Gene expression Flashcards
(44 cards)
1
Q
What is a genetic mutation?
A
- Alteration in a base in a base sequence
- Occurs during DNA replication during interphase
2
Q
Explain the effect of genetic mutation
A
- Change in the base sequence = change in the amino acid sequence = modified 3’
- Bonds form in different places = different shape = non-functioning protein
- Can also result in cancer
3
Q
Examples of mutagenic agents
A
- Radiation: Alpha/Beta/Gamma/X-ray can damage and disrupt DNA structure
- Carcinogen: Tobacco smoke/ Mustard gas/ Peroxide chemicals that can interfere with DNA structure + transcription
4
Q
How many types of genetic mutations?
A
6 types:
1) Addition
2) Deletion
3) Substitution
4) Inversion
5) Duplication
6) Translocation
5
Q
Describe addition mutation
A
- Extra base added
- Causes frameshift to right
- Altered codons = code for multiple different amino acids = different amino acid sequence = non-functional protein
6
Q
Describe deletion mutation
A
- Deletion of a base
- Causes frameshift to left
- Altered codons = code for different amino acid sequence = non-functional protein
7
Q
Describe substitution mutation
A
- 1 base swapped for another
- Number of bases stays same = no frameshift = only 1 codon changes
- Genetic code = degenerate = 1 codon could still code for same amino = no impact to protein
8
Q
Describe inversion mutation
A
- Section of bases detach from DNA sequence but when re-attaching = inverted = code read back to front
- Can cause different amino to be coded for that region
9
Q
Describe translocation
A
- Section of bases detaches from 1 chromosome and attaches to another chromosome
- Causes significant difference on gene expression = phenotype change
10
Q
What is a stem cell?
A
Undifferentiated cells that can continually divide and become specialized
11
Q
Describe a totipotent cells
A
- Divide and produce any type of body cell
- During development these cells only translate only 1 part of their DNA = specialization
- Occur for a limited time in early embryo
12
Q
Describe pluripotent cells
A
- Divide and produce ALMOST any body cell
- Found in embryo a few days after fertilization
13
Q
Uses of pluripotent cells
A
- Used in research to potentially use in treating human disorders
- Could be used to regrow damaged cells e.g. burnt skin, beta cells for diabetes, neurons in Parkinson’s
14
Q
Issues with pluripotent cells
A
- Treatment with stem cells can continue dividing causing uncontrollable growth = create tumor
- Ethical: If it is ok to make a therapeutic clone of yourself + make embryo for stem cells then to destroy it
15
Q
Describe multipotent cells
A
- Divide and produce into limited number of cells e.g. all blood cells
- Found in mature mammal cells e.g. bone marrow
16
Q
Describe unipotent cells
A
- Divide and produce only 1 type of cell
- Found in mature mammal cells e.g. skin cells
17
Q
Sources of stem cells
A
1) Embryos: For a limited time post fertilization = pluripotent
2) Umbilical cord blood: Like adult stem cells = multipotent
3) Placenta: Limited types of specialized cells = multipotent
4) Adult stem cells: Can repair within certain tissue + organs = multipotent/unipotent
18
Q
Explain induced pluripotent stem cells
A
- Altering adult unipotent stem cells to make them in the state of pluripotency
- This is done using transcriptional factors
- Similar to embryonic cells without the ethical issue of destroying embryos
19
Q
What is epigenetics?
A
- Heritable change in gene function without changing DNA base sequence
- Changes caused by environment
20
Q
Factors that effect epigenetics
A
- Diet/Stress/Toxins
- Can add chemical tags to DNA which controls gene expression
21
Q
What is the epigenome?
A
Single layer of chemical tags on DNA which impacts the shape of the DNA-histone complex
22
Q
How does the epigenome effect gene expression?
