6.1.1 Cellular Control Flashcards
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
deletion
insertion
- of one or more nucleotides or base pairs within a gene
3
Q
what is point mutation
A
when only one nucleotide is affected by mutation
4
Q
what happens in a substitution mutation
A
- changes the codon in which the nucleotide has been substituted in
- if new codon codes for a different amino acid, this will change the primary structure of the protein
- but genetic code is degenerate, so might still code for the same amino acid
- so no change to protein synthesised
5
Q
when will a substitution mutation be important, and what is this based on
A
- depends on the position and involvement of the amino acid in R-group interactions within the protein
- if for an enzyme, amino acid might play important role in the active site, so may not function any longer
6
Q
what do insertion and deletion mutations result in
A
a frameshift mutation
7
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)
8
Q
what is the effects of mutations
A
no effect
damaging
beneficial
9
Q
what happens if there is a no effect mutation
A
- no effect on phenotype
- as normally functioning amino acids are still synthesised
10
Q
what happens if there is a damaging mutation
A
- when proteins are no longer synthesised or are non-functional
- can interfere with essential processes
11
Q
what happens if there is a beneficial mutation
A
- protein synthesised with have a new and useful characteristic in phenotype
12
Q
when do mutations occur
A
spontaneously, often during DNA replication
13
Q
what are the rate of mutations increased by
A
mutagens
14
Q
what are mutagens
A
chemical, physical or biological agent which causes a mutation
15
Q
what are some examples of mutagens
A
- ionizing radiation such as x-rays
- deaminating agents
- alkylating agents
- base analogs
- viruses
16
Q
what are chromosome mutations
A
- affect the whole chromosome or number of chromosomes within a cell
- can be silent or affecting
17
Q
what are the types of chromosome mutations
A
- deletion, where a section of chromosome breaks off and is lost within a cell
- duplication, where sections of the chromosome get repeated
- translocation, where a section of one chromosome breaks off and joins another non-homologous chromosome
- inversion, where a section of chromosome breaks off, is reversed, and joins back
18
Q
why is gene regulation important
A
- the entire genome of an organisms is present in every prokaryotic/eukaryotic cell with nucleus
- need to regulate which genes are actually needed, so can turn on or off genes and control the rate of product synthesis on demand
19
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
20
Q
what are the different stages of cell regulation
A
transcriptional (genes turned on and off)
post-transcriptional (mRNA can be modified which regulates translation)
translational (can stop or start translation)
post-translational ( proteins being modified after translation to change their functions)
21
Q
explain the relationship between DNA, histones and chromatin
A
- DNA is a very long molecule
- wound around proteins called histones in eukaryotic cells
- resulting DNA/protein complex is called chromatin
22
Q
how is chromatin remodelling an example of transcriptional regulation
A
- heterochromatin is tightly wound DNA which causes chromosomes to be visible during cell division
- euchromatin is loosely wound DNA present during interphase
- transcription of genes is not possible when DNA is tightly wound as RNA polymerase cannot access the genes
- DNA which is loosely wound can be easily transcribed
- explains why protein synthesis does not occur during cell division but interphase
23
Q
what is epigenetics
A
control of gene expression by the modification of DNA
24
Q
how does histone modification act as a transcriptional regulation factor
A
- histones can be changed to increase or decrease the degree of packing
- DNA packs around histones because they are positively charged and it is negative
- can add acetyl groups (acetylation) or phosphate groups (phosphorylation) to reduce positive charge, so DNA coils less likely and certain genes can be transcribed
- can add methyl (methylation) groups which makes histones more hydrophobic, bind to each other more tightly and DNA coils more tightly, preventing transcription of certain genes
25
what is an operon
a group of genes that are under the control of the same regulatory mechanism and are expressed at the same time
- more common in prokaryotes than eukaryotes as they are smaller and simpler genomed
26
why are operons efficient
if a certain gene product is not needed, then all of the genes involved can be switched off
27
what is the preferred respiratory substrate of many bacteria, and if not available, what is used
- glucose, as easy to metabolise
- if not, lactose will be used
28
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
29
what can be used to describe lac Y/Z/A
structural genes, as they code for 3 enzymes
- B-galactosidase, lactose permease and transacetylase
- transcribed onto a single long molecule of mRNA
30
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
31
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
32
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
33
what are examples of post-transcriptional control of gene regulation
- pre-mRNA is modified forming mature mRNA before it can bind to ribosome
- a cap (modified nucleotide) is added to 5' end and tail (long chain of adenine nucleotide) is added to the 3' end - help to stabilise mRNA and help with ribosome binding
- SPLICING: RNA is cut at specific point, with introns (non-coding DNA) is removed and exons are joined
- both WITHIN THE NUCLEUS
- RNA editing also occurs like point mutations , resulting in synthesis of different proteins with different functions
- increases the range of proteins that can be produced from a single mRNA molecule
34
what is the role of cyclic AMP (cAMP)
- binding of RNA polymerase still results in a slow transcription rate
- not enough to properly metabolise lactose at rate needed
- can be sped up by binding of a cAMP repressor protein CRP, which only works when bound to cAMP
- ( a secondary messenger)
- more glucose = less cAMP = less lactose metabolism
35
what are examples of translational control
- degradation of mRNA= more resistant the molecule, longer it will last in cytoplasm, greater quantity of protein synthesised
- binding of inhibitory proteins to mRNA prevents it binding to ribosomes and synthesis of proteins
- activation of initiation factors which aid in binding of mRNA to ribosomes
36
explain protein kinases as translational control
- protein kinases are enzymes that catalyse the addition of phosphate groups to proteins
- changes the tertiary structure
- so the function
- and many enzymes are activated by phosphorylation, so an important regulator or cell activity
37
what examples of post-translational control
- addition of non-protein groups (carb, lipid, phosphate)
- modifying amino acids and formation of bonds, e.g. disulfide bridges
- folding/shortening of proteins
- modification by cAMP
38
what are homeobox genes
a group of genes containing a homeobox
39
what is the homeobox
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
40
what is the homeodomain
part of the protein coded by the homeobox
- binds to DNA and switched genes on and off
41
what type of genes are homeobox genes
regulatory genes - switch genes on and off
42
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)
43
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
44
what is a common feature of body plans
- they are segmented, with segments multiplied over time and specialised to perform different functions
45
what are the examples of symmetry in body shape
- radial, like jellyfish (diploblastic animals with 2 layers of tissue) = only top and bottom, not left or right
- bilateral = have left side, right side, head and tail
- asymmetry, like sponges = no lines of symmetry
46
what is apoptosis
programmed cell death
47
what are some uses of apoptosis
- removes unwanted cells and tissues
- remodelling of tissue (release chemicals stimulating mitosis and cell proliferation)
- hox genes regulate apoptosis and mitosis
48
what is stress and what does it impact
condition produced when homeostatic balance within an organisms is upset
- influences the expression of regulatory genes, and can be caused internally or externally
- apoptosis and genes controlling cell cycle can respond to this
49
what are external factors impacting gene expression
change in temperature
change in light intensity
50
what are internal factors impacting gene regulation
release of hormones
psychological stress
- drugs can also impact regulatory genes
51
when do factors impacting gene regulation have the most impact
during growth and development of an organisms
