Cell Communication Flashcards
What do signal transduction pathways do?
Convert extracellular signals into cellular responses
What are the 2 types of cell communication?
Local signalling
Long distance signalling
What is local signalling?
Neighbouring cells communicate through cell junctions, cell-to-cell recognition or local regulators
What is long distance signalling?
Distant cells in multicellular organisms communicate using chemical messengers (hormones)
What are the 3 types of local signalling?
Direct contact : via cell junctions - both animal and plant cells
Cell-cell junctions : via surface molecules - animal cells only
Local regulators : in paracrine/synaptic signalling - animal cells only
What is direct contact?
Cell communication via cell junctions
What is cell-cell recognition?
Cell communication via surface molecules
Give an example of surface molecules used in cell-cell recognition
Membrane carbohydrates
What are local regulators?
In paracrine/synaptic signalling (animal cells only)
What do cell junctions do?
Coordinate the function of neighbouring cells in a tissue
What is paracrine signalling?
Animal cells communicate using local regulators into the extracellular fluid
What are local regulators?
Messenger molecules that travel only short- distances such as neurotransmitters
What is synaptic signalling?
A nerve cells releases neurotransmitter molecules into a synapse stimulating the target cell.
What are the 3 types of cell junctions?
Communicating junctions
Occluding junctions
Anchoring junctions
What are two examples of communicating junctions?
Gap junctions : in animal cells, no cytoskeletal connection
Plasmodesmata : in plant cells , no cytoskeletal connection
Both types allow molecule exchange between cells
What is an example of occluding junctions?
Tight junctions : connect with actin microfilaments - prevents intracellular communication
What are 4 examples of anchoring junctions?
Desmosomes : connects with intermediate filaments - anchors cells through the ECM
Adherens junctions : connects with actin filaments
Focal adhesions - connects cells with ECM - Connects with actin filaments
Hemidesmosomes - connects cells with ECM - connects with intermediate filaments
What is the function of tight junctions?
Prevents intercellular communication
What is the function of desmosomes?
Anchor cells through ECM
What is the function of gap junctions?
Allows molecule exchange between cells
What are plasmodesmata?
Channels connecting neighbouring cells in plant cells - which allow cell communication and molecule exchange
What is the name of the membrane protein that makes up the cytoplasmic channels?
Connexins
What can pass through gap junctions?
Small molecules and Ions
Where are gap junctions located?
Along the apical surfaces of cells of various tissues such as epithelial cells and heart muscle
Give one important ion which is transported through the gap junctions?
Calcium ion between neighbouring smooth muscle
–> synchronised contraction of intestine and uterus during birth
Where are tight junctions found?
Underneath the apical surface of epithelial cells
What do tight junctions do?
Inhibit cell to cell communication
Prevent leakage of extracellular fluid from a layer of epithelial cells
Which 2 transmembrane proteins are tight junctions made out of?
Claudin and Occludin
What is the cytoplasmic part of occludin linked to?
Actin microfilaments
What is the name of the transmembrane adhesion (linker) proteins?
Cadherins/ Integrins
How do desmosomes anchor to the cytoplasm?
Through intermediate filaments
How do desmosomes connect to other cells ?
Via transmembrane adhesion proteins
What is the name of the transmembrane adhesion protein that desmosomes use to connect to other cells?
Cadherins
What do desmosomes connect with in epithelial cells?
Keratin
What do desmosomes connect with in heart muscle cells and smooth muscle cells?
Desmin
Why do some muscle tears occur?
Due to rupture of desmosomes
What do focal adhesion connect to the ECM through in extracellular connections?
Integrins
What does intern cytoplasmic domain connect to the actin microfilaments with?
Actin filaments
What is the basement membrane?
Specialized ECM type that separated an endothelial cell layer from the underlying connective tissue
Where are hemidesmosomes located?
Basal surface of epithelial cells
How do hemidesmosomes stabilise epithelial cells?
By anchoring them to the ECM through integrins - integrins binds them to the basement membrane through laminin (glycoprotein)
What are the 3 stages of cell signalling?
