Cell Biology Final Exam

The flow of genetic information is controlled by a series of biochemical reactions that result in the production of proteins, each with its own specific order of amino acids. This series of reactions represents the central dogma of cell and molecular biology! Choose the correct series of biochemical events from the options presented here.

a. replication, transcription, translation
b. replication, translation, transcription
c. translation, transcription, replication
d. translation, replication, transcription

a. replication, transcription, translation

The ______ _______ is made up of two concentric membranes and is continuous with the membrane of the endoplasmic reticulum.

a. plasma membrane
b. Golgi network
c. mitochondria membrane
d. nuclear envelope

d. nuclear envelope

What unit of tenth would you generally use to measure a typical plant or animal cell?

a. centimeters
b. millimeters
c. micrometers
d. nanomaters

c. micrometers

An ionic bond between two atoms if formed as a result of the ____.
a. sharing of electrons.
b. loss of electrons from both atoms.
c. loss of a proton from one atom.
d. transfer of electrons from one atom to the other.

d. transfer of electrons from one atom to the other.

Glucose is to starch as ________ is to ______.
a. RNA, DNA
b. amino acid, protein
c. DNA, RNA
d. lipid, polysaccharide
e. all of the above

b. amino acid, protein

Both DNA and RNA are synthesized by covalently linking a nucleotide triphosphate to the previous nucleotide, constantly adding to a growing chain. In the case of DNA, the new strand becomes part of a stable helix. The two strands are complementary in sequence and antiparallel in direction. What is the principal force that holds these two strands together?

a. hydrophobic interactions
b. hydrogen bonds
c. covalent bonds
d. van der Waals interactions
e. ionic bonds

b. hydrogen bonds

Lipids differ from other biological molecules such as carbohydrates, proteins, and nucleic acids in that they:

a. do not have specific shapes
b. are much larger
c. contain nitrogen atoms
d. do not contain carbon
e. are not truly polymers

e. are not truly polymers

Which of the following statements about amino acids is true?

a. Sixty-four amino acids are commonly found in proteins.
b. Most of the amino acids used in protein biosynthesis have charged side chains.
c. Amino acids are often linked together to form branched polymers.
d. All amino acids contain an NH2 and a COOH group.
e. Yeast cells use different kinds of amino acids than human cells.

d. all amino acids contain an NH2 and a COOH group

The energy used by the cell to generate specific biological molecules and highly ordered
structures is stored in the form of _____________.
a. Brownian motion.
b. heat.
c. light waves.
d. chemical bonds.

d. chemical bonds.

ΔG° indicates the change in the standard free energy as a reactant is converted to product.
Given what you know about these values, which reaction below is the most favorable?

a. ADP + Pi ==> ATP ΔG° = +7.3 kcal/mole
b. glucose 1-phosphate ==> glucose 6-phosphate ΔG° = -1.7 kcal/mole
c. glucose + fructose ==> sucrose ΔG° = +5.5 kcal/mole
d. glucose ==> CO2 + H2O ΔG° = -686 kcal/mole

d. glucose ==> CO2 + H2O ΔG° = -686 kcal/mole

The equilibrium constant (K) for the reaction YàX can be expressed with respect to the
concentrations of the reactant and product molecules. Which of the expressions below
shows the correct relationship between K, [Y], and [X]?

a. K = [Y]/[X]
b. K = [Y] * [X]
c. K = [X]/[Y]
d. K = [X] - [Y]

c. K = [X]/[Y]

Oxidation is the process by which oxygen atoms are added to a target molecule. Generally, the
atom that is oxidized will experience which of the following with respect to the electrons in
its outer shell?
a. a net gain
b. a net loss
c. no change
d. an equal sharing

b. a net loss

If proteins A and B have complementary surfaces, they may interact to form the dimeric
complex AB. Which of the following is the correct way to calculate the equilibrium
constant for the association between A and B?

a. kon/koff = K
b. K = [A][B]/[AB]
c. K = [AB]/[A][B]
d. (a) and (c)

d. (a) and (c)

