Lecture 19 - ER, Trafficking, Cotranslational Import

Question 1

Functions of Smooth ER (SER) (4)

Answer 1

1. Lipid synthesis
2. Production steroid
3. Detoxification
4. Sequestration

Question 2

Production steroid hormones happens using what compounds

Answer 2

like glucocorticoids, androgens, and estrogens — endocrine cells

Question 3

what is Detoxification

Answer 3

liver cells contain
enzymes that modify foreign compounds

Question 4

what is Sequestration

Answer 4

(storage) of Ca2+ in
muscle cells

Question 5

Functions of Rough ER (RER) (4)

Answer 5

1. Synthesis of membrane phospholipids.
2. Glycosylation of proteins
3. Protein folding — quality control
4. Protein synthesis, modification, and transport

Question 6

what is Glycosylation of proteins

Answer 6

Addition of carbohydrate chains to specific proteins

Question 7

what does Protein folding — quality control involve

Answer 7

the activity of molecular chaperones, a specific type of protein that assist in the folding process

Question 8

what is this process called?

• Proteins targeted to ER.
• Proteins targeted to other endomembrane compartments (soluble and transmembrane).
• Proteins targeted to plasma membrane (secreted and transmembrane)

Answer 8

Protein synthesis, modification, and transport

Question 9

In the cytoplasm, ribosomes synthesize what from what?

Answer 9

polypeptides from mRNA

Question 10

All protein translation begins on what

Answer 10

free ribosomes (i.e. not associated with the ER)

Question 11

Translation is completed in 1 of 2 ways:

Answer 11

FREE or ER BOUND ribosomes

Question 12

what proteins and molecules are involved in translation completed on free ribosomes?

Answer 12

• Cytosolic proteins
• Peripheral membrane proteins
• Proteins targeted to nucleus, mitochondria, peroxisomes, chloroplasts
  RER and Protein Translation

Question 13

For translation completed by ribosomes associated with ER membrane, what proteins are involved?

Answer 13

• Secreted proteins
• Integral membrane proteins
• Soluble proteins associated with inside (lumen) of endomembrane system (i.e. proteins that function within the ER, Golgi, lysosomes)

Question 14

How is the site of translation determined?

Answer 14

Ribosomes are targeted to the ER membrane by a specific signal
sequence

Question 15

The signal sequence is Located in

Answer 15

the amino-terminus (N-terminus)

Question 16

The signal sequence Contains several

Answer 16

consecutive hydrophobic amino acids

Question 17

The signal sequence directs

Answer 17

synthesis to the ER compartment

Question 18

Protein moves through channel into ER for what

Answer 18

cotranslational import

Question 19

in Cotranslational Protein Import, After translation of _______ ______, a Signal Recognition Particle (SRP) binds to signal sequence and ______ the translation process.

Answer 19

SIGNAL SEQUENCE, STOPS

Question 20

in Cotranslational Protein Import, SRP binds _____ ____ to target the whole translation complex to ____ (SRP + ribosome + mRNA + new polypeptide)

Answer 20

SRP receptor, ER

Question 21

in Cotranslational Protein Import, _____ is released and ribosome binds to ________. Once this is done, protein synthesis resumes

Answer 21

SRP, translocon

Question 22

in Cotranslational Protein Import, ________ enters the ER (through the translocon) as it is translated. In the end,
the signal peptide is _______ ____ and chaperone folds the protein.

Answer 22

Polypeptide, cleaved off

Question 23

Movement of cellular components:
To the plasma membrane via biosynthetic/secretory pathway =

Answer 23

exocytosis

Question 24

Movement of cellular components: From the plasma membrane → organelle within cell via endocytic pathway =

Answer 24

endocytosis

Question 25

Examples of exocytosis:

Answer 25

Organelle → Plasma membrane
Secretion of neurotransmitter from
pre-synaptic neuronal cells

Question 26

Examples of endocytosis:

Answer 26

Plasma membrane → Organelle
Uptake of Low Density Lipoprotein (LDL) particle in liver cells