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University of South Carolina-Columbia
CHEM 333 Bio Cell and Molc. Exam 4
Questions and Answers 2026 Latest Update
What does a target cell require to respond to an extracellular molecule?
(three things) Ans: Access to the signal molecule, appropriate intracellular
signaling pathways, and the presence of an appropriate receptor for the
signal molecule
T/F Each type of extracellular signal molecule induces a similar response in
different target cells Ans: False
The GTP binding proteins that act as molecular switches inside the cells are
active when what happens? Ans: When GTP is bound
Which components of a G protein can on its own activate target proteins in
an intracellular signaling pathway? Ans: alpha subunit and beta gamma
complex
Small intracellular signaling molecules are often called: Ans: secondary
messengers
Ras is activated by a Ras-activating protein that does what? Ans: causes Ras
to exchange GDP for GTP
The phosphorylated tyrosines on activated RTKs do what? Ans: serve as
binding sites for a variety of intracellular signaling proteins
As a cell grows, which microtubule-associated protein pulls the Golgi
apparatus inward, toward the nucleus? Ans: Dynein
Acetylcholine binds to a GPCR on heart muscle, making the heart beat more
slowly. The activatedreceptor stimulates a G protein, which opens a K+
channel in the plasma membrane, as shown in Figure1. Which of the
following would repress or weaken this effect of the acetylcholine signaling
© 2026 All rights reserved
, 2 | Page
molecule?(A) mutations in the acetylcholine receptor that weaken the
interaction between the receptor and the Gprotein
(B) addition of a drug that prevents the α subunit from exchanging GDP for
GTP
(C) mutations in the acetylcholine receptor that weaken the interaction
between the receptor andacetylcholine
(D) all of the above
(See Exam 4 practice problems for figure) Ans: D. All of the above
As a cell grows, which microtubule-associated protein pulls the ER
membrane outward, stretching it like a net? Ans: Kinesin
If GTP hydrolysis occurs on a tubulin molecule at the plus end of a
microtubule protofilament before another tubulin molecule is added, what
typically happens? Ans: The microtubule depolymerizes
Which end of a microtubule is embedded in the centrosome? Ans: the minus
end
What is the name of the thin sheetlike structures that a fibroblast regularly
extends during cell crawling? Ans: Lamellipodia
T/F Myosins are motor proteins that use the energy of ATP hydrolysis to
move along actin filaments. Ans: True
What is the main function of intermediate filaments? Ans: They enable cells
to withstand mechanical stress that occurs when cells are stretched
The hydrolysis of bound ATP to ADP in an actin filament ___________
(increases, decreases, N/A) the strength of binding between monomers in
the filament Ans: decreases
T/F Cell signaling can act in a variety of ways, initiating responses either
slowly or rapidly Ans: True
Which of the following is NOT a method of long-range signaling?
Endocrine
© 2026 All rights reserved
University of South Carolina-Columbia
CHEM 333 Bio Cell and Molc. Exam 4
Questions and Answers 2026 Latest Update
What does a target cell require to respond to an extracellular molecule?
(three things) Ans: Access to the signal molecule, appropriate intracellular
signaling pathways, and the presence of an appropriate receptor for the
signal molecule
T/F Each type of extracellular signal molecule induces a similar response in
different target cells Ans: False
The GTP binding proteins that act as molecular switches inside the cells are
active when what happens? Ans: When GTP is bound
Which components of a G protein can on its own activate target proteins in
an intracellular signaling pathway? Ans: alpha subunit and beta gamma
complex
Small intracellular signaling molecules are often called: Ans: secondary
messengers
Ras is activated by a Ras-activating protein that does what? Ans: causes Ras
to exchange GDP for GTP
The phosphorylated tyrosines on activated RTKs do what? Ans: serve as
binding sites for a variety of intracellular signaling proteins
As a cell grows, which microtubule-associated protein pulls the Golgi
apparatus inward, toward the nucleus? Ans: Dynein
Acetylcholine binds to a GPCR on heart muscle, making the heart beat more
slowly. The activatedreceptor stimulates a G protein, which opens a K+
channel in the plasma membrane, as shown in Figure1. Which of the
following would repress or weaken this effect of the acetylcholine signaling
© 2026 All rights reserved
, 2 | Page
molecule?(A) mutations in the acetylcholine receptor that weaken the
interaction between the receptor and the Gprotein
(B) addition of a drug that prevents the α subunit from exchanging GDP for
GTP
(C) mutations in the acetylcholine receptor that weaken the interaction
between the receptor andacetylcholine
(D) all of the above
(See Exam 4 practice problems for figure) Ans: D. All of the above
As a cell grows, which microtubule-associated protein pulls the ER
membrane outward, stretching it like a net? Ans: Kinesin
If GTP hydrolysis occurs on a tubulin molecule at the plus end of a
microtubule protofilament before another tubulin molecule is added, what
typically happens? Ans: The microtubule depolymerizes
Which end of a microtubule is embedded in the centrosome? Ans: the minus
end
What is the name of the thin sheetlike structures that a fibroblast regularly
extends during cell crawling? Ans: Lamellipodia
T/F Myosins are motor proteins that use the energy of ATP hydrolysis to
move along actin filaments. Ans: True
What is the main function of intermediate filaments? Ans: They enable cells
to withstand mechanical stress that occurs when cells are stretched
The hydrolysis of bound ATP to ADP in an actin filament ___________
(increases, decreases, N/A) the strength of binding between monomers in
the filament Ans: decreases
T/F Cell signaling can act in a variety of ways, initiating responses either
slowly or rapidly Ans: True
Which of the following is NOT a method of long-range signaling?
Endocrine
© 2026 All rights reserved
