Ch05 Chemical Messengers

APK2105C @ UF | Dr. Nguyen | Module 2 | Ch05 Chemical Messengers

gap junctions

Intercellular communication that occurs through _____ ________, including via electrical and metabolic coupling.

chemical messengers

Most common method of intercellular communication, involving the use of ________ __________ and ligands.

ligand

chemical messenger molecule which binds proteins reversibly

paracrines, neurotransmitters, hormones

What are the 3 functional classes of chemical messengers?

paracrines

Chemical messengers that reach target (adjacent/nearby) cells via simple diffusion.

autocrines

Chemical messengers that act on the cell that secreted them (if it has the receptor).

neurotransmitters

Chemical messengers involving synaptic signaling and that are synapse-specific (e.g. ACh → muscle cells).

hormones

Chemical messengers that are usually released from glands (exception: neurohormones) into the bloodstream. All cells are exposed, but only those w/ receptors are affected.

histamine

An example of a paracrine is ________, which is part of the inflammation response (increased blood flow to the area).

capillaries, leaky

Histamine breaks down _______, causing them to be more “_____.”

antihistamines

Side effects (e.g. drowsiness) of ___________ result b/c they block histamine receptors universally.

chemical structure

A molecule’s _______ ________ determines its mechanisms of synthesis, release, transport, and signal transduction.

plasma membrane

If a chemical messenger is lipophobic / hydrophilic, where are its receptors found in the target cell?

cytosol

If a chemical messenger is lipophilic / hydrophobic, where are its receptors found in the target cell?

steroid

If a chemical messenger is functionally classified as a hormone, what is its general class?

eicosanoid

If a chemical messenger is functionally classified as a paracrine, what is its general class?

amines, peptides/proteins

If a chemical messenger is functionally classified as a paracrine, neurotransmitter or hormone, what is its general class?

amino acids

If a chemical messenger is functionally classified as a neurotransmitter, what is its general class?

glutamate, aspartate, glycine, GABA

What 4 amino acids function as neurotransmitters in the CNS?

dopamine, norepinephrine, epinephrine

What are the 3 catecholamines?

dopamine, epinephrine

Catecholamine synthesis — ________ is a precursor to norepinephrine, which is a precursor to ________.

neurotransmitter

Dopamine acts as a…

neurotransmitter

Norepinephrine acts as a…

hormone

Epinephrine acts as a…

neurotransmitter

Serotonin acts as a…

paracrine

Histamine acts as a…

thyroid hormone

The ONLY amine messenger that is lipophilic (receptor located on cell nucleus) is…

amine messengers

The catecholamines (i.e. dopamine, norepinephrine, and epinephrine), serotonin, histamine, and thyroid hormones are all ______ ________ w/ their receptors located on the plasma membrane (EXCEPT thyroid hormones).

amine group

Identify: -NH₂

cytosol

Where are amine messengers (except thyroid hormones) synthesized?

peptides/proteins, amines, and amino acids

3 types of hydrophilic/lipophobic messengers w/ receptors located on the plasma membrane

cleaved; Golgi; exocytosed

In peptide/protein synthesis, polypeptides are ________ by proteolytic enzymes to form active peptides, which travel via transport vesicles to the _______ and are then _________.

steroid messengers

Messengers derived from cholesterol that ALWAYS function as hormones and are lipophilic, w/ their receptors located (mostly) in the cytosol.

SER or mitochondria; released immediately

Where are steroids synthesized? Are they stored in the cells where they’re made or are they released immediately?

eicosanoid messengers

Paracrine messengers derived from arachidonic acid (a fatty acid) and that are lipophilic/hydrophobic, w/ their receptors located in the cytosol.

arachidonic acid; membrane

In eicosanoid synthesis, phospholipase A₂ removes _______ _______ (a fatty acid chain) from a _______ phospholipid.

inflammatory and pain pathways

Eicosanoids — Are leukotrienes & prostaglandins involved in inflammatory and pain pathways, or blood clot formation?

blood clot formation

Eicosanoids — Are prostacyclins & thrombaxanes involved in inflammatory and pain pathways, or blood clot formation?

aspirin; COX

_______ is an NSAID that non-selectively blocks all ____, leading to negative effects, such as becoming more prone to stomach ulcers.

