Unit 6: Cell Communication Flashcards
Identify the abbreviation
ECM
extracellular matrix
Define / describe the
extracellular matrix
Network of proteins and other molecules that surround, support, and help anchor cells
Why do cells communicate?
- Help maintain homeostasis
- Determine when to grow & develop
Identify the types of
Cell Junctions
In animals: gap junctions
In plants: plasmodesmata
How do cells communicate via cell junctions?
Chemical messages within the cells can be transferred directly from one cell to another
Note that no extracellular (outside of the cell) ligand is required
Describe
Cell communication via direct contact
Protein, glycoprotein, or glycolipid that is embedded on membrane of one cell acts as a ligand for a receptor on another cell
The two cells must come into direct contact
AKA juxtacrine signaling
Cell communication via
direct contact
Examples / commonly found in…
Immune system (ex: when white blood cell contacts pathogen)
Embryonic development
Cell communication via
cell junctions
Examples / commonly found in…
Smooth and cardiac muscle - allows for very rapid transmission of signal between cells within a muscle fiber
Define
Paracrine signaling
Sending molecule secretes ligand into area
Target cells are nearby
Note: This type of signaling often depends on concentration of ligand; more ligand may mean a stronger response or the target cell may require a certain threshold of ligand before it can respond
Paracrine signaling
Examples / commonly found in…
Immune system - ex: immune cells may secrete histamine or other cytokines, which cause nearby cells to respond
Synaptic transmission is technically a form of paracrine signaling
Define
Synaptic transmission
A specialized form of paracrine signaling that occurs in the nervous system, between the terminal end of one neuron and a dendrite of another neuron
The two neurons are close to each other, with a gap between them (the synapse) into which the ligand is secreted
Define
Endocrine signaling
Long distance cell signaling where a ligand is secreted from a gland into the blood stream
Can allow for very small amounts of ligand to cause response throughout the entire body
Ligands in the immune system are called
cytokines
Ligands in the endocrine system are called
hormones
Ligands in the nervous system are called
neurotransmitters
List the
Three stages of
signal transduction
- Reception
- Transduction
- Response
What characteristic of ligands determines if it will bind to extracellular or intracellular receptors?
Small, nonpolar substances diffuse through the membrane and bind to intracellular receptors
Large and/or polar substances cannot diffuse into the cell and must bind to cell surface receptor
List three common examples of
cell surface receptors
- GPCRs
- RTKs
- Ligand-gated ion channels
Define
GPCR
G Protein Coupled Receptor
* Cell surface receptor that is associated with a G-protein within the cell
* Binding of ligand often causes a change to the G-protein and whether it is attached to GDP (in inactive state) or GTP (in active state)
Define
RTK
Receptor Tyrosine Kinase
* Cell surface receptor that has an intracellular kinase domain
* Binding of a ligand often causes one RTK to find another active RTK (called dimerization)
* Dimerized RTKs phosphorylate each other to become active, then can phosphorylate other relay proteins within the cell
Define
Ligand Gated Ion Channels
- Ion channels that have a receptor for specific ligand
- Binding of the ligand often opens (or sometimes closes) the channel
- Remember: Like all channels, these are still specific to the substance that can move through and the substances will still diffuse down their concentration or electrochemical gradients
Define
Intracellular Receptors
- Have ligand that is small and nonpolar, such as steroid-based hormones (made from cholesterol)
- Binding of ligand often causes movement of ligand/receptor into the nucleus, where it acts as a transcription factor
What are common components of signal transduction pathways in the cell?
- Cytoplasmic region of receptor has enzymatic activity to start process
- Phosphorylation cascades
- Amplification
- Second messengers
Describe
Cell-surface receptors
Transmembrane proteins that have two important regions:
* Outside of the cell (extracellular domain) has a receptor, which is capable of binding to a specific ligand
* Inside the cell (cytoplasmic domain) has an enzyme or protein-binding area that is only active when the extracellular domain is bound to its ligand
Describe
Phosphorylation Cascades
Addition of phosphate group (AKA phosphorylation) causes activation of protein
* Kinases: Add phosphate groups to specific proteins (often other kinases)
* Phosphatases: Remove phosphate groups
Define/describe
Kinases
Enzymes that add phosphate groups to other proteins
Usually uses ATP
Define/describe
Phosphatases
Enzymes that remove phosphate groups from other proteins
Define/describe
Second messengers
Small, polar, non-protein substances
Able to be made and diffuse quickly in the cytoplasm
Lead to changes in activity of other proteins
List
Common second messengers
To know for AP Biology:
* Ca2+
* cAMP
Also worth knowing…
* IP3 (inositol triphosphate)
* DAG (diacylglycerol)
Describe
cAMP
Cyclic Adenosine Monophosphate
Made from ATP
What enzyme makes cAMP
Adenylyl cyclase
(sometimes called adenylate cyclase)
What is
Amplification
Each part of a signal transduction pathway can cause a greater and greater effect, allowing one or only a few molecules to lead to faster/ bigger responses
Often due to each protein in a pathway being able to activate many of the next protein in the pathway
What are common responses in cell signaling pathways?
- Regulation of gene expression
- Regulation of enzyme activities or other protein activities
- Cell growth / division
- Movement of material within the cell (including moving vesicles for endo- or exocytosis)
- Movement of the cell itself
- Apoptosis
Define
Apoptosis
Programmed cell death
Often for cells that are not needed by the organism (such as cells between fingers or immune cells that are self-reactive) or for damaged cells
Why can different cells respond to the same ligand in different ways?
All cell types express different sets of genes (differential gene expression)
This leads to different cells having different combinations of receptors and signal transduction pathway molecules
Ex: Insulin can cause fusion of vesicle containing GLUT4 proteins to a cell membrane in a cell that has active genes for insulin receptors, GLUT4 proteins, and all necessary proteins in the pathway. Cells that don’t express those genes won’t make the proteins to allow for this response.
What do these symbols:
→ ⊣
mean in signaling pathways?
→ causes, activates, increases, phosphylates, etc
⊣ blocks, stops, deactivates, decreases, etc
