Control Of Gene Expression Flashcards
1
Q
What is a mutation?
A
Random change to genetic material
NOT ALL MUTATIONS ARE HARMFUL!!!
2
Q
What are the are the two aspects that a mutation may affect?
A
Chromosomes or genes
3
Q
What kind of mutations affect chromosomes?
A
Incorrect segregation of chromosomes (non-disjunction)
Translocational mutations
4
Q
What kind of mutations affect genes?
A
Changes to base coding and order
Mutagenic chemicals
Replication errors
Ionising radiation
5
Q
What are point mutations and what are the different types of point mutation?
A
Point mutations are the substitution of a base in game coding of DNA or RNA
Silent
Missense
Nonsense
6
Q
What is a silent mutation?
A
Where the substitution of a base still codes for he same original amino acid and Therefore has no effect.
7
Q
What are missense mutations?
A
Substitution of a base which changes he code to code for a different amino acid and therefore will produce a different primary structure and hence a different protein or a non functioning protein
8
Q
What are nonsense mutations?
A
Substitution of a base that changes the code to code for a stop codon which would terminate the rest of the genetic code preventing a protein from being coded for properly.
9
Q
What are indel mutations?
A
The addition or deletion of a base in the genetic code.
10
Q
How can an indel mutation cause a frameshift?
A
When a number of bases added or deleted via an indel mutation is not a multiple of three, then a frameshift will occur.
11
Q
What is a frameshift
A
When bases on the genetic code get moved a number of places so the code is read differently and could potentially code for different amino acids
12
Q
What is a duplications mutation?
A
When a codon gets repeated a number of times in the coding of s gene.
(This does not cause a frameshift)
This is the cause for Huntington’s disease
13
Q
What is an inversion mutation?
A
When a codon gets inverted and is hence read in the opposite direction and therefore may not code for the correct amino acid.
14
Q
How are eurythrocytes specialised?
Red blood cells
A
Small with a biconcave shape to increase their surface area.
They are flexible
They have lost most of their organelles and therefore have room to carry haemoglobin
Carry O2 from the lungs to respiring tissues
15
Q
How are neutrophils specialised?
A
Twice the size of a red blood cell
Have a multilobed nucleus
Chemotaxis
Injest invading pathogens
16
Q
How are sperm cells specialised?
A
Haploid nucleus and little cytoplasm
Lots of mitochondria for energy to swim
Undulipodium
Long and thin (streamlined)
17
Q
How are epithelial cells specialised?
A
Squamous cells so one cell thick
Flattened shape
May contain cilia
All help improve efficiency of diffusion
18
Q
How is epithelial tissue specialised?
A
Lines surfaces (eg skin digestive system or organs) Made from epithelial cells Have a short cell cycle (divide 2-3 times a day) Specialised to carry or particular functions.
19
Q
How is connective tissue specialised?
A
Non living extra cellular matrix
Separates living cells within tissues and enables the cells to width stand forces (eg weight)
Blood/cartilage/ bones/tendons/ skin all contain connective tissue.
20
Q
How is muscle tissue specialised?
A
Skeletal muscle- packaged by connective tissue enabling movement of limbs
Smooth muscle- propelled substances through blood vessels and organs
Cardiac muscle- myogenic and therefore can pump blood around the body
21
Q
How is nerve tissue specialised?
A
Able to conduct electricity
22
Q
How do cells eventually form an organ system?
A
Cells form tissues which form organs which form organ systems.
23
Q
Name some organ systems
A
Digestive Reproductive Respiratory Circulatory Immune Musculoskeletal Nervous Endocrine Lymphatic
24
Q
What are stem cells?
A
Undifferentiated cells capable of becoming any cell in the organism.
25
What are totipotent cells?
Cells in the zygote which have not yet differentiated into embryonic or placental cells
26
What are pluripotent cells?
Once a cell has become an embryonic cell, they could then differentiate into any somatic cell (body cell)
27
What are multipotent cells?
Cells that are only able to differentiate into specific cells and form specific tissues
( progenitor cells)
28
What are unipotent cells?
Cells that only have one job and therefore cannot be differentiated into any other cell.
29
What are IPSP’s?
Induced Pluripotent Stem Cells
Made by reprogramming differentiated cells to make them undifferentiated
30
How can stem cells be used?
Bone marrow transplants:
Treat blood diseases (like sickle cell anemia)
Treat cancer
Treat disease of the immune system
Drug research:
Remove the need for vivisection
Regenerative medicine:
Repair or replace damaged tissue or cells
Replace organs
Repair nerve tissue
31
What are transcription factors?
They are proteins or short non coding sections of DNA
They act in the nucleus
The action of transcription factors may be regulated by other molecules
32
What do transcription factors do?
Stimulate the transcription of DNA to RNA in order to activate a particular gene
33
Explain how oestrogen cause a transcription factor to stimulate a gene transcription
1. Oestrogen is lipid soluble and therefore can diffuse through the phospholipid bilayer.
2. Oestrogen binds to a transcription factor due to their specific and complementary binding sites.
3. The binding of oestrogen causes the binding site for DNA on the transcription factor to change meaning the Transcription factor is now activated (can bind to the DNA
4. The transcription factor enters the nucleus through a nuclear pore and binds to the DNA molecule
5. The combination of the transcription factor with DNA stimulates the transcription of a gene
34
What is siRNA?
