The Control Of Gene Expresion (3.8) Flashcards
1
Q
When do gene mutations arise?
A
During DNA replication
2
Q
What are the types of gene mutation?
A
Addition, deletion, substitution, inversion, duplication, translocation of bases
3
Q
Gene mutations occur ____________.
A
Spontaneously
4
Q
What is a mutagenic agent?
A
Something that increases the rate of mutation
5
Q
What is an addition mutation?
A
Adding a nucleotide
6
Q
What is a deletion mutation?
A
Removing a nucleotide
7
Q
What is a substitution mutation?
A
Changing one nucleotide for another
8
Q
What is an inversion mutation?
A
A segment of a chromosome breaks off and reattaches elsewhere in the opposite direction
9
Q
What is a duplication mutation?
A
One or more copies of a DNA segment are produced
10
Q
What is a translocation mutation?
A
Moving of a section of DNA from one chromosome to another
11
Q
What is the definition of a mutation?
A
A change in the sequence of nucleotides/ bases in the DNA
12
Q
What processes produces new combinations of alleles?
A
crossing over
Independent segregation of homologous chromosomes
Random fertilisation
13
Q
What is a totipotent cell?
A
Stem cell
14
Q
Totipotent cells can divide and produce any type of body ____.
A
Cell
15
Q
Totipotent cells occur only for a ______ time in early mammalian embryos.
A
Limited
16
Q
Pluripotent stem cells can divide in u___________ numbers and can be used in treating human disorders.
A
Unlimited
17
Q
During embryonic development as new cells are made some of the genes are “switched off” (no longer transcribed). These cells are called _____________.
A
Pluripotent
18
Q
In adults cells are highly specialised and referred to as ____________ ie can differentiate a they divide into a limited number of cell types
A
Multipotent
19
Q
In eukaryotic cells when a gene is transcribed pre mRNA is made. What is the difference between pre mRNA and mRNA?
A
Pre mRNA contains introns and exons. MRNA only contains exons because the intros are spliced out
20
Q
What is the difference between the coding strand of a gene and pre mRNA?
A
DNA is made of nucleotides with the bases Adeneine, thymine, guanine and cytosine whereas in RNA is adenine, uracil, guanine and cytosine
The mRNA strand has as sequence of bases that is complementary to the sequence on the DNA rather than the same as. RNA nucleotides have the sugar ribose whereas DNA nucleotides have deoxyribose
21
Q
How does mRNA leave the nucleus?
A
Nuclear pores
22
Q
How many codons on mRNA attach to a ribosome during translation at any one time?
A
2
23
Q
What is the name of the bond formed between two amino acids in the polypeptide chain? What is needed for this bond to form?
A
Peptide
ATP is hydrolysed to release energy
24
Q
What happens to the polypeptide as it is being made?
A
It is folded and transported along the rough Endoplasmic reticulum
25
What is a transcription factor?
A protein that controls the transcription of genes by binding to a specific sequence of DNA
They ensure that genes are being expressed in the correct cells, at the correct time and to the right level
26
What is the upstream part of a gene?
Refers to the DNA before the start of the coding region
27
What is a promoter?
A section of DNA upstream of the coding region that is the binding site for proteins that control the expression of the gene
28
How do transcription factors enter the nucleus?
From the cytoplasm through nuclear pores
29
Some transcription factors bind to the ________ region of a gene
Promoter
30
How do transcription factors interact with RNA polymerase?
Either by assisting RNA polymerase binding to the gene (to stimulate expression of the gene) or by preventing it from binding (to inhibit gene expression)
31
What hormone works as a transcription factor?
Oestrogen
32
Oestrogen is hydro________ and ______ soluble.
Hydrophobic
Lipid soluble
33
Describe the oestrogen stimulation pathway.
1. Oestrogen diffuses into the cytoplasm
2. Oestrogen diffuses through the nuclear pore into the nucleus
3. Oestrogen attaches to an oestrogen receptors that is held within a protein complex, this cases the oestrogen receptor to undergo a conformational change
4. The new shape of the oestrogen receptor allows it to detach from the protein complex and diffuse towards the gene to be expressed
5. The oestrogen receptor binds to a cofactor which enables it to bind to the promoter region of the gene, this stimulates RNA polymerase binding and gene transcription
34
What is RNAi?
Interfering RNA
35
Why may gene expression and protein synthesis be stopped?
