Test 3. Lecture 31 Flashcards
Within a tissue, cells are often linked by __________, open channels
through the plasma membrane
gap junctions
“gap junctions”
- When open, they ____________ to diffuse freely
between neighboring cells. - They couple both the metabolic activities and the electric responses
of the cells. - In electrically EXCITABLE CELLS, such as heart muscle, ______________ couples and synchronizes the contractions of
neighboring cells. - Gap junctions also allow passage of signaling molecules, such as
___________
, potentially coordinating responses of cells in tissues.
allow ions and small molecules
passage of ions
through gap junctions
cAMP and Ca2+
Gap junctions consist of trans-membrane proteins in the ___________family.
Six connexins form a __________, a cylinder with an open aqueous pore in its
center
connexin
connexon
Connexons of adjacent cells align, forming open channels between the two
_________
cytoplasms
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.
electrical synapse.
Adhesion between plant cells is mediated by the cell walls.
The _________, a pectin-rich region, acts as a glue to hold adjacent cells
together.
middle lamella
Adjacent plant cells communicate through cytoplasmic connections called
__________. Their function is analgous to gap junctions
plasmodesmata
______________ 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.
Plasmodesmata
- 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. - 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. - Many cancers arise from problems in signaling pathways that control
normal cell proliferation.
introduction
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.
Direct cell-cell signaling
Signaling by secreted molecule
____________:Signaling molecules (hormones) are secreted by specialized endocrine cells and
carried through the circulation to target cells at distant body sites.
Example: estrogen
Endocrine signaling
_____________:Molecules released by one cell act on neighboring target cells.
Example: neurotransmitters
PARACRINE SIGNALING
________________: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.
Autocrine signaling
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: _____________
Intracellular
Steroid hormones, thyroid hormone, vitamin D3
, and retinoic acid.
Steroid hormones are synthesized from __________
cholesterol:
_____________, ___________,__________are the sex steroids, produced by
the gonads.
Testosterone, estrogen, and progesterone
Corticosteroids from the adrenal gland:
_____________—stimulate production of glucose.
____________—act on the kidney to regulate salt and water balance.
Glucocorticoids
Mineralocorticoids
___________-is an insect hormone that triggers metamorphosis of larvae to adults.
Ecdysone
_______________ are plant steroid hormones that control several processes,
including cell growth and differentiation.
Brassinosteroids
________________: synthesized from tyrosine in the thyroid gland; important in
development and metabolism.
Thyroid hormone
______________
regulates Ca2+ metabolism and bone growth.
Vitamin D3
__________-and _________-: synthesized from vitamin A; important in vertebrate
development
Retinoic acid and retinoids
“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.
nuclear receptor superfamily.
transcription factors
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.
thyroid hormone receptor
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.
paracrine signaling molecule
The main target of NO is guanylyl cyclase. NO binding stimulates
synthesis of the ___________________
cyclic GMP (a second messenger).
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____________________
second messenger
muscle cell
relaxation and blood vessel dilation.
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.
NO
______________:
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.
neurotransmitters
Many neurotransmitter receptors are____________________
Neurotransmitter binding opens the channels.
ligand-gated ion channels.
Other neurotransmitter receptors are coupled to _______________— a major group of
signaling molecules that link cell surface receptors to intracellular responses.
G proteins
_________________:
include 1. peptide hormones, 2. neuropeptides, and 3.
polypeptide growth factors.
Peptide signaling molecules
_____________ include insulin, glucagon, and pituitary gland hormones (e.g.,
growth hormone, follicle-stimulating hormone, prolactin).
Peptide hormones
_____________ 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.
Neuropeptides
Enkephalins
endorphins
neurohormones
define NEUROHORMONES
natural analgesics that decrease pain responses; they bind to the same receptors on
brain cells as morphine does
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.
- Nerve growth factor (NGF)
- Epidermal growth factor (EGF)
- Platelet-derived growth factor (PDGF)
- Cytokines
- Membrane-anchored growth factors
______________: 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.
Intracellular signal transduction
