(Cell) Cell Communication Flashcards
The series of steps by which a signal on a cell’s surface is converted to a specific cellular response is called:
Signal Transduction Pathway
What are the two forms of communication by direct contact between cells?
Cell junctions
Cell-cell recognition
Describe cell junctions
Both animals and plants have cell junctions that allow molecules to pass readily between adjacent cells without crossing plasma membranes
Describe cell-cell recognition
Two cell sin an animal may communicate by interaction between molecules protruding from their surfaces
What cells can communicate via cell-cell recognition?
Animal cells
What cells can communicate via cell junctions?
Animal and plant cells
What are two types local signalling?
Paracrine signalling
Synaptic signalling
Describe paracrine signalling
A secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid
Describe synaptic signalling
A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell
What is the main form of long-distance signalling?
Hormonal signalling
Describe hormonal signalling
Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all body cells
What are the three stages of cell signaling?
1 Reception
2 Transduction
3 Response
Describe reception (step 1 of cell signalling)
The target cell’s detection of a signalling molecule coming from outside the cell
What does it mean for the chemical signal to be “detected”?
When the signalling molecule binds to a receptor protein located at the cell’s surface or inside the cell
Describe transduction (step 2 of cell signalling)
The binding of the signalling molecule changes the receptor protein in some way, initiating the process of transduction
Describe response (step 3 of cell signalling)
The transduced signal finally triggers a specific cellular response
What does the signalling molecules behave like?
Ligands
What are ligands?
The term for a molecule that specifically binds to another molecule, often a larger one
What are three major types of membrane receptors?
G protein-coupled receptors
Receptor tyrosine kinases
Ion channel receptors
Where are intracellular receptor proteins found?
Found in either the cytoplasm or nucleus of target cells
What do G protein-coupled receptor proteins look like?
Each have 7 alpha-helices spanning the membrane
What diseases are caused by the interference with G-protein function? (3)
Cholera
Pertussis (whooping cough)
Botulism
What side of the membrane is the G-protein attached to?
The cytoplasmic side of the membrane
What two guanine nucleotides serve as the on-off switch for the G-protein?
GDP and GTP
What does GTP stand for?
Guanosine triphosphate
What guanine nucleotide is bounded to the G-protein when it is inactive?
GDP
What are the three main components of the G protein-coupled receptors?
G protein-coupled receptor
G protein
Enzyme
What happens when the appropriate signalling molecule attaches to the G protein-coupled receptor?
Binds the inactive G protein, replacing GDP with GTP, activating the G protein
What happens when the G protein is activated? (2)
Diffuses along membrane, and binds to an enzyme, altering the enzymes shape and activity
When enzyme is activated, it can trigger the next step in a pathway leading to a cellular response
After activating the enzyme, what happens to the G protein?
Serves as an enzyme (GTPase), hydrolyses the GTP and GDP, and becomes inactive again
Receptor tyrosine kinases belong to a major class of plasma membrane receptors characterized by what?
Having enzymatic activity
What is a kinase?
An enzyme that catalyses the transfer of phosphate groups
What part of the receptor protein extending into the cytoplasm functions as what in receptor tyrosine kinases?
Tyrosine kinase
What does tyrosine kinase do?
Catalyses the transfer of a phosphate group from ATP to the amino acid tyrosine on a substrate protein
Identify the extracellular, membrane spanning and intracellular components of receptor tyrosine kinase proteins
Extracellular: Ligand-binding site
Membrane spanning: Alpha-helix
Intracellular: Tail, composed of multiple tyrosine
Before signalling molecule binds, the receptors exist as __________ ____________
Individual polypeptides
When a signalling molecule attaches, what happens to the receptor polypeptides?
Causes two receptor polypeptides to associate closely with each other, forming a dimer (dimerization)
What does the dimerization of receptor tyrosine kinase proteins do?
Activates the tyrosine kinase region of each polypeptide; Each tyrosine kinase adds a phosphate from an ATP molecule to a tyrosine on the tail of the other polypeptide
Where do the activated tyrosine kinases give their phosphate to?
Given to relay proteins, activating them and triggering a transduction pathway, leading to a cellular response
What is a ligand-gated ion channel?
A type of membrane receptor containing a region that can act as a “gate” when the receptor changes shape
Some ligand-gated ion channels are controlled by electrical signals instead of ligands, what are these called?
Voltage-gated ion channels
What are ligand-gated ion channels and voltage-gated ion channels crucial in?
The nervous system
What special proteins control which genes are turned on?
Transcription factors
How can intracellular receptors get through the phospholipid bilayer?
Hydrophobic enough
Small enough to cross
What are two examples of hydrophobic chemical messengers?
Steroid hormones
Thyroid hormones
What is an example of a signalling molecule small enough to pass through the phospholipid layer?
Nitric oxide (NO)
How does testosterone turn on genes? (5)
The steroid hormone testosterone passes through the plasma membrane
Testosterone binds to a receptor protein in the cytoplasm, activating it
The hormone-receptor complex enters the nucleus and binds to specific genes
The bound protein acts as a transcription factor, stimulating the transcription of the gene into mRNA
The mRNA is translated into a specific protein
What is the general name for an enzyme that transfers phosphate groups from ATP to a protein?
Protein kinase
What are enzymes that can rapidly remove phosphate groups from proteins called?
Protein phosphatases
What is the process of removing phosphate groups called?
Dephosphorylation
What are the 5 steps of the phosphorylation cascade?
A relay molecule activates protein kinase 1
Active protein kinase 1 transfers a phosphate from ATP to an inactive molecule of protein kinase 2, thus activating this second kinase
Active protein kinase 2 then catalyses the phosphorylation (and activation) of protein kinase 3
Finally, active protein kinase 3 phosphorylates a protein that brings about the cell’s response to the signal
* Enzymes called protein phosphatases (PP) catalyse the removal of the phosphate groups from the proteins, making them inactive and available for reuse
Many signalling pathways also involve small, nonprotein, water-soluble molecules or ions called ______ __________
Second messengers
What are the two most widely used second messengers?
Cyclic AMP (cAMP) and Calcium ions (Ca2+)
What is cAMP converted from? By what?
cAMP is converted from ATP
Converted by the enzyme adenylyl cyclase
What enzyme inactivates cAMP to AMP?
Phosphodiesterase
What is the immediate effect of cAMP?
Usually the activation of serine/threonine kinase called protein kinase A
