genetics of living systems Flashcards
4 ways genes are regulated
- Transcriptional - genes turned on and off
- post transcriptional -mRNA can be modified which regulates translation of certain proteins
- translational - can be stopped or started
- post translational - proteins can be modified after translation in other organelles
TRANSCRIPTIONAL CONTROL
- 3 different methods
- Chromatin remodelling
- Histone modification
- trancription factors (lac operon in bacteria)
Chromatin remodelling
what is heterochromatin?
HETEROCHROMIN
—> TIGHTLY wound DNA
—>causes chromatin to be visible during cell division
—> no transcription as RNA polymerase cant access genes
—> ensures NO PROTEIN SYNTHESIS DURING DIVISION
Chromatin remodelling
What is euchromatin?
EUchromatin
—> loosely wound DNA
—> can be freely transcribed
Chromatin remodelling
why is it used?
ensures protein synthesis only occurs during interphase
—> as it is time + energy consuming
Histone modification
histones can be modified to increase/decrease degree of DNA packing
histones are positively charged, DNA is negatively charged
how to cause DNA to coil less tighly
ACETYLATION- addition if acetyl group
PHOSPHORYLATION- addition of phosphate group
—> these reduce +ve charge on histones
—> increased repulsion
=> allows certain genes to be transcripted
how to cause DNA to be bound more tightly
METHYLATION- addition if methyl group
—>makes histones more hydrophobic
—>DNA coils more tighly
—> prevents transcription
what is epigenetics?
external control of gene expression by modificstion of DNA
LAC OPERON
type of genes in lac operon
structural genes
LAC OPERON
genes in lac operon
lacZ - gene codes for enzyme that breaks down lactose
lacY - gene codes for channel protein to allow lactose into bacterium
lacA - idgaf
LAC OPERON
why do bacteria need operons?
-more common in prokaryotes as they are more simple/small structure
=> efficient way of saving resources bc if gene products arent needed, all of genes involved in production can be turned off
LAC OPERON
what gene codes for the repressor?
regulatory gene —> lacI
repressor gene function
codes for repressor protein( transcription factor)
which binds to the OPERATOR
RNA POLYMERASE cant carry out
transcription
LAC OPERON
when lactose is present
- lactose binds to repressor protein which inactivates it
- repressor cant bind to operator anylonger
- RNA polymerase can bind to PROMOTER and carry out transcription
- three structural genes are synthesised
role if Cyclic AMP (cAMP)
RNA polymerase carrys out transcription slowly
needs to be increased to prod right amount of proteins
—> cAMP binds to cAMP receptor protein (CRP)
- activates CRP
which increases transcription rate
role of cAMP
when glucose is low
high lvls of cAMP produced
- more cAMP - CRP compexes
- more freq transcription
POST TRANSCRIPTIONAL CONTROL
splicing
after transcription pre mRNA is made
=> cap added to 5’ end
=> poly adenine tail added to 3’ end
HELPS KEEP mRNA STABLE
SPLICING CAN TAKE PLACE
to make multiple different proteins from one gene
—>introns ( non coding parts) cut off and removed
—> exons (coding parts)joined together
POST TRANSCRIPTIONAL CONTROL
RNA editing
change nucleotide base SAME CHANGES AS MUTATION - addition -deletion - substitution
TRANSLATIONAL CONTROL
3 methods
mRNA degradation
-more resistant molecule the longer it will last
POST TRANSLATIONAL CONTROL
modifications to proteins
Mutation
change in sequence of bases in dna
types of mutations
substitution
deletion
insertion
mutations
substitution?
single nucleotide changes in a codon
=>change in codon
=> may cause change in primary structurr
=> degenerate nature of DNA means codon could still code for the same amino acid
