Bio Midterm 2 Flashcards
(168 cards)
Mechanisms of Intercellular Communication (ie between cells)
- Direct communication
- Gap junctions
- Membrane (tunneling) nanotubes
- Mechanosignals
(GMM) - Indirect Communication
- Chemical messengers
Gap junctions
- Connexons and intercalated disks are gap junctions
Connexons: subunits that form a channel (gap function), pore size is very small: permits passage of sugars, amino acids, ions between cells ie metabolic and electric exchange found in ALL CELLS EXCEPT MATURE SKELETAL MUSCLE
- since bones do not connect
Intercalated (cardiac) disks: type of gap junction in cardiac muscle. Allows for rapid and coordinated propagation of action potentials for rhythmic contractions. Smaller than connexons; can be acutely regulated (activated/deativated) by phosphorylation/dephosphorylation
Membrane Nanotubes
Nanotubes are formed in the plasma membrane. They are longer than gap junctions and have a larger pore diameter
- Transfer of nucleic acids, even small organelles, between cells
- Might be a way to transfer cellular componenents from stressed to healthy cells
Mechanosignal Tranduction
Conversion of mechanical stimuli into a cellular response
- Direct physical stress to cells, eliciting a chemical or metabolic response
eg 1: pulsatile and shearing stresses from blood flow on arterial endothelial cells
- Can induce formation of new blood vessels
- If excessive, mediates vascular inflammation and progression of atherosclerosis
eg 2: mechanical stress to muscle fibers from weightlifting resulting in increased protein synthesis
eg 3: remodelling of bone and cartilage through physical stresses (such as weightlifting)
ex 4: conversion of pressure on skin into a neural (electrical) impulse
eg 5: conversion of a sound wave in an electrical signal (hearing)
What are indirect intercellular communication
- Chemical messengers
Autocrine communication is also possible when a messenger acts back on the cell that produced the chemical messenger, but this would probably be considered more of a direct communication
What are the types of indirect intercellular communication?
(a) Paracrine (para close)(acts on a nearby cell): examples of signalling; clotting factors, growth factors eg estrogen (promotes ovary maturation)
- Remember that lots of secreted hormones can act in a paracrine manner and can also act in an endocrine manner
(b) neurostransmitters: synapse is a short distance, neurostransmitter signal must be tightly controlled, not too many molecules released, need an auto shutoff (reuptake or deviation) axons can be long!
(c) hormones: can be water or lipid-soluble, must corss boundaries (membranes), and have target specificity (receptors)
What are the different types of hormones?
Hydrophilic: Water loving: eg insulin, epinephrine, serotonin
- Typically stored in secretory cell
- Dissolved in plasma; no need for carrier!
- Crossing a lipid membrane presents a barrier-so, generally secreted by fusing secretory vesticles to membrane and releasing (exocytosis)
Hydrophobic messenger: Water hating (or lipid-loving)
- Eg steroid and sex hormones (estrogen, testerone, cortisol)
- Storage is typically more limited (ie made on demand)
- Cannot dissolve in plasma; needs a carrier
- Crossing a lipid membrane shouldn’t present a barrier
What is the goal of chemical signal transduction?
To change overall profile of cellular protein/enzymatic activity
What is the process of hydrophobic lipid-soluble chemical messengers
They bind to cystosolic or nuclear receptors (fatty), turns on genes to make new proteins (eg enzymes)
What is the process of hydrophilic lipid-soluble chemical messengers
Binds to cell surface (plasma membrane) receptor, directly, or via second messengers, alters the activity of exisiting enzymes/proteins
Where does amplifiication and signal transduction occur in lipophilic messengers (hydrophobic)
Where does amplification occur?
- Step 3: one hormone/receptor complex can cause many mRNA to be formed
- Step 5: many proteins are formed from each mRNA
Where does signal and hydrophilic messengers take place in hydrophilic messengers
An example with G-proteins
(guanosine nucleotide-binding proteins)
-cAMP is the second messenger
Note the ensuing cascade… activation of one protein (protein kinase A) activates another
- In cytoplasm: A “kinase” phosphorylates a target, and usually uses ATP as the phosphate donor
ONE MESSENGER MOLECULE LEADS TO PHOSPORYLATION OF MILLIONS OF PROTEINS
Signaling systems include?
Can also include, channel-linked receptors (neurostransmitters), and other second messengers (Ca2+, cGMP)
What is phenomenal amplification?
Need to turn a signal off! phospdiesterase breaks down cAMP very rapidly
Process:
- epinephrine (chemical messenger)
- Increase cAMP formation
- Activates Protein kinase A
- Activates hormone sensitive lipase
- Activates liplysis and release of fatty acids to provide fuel during excercise
Chemical classes for lipophobic (water-soluble) and fat-soluble
Water soluble: amino acids, peptides
Lipophilic (fat-soluble): steroids, eicosanoids, thyroid hormones)
Storage in secretory cell
Water soluble: secretory vesicles
Fat-soluble: none
Mechanism of secretion
Water soluble: exocytosis
Fat-soluble: diffusion
Transport in blood
Water soluble: dissolved water soluble
Fat-soluble: bound to carrier protein
Location of receptor
Water soluble: plasma membrane
Fat-soluble: cystosol or nucleus
Signal transduction mechanism
Water soluble: open/close ion channels, activate membrane-bound enzymes G proteins
Fat-soluble: after transcription of mRNA (alter protein synthesis_
Relative time to onset of response
Water soluble: fast
Fat-soluble: slow
Relative duration of response
Water soluble: short
Fat-soluble: long
Relative half-life
Water soluble: short
Fat-soluble: long
Combining neural and endocrine singaling: the neurendocrine (neurocrine) signaling system
Examples:
- Norepinephrine
- Antidiuretic hormone