Test 3. Lecture 31

Question 1

Within a tissue, cells are often linked by __________, open channels
through the plasma membrane

Answer 1

gap junctions

Question 2

“gap junctions”

1. When open, they ____________ to diffuse freely
   between neighboring cells.
2. They couple both the metabolic activities and the electric responses
   of the cells.
3. In electrically EXCITABLE CELLS, such as heart muscle, ______________ couples and synchronizes the contractions of
   neighboring cells.
4. Gap junctions also allow passage of signaling molecules, such as
   ___________
   , potentially coordinating responses of cells in tissues.

Answer 2

allow ions and small molecules

passage of ions
through gap junctions

cAMP and Ca2+

Question 3

Gap junctions consist of trans-membrane proteins in the ___________family.

Six connexins form a __________, a cylinder with an open aqueous pore in its
center

Answer 3

connexin

connexon

Question 4

Connexons of adjacent cells align, forming open channels between the two
_________

Answer 4

cytoplasms

Question 5

Specialized gap junctions occur on specific nerve cells and form an
____________

Individual connexons can be opened or closed. When open, they allow rapid
passage of ions between the two nerve cells.

Several human diseases are associated with connexon mutations.

Answer 5

electrical synapse.

Question 6

Adhesion between plant cells is mediated by the cell walls.

The _________, a pectin-rich region, acts as a glue to hold adjacent cells
together.

Answer 6

middle lamella

Question 7

Adjacent plant cells communicate through cytoplasmic connections called
__________. Their function is analgous to gap junctions

Answer 7

plasmodesmata

Question 8

______________ form by incomplete separation of daughter cells following
mitosis.

At each one, the plasma membrane of one cell is continuous with that of its
neighbor, creating a channel between the two cytosols.

An extension of the smooth ER passes through the pore, leaving a ring of
surrounding cytoplasm through which IONS AND SMALL MOLECULES CAN PASS FREELY

Plasmodesmata can open or close, allowing regulated passage of
macromolecules and regulatory molecules such as transcription factors.

PROTEINS AND LIPIDS can be targeted to plasmodesmata in response to
specific signals.

Answer 8

Plasmodesmata

Question 9

1. Bacteria and unicellular eukaryotes respond to environmental signals and
   to signaling molecules secreted by other cells for mating and other
   communication.
   In multicellular organisms, cell-cell communication is highly sophisticated.
   Each cell must be carefully regulated to meet the needs of the organism
   as a whole.
2. A variety of signaling molecules are secreted or expressed on the surface
   of one cell, and bind to receptors expressed by other cells.
   Binding of signal molecules to receptors initiates a series of reactions that
   regulate all aspects of cell behavior.
3. Many cancers arise from problems in signaling pathways that control
   normal cell proliferation.

Answer 9

introduction

Question 10

Signaling molecules range in complexity from simple gases to proteins.
Some carry signals over long distances; others act locally.
They also differ in modes of action:

• Some cross the plasma membrane and bind to intracellular receptors;

• others bind to receptors on the cell surface.
Modes of cell signaling include:

• _________—direct interaction of a cell with its neighbor,
(e.g., via integrins and cadherins).

• _____________-—three categories are based on the
distance over which signals are transmitted.

Answer 10

Direct cell-cell signaling

Signaling by secreted molecule

Question 11

____________:Signaling molecules (hormones) are secreted by specialized endocrine cells and
carried through the circulation to target cells at distant body sites.
Example: estrogen

Answer 11

Endocrine signaling

Question 12

_____________:Molecules released by one cell act on neighboring target cells.
Example: neurotransmitters

Answer 12

PARACRINE SIGNALING

Question 13

________________:Cells respond to signaling molecules that they themselves produce.
Example: T lymphocytes respond to antigens by making a growth factor that
drives their own proliferation, thereby amplifying the immune response.

Answer 13

Autocrine signaling

Question 14

Receptors may be located on the (1) cell surface or (2) inside the cell.
_____________ respond to small hydrophobic molecules that can diffuse
across the plasma membrane.

Examples: _____________

Answer 14

Intracellular

Steroid hormones, thyroid hormone, vitamin D3
, and retinoic acid.

Question 15

Steroid hormones are synthesized from __________

Answer 15

cholesterol:

Question 16

_____________, ___________,__________are the sex steroids, produced by
the gonads.

Answer 16

Testosterone, estrogen, and progesterone

Question 17

Corticosteroids from the adrenal gland:

_____________—stimulate production of glucose.

____________—act on the kidney to regulate salt and water balance.

Answer 17

Glucocorticoids

Mineralocorticoids

Question 18

___________-is an insect hormone that triggers metamorphosis of larvae to adults.

Answer 18

Ecdysone

Question 19

_______________ are plant steroid hormones that control several processes,
including cell growth and differentiation.

Answer 19

Brassinosteroids

Question 20

________________: synthesized from tyrosine in the thyroid gland; important in
development and metabolism.

Answer 20

Thyroid hormone

Question 21

______________

regulates Ca2+ metabolism and bone growth.

