Problem Set 5

Lectures 14-15

Which 3 types of filaments exist in human cells?

1. Microfilaments

2. Microtubules

3. Intermediate Filaments

True/False: The (-) end of an F-actin filament corresponds to the end at which the ATP binding cleft is buried.

False

At which end of a microtubule does GTP-tubulin preferentially assemble?

(+) end

Assign the direction (+ or -) that the following motors migrate towards on their respective filaments:

1. Kinesin: ______

2. Dynein: ______

3. Myosin: ______

1. (+)

2. (-)

3. (+)

True/False: Actin subunits in microfilaments are initally bound to ATP. Their corresponding molecular motor myosin also requires ATP.

True

In F-actin filaments, the ATP-binding cleft is oriented to the ___ end

(-)

True/False: GTP in the alpha subunit of tubulin can hydrolyzed to GDP.

False

At which end of a microfilament does ATP-actin preferentially assemble?

(+) end

Intermediate filaments hydrolyze:

1. ATP

2. GTP

3. CTP

4. None of the above

4. None of the above

True/false: Intermediate filaments assemble preferentially at their (+) end.

False

Which protein assembly organizes cristae in Mitochondria?

MICOS

True/False: Mitochondrial genomes are stored in the intermembrane space

False — it is stored in the matrix

Mitochondrial targeting sequences are:

amphipathic, N-terminal

What is the peroxisomal import receptor?

Pex5

Proteins that are imported into peroxisomes translocate the membrane is what state?

Folded

Which organelle has a monolayer?

Lipid droplets

Which organelles have two bilayers?

Mitochondria and Nucleus

True/False: The pH in the lumen of a late endosome is higher than in an early endosome

False — it is lower than in the early endosome

True/False: In SDS-PAGE, proteins with a lower molecular weight migrate slower than those with a higher molecular weight

False — they migrate faster

What does the “positive inside” rule refer to?

1. positively charged residues outside a TMD are oriented to the cytosol

2. positively charged residues outside a TMD are oriented to the ER lumen

1. positively charged residues outside a TMD are oriented to the cytosol

If N-glycosylated secretory proteins do not fold properly, they are recognized by the lectin __

OS-9

COPII vesicles mediate transport: _____

between the ER and the Golgi

The small GTPase ARF1 controls the formation of:

1. COPI

2. COPII

3. GEECs

4. caveolae

1. COP1

For which sorting signal does coatomer select?

1. NPXY

2. FF

3. DD

4. KK

4. KK

True/False: In the stable compartments model, the majority of Golgi-resident enzymes are incorporated into COPI vesicles:

False — cisternae vesicles

Charged carbohydrates like NANA are added to N-glycans in the:

1. cis-Golgi

2. medial-Golgi

3. trans-Golgi

3. trans-Golgi

In Golgi cisternae, resident enzymes are found at the:

1. highly-curved rims

2. flat centers

2. flat centers

Where are clathrin-coated vesicles NOT formed?

1. ER

2. Golgi

3. PM

1. ER

Which of the following proteins do NOT contribute to CCV budding?

1. cargo proteins

2. APs

3. dynamin

4. Hsc70

4. Hsc70

Which of the following sequences targets proteins to the lysosome?

1. KKLA

2. WAAW

3. QHEY

4. DELL

3. QHEY

Both phagocytosis and micropinocytosis require:

1. COPI

2. COPII

3. CCVs

4. actin

4. actin

Which process is the protein VPS4 involved in?

1. COPI vesicle formation

2. COPII vesicle formation

3. CCV vesicle formation

4. MVB vesicle formation

4. MVB vesicle formation

True/False: Caveloae are rich in dolichol

False — depend of cholesterol

In F-actin filaments, the ATP-binding cleft is oriented to the:

1. (-) end

2. (+) end

1. (-) end

True/False: GTP in the alpha subunit of tubulin can be hydrolyzed to GDP

False — GTP is never hydrolyzed in the alpha subunit

At which end of a microfilament does ATP-actin preferentially assemble?

1. (-) end

2. (+) end

2. (+) end

Intermediate filaments hydrolyze:

1. ATP

2. GTP

3. CTP

4. None of the above

4. None of the above

True/False: Intermediate filaments assemble preferentially at their (+) end

False — (-) and (+) don’t correspond to charge!