1
Q
what is a mutation
A
change in the sequence of bases in DNA
2
Q
what are the 3 reasons why mutation might occur
A
substitution [one or more bases swapped for another]
deletion [one or more bases removed]
insertion [one or more bases added]
3
Q
what is point mutation
A
when only one nucleotide is affected by mutation
4
Q
what happens when mutations change the order of DNA bases in a gene
A
- the order of DNA bases determine the order of amino acids in a particular protein
- if a mutation occurs, the primary structure (amino acid chain) of the protein it codes for could be altered
- this could change the final 3D shape of the protein, so no longer works properly
- e.g. active site not forming properly, so the substrate cannot bind to them
5
Q
what do insertion and deletion mutations result in
A
a frameshift mutation
6
Q
explain a frameshift mutation
A
- as genetic code is read/transcribed in non-overlapping triplets
- when you add or remove a nucleotide
- this will move the reading frame of sequence bases
- so every successive codon will be changed from the point of mutation
- still takes place if multiple are added, unless a multiple of 3 is changed
- will not change the reading frame, but the protein formed will still be changed (lost or gained new amino acid)
7
Q
what is the effects of mutations
A
no effect
damaging
beneficial
8
Q
what happens if there is a no effect mutation
A
- no effect on phenotype
- as normally functioning amino acids are still synthesised
- as the genetic code is degenerate, so some amino acids are coded for by more than one triplet
- or because the triplet does code for a different amino acid, but it is chemically similar to the other, so functions like the original
- or because the mutated triplet codes for an amino acid not involved in the proteins function, e.g. in enzyme, far away from active site, so works normally
9
Q
what happens if there is a damaging mutation
A
- have a disadvantageous effect on the organisms, so decrease its chance of survival
- when proteins are no longer synthesised or are non-functional
- can interfere with essential processes
- e.g. in CF, is caused by deletion of 3 bases in gene coding for CFTR protein, causing the protein to fold incorrectly, so is broken down, leading to excess mucus production, affecting the lungs of sufferers
10
Q
what happens in a damaging mutation, where whether the protein is produced or not is affected
A
- if a mutation occurs at the start of a gene
- means RNA polymerase cannot bind to it
- transcription doesn’t begin
- protein coded for is not made
- so loss of production of a protein
- harmful, e.g. causing genetic disorders
11
Q
what happens if there is a beneficial mutation
A
- protein synthesised with have a new and useful characteristic in phenotype, having an advantageous effect on organism, so increasing the chance of survival
- e.g. certain bacterial enzymes break down certain antibiotics
- mutations can occur, leading to genes coding for these enzymes to work on a wider range of antibiotics
- beneficial, as leads to antibiotic resistance, help to survive
12
Q
when do mutations occur
A
spontaneously, often during DNA replication
13
Q
why do genes need to be switched on and off
A
- all the cells in an organism carry the same genes and DNA (entire genome present in every cell)
- but each cell has a different structure and function
- this is because not all genes in a cell are expressed
- but rather selectively switched on and off
14
Q
what does genes being switched on and off mean for a cell
A
- cells show different gene expression
- so different proteins are made
- and these proteins modify the cell
- determining the cell structure
- and controlling cell processes (including the expression of more genes, which produce more proteins)
15
Q
what is it meant by a gene being expressed
A
being transcribed and used to make a functional protein
16
Q
what is the basic difference between gene regulation in prokaryotes and eukaryotes
A
- prokaryotes only have to respond to changes in the external environment
- multicellular organisms also have to respond to internal conditions, and is important for cells to specialise
17
Q
what are the different stages of cell regulation
A
transcriptional (the role of transcription factors and lac operon)
post-transcriptional (the editing of primary mRNA and removal of introns to produce mature mRNA)
post-translational (the activation of proteins by cyclic AMP)
18
Q
how is gene expression controlled at the transcriptional level
A
- via altering the rate of transcription of genes
- e.g. increased transcription produces more mRNA, which can be used to make more protein
- controlled via transcription factors
19
Q
what are transcription factors
A
proteins that bind to DNA and switch genes on and off by increasing or decreasing the rate of transcription
- increase = activators
- decrease = repressors
20
Q
how do transcription factors control the rate of certain protein synthesis
A
- the shape of a transcription factor determines whether it can bind to DNA or not
- the shape can sometimes be altered by the binding of some molecules, e.g. certain hormones or sugars
- so the amount of a certain molecule in an environment or in a cell can control the synthesis of some proteins
- by affecting transcription factor binding
21
Q
how do transcription factors appear in eukaryotes
A
- they bind to specific DNA sites near the start of their target genes (the genes they control the expression of)
22
Q
how do transcription factors appear in prokaryotes
A
- they bind to operons
23
Q
what is an operon
A
a group of genes that are under the control of the same regulatory mechanism and are expressed at the same time
- section of DNA containing a cluster of structural genes, that are transcribed together, as well as control elements and sometimes a regulatory gene
- EXPRESSED TOGETHER!!
