Chapter 11 Flashcards
The stage of cell signaling in which the signal is converted to a form that can bring about a response in the cell is called
Transduction
Second messengers tend to be small and water-soluble. This accounts for their ability to
Rapidly move throughout the cell by diffusion
What effect does ligand binding have on receptor tyrosine kinase proteins?
Ligand binding causes them to phosphorylate and form dimers
A difference between the mechanisms of cAMP and Ca2+ in signal transduction is that __ and Ca2+ __
cAMP is synthesized by an enzyme in response to a signal and Ca2+ is released from intercellular stores
What happens during the process of paracrine signaling?
Numerous cells simultaneously receive and respond to the molecules of growth factor produced by a single cell in their vicinity
In a phosphorylation cascade, __ phosphorylate proteins, and __ dephosphorylate them
Protein kinases
Protein phosphates
What is the general name for an enzyme that transfers phosphate groups from ATP to other molecules?
Protein kinase
In which part of the cell are calcium ions usually found?
Endoplasmic reticulum
cAMP usually directly activates
Protein kinase A
Second messenger
Small, nonprotein components of signal transduction pathways
Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because
They amplify the original signal manifold
Phosphorylatation cascade
When relay molecules in signal transduction pathways are protein kinases and they act on other protein kinases in the pathway
-amplified the original signal many times over because each kinase in the cascade can act on many molecules of its substrate
Certain yeast cells secrete a molecule called the -factor. The purpose of this molecule is to
Stimulate an a yeast cell to grow toward the cell
Testosterone and estrogen are lipid-soluble signal molecules that cross the plasma membrane by simple diffusion. If these molecules can enter all cells, why do only specific cells respond to their presence?
Nontarget cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cell’s nucleus
A number of important signaling molecules can enter cells through the plasma membrane because
They are either hydrophobic enough or small enough to cross the hydrophobic interior of the membrane
Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because
They amplify the original signal manifold
After a signaling molecule binds to a G protein-coupled receptor, what activates the associated G protein?
GTP displaces GDP on the G protein
Protein kinase
An enzyme that transfers phosphate groups from ATP to a protein
What happens in a phosphorylation cascade?
A series of different proteins in a pathway are phosphorylated in turn, each protein adding a phosphate group to the next one in line
Protein phosphates
Enzymes that can rapidly remove phosphate groups from proteins — dephosphorylation
Turns off the signal transduction pathway when the initial signal is no longer present
Also make the protein kinases reusable, enabling the cell to respond again to an extra cellular signal
What is the general name for an enzyme that transfers phosphate groups from ATP to other molecules?
Protein kinase
Kinase
Any enzyme that catalyzes the transfer of phosphate groups
Tyrosine kinase
An enzyme that catalyzes the transfer of a phosphate group from ATP to the amino acid tyrosine on a substrate protein
In which part of the cell are calcium ions usually found?
Endoplasmic reticulum
What happens during the process of paracrine signaling?
Numerous cells simultaneously receive and respond to the molecules of growth factor produced by a single cell in their vicinity
Cell-to-cell recognition
Communication between adjacent cells occurs between membrane-bound cell-surface molecules
Synaptic signaling
Molecules diffuse across the synapse between adjacent nerve cells
Hormonal signaling
Long distance signaling
Endocrine signaling
Specialized cells release hormone molecules, which travel via the circulatory system to other parts of the body, where they reach target cells that can recognize and respond to the hormones
Paracrine signaling is a type of
Local signaling in animals
Growth factors
Stimulate nearby target cells to grow and divide
The stage in which a chemical signal is detected when the signaling molecule binds to a receptor protein located at the cell’s surface is called
Reception
Transduction
The signal is converted to a form that can bring about a cellular response
Process of cell signaling
Reception
Transduction
Response
Reception
Target cell’s detection of a signaling molecule coming from outside the cell
Process of transduction
The binding of the signaling molecule changes the receptor protein in some way and initiates the process
Transduction stage converts
The signal to a form that can bring about a specific cellular response
Third stage of cell signaling (Response)
The transduced signal finally triggers a specific cellular response
Glycogen metabolism in liver cells
The hormone epinephrine binds to a specific receptor on the plasma membrane of the liver cell
A small G protein located at the plasma membrane. Cancer cells divide uncontrollably.
What change occurred?
A mutation that means Ras cannot hydrolyze GTP to GDP
What happens to cells undergoing apoptosis?
Cells shrunk and form lobes, which are eventually shed as membrane fragments
Second messengers tend to be water soluble and small. This accounts for their ability to
Rapidly move throughout the cell by diffusion
Why does testosterone not affect all cells in the body?
Only certain cells have cytoplasmic receptors for testosterone
The process of phosphorylation is very important as a cellular mechanism for regulating protein activity. Phosphorylation does this by
Activating or inactivating proteins
A small molecule that specifically binds to a larger molecule is called a
Ligand
G protein linked receptors __, whereas receptor tyrosine kinases __
Are not enzymes
Have enzymatic function
When a platelet contacts a damaged blood vessel, it is stimulated to release TA2. TA2 in turn stimulates vascular spasm and attracts additional platelets to the injured site. In this example, TA2 is acting as a
Local regulator
In many cases of local signaling
Messenger molecules are secreted by the signaling cell
How does adenylyl cyclase help transmit signals within a cell?
