6.1.1 Cellular Control Flashcards
(76 cards)
1
Q
Define Mutation
A
a change in the sequence of bases in DNA
2
Q
How does a change in a DNA Sequence occur?
A
substitution, deletion, insertion of 1 or more nucleotides (or base pairs)
3
Q
Define Point mutation
A
a mutation affecting only one nucleotide in a gene sequence
4
Q
Define Substitution
A
a mutation where 1 or more nucleotides are substituted for another in a DNA strand
5
Q
Define Deletion
A
a mutation where one or more nucleotides are deleted and lost from the DNA strand
6
Q
Define insertion
A
a mutation where one or more extra nucleotides are inserted to the DNA strand
7
Q
Define frame shift mutation
A
the insertion or deletion of 1 or more nucleotides which leads to frame-shift mutation
- shifts reading frame of the sequence of bases/amino acids as it will change every successive codon from the point of mutation
- this alters the tertiary structure of the protein
8
Q
Define Silent mutation
A
a substitution mutation that changes a single DNA nucleotide but does not affect the sequence of amino acids that make up the gene’s proteins
9
Q
Define Nonsense mutation
A
a substitution mutation of a single base pair that leads to the appearance of a stop codon where previously there was a codon specifying an amino acid
10
Q
Define missense mutation
A
a substitution mutation that changes the nucleotide sequence which changes the amino acid and alters the properties of the protein
- two types : loss of function, gain of function
11
Q
Define Gene mutation
A
a change in the DNA sequence of a single gene
12
Q
Define Chromosome mutation
A
a change in the number of chromosomes or gene arrangement of chromosomes
13
Q
Why can a change in the sequence of nucleotides of a gene affect the function of the protein produced from that gene?
A
- the sequence of nucleotides could be mutated to a new sequence that codes for a different amino acid triplet
- therefore a different protein = the new protein won’t carry out the same functions
14
Q
Describe how a mutation can have a neutral effect? give an example
A
- mutations can be silent - causing no change to proteins
e.g. a mutation of a sequence of nucleotides can lead to no change in sequence of amino acids as the genetic code is degenerate - no effect on phenotype of an organism bc normally fuctioning proteins are still synthesised
15
Q
Describe how a mutation can have a harmful effect? give an example
A
when the phenotype of an organism is affected in a negative way - bc proteins are no longer synthesised or proteins synthesised are non-functional
e.g. nonsense mutations
16
Q
Describe how a mutation can have a beneficial effect? give an example
A
when a protein is synthesised that results in a new and useful characteristic
e.g. a mutation in a protein present in the cell surface membranes of human cells -HIV cannot bind and enter
17
Q
What are the 3 types of mutagen? give an example of each
A
- Physical mutagens - x-rays
- Chemical mutagens - deaminating agents
- Biological agents - viruses, alkylating agents
18
Q
Define mutagen
A
a chemical/physical/biological agent which causes mutations
19
Q
What are the 4 types of chromosome mutation?
A
- deletion - section of chromome breaks off and is lost within cell
- duplication - sections of dna duplicated on chromosome
- translocation - section of 1 chromosome breaks odd and joins another non-homologous chromosome
- inversion - section of chromosome breaks off, is reversed and joins back onto chromosome
20
Q
Explain the possible effects of substitution mutation.
(no effect, damaging, beneficial)
A
- no effect - no effect on phenotype bc normally functioning proteins still synthesised
- damaging - phenotype affected in negative way bc proteins no longer synthesised/proteins synthesised non-functional
- beneficial - protein synthesised results in new and useful characteristic in phenotype
21
Q
Explain possible effects of insertion or deletion mutations
A
- frameshift mutation
- move shift triplet code
- distrupts reading of triplet codon
- changes every successive codon from point of mutation
- changes protein structure
22
Q
Define gene expression
A
- genetic information in DNA converted into instructions for making proteins
23
Q
Define epigenetics
A
- control of gene expression by modification of DNA
24
Q
What are the four levels at which genes (or proteins) are regulated?