The study of enzymes also includes an examination of how the activity is regulated. Molecules
that can act as competitive inhibitors for a specific reaction are often similar in shape and
size to the enzyme's substrate. Which variable(s) used to describe enzyme activity will
remain the same in the presence or absence of a competitive inhibitor?

a. V
b. Vmax
c. Vmax and Km
d. Km

b. Vmax

You receive a 10 mg dose of Tegretol, which has a half-life of 20 hours. How much of this
drug will be left in your system after 3 half-lives have passed, considering normal enzymatic
conditions?

a. 7.5 mg
b. 5 mg
c. 2.5 mg
d. 1.25 mg
e. 0.625 mg

d. 1.25 mg

A normally functioning protein is converted into a prion by

a. a genetic mutation.
b. cleavage of the protein into smaller pieces.
c. a change in its conformation.
d. covalent bonding to another protein to form protein aggregates.

c. a change in its conformation.

You are studying a biochemical pathway that requires ATP as an energy source. To your
dismay, the reactions soon stop, partly because the ATP is rapidly used up and partly
because an excess of ADP builds up and inhibits the enzymes involved. You are about to
give up when the following table from a biochemistry textbook catches your eye.

Rxn 1. creatine + ATP ==> creatine phosphate + ADP (+3 kcal/mole)
Rxn 2. ATP + H2O ==> ADP + phosphate (-7.3 kcal/molecule
Rxn 3. pyrophosphate + H2O ==> 2 phosphate (-7kcal/mole)
Rxn 4. glucose 6-phosphate + H2O ==> glucose +phosphate (-3.3 kcal/mole)

Which of the following reagents are most likely to revitalize your reaction?

a. a vast excess of ATP
b. glucose 6-phosphate and enzyme D
c. creatine phosphate and enzyme A
d. pyrophosphate

c. creatine phosphate and enzyme A

This is the other question that was dropped. An excess of ATP will initially restore the
reactions, but as ATP is hydrolyzed, ADP will build up and inhibit the enzymes again.
Pyrophosphate does not look like ATP and is therefore unlikely to be used by the enzymes as
an alternative energy source. Pyrophosphate + enzyme D will just heat things up. What you
need is a high-energy source of phosphate that can convert ADP back to ATP. Because the
ΔG° of the reaction

ATP + creatine ==> ADP + creatine phosphate

catalyzed by enzyme A is greater than zero, the addition of creatine phosphate and enzyme A
can be used to form ATP from ADP, regenerating the ATP while also forming creatine as a
waste product.

Lysozyme is an enzyme that specifically recognizes, and breaks down bacterial polysaccharides.
Lysozyme is an effective antibacterial agent. Into what classification of enzymes does
lysozyme fall?

a. isomerase
b. protease
c. nuclease
d. kinase
e. hydrolase

e. hydrolase

Although all protein structures are unique, there are common structural building blocks that are
referred to as regular secondary structures. Some proteins have α helices, some have β
sheets, and still others have a combination of both. What makes it possible for proteins to
have these common structural elements?

a. specific amino acid sequences
b. side-chain interactions
c. hydrogen bonds along the protein backbone
d. the hydrophobic-core interactions
e. a zombie bite.

c. hydrogen bonds along the protein backbone

The figure below is a representation of the structure of a protein. What type of secondary
structure does this protein possess?

a. coiled coils
b. α-helix
c. β-sheet
d. coiled coils and β-sheet
e. α-helix and β-sheet

e. α-helix and β-sheet

Which of the following is the strongest evidence that protein structure and function are
correlated?
a. Denatured (unfolded) proteins do not function normally.
b. Proteins function best at certain temperatures.
c. Proteins have four distinct levels of structure and many functions.
d. Enzymes tend to be globular in shape.

a. Denatured (unfolded) proteins do not function normally.

You identify an enzyme with a total of four active sites. When you denature the protein and
study its composition, you find that each active site occurs on a different polypeptide.
Which of the following hypotheses does this observation support?
a. The enzyme is subject to regulation.
b. The enzyme requires a cofactor to function normally.
c. The protein's structure is affected by temperature and pH.
d. The protein has quaternary structure.

d. The protein has quaternary structure.

