Post Transational Modifications

Question 1

What is post-translational modification?

Answer 1

Additional processing after a protein is made

Question 2

What is proteolytic cleavage?

Answer 2

Breaking peptide binds to remove part of the protein

Question 3

What is chemical modification?

Answer 3

Addition of functional groups to amino acid residues

Question 4

What kind of proteins are synthesised on free ribosomes?

Answer 4

Proteins for cytosol or posttranlational import into organelles

Question 5

What kind of proteins are synthesised by ribosomes on the RER?

Answer 5

Proteins for membrane or secretory pathway

Question 6

What is required for protein sorting?

Answer 6

Signal
Receptor
Translocation machinery
Energy

Question 7

What must proteins targeting peroxisomes have?

Answer 7

Must have the peroxisomes targeting sequence -Serine, lysine, leucine at c terminus usually
This is recognised by the pex5 which binds to cargo protein
This binds to the 13 per protein channel across peroxisomal membrane
ATP hydrolysis recycles PTS receptor

Question 8

What disorders are caused if peroxisomes targeting goes wrong?

Answer 8

Peroxisomes biogenesis disorders
Zellweger syndrome
Rhizomelic chondroysplasia punctata

Question 9

What is constitutive secretion?

Answer 9

All the time/continuous secretion

Question 10

What do endocrine cells secrete?

Answer 10

Hormones

Question 11

What do exocrine cells secrete?

Answer 11

Digestive juices

Question 12

What do neurocrine cells secrete?

Answer 12

Neurotransmitters

Question 13

What is a signal sequence?

Answer 13

At the n terminus
5-30 amino acids in length
Form alpha helix
Central region hydrophobic

Question 14

What is the signal recognition particle?

Answer 14

Receptor needed to bind the signal peptide on proteins destined for the ER
6 proteins and a short piece of RNA
Recognises signal peptide and ribosome

Question 15

What are the functions of the endoplasmic reticulum?

Answer 15

Insert proteins into membranes
Specific proteolytic cleavage
Glycosylation
Forms S-S bonds 
Folds proteins
Assembles multisubunit proteins 
Hydroxylation of selected lys and pro residues

Question 16

What is glycosylation?

Answer 16

Addition of sugars

Question 17

Why is glycosylation of proteins important?

Answer 17

Correct protein folding
Protein stability
Facilitates interactions with other molecules
Deficiencies in n linked glycosylation leads to CDG

Question 18

What protein helps from disulphide bonds?

Answer 18

Disulphide isomerise

Question 19

What happens if there are folding problems with a protein?

Answer 19

May be trapped in misfolded conformation
Mutation
Incorrectly associate with another sub unit

Question 20

What do ER chaperones do?

Answer 20

Retain unfolded proteins in ER

Act as sensor to monitor extent of protein mis folding

Question 21

What happens if misfolding of proteins cannot be corrected?

Answer 21

Degradationin cytosol

Accumulate to toxic levels and cause disease

Question 22

Where does o linked glycosylation occur and what happens?

Answer 22

In Golgi

Sugar attach to hydroxyl group of serine and threonine

Question 23

What is proteolytic cleavage?

Answer 23

Breaking of a peptide bond to remove part of the protein

Question 24

What is chemical modification?

Answer 24

Addition of functional groups to amino acid residues