Lecture 11 Flashcards
What is an srp
Give an example
A signal recognition particle
A ribonucleoprotein
What is a signal peptide
The n terminal sequence of a pre protein that gets cleaved off
Also called a leader sequence
How do signal recognition particles (SRP) and signal sequences interact
The ribosome is making the protein and adds a n terminal signal sequence to it
The sequence is recognized by the SRP
SRP takes the ribosome to the ER membrane
Protein gets made and released into the ER where the signal peptide is removed and the protien can fold
What does the processing of insulin require
PTM
What is the steps of processing insulin
A: preproinsulin: insulin with signal sequence
B: proinsulin: the signal sequence is cut off but this is still not active form of the final product
C: insulin: the terminus is cut off , now active dimer
What’s an example of a proprotein
What’s the active form of this
What would it have if it were a preoproprotein
Zymogen
Requires a type of cleavage to become active
Trypsin
Would have a signal sequence
When does the first cut of a preproprotein (cleave singal sequence ) happen
The. The second cut
First cut happens right as it gets translated and goes into the er, so its now proprotein
2nd cut happens in the secretory vesicles of the golgi now protein
Now active
What is glycosylation
What does it help with
Attaching carbohydrates to proteins
Solubility and stability
Shield against degredation (since glycosylation is a big structure)
Act as a label for recruitment or target proteins to specific areas of the cell
What are the types of extracellular glycosylation
N linked: on asparagine primary amine
O linked: on ser or thr oh
O linked less common
What are the types of intracellular glycosylation
Only a single sugar gets attached
Which is N acyetlglucosamine (glcNAc)
What is the motif for n linked glycosylation
Asn -x- ser/thr
Ser or thr
X is Any except proline
Glycosislation starts and ends where
Starts in the er then to the golgi then protein with sugar gets secreted
What is GlcNAC
N-acetylglucosamine
This gets added to the asparagine for n linked glycosylation
What is DPP (dolichol pyrophosphate)
Spans the ER membrane and more and more sugars get added to it by UDP (uridine diphosphate, carrier of sugars)
The DPP with 5-6 sugars eventually flips to the other side of the membrane (through the use of flippase)
Then the sugars (now in the ER lumen) get added on to the target protein
ALL N LINKED ARE MADE IN
The ER
Then secreted to the golgi
All glycosyltranferase need a
UDP to attach sugars to DPP
If glycosylation happens intracellular how does it happen
Only one sugar is added and the protien is not flipped (since already in the intracellular cell)
Mainly a eukaryotic thing
What’s sugar is added in n linked
And o link
GlcNAC
Galnac
What makes region of the histone more of less accessible
What does this mean
PTM
PTM can regulate transcription
What PTM happen on histone tails
Acetylation
Methylation
Phosphorylation
How many types of histone are wrapped around the DNA
4
H2A H2B H3 H4
The tails of histones do what
They recruit proteins and molecular markers to either turn the genes on or off
The backbone of dna is _____ charged
What does this mean for histones
negatively due to phosphate
This means dna is bound tightly to the + histones
When dna less tightly bound what metal causes this to happen
Mg2+ since it bound to atp most of the time
Counteract the charge of histone proteins
DNA might be more exposed due to being bound to mg rather than the histone protein
What is lysine acetylation
Acetyltranferase (HAT) puts acetyl on lysine in the tail
The acetyl cancels the + charge of the histone tail
Now histone not tight bound to dna
Backbone exposed and transcription happens
What is lysine methylation
What is used as a methyl donor
Done by its own methyltransferase
Can and 1 2 or 3 methyl’s to the amine of lysine
Makes the lysine more hydrophobic, so it cancels the charge interaction with the dna
since sticky it can recruit also another protein
They use SAM as a methyl donor
What is argenine methylation
Can methylate on either side of the nh2 of the arg guanidinium group
Assymetric: bith methyl’s on one nh2
Symmetric: one methyl on each nh2
Usually no trimethylation because of steric hindrance
What is the histone code
Many PTM arrangement on histone tails a required together to have an effect
These many modifications is the histone code
What are bromodomains
Domain on another protein that recognizes histone acetyl groups on lysine
Not a protein itself, it’s a domain
What are chromodomains
Recognize methylated lysines or Argentines on histones
Ex. If something has a HAT domain, and a bromodomain actelyate. It’s target first need to be acetylated so the bromo domain recognizes it then it can do HAT
Proteins can have both
Bromo and chromodomains