A series of hydrophobic side chains will congregate together as a protein folds in an aqueous
solution and be stabilized by ________.

a. disulfide bonds
b. van der Waals interactions
c. hydrogen bonds
d. quaternary structure bonds

b. van der Waals interactions

At which level of protein structure are interactions between the side chains (R-groups) most
important?

a. primary
b. secondary
c. tertiary
d. quaternary
e. These are important at all levels.

c. tertiary

You have isolated a previously unstudied protein, identified its complete structure in detail, and
determined that it catalyzes the breakdown of a large substrate. You notice it has two
binding sites. One of these is large, apparently the bonding site for the large substrate; the
other is small, possibly a binding site for a regulatory molecule. What do these findings tell
you about the mechanism of this protein?

a. It is probably an enzyme that works through allosteric regulation.
b. It is probably a structural protein that is involved in cell-to-cell adhesion.
c. It is probably an enzyme that works through competitive inhibition.
d. It is probably a cell membrane transport protein-like an ion channel.
e. It is probably a structural protein found in cartilage or skeletal tissue.

a. It is probably an enzyme that works through allosteric regulation.

Sodium ions, oxygen (O2), and glucose pass directly through lipid bilayers at dramatically different rates. Which of the following choices presents the correct order, from fastest to slowest?

a. glucose, oxygen, sodium ions
b. glucose, sodium ions, oxygen
c. oxygen, sodium ions, glucose
d. oxygen, glucose, sodium ions

d. oxygen, glucose, sodium ions

Choose the correct order of terms to complete the following statement.

Membrane lipids are _____ molecules, composed of hydrophilic portion and a hydrophobic portion. All cell membranes have the same _______ structure, with the _____ of the phospholipids facing into the interior of the membrane and the _______ on the outside. The most common lipids in most cell membranes are the _____.

a. amphipathic, lipid bilayer, fatty acid tails, hydrophilic head groups, phospholipids
b. glycolipids, lipid bilayer, fatty acid tails, sugars, amphipathic
c. amphipathic, lipid bilayer, sterols, sugars, glycolipids
d. amphipathic, lipid bilayer, fatty acid tails, hydrophilic head groups, glycolipids
e. hydrophobic, amphipathic, fatty acid tails, hydrophilic head groups, glycolipids

a. amphipathic, lipid bilayer, fatty acid tails, hydrophilic head groups, phospholipids

The specialized functions of different membranes are largely determined by the ____________
they contain.

a. phospholipids
b. glycolipids
c. proteins
d. fatty acid tails

c. proteins

The specialized functions of different membranes are largely determined by the ____________
they contain.
a. phospholipids
b. glycolipids
c. proteins
d. fatty acid tails

c. proteins

Where does most new membrane synthesis take place in a eukaryotic cell?

a. in the Golgi apparatus
b. in the endoplasmic reticulum
c. in the plasma membrane
d. in the mitochondria
e. on ribosomes

b. in the endoplasmic reticulum

Membrane lipids are capable of many different types of movement. Which of these does not occur
spontaneously in biological membranes?

a. switching between lipid layers
b. lateral movement
c. rotation
d. flexing of hydrocarbon chains

a. switching between lipid layers

Membrane proteins, like membrane lipids, can move laterally by exchanging positions with other
membrane components. Which type of membrane proteins is expected to be the least mobile,
based on their function?

a. channels
b. anchors
c. receptors
d. enzymes

b. anchors

Cell membranes are fluid, and thus proteins can diffuse laterally within the lipid bilayer. However,
sometimes the cell needs to localize proteins to a particular membrane domain. Which of the
four mechanisms listed below can a cell use to restrict a proteins to a particular domain in the
cell membrane.

