Lectures 16-23

EXAM QUESTION!

What is the most important receptor involved in the unfolded protein response (UPR)?

PERK

The unfolded protein response involves ...

a. translation of most proteins.
b. increased synthesis of chaperones.
c. decreased proteasome activity.
d. all of the above.

b. increased synthesis of chaperones

UPR doesn't involve the proteasome at all

T/F: Smooth ER is abundant in cells actively synthesizing steroid hormones.

true

Steroid-secreting cells are characterized by abundant smooth endoplasmic reticulum whose membranes contain many enzymes involved in sterol and steroid synthesis. These cells synthesize cholesterol as a precursor for steroid hormones or take up this substrate from plasma lipoproteins.

he major site at which membrane lipids are synthesized is the ...

a. cytosolic side of the ER membrane.
b. cytosol.
c. lumenal side of the ER membrane.
d. cytosolic side of the Golgi membrane.

a. cytosolic side of the ER membrane.

T/F: Vesicle formation is driven by the binding of clathrin or COP proteins.

true

A KDEL sequence is necessary for ...

a. lysosomal enzymes to reach the lysosome.
b. transmembrane proteins to be targeted to the plasma membrane.
c. binding to KDEL receptors and transport through the trans-Golgi network.
d. the transport of resident ER proteins from the Golgi to the ER.

d. the transport of resident ER proteins from the Golgi to the ER.

T/F: The main method by which a cell gets rid of old

worn-out organelles is exocytosis.

it is phagocytosis

What are the two families of small GTP-binding proteins that are involved in the formation of coated vesicles?

Rab and ARF proteins

T/F: Like many proteins

most cellular phospholipids are synthesized in association with the rough ER.

happens in the smooth ER

The trans-Golgi network is the ...

a. intermediate compartment between the ER and the Golgi.
b. part of the Golgi where fusion of vesicles from the ER occurs.
c. exit part of the Golgi where sorting of proteins to the lysosomes

plasma membrane

T/F: Synthesis of phospholipids occurs mostly on the cytoplasmic side of the ER.

true

Clathrin-coated vesicles are involved in ...

a. retrieval of ER resident proteins from the cis Golgi or the ER-Golgi intermediate compartment.
b. uptake of extracellular molecules by endocytosis and the transport of molecules from the trans-Golgi network to the lysosomes.
c. transport from the ER to the Golgi.
d. recycling of Golgi resident proteins during cisternal maturation.

b. uptake of extracellular molecules by endocytosis and the transport of molecules from the trans-Golgi network to the lysosomes.

T/F: Flippases are enzymes which flip proteins from one face of the phospholipid bilayer to the other face.

false

they flip phospholipids instead of proteins (read carefully)

The major model of vesicle fusion holds that actual fusion of a vesicle with its target membrane is driven by the interaction of pairs of proteins called vesicle and target ...

SNAREs

T/F: Resident ER proteins destined to remain in the lumen of the ER are marked by retrieval sequences and if these proteins are exported from the ER to the Golgi

they are recognized by a recycling receptor in the ERGIC or the Golgi and selectively returned to the ER.

Which of the following would you expect to find at high concentrations in lysosomes?

a. Proteins destined for secretion.
b. Glycosylation enzymes
c. Degradative enzymes
d. Recycling endosomes

c. Degradative enzymes

T/F: Trafficking of proteins in a cell is distinguished solely by different protein sequences

such as nuclear localization signal

careful of the word "solely"

The process by which cells degrade their own components by enclosing them in ER membrane is ...

autophagy

degrading their own cellular materials

T/F: Lysosomes are formed when transport vesicles from the trans-Golgi network fuse with a late endosome.

true

Which coat protein directs retrograde vesicular transport from the ERGIC or Golgi to the endoplasmic reticulum?

COPI (retrograde)

T/F: Gaucher disease is a malady caused by a deficiency in a specific lysosmal enzyme.

true

Where would you expect a protein synthesized on free ribosomes to end up?

a. nucleus
b. extracellular
c. cytosol
d. membrane

Nucleus and cytosol

T/F: the electrochemical gradient within the mitochondria is a result of differential distribution of free electrons.

false

gradient is of protons (H+) so through the hydrogen instead of free ribosomes

T/F: all mitochondria use the universal code.

false

Most mitochondrial genomes consist of...

several circular DNA molecules

T/F: Most mitochondrial proteins are coded for by the mitochondrial genome.

false

most are coded for by the mitochondrial proteome (nuclear genomic DNA)

The outer mitochondrial membrane contains proteins that

a. synthesize ATP
b. pump protons
c. transport pyruvate and ADP
d. direct translocation

d. direct translocation

Everything else is done on the inner membrane

T/F: Mitochondria lacking mitochondrial DNA are soon unable to make ATP by oxidative phosphorylation.

true

Mitochondria differ from other organelles such as lysosomes and the Golgi apparatus in that they ...

contain their own genomes

T/F: Mitochondria contain about 1

500 different proteins.