A cell may not want to turn all mRNA into a protein
To protect the cell from infection by viruses
36
Describe how gene expression is blocked?
- two RNA strands form a complementary base pairing with hydrogen bonds, linking the bases together - this forms dsRNA (double stranded RNA)
- dsRNA then gets cut by the dicer enzyme
- small interfering RNA (siRNA) is formed from the dsRNA being cut by the dicer enzyme
- siRNA forms a RISC complex (RNA induced silencing complex) with an enzyme and one stand is destroyed
- the siRNA molecule guides the enzyme to an mRNA molecule by pairings is bases with the complementary ones on a section on the mRNA molecule
- the enzyme cuts the mRNA into smaller sections
- the mRNA is no longer capable of being translated into a polypeptide
37
Describe how gene expression is blocked.
- two RNA strands form a complementary base pairing with 1._________ bonds, linking the bases together - this forms dsRNA (2. ______ _________RNA)
- dsRNA then gets cut by the 3. ______enzyme
- small interfering RNA (4._____) is formed from the dsRNA being cut by the dicer enzyme
- siRNA forms a RISC complex (RNA induced silencing complex) with an enzyme and one strand is 5._________
- the siRNA molecule guides the enzyme to an mRNA molecule by pairings is bases with the 6. _____________ ones on a section on the mRNA molecule
- the enzyme cuts the mRNA into smaller sections
- the mRNA is no longer capable of being 7. ___________into a polypeptide
1. Hydrogen
2. Double stranded
3. Dicer
4. SiRNA
5. Destroyed
6. Complementary
7. Translated
38
What are epigenetics?
Heritable changes in gene function without changes to the base sequence of DNA
39
What is the epigenome?
All of the chemical modifications to all the histone proteins and DNA
40
The DNA in the nucleus is wrapped around _________ proteins.
Histone
41
What causes changes in the epigenome?
The environment
42
If the DNA is wound more tightly around a histone in a certain area, the genes on this section of DNA are switched off. What does this mean about the expression of the gene?
The gene is hidden from transcription factors and RNA polymerase, meaning the gene cannot be expressed
43
DNA is wrapped around histone proteins which form a ____________.
Nucleosome
44
What is the chemical formula for an acetyl group?
COCH3
45
Acetylation happens to ________.
Histones
46
Acetylation happens to ________.
Histones
47
What is adding acetyl to a histone called?
Acetylation
48
Acetylation causes gene expression to be _________?
Stimulated
49
Why does acetylation of Histones lead to stimulated gene expression?
Adding acetyl to an amino acid removes the ionic bonds between the histone protein and DNA
This causes the DNA to become less tightly wrapped so RNA polymerase and transcription factors can easily bind and therefore gene expression is stimulated.
50
Describe the ionic bond between a histone protein and DNA.
ionic bond between the positively charged R-group of the histone protein and the negatively changed phosphate backbone of DNA
51
What is the removal of an acetyl group called?
Deacetylation
52
Deacetylation _______ gene expression
Inhibits
53
Describe how Deacetylation inhibits gene expression.
Removal of acetyl returns the amino acid to its positively charged sate which has a stronger attraction to the DNA molecule and therefore inhibits transcription
54
Methylation happens to ___.
DNA
55
What is the chemical formula for a methyl group?
CH3
56
Methyl groups can be added to a carbon molecule on c________ bases.
Cytosine
57
How does methylation inhibit gene expression?
The addition of methyl groups suppresses the transcription of the affected gene because the methylated bases attract proteins that bind to the DNA.
58
Demethyation _____________ gene expression
Stimulateds
59
What is a carcinogen?
Something that increases the chance of harmful mutations that can lead to cancer
60
What are the 3 types of cancer treatment?
Chemotherapy
Radiotherapy
Surgery
61
Benign tumour:
- _____ rate of growth
- same appearance of surrounding _______
- well defined shape, often in a c______
- ______ invades surrounding tissue (due to having a membrane)
- _____ metasises
Slow
Tissue
Capsule
Never
Never
62
Malignant tumour:
- _____ rate of growth
- ab_______ shape
- doesn’t resemble surrounding ______
- usually ______ surrounding tissue
- _______ metasises
Fast
Abnormal
Tissue
Invades
Usually
63
What are the 2 genes that are involved in causing cancer if they mutate or have epigenetic changes?
