Chapter 11 Cell Communication Flashcards
_________ is absolutely essential for multicellular organisms
Cell-to-cell communication
What indicates to biologists that cell-cell signaling has been conserved in evolution over time?
Biologists have discovered universal mechanisms of cellular regulation involving the same small set of cell-signaling mechanisms.
How do cells most often communicate?
Cells most often communicate by chemical signals, although signals may take other forms.
How does yeast use cell signaling?
• Saccharomyces cerevisiae, the yeast of bread, wine, and beer, identifies potential mates by chemical signaling.
What are the two yeast sexes?
There are two sexes, a and alpha
Describe the three steps in yeast mating.
- Exchange of mating factors- a and alpha each secrete a signaling molecule which binds to the receptor of the other mating type
- Mating-the two cells grow toward each other and undergo other cellular changes
- New alpha/a cell-The two cells fuse, or mate, to form an a/alpha cell containing the genes of both cells
What is a signal transduction pathway?
the process by which a signal on a cells surface is converted into a specific cellular response
Describe how cells communicate by direct contact.
-Cell junctions in animal and plant cells- signaling substances dissolved into the cytosol can pass through easily
What are the cell junctions in animal cells? Plant cells?
- Gap junctions
- Plasmodesmata
Describe another way that animal cells can communicate by direct contact. What is this used for?
- Membrane bound cell surface molecules (cell-cell recognition)
- Embryonic development and the immune response
What do local regulators do?
signals that influence cells in the local vicinity
Name one type of local regulators.
Growth Factors- stimulate nearby target cells to grow and multiply
Name the two types of local signaling.
paracrine and synaptic
What is paracrine signaling?
when numerous cells simultaneously receive and respond to growth factors produced by a single cell in their vicinity
What is synaptic signaling?
a nerve cell produces a neurotransmitter that diffuses across a synapse to a single cell that is almost touching the sender
The transmission of a signal through the nervous system can also be considered and example of _________
long distance signaling
Name a feature of plant communication that is not well understood.
Local signaling is not well understood because of cell walls
What is used for long distance signaling?
hormones
How do hormones work in animals?
specialized endocrine cells release hormones into the circulatory system, by which they travel to other parts of the body
What are plant hormones called? And how do they travel?
Plant hormones called growth regulators may travel in vessels but more often travel through air diffusion
Describe two different plant and animal hormones.
- Ethylene (C2H4) - promoted fruit ripening and regulated growth in plants- capable of passing through cell walls
- Insulin- regulates blood sugar levels in mammals- protein with thousands of atoms
What are the three stages of signaling?
reception, transduction, and response
What did E. W. Sutherland’s work focus on?
how epinephrine stimulates the breakdown of glycogen in the liver and skeletal muscle
How does epinephrine work?
- released from adrenal gland during physical or mental stress
- mobilizes fuel reserves
What enzyme does epinephrine activate?
- cytosolic enzyme- glycogen phosphorylase
What is a ligand?
a small molecule that binds with specificity to a larger molecule
What occurs when a ligand binds to a receptor?
- causes the receptor protein to undergo a change in shape
- activates receptor to interact with other molecules
- may cause aggregation of receptor molecules, leading to further molecular events
What are most signal receptors like?
most signal receptors are plasma membrane proteins whose ligands are large water soluble molecules that are too larges to cross the plasma membrane
If receptor proteins are not on the membrane they may be__________
Intracellular
Where may signal receptors be dissolved inside a cell?
in the cytosol or nucleus
What must intracellular signals be to pass through the cellular membrane?
hydrophobic enough or small enough
Name a hydrophobic messenger and a small messenger.
- hydrophobic messengers include the steroid and thyroid messengers of animals
- nitric oxide is a gas whose small size allows it to pass between membrane phospholipids
Name an intracellular hormone. Describe how it works.
Testosterone
- cytosol of target cells contains receptor molecules that bind testosterone activating the receptor
- activated proteins enter the nucleus and turn on specific genes that control male sex characteristics
What do transcription factors do?
control which genes are turned on and may be transcribed into messenger RNA
What are the three types of membrane receptors?
G-protein linked receptor, receptor tyrosine kinases, and gated ion channels
What does a G-protein linked receptor consist of?
a receptor protein linked with a G-protein on the cytoplasmic side
What spans the membrane in a G-protein linked receptor?
7 alpha helices
What are three signaling molecules that G-protein linked receptors bind?
yeast mating factors, epinephrine, neurotransmitters
What does a G protein act like?
-an on/off switch
Name the 4 steps in G-protein linked receptors
- GDP is bound to the G-protein, and it is inactive
- Signal binds to the outside of the receptor and G-protein binds GTP and becomes active
- G-protein leaves receptor and diffuses along the plasma membrane to bind to an enzyme, altering its activity
- activated enzyme triggers next step in a pathway
What happens when he G-protein activates its pathway?
The g-protein acts as a GTPase enzyme to hydrolyze GTP to GDP, turning the G-protein off and returning to its original state
What do G-protein systems function in?
- embryonic development
- vision, and smell
What diseases involve G-portien linked receptors?
Bacterial infections such a cholera and botulism
When is the tyrosine kinase receptor system effective?
when the cell needs to trigger several signal transduction pathways and cellular responses at once
What does the tyrosine kinase receptor system help the cell to do?
-regulate and coordinate many aspects or cell growth and reproduction
What is a kinase?
an enzyme that catalyzes the transfer of phosphate groups
What does the cytoplasmic side of a tyrosine kinase receptor function as and what does that mean?