What is the major site of energy production in the form of ATP in human cells? (2 answers)

inner mitochondrial membrane AND the mitochondrial matrix

T/F: In mitochondria

the pH of the matrix is higher than the pH of the intermembrane space.

The human mitochondrial genome encodes only 22 tRNAs. This limited array of tRNAs can read the 64 possible triplet codons through extreme wobble in base pairing at the third codon position and the use of a(n) ___ genetic code.

non-universal mitochondrial

T/F: The mitochondria is the only organelle to contain a double-membrane.

false

nucleus has a double membrane

Human diseases caused by mutations in mitochondrial genomes ...

are inherited from the mother

egg is huge relative to the sperm so it has a huge cytosol and thousands of mitochondria

the only job of the sperm is to build DNA

T/F: DNA replication

transcription and translation occur in mitochondria.

Assuming that human mitochondria contain about 1

500 different proteins

T/F: The most common genes in mitochondrial DNA are tRNA genes.

true

Which of the following is not one of the functions of the cytoskeleton?

a. To provide a structural framework for the cell
b. Cell locomotion
c. Protein translocation into the ER
d. Intracellular movement of organelles and other structures

c. Protein translocation into the ER

T/F: Actin exists in two forms

a globular G form and a filamentous F form.

Which of the following is not true of the assembly of actin filaments?

a. It begins with the formation of an aggregate of three actin monomers.
b. It requires ATP.
c. Polymerization occurs from both the plus and minus ends.
d. Polymerization is faster from the plus end than from the minus end.

b. It requires ATP

Can bind without ATP but it will be slower

T/F: In muscle

every myofibril is organized as a chain of contractile units called myocytes.

its called a sarcomere

Which of the following is not a function of actin-binding proteins?

a. Filament initiation and polymerization
b. End capping
c. Filament severing/depolymerization
d. Incorporation of microfilaments into the extracellular matrix

d. Incorporation of microfilaments into the extracellular matrix

Associate with the extracellular matrix

T/F: Microtubules are approximately 1/3 the diameter of actin filaments.

false

microtubules are 25nm while actin filament are 7nm

Role of Actin

smallest of the microfilaments

Role of Profilin

an ATP/ADP exchange factor

Role of Formin

nucleates or seeds initial polymerization of actin filaments

Role of Arp2/3

initiates growth of filament branches

Role of Cofilin

severs filaments creating 2 new ends

T/F: Microvilli such as those found in intestinal epithelial cells are are largely composed of actin filaments organized into bundles.

true

The major cation responsible for regulating actin-myosin contraction is ...

calcium

The basis for muscle contraction is the ...

a. rotation of myosin fibers around actin fibers.
b. expansion of the sarcomere.
c. sliding of myosin and actin fibers past each other.
d. movement of the Z discs away from each other.

c. sliding of myosin and actin fibers past each other

According to the chemiosmotic theory

what is produced by the electron transport chain that is used to drive ATP synthesis by oxidative phosphorylation?

Arp2/3 plays a role in cell migration by...

catalyzing branch point formation int he developing actin network at the leading edge

Both calcium ions and ATP are needed for muscle contraction because...

Calcium provides the access for myosin action

Where is Ca+ reserve stored in the cell?

sarcoplasmic reticulum

T/F: someone with a disease that inhibits hydrolysis of ATP can move their muscles.

true

only one movement

What is Rigor Mortis?

Postmortem change resulting in the stiffening of the body muscles due to chemical changes in their myofibrils. Without ATP

What is Botulism?

Rare illness caused by a toxin that interferes with the release of acetylcholine from the end of the nerve. Acetylcholine attaches to the muscle causing contraction and if it not available

Dynein and kinesin are similar in that they consist of heavy chains with globular heads which bind both .... and ....

ATP

microtubules

T/F: The cycle of alternating growth and shrinkage of microtubules is referred to as dynamic instability

or rescue and catastrophe.

EXAM MATCHING QUESTION!!!

