Cell Communication

4 types of signaling

Paracrine

Endocrine

Autocrine

Direct Signaling

Paracrine signaling

Move by diffusion through extracellular matrix

Endocrine signaling

Signals are sent from distant cells, typically produce a slower response with a long lasting effect

Autocrine signaling

Signaling cells can bind to the ligand that they release, cell signals itself

Direct signaling

Small signaling molecules move across gap junctions between cells

What kind of chemical signaling is this?

Autocrine signaling

What kind of chemical signaling is this?

What kind of chemical signaling is this?

Direct signaling

What kind of chemical signaling is this?

Paracrine signaling

What kind of chemical signaling is this?

Endocrine signaling

What kind of cell signaling is a neurotransmitter?

Paracrine signaling

What can some enzymes do to neurotransmitters?

They can degrade some types and cause the signal to be terminated.

Sometimes we can inhibit these enzymes intentionally to speed up acetylcholine activity through the means of medication

Synaptic gap

distance between the presynaptic cell and the postsynaptic cell

What part of the neuron receives signals?

Dendrites

What parts of the neuron sends signals?

Terminal buttons

What is the body of the neuron called?

The soma

What’s going on here?

A nerve impulse travels down the axon and gets absorbed by the synaptic knob, forming a synaptic vesicle, which holds all of the content of the nerve impulse

The synaptic vesicle then travels down the knob and releases the signal at the synaptic gap.

Acetylcholine

Controls skeletal muscles and may function in the sleep-wake cycle, learning, memory, and mood

What is acetylcholine made out of?

Acetyl-CoA and choline.

Acetylcholine is broken down by…

Acitylcholinesterase

What’s going on here?

Acetylcholine is made out of acetyl-CoA and choline. The acetylcholine is put into a synaptic vessel and exits the cell, bound to a receptor. Acetylcholine is broken into acetate and choline by acetylcholinesterase.

Drugs

Any substance that alters body function when it is introduced from an external source

Agonist

Activates cell signaling (activates cell receptors), making it faster

Botulinus venom is an…

Antagonist, it prevents ACh release.

Black widow spider venom is an …

Agonist. It increase release of ACh

Organophosphorus Insecticides: how does it work?

Antagonist

OP blocks acetylcholinesterase → ACh is not being broken down → accumulation of ACh

Is nicotine an agonist or antagonist?

Both

Low doses → Agonist

High Doses → Antagonist

Antagonist

Slows down cell signaling by inhibiting receptors

Nicotine at low doses

activates receptors → acts as an agonist →increased heart rate and dopamine release

Nicotine at high doses

receptors are constantly activated → receptors are desensitized → receptors stop responding (or slowed permanently)

Histamine

Neurotransmitter responsible for allergy symptoms

Antihistamine function

Blocks histamine receptors

Receptor

A molecule which a hormone or a neurotransmitter reacts with to get a response from a target cell

What are the messenger molecules?

Hormones

Neurotransmitters

Hormones

Travel through the bloodstream to reach their target cell

Effects last longer, takes longer for effect to kick in

Secreted by the endocrine system\

ex. epinephrine

Neurotransmitter

Travel between neurons quickly

Effects are short-lived, kick in really fast (fraction of a second)

ex. acetylcholine

What does the endocrine system include?

All cells that secrete hormones into the blood stream

Do hormones carry out chemical reactions?

nope, they are just messengers

Who is the boss of the endocrine system?

The hypothalamus

How does the hypothalamus talk to other tissues?

Direct neural control

Direct release of hormones

Indirect control through release of regulatory hormones

Direct neural control

hypothalamus → adrenal gland → epinephrine

Hypothalamus send nerve signals directly to the adrenal gland

Direct release of hormones

hypothalamus → antidiuretic hormone

Hypothalamus produces hormones that get sent down into the bloodstream

Indirect control through release of regulatory hormones

hypothalamus → pituitary gland → thyrotropin → thyroid gland → thyroid hormones

Hypothalamus releases activating/inhibiting hormones which causes the pituitary to speed up/slow down the release of their hormones

3 main classes of hormones

Amino acid derivatives

Polypeptides

Steroids

Example of amino acid derivatives as hormones

Melatonin

Example of polypeptides as hormones

vasopressin

Example of steroids as hormones

estradiol

Which hormone class can actually go inside the cell?

Steroids

Why can steroids enter the cell directly?

They are hydrophobic and nonpolar

Once a steroid is inside the cell, what does it need to remain stable before activation?

A chaperone protein

Why can’t polypeptides and amino acid derivatives enter the cell?

They are water-soluble

How can non-steroid hormones send signals to cells?

They bind to a receptor molecule on the cell membrane. That cell membrane activates a G-protein, which activates an effector enzyme. This effector enzyme converts ATP to cAMP which will go on to activate other reactions.

What is the role of cAMP in non-steroid signal transduction

it is the second messenger

Second messenger

Carries the cell signal inside the cell when a hormone can’t enter

Thyroxine

Iodine-containing hormone produced by the thyroid gland

What causes goiters?

low iodine (more is needed) → more thyroxine is made → thyroid is enlarged to make more thyroxine

Epinephrine

Increase the availability of glucose as a source of energy

Released from adrenal glands when we need an instant response to danger

Takes a few seconds to kick in

Epinephrine is an amino acid derivative. How does it do signal transduction?

Via second messenger cAMP

How does epinephrine increase glucose availability?

breaks down more glycogen into glucose-6-phosphate, then converts to glucose through glycolysis.

glucose released into the bloodstream for energy

What is the largest class of hormones?

Polypeptides

Average size for polypeptide hormones

~100 - 150 amino acids, there are outliers on both sides tho

Propagation of the signal methods

Signal transduction

Dimerization

Signaling Pathway

Signal integration

Signal transduction

Ligand binds to a receptor and the signal gets transmitted through the cell membrane into the cytoplasm

Dimerization

two receptors bind to each other to form a stable complex

Signaling pathway

chain of events that occur after a ligand binds to a receptor; think second messengers, enzymes, activated proteins

Signal integration

Signals from 2+ receptors can merge and activate the same response in a cell

Difference between dimerization and signal integration

dimerization → receptors link to activate

signal integration → different signals merge in the cell to control the response

Response to the signal: Gene Expression

The signal outside the cell changes what genes are active inside the cell.

Apoptosis

Self induced cell death