7.2 transcription and gene expression Flashcards
transciption direction
5’ to 3’
strcutrure of nucleosomes
- eukaryotic DNA wrapped around 8 histone proteins
- histone proteins have protruding tails – determine how tigthly the DNA is packaged
- histone tails pos charge, associate w neg charge DNA
modification of histone tails to increase transcription
add an acetyl group to the tail = neutralises charge = DNA less tightly coiled
modification of histone tail to reduce transcription
add a methyl grp to tail = maintain pos charge = more coiled DNA
2 types of chromatin
- hetero chromatin (methylation)
supercoiled DNA, not accessible for transcription - eu chromatin (acetylation)
DNA is loosely packed, accessible for transcription machinery
increased direct methylation of DNA
decreases gene expression
(prevents binding of transcription factors)
- genes that r not transcribed exhibit more dna methylation
possible causes of changes to DNA methylation
- parental genes
- maternal diet during pregnancy
- environmental
- infant exposure to microbes
- diet
- lifestyle
- old age related changes
define epigenetics
the study of CHANGES in PHENOTYPE as a result of VARIATION in GENE EXPRESSION LEVEL
epigenetic analysis shows … point+3
DNA methylation patterns may change over the course of a lifetime
- influcened by heredity
- diff cell types diff DNA m patterns
- environmental factors
transcription defintiion
process by which DNA sequence is copied into a COMPLEMENTARY RNA sequence by RNA POLYMERASE
3 stages of transcription
- inititation
- elongation
- termination
transcription 1st stage initiation
RNA polymerase binds to the promoter and causes the unwinding and separating of the DNA strands (in rep its helicase)
transcription 2nd stage elongation 4
- RNA polymerase moves along the coding sequence
– Free nucleotides exist in the cell as ribonucleoside triphosphates (NTPs), which line up opposite their complementary base partner
– RNA polymerase covalently binds the NTPs together in a reaction that involves the release of the two additional phosphates
– Synthesising RNA in a 5’ → 3’ direction
transcription 3rd stage termination
RNA polymerase reaches the terminator, both the enzyme and nascent RNA strand detach and the DNA rewinds
the literal only thing that is used in transcription
RNA polymerase
template strand in transcription: read from
3’ to 5’
syntesis of RNA strand from template strand in transcirtion:
5’ to 3’
- 5’ phosphate linked to 3’ end of growing mRNA strand
3 post transcriptional events to form mature mRNA
- Capping
- Polyadenylation
- Splicing
CHILD PROTECTIVE SERVCEIS
post transcriptional dolling up! capping – what is it and which end
- Addition of a methyl group to the 5’-end of the transcribed RNA
function of methylated cap in capping
- Provides PROTECTION against degradation by exonucleases
- Allows the transcript to be RECOGNISED by the cell’s TRANSLATIONAL machinery (e.g. nuclear export proteins and ribosome)
post transcriptional modification like a car vroom: poly ade nylation WHAT and WHERE
- Addition of a long chain of adenine nucleotides (a poly-A tail) to the 3’-end of the transcript
FUNCTION of poly-a tail (poly ade nylation)
- Improves the STABILITY of the RNA
transcript - FACILITATES the EXPORT of RNA transcript from the nucleus
splicing?? in post trascriptional hee hees. hint its what it says on the tin
- non coding sequences (introns) must be removed
- coding regions (exons) fuse tgt to form continuous after introns removed
- introns = intruding sequences VS exons = expression sequences
alterantive splicing uh oh
- selective removal of specific exons !!! (coding/expressing sequence)
= formation of diff polypeptide
what are coding genes and non coding genes called (in splicing after transcription)
exons (expressing sequences)
introns (intruding sequences)
gene expression can be regulated by proteins that …
theres TWO groups sike
they mediate binding of RNA poly (the thing that does transcripton) to the promoter
- transcription factors (promotor)
- regulatory proteins (outside proomotr)
how do transcription factors regulate gene expression
these bitches are proteins by the way. they are helpful! they kick start transcription i think
- they form a complex with RNA polymerase at the promotor – cannot initiate transcription without them
how do regulatory proteins regulate gene expression. there are 2 types
bind to sequences OUTSIDE the promoter, INTERACT w transctiption factors its buddy ol pal
- ACTIVATOR proteins bind to ENCHANCER sites – incr (mediating complex formation
- REPRESSOR proteins bind to SILENCER sequences – decr (preventing complex formation)
regulatory proteins their 2 types and their repsectve binding sequcens
Activator – enchancer sites
repressor – silencer sites
what are control elements
DNA sequences that regulatory proteins and transcription factors bind to
- some close to promotor (proximal elements), some far (distal elements)
- most genes have multiple – tightly controlled and coordinated gene expression
regulatory proteins bind to which control element and transcription factors bind to which
reg – distal
tf – proximal
closeness to promotor
3 components of a gene
- promotor (non coding)
- coding sequence
- terminator
what is a promoter and where is it located
The non-coding sequence responsible for the initiation of
transcription
The core promoter is typically located immediately upstream of the gene’s coding sequence
function of promoter + how its affected
Functions as a binding site for RNA polymerase
– binding of RNA poly to promoter mediated and controlled by array of transcription factors
– These transcription factors bind to either proximal control elements (near the promoter) or distal control elements (at a distance)
what is the coding sequence of DNA in transcription
- The region of DNA that is transcribed by RNA polymerase
this is the TEMPLATE STRAND
what is the terminator on a sequence of DNA being trasncribed
- RNA polymerase will transcribe DNA until reaches a terminator sequence
- mechanism for transcriptional termination differs between prokaryotes and eukaryotes
antisense vs sense strand
- strand transcribed (template) // strand not transcribed (coding)
- complementary to RNA // identiacal to RNA (T not U tho)
what triggers changes within the cell to moderate its gene expression
chemical signals –> changes in levels of reg proteins or trans factors (in response to stimuli)
some examples of environment having impact on gene expression
- hydrangeas flower colour change depending on soil pH
- some fish change gender (mate availiabiliy)
- humans diff amts of melanin (dep. on light exposure)