1. The protein can be attached to the cell cortex inside the cell.
2. The protein can be attached to the extracellular matrix outside the cell.
3. The protein can be attached to other proteins on the surface of a different cell.
4. The protein can be restricted by a diffusion barrier, such as that set up by specialized
junctional proteins at a tight junction.)

a. 1, 2, and 3 are correct
b. 1, 3, and 4 are correct
c. 1, 2, 3, and 4 are correct
d. 2, 3, and 4 are correct
e. none of these are mechanisms used by cells to localize protein domains.

c. 1, 2, 3, and 4 are correct

Glucose movement from the lumen of the small intestine across the membrane of intestinal
epithelial cells occurs using which of the following processes, and moves glucose
__________________?

a. Glucose/Na+ antiporter; down its concentration gradient
b. Glucose/Na+ antiporter; against its concentration gradient
c. Glucose/Na+ symporter; down its concentration gradient
d. Glucose/Na+ symporter; against its concentration gradient
e. Glucose uniport; down its concentration gradient

d. Glucose/Na+ symporter; against its concentration gradient

Some cells have aquaporins—channels that facilitate the flow of water molecules through the
plasma membrane. For these cells, what regulates the rate and direction of water diffusion
across the membrane?

a. aquaporin conformation
b. resting membrane potential
c. solute concentrations on either side of the membrane
d. availability of ATP

c. solute concentrations on either side of the membrane

Which of the following statements describe certain properties of a passive transporter and the
molecule it moves across the membrane?

a. The transporter requires ATP to function.
b. The direction the molecule move across the membrane is determined by the orientation of
the transporter.
c. The transporter binds to the molecule prior to transferring it across the membrane.
d. The transported molecule diffuses through an open pore in the membrane.
e. Movement of the molecule against its concentration gradient is coupled with the movement
of another molecule going down its concentration gradient.

c. The transporter binds to the molecule prior to transferring it across the membrane.

When an action potential reaches a nerve terminal, what type of voltage-gated channels are opened
and result in the fusion of synaptic vesicles with the cell membrane?

a. Ca2+
b. Cl-
c. K+
d. Na+
e. Mg2+

a. Ca2+

At the time indicated by letter A, ions are able to flow predominately through which type of
channel?

a. voltage-gated Na+ channels
b. voltage-gated K+ channels
c. K+ leak channels
d. Na+ leak channels
e. Ca2+ channels

c. K+ leak channels

At the time indicated by letter B, voltage-gated sodium channels are:

a. open.
b. closed.
c. inactivated.
d. polarized.

a. open

At the time indicated by letter C, ions are predominately flowing through which type of channel?

a. voltage-gated Na+ channels
b. voltage-gated K+ channels
c. K+ leak channels
d. Na+ leak channels
e. Ca2+ channels

b. voltage-gated K+ channels

How would you expect most nucleotides to be absorbed from the lumen of the intestine into
intestinal epithelial cells?

a. by passing directly through the membrane.
b. via a nucleotide pump
c. through a pore in a channel
d. via coupled transport with Na+
e. by endocytosis

d. via coupled transport with Na+

Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell.
Which of the following ions is the most abundant inside a typical mammalian cell?

a. Na+
b. K+
c. Ca2+
d. Cl-

b. K+

The stimulation of auditory nerves depends on the opening and closing of channels in the auditory
hair cells. Which type of gating mechanism do these cells use?

a. voltage-gated
b. extracellular ligand-gated
c. intracellular ligand-gated
d. mechanically-gated

d. mechanically-gated

After eating an especially tasty grinder with taco meat at the Red Pepper, you are thankful for
having functional taste receptors in your mouth. What general class of receptor is typically
responsible our ability to enjoy this fine culinary flavor?

a. receptor tyrosine kinases
b. voltage-gated ion channels
c. receptor serine/threonine kinases
d. G protein-coupled receptors
e. ion channel-linked receptors

d. G protein-coupled receptors

Which type of receptors do steroid hormones generally employ?

a. Enzyme-coupled receptors
b. G-protein-coupled receptors
c. Ion-channel-coupled receptors
d. Cytoplasmic receptors

d. Cytoplasmic receptors

In most cases protein kinases

a. hydrolyze proteins
b. polymerize amino acids
c. stimulate adenylyl cyclase
d. bind cGMP
e. add phosphate groups to proteins

e. add phosphate groups to proteins

The GTP-binding proteins that act as molecular switches inside cells:

a. are active only in their trimeric forms.
b. are active when GDP is bound.
c. are active when GTP is bound.
d. turn themselves on by hydrolyzing GTP to form GDP.
e. turn themselves on by phosphorylating GDP to form GTP.

c. are active when GTP is bound.

