Section 8- Gene expression Flashcards
What are mis-sense mutations?
Incorrect amino acid which may produce a malfunctioning protein
What is a nonsense muation?
STOP codon
Truncates protein into something smaller
What is a silent mutation?
Not harmful
What is a base duplication?
A number of bases are repeated causing a frameshift to the right
What is a base inversion?
A number of bases are reveresed
What is translocation mutation?
A number of bases are removed from one chromosome and become inserted in a different gene
What is a whole chromosome mutation?
Insertion of another chromosome
What are the effects of mutations?
Production of new advantageous protein = gain of reproductive advantage
Neutral mutation = no change
Production of disadvantageous protein = fatal or disease causing
What is a stem cell?
An undifferentiated cell
What is stem cell diferentiation?
Specialising cells
Replaces dead or damaged cells throughout the life of the organsim
What does totipotent mean?
A fertilised eff has the potential to form every type of human cell
What does pluripotent mean?
Capable of producing all cells derived from a particular germ layer
Restricted number
What is multipotent?
Can make a restricted range of related cell types
What is unipotent?
Able to make only one cell type
What happens with stem cells in plants?
Maintain totipotency in form of meristem cells
Cutting/ tissue culture can be used to produce whole plants or plant organs under the right growth conditions
What percentage of genes are being used at any one time?
3-5% of their genes at any given time
What are transcription factors?
Proteins which move in from the cytoplasm and bind to DNA at specific sites
What is a promoter region?
The specific site on DNA which transcription factor binds to
How do transcription factors activate a gene?
Allow RNA polymerase to attach to the DNA chain and start transcription
What is transcription initiated by?
RNA polymerase AND transcription factors binding to the DNA
What are transcription factors activated by?
Stimulated by hormones or growth factors
How does oestrogen stimulate the expression of a gene?
Oestrogen is lipid soluble so diffuses through membrane
It combines with receptor site on the transcription factor (complementary binding)
Causes change of shape to the transcription factor causing it to release the inhibitor molecules
Transcription factor enters the nucleus through a nuclear pore and combines with DNA activating transcription
What are epigenetics?
It is the study of heritable changes in gene function that do not involve changes to the base sequence of DNA
What is the epigenome and what it is determined by?
It is the combination of chemical tags present on DNA
Determined by environmental factors
What do histones allow for?
Allow eukaryotic DNA to coil and condense
What happens if DNA is tightly wrapped around histones?
Genes are inaccessible for transcription
Epigenetic silencing
What happens is DNA is loosely wrapped around histones?
Genes are accessible and easily transcribed
What is acetylation?
Adding of acetyl group to histone group
Leads to activation of genes causing DNA to uncoil
Switches gene on
What happen when acetyl groups are removed?
Gene is inactivated
DNA coils slightly
Gene switched off
What is hypo-methylation?
Hypo (low) methylation increases transcription
Of cytosine
What is hyper-methylation?
Hyper (high) methylation inhibits transcription
Of cytosine
What can cancer be associated with?
Reduced DNA methylation of proto-oncogenes which oncogenes
Increased methylation of promotor regions causing deactivation of tumour suppressor genes
What are oncogenes?
Acts to promote tumour growth
Mutated proto-oncogenes
What are tumour suppressor genes?
Prevents formation of tumour by preventing cell cycle
Control cell division by inhibiting the proto-oncogenes, repairing DNA and activating cell death
How can diseases be treated with gene expression?
Enzymes involved in acetylation or methylation inhibited
How can disease be diagnosed with gene expression?
Relies on detection of levels of methylation and acetylation relative to ‘normal’ levels
What is the effect of siRNA on gene expression?
- Enzyme cuts double-stranded molecules of RNA into siRNA
- siRNA combines with enzyme and is broken down in to separate strands
- siRNA molecule guides enzyme to mRNA molecule by complimentary base pairing
- Enzyme cuts mRNA into smaller sections
mRNA can no longer be translated into polypeptide
Gene is not expressed
What does siRNA stand for?
Small interfering RNA
What are carcinogens and what do they do?
Cancer causing agents
Cause changes to genes that control cell division
What are benign tumours?
Grow slowly but can get very large
Tend to remain as a distinct structure and only affect a specific part of the body
Less likely to be life threatening but can disrupt functioning of organs
Can be removed by surgery alone
What are malignant tumours?
Grow rapidly and can get very large
Tend to extend into surrounding tissues
Develop own blood and lymph systems
May spread to other areas of the body by metastasis
Treatment may involve radiotherapy and chemotherapy as well as surgery
What are proto-oncogenes and what do they control?
Stimulate cells division and control rate of cell division
A specific proto-oncogene needs to be switched on by a growth factor or hormone to cause cell to grow and divide
What can a proto-oncogene mutate into and what is the result?
Can mutate into an oncogene
Results in gene activation in the absence of a growth factor
One copy of a mutated proto-oncogene is enough to stimulate cells to divide out of control
What can a tumour suppressor gene mutate into?
Can become inactivated
Allows rate of cell division to increase or DNA not to be replicated
Both copies of the gene need to be mutated to cause cancer
What are induced pluripotent stem cells?
Type of pluripotent cell that is produced from unipotent stem cells
Body cells are genetically altered in a lab to make them have characteristics of embryonic stem cells
No need for embryos
All possible type of specialised cells
What is the human genome project?
Aim:
To identify all genes in human DNA
Find where each gene is located
Determine sequence of bases
What was the estimated cost and time of the human genome project?
Time = 15 years - took 13 years
Cost = $3 billion
What is whole-genome shotgun sequencing?
When researchers cut DNA into small easily sequenced sections and use a computer algorithm to align overlapping segments
What is whole-genome shotgun sequencing and how is it used to sequence DNA?
Involves researchers cutting the DNA into many small, easily sequenced sections
Then using computer algorithms to align overlapping segments to assemble entire genome
What are single nucleotide polymorphisms (SNPs)?
Single-base variations in the genome that are associated with disease and other disorders
Why is it easy to determine the proteome of prokaryotes?
No introns
Only one circular piece of DNA, not associated with histones
How can the methylation of tumour suppressor genes lead to cancer?
No transcription due to methylation
No control of mitosis
Protein produced prevents cell division
What is methylation?
Attracting enzymes that can add or remove methyl groups to cytosine
What is the DNA-histone complex?
Where the association of histones with DNA is weak, the DNA-histone complex is less condensed
DNA is accessible by transcriptional factors
Can initiate production of mRNA, switch on the gene
How can hypomethylation cause cancer?
Reduced methylation
Occurs in oncogenes, leading to their activation
How can increased oestrogen in menopausal women cause cancer?
Release inhibitor molecule that prevents transcription causing proto-oncogenes to develop into oncogenes
Oncogenes increase rate of cell division leading to development of a tumour
What is the process of genome sequencing?
Extract samples of DNA from cells
Cut DNA into sections of varying lengths
Amplify DNA
Sequence short sections of DNA
Place sections in order by matching overlapping regions
Why would siRNA only affect gene expression in cells infected with HIV?
Only infected cells contain mRNA
What are 2 ways in which the structure of siRNA differs from mRNA?
siRNA is double stranded
siRNA is smaller