A
- Transcriptional - genes turned on and off
e.g. lac operon + chromatin remodelling - Post-transcriptional - mRNA can be modified to regulate translation and types of proteins produced
e.g. RNA processing - Translational - gene translation can be stopped and started
e.g. degradation of mRNA - post-translational - proteins can be modified after synthesis to change their functions
e.g. folding/shortening proteins
25
What is trascription?
turning genes on and off
e.g. chromatin remodelling and lac operon
26
Define - chromatin , heterochromatin and euchromatin
1. chromatin - uncondensed DNA wound around histone proteins (+ve charge)
2. heterochromatin - tightly wound DNA causing chromosomes to be visible during cell division
3. euchromatin - loosely wound DNA
27
Why is gene expression not possible in heterochromatin but is possible in euchromatin?
- when DNA tightly wound (heterochromatin) transcription not possible as RNA polymerase cant access the gene
- in euchromatin DNA loosely wound so RNA polymerase can access gene and do trancription
28
How can histone modification (increase or decrease packing degree) affect gene expression?
- histones can be modified to increase or decrease degree of packing
- if packing degree decreaeses DNA can be transcribed
- if packing degree increaes DNA cannot be transcribed.
29
is chromatin remodelling a eukaryote or prokaryote example of .....?
- chromatin remodelling is a eukaryote example of *transcription*
30
- in eukaryotes ........ ...... control transcription of genes.
- factors stopping transcription are .....
- factors starting trascription are .......
-
- 1 transcription factors
- 2 repressors
- 3 activators
31
Define operon
- a group of genes controlled by the same regulatory mechanism and are expressed at the same time
32
is the lac operon a eukaryote or prokaryote example of …..?
- prokaryote
- example of transcription
33
Draw a diagram to show the lac operon and its associated regulatory gene.
34
What is the role of the regulatory gene and the name of the one associated with the lac operon?
- Regulatory gene - codes for a repressor protein (that prevents the transcription of the structural genes in absence of lactose)
- lac I
35
What does the repressor protein do?
- coded for by a regulator gene
- repressor protein: prevents transcription of the structural genes in the absence of lactose
36
describe the roles of:
- regulatory gene
- structural genes
- operator region
- promotor region
of lac operon for metabolism of lactose
- repressor protein bind to the operator
- repressor protein blocks RNA polymerase binding site on promoter
- RNA polymerase cannot bind to DNA and start transcription of structural genes
OR
- RNA polymerase binds to the promotor region which releases lactose/repressor protein complex from the operator region allowing transcription to begin
37
How does the lac operon work when lactose is absent from growth medium but glucose is present?
1. regulatory gene Lac I codes for repressor protein which binds to the operator
2. No lactose to bind to the repressor protein and so doesnt change proteins shape
3. RNA polymerase cannot bind to promoter region due to shape of repressor protein blocking promoter
4. transcription of structural genes cant occur
38
What are structural genes?
- give the 3 structural genes of the lac operon
- structural genes: proteins/enzymes which are not involved in DNA regulation
- 1. lac Z
- 2. lac Y
- 3. lac A
- all produce enzymes to metabolise glucose
39
How does the lac operon work when glucose is absent from growth medium but lactose is present?
1. Lac I codes for repressor protein which binds to operator
2. lactose binds to repressor protein and causes a change in the proteins shape
3. repressor protein is released from the operator as it can no longer bind to it
4. unblocked promoter so RNA polymerase can bind to promoter and transcribes 3 structural proteins
5. enzymes synthesised to metabolise lactose
40
What binds to the promotor?
- section of DNA sequence where RNA POLYMERASE binds to
41
What binds to the operator?
- section of DNA sequence where repressor protein binds to
42
What is the role of cAMP in lac operon
- cAMP increases rate of transcription
- cAMP receptor protein binding to RNA polymerase
43
What is post-transcriptional gene expression?
primary mRNA made in transcription is modified to regulate translation and types of proteins produced
e.g. rna processing
44
Why is mRNA in eukaryotic cells edited?
