TA Section 5 (3/14)

The nuclear envelope has...

• a single phospholipid bilayer

• two phospholipid monolayers

• two phospholipid bilayers

The smooth ER or "sarcoplasmic reticulum" is important in muscle cells for controlling ___ levels.

• calcium

• sodium

• potassium

• phosphate

Free polysomes and rough ER polysomes use the same pool of ribosomal subunits, which are in the ____ when not in use.

• rough ER

• smooth ER

• cytosol

• nucleus

Ran-GTP/GDP is involved in transporting cargo in and out of the ER.

• True

• False

Answer explanation

Ran-GTP/GDP is involved in transport across nuclear pores.

Transport in and out of the ER typically occurs via vessicles.

What is responsible for removing the ER signal sequence from newly-synthesized proteins that belong in the ER?

• signal recognition particle (SRP)

• protein translocator

• signal peptidase

• SRP receptor

Which of the following will be cleaved off of a double-pass membrane protein in the ER membrane?

• ER signal sequence

• start-transfer sequence

• stop-transfer sequence

Answer explanation

The start- and stop-transfer sequences are alpha helices of hydrophobic amino acids that can be embedded into the membrane. Therefore, they are functional parts of the protein and are not removed.

ER --> Golgi --> Exterior of cell would be a common path for vessicles during ...

• exocytosis

• endocytosis

• lysosomal digestion

• peroxisomal digestion

___-coated vesicles transport cargo between the ER and cis Golgi

• COP

• Clatherin

• V-SNARE

• T-SNARE

The purpose of V- and T-SNARES are to dock vesicles to the nearest membrane.

• True

• False

Answer explanation

T-SNAREs on Target membranes specifically bind V-SNAREs on Vesicles in order to ensure vesicles reach the correct compartment.

Docking is done by the Rab protein on the vesicle binding to a tethering protein on the target membrane.

____ break down cell components, while ____ break down fatty acids and toxins.

• Peroxisomes, lysosomes

• Lysosomes, peroxisomes

• Endosomes, lysosomes

• Lysosomes, endosomes

Answer explanation

Endosomes are mostly responsible for sorting and delivering endocytosed materials to their destination.