A2 gene expression (topic 8) Flashcards
house keeping genes def
genes that are essential for survival that are always switched on
eg respiration
totipotent cells (stem cells)
can divide and produce ANY type of body cell
found in the blastomere of an embryo at an early stage
pluripotent cells (stem cells)
can divide into MANY different types of cells
often used to replace damaged tissues in human disorders
multi potent cells (stem cells)
can divide into A LOT of cells
stem cells general def
undifferentiated cells that keep dividing to give rise to other cell types.
regulating gene expression at transcription
(and oestrogen example)
transcription factors => proteins move in from the cytoplasm and bind to DNA promoter region
this stimulates RNA polymerase to join and start transcription / or stops it
OESTROGEN:
- lipid soluble so can freely diffuse across cell membrane into nucleus where it binds to a receptor molecule on a transcription factor.
- this alters the shape of the DNA binding site on the transcription factor and makes it able to bind to the DNA
- stimulates the transcription of the gene that makes up the DNA
regulating gene expression at translation (small interfering RNA)
siRNA switches off genes short term. it binds to a complementary sequence of mRNA.
mRNA is usually single stranded so the cell detects this double serenaded form as abnormal, and enzymes break it down, preventing translation
epigenetics def (+ dna methylation and acetylation)
heritable changes in gene function without changes to the base sequence of DNA (environmental factors can make changes to the functions of inheritable genes)
DNA methylation => methyl groups are added to cytosine bases. it modifies function of DNA, typically acting to inhibit gene transcription (it prevents transcription factors binding to dna and stimulates decreased acetylation of histones).
DNA acetylation => decreased acetylation (taking COCH3 off) increases histones +ve charge, so they bind to DNA more tightly. this means transcription factors can’t access the DNA so the gene is switched off.
eukaryotic DNA (info about it being wrapped around histones)
if DNA is wound tightly around histones, gene is effectively switched off.
if it’s loosely wound, gene may be switched on so it can be transcribed into mRNA and translated
what is epigenome
chemical ‘tags’ that can attach to DNA and histones
they affect how tightly wound the DNA is around the histones
flexible system so it changes in response to environment and current cell needs
mutations types (6 of them)
insertion / deletion => one or more nucleotide pairs are inserted or deleted from the sequence (causes a frame shift)
substitution => a nucleotide is changed (degenerate code so not major)
duplication => one or more bases repeated (causes frame shift)
inversion => group of bases separated from the DNA sequence and rejoin at the same point but in reverse order
translocation => group of bases separated from DNA sequence and inserted back in on another chromosome (leads to significant effects on phenotype)
causes of mutations
chemical mutagens => alcohol, benzene, asbestos and tar
ionising radiation => alpha, beta, UV and X-ray
spontaneous errors => in DNA replication
proto-oncogenes def
stimulate cell division => by producing proteins that stimulate division, can cause cancer if mutated
can also stimulate apoptosis
oncogenes def
formed from mutated proto-oncogenes
permanently switched on so cell division is uncontrolled.
permanently activates a cell surface receptor or coding for a growth factor
mutated tumour suppressor genes
can become inactive so cell division doesn’t stop
- due to methylation
inactivates the gene as it stops transcription
