Topic 7.2 Gene Expression Flashcards
What is the significance of coiling of histones?
Coiling makes DNA less accessible
What are enhancer regions
They are found further away from gene
And tend to make DNA more or less condensed = accessible for transcription(affect binding with DNA/RNA polymerase)
What are transcription factors? (1 mark)
Protein That Controls transcription of genes (by binding to DNA)
That enhances/suppress DNA expression
How do transcription factors work?
Enter nucleus from cytoplasm
Bind to DNA near target gene
Either increase or decrease rate of transcription
What is the promoter region
Found closer to gene
Enable binding of RNA polymerase - promote transcription
What is epigenetics?
Heritable and reversible modifications to DNA without involving changes to nucleotide sequence
How can a transcription factor increase rate of glycolysis? (3 marks)
- switch on gene expression
- bind to promoter region - stimulate protein synthesis
- for enzymes involved in glycolysis
What are nucleosomes?
Cluster of histones(8 of them)
How to enhance transcription?
- DNA demethylation
- histone acetylation
How does DNA methylation work? How?
- silences sequence of genes
- by adding methyl group (by phosphodiester bond) (usually to Cytosine on CpG site)
- histones are more packed = less accessible for transcription
- stops transcription factors from binding to promoter region
So opposite promotes transcription
How does histone acetylation increase transcription?
- reducing positive charge of histone proteins, reduce histone acetylation
- (dna is negative charge)
- less charge difference hence attraction
- so more available for transcription
State the meaning of the term DNA methylation. (1 mark)
A methyl group added to a CpG site (usually cytosine next to a guanine)
Why is DNA methylation essential in growth of embyro? What happens when? (3 marks)
- level of DNA methylation increases after blastocyst stage
- because genes are switched off, cannot be transcribed
- causing cells to become differentiated
What is splicing?
Removing introns and joining exons (from pre-mRNA)
Cutting mRNA for gene to be synthesised into protein
What is meant by epigenetics?
Heritable change in gene function without change to base sequence DNA
What is a CpG site?
Cytosine next to Guanine
Where methyl group can attach to for methylation to silence gene expression
Why can different polypeptide products (proteins) result from the same gene?
Post transcription modification of mRNA
What enzyme performs splicing of pre mRNAs?
Spliceosomes
How does the addition of transcription factor / hormone causes the human gene to be switched on?
- interaction on cell membrane
- TF activated after binding to specific gene sequences
- mRNA produced, RNA polymerase used
Explain how a cell differentiates into either X cell or Y cell. (4 marks)
- by epigenetic modification
- like DNA methylation or histone acetylation
- genes needed in both cell types turn on
- genes needed in one but not the other cell type switches off
- causing proteins to be made that are specific to the cell type
Explain why stem cells are used to produce vaccines rather than bone marrow cells. (2 marks)
- stem cells are pluripotent
- so can divide into wider range of cell types
Where are pluripotent cells obtained from?
Late embryo
Describe how iPS cells can be produced. (3 marks)
- fibroblasts are used
- specific genes are put into cells
- eg Oct4, Sox2
- using vector / virus
How can iPS cells be used to cure a genetic disease in the retina involving dysfunctional cells? (2 marks)
- replace dysfunctional cells with funcitonal cells derived from iPS cells
- iPS cells are injected into the retina then develops into normal retinal cells
The tissue formed by an embryonic cell is called the ‘fate’ of the cell.
Explain how the scientist could identify the fate of the repositioned cell. (2 marks)
- examine cells from different tissues under a microscope
- cells descended from repositioned cell are fluorescent due to traces of dye injected
The tissue formed by an embryonic cell is called the ‘fate’ of the cell.
Explain how a scientist can figure out if a cell has changed its fate. (2 marks)
- cell would still be pluripotent
- so cell signalling in the new position could determine the fate of the cell
- causing activation of TF for transcription of genes (relevant to the new position)
- leading to synthesis of proteins into diff tissues
Describe the differences between totipotent, multipotent and pluripotent stem cells during the development of an embryo. (3 marks)
- zygote/morula are totipotent stem cells as they give rise to all cell types
- blastocyst contain pluripotent cells, they give rise to most cell types
- cells in developing embryo are multipotent, can only become some cell types
Why is DNA methylation involved in the development of an embryo? (2 marks)
- genes silenced, cannot be transcribed
- so cells become differentiated
How is DNA demethylation involved in a conversion of cells? (2 marks)
- demethylation results in gene being activated
- so transcription gene takes place, producing protein that causes change in fibroblast cells