Small interfering RNA
A molecule that inhibits gene expression.
35
How does siRNA inhibit gene expression?
1. The dsRNA is cut into smaller pieces of dsRNA by an enzyme.
2. These small dsRNA molecules associate with a RISC molecule which forms two strands of siRNA.
3. Still associated with the RISC molecule, the siRNA strand binds to the mRNA (as it is complementary)
4. This causes the mRNA to be spliced into smaller pieces and translation does not occur into a protein hence the gene is not expressed.
36
What is the epigenome?
Chemical tags attached to DNA enabling genes to be turned on or off.
This will make the DNA available/unavailable to the transcription factors
(Tags may be modified in response to the environment)
37
Give examples of epigenetic modification.
Decreased acetylation of DNA
Methylation of DNA
38
How are transcription factors blocked from binding to DNA?
1. DNA contains negatively charged phosphate groups.
2. The removal of acetyl groups increase the positive charge on histones (de-acetylated)
3. Therefore there is increased attraction between the positive charges on histones and the negative phosphates of DNA.
4. This means that DNA binding sites are blocked by the histone proteins and as a result transcription factors cannot bind to the DNA and no gene is expressed (switched off)
39
How does methylation of DNA inhibit transcription factors from binding?
Methylation is the addition of a methyl (CH3) group on to cytosine.
This prevents the binding of transcription factors
This also attracts proteins that induce de-acetylation.
40
Are epigenomes inherited?
Epigenetics may be responsible for inherited traits
41
How can methylation and acetylation be linked to disease?
Methylation silences genes (deactivated)
Also increase de-acetylation
Acetylation promotes genes (activated)
Acetylation could be linked to cancer as this may be what causes the promotion of cell division (usually a silent gene) at the wrong time and therefore causes the uncontrollable cell division.
42
What is cancer?
A group of diseases that cause damage to genes which regulate the cell cycle and mitosis, therefore leading to the uncontrolled cell division
43
What are the two types of tumour?
Benign- non cancerous
| Malignant- cancerous
44
What are properties of benign tumours?
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Grow slowly
Well define capsule
Not invasive
Well differentiated
Do not metastasise
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45
What are properties of malignant tumours
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Grow rapidly
No encapsulated
Invasive
Poorly differentiated
Can spread distantly
(Metastasise)
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46
What is metastasis
Where part of a Tumour breaks off and travels to another location in the body vis the blood and starts a secondary tumour.
47
How does cancer develop?
Via the mutation of proto-oncogenes (usual genes that’s code for proteins stimulating cell division) forming oncogenes
Or the hypermethylation of tumour suppressor genes.
48
What are oncogenes?
Mutated proto oncogenes which stimulate a cell to divide.
| Hey are permanently switched on and can therefore promote cell division in the absence of growth factors.
49
What are proto-oncogenes?
Genes that code for proteins that stimulate cell division when attached to a growth factor
50
How does a mutation of a tumour suppressor genes cause cancer?
Usually inhibit cell cycle.
Hypermethylation of these genes causes them to be turned off and therefore cannot produce the protein that prevents the cell to divide
Therefore no control of cell division leading to a tumour.
51
What is DNA sequencing?
Technique that allows genes to be isolated and read.
| Based on interrupted PCR
52
What are the stages in DNA sequencing?
1. Interrupted PCR:
DNA fragments are mixed with free nucleotide bases. Some of these bases are terminator nucleotides
(Stop the complementary base pairing on ssDNA)
2. Separate fragments using electrophoresis:
After separating the fragments on the gel using electrophoresis we can use an autoradiogram to obtain the bases.
3. Automated sequencing
Or use fluorescent dyes on the terminator nucleotides producing a visible gene sequence.
53
What is the proteome?
All the proteins produced by s genome at a specific time and in specific conditions.
54
How can genomes be sequenced?
These days using automated methods
55
What are the uses of sequencing genomes?
Enables the sequences of proteins that derive from the genetic code in organisms to be determined.
His may have used for the identification of antigens or use in vaccine production.
56
What are some issues with sequencing more complex organisms genomes?
The presence of non coding DNA and regulatory gender means that the genome is not as easily translated into the proteome.
57
What is recombinant DNA technology?
Technology that allows genes to be manipulated altered and transferred from organisms to organism.
58
What two cloning methods are used to produce / amplify recombinant DNA fragments?
In vitro cloning- using the polymerase chain reaction
In vivo cloning- transferring fragments to a host cell using a vector
59
What are the various methods for producing DNA fragments?
- Conversion of mRNA to complementary/ copies DNA (cDNA) using reverse transcriptase.
- using restriction enzymes to cut a fragment containing be desired gene from DNA
- creating the gene in a gene machine
60
How can DNA Fragments be produced using reverse transcriptase?