Answer 21

Vitamin D3

Question 22

__________-and _________-: synthesized from vitamin A; important in vertebrate
development

Answer 22

Retinoic acid and retinoids

Question 23

“glucocorticoid action

Receptors for these molecules: members of ______________

They are ____________ that have domains for ligand binding, DNA binding,
and transcriptional activation.
The steroid hormones and related molecules directly regulate gene expression.

Ligand binding regulates their
function as activators or
repressors of genes.
Some nuclear receptors are
inactive in the absence of
hormone:
• Glucocorticoid receptor is
bound to Hsp90 chaperones in
the absence of hormone.
• Glucocorticoid binding
displaces Hsp90 and leads to
binding of regulatory DNA
sequences.

Answer 23

nuclear receptor superfamily.

transcription factors

Question 24

Hormone binding can alter the activity of a receptor:

• In the absence of hormone, _____________- is associated with a
corepressor complex and represses transcription of target genes.

• Hormone binding results in activation of transcription.

Answer 24

thyroid hormone receptor

Question 25

Nitric oxide (NO) is a \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ in the nervous, immune, and
circulatory systems.

• It can cross the plasma membrane and alter the activity of enzymes.
• NO is synthesized from arginine. nitric oxide synthase (NOS)
• Its action is restricted to local effects, because
• it is extremely unstable, with a half-life of only a few seconds.

Answer 25

paracrine signaling molecule

Question 26

The main target of NO is guanylyl cyclase. NO binding stimulates
synthesis of the ___________________

Answer 26

cyclic GMP (a second messenger).

Question 27

A ________________- is a molecule that relays a signal from a receptor to
a target inside the cell.

NO can signal DILATION OF BLOOD VESSELS: Neurotransmitters act on
endothelial cells TO STIMULATE NO SYNTHESIS.

NO diffuses to SMOOTH MUSCLE CELLS and stimulates cGMP production.
cGMP induces____________________

Answer 27

second messenger
muscle cell

relaxation and blood vessel dilation.

Question 28

Carbon monoxide (CO), also functions as a signaling molecule in the
nervous system.

It is related to _________ and acts similarly as a neurotransmitter and mediator of
blood vessel dilation.

Answer 28

NO

Question 29

______________:

 carry signals BETWEEN NEURONS or from NEURONS TO OTHER TARGET CELLS

 are released when an action potential arrives at the end of a neuron.

 diffuse across the synaptic cleft and bind to receptors on the target cell surface.

 hydrophilic; can’t cross plasma membranes and must bind to cell surface receptors.

Answer 29

neurotransmitters

Question 30

Many neurotransmitter receptors are____________________

Neurotransmitter binding opens the channels.

Answer 30

ligand-gated ion channels.

Question 31

Other neurotransmitter receptors are coupled to _______________— a major group of
signaling molecules that link cell surface receptors to intracellular responses.

Answer 31

G proteins

Question 32

_________________:
include 1. peptide hormones, 2. neuropeptides, and 3.
polypeptide growth factors.

Answer 32

Peptide signaling molecules

Question 33

_____________ include insulin, glucagon, and pituitary gland hormones (e.g.,
growth hormone, follicle-stimulating hormone, prolactin).

Answer 33

Peptide hormones

Question 34

_____________ are secreted by some neurons.

____________AND _________ act as neurotransmitters and as NEUROHORMONES—
natural analgesics that decrease pain responses; they bind to the same receptors on
brain cells as morphine does.

Answer 34

Neuropeptides

Enkephalins
endorphins

neurohormones

Question 35

define NEUROHORMONES

Answer 35

natural analgesics that decrease pain responses; they bind to the same receptors on
brain cells as morphine does

Question 36

Five polypeptide growth factors:

1) )_____________is a member of the neurotrophin family that regulates
development and survival of neurons.
2) _______________stimulates cell proliferation. It is the prototype for
the study of growth factors.
3)_______________ is stored in blood platelets and released
during blood clotting at the site of a wound.
It stimulates proliferation of fibroblasts, contributing to regrowth of the damaged tissue.
4) _____________ regulate development and differentiation of blood cells and activities of
lymphocytes during the immune response.
5) _________________ remain associated with the plasma
membrane and function as signaling molecules in direct cell-cell interactions.

Answer 36

1. Nerve growth factor (NGF)
2. Epidermal growth factor (EGF)
3. Platelet-derived growth factor (PDGF)
4. Cytokines
5. Membrane-anchored growth factors

Question 37

______________: The surface receptors regulate intracellular
enzymes, which then transmit signals from the receptor to a series of additional
intracellular targets.

The targets of signaling pathways frequently include transcription factors.
Ligand binding to a receptor initiates a chain of intracellular reactions, ultimately
reaching the nucleus and altering gene expression.

Answer 37

Intracellular signal transduction