- functions as a tyrosine kinase- transferring atp from ATP to tyrosine on a substrate protein
What are the parts of a tyrosine kinase receptor?
- extracellular signal binding site
- single alpha helix spanning membrane
- intracellular tail with several tyrosine
Describe the steps in a tyrosine kinase receptor.
- signal molecule binds
- two receptors dimerize
- activates tyrosine tail
- tyrosines add phosphate groups from ATP to the other tyrosine
- phosphorylates a variety of specific relay proteins that bind to tyrosine molecules
- activated relay proteins trigger many different transduction pathways and responses
What is a ligand gated ion channel?
membrane receptor that can act as a gate when the receptor changes shape
How does a ligand gated ion channel work?
When a signal molecule binds as a ligand to the receptor protein the gate opens to allow the flow of ions through a channel receptor
What are ligand gated ion channels important to in the body?
nervous system
How do ligand ion channels operate in the nervous system?
-Neurotransmitter molecules released at a synapse between two neurons bind as ligands to ion channels on the receiving cell
What may gated ion channels respond to?
electrical signals instead of ligands
Transduction is usually______
a multistep pathway, these pathways amplify a signal, and provide more opportunities for coordination and regulation
Signal transduction pathways act like____
falling dominoes
What do most of the relay molecules in transduction have in common?
mostly proteins
What occurs at each step of transduction?
- the signal is transduced into a different form by a conformational change brought about by phosphorylation
Where does most phosphorylation occur?
serine or threonine amino acids of the substrate protein
What is it called when protein kinases act on other protein kinases in a pathway?
phosphorylation cascade
Why does phosphorylation lead to a conformational change?
because of the interaction between the newly activated phosphate group and charged or polar amino acids on the protein
What does phosphorylation of a protein do?
converts it from an inactive form to an active form
What does abnormal activity of protein kinases do?
can cause abnormal cell growth and may contribute to the development of cancer
What turns off a signal transduction pathway?
protein phosphatases
Name two functions of protein phosphatases.
- removing phosphate groups from proteins
- make protein kinases available for reuse
The activity of a protein regulated by phosphorylation depends on_______
the balance of active kinase molecules and active phosphatase molecules
What are second messengers?
small, water soluble, non-protein molecules or ions
How do second messengers travel through the cell?
they rapidly diffuse
What pathways do second messengers participate in?
pathways initiated by both G-protein coupled receptors and tyrosine kinase receptors
What are two of the most widely used second messengers?
cyclic AMP and calcium ions
Describe a second messenger in epinephrine’s pathway.
- Binding by epinephrine increases concentration of cAMP in cytosol
- Receptor activates adenylyl cyclase which converts ATP to cAMP
- cAMP is short lived as phosphodiesterase converts it to AMP
What is the effect of caffeine on the body?
- artificial way to keep the body alert
- blocks conversion of cAMP to AMP maintaining the system in a state of activation without epinephrine
What may cAMP activate?
kinase A- which then phosphorylates various other proteins
How can G-protein systems regulate cell metabolism?
Regulation of cell metabolism is provided by G-protein systems that inhibit adenylyl cyclase
How does cholera cause disease?
- disrupts G-protein signaling pathways
- colonizes in the small intestine and produces a toxin that modifies a G-protei that regulates salt and water secretion
- protein remains stuck in its active form and continuously stimulates adenylyl cyclase to make cAMP
- intestinal cells secrete large amounts of water and salts into the intestines causing diarrhea
Many signal molecules in animals induce responses through transduction pathways that release _______?
-Calcium ions
What is the function of calcium in animal cells? Plant cells?
Animal cells- contraction of muscle cells, secretion of certain substances, cell division
Plant cells- pathway for greening in response to light
Calcium ion concentration is _____ in the cytosol than outside the cell.
lower
What mechanisms attempt to maintain correct calcium ion concentration?
Protein pumps transport Ca2+ outside the cell or into the ER.
What does low calcium concentration in the cytosol mean?
small changes in the numbers of ions causes a large percentage change in calcium concentration
What second messengers are involved in the release of calcium ions?
DAG diacylglycerol
IP3 inositol triphosphate
How are DAG and IP3 created?
When phospholipase cleaves membrane phospholipid PIP2
What does IP3 do?
activates a gated-calcium channel, releasing calcium ions from the ER
List examples of responses.
- turning on or off genes
- synthesis of enzymes or other proteins
- change in cell metabolism
What are are the two benefits of signaling pathways with multiple steps?
- amplify the response to a signal
- they contribute to the specificity of the response
What happens when different cells receive the same signal? What are different examples of this?
they produce different responses
Epinephrine triggers liver cells to break down glycogen, and heart cells to contract
What are scaffolding proteins?
relay proteins to which several other relay proteins attach
What do scaffolding proteins do?
enhances the speed accuracy and efficiency of signal transfer
What is just as important as activating mechanisms?
inactivation mechanisms, because for a cell to remain alert each molecular pathway must last a short time and must not be locked into one state
Binding of signal molecules to receptors must be _______ .
Reversible
What disease involves defecting or missing relay proteins?
Wiskott-Aldrich syndrome
What is apoptosis?
programmed or controlled cell suicide
What occurs during apoptosis?
a cell is hoped and packages into vesicles that are digested by scavenger cells
When does apoptosis result?
when specific proteins that “accelerate” apoptosis override those that “put brakes on” apoptosis
When does apoptosis most effectively shape and organism?
embryonic development
What are caspases?
the main proteases that carry out apoptosis
What can apoptosis be triggered by?
- an extracellular death signaling ligand
- DNA damage in the nucleus
- Protein misfolding in the ER
