unit 3

Question 1

What is protein translocation?

Answer 1

Moving a protein a protein across a membrane.

Question 2

What is cotranslational transport?

Answer 2

Transport in ribosome from cytoplasm to ER

Question 3

What are three ways that proteins are sorted?

Answer 3

Gated transport, vesicular transport, protein translocation

Question 4

What is the endomembrane system? What organelles makes it up?

Answer 4

Network of membranes related through physical contact or by transfer of vesicles. Made up of ER, golgi, endosomes, lysosomes

Question 5

What path does vesicular transport take? What are the main steps?

Answer 5

ER –> golgi –> final location
1) vesicles bud off from donor membrane
2) moved via motor proteins on microtubules and microfilaments of cytoskeleton
3) fused with membrane of acceptor protein (destination organelle)

Question 6

What are the two modes of secretion (and definitions)?

Answer 6

Constitutive: Materials transported in secretory vesicles continually
Regulated: Materials stored in vesicles and discharged in response to stimuli

Question 7

How does the ER signal sequence direct ribosomes to ER membrane?

Answer 7

1) ER signal sequence on mRNA is translated and binds to srp on ribosome
2) ribosome travels to ER and srp binds to srp receptor (gtp hydrolysis)
3) translocon opens (facilitated by gtp hydrolysis)
4) translated protein send through protein translocator during translation
5) once translocon opened, translation resumes

Question 8

What is a protein translocator (translocon)

Answer 8

A protein embedded in ER membrane that allows for co-translational transport of proteins. When srp and srp receptor bind to gtp and hydrolyse it, translocon opens and ribosome binds to it, allowing protein to ender rough ER

Question 9

What is the srp

Answer 9

Comples thatr ecognizes ER signal sequence as it emerges from a ribosome and helps direct the ribosome to the ER by binding to the srp receptor on the ER and initiating th eopening of a protein translocator

Question 10

Where is the ER signal sequence located?

Answer 10

N-terminus of mRNA strand?

Question 11

What is the NPC

Answer 11

Nuclear pore complex. Proteins within the nuclear pore in the nuclear membrane that control which substances enter and leave the nucleus.

Question 12

What is the nuclear basket?

Answer 12

Hold up structure of the NPC and regulate transport

Question 13

What is the nuclear envelope?

Answer 13

A double membrane with nuclear pore complexes.

Question 14

What are the steps of nuclear import?

Answer 14

1) Cargo protein has NLS (nuclear localization signals), which contain importin. NLS binds nuclear import receptors, which recognize the importin
2) Cargo-bound transport receptor binds to FG nups (nucleoporins)
3) Cargo released inside the nucleus when transport receptor bound by Ran-GTP
4) Transport receptor still bound to Ran-GTp diffuses through FG-nups to cytosol, where Ran GTP is released

Question 15

Is NLS sufficient for transport of proteins into the nucleus?

Answer 15

Yes

Question 16

Explain the Ran GTPase cycle?

Answer 16

Ran is bound to GDP in the cytosol. When it enters the nucleus, Ran GEF facilitates the unbinding of Ran to GDP and binding to GTP. (After the cargo protein has localized) Ran-GTP then diffuses back into the cytosol, where Ran-GAP hydrolyzes Ran-GTP, leading to Ran-GDP. The cycle can then restart.

Question 17

What are the different types of molecules/proteins involved in cell signaling?

Answer 17

Extracellular signaling molecule –> receptor protein –> intracellular signaling molecules –> effector proteins

Question 18

How does cell signaling work (basics)

Answer 18

Ligand binds to receptor, receptors on target cells receive extracellular message, effectors altered in response to ligand, second messenger or protein recruitment system lead to cellular response

Question 19

What are the 4 forms of intercellular signaling

Answer 19

Contact-dependent, paracrine, synaptic (type of paracrine, just at a synapse) , endocrine

Question 20

What is paracrine signaling?

Answer 20

The cell has receptors on its surface that respond to released messengers produces by other cells nearby

Question 21

What is autocrine signaling?

Answer 21

The cell has receptors on surface that respond to released messengers produced from itself

Question 22

What is endocrine signaling?

Answer 22

Messenger moelcules reach their target through the bloodstream

Question 23

What are GCPRs and how do they work?

Answer 23

G coupled protein receptors. Signal molecule activates receptor and G protein, leading to activated enzyme

Question 24

What are protein kinases?

Answer 24

Proteins that covalently add one or more phosphate groups to specific amino acids at hydroxyl groups

Question 25

How do GTp binding proteins work?

Answer 25

They switch between two conformational states. GTP bound is “on” and GDP bound is “off”. Usually with GTPase activity to hydrolyze GTP

Question 26

What are GTPase activating proteins (GAPS)?

Answer 26

They activate GTPases to increase the rate of hydrolysis of bound GTP. Results in turning GTP binding protein “off”

Question 27

What are guanine nucleotide exchange factors (GEFs)?

Answer 27

They promote release of bound GDP in exchange for GTP, results in turning GTP-binding protein “on”