A
- PROKARYOTES
- the region that RNA polymerase binds to in order to transcribe structural genes
- switches Z and Y genes on/off
24
Q
promoter region
A
- PROKARYOTES
- binding site of RNA polymerase for transcription of Z and Y
- can be blocked or not
25
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
26
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
27
role of cAMP in the lac operon
- PROKARYOTES
1. cAMP levels rise 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 for lactose metabolism
28
transcription factors
- EUKARYOTES
- proteins that bind to the promotor sequence to allow RNA polymerase to bind control transcription of the target gene
29
2 types of post-transcriptional modification - splicing and RNA editing
- EUKARYOTES
RNA processing
- 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, introns are removed
- ensures only the coding sections of DNA are used to form proteins
RNA editing
- nucleotide sequence of mRNA sequence changed through addition, deletion, substitution
- can result in synthesis of different proteins
30
intron
non-coding sequences that won't be translated
31
exon
coding sequences of DNA that will be translated into polypeptides
32
translational control
- degradation of mRNA - eliminating mRNA that is no longer required in the cell
- binding of inhibitory proteins to mRNA prevents it binding to ribosomes and its synthesis
- activation of initiation factors aiding the binding of mRNA to ribosomes
- protein kinase - catalyse addition of phosphate groups to proteins to change the tertiary structure and function
33
post-translational control
- 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
34
morphogenesis
- development of an organism from eg. an egg or seed
- regulation of the pattern of development
- it's controlled by homeoboxes
35
homeobox gene
- contains a homeobox
- around 180 base pairs long (codes for 60 amino acids - the homeodomain) - highly conserved
- homeodomain - binds to DNA and switches other genes on and off
36
how are homeobox genes highly conserved?
- they are found in all organisms and are all similar
- they have not evolved much
- this is because many mutations to homoebox genes resulted in disrupted development making them less likely to survive
37
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
38
what is a hox gene and what does it control?
- a subset of homeobox genes in animals containing homeobox sequences essential for the correct positioning of body parts
- controls no. of body layers, symmetry of body, arrangement of body parts, segmentation of body into head, thorax, abdomen etc
39
how do hox genes control body plan?
1. homeobox sequences encode the homeodomain
2. homeodomain acts as transcription factor and binds to DNA
3. this switches developmental genes on or off
4. this modifies the transcription of proteins necessary for the development of body plans
40
homeodomain
- coded for by homeobox sequence
- a part of a hox protein that binds to DNA
- operates as a transcription factor
41
effects of mutations of hox genes
- body plan is disrupted
- eg. leg growing where an antennae should be
42
types of symmetry in body plans of animals
- radial symmetry - around a central axis eg. starfish
- bilateral symmetry - left and right sides are symmetrical
- asymmetry - no lines of symmetry eg. sponges
43
apoptosis steps
- programmed cell death
- cells undergoing this can also release chemicals to stimulate mitosis
1. an internal/external stimulus triggers apoptosis and 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
44
apoptosis examples
- tadpole tail falls off when it changes into a frog
- shedding of lining of uterus
- removal of skin between finger or toes
45
metamorphosis
a major change in structure of an organism as it changes from one stage of its life cycle to the next
46
proto-oncogenes
stimulate cell division
- too much of this results sin tumor
47
tumor-supressor genes
reduce cell division
- can stimulate apoptosis in cells with damaged DNA that cannot be repaired
48
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