Many of the extracellular signal molecules that regulate inflammation are released locally from cells
at the site of infection. What form of cell-to-cell signaling is being used?

a. Endocrine
b. Paracrine
c. Neuronal/synaptic
d. Contact-dependent

b. Paracrine

During nervous-system development in Drosophila, the membrane-bound protein Delta acts as an
inhibitory signal to prevent neighboring cells from developing into neuronal cells. Delta is
involved in ______________ signaling.

a. endocrine
b. paracrine
c. neuronal
d. contact-dependent

d. contact-dependent

Foreign substances like nicotine, morphine, and menthol exert their initial effects by _____.

a. killing cells immediately, exerting their physiological effects by causing cell death.
b. diffusing through cell plasma membranes and binding to transcription factors to change
gene expression.
c. interacting with cell-surface receptors, causing the receptors to transduce signal
inappropriately in the absence of the normal stimulus.
d. removing cell-surface receptors from the plasma membrane.

c. interacting with cell-surface receptors, causing the receptors to transduce signal
inappropriately in the absence of the normal stimulus.

The figure below shows the pathway through which nitric oxide (NO) triggers smooth muscle
relaxation in a blood-vessel wall. Which of the following situations would lead to relaxation of
the smooth muscle cells in the absence of acetylcholine?

a. a smooth muscle cell that has a defect in guanylyl cyclase such that it cannot bind NO
b. a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts
GTP to cyclic GMP
c. a muscle cell that has cyclic GMP phosphodiesterase constitutively active
d. a drug that blocks an enzyme involved in the metabolic pathway from arginine to NO

b. a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts
GTP to cyclic GMP

The following happens when a G-protein-coupled receptor activates a G protein.

a. The β subunit exchanges its bound GDP for GTP.
b. The GDP bound to the α subunit is phosphorylated to form bound GTP.
c. The α subunit exchanges its bound GDP for GTP.
d. It activates the α subunit and inactivates the βγ complex.

c. The α subunit exchanges its bound GDP for GTP.

The length of time a G protein will signal is determined by _______.

a. the activity of phosphatases that turn off G proteins by dephosphorylating Gα.
b. the activity of phosphatases that turn GTP into GDP.
c. the degradation of the G protein after Gα separates from Gβγ
d. the rate of GTPase activity of Gα

d. the rate of GTPase activity of Gα

Activated protein kinase C (PKC) can lead to the modification of the membrane lipids in the
vicinity of the active PKC. Figure Q16-38 shows how G proteins can indirectly activate PKC.
You have discovered the enzyme activated by PKC that mediates the lipid modification. You
call the enzyme Rafty and demonstrate that activated PKC directly phosphorylates Rafty,
activating it to modify the plasma membrane lipids in the vicinity of the cell where PKC is
active; these lipid modifications can be detected by dyes that bind to the modified lipids. Cells
lacking Rafty do not have these modifications, even when PKC is active. Which of the
following conditions would lead to signal-independent modification of the membrane lipids by
Rafty?

a. the expression of a constitutively active phospholipase C
b. a mutation in the GPCR that binds the signal more tightly
c. a Ca2+ channel in the endoplasmic reticulum with an increased affinity for IP3
d. a mutation in the gene that encodes Rafty such that the enzyme can no longer be
phosphorylated by PKC

a. the expression of a constitutively active phospholipase C

In a crawling cell, what is important for making transient adhesions while it crawls?
a. connexons
b. cilia
c. cadherins
d. adherens junctions
e. integrins

e. integrins

In the extracellular matrix of animal tissues, which of the following molecules allows the
matrix to resist compression?
a. Elastin
b. Proteoglycans
c. Collagen
d. Fibronectin
e. Integrin

b. Proteoglycans

What are the main structures providing tensile strength in animal connective tissues, such as
tendons?
a. keratins
b. vimentins
c. laminins
d. actin filaments
e. collagens

e. collagens

As the Na+/K+ ATPase pump is synthesized on ribosomes, what signal sequence would
you expect to be translated?
a. endoplasmic reticulum signal sequence
b. nuclear localization signal
c. mitochondria signal sequence
d. lysosome signal sequence
e. no signal sequence

a. endoplasmic reticulum signal sequence

For both actin and microtubule polymerization, ATP, or GTP, hydrolysis will
a. stabilize the filaments once they are formed.
b. increase the rate at which subunits are added to the filaments.
c. promote nucleation of filaments.
d. decrease the binding strength between subunits on filaments.

