Chapter 20 - Gene Expression Flashcards
Define mutation
A sudden change in the amount or the arrangement of the genetic material in a. cell
Define gene mutation
A change to one or more nucleotide bases in DNA resulting in a change in genotype which may be inherited
When may gene mutations arise?
During the replication of DNA
What is a substitution of base?
A nucleotide in a DNA molecule is replaced by another nucleotide with a different organic base
What are the three consequences of base substitution?
- Formation of stop codon and hence protein synthesis stops
- Formation of different codon and different acid and hence a possible nonfunctional protein
- Formation of different codon but same amino acid so no effect
Define frame shift
Where a DNA base is deleted ands the reading frame containing each three letters is moved to the left by one
Define deletion of base
A loss of a nucleotide from a DNA sequence
Define and describe addition of bases
An extra base becomes inserted and frame shift to the right occurs unless n3 bases are inserted
Define and describe duplication of bases
Where one or more bases are repeated causing frameshift to the right
Define and describe inversion of bases
When a group of bases becomes separated and rejoins the DNA in inverse order causing a reversed effect on the amino acids
Define and describe translocation of bases
Where a group of bases become separated and inserted on a different chromosome causing abnormal phenotypes
Define and describe two mutagenic agents
- High energy ionising radiation which disrupt the structure of DNA
- Chemicals such as nitrogen dioxide disrupt the structure of DNA or interfere with transcription
Why may mutations be “good?”
They created genetic diversity necessary for natural selection and speciation
Why may mutations be “bad?”
They produce harmful effects and can disrupt cellular activities
What causes a cell to become specialised?
Expression of certain genes
Define totipotent stem cell
A cell derived from a fertilised egg able to differentiate into any type of cell found in the body and into embryonic cells
Why do cells specialise instead of expressing all genes?
Prevent wastage and to carry out functions more effectively
Give the two ways in which genes are prevented from expressing themselves
- Prevention of transcription (no mRNA)
- Prevention of translation
How do stem cells replenish themselves?
Self renewal
Give four origins of mammalian stem cells
- Embryonic stem cells
- Umbilical cord blood stem cells
- Placental stem cells
- Adult stem cells
Define pluripotent cell
Cells that can differentiate into almost any type of cell but cannot form extra embryonic cells
Define multipotent cell
Cells found in adults that can differentiate into a limited number of specialised cells. Examples include adult and umbilical cord stem cells
Define unipotent cell
A cell derived from multipotent cells that can differentiate into one type of cell
What are induced pluripotent cells?
Pluripotent cells created from unipotent cells by expressing genes which are currently not expressed
What is added to embryonic stem cells to cause them to differentiate in in vitro conditions?
Differentiation factors
What are transcriptional factors?
Molecules that bind to a specific site on DNA to begin the process of transcription
Describe how oestrogen regulates transcription
- Lipid soluble so freely diffuses into the cell membrane
- Binds to receptor on transcription factor and changes shape making it complementary/removes inhibitor
- Transcription factor moves into nucleus and binds to DNA to start transcription
What is epigenetics?
Heritable changes in gene function without changes to the base sequence of DNA
What is the epigenome?
The second layer found in DNA created by the chemical tags on histones
Why is the epigenome flexible?
The chemical tags on histones can respond to environmental changes
Describe how the epigenome is altered
- Environmental signal stimulates proteins to carry messages
- Protein passes this into nucleus
- Protein attaches to DNA causing acetylation or methylation
What is the effect of acetylation?
Activation of gene
Describe the consequence of less condense DNA-histone complexes
A weak association between DNA and histones leaving DNA accessible to transcription factors
Describe the consequences of more condense DNA-histone complexes
A strong association between DNA and histones leaving DNA not accessible to transcription factors
What is acetylation?
The process whereby an acetyl group is transferred to a molecule
How is DNA acetylated?
- Acetylecoenzyme A donates an acetyl group to DNA
What is the effect of deacetylation on DNA?
- Increases positive charge of histones
- Increases attraction to phosphate groups
- Association stronger
- Not accessible to transcription factors
What is methylation of DNA
Addition of methyl (CH3) to cytosine bases
How does methylation inhibit transcription?
- Prevention of transcription factors binding to DNA
- Attracts proteins that induce deacetylation making DNA inaccessible to transcription factors
How can methylation increase the chances of mutations?
- Some genes repair DNA
- Increased methylation leads to genes being switched off
- Protein that repairs damaged base sequences not produced
- Cancer is a consequence
What is small interfering RNA (siRNA)?
A type of RNA that destroys mRNA before translation
How is siRNA produced?
- Enzyme cuts large double stranded molecules of RNA into siRNA
How does siRNA prevent translation?
- After siRNA is produced, it combines with an enzyme
- Bases on siRNA bond with bases on mRNA
- Enzyme cuts the mRNA into smaller sections
- mRNA no longer capable of being translated
What are proto-oncogenes?
Cells that stimulate cells to divide by producing proteins that stimulate cell division
How do proto-oncogenes stimulate cell division?
- Produce proteins that stimulate cell division
- Activates genes that cause DNA to replicate
What are oncogenes?
Mutated proto-oncogenes that produce a permanently activated receptor or code for a growth factor in excessive amounts
What are tumour suppressor genes?
Cells that control cell division, cause the cell cycle to stop when damage occurs and programme apoptosis
What occurs when a tumour suppressor gene mutates?
Cell division is not regulated and cells divide rapidly and out of control
How does hypermethylation lead to cancer?
- Occurs in specific region of tumour suppressor genes
- Tumour suppressor gene inactivated
- Transcription inhibited
- Hence increased cell division occurs leading to a tumour
How can increased oestrogen concentration cause tumour formation?
- Oestrogen binds to transcription factor
- Activates genes that promote cell division
- Tumour forms
Why are genome projects useful?
- Understand inherited disease
- More understanding means more medicine and cures
- More predictions on likelihood of particular disease and so can avoid risk factors
- Understand evolution
Why is it easy to determine the proteome of a prokaryote?
- Majority of prokaryotes have one circular piece of DNA
- No noncoding portions of DNA
Why is it useful to know the proteome of pathogens?
So we can analyse the antigens and use this for vaccines
