L10 Flashcards
Digestive enzymes, Preprohormones, protein splicing what examples of protein modifications
Cleavage
Collagen is an Example of What protein modification
Hydroxylation
Lysosomal enzymes, Transcription factors Are examples of what type of protein modifications
Phosphorylation
Membrane, Secretory proteins Are examples of what type of protein modifications
Glycosylation
lipoproteins Are example of what types of protein modifications
Lipidation
Histone Proteins are example of what type of protein modifications
Acetylation
%?
Phosphorylation
Glycosylation
Acetylation
> 30%
50%
80-90%
Category 1 proteins are ___while category 2 proteins are ___
Post translation
Co-translation
Why are C2 proteins co-transnational
Because their modification is continued in the golgi
When do proteins become active
After modifications
What sends a protein to its target site
Ts
Specific modifications in some proteins help in achieving
Proper folding
Stability
Activity
Proteins are placed in two main categories based on
Location and target
In this category, Synthesisstartsonthefreeribosomes, but complete in the rough ER
C2
In this category, Synthesis starts and completes in the ribosomes
C1
In c1, this TS is cleaved
Mitochondrial TS
This protein has nonTs
Cytosol
If TS of C1 is lost due to mutation —>
If TS of c1 is cleaved —>
Cytoplasm
Normalm
When do proteins of C1 reach their site?
Post-synthesis
Translocation of c1 proteins require
Chaperons and receptors
What is the job of chaperons ?
Protect protein
Translocation
Ts of Mitochondrial proteins is in which terminal?
N
What is the mechanism of mitochondrial proteins
1-proteins are unfolded and binds with Chapiron HSP70 and receptors on the mitochondrial membrane
2-This binding leads to h opening of
mitochondrial membrane channels
through which these proteins moved
into the matrix
3-After reaching the matrix, the TS is
cleaved, protein folds & becomes active
Smaller proteins can ___ through nuclear pores / channels
Larger proteins are imported through the nuclear pores in an___ manner
diffuse freely
energy dependent
What do nuclear proteins require to move through nuclear channels?
Selective receptors
Nuclear proteins have Ts at the
N terminal
Which type of peroxisomal proteins are translocated
Folded
Peroxisomal proteins have ts at
Skf- c terminal
What does Peroxisomal proteins require for their translocation
Binding proteins and receptors
Why must ribosomes couple to rER?
1-Ribosomes do not have modifying enzymes
Modifying enzymes are present in the rER & Golgi Therefore, ribosomes must couple to rER
Which signal is used to couple?
Signal peptide
Which ribosomes are attached to to rER?
Only those who synthesize proteins having N-terminal signal peptide
A signal peptide (SP) is present as an___ sequence in a protein
N-terminal
T/F: SP is not consensus
T
The middle sequence of the
SP is (hydrophobic or hydrophilic)
hydrophobic
Note :The only part which is consnesus is the middle part, all are hydrophobic
What is the mechanism of coupling to rER?
Sp +SRP (6proteins+mRNA) = arrest translation?( prevent wrong folding) + binf to SRP on ER.
SRP then hydrolize GTP, dissociates from receptor
SP is not present in some mature proteins why?
In some cases, the ‘SP’ is cleaved in the ER by signal peptidase
ER membrane has 2 types of receptors what are they
Ribosomal
SRP
Are part of the ER membrane
Integral membrane proteins
Require to topogenic and anchor sequence for their crossing and anchoring to the lipid layer
Integral membrane proteins
Integral membrane proteins Require topogenic and anchor sequence why?
for their crossing and anchoring to the lipid layer
Which proteins are glycosylated or modified
only the intracellular epitose
What are the five types of modifications that occurs in the rough ER
Formation of disulfide bond
N- linked glycosylation
Folding of proteins
quality control
oligomerization
Disulfide bonds are important for __
They may be formed in __or__
Protein folding
Intra-chain / interchain
#Inter-chain = 2 different proteins = oligomerization
Disulfide bond formation is catalyzed by
glutathione oxidase
In Protein glycosylation ___ carbohydrates selectively added to certain amino acids in a polypeptide
Complex
N-linked glycosylation occurs at the ___group in__
NH2 group
Asn
O-linked Glycosylation occurs at the group __in__
Oh
Ser, thr
Where does N-linked glycosylation occur? And why
ER. Because the enzymes needed for modifications are only present in the ER there are no enzymes for modifications in the ribosomes
Whre does N-linked glycosylation start and end
Start er
End golgi
The part of glycosylation that completes in the Golgi is also known as
terminal glycosylation
Where is the carbohydrate attached in the protein? 
NH2 group
Why you ask, because its N-linked glycosylation
Not every amino acid will be glycosylated. What is the condition that must be satisfied for Glycosylation to occur
Asn-x-ser-thr
primary proteins are susceptible to form wrong protein-protein interactions & aggregations in RER why?
Because of the high number of proteins density present
How to avoid wrong protein protein interactions in the rough ER
By chaperones
Mention the eight chaperones
HSP: 40 60 70 90 100
bip
calnexin
Careticulin
prevent incorrect folding, denaturation & aggregation
Chaperones
bind to the exposed hydrophobic aa
Chaperones
have ATPase activity
Chaperoned
Quality control check occurs in
rER
T/F: only the correctly
folded proteins are allowed to move from rER to the Golgi for their final processing
T
Mis-folded proteins cannot move to the Golgi they are degraded in__
proteasomes
Protein trafficking, which is ___occurs via ___
Movement of proteins from ER to Golgi
Bound globular vesicles
What is the sensor that recognizes an incorrectly folded protein
GT
Explain the mechanism of quality control
1-GT 👀 wrong protein , adds G
2-Calnexin (chaperone) captures proteins and folds it
3-G II 👀 protein —G
This enzymes recognizes a folded proteins with glucose
G II
This enzyme captures an unfolded protein with glucose
Calnexin
Mention 3 Types of protein modifications in Golgi
Terminal glycosylation (N completes)
O-linked glycosylation ( starts and complete in the Golgi apparatus)
Sorting/packaging (from trans)
O-linked glycosylation Occurs at which structure of the protein
Primary
Explain the lysosomal proteins sorting mechanism
1-Lysosomal proteins carry M6P —> to bind and sort proteins by MP6R
- Protein + MP6R
2-MP6 ❌MP6R in endosome —> acidic
3-MP6 -Phosphate
4- M6PR recycled to the Golgi as a major pathway
5-MPR recycled to the PM in a minor pathway
What sequence does ER protein have and where is it
KEDL at c terminal
Why is a KEDLE sequence required for ER proteins
for their retention by rough ER in case of wrong escape to the Golgi
Slide 33 and 32 add them here
Require special modification (integral membrane proteins /membrane proteins)
Membrane proteins
Note: Membrane proteins are glycosylated which faces the lumen ER, Golgi & vesicle Upon targeting the glycosylated part becomes extracellular
In the membrane bound proteins the modified part is facing__
Anteriorly Towards the lumen ER, Golgi and vesicles
Which proteins have signals and which do not
Secretory proteins have no signals
proteins that will function inside the cells need signals
Which proteins will be modified membrane proteins or integral proteins?
Membrane proteins
What makes intracellular epitose special Compared to others
They are glycosylated or modified