- tumour suppressor genes
- proto oncogenes
64
How do tumour suppressor genes work?
These genes code for proteins that inhibit cell division and prevent the formation of tumours
65
What is a proto-oncogene?
A gene that normally helps grow and divide to make new cells
66
How is an oncogene formed?
A proto-oncogene mutuates and becomes activated when its not supposed to be, this results in uncontrolled cell division
67
How can a mutation of a tumour suppressor gene lead to uncontrolled cell division?
A loss of function mutation means that the genes cannot slow down cell division
There is no initiation of apoptosis and no cell cycle arrest
68
How can increased oestrogen concentrations lead to cancer?
Oestrogen binds to the transcription factor activating genes that promote cell division which can lead to tumour formation
69
What is the genome?
All of the genes present in an organism
70
What is the proteome?
All of the proteins that are expressed in an organism
71
How can the genome project help with understanding evolutionary relationships?
Can help with classification
Help identify subspecies
The more separated organisms are on an evolutionary tree, the more different their DNA
72
How can the genome project help contribute to personalised medicine?
Diagnose diseases before they become present e.g finding severe immune problems in a baby
73
What are some of the ethical considerations surrounding the human genome project?
Knowing someone’s genome makes exploiting their genome a possibility
- > cloning
-> designer babies
-> ‘playing God’ argument
74
How long does it take sequence a human genome?
26 hours
75
What are the 3 methods of producing gene fragments?
- reverse transcriptase
- restriction enzymes
- gene machine
76
How does reverse transcriptase produce gene fragments?
- mRNA is combined with a reverse transcriptase enzyme and forms a single strand of complementary DNA (cDNA)
- DNA polymerase (enzyme) is then used to convert the single strand of cDN into a double-stranded DNA molecule which contains the desired code for the gene
77
Why is the reverse transcriptase technique of producing gene fragments considered advantageous?
It is easier to find the gene as:
- specialised cells will make very specific types of mRNA
- the mRNA doesn’t contain introns
78
What is an example of a restriction enzyme?
Restriction endonucleases
79
How do restriction enzymes produce gene fragments?
Bind to a specific restriction site on DNA
Separate strands of DNA by cutting sugar phosphate backbone
Sticky ends result in one strand of the DNA fragment being longer than the other strand, making it easier to inert into the desired gene of the other organism (from complementary hydrogen bonds)
80
Where on the DNA do restriction enzymes bind to?
Restriction site
81
How do gene machines work?
Use computers to generate the nucleotide sequence to produce DNA
Short fragments of DNA are first produces which are then joined to make longer sequences and then inserted into vectors e.g plasmids
82
Describe the process of in Vivo amplification.
- a vector is cut open at a specific site using a restriction enzyme creating sticky ends
-the same restriction enzyme is used to cut the target DNA fragment, creating complementary sticky ends
- DNA ligaments forms phosphodiesther bonds between the sugar and phosphate groups on the two strands of DNA, joining the sticky ends of the vector and DNA fragment together
- the newly formed combined DNA molecule is known as recombinant DNA
83
What are marker genes?
Genes that indicate which host cells took up recombinant DNA
84
How do marker genes work?
- inserted into vectors alongside target genes
- transformed cells are cultivated on selective agar plates
- only transformed cells can then be cultured to mass-produce the target DNA fragment through cellular division
85
Why is a promoter region and terminator region added to a plasmid in in vivo amplification?
To signal where transcription should start and end
86
What are the 3 stages of in vitro amplification?
Denaturing
Annealing
Extension
87
Describe the 3 stages of in vitro amplification?
Denaturing - hydrogen bonds broken - 95’C
Annealing - primer forms hydrogen bonds to complementary base pairs on template strand - 55’C
Extension - free nucleotides match up with the template (by complementary base pairing) and Taq DNA polymerase joins the nucleotides with phosphodiethster bonds
88
What are the 4 uses of gene technology?
Recombinant proteins
Insulin
Factor VIII
Gene therapy
89
Describe how gene therapy is a use of gene technology.
-Treats diseases that are caused by a mutation gene e.g recessive cystic fibrosis gene
- if the mutation is in the recessive allele, a dominant allele is inserted into the genome - the dominant allele counteracts the mutant alleles
- if the mutation is in the dominant allele, an allele that ‘silences’ the mutant allele is inserted into the genome
- a vector is used to insert the target gene into the genome
90
State and explain the 2 types of gene therapy.
