20. Gene Expression Flashcards
Describe what is meant by substitution of bases.
- nucleotide is ‘swapped’
- may cause STOP codon stopping translation of polypeptide
- ## may result in a change in one amino acid, may not - degenerative code
What is meant by frame shift?
- entire sequence moves to left (or right)
- sequence from that point on is wrong
When does frame shift occur?
- deletion of base
- addition of base
- duplication of base
What is meant by inversion mutation?
Group of bases separates from one sequence of DNA and rejoin in inverse order.
What is meant by translocation mutation?
Bases separate and join a different one.
What is meant by mutagenic agents?
Something that increases rate of mutation
Name two types of mutation agents, give examples.
High energy ionising radiation
- a/b partials
- X-ray
- UV
Chemicals
- nitrogen dioxide
- benzopyrene, inhibits tumour suppressor gene
Give 5 types of mutations
- substitution
- addition/ deletion
- duplication
- inversion
- translocation
What is meant by cell differentiation
The process of cells becoming specialised, suited for specific role
What are the four types of stem cells?
- totipotent
- pluripotent
- multipotent
- unipotent
Where are totipotent cells found
Early embryos (no later that 16 days)
Where are pluripotent cells found?
Embryos
What two types of stem cells are found in bone marrow?
Multipotent
Unipotent
What are ethical issues with using pluripotent cells in research and treating human disorders?
How are they overcome?
Use of pluripotent involves killing of embryos
Induced pluripotent cells (IPC)
- genes that have been ‘switched off’ during differentiation are switch back on using transcription factors
What is a carcinogen?
chemicals that can alter the structure of DNA and interfere with transcription.
What is the role of transcription factors?
‘switches on gene’ binding of TS factor and DNA initiates transcription
What is the role of hormones in the action of transcription factors?
give an example.
Activate DNA binding site of transcription factors
oestrogen
How is oestrogen specific to its function? (activating transcription factor)
- lipid soluble, enter cytoplasm easily
- complementary shape to receptor on transcription factors
Describe how a hormone can switch on a gene and start transcription.
- oestrogen diffuses into cytoplasm
- oestrogen binds to receptor on transcription factor
- DNA binding site changes shape, now complementary to DNA
- transcriptional factor can now enter nucleus through nuclear pore
- binding of transcriptional factor with DNA stimulates transcription of gene.
What is meant by epigenetics?
Environmental factors cause changes in gene function without altering DNA base sequence.
What is meant by epigenome?
shape of DNA-histone complex, describes ‘tags’ (acetyl and methyl)
Explain the impact that decreased acetylation has on transcription.
Decreased acetylation inhibits transcription.
- Histones become more positive, more attracted to the phosphate group of DNA
- Histones are strongly associated with DNA, transcription factors unable to bind
How does methylation inhibit transcription?
- Methyl group prevents transcription factors from binding to cytosine group
- Attracts proteins that condense DNA-histone complex
Cancer is caused by…
mutations is genes that regulate mitosis.
What are oncogenes?
mutated proto-oncogenes, can be permanently activated, cells divide continuously.
What do proto-oncogenes code for?
proteins involved in initiation of DNA replication and mitosis
What is the role of tumour-suppressor genes?
- slow down division
- cell death
… if DNA copying error is detected, identifying and destroying mutated cells
Describe benign tumours. (3)
- grow at slow rate
- non-cancerous
- adhesion keeps cells together in capsule, remains localised
Describe malignant tumours. (4)
- grow rapidly
- cancerous
- metastasis occurs due to no adhesive, spreads across body
- recurrence likely
Explain how the menopause can be linked with breast cancer.
No oestrogen being produced in ovaries, fat cells in breast produce it instead. High (localised) concentration can lead to breast cancer.
Oestrogen can bind to genes to initiate transcription, if proto-oncogene is activated, (= oncogene), tumour will develop.
knock on effect larger tumour = more oestrogen
Genome
entire genetic material of an organism (contained in nucleus)
What is meant by ‘sequencing genomes’?
working out entire base sequence for all DNA in cell
Why are simpler organisms’ genomes easier to sequence?
does not have introns or regulatory genes,
How can DNA sequencing be used to fight disease?
genome of simple organisms can be used to sequence their proteome.
proteome can be used to identify potential antigens to use in vaccines
How can translocation be inhibited by siRNA
- enzyme breaks down RNA into siRNA
- siRNA binds to enzyme
- siRNA takes enzyme to mRNA and attaches to it (complementary base pair)
- enzyme breaks down mRNA, cannot be translocated