Reception
Transduction
Response
What is the definition of reception?
Signalling molecule binds to a receptor protein, causing it to change shape
What are the 2 types of receptors?
Plasma membrane
Intracellular
What are the 2 type of inrtacellular receptors?
Cytoplasmic
Nuclear proteins
What kind of signalling molecule (ligand) can bind to these receptors?
Small or hydrophobic
Can readily cross the plasma membrane and use these receptors
such as steroid hormones
What are the 2 types of steroid hormones?
Estrogens
Androgens
What are the 2 types of steroid hormones?
Estrogen receptors (ERs) and adrogen receptors (ARs)
What is the drug used for breast cancer?
Tamoxifen
What is tamoxifen’s mode of action?
Estrogen antagonist - binds to the ER and prevents estradiol binding
Describe the mode of action for steroid hormones which act via intracellular receptors
- Steroid hormones passes through the plasma membrane
- Hormone binds to a receptor protein in the cytoplasm activating it
- Hormone-receptor complex enters the nucleus and binds to specific genes
- Bound protein stimulates the transcription of the gene to mRNA
- mRNA is translated into a protein
What are the 3 main types of plasma mambrane receptors?
G-protein-coupled
Tyrosine kinase
Ion channels
What are G protein-coupled receptors?
Plasma membrane receptors linked to a G protein
What are G proteins?
Proteins bounds to GDP/GTP
What happens to the G-protein if GDP is bound to the G-protein?
G protein is inactive
What happens to the G protein if GTP is bound to the G protein?
G protein is active
What are protein kinases?
Enzymes that phosphorylates protein substrates - adds a phosphate group to them
What are receptor tyrosine kinases?
Transmembrane receptors that attach phosphates to tyronsine residues
What are the 2 domains of receptor tyrosine kinases?
Extracellular ligand binding domain
Intracellular domain with tyrosine kinase activity
What kind of receptors are commonly growth factor receptors?
Receptor tyrosine kinase
What happpens when a growth factor binds to their receptor tyrosine kinase?
Activation of signal transduction pathways such as the MAPK pathway
What can abnormal tyrosine kinase receptors contribute to?
Rise of certain types of cancer
What kind of abnormalities of receptor tyrosone kinases can lead to cancer?
Truncated receptors that function in the absense of signallin molecules.
Overexpression/ amplification of receptors
Give an example of a receptor that can be overamplified/ over expressed
EGFR
Epirdermal Growth Factor Receptor
Contribute to breast cancer –> HER-2
What are some anti-cancer drugs that block tyrosine kinase activity?
Herceptin
What is the mode of action for anti-cancer drugs?
Competes with the EGF to bind to the receptor
What are ion channel receptors ?
Acts as a gate which opens when the receptor changes shape
What is transduction?
Signal from the receptor from the receptor converted to a form that can cause a specific cellular response.
What are protein kinases?
Enzymes that add a phosphate to the next protein kinase in line
Active protein kinases
What are phosphates?
Enzymes that remove the phosphates
Deactivate the protein kinases
What are second messengers?
Small, non-protein, water soluble molecules or ions that acts in signal transduction pathways.
How is cAMP produced?
ATP + Adenylyl cyclase (enzyme)
What happens in signal transduction pathways?
Cascades of molecular interactions that relay signals from receptors to target molecules in the cell
What are examples of 4 second messengers?
cAMP
Calcium ions
DAG (Diacylglycerol)
IP3 (Inositol Triphosphate)
Where are calcium ions released to ?
Cytosol of the cell
What is the function of calcium ions?
Cells are able to regulate its concentration in the cytosol
Where are calcium ions stored?
S.E.R
Matrix of the mitochondria
What is the function of IP3?
Triggers an increase in calcium concentration in the cytosol
What is a first messenger?
Signal molecule such as epinephrine
What happens at response?
Transduced signal triggers a specific response
What are the 2 responses cell signalling leads to?
Cytoplasmic response
Nuclear response
What is nuclear response to a signal?
Activates transciption factors that turn gene expression on or off.
Give an example of a nuclear response to a signal
MAPK signalling cascade
