Gene Expression (Chapter 20) Flashcards
Define Substitution Mutation
Replacement of a base by a different base
Define Mis-Sense Mutation
Incorrect amino acid inserted
Define Nonsense Mutation
Stop codon produced early
Define Silent Mutation
Same amino acid coded for due to degenerate code
Define Deletion Mutation
A base is deleted which causes a frame shift which alters the following triplet codes so there are incorrect codons and an incorrect amino acid sequence.
What happens when there is a change in amino acid sequence?
Change in H, Ionic bonds and disulphide bonds so tertiary structure is altered so a non functional protein/enzyme is formed (no enzyme-substrate complex formed)
What are stem cells?
Undifferentiated cells
Why are stem cells used in treatment?
- Produce normal/healthy polypeptide
- No faulty or defective polypeptide produced
- Stem cells continuously divide
Define Epigenetics
Heritable changes in gene function without changes to the base sequence of DNA.
How does SIRNA prevent translation?
- SiRNA binds to/destroys mRNA
- Prevents translation of CENP-W
- Reduces protein production
What is a tumour?
Mass of unspecialised cells formed by uncontrolled cell division.
How do tumours cause harm?
Damage organ concerned, form blockages or place pressure on other organs.
Why is cancer more common in older people?
Cancer takes time to develop and immune system is less effective on older people.
What is a benign tumour?
Cannot spread to other parts of the body and cannot invade neighbouring tissues.
How does methylation cause cancer?
1) Methyl group can be added to both copies of a tumour suppressor gene.
2) The transcription of tumour suppressor genes is inhibited.
3) Protein is not produced which prevents cell division.
4) Uncontrolled cell division/no control of mitosis
How does sunbathing cause cancer?
Suns radiation contains ultra violet radiation (mutagenic agent) that causes the mutation of genes which controls division.
Fair skin has less melanin that protects against UV radiation.
Why is it important to destroy all cells of a tumour?
Cells can break off (metastasise) and remaining cells can divide and form new tumour.
Describe the stages of altered DNA leading to cancer
1) DNA altered by mutation
2) Changes base sequence of gene controlling cell growth/oncogene or of tumour suppressor gene
3) Change protein structure of protein they code for
4) Tumour suppressor gene produces protein which inhibits cells division, therefore cannot do if mutated
5) Leads to mitosis so uncontrolled cell division.
Describe totipotent cells
Can divide and produce any type of body cell by only translating part of their DNA.
Where are pluripotent cells found?
Embryos
Where are multipotent cells found?
Adult mammals
Where are unipotent cells found?
Adult mammals
Describe pluripotent cells
Can self-renew and differentiate into any type of cell except the cells that make up the placenta.
Describe multipotent cells
Can only differentiate and divide into a limited number of cell types
Describe unipotent cells
Can only differentiate into a single type of cell e.g. cardiomyoblasts can only differentiate into cardiomyocytes.
Describe induced pluripotent cells
Unipotent stem cells that have been reprogrammed to become pluripotent by using protein transcription factors to express genes associated with pluripotency
