Topic 8A: Flashcards
1
Q
What are benign tumours?
A
- Not cancerous
- Grow more slowly
- Harmless but can put pressure on organs and impact function
2
Q
What are malignant tumours?
A
- Cancerous
- Grow rapidly
- Invade other tissues
3
Q
What is a mutation?
A
- Any change in base sequence of DNA
- Can change the primary structure of amino acids
- Position of H bonds can change in secondary and tertiary structures
4
Q
What are frameshift mutations?
A
- Causes all bases after the point of mutation to change
5
Q
What is a substitution?
A
- One nucleotide replaced by another with a different base
6
Q
What is an addition?
A
- Extra nucleotide added -> adds extra base to the sequence
7
Q
What is a deletion?
A
- One nucleotide removed
8
Q
What is a duplication?
A
- One or more bases repeated
9
Q
What is an inversion?
A
- A sequence of bases reversed
10
Q
What is a translocation?
A
- Sequence of bases moved either within the same chromosome or to a different chromosome
11
Q
Which mutations do not cause a frameshift?
A
- Substitution
- Inversion
12
Q
What 3 ways can mutagenic agents act?
A
1 - Act as a base -> chemical called base analogs can substitute for a base during DNA replication changing base sequence
2 - Altering bases -> some chemicals can delete / alter bases
3 - Changing structure of DNA -> some types of radiation can do this causing problems during DNA replication
13
Q
How do tumour suppressor genes usually act?
A
- Produce proteins that stop cells dividing, cause apoptosis or anchor cells in place
- Slow cell division
14
Q
What happens when tumour suppressor genes mutate?
A
- Protein not produced
- Cells divide uncontrollably causing a tumour
15
Q
How do proto-oncogenes usually act?
A
- Code for proteins that stimulate cell division
16
Q
What happens when proto-oncogenes mutate?
A
- Form oncogenes
- Overactive so cause uncontrolled cell division
17
Q
What are features of tumour cells?
A
- Irregular shape
- Larger and darker nucleus
- Different antigens
- Divide more rapidly
- Don’t produce all needed proteins
18
Q
What happens when tumour suppressor genes hypermethylated?
A
- Not transcribed
- Proteins not made
- Increase cell division
19
Q
What happens when proto-oncogenes hypomethylated?
A
- Act as oncogenes
- Increase in protein production
- Increased division
20
Q
What 3 ways can oestrogen increase the risk of breast cancer?
A
1 - Can stimulate breast cells to divide and replicate - increases chances of mutations
2 - If cells become cancerous - divide faster than usual
3 - Able to introduce mutations directly into DNA of certain breast cells
21
Q
What genes are permanently expressed?
A
- Those that code for respiratory enzymes
22
Q
What are stem cells?
A
- Undifferentiated cells that can specialise into other cell types
- Can self renew and differentiate
23
Q
How does differentiation occur?
A
- All cells have same genes - not all expressed
- In correct conditions some genes expressed - mRNA transcribed from specific genes
- Translated into proteins which modify the cell structure and processes
- Changes make the cell specialised
24
Q
What are totipotent stem cells?
A
- Form any body cell
25
What are pluripotent stem cells?
- Can become any embryonic cells - not placenta
26
What are multipotent stem cells?
- Can differentiate into a few cell types
27
What are unipotent stem cells?
- Can only produce one type of cell
28
What are cardiomyocytes?
- Heart muscle cells made from a unipotent stem cell
- Heart has regenerative capacity
29
How are adult stem cells used and features?
- From bone marrow etc
- Little risk to remove
- Less flexible - only multipotent
- Can use own stem cells - less risk of rejection
30
How are embryonic stem cells used and features?
- Produced by IVF
- After 4-5 days remove stem cells
- Rest destroyed
- More useful - pluripotent
31
What are iPS cells and how are they produced?
- Reprogram adult stem cells to be pluripotent - made to express transcription factors associated with pluripotency
- Factors introduced by modified virus - has genes for transcription factors
32
What are ethics about embryonic stem cells?
- Destroys potential foetus - wrong to destroy something that has the 'right to live'
- Fewer objections to unfertilised eggs that are artificially activated to divide
- Some think they should only use adult stem cells - but much less fluid
33
Describe totipotency in plant cells?
- Many plant cells can develop into other cells
- Can be grown in a test tube - cuttings - can form clones of genetically identical plants
- Plants have higher totipotency than animals
34
What is a plant callus?
- Mass of unorganised and undifferentiated plant cells cultured on agar gel medium
35
What is transcription controlled by?
- Transcription factors
36
How do activator transcription factors work?
- Binds to promotor region of the gene to be transcribed
- Help RNA polymerase bind in position (at start of gene)
- Gene transcribed, mRNA produced, protein made
37
How do repressor transcription factors work?
- Binds to promotor region of DNA - prevents RNA polymerase binding
- Gene not transcribed, no mRNA, no protein made
38
How does oestrogen affect transcription?
- Lipid soluble - diffuses through phospholipid bilayer
- Complimentary shape to receptor on transcription factor
- Forms oestrogen - oestrogen receptor complex - alters DNA binding site on transcription factor
- Factor now enters nucleus - binds to promotor region of DNA, activates transcription positioning RNA polymerase at the start of the gene
39
How does siRNA work?
- mRNA leaves nucleus to cytoplasm
- Double stranded siRNA associates with several proteins, unwinds - single strand binds to target mRNA
- Base sequence complimentary to target mRNA
- Associated proteins cut mRNA into fragments so it cannot be translated
- Fragments move to processing body which degrades them
- Similar process with miRNA in plants
40
In what organisms does miRNA work?
- mammals
41
How does miRNA work?
- Not fully complimentary to target mRNA
- Less specific so may target more than one mRNA molecule
- Associates with proteins and binds to target mRNA in cytoplasm
- miRNA-protein complex physically blocks translation of target mRNA
- mRNA moved to processing body - either stored or degraded
- When stored - can be returned and translated another time
42
Define epigentics
- Heritable changes in gene function without changes to the base sequence of DNA
43
What is epigenetic control?
- Determines whether a gene is expressed
- Attachment or removal of chemical groups (epigenetic marks) to or from DNA or histone proteins
- Don't alter base sequence, alter ease of transcription
44
How can epigenetics be inherited?
- Most epigenetic marks on DNA removed between generations - some escape and passed on
- Expression of some genes in offspring can be affected by environmental changes that affected their parents etc
45
What is a methyl and what does it attach to?
- CH3
- DNA
46
How does methylation work?
- Attaches to CpG site - where cytosine and guanine next to each other on a strand
- Increased methylation changes DNA structure so that transcriptional machinery (RNA polymerase etc) cannot bind
- No transcription - gene not expressed - protein not produced
47
What is an acetyl group and where does it attach?
- COCH3
- Histones
48
How does acetylation work?
- When acetylated - chromatin less condensed
- Enzymes and transcription factors can access DNA allowing transcription
- Less acetylated - more condensed - less transcription
- Histone deacetylase (HDAC) enzymes remove acetyl groups