A
- If DNA tightly wound = won’t be expressed
- If DNA unwound = will be expressed
- Tightly wound = transcription factors cannot bind = changes from the environment to epigenome = inhibits transcription
23
Q
Explain methylation of DNA
A
- Increase = tightening = inhibits transcription
- Methyl group attaches to cytosine
- Prevents transcriptional factors from binding
24
Q
Explain acetylation of DNA
A
- Decrease = tightening = inhibits transcription
- Acetyl groups attach/detach from histone proteins
- Makes DNA + histone more strongly associated = harder for transcriptional factors to bind
25
Explain how mutations effects tumor suppressor genes
- Mutation = don't produce proteins to slow down cell division = division continues
- Mutated cells not identified and destroyed
- Causes BRCA1/BRCA2 linked to breast cancer
26
Explain how abnormal methylation effects tumor suppressor genes
- Hypermethylation: Increased number of methyl groups = tightens = inhibits transcription = gene inactivated
- Hypomethylation: Reduces number of methyl groups = causes oncogenes that control mitosis = permanently turned on = continuous cell division
27
Function of transcriptional factors
- Stimulate/inhibit transcription of target genes
- Turn on/off genes so only certain proteins are produced in particular cells
- This causes cells to become specialized
28
Explain how transcriptional factors affect transcription in protein synthesis
- Once activated transcriptional factor proteins move into the nucleus
- Bind to different base sequences that they are complementary to
- Binding = enables RNA polymerase binding = transcription starts = mRNA made
29
Explain how estrogen initiates transcription
- It is a steroid hormone that binds to the receptor site on the transcriptional factor
- This causes a change in shape/ 3' = TF now complementary and able to bind to DNA = initiates transcription
30
Describe RNA interference
- Translation of mRNA is inhibited
- Transcribed mRNA is destroyed before it can be translated into a polypeptide by siRNA
31
Describe how siRNA works
-Enzyme cuts mRNA into siRNA
- 1 strand of siRNA combines with an enzyme
- The siRNA/enzyme complex binds to complementary bases on another mRNA
- Binding = cutting up of mRNA = cannot be translated
32
What is cancer?
- Mutation occurs in genes that are involved in mitosis
- Mutation = non-functioning protein = unregulated mitosis = uncontrollable cell division = tumor
33
Describe benign tumors
- Non-cancerous
- Can grow large but at a slow rate
- Produce adhesive molecules that stick them together to a particular tissue
- Surrounded by capsule = compact = easier to remove by surgery
- Impact is localized = not life-threatening depending on location
34
Describe malignant tumors
- Cancerous
- Grow large and rapidly as the cell nucleus grows and becomes unspecialized again
-Don't produce adhesive molecules = metastasis = tumor breaks off and spreads
- No surrounding capsule = grows into surrounding tissue = develops it's own blood supply
- Threat of spread = life-threatening so treatment required is extensive and can reoccur
35
What causes tumor development?
1) Mutated oncogenes
2) Mutated tumor suppressor genes
3) Abnormal methylation
4) Increased estrogen concentration
36
Explain how a mutation in oncogenes causes tumor development
- Proto-oncogene: Code for protein that initiates DNA replication/mitosis
- Mutated proto-oncogene = oncogene = permanently activated = uncontrollable cell division = tumor
37
Explain how a mutation in tumor suppressor genes causes tumor development
- Tumor suppressor genes: Code for proteins that slow down cell division + cell death if there is copying errors
- Mutated gene = protein not produced = uncontrollable cell division + mutated cells not identified and destroyed = tumor
38
Explain how abnormal methylation causes tumor development
- Hypermethylation of tumor suppressor gene: Increases methyl groups = tightening = inactivates gene = turned off = protein not produced = cell division continues = tumor
- Hypomethylation of oncogene: Decrease methyl group = loosening = gene permanently switched on = cell division continues = tumor
39
Explain how increased estrogen concentrations cause tumor development
- Estrogen is produced in fat cells in breast tissue post menopause
- Estrogen can interfere with the genes in the cell cycle = tumor
- Tumor can cause production of even more estrogen + attract WBC = increased tumor size
40
What is a genome?
Entire genetic material of an organism in the nucleus of a cell
41
What is genetic sequencing?
Working out the DNA base sequence for all the DNA in a cell
42
Describe genome sequencing
- HGP took 13 years to complete in 2003
- Methods for sequencing are continuously being improved and updated
- Now an automated process
43
Describe genome sequencing for simpler organisms
- DNA doesn't contain introns = genome can be used to sequence proteins = derive proteome
- Useful to identify potential antigens for vaccines
44
Describe genome sequencing for complex organisms
- DNA has introns and regulatory genes = genome cannot easily be translated into proteome