- eukaryotic DNA contains introns and extrons
- introns are edited out of DNA
45
Define intron
- regions that do not code for proteins
46
Define exons
regions that do code for proteins
47
What is pre-mRNA
the product of transcription that contains introns and exons
48
What is mature mRNA?
modified pre-mRNA that can bind to a ribosome and code for proteins
49
Define RNA processing
- preparing RNA to leave nucleus
50
Define RNA editing
- the nucleotide sequence of mRNA molecules is changed through base addition, deletion, substitution
51
Describe the 4 steps on how pre-mRNA is modifiedn to produce mature mRNA
1. RNA SPLICING - introns are removed from from mRNA
2. ADD CAP TO 5' END - (cap is modified nucleotide)
3. ADD TAIL TO 3' END - (tail is a long chain of adenine nucleotides)
- tail + cap help: stabilise mRNA and delay degradation in cytoplasm
4. further mRNA editing through substitution, insertion and deletion
52
Where is pre-mRNA modified (post-transcription)?
in the nucleus
53
What is the benefit of mRNA modification (post-transcription)?
make different versions of mRNA to => synthesise different proteins with different functions
54
What is translational control?
regulates protein synthesis
55
What are the 3 mechanisms in translational control which regulate translation?
2 - down regulate translation (dont want translation)
1- does do translation
Down regulate translation via:
1. degradation of mRNA - eliminates mRNA - no mRNA = no translation
2. inhibiatory proteins bind to mRNA - prevents mRNA binding to ribosomes = prevents protein synthesis
Translation does happen:
3. activate initiation factors
help mRNA bind to ribosomes
56
What is the role of protein kinases in regulating gene expression/protein activity
protein kinases enzymes:
- catalyse adding of PO4 group to proteins
- changes tertiary structure and therefore function of the protein
57
What is post translational control?
modification of proteins that have been synthesised
58
What are the 4 ways which proteins can be modified to do post translational control?
1. Adding non-protein groups - e.g. carbohydrate chains,lipids, phosphates
2. Modifiy amino acids and therefore the formation of bonds - e.g. modify AA to form disulfide bridges (add sulfate)
3. Fold/shorten proteins - affects tertiary (3d structure)/quaternary (combination of subunits)
4. Modification by cAMP - e.g. (1) cAMP + CRP - bind to RNA polymerase and increase rate of transcription of structural genes
e.g. (2) cAMP + kinases -> activate other enzymes/proteins
59
Define homeobox gene
- a group of genes which all contain a homeobox
60
Define body plan
the general structure of an organism
61
Define morphogenesis
the regulation of the pattern of anatomical development
62
Define homeodomain
part of a protein which binds to DNA and switches genes on and off
63
Define hox gene
the group of homeobox genes that are only present in animals
64
What are the 3 kindgoms which all have very similar homeobox genes?
- animalia
- plants
- fungi
65
How are homeobox genes similar across life and how they differ?
- homeobox is section of DNA that is 180 base pairs long and codes for part of protein 60 amino acids long - it is highly conserved
- differ: mutations
66
What is meant by highly conserved?
- one that has remained relatively unchanged
67
What is the role of Hox genes in controlling the body plan of animals?
- responsible for correct positioning of body parts
68
How do hox genes control development? (5 steps)
1. homeobox sequences of hox gene code for a part of the protein called the homeodomain
2. homeodomain binds to specific sites on DNA -
3. enables protein to act as transcription factor either activate or repress transcription
4. homeodomain binds at start of developmental genes so alters production of proteins involved in body plan development
69
What are 3 function types of homeobox genes and give examples for each
1. symmetry - e.g. bilateral symmetry
2. mitosis - cell division and proliferation e.g. increase number of cells leading to growth
3. apoptosis - cell death and also release chemical signals which stimulate mitosis - leads to remodelling of tissue e.g. digits on hands and feet
70
Define apoptosis
programmed cell death
71
What is the process of apoptosis
- removes unwanted cells and tissues to shape different body parts
- cells undergoing apoptosis can also release chemical signals which stimulate mitosis and cell proliferation leading to remodelling of tissues
72
How is apoptosis controlled?
- hox genes control apoptosis
- increased transcription of genes responsible for apoptosis
73
What is the role of mitosis in growth and development?
- results in cell division and proliferation
- increases number of cells leading to growth
74
How can apoptosis be used during growth and development?
- releases chemical signals to stimulate mitosis
75
What are factors that affect expression of regulatory genes?
environmental:
- internal - stress
- external - changes in temp/light intensity
76
Define stress in relation to homeostasis and describe factors that may influence the rate of mitosis or apoptosis?
stress - condition produced when homeostatic balance within an organism is upset
factors: - change in temperature or intensity of light