It converts ATP to cAMP, which then broadcasts the signal to the rest of the cell
A G protein is active when
GTP is bound to it
In liver cells, epinephrine stimulates the breakdown of glycogen. As the signal transduction pathway progresses
The signal is amplified
Cellular messaging
Cells can signal each other and interpret the signals they receive from other cells and the environment
Signals are most often chemicals
The same small set of cell signaling mechanisms shows up in diverse species and processes
Response is often phosphorylation
In local signaling
Animal cells may communicate by direct contact
Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells
Signaling substances in the cytosine can pass freely between adjacent cells
Synaptic
In long distance, plants and animals use chemicals — hormones
Hormonal signaling in animals is endocrine signaling
Cells receiving signals go through 3 processes:
Reception
Transduction
Response
In reception…
The target cell detects a signaling molecule that binds to a receptor protein on the cell surface
In transduction…
The binding of the signaling molecule alters the pathway
The binding between a signal molecule (ligand) and receptor is
Highly specific
A shape change in a receptor is often the initial transduction of the signal
Most signal receptors are plasma membrane proteins
Most water soluble signal molecules bind to specific sites on receptor proteins that span the plasma membrane
3 types of membrane receptors
GPCR G protein coupled receptors RTK Receptor tyrosine kinases Ion channel receptors (Ligand-gated ion channel)
GPCRs are
Largest family
Cell surface transmembrane receptors that work with the help of a G protein
Phosphorylated
Energy rich GTP
RTK
Membrane receptors
Attach phosphates to tyrosines
A receptor tyrosine kinase can trigger multiple signal transduction pathways at once
A ligand-gated ion channel receptor acts
Like a gate when the receptor changes shape
When a signal molecule binds as a ligand to the receptor, the gate allows specific ions, such as Na+, Ca2+ through a channel in a receptor
Intercellular receptors
Found in cytoplasm or nucleus of target cells
Small or hydrophobic chemical messengers can readily cross the membrane and activate receptors
An activated hormone-receptor complex can act as
A transcription factor, turning on specific genes
Transduction
Signal transduction usually involves multiple steps
Multi step pathways can greatly amplify a signal
Multistep pathways provide more opportunities for coordination and regulation of the cellular response
Protein phosphorylation
Protein kinases transfer phosphates from ATP to protein — phosphorylation
Many relay molecules in signal transduction pathways are protein kinases, creating a phosphorylation cascade
The cell’s response to an extracellular signal is called
The output response
Response may occur
In cytoplasm or nucleus
Regulate the synthesis of enzymes or other proteins
Many pathways regulate the synthesis of enzymes or other proteins, usually by turning genes on/off in nucleus
The final activated molecule in the signaling pathway may
Function as a transcription factor
Signaling pathways can also affect the overall
Behavior of a cell
Transcription factors control
Which genes are turned on, which genes are transcribed into mRNA
Protein kinase
An enzyme that transfers phosphate groups from ATP to a protein
RTK is a
Specific kind of protein kinase that phosphorylates tyrosines on the other receptor tyrosine kinase in a diner
Phosphorylation cascade
Many relay molecules in signal transduction pathways are protein kinases, and they often act on other protein kinases in the pathway
Sometimes can decrease the activity of a protein
Change in shape alters
Function of protein
Protein phosphatases
Enzymes that can rapidly remove phosphate groups from proteins
Called dephosphorylation
Turns off the signal transduction pathway when initial signal is no longer present
Makes protein kinases available for reuse, enables cell to respond again to an extracellular signal
Second messengers
Small
Non-protein
Water soluble molecules or ions
Readily spread throughout the cell by diffusion
First messenger is considered
To be the extracellular signaling molecule
Ligand—binds to membrane receptor
Binding of epinephrine to the plasma membrane of a liver cell elevates the cytosolic concentration of a compound called
Cyclic AMP
cAMP
Adenylyl Cyclase
An enzyme embedded in the plasma membrane, converts ATP to cAMP in response to an external signal
Protein kinase A
Activation of a serine/threonine kinase
Because different kinds of cells turn on different sets of genes…
Different kinds of cells have different collections of proteins
The response of a cell to a signal depends on
Its collection of signal receptor proteins, relay proteins, and proteins needed to carry out the response
The efficiency of signal transduction is increased by the presence of
Scaffolding proteins
Scaffolding proteins
Large relay molecules with several other relay proteins are attached
The binding of signaling molecules to receptors is
Reversible
Cells that are infected, damaged, or have reached the end of their functional life span often undergo
“Programmed cell death”
Apoptosis
What happens during apoptosis?
The cell shrinks and becomes lobed
Cell’s parts are packed up in vesicles that are engulfed and digested by specialized scavenger cells, leaving no trace
Different types of cells can respond differently to the same signaling molecule. What explains this apparent paradox?
Different types of cells possess different proteomes
Early work on signal transduction and glycogen metabolism by Sutherland indicated that
The signal molecule did not interact directly with the cytosolic enzyme, but required an intact plasma membrane before the enzyme could be activated
Steroid hormones can enter a cell by simple diffusion. Therefore steroids
Do not imitate cell signaling by interacting with a receptor in the plasma membrane
Receptors for signal molecules
May be found embedded in the plasma membrane, or found within the cytoplasm or nucleus
Testosterone does not affect all cells of the body because
Not all cells have cytoplasmic receptors for testosterone
What event would activate a G protein?
Replacement of GDP with GTP
The cellular response of a signal pathway that terminates at a transcription factor would be
The synthesis of mRNA
Phosphorylation can
Either activate or inactivate a protein
The source of phosphate for a phosphorylation cascade is
ATP
What is not a potential source of Ca2+ that can be released into the cytoplasm?
Lysosomes
Signal transduction pathway
Sequence of changes in a series of different molecules