d. decrease the binding strength between subunits on filaments

Cell movement involves the coordination of many events in the cell. Which of the
following phenomena is not required for cell motility?
a. Myosin-mediated contraction at the rear of the moving cell.
b. Integrin association with the extracellular environment.
c. Nucleation of new actin filaments.
d. Release of Ca2+ from the sarcoplasmic reticulum.

d. Release of Ca2+ from the sarcoplasmic reticulum.

Phosphorylation of nuclear lamins regulates their assembly and disassembly during mitosis.
You add a drug to cells that are undergoing mitosis that inhibits the activity of the enzyme
that dephosphorylates nuclear lamins. What do you predict will happen to these cells?
a. The nuclear membrane will not be broken down during mitosis, so no chromosome
separation will occur.
b. The nuclear membrane will not reform after chromosome separation, so the
daughter nuclei will not form.
c. Mitosis will occur as normal, as lamins are not involved in chromosome separation.
d. Mitosis will occur normally, but cytokinesis will be disrupted and a cell with two nuclei
will result.

b. The nuclear membrane will not reform after chromosome separation, so the
daughter nuclei will not form.

The figure below shows how normal signaling works with a Ras protein acting downstream
of a receptor tyrosine kinase. You examine a cell line with a constitutively active Ras
protein this is always signaling. Which of the following conditions will turn off the
signaling in this cell line?
a. addition of a drug that blocks protein Y from interacting with its target
b. addition of a drug that increases the activity of protein Y
c. addition of a drug that prevents protein X from activating Ras
d. addition of a drug that increases the affinity of protein Y and Ras

a. addition of a drug that blocks protein Y from interacting with its target

Growth factors, such as platelet derived growth factor (PDGF) and insulin, typically
activate what general class of receptors?
a. Ion channel linked receptors
b. G protein-linked receptors
c. Receptor tyrosine kinases
d. Receptor tyrosine phosphatases
e. Serine/threonine receptor kinases

c. Receptor tyrosine kinases

Calcium initiates skeletal muscle contraction by
a. binding to myosin, causing a conformational change that triggers the "power stroke."
b. stimulating the hydrolysis of ATP needed for myosin binding to actin.
c. changing the conformation of troponin and tropomyosin so myosin can bind to
actin
d. changing the conformation of actin filaments.
e. triggering an action potential

c. changing the conformation of troponin and tropomyosin so myosin can bind to
actin

A protein kinase can act as an integrating molecule in signaling pathways if it
a. is activated by two or more proteins in different signaling pathways.
b. phosphorylates more than one substrate.
c. catalyzes its own phosphorylation.
d. initiates a phosphorylation cascade involving two or more protein kinases.

a. is activated by two or more proteins in different signaling pathways.

Gene expression differs among differentiated cell types within an organism. This means
that
a. different genes are found in the DNA of different cells in the organism.
b. different mRNAs and proteins are produced in different cell types.
c. DNA sequences are modified in different cell types.
d. the cells had to be infected by a virus.
e. alternative DNA splicing has occurred.

b. different mRNAs and proteins are produced in different cell types.

People with the rare disease pachyonychia congenita have thickened and often abnormally
shaped nails, and may have hair that is abnormally twisted, kinked, brittle, or coarse. Which
of the following proteins are abnormal in this disease?
a. tubulin
b. actin
c. collagen
d. keratin
e. vimentin

d. keratin

What is the role of the nuclear localization sequence in a nuclear protein?
a. It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear
pore.
b. It is a hydrophobic sequence that enables the protein to enter the nuclear membranes.
c. It aids protein unfolding in order for the protein to thread through nuclear pores.
d. It prevents the protein diffusing out of the nucleus via nuclear pores.

a. It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear
pore.

