Gene expression Flashcards
What is a gene mutation
A change in the base sequence of DNA
What is a mutagenic agent
A factor that increases the rate of mutation
How can a gene mutation lead to production of a non functional enzyme/protein
Changes sequence of base triplets so codons on MRNA
Changes sequence of amino acids
Changes position of all bonds
Changes tertiary structure
Enzymes specific - active site changes, substrate cannot bind
Different gene mutations
Substitution - base is replaced
Addition - base is added
Deletion - base is lost
Duplication - base is repeated
Inversion - a sequence of bases detaches and rejoins in the same position in the reverse order
Transolcation - sequence of bases detach and inserted in a different location within the same chromosome
Explain why not all gene mutations affect order of amino acids
Some substitutions only change 1 triplet code
Genetic code is degenerate
Some mutations occur in introns which don’t code for AA so are removed through splicing
Explain why a change in amino acid sequence is not always harmful
May not change tertiary structure
May give a selective advantage
What is a frameshift
Mutation changes the number of nucleotides by a number not divisible by 3
Shifts the way genetic code is read
How can mutations lead to production of shorter polypeptides
Deletion or translation
What are stem ce;;s
Unspecialised cells capable of dividing by mitosis and differentiating into other cells
Totipotent cells
Occur in embryos
Can divide and diffrentiate into any type of body cell
Pluripotent cells
Found in embryos
Can divide and diffrentiate into most types of cells
Multipotent cells
Found in mature mammals
Can divide and diffrentiate into limited cell type
Unipotent cells
Only one cell type
How can stem cells be used to treat human disorders
Translated into patients to divide in unlimited numbers
Then diffrentiate into required healthy cells
What are transcription factors
Proteins which regulate the transcription of target genes by binding to a specific DNA base sequence on a promoter region
How can transcription be regulated using TF
Move from cytoplasm to nucleus
Bind to DNA at specific base sequence on promoter gene
inhibits or promotes transcription by allowing DNA polymerase to bind
How does oestrogen affect transcription
Diffuses into the cell and oestrogen binds to its receptor (an inactive TF)
This changes the shape of the inactive TF forming an active TF
This diffuses into the nucleus and binds to a specific DNA base sequence on the promoter region
This stimulates transcription of target gene forming MRNA by helping RNA polymerase bind
Explain why oestrogen only affects target cells
Other cells don’t have oestrogen receptors
What is epigenetic
Heritable changes in gene function without changing the base sequence
Caused by environmental factors
What is the epigenetic control in inhibiting transcription
increased methylation
Decreased acetylation
What is the epigenetic control in allowing transcription
Decreased methylation
Increased acetylation
How can methylation inhibit transcription
Increased methylation
DNA wrapped more tightly around histones
Preventing TF and DNA polymerase binding
How can acetylation inhibit transcription
Decreased acetylation of histones increases positive charge of histones
So histones bind to DNA as it is more negatively charged more tightly
preventing TF and DNA polymerase binding
Explain the relevance of epigenetics on disease development and treatment
Environmental factors (eg. diet, stress, toxins) can lead to epigenetic changes
● These can stimulate / inhibit expression of certain genes that can lead to disease development
○ Increased methylation of DNA OR decreased acetylation of histones inhibits transcription
○ Decreased methylation of DNA OR increased acetylation of histones stimulates transcription
● Diagnostic tests can be developed that detect these epigenetic changes before symptoms present
● Drugs can be developed to reverse these epigenetic changes
What is RNA interference
Inhibition of translation of MRNA produced from target genes by RNA molecules
This inhibits expression of a target gene
Describe the regulation of translation by RNA interference
SIRNA bind to a protein
It is synthesised as double stranded RNA
Single stranded SIRNA binds to target MRNA on complementary base sequence
Leads to hydrolysis of MRNA into fragments
Preventing transaltion
How to tumours form
Mutations in DNA can lead to uncontrolled cell division
Mass of abnormal cells - tumour
Function of tumour suppressor genes
They code for proteins that slow the cell cycle or cause apoptosis for tumour cells
Explain the role of tumour suppressor genes in the development of tumours
A mutation in DNA base sequence can lead to the production of a non functional protein by changed AA sequence
Decreased acetylation of increased methylation prevents:
- Production of protein
- Polymerase and Tf binding so inhibits transcription
-Leads to uncontrolled cell division
Function of proto Onco genes
Stimulate cell division
Role of oncogenes in development of tumours
Mutation in DNA leads to overproduction of a protein
Decreased methylation or increased acetylation increases production of protein
Stimulates RNA polymerase to bind
Stimulates transcription
Uncontrolled cell division
