What are 4 methods of cell to cell communication and what they are.
- Gap junctions: direct cytoplasmic transfer from - one cell to the next
- large molecules cannot pass through
- only way electrical signal can pass cell to cell
2. Contact-dependent signals: molecules on membrane surface bind to surface molecules - includes CAMs (cell adhesion molecules), integrins transfer signals in both directions
- requires membranes on both cells to interact
- chemicals that diffuse: via extracellular fluid to act on cells close by
- long-distance communication: combo of chemical signals via blood or endocrine glands
- only target cell receptors respond
Which protein do gap junctions form from?
It forms from membrane spanning protein: connexions.
When do we have contact dependent signals?
occurs in immune system and during growth
Name the 2 types of signals and the difference between them.
- autocrine signal: acts on the same cell that secreted
2. Paracrine: acts on the cell adjacent to it
Describe cytokines.
Cytokines: act as oth local and long distance signals
- synthesized and secreted by nucleated cells (not specialized cells)
- control cell development, differentiation and immune responses
- broader spectrum of target cells than hormones
- made on demand (not stored)
What are the general features of signal pathways?
- followed by paracrine or autocrine molecules and hormones
- depends on the presence of target receptors
- have a ligand (signal molecule that brings info to target cell)
- ligand-receptor binding activates receptor
- receptor activates one or more signals in the cell
- last signal initiates the synthesis as target protein or modification of existing as the response
Where are receptors located?
- ligand/receptor binding is dependent on whether it is…
- … can diffuse through the PL bilayer binding to … receptors
On the cell membrane or in the cell.
- lipophobic or lipophilic
- lipophilic can diffuse through binding to cytosol or nucleus receptor
Compare the speed of lipophobic and lipophilic ligands.
Lipophilic: slower, diffuse directly in
Lipophobic: rapid, bind to extra cellular receptor
What is a biological signal transduction?
converts chemical signals to cellular responses
What doe second messengers do?
- alter gating of ion channels
- increase intracellular calcium (to bind to protein to change their function like in contraction)
- change enzyme activity like using kinases/phosphorylases
What does the tyrosine kinase receptor pathway do?
Its ligand binds to it and activates it on the cytoplasmic side where it phosphorylates a protein using ATP (hydrolysis)
Explain what GPCRs do.
They use G proteins and bind to nucleotide guanosine. These G coupled protein receptors are membrane spanning and cross the PL bilayer 7 times.
Once they are activated: open ion channels in membranes and alter enzyme activity on cytoplasmic side of membrane
Give an example of GPCR.
Adenylyl cyclases- cAMP
Signal molecule binds to GPCR which binds to adenylyl cyclase which converts ATP to cAMP (a second messenger). cAMP activates PKA which phosphorylates proteins and initiates cell response.
PLC system
Signal molecule binds to GPCR which binds to PL-C. This will take a phospholipid from membrane and turn it to DAG + IP3. IP3 diffuses into cytoplasm binds to ligand gated calcium channels which releases calcium from its stores in the ER. DAG stays in the membrane and activates PKC where it phosphorylates proteins. Both give the cellular response.
Describe a receptor-channel.
If a ligand binds to a channel receptor, it will have the most rapid response which either opens or closes the gate.
eg. ion channel can change the sodium, potassium or chlorine permeability if an ECsignal binds to it. This changes the electrical signal causing a response from voltage-sensitive proteins.
Why are calcium ions versatile messengers?
It can enter the cell through voltage gated, channel, ligand or mechanically gated channels.
What is the difference agonist and antagonist ligand?
- primary ligan: activates a receptor
- agonist: also activates receptor (only)
- > both initiate a response - antagonist: blocks receptor activity, there is no response.
What is the purpose of the endocrine and nervous system?
They both function to achieve and maintain homeostasis.
Both systems working as one is the neuroendocrine system.
Communication, integration and control
Neurons: can release neurotransmitters and neurohormones (hormones created and produced by neuroendocrine gland) into blood.
Make general distinctions between nervous and the endocrine system.
Nervous system:
-nerve cell terminates on specific target cell (wired for specific transmission to a target)
-neurotransmitters are rapid and short lived
-neurons stimulate muscle and glands across a synapse only
Endocrine system:
-wireless (endocrine glands are not linked to their target cells.)
- endocrine chemical messengers are secreted into blood and delivered to distant target sites.
-hormones are slow and longer lasting
-hormones diffuse in blood and can access most tissues and cells
How is neural specificity achieved?
- due to anatomic proximity between nerve cell and target cells
- unlike endocrine system: it does not rely on message and cell having the right receptor
- the muscle selected to move depends on the neuron that releases the ACh since all motor neurons have ACh receptors
- sharply contrasts endocrine system
Describe main features of the endocrine system.
- ductless
- made of glandular epithelium (manufacture and secrete hormones)
- endocrine glands: secrete hormones
- exocrine glands secrete products
- glands are widely scattered throughout the body
- some are made of neurosecretary tissue: modified neurons that secrete chemical messengers which diffuse into blood stream rather than across a synapse (adrenal medulla)
What is the major function of the hypothalamus?
- “master gland”
- receives input and acts accordingly
- controls the release of anterior pituitary hormones via releasing and inhibiting factors
What are the 6 secreted anterior pituitary hormones?
- TSH: t3/t4 - brain development, metabolism and reproduction
- ACTH: stimulates cortisol secretion from adrenal cortex
- GH: growth hormone - growth and metabolic effect
- FSH & LH: follicle stimulating hormone & luteinizing hormone - ovulations, gonads, leydig cells to stimulate testosterone, androgen binding protein expression by sertoli cells
- PRL: prolactin - milk synthesis from mammary glands
- MSH: melanocyte stimulating hormone
What hormones at released from the posterior pituitary?
It mainly stores hormones but does release 2 hormones into veins.
- vasopressin - ADH acts on kidneys
- Oxytocin: milk let downt and uterine contraction
What is the function of the pineal gland?
produces melatonin - controls biological rhythm (circadian)
