Problem Set 6

Lectures 16-17

The average cell cycle of a human cell takes 24 h. Which stage in the cell cycle takes the longest amount of time, and which one is the shortest?

Longest: S phase (S)

Shortest: Metaphase (M)

Name the three types of microtubules that form the mitotic spindle:

1. astral MTs (microtubules)

2. kinetochore MTs

3. polar/interpolar MTs

True/False: Cyclin-dependent kinases (CDKs) are fully activated by the kinase CAK.

False — Activated by CAK, Wee1, and CDC25 (not just CAK)

True/False: Cancer cells have highly abnormal karyotypes.

True

True/False: Most cancer cells exhibit a loss of tumor suppressor p53.

True

True/False: Within tumors, the main mode of energy production is oxidative phosphorylation.

False — Aerobic glycolysis

True/False: CAK is required for full activity of CDKs

True

Myosin migrates to the:

1. (-) end

2. (+) end

2. (+) end

Dynein migrates to the:

1. (-) end

2. (+) end

1. (-) end

Kinesin migrates to the:

1. (-) end

2. (+) end

2. (+) end

True/False: When the motor head in kinesin binds to MTs tightly, it is ADP bound

False — It is ATP bound (ADP bound is weak)

True/False: When the motor head in myosin binds microtubules tightly, it is ADP bound

False — it is ATP bound

True/False: Centrosomes organize microtubules in human cells. The (+) end of MTs point to the cell periphery

True

The Golgi ribbon is pulled towards the perinuclear region by the motor protein:

1. kinesin

2. dynein

3. myosin

4. none of the above

2. dynein

You have isolated a protein complex with a total molecular mass of 400 kDa. When performing SDS-PAGE (without reducing agents), you observe three bands corresponding to 200, 160, and 40 kDA. When repeating the SDS-PAGE a second time but in the presence of beta-mercaptoethanol, you observe bands corresponding to 160, 100, and 40 kDa. What is the subunit composition of the complex?

1. 3 subunits — 160, 100, 40 kDa

2. 4 subunits — 160, 100, 100, 40 kDa

3. 3 subunits — 200, 160, 40 kDa

4. 4 subunits — 200, 160, 100, 40 kDa

5. 2 subunits — 160, 40 kDa

2. 4 subunits — 160, 100, 100, 40 kDa (beta-mercaptoethanol reduces 200 into 2 subunits (100, 100))

One of the following ions has a higher concentration inside the cell than outside. Which one?

1. K+

2. Na+

3. Cl-

4. HCO3-

1. K+

The concentration of chloride ions is 4 mM inside the cell, and 116 mM outside. Which anion balances this chemical gradient?

Proteins!

The Vmax of glucose transport into human cells depends on the

1. affinity of the transport towards glucose

2. the number of transporters in the PM

2. the number of transporters in the PM

The four main types of extracellular signalling pathways are endocrine, autocrine, cell-cell contacts, and ____

Paracrine

Which effect do GPCRs have on trimeric G-proteins:

1. act as GAPs

2. act as GEFs

3. trigger endocytosis

4. trigger tyrosine phosphorylation

2. act as GEFs

PKC is activated by:

1. DAG

2. TAG

3. PC

4. CL

1. DAG

What is the ‘mesoscale’ organization of proteins?

Protein to organelle level organization

Intrinsically disordered proteins are enriched in which of the following amino acids?

1. Leu, L

2. Lys, K

3. Met, M

4. Pro, P

4. Pro, P

Which amino acid residues do SH2 domains bind to?

1. phospho-serine

2. phospho-threonine

3. phospho-lysine

4. phospho-tyrosine

4. phospho-tyrosine

True/False: Nucleoli are separated from the nucleoplasm by a membrane bilayer

False — Nucleoli lives in the nucleoplasm

Nuclear Export Signals are:

1. acidic

2. basic

3. hydrophobic

4. amphipathic

3. hydrophobic

Nuclear Localization Signals are:

1. acidic

2. basic

3. hydrophobic

4. amphipathic

2. basic

The general import pore in mitochondria is:

1. Tom20

2. Tom22

3. Tom40

4. Tom70

3. Tom40

Peroxisomal targeting sequences (PTS) are recognized by:

1. Pex1

2. Pex5

3. Pex6

4. Pex14

2. Pex5

Why are lipid droplets (LDs) the only organelle surrounded by a lipid monolayer?

They bud from between the PM leaflets

In F-actin, the minus-end corresponds to:

1. the end at which the ATP-binding cleft is exposed

2. the end at which the ATP-binding cleft is buried

1. the end at which the ATP-binding cleft is exposed

True/False: Microtubules assemble ATP-tubulin dimers at their (+) end

False — Beta-tubulin (-) end

Which tubulin subunit does not hydrolyze its GTP:

1. alpha

2. beta

3. gamma

1. alpha

True/False: All motor proteins are GTPases

False — there are 3 filament systems

What does binding of ATP to the motor head in kinesin cause?

Binding of ATP causes conformational change causing the linker to swing forward and dock into the head. This is the power stroke!

Which 3 phases characterize the interphase in a human cell cycle?

G1, S, G2

The nuclear envelope abruptly breaks down during:

1. prophase

2. prometaphase

3. metaphase

4. anaphase

2. prometaphase

True/False: The phosphatase Cdc25 removes an inhibitory phosphorylation site on CDKs

True

True/False: The protein p53 is an oncogene

False — p53 is inactivated in tumors (loss-of-function, tumor supressor)

Why can RTKs act as oncogenes (gain-of-function mutations)?

RTKs can get gain-of-function mutations (oncogenic) which makes them always signaling or always on to promote cell growth and cell division

Which of the following is NOT a tumor suppressor:

1. p53

2. p14ARF

3. Cdk2

4. myc

4. myc