An alternative to this are COX-2 selective inhibitors.

hydrophilic; exocytosis

________ (lipophobic) messengers are secreted by _________ and are able to dissolve in blood.

Lipophilic; diffusion; carrier; hormone

________ (hydrophobic) messengers are secreted by ________ and either bind to _______ proteins or remain a free _______.

free hormones

______ ________ are not bound to carrier proteins b/c as they travel through the blood, they will need to bind to their receptors and they can’t be bound to a carrier protein and receptor simultaneously.

clumping; evenly

Lipophilic proteins must be bound to carrier proteins to prevent ________ and instead be _______ distributed in the blood.

reversibly; to maintain ratio (<1% free hormones, >99% bound to carrier proteins)

Do lipophilic messengers bind reversibly or irreversibly to carrier proteins in the blood? Why?

True

True or False: Receptors are specific to a class of messenger and have different affinities for specific chemical messengers within a class.

False

True or False: Target cells have only one type of receptor.

messengers

Factors that affect messenger + receptor binding — concentration of ?

receptors

Factors that affect messenger + receptor binding — concentration of ?

up-regulation

An increase in number of receptors (higher than normal), due to chronically low messenger concentrations. Done to increase the chances of messengers to bind to the receptors.

down-regulation

A decrease in number of receptors (lower than normal), due to chronically high messenger concentrations. Done to prevent a potentially bigger cellular response.

receptor affinity

Factors that affect messenger + receptor binding — ?

saturation

The higher the receptor affinity, the faster it will reach…

agonists

Ligands that cause cellular response when receptor binding occurs

antagonists

Ligands that prevent cellular response when receptor binding occurs. Compete w/ agonist molecules for receptor binding sites.

adrenergic receptors; ß₂; agonist

Epinephrine binds to __________ _________, specifically, ____ receptors (which are abundant in the heart). It acts as an _______, causing faster/harder contractions.

antagonists; epinephrine; BP

ß-blockers are ß₂-__________, not allowing _________ to bind to the receptors in the heart, causing it to beat slower and w/ less force, thereby lowering ____.

lipophilic; cytosol; nucleus

If a receptor is intracellular, it means the messenger is _________ (hydrophobic). The receptor can be either in the _______ or _______.

lipophobic; open

If a membrane-bound receptor is a channel-linked receptor (ligand-gated channel), it means the messenger is _________ (hydrophilic). The messenger will cause the channel to ______.

closed

Is a channel-linked receptor always open, closed, or either?

True

True or False: A channel-linked receptor can act both as a receptor and a channel.

fast response

Does a channel-linked receptor (ligand-gated channel) induce a fast or slow response?

intracellular; second messenger; quickly

Channel-linked receptors (ligand-gated channels) can interact w/ ________ proteins for varied response. For example, when calcium enters a cell through the channel, it can act as a ________ ________.

Effects occur ______ but binding is brief, so overall effects are short-lived.

enzyme-linked receptor

Membrane-bound receptor that gets activated when a ligand binds to it (fast response), leading to a series of biochemical reactions inside the cell (e.g. covalent regulation).

tyrosine kinases

What is the most common type of enzyme-linked receptor involved in cellular signaling?

G-protein linked receptor

Membrane-bound receptor that activates a G-protein when a ligand binds, initiating a signaling cascade via second messengers within the cell, thereby having a slow response.

either

Is a G protein-linked receptor always open, closed, or either?

effectors

In G-protein linked receptors, membrane-bound ion channels or enzymes (i.e. G_s and G_i)

enzymes

Activation of G-protein regulated _________ result in the production or activation of a second messenger

cAMP, cGMP, DAG, IP3, calcium

What are the 5 major second messengers?

inhibits; cAMP; increase

Caffeine ________ the enzyme cAMP phosphodiesterase, which degrades _______, causing an _______ of it due to its lack of degradation.

signal amplification

The process by which a single signaling molecule leads to the production of many secondary messengers, resulting in a larger cellular response.