Exam 3- Post Translational Modifications

Question 1

What is dictates protein shape?

Answer 1

Folding + Post translational modifications

Question 2

How is folding achieved?

Answer 2

Chaperons and Chaperonins

Question 3

What are the three categories of post translational modifications

Answer 3

Non-Reversible

Seldom Reverted

Rapidly Reverted

Question 4

What’s the non-reversible PTM

Answer 4

cleavage

once it is cut it cant be put back together

Question 5

What are the seldom reverted PTM?

Answer 5

Carbs and Lipids

Question 6

What are the rapidly reverted PTM

Answer 6

Phosphorylation
Ubiquitinylation
SUMOylation

Question 7

Protein cleavage is frequent for what pathway?

Answer 7

For targeting from sec pathway.

Cut off signal sequence

Question 8

Protein glycosylation occurs either at:

Answer 8

N link or O link

Question 9

Where is N linked glycosylation

Answer 9

to an Asn residue 4 residues from the N term end

N-Glycosylation involves the transfer of a pre-formed chain made of 14 different sugars.

The vast majority of proteins that are translocated into the ER are CO-TRANSLATIONALLY N-Glycosylated.

Question 10

Where is an O linked glycosylation

Answer 10

to Ser or Thr residue

O-Glycosylation involves the addition of one sugar at a time.

Question 11

For N-glyco the removal of 3 glucose residues targets the protein where?

Answer 11

ER

Question 12

For N-glyco the removal of 3 glucose residues, and removing mannose and adding other sugars targets the protein where?

Answer 12

to the Golgi

Question 13

What does glycosylation do to proteins? Why is it important? Where in the cell are most N-Glycosylated proteins?

Answer 13

Adds sugars to proteins making them “sticky”, allowing them to play a role in cell adhesion and cell to cell communication.

Question 14

What are the 3 types of lipid additions to proteins?

Answer 14

Myristoylation
Farnesylation
Palmitoylation

Question 15

what is Myristoylation

Answer 15

adding 14 carbon myristic acid to N term glycine after removing Met 1

Question 16

what is Myristoylation going to after?

Answer 16

inner face of plasma membrane

Question 17

what is Farnesylation

Answer 17

adding 15 Carbon farnesyl acid to the 4 amino acid from the N term which is Cys’ Sulfur residue. Then cleaving the 3 AAs making Cys the terminal. Then adding ester group to the N term Carboxyl of Cys.

Question 18

Which protein is farnesylated?

Answer 18

Ras Protein

Cancer cell growth

Question 19

What is Palmitoylation

Answer 19

Adding 16 Carbon palmitolaic acid to the Cys reside in the middle of the chain.

Question 20

What is Palmitoylation send the protein?

Answer 20

Cystolic face of the plasma membrane

Question 21

What’s the main effect of lipidation on proteins?

Answer 21

Allows them to associate with membranes.

Question 22

What’s a GPI anchor? How is it added to the protein? What’s the final topology and location of ALL GPI anchored proteins?

Answer 22

Added to the protein inside lumen of the ER at C-terminus.

Always targets proteins the extracellular side of the plasma membrane

ALL GPI proteins end up at PM and are facing the extracellular environment.

Question 23

What is phosphorylation?

Answer 23

Attachment of phosphate group to the protein, through covalent association.

Causes conformational change in protein, altering its function.

Mediated by protein kinases.

Regulates the activity of enzymes involved in cellular metabolism.

Question 24

What are the main residues that can be phosphorylated?

Answer 24

Serine and Threonine

Tyrosine

Question 25

What’s a kinase?

Answer 25

enzyme that transfer phosphate groups from ATP to hydroxyl groups of the side chains of amino acids

Question 26

Main types of kinases?

Answer 26

Serine and Threonine kinases

Tyrosine has its own kinase

Question 27

What’s a phosphatase?

Answer 27

Enzyme that removes phosphate groups from proteins.

Question 28

Is the active form of a protein always the phosphorylated one?

Answer 28

No phosphorylation can activate and deactivate

Question 29

What is a signal transduction pathway?

Answer 29

The cascade of events triggered by a signal received at the plasma membrane – usually results in the transcription of a specific set of genes. Signal transduction pathways usually involve a series of phosphorylation and de-phosphorylation events.

Question 30

How much does phosphorylation change the molecular weight?

Answer 30

1-4kD shift

Question 31

What is Ubiquitin?

Answer 31

Ubiquitin is a small protein (only 76 amino acid residues long) that can be post-translationally conjugated to other proteins via iso-peptide links formed between the C-terminal glycine residue in Ubiquitin and the epsilon-amino group in Lysine residues located within the target protein to be Ubiquitinylated.

Question 32

What is SUMO?

Answer 32

SUMO stands for Small Ubiquitin-like Modifier; hence, SUMO is a Ubiquitin-like protein that can also be post-translationally conjugated to other proteins in the same way as Ubiquitin.

Unlike ubiquitin SUMO has its N term exposed to interact as well as its C term

96 amino acids

added to Lysines

Does NOT target for degradation and does NOT form poly-SUMO chains

Question 33

What’s the main effect mediated by the conjugation of Ubiquitin to a target protein?

Answer 33

Ubiquitinylation usually targets the modified protein to be degraded by the PROTEASOME. To do this, proteins need to be conjugated not with single Ubiquitin molecules but with long chains of Ubiquitin (poli-Ubiquitinylation).

Question 34

what’s the PROTEASOME?

Answer 34

Protein shredder of the cell, can break down proteins into individual amino acids.

Question 35

What’s the main effect mediated by the conjugation of SUMO to a target protein?

Answer 35

SUMO is a match maker - The protein can interact with other proteins it couldn’t interact with before, even after SUMO is removed.

effects associated with SUMOylation are changes in cellular localization, changes in the ability of the modified protein to establish specific protein-protein interactions, changes in the transcriptional activation power of transcription factors

Question 36

Is the binding of small molecules to a protein a type of post-translational modification?

Answer 36

NO (because to be considered a post-translational modification the molecule added must be covalently associated to the protein) small molecules are not covalently attached, but the binding of small molecules to a protein can exert dramatic changes in protein shape and function.

Question 37

What is allosteric regulation?

Answer 37

Regulation of enzyme activity by molecule binding at a site different from the enzymatically active site

Question 38

2 examples of adding small molecules to proteins.

Answer 38

Binding of small molecules – exemplified by the binding of the heme group to the globin peptide producing hemoglobin,

and the binding of GTP to GTPases such as eIF2 and Ran. Small molecules can add extra functions to proteins.

Question 39

What is feedback inhibition?

Answer 39

Involves a series of different enzymes. Final product made in the series, inhibits the activity of the very first enzyme (thereby controlling its own concentration)