3.8.2 Gene Expression Flashcards
1
Q
What are stem cells?
A
- undifferentiated cells
- that can specialise into other cell types
- can continually divide by mitosis
2
Q
What makes a cell specialised? (1 mark)
A
- different genes switched on or off
3
Q
What is a totipotent cell?
A
- can become any type of cell
- any body cell type AND extra-embryonic or placental cells
4
Q
What is a pluripotent cell?
A
- can become any body cell type
- so can make entire organism (eg late embryonic and fetal stem cells)
5
Q
What is a multipotent cell?
A
- more differentiated
- can become more than 1 cell type eg adult stem cells
- but not any cell
- eg hematopoetic stem cells in bone marrow
6
Q
What is a unipotent cell?
A
- specialised - can only become one cell type
- eg cardiomyocyte
7
Q
How are induced pluripotent stem cells produced?
A
- can be produced from unipotent cells (fully differetiated)
- unipotent cells genetically altered in a lab to become pluripotent
- involves adding protein transcription factors to switch on genes
8
Q
What makes a cell specialise? (Longer answer)
A
- proteins called transcription factors
- attach to a promoter region of the DNA
- the RNA polymerase enzyme can now bind
- forming a transcription initiation complex
- transcription can now begin
- transcription will only occur if all the transcription factors are present - how genes can be switched on
- mRNA produced during transcription and translated into a polypeptide at ribosomes
9
Q
What is a transcription factor?
A
- protein that moves from cytoplasm to DNA
- binds to a specific promoter
- leads to pre-mRNA production by allowing binding of RNA polymerase to DNA
10
Q
Advantages of treating a genetic disease with iPS
A
- use of iPS cells is long term
- less chance of rejection from immune response
- just a single treatment
- gene therapy can cause harmful side effects from using viruses
- disadvantage: continually dividing cells may cause cancer
- but low risk of cancer, cancer could be easily treatable
11
Q
Role of oestrogen in initiating transcription
A
- oestrogen diffuses through phospholipid bilayer
- oestrogen binds to its receptor on the transcription factor
- this changes the shape of the transcription factors, changing the shape of the DNA binding site
- the transcription factor enters the nucleus via nuclear pores and binds to its complementary promoter site on DNA to stimulate transcription of the gene
- (mRNA is produced and then translated at the ribosomes so the gene is expressed- switched on)
12
Q
What type of hormone is oestrogen?
A
Steroid
13
Q
Role of RNA interference in inhibition of translation
A
- RNA dependent RNA polymerases (RDRs) produce double stranded (ds) RNA molecules from mRNA
- an enzyme cuts the ds RNA into small sections - small interfering RNA (siRNA)
- one of the two siRNA strands combines with a complex of molecules (RISC) which cuts the mRNA. Requires energy from ATP hydrolysis
- siRNA guides RISC complex to any mRNA complementary to the RISC so that it can’t be translated into a protein. Gene isn’t expressed
14
Q
What are the uses of siRNA
A
- block disease causing genes and prevent disease
- to identify the roles of genes in a biological pathway
15
Q
What is epigenetics?
A
- heritable changes in gene function caused by environmental factors
- without changing the DNA base
16
Q
Summary of methylation and acetylation
A
- methylation mutes - gene off. Cytosines
- acetylation activates - gene on. Histones
17
Q
Acetylation explanation
A
- histones more negative
- decreased attraction to DNA
- DNA more losely packed/less condensed
- DNA more accessible to transcription factors
- transcription occurs - RNA polymerase binds
- gene switched on
18
Q
De-acetylation of DNA
A
- histones more positive
- increased attraction to DNA
- DNA more tightly packed/less condensed
- DNA inaccessible to transcription factors
- no transcription occurs
- gene switched off
19
Q
Methylation of DNA nucleotides explanation
A
- methyl group (CH3) added to cytosine
- this makes DNA inaccessible to transcription factors
- RNA polymerase can’t bind
- gene switched off
20
Q
Un- methylated DNA explanation
A
- DNA more accessible to transcription factors
- RNA polymerase can bind
- gene switched on
21
Q
How can methylation cause cancer?
A
- Methylation of tumour suppressor gene
- methylation prevents transcription of a gene
- protein which prevents cell divison or causes cell death (apoptosis) is not produced
- no control of cell division or mitosis
22
Q
Another mutation causes cancer
A
- proteins not produced
- cancer cells have faulty DNA
- cells with faulty DNA divide
- uncontrolled cell division produces cancer
23
Q
How can transcription factors be used to reprogram cells
A
- attach to gene promoter region
- stimulate/inhibit transcription
