Lc. 10 (cell communication)

Question 1

What property prevents the ligands of cell-surface receptors from entering the cell?
a) The molecules bind to the extracellular domain.
b) The molecules are hydrophilic and cannot penetrate the hydrophobic interior of the plasma membrane.
c) The molecules are attached to transport proteins that deliver them through the bloodstream to target cells.
d) The ligands are able to penetrate the membrane and directly influence gene expression upon receptor binding.

Answer 1

b) The molecules are hydrophilic and cannot penetrate the hydrophobic interior of the plasma membrane.

Question 2

The secretion of hormones by the pituitary gland is an example of _______________.
a) autocrine signaling
b) paracrine signaling
c) endocrine signaling
d) direct signaling across gap junctions

Answer 2

c) endocrine signaling

Question 3

Why are ion channels necessary to transport ions into or out of a cell?
a) Ions are too large to diffuse through the membrane.
b) Ions are charged particles and cannot diffuse through the hydrophobic interior of the membrane.
c) Ions do not need ion channels to move through the membrane.
d) Ions bind to carrier proteins in the bloodstream, which must be removed before transport into the cell.

Answer 3

b) Ions are charged particles and cannot diffuse through the hydrophobic interior of the membrane.

Question 4

Endocrine signals are transmitted more slowly than paracrine signals because ___________.
a) the ligands are transported through the bloodstream and travel greater distances
b) the target and signaling cells are close together
c) the ligands are degraded rapidly
d) the ligands don’t bind to carrier proteins during transport

Answer 4

a) the ligands are transported through the bloodstream and travel greater distances

Question 5

A scientist notices that when she adds a small, water-soluble molecule to a dish of cells, the cells turn off transcription of a gene. She hypothesizes that the ligand she added binds to a(n) ______ receptor.
a) Intracellular
b) Hormone
c) Enzyme-linked
d) Gated ion channel-linked

Answer 5

c) Enzyme-linked

Question 6

What is the function of a phosphatase?
a) A phosphatase removes phosphorylated amino acids from proteins.
b) A phosphatase removes the phosphate group from phosphorylated amino acid residues in a protein.
c) A phosphatase phosphorylates serine, threonine, and tyrosine residues.
d) A phosphatase degrades second messengers in the cell.

Answer 6

b) A phosphatase removes the phosphate group from phosphorylated amino acid residues in a protein.

Question 7

Apoptosis can occur in a cell when the cell is ________________.
a) damaged
b) no longer needed
c) infected by a virus
d) all of the above

Answer 7

d) all of the above

Question 8

What is the effect of an inhibitor binding an enzyme?
a) The enzyme is degraded.
b) The enzyme is activated.
c) The enzyme is inactivated.
d) The complex is transported out of the cell.

Answer 8

c) The enzyme is inactivated.

Question 9

A scientist notices that a cancer cell line fails to die when they add an inducer of apoptosis to his culture of cells. Which hypothesis could explain why the cells fail to die?
a) The cells have a mutation that prevents the initiation of apoptosis signaling.
b) The cells have lost expression of the receptor for the apoptosis-inducing ligand.
c) The cells overexpress a growth factor pathway that inhibits apoptosis.
d) All of the above.

Answer 9

d) All of the above.

Question 10

Which type of molecule acts as a signaling molecule in yeasts?
a) steroid
b) autoinducer
c) mating factor
d) second messenger

Answer 10

c) mating factor

Question 11

Quorum sensing is triggered to begin when ___________.
a) treatment with antibiotics occurs
b) bacteria release growth hormones
c) bacterial protein expression is switched on
d) a sufficient number of bacteria are present

Answer 11

d) a sufficient number of bacteria are present

Question 12

Autocrine Signaling

Answer 12

this signal may be produced and received by the same cell

Question 13

Direct Signaling (GAP junctions)

Answer 13

signal travels from one cell to another without ever leaving the cytoplasm

Question 14

Endocrine Signaling

Answer 14

signal must travel a long distance to reach the target cell

Question 15

paracrine signals

Answer 15

yield a quick, short-lived response

Question 16

Some receptors are located inside of a cell. If this is the case, then the signaling molecules must by small and hydrophobic so they can cross the

Answer 16

Correct answer:
cell membrane

Question 17

Most receptors detect signaling molecules while they are still outside the cell. The receptors need three domains:

1. an external ligand-binding domain called the _________
2. a hydrophobic membrane-spanning region called a ________
3. an ____________ domain inside the cell.

Answer 17

1. Correct answer:
   extracellular
   domain
2. Correct answer:
   transmembrane
   domain
3. Correct answer:
   intracellular

Question 18

The G-protein coupled receptor has GTP and GDP bound states.

Before the signaling molecule (aka ligand) binds the extracellular domain of the receptor, the intracellular components of the receptor are bound to (a)_________

Immediately after the signaling molecule (aka ligand) binds the extracellular domain of the receptor, the intracellular components of the receptor exchange (b)______ for (c)________

Answer 18

a) Correct answer:
GDP

b) Correct answer:
GDP

c) Correct answer:
GTP

Question 19

Pick all the statements below that are true about intracellular signaling.
a) enzymes in the signaling pathway amplify the signal
b) multiple steps are often involved
c) events that occur after the ligand binds the receptor are referred to as upstream events

Answer 19

a) enzymes in the signaling pathway amplify the signal

b) multiple steps are often involved

Question 20

Order the events below for signaling via an enzyme-linked receptor. (CORRECT)

signaling molecule binds the ligand-binding domain

receptors bind together forming a dimer.

Multiple molecules of ATP are hydrolyzed to ADP. The phosphate group that is released from each ATP molecule is transferred to the intracellular domain of the receptor

The phosphate group is transferred to the an intracellular molecule.

Question 21

Ion channel-linked receptors respond to a signaling molecule by letting specific ions pass through. Put the events below in order. (CORRECT)

extracellular ligand binds the extracellular ligand-binding domain on the ion channel.

a conformation change occurs, causing the channel to open

ions pass through the channel which is lined with hydrophilic amino acids.

release of the ligand causes the channel to close

movement of ions through the channel ceases