A centrosome is ...

a. a cylindrical structure made up of nine triplets of microtubules.
b. a chromosomal region that connects sister chromatids during mitosis and attaches them to the spindle.
c. a protein structure that binds centromeres and mediates the attachment of chromosomes to the spindle.
d. the major microtubule-organizing center in animal cells.

a. a cylindrical structure made up of nine triplets of microtubules (centriole)

b. a chromosomal region that connects sister chromatids during mitosis and attaches them to the spindle (centromere)

c. a protein structure that binds centromeres and mediates the attachment of chromosomes to the spindle (kinetochore)

d. the major microtubule-organizing center in animal cells (centrosome)

T/F: Kinesins and dyneins are molecular motor proteins.

true

Whether a microtubule shrinks or grows is determined by ...

a. the rate of GTP-bound tubulin addition relative to the rate of tubulin GTP hydrolysis.
b. the phosphorylation state of ß-tubulin.
c. the rate of ATP hydrolysis relative to the rate of ATP-bound tubulin addition.
d. the presence or absence of gamma-tubulin.

a. the rate of GTP-bound tubulin addition relative to the rate of tubulin GTP hydrolysis

T/F: Epidermolysis bullosa simplex is a skin disease caused by a mutation in the gene encoding keratin.

true

Myosin II is found in skeletal muscle and the contractile ring. It is a two-headed myosin with tails that can form thick filaments. Other myosins

such as myosin I or myosin V

T/F: All cytoskeletal filaments have polarity.

false

intermediate filaments do not have polarity while all the rest do

Like myosins

kinesins and dyneins are both families of proteins. Which statement is true of all kinesins and dyneins?

a. They are microtubule-dependent motors.
b. They are minus-end-directed motors.
c. The motor activity of the proteins resides in their light chains.
d. They are plus-end-directed motors.

T/F: Desmosomes are specialized junctions that help hold cells together

while their counterpart hemidesmosomes prevent cell-to-cell contact.

Which statement about intermediate filaments is true?

a. Rather than consisting of a single type of protein

they can be made up of a number of different proteins.
b. They are involved in cell movement.
c. The basic structure of an intermediate filament protein is a globular head and a long a-helical tail.
d. Like microfilaments

T/F: Actin and beta-tubulin are enzymes.

true

Microtubules are assembled from ...

a. a-tubulin dimers.
b. b-tubulin dimers.
c. alternating a-tubulin dimers and b-tubulin dimers.
d. dimers of a- and b-tubulin.

d. dimers of a- and b-tubulin

EXAM QUESTION!

T/F: All cytoskeletal filaments can be regulated by phosphorylation.

true

intermediate filaments

Rings of the protein ___ in the pericentriolar material nucleate microtubule assembly.

g-tubulin

Which statement about integrins is false?

a. The b subunit binds divalent cations.
b. Each subunit has a large extracellular head group.
c. Each subunit has a short cytoplasmic domain that interacts with intracellular proteins such as talin

a-actinin

Adherens junctions and desmosomes may be distinguished from each other based on of ....

a. the presence of cadherins versus integrins.
b. the linkage of cadherins either to actin filaments or to intermediate filaments

respectively.
c. whether the cadherins are linked directly or indirectly to the cytoskeletal elements.
d. whether the linkage is between two cells or between a cell and the extracellular environment.

EXAM QUESTION

Which of the following is an example of endocrine signaling?

a. Epinephrine release by motor neurons at the neuromuscular junction and binding to receptors on adjacent skeletal muscle cells.
b. Antigen stimulation of T lymphocytes

leading to the stimulation and synthesis of a growth factor that drives their own proliferation.
c. Insulin release by b cells in the pancreas

A major function of tight junctions is to ....

a. create strong cell-cell adherence.
b. promote the intermixing of proteins between the apical and basolateral surfaces of cells.
c. seal the space between adjacent cells to provide

for example

T/F: All signaling molecules bind to receptors on the cell surface.

false

Many steroids are derived from ...

a. phospholipids
b. fatty acids
c. cholesterol
d. receptors
e. LDL

c. cholesterol

T/F: Most signaling molecules have a transient effect on cells.

true

transient effect on cells rather than permanent effect

The term "paracrine signaling" refers to ...

a. signaling between cells located far from each other.
b. stimulation of a cell by substances produced by the cell itself.
c. signaling between cells located close to each other.
d. signaling between parenchyma cells.

c. signaling between cells located close to each other

Which steroid hormone(s) is(are) not secreted by the gonads?

a. Corticosteroids
b. Progesterone
c. Estrogen
d. Testosterone

a. Corticosteroids

T/F: Signaling molecules that activate cell surface receptors are essentially the same as those that activate intracellular receptors.

false

cell surface receptors do not move or travel through the cell while the intracellular receptors do

T/F: Intracellular signaling pathways provide multiple opportunities for the amplification of a response to an extracellular signal.

true