Somatic therapy - altering of alleles in adult body cells
Germiline therapy - altering of alleles in sex cells (illegal in humans)
91
Describe how recombinant proteins are a use of gene technology.
Recombinant proteins are produces using bacteria, yeast or animal cells. (Used for therapeutic purposes e.g infectious diseases, diabetes, cancer)
Most are generated using eukaryotic cells instead of prokaryotic cells because eukaryotic cells can perform post-translational modifications (facilitated by the Golgi apparatus - produce specific proteins necessary to produce functional human proteins)
92
What are the advantages of using recombinant proteins?
- cost-effective
- faster
- human-like proteins can be engineered to have desired features
93
Describe how insulin is a use of gene technology?
- bacterial plasmids are modified to include the human insulin gene by in vivo amplification
- recombinant plasmids are inserted into bacteria - once the transgenic bacteria are identified (by markers) they are isolated, purified and placed in fermenters
- transgenic bacteria multiply by binary fission and express the human protein insulin which is then extracted and purified
94
What are the advantages of insulin as a gene technology?
- identical to human insulin
- reliable supply available
- fewer ethical, moral or religious concerns as proteins are not extracted from cows or pigs
- fewer rejection problems
- cheaper to produce in large volumes
95
Describe the role of factor VIII as a gene technology.
Factor VIII is a blood clotting protein that haemophiliacs cannot produce
Kidney and ovary hamster cells have been genetically modified to produce factor VIII
Once modified these recombinant cells are cultured and factor VIII is extracted and purified and used as an injectable treatment for haemophilia
96
Describe the role of factor VIII as a gene technology.
Factor VIII is a blood clotting protein that haemophiliacs cannot produce
Kidney and ovary hamster cells have been genetically modified to produce factor VIII
Once modified these recombinant cells are cultured and factor VIII is extracted and purified and used as an injectable treatment for haemophilia
97
What is an advantage of factor VIII as a gene technology?
Less risk of transmitting infection e.g HIV
98
What is genetic fingerprinting?
A method of determining the genetic relationships and the genetic variability within a population
99
What should happen to the DNA before gel electrophoresis?
Amplified using PCR
Restriction endonucleases cut the DNA into fragments close the the VNTR region
100
What is a variable tandem repeat region?
A section of DNA that contains repeated DNA sequences and vary between people (except for identical twins)
101
What is gel electrophoresis?
A method of separating molecules according to their size/mass and overall charge
102
What is gel electrophoresis?
A method of separating molecules according to their size/mass and overall charge
103
How is a molecule separated by its charge in gel electrophoresis?
Positively charged molecules will move towards the cathode (negative pole) and negatively charged molecules will move towards the anode (positive pole)
104
Where does DNA move to in gel electrophoresis?
Moves towards the anode as it is negatively charges (due to phosphate groups)
105
How do different sized molecules move in gel electrophoresis?
Smaller molecules move quickly
Larger molecules move slowly
106
How does the type of gel use effect gel electrophoresis?
Different gels have different sized pores which affects the speed the molecules can move through them
107
What is a DNA probe?
Short single stranded DNA molecule which is complementary to a sequence to be detected
It either uses radioactive isotopes or fluorescent dye to detect the DNA sequence
108
What are some of the applications of genetic fingerprinting?
Identity suspects for a crime or a corpse
Identify individuals who are at risk of developing particular diseases
Determine familial relationships for paternity cases
Species conservation (reduces the chances of interbreeding in breeding programmes)
Drug response prediction
This is all possible as everyone has a unique number of inherited VNTRs (except identical twins)
109
what are the steps involved in calculating chi squared on a genetic cross?
Record observed values
Find the expected value using a punnet square and the total number of offspring
Calculate chi squared value
Use chi-square table and degrees of freedom to find where the p-value falls
Make conclusions based on the p-value
110
What is the expected ratio in a dihybrid cross?
9:3:3:1
111
Describe how the probability of linked genes are determined?
- linked genes are found on the same chrosome:
- if P>0.05 (probability that the difference is due to chance) it is likely that the genes are not linked
- if P<0.05 it is likely that the genes are linked this is because two of the possible gamete phenotypes are only produced as a result of crossing over, which might not occur. Especially if the genes are close together on the chromosome
