Chapter 24: Cell Communication

What are the four categories of signaling?

Paracrine, Endocrine, Autocrine, Direct (across gap junctions)

Paracrine signaling

move by diffusion through extracellular matrix, examples include synaptic signals and neurotransmitters

Endocrine signaling

signals from distant cells, typically produce a slower response with a long-lasting effect (e.g., hormones)

Autocrine signaling

signaling cells that can also bind to the ligand that is released, such that the signal and target cell can be the same or similar to each other (cell death signaling)

Direct signaling across gap junctions

intracellular mediators that allow small signaling molecules to move between cells

What is the function of acetylcholine?

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

Many drugs act as

acetylcholine synapses

Is botulinus toxin an agonist or antagonist?

antagonist

How does botulinus toxin work?

binds to presynaptic neuron and prevents ACh release, causes muscle paralysis (botox)

Is black widow venom an agonist or antagonist?

agonist

How does black widow venom work?

opposite reaction of botulinus toxin (increased release of ACh), causes muscle cramps and spasms

Are organophosphorus insecticides agonists or antagonists?

antagonists

How do organophosphorus insecticides work?

they block the action of acetylcholinesterase, resulting in overstimulated nerves --> muscle contraction/weakness, lack of coordination

Is nicotine an agonist or antagonist?

both, it acts as an agonist at low doses and an antagonist at high doses

How does nicotine effect the body?

it irreversibly blocks the ACh receptors in the body and causes degeneration

Histamine is a neurotransmitter responsible for symptoms of

an allergic reaction

Antihistamines are drugs that block

histamine receptors

Histamine also causes release of __ acid

stomach

Receptor

a molecule/protein with which a hormone, neurotransmitter, or other biochemically active molecule interacts to initiate a response in a target cell

What are some characteristics of hormones?

secreted by cells of the endocrine system, travel through bloodstream to reach targets, responses begin in seconds to hours and last for extended periods of time, may affect many different tissues/organs

What are some characteristics of neurotransmitters?

travel between a neuron and a neighboring neuron/cell to transmit a nerve impulse, takes only a fraction of a second to reach target, effects are short-lived, synthesized and released relatively close to target

Do hormones carry out chemical reactions?

no, they are just messengers

What is the "boss" of the endocrine system?

the hypothalamus

What are the three ways that the hypothalamus "talks" to other tissues?

direct neural control, direct release of hormones, and indirect control through release of regulatory hormones

What is the pathway in direct neural control?

hypothalamus --> adrenal gland --> epinephrine

What is the pathway in direct release of hormones?

hypothalamus --> antidiuretic hormone

What is the pathway in indrect control through release of regulatory hormones?

hypothalamus --> pituitary gland --> thyrotropin --> thyroid gland --> thyroid hormones

What are the three main classes of hormones?

amino acid derivatives, polypeptides, and steroids

What is one example of an amino acid derived hormone?

melatonin

What is one example of a polypeptide derived hormone?

vasopressin

What is one example of a steroid derived hormone?

estradiol

Steroids can enter the cell ___ because they are ____ and ___.

directly; hydrophobic; nonpolar

Polypeptide and amino acid derivative hormones are __-___, so they (can/can't) enter the cell.

water-soluble; can't

How do polypeptide and amino acid derivative hormones deliver messages?

they bind to receptors on the cell surface, releasing a second messenger

Where/why is thyroxine produced?

produced by the thyroid gland when iodine levels are low

Where/why is epinephrine produced?

produced and released from the adrenal glands when we need an instant response to danger, increases the availability of glucose as a source of energy

What is the largest class of hormones?

polypeptides

What are the three types of steroid hormones?

mineralocorticoids, glucocorticoids, sex hormones

Steroid hormones all share a common

4 ring structure

Signal transduction

when a ligand binds to a receptor and the signal is transmitted through the cell membrane and into the cytoplasm continuing the signal

Dimerization

two receptors bind to each other to form a stable complex

Signaling pathway

chain of events including second messengers, enzymes and activated proteins that follow ligand binding to a receptor

Signal integration

signals from two or more different cell-surface receