HYS CH7.5 Control of Expression in Eukaryotes

Question 1

How is DNA stored with histones and chromosomes?

Answer 1

around 200 bp wrap around a histone protein complex forming a nucleosome

euchromatin (LIGHT) - beads on a string is good for transcription

heterochromatin (DARK) - so compact and less excessible and shuts off genes, highly methylated

Question 1

which is least accessible for transcription? euchromatin or heterochromatin

Answer 1

heterochromatin is more inaccessible

Question 2

DNA methylation of what bases causes what?

Answer 2

DNA methylation to cytoseine and adenine methods hinders RNA polyemrase to transcribe and makes it more compact

Question 3

how do we modify histone to affect transcription?

Answer 3

adding methyl, acetyl, phosphate groups decrease affinity for DNA and makes DNA molecule more accessible for transcription

removing the groups makes it more compact and less accessible

they can also be displaced and reveal acess poitns for transcription

Question 4

promoters and enhancers

Answer 4

promoters: 25-35 bp upstream of transcription start site
enhancers: more than 25 bp away from transcription start site
- group of several response elements control of gene exp by many signals

Question 5

response elements are where

Answer 5

in promoter regions

Question 6

transcription factors

Answer 6

selective TFs bind to specific response elements in certain genes (enhancers)

general TFs help recruit RNA polymerase

have 2 domains: DNA binding and activation domain
DNA binding binds to response element
activation domain allows for binding of several Tfs and other regulatory proteins such as RNA polymerase and histone acetylases

Question 7

splicing

Answer 7

happens many ways and makes different versions

Question 8

how do we regulate which transcripts after export

Answer 8

with poly A tail that delays exonucleases and effects signal presentation for time to transcribe

Question 9

what is gene amplification and how does it work?

Answer 9

when expression is low it must be amplified in response to growth factors, hormones and use enhancers and DNA duplication

enhancers: more than 25 bp away from transcription start site
- group of several response elements control of gene exp by many signals
- in introns, can be far away
- DNA must often bend in hairpin to bring elements together

molecules like cAMP bind to receptors like cyclic AMP response binding element CREB which bind to response elements

Question 10

gene duplication

Answer 10

cells increase expression of a gene product by duplicating relevant genes, even in series on same chromosme or in parallel by helliases opening DNA replication

Question 11

histone acetylases

Answer 11

TFs that bind DNA and recruit coactivators in chromatin remodeling uses actylate lysine resides in aminto terminal tail regions of histone proteins

acetylation dec + charge on lysine resides and weakes interaction of histone with DNA which opens the chromatin condensation and allows for easier acess of transcriptional machinery

Question 12

histone deacetylases

Answer 12

proteins that function to remove acetyl groups from histones –> closed chromatin conformation and overall decrease in expression

Question 13

UTR regions

Answer 13

in 5’ and 3’
ribosomes uses 5’ UTR to bind
3’ uses secondary structures to stabilize

Question 14

cancers and gene expression

Answer 14

genes replicating cell cycles and division

Question 15

oncogenes

Answer 15

promote cell division
normally represses
overexpressed in cancer cells
more cell division –> tumor

activation: proto-oncogenes become oncogenes via point mutations, chromosmal translocations

Question 16

tumor sepressor genes

Answer 16

supress cell division and are involved in DNA repair

when incorrectly OFF, they divide more, incr tumor or increase DNA damage –> tumor promoting mutations