Unit 4: Cell Communication Flashcards
Parts involved in cell communication
Secreting cell
Ligand
Target cell (has receptor for specific ligand)
Define
Autocrine signaling
Cell that secretes a ligand also has receptors and is also the target cell
Importance / Relevance of
Autocrine signaling
- Developing cells reinforce cell type
- Cancers increase their own growth
Define
Paracrine signaling
Ligand can diffuse from secreting cell to target cell
Importance / Relevance of
Paracrine signaling
Developing tissues will specialize based on what types of cells are around it
Example of
Paracrine signaling
Developing tissues
Nervous system
Parts of
Nerve cell signaling
- Presynaptic neuron releases neurotransmitter
- Neurotransmitter diffuses across small gap (synapse)
- Postsynaptic neuron responds to neuron
Define
Cell-to-cell signaling
Direct contact between two cells;
Proteins on the surface of one cell acts as a ligand to bind to the receptor of a target cell
Importance / Relevance of
Cell-to-cell signaling
Immune cells “activate” each other by direct contact
What type of signaling involves the sharing of cytoplasm between cells?
In animals: Gap junctions
In plants: Plasmodesmata
Define
Endocrine signaling
Target cell is a far distance from the secreting cell
Parts of endocrine signaling pathways in vertebrates
Glands secrete the ligand (called hormones)
Hormones travel in circulatory system
List
Endocrine organs
Hypothalamus, adrenal glands, sex organs (ovaries or testes), others
Steps of
Signal transduction
- Reception: Signal hits target cell
- Transduction: Cell relays message within cytoplasm
- Response
Description of
Reception
(in signal transduction)
Signal (chemical, electrical, touch, etc) reaches receptor on target cell;
Cytoplasmic portion of receptor changes due to the signal;
Receptor changes to initiate transduction cascade
Examples of
Cell surface receptors
G-Protein coupled receptors
Receptor tyrosine kinases
Receptor mediated ion channels
Describe
G-protein coupled receptors
GPCR with no ligand: Internal portion of GPCR is bound to G protein/GDP (guanosine di-phosphate)
When ligand binds, G protein separates from GDP and binds to GTP
G protein/GTP is “active” and separates from GPCR; can then affect other molecules in the cell
Define
Second messenger
Small, soluble molecules that move within the cytoplasm during transduction (ex: cAMP, Ca2+)
Define
Kinase
An enzyme that phosphorylates a protein (often another kinase or enzyme)
Define
Phosphatase
An enzyme that removes the phosphate group from a protein; often “inactivates” the other protein
Describe
Phosphorylation cascades
A series of kinases phosphorylate each other and other molecules, allowing for a signal to be amplified in the cytoplasm
Define
Amplification
A single ligand can lead to exponentially greater changes within the cell because each step in a transduction cascade can activate multiple of the next step
Explain why different cell types respond to different signals or respond differently to the same signal
Each cell type has unique sets of receptors and transduction proteins.
- Only those with the right receptor can respond
- How the receptor interacts with cytoplasmic molecules will differ between cell types
List examples of
Responses
(in signal transduction)
- Increase/decrease transcription
- Change amounts/types of enzymes
- Lead to or prevent cell growth/division
- Change what membrane proteins are present (pumps, fac. diffusion, and other receptors)
- Endocytosis or exocytosis
- Apoptosis
Relate cell signaling to tumors / cancers
Unregulated cell growth due to:
- Up/down-regulation of production of cyclins
- Cancerous cells often:
- fail to respond to signals to stop growth
- over-respond to signals to grow
- constitutively say active even without the signal present
Define
Homeostasis
Maintaining an internal environment that differs from external environment
Relate cell signaling to negative feedback
- Change in conditions is sensed by a sensor cell, which will have signal transduction pathway that leads to a response
- Response of the sensor is often the release of ligand to communicate with other cells
- Eventually, effector cells will receive signal and respond by negating the original stimulus
Define
Negative feedback
Responding to a change in conditions by negating that change
Define
Positive feedback
Responding to a change in conditions by amplifying that change
Examples of
Negative feedback
Temperature regulation
Glucose regulation
Oxygen/CO2/pH regulation
Solute regulation (osmotic balance)
Blood pressure regulation
Describe
Thermoregulation
Increased body temp → Sensed by brain → Signals sent to effectors include (1) sweat glands, which produce sweat; (2) blood vessels, which dilate
Decreased body temp → Sensed by brain → Signals sent to effectors include (1) Blood vessels, which constrict; (2) Muscles, which shiver
Describe
Glucose regulation
- High glucose
- Sensor: Pancreas
- Response by pancreas: Secrete insulin
- Insulin target: Liver and muscle cells
- Response of liver/muscle cells: Increase glucose uptake and conversion to glycogen
- Result: Blood glucose levels drop and glucose is stored as glycogen
- Low glucose
- Sensor: Pancrase
- Response by pancreas: Secrete glucagon
- Glucagon target: Liver cells
- Response of liver cells: Increase hydrolysis of glycogen and release into blood
- Result: Blood glucose increases