24
Q
what is a structural gene
A
a gene that codes for a useful protein
25
what are the control elements in an operon
- a promoter (a DNA sequence located before the structural gene that RNA polymerase bind to)
- an operator (a DNA sequence that transcription factors bind to)
26
what is a regulatory gene
- a gene that codes for an activator or repressor, so proteins that control the expression of, and switch genes, on and off
27
why are operons efficient
if a certain gene product is not needed, then all of the genes involved can be switched off
28
what is the preferred respiratory substrate of many bacteria, e.g. e.coli, and if not available, what is used
- glucose, as easy to metabolise
- if not, lactose will be used
- the genes that produce enzymes to respire lactose are found at the lac operon
29
what does the lac operon consist of
- a promoter region (where RNA polymerase binds)
- an operator region (where the repressor protein binds)
- structural genes lac YZA
- regulatory gene Lac I a short distance away
30
what can be used to describe lac Y/Z/A
structural genes, as they code for 3 enzymes that help bacteria digest lactose
- B-galactosidase, lactose permease and transacetylase
- transcribed onto a single long molecule of mRNA
31
what is the regulatory gene present in the lac operon
LacI
- located near the operon and codes for the repressor protein - the transcription factor
- that prevents the transcription of the structural genes in the absence of lactose
32
what happens in the absence of lactose
- repressor protein binds to the operator region
- prevents RNA polymerase from binding to the promoter
- blocks transcription, meaning genes XYZ cannot be expressed, resources not wasted
33
what happens in the presence of lactose
- lactose binds to repressor protein
- changes its shape, so can no longer bind to operator region
- means that RNA polymerase can bind to the promoter region
- and begin transcription
34
what are examples of post-transcriptional control of gene regulation
- mRNA is edited
- in EUKARYOTIC DNA:
- introns: sections of DNA that don't code for amino acids
- exons: sections of DNA that do code for amino acids
- during transcription, both copied into mRNA, containing exons and introns
- called primary mRNA transcripts (pre-mRNA)
- introns are REMOVED from pre-mRNA
- process called SPLICING
- and the exons are joined
- forms mature mRNA strands
- takes place IN THE NUCLEUS
- the mature mRNA then leaves the nucleus for next stage of protein synthesis: translation
35
how is gene regulation regulated at post-translational level
via cAMP activating certain proteins, e.g. kinase A
36
why does protein activation take place post-translation, and what is this controlled by
- some proteins are not functional straight after they have been synthesised
- they need to be activated to work and become a functional protein
- controlled by molecules, e.g. hormones and sugars
37
how does cAMP take part in protein activation
- certain molecules, e.g. hormones and sugars
- bind to cell membranes and trigger the production of cyclic AMP inside the cell
- cAMP then activates proteins inside the cell
- by altering their 3D structure
- e.g. altering the 3D structure to change the active site of an enzyme, so it becomes more or less active
- acts as a SECONDARY MESSENGER (relays information from control molecule, hormone, to the inside of the cell)
38
how does cAMP activate protein kinase A (PKA)
- PKA is an enzyme made of 4 subunits
- when cAMP is not bound, the 4 units are bound together and inactive
- when cAMP binds, it changes the enzymes 3D structure
- releases the active subunits
- so that PKA is now active
39
what are body plans
the general structure of an organism
40
what are the development of body plans controlled by
proteins, that help set up the basic body plan so everything is in the right place
41
what are homeobox genes
a group of genes containing a homeobox
42
what is the homeobox (sequences)
section of DNA 180 base pairs long coding for a part of the protein 60 amino acids long
- is highly conserved in plants, animals and fungi (meaning body plan development is controlled in a similar way, and conserved so sequences have changed very little during the evolution of different organisms that possess these homeobox sequences)
43
what is the homeodomain
part of the protein coded by the homeobox (sequences)
- binds to specific sites on the DNA, enabling proteins to work as a transcription factor
- bind to DNA at the start of the developmental genes, activating or repressing transcription, so altering the production of proteins involved in the development of the body plant
44
what type of genes are homeobox genes
regulatory genes - switch genes on and off
45
what are hox genes
one group of homeobox genes only present in animals
- responsible for the correct positioning of body parts
- found in clusters (4 clusters on different chromosomes in mammals)
46
how do hox genes express
- the order in which genes appear along the chromosome is the order in which the effects are expressed in the organism
47
what is a common feature of body plans
- they are segmented, with segments multiplied over time and specialised to perform different functions
48
what is apoptosis
programmed cell death
49
what are the steps once apoptosis is triggered
1) enzymes inside the cell break down important cell components, such as proteins in the cytoplasm and DNA in the nucleus
2) as the cell's contents are broken down, cell begins to shrink and breaks up into fragments
3) the cell fragments are engulfed by phagocytes and digested
50
what is mitosis
part of the cell cycle where one cell divided to form 2 daughter cells
51
how does apoptosis and mitosis work together to control the development of body plans
- mitosis and differentiation create the bulk of body parts
- apoptosis refines the parts by removing unwanted substances
- (e.g. tadpoles get their tale cells removed and human digits (fingers and toes) are originally connected when first developing, but the connecting tissue undergoes apoptosis)
- AS:
- during development, genes that control apoptosis and those that control mitosis are switched on and off in appropriate cells (hox genes)
- so some cells die, some new cells are produced
- so CORRECT BODY PLAN DEVELOPS
52
what can genes regulating apoptosis and the cell cycle respond to
stimuli
53
what are external factors impacting gene expression, and therefore apoptosis and the progression through the cell cycle, and how do they impact it
- stress caused by a lack of nutrient availability
- could result in gene expression that prevents cells from undergoing mitosis
- attack by a pathogen
- triggers gene expression leading to apoptosis
54
what are internal factors impacting gene expression, and therefore apoptosis and the progression through the cell cycle, and how do they impact it
- DNA damage
- if detected during the cell cycle
- means genes are expressed which cause the cell cycle to be paused
- could also trigger apoptosis
55
when do factors impacting gene regulation have the most impact
during growth and development of an organisms