Figure B shows different adhesions of intestinal epithelial cells. What type of adhesion
protein is present at the site indicated by #4?
a. Cadherin
b. Adheren
c. Integrin
d. Selectin
e. Laminin

a. Cadherin

Cilia are primarily composed of
a. actin.
b. flagellin.
c. intermediate filaments.
d. microtubules.
e. collagen

d. microtubules

A major regulator of the cell cycle is a protein called cyclin. Cyclin levels gradually
increase before mitosis, and then their levels suddenly drop when mitosis nears completion.
Interestingly, mRNA levels for cyclin are constant throughout the cell cycle. What would
you expect to be responsible for the rapid drop in cyclin levels at the end of mitosis?
a. A decreased transcription of cyclin gene.
b. A decreased translation of cyclin.
c. A decreased in the rate of splicing.
d. An increase in ubiquitin addition to cyclins.
e. An increase in exocytosis of cyclins.

d. An increase in ubiquitin addition to cyclins.

In the axons of neurons, vesicles and organelles are transported both towards and away
from the cell body. This bi-directional movement is due to
a. groups of microtubules oriented in opposite directions.
b. motor proteins that can move forward or reverse on a single microtubule.
c. different motor proteins that move in opposite directions along the same
microtubules.
d. motor proteins moving away from the cell body, and diffusion towards the cell body.

c. different motor proteins that move in opposite directions along the same
microtubules.

Cytochalasin D is a toxin that binds to the plus ends of actin filaments, capping the plus
end and preventing the loss or gain of actin monomers to that end. If cytochalasin binds to
an actin filament in a cell, what will likely happen to that filament?
a. increase in length
b. decrease in length
c. length will remain unchanged
d. undergo treadmilling

b. decrease in length

Which is the main function of intermediate filaments?
a. They enable cells to crawl.
b. They enable cells to withstand the mechanical stress that occurs when cells are
stretched.
c. They enable muscle cells to contract.
d. They provide tracks for guiding intracellular transport.
e. They segregate chromosomes during cell division.

b. They enable cells to withstand the mechanical stress that occurs when cells are
stretched.

Which of the following statements is true for the synthesis and localization of multi-pass
membrane proteins?
a. They are directed to the ER where multiple start and stop transfer sequences
direct their placement into the membrane.
b. They are directed to the ER where all hydrophobic amino acids are made into helices
and placed in the membrane.
c. Once they are synthesized they enter the ER and are processed for placement in the
membrane.
d. When bound to the signal-recognition particle in the cytoplasm they are directed to the
ER and translated into the lumen.

a. They are directed to the ER where multiple start and stop transfer sequences
direct their placement into the membrane.

Of the following steps in protein localization identify all that are used for translocation of
proteins into mitochondria.
I The protein contains a signal sequence
II The protein binds to a localization signal in the cytoplasm.
III The protein is completed translated prior to localization.
IV The protein unfolds as it enters the organelle.
V Chaperone proteins help move the protein into the organelle.
a. Only I, II, and III are used.
b. Only II, III, and V are used.
c. Only I, III, and IV are used.
d. Only I, III, IV, and V are used.
e. All the above are used for translocation of proteins into mitochondria.

d. Only I, III, IV, and V are used.

Which of the following statements about enzyme-coupled receptors, like Receptor
Tyrosine Kinases, is False?
a. These receptors can function as local mediators.
b. These receptors are often associated with cell growth.
c. The receptors have fast response times.
d. The receptors act at low signal concentrations.
e. The receptors often change gene expression.

c. The receptors have fast response times.

Many proteins contain a sorting signal that determines whether the protein ends up in
mitochondria, the endoplasmic reticulum or the cytosol. What is the sorting signal for
proteins?
a. Part of the amino acid sequence of the protein.
b. Whether or not the protein is phosphorylated.
c. Small polypeptides that bind to newly made proteins.
d. A special chemical tag called sortin that is covalently attached to the protein.
e. The sequence of the 3' untranslated region of its mRNA.

a. Part of the amino acid sequence of the protein.