Lecture 14 Learning Objectives

Question 1

The structure of the nuclear enevlope

Answer 1

the nuclearl evelope is a double membrane orgnalle containing and outer and inner membrane. both of these membranes meet at the Nuclear Pore Complex

Question 2

The Outer Membrane of the Nuclear Envelope is..

Answer 2

continous with the ER

Question 3

Nucleolus function

Answer 3

rRNA and ribosome synthesis

Question 4

Speckles

Answer 4

higher in pre-mRNA splicing factors

Question 5

Cajal body function

Answer 5

snRNP assembly

Question 6

What is the ER cisterane

Answer 6

membrane sacs

Question 7

what is the ER Lumen

Answer 7

space encosed by the membrane sacs

Question 8

Describe the structure and function of nucleoli.

Answer 8

a non-membrane-bound structure within the nucleus of eukaryotic cells that serves as the site for ribosome biogenesis

Question 9

What is the RER

Answer 9

The rough ER is a membrane-bounf ribosome on the cytosilic face

Question 10

What is the function of the RER

Answer 10

Protein syntehsis, protein modification, and protein quality control

Question 11

protien syn

What are soluble proteins?

Answer 11

lumen of organelles

Question 12

Protein syn

what are integral membrane proteins ?

Answer 12

membrane of organelles

Question 13

What is the ER singal sequence?

Answer 13

hydrophobic amino acids in N-term of growing polypeptide chain

Question 14

What is the SER

Answer 14

The smooth ER is the absence of ribosomes

Question 15

What is the function of the Smooth ER?

Answer 15

syntehsis of lipids, carbohydrate metabolism, drug detoxification, and calcium storage

Question 16

How does phospholipid synthesis work in the Smooth ER?

Answer 16

flip flop new phospholipids into exoplasmic leaflet (flippase/scramblase)

Question 17

Proteins that go to the ER must have an ER Signal Sequence

Answer 17

Recognized during co-translation. The SS is what targets ribosome-nascent chain complex to ER membrane

Question 18

SRP (Signal Recognition Particle) is the key targeting mechanism

Answer 18

1. Translation begins in cytosol
2. SRP binds the singal pepride
3. SRP–ribosome complex docks onto the ER
4. SRP releeases the ribosome to teh translocon
5. Translation resumes; protein is threaded into the ER lumen

Question 19

What is co-translation translocation?

Answer 19

When a protein imported into the ER while being translated (call back to ER singal sequence)

Question 20

What is Post-translation translocation?

Answer 20

Protien import into ER after translation. This requires ATP Hydrolysis by chaperon BiP.

Question 21

Is a protein targeted to ER going through a co-translational or post-translational traffic?

Answer 21

BOTH

Question 22

Which statement best distinguishes nuclear import from ER import?
A. Nuclear import is co-translational; ER import is post-translational
B. Nuclear import involves a gated pore; ER import does not
C. Nuclear import requires energy; ER import does not
D. ER import is reversible; nuclear import is not

Answer 22

A. Nuclear import is co-translational; ER import is post-translational

Question 23

What is the primary function of the signal recognition particle (SRP)
during protein synthesis?
A. Folding nascent proteins inside the nucleus
B. Directing ribosomes to mitochondria
C. Stopping translation temporarily and targeting the ribosome to
the ER
D. Adding sugar residues to glycoproteins

Answer 23

C. Stopping translation temporarily and targeting the ribosome to
the ER

Question 24

How are protiens inserted into the ER

Answer 24

Single pass transmembrane proteins

Question 25

What are SPTP?

Answer 25

n ER signal sequence in the N-ter (hydrophobic). The ER singal sequence is cleaved. The internal stop transfer sequence halts translation and ribosomes complete translation in cytosol

Question 26

What is the internal start transfer sequence?

Answer 26

A signal anchor sequence by SRP, the sequence is not cleaves. Orientation of the start-transfer sequence at the time of insertion determines which terminus of the polypeptide ends up in the ER lumen versus the cytosol.

Question 27

# Single pass transmembrane proteins TYPE II

Answer 27

C-ter (ER lumen) N-ter (Cytosol)

Question 28

# Single pass transmembrane proteins TYPE III

Answer 28

N-ter (ER lumen) C-ter (Cytosol

Question 29

Multi-pass transmembrane proteins

Answer 29

alternating internal start transfer and stop transfer sequences. These sequences are not cleaned in multi-pass transmembrane proteins.

Question 30

Explain the post-translational modifications and folding processes that occur in the rough ER.

Answer 30

Protein folding (co-translation) is whenchaperons maintin polypeptide unfolded until translation is completed

Question 31

What does BiP bind to?

Answer 31

Polypeptide

Question 32

What do Calnexin/calreticulin bind to?

Answer 32

oligosaccharides

Question 33

What are disulfide bonds?

Answer 33

(co-translational) = covalent bond between two cysteine amino acids (-S-S-).

Question 34

Glycosylation function

Answer 34

proper folding that protects from aggregation and proteolysis , sorts protein into the secretary pathway

Question 35

Modification of N-linked

Answer 35

3 glucose and 1 mannose branches are removed before the protein is transported to cis-Golgi for further processing.

Question 36

If protein is improperly folded:

Answer 36

glycosyl transferase adds a terminal glucose.

Question 37

Where are Misfolded and unfolded proteins exported to?

Answer 37

cytosol for proteasomal degradation.

Question 38

Discuss the strategies used by the ER to retain resident proteins.

Answer 38

Residnet ER proteins, Folding (e.g., chaperones like BiP), post-translational modifications (e.g., glycosylation), and the assembly of multi-subunit protein complexes, C-terminal amino acid sequence signal\

Question 39

What are residetn ER proteins?

Answer 39

proteins with ER specific functions

Question 40

What is C-terminal amino acid sequence signal

Answer 40

retrieval (retrograde) from GA into ER

Question 41

cytosolic ribosomes synthesize proteins that are

Answer 41

to be localized in a membrane or to be excreted from a cell