1. Select a cell that readily produces the protein (eg beta cells of langerhans from the pancreas are used to produce insulin)
2. These cells have large quantities of the relevant mRNA which can more easily be extracted.
3. Reverse transcriptase is used to make cDNA from the mRNA and then the cDNA is made into dsDNA by DNA polymerase.
4. This is now in double stranded form of the DNA required
61
How can DNA fragments be produced using restriction endonucleases?
The DNA is cut as a recognition site using a specific restriction Endonuclease ( in order to produce sticky ends and not blunt ends)
Which therefore enables this fragment of DNA to be inserted into a vector
62
Why are sticky ends important?
The ends of the DNA fragment are left with impaired nucleotide bases which can the pair with the DNA of another organism producing recombinant DNA
63
How are DNA fragments produced using s gene machine?
The desired gene sequence is inputted into s computer which sequences the gene quickly.
64
I what are the stages in recombinant DNA technology?
1. Isolation- of the DNA fragments that have the gene desired for
2. Insertion- of the DNA fragment into a vector
3. Transformation- transferring the DNA (in a vector) into a suitable host cell
4. Identification- of the host cell that have successfully taken up the gene by use of gene markers
5. Growth/cloning- of the population of host cells.
65
How is a gene isolated?
The DNA fragment containing the desired gene is cut using reverse transcriptase, restriction endonucleases or a gene machine.
66
How is a gene inserted into a vector?
The DNA fragment must be prepared by adding promoter and terminator regions so the DNA can be transcribed properly.
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The vector ( usually a plasmid with 2 antibiotic resistant genes) is cut using the same restriction endonucleases to produce complementary stick ends to the DNA fragment.
The DNA is then stuck into the vector by DNA ligase
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Not all plasmids in a mixture with have the DNA inserted into it and instead just reform.
67
How are the vectors put into a host cell? (Transformation)
1. Heat shock he bacteria(host cell) at 60 degrees as well as exposing them to calcium 2+ ions (via CaCl)
2. Make the bacteria ice cold enables the membranes to be permeable and therefore may uptake the vectors
68
How can the host cells with the recombinant DNA be identified?
Using gene markers ( usually antibiotic resistance, green fluorescent protein or enzyme markers)
69
How do antibiotic resistance gene markers work?
1. The plasmids have 2 antibiotic resistance genes in their DNA.
2. One of the abs genes will have been interrupted by the desired DNA gene and therefore will not work.
3. Grow all the bacteria on an agar. Transfer these populations to the first abs plate ( where only the bacteria grow if they take up a plasmid with the abs genes)
4. Transfer these populations to he second abs plate ( where the bacteria only grow if their abs gene is not interrupted and hence do not have the desired gene)
5. Identify those with the desired gene on the first abs plate and regrow those populations .
70
What is genetic fingerprinting?
Technique used see how closely related two individuals are
It relies on the non coding sections of DNA which get repeated.
71
What are VNTR’s?
Variable number tandem repeats
Repeated non coding bases of DNA
They are unique in every individual except identical twins
72
How is genetic fingerprinting done (method)?
1. Extract sample (could use PCR)
2. Digest the sample with restriction endonucleases
3. Use gel electrophoresis to separate the fragments
4. Add probes to identify bands of interest
5. Pattern of bands visualised and compared
The few differences in VNTR’s then the more closely related the two individuals are.
73
What is genetic fingerprinting used for?
Maternity/paternity disputes
Forensic science
Plant and animal breeding
Analysis of disease
74
What are DNA probes?
Short single stranded length of DNA that has some label attached making it easily identifiable.
Radioactively labelled
Fluorescently labelled
75
What is DNA hybridisation?
Technique used to locate specific alleles of genes.
76
What is in vitro cloning and what is it used for?
Using the polymerase chain reaction to amplify /clone fragments of DNA
77
How is PCR done?
1. Mixture of DNA polymerase, primers, nucleotides and magnesium ions are put into a thermocycler
2. This is heated to 95 degrees to separate the DNA strands by breaking he hydrogen bonds
3. Cooled to 68 degrees allowing the primers and ssDNA to anneal
4. Polymerase may now bind to the bits of dsDNA (promoter regions)
5. Heated to 72 degrees as this is the optimum temperature for DNA polymerase to begin to synthesis DNA
6. Process is repeated s number of times and the DNA fragments increase exponentially.
78
What are the advantages of using PCR?
Rapid to produce copied DNA fragments
| No living things involved
79
What are the uses of PCR?
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Used for:
Tissue typing
Forensic science
Detecting mutations
Research
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80
What is electrophoresis?
A technique used to separate different sized fragments of DNA
81
What would you see on an electrophoresis plate?
Heaviest fragments move slower and therefore now as far
Lighter fragments move faster and further
82
What is genetic screening?
The study of s persons DNA to identify genetic differences or susceptibility to particular diseases or abnormalities.
83
What is personalised medicine?
Type of medications that has the treatment customised to the individual patient
84
What is genetic counselling?
The giving of advice to prospective parents concerning the risks of genetic disorders in a future child.
85
What are tumour suppressor genes?
Genes that code for a particular protein which prevents the cell cycle (stops mitosis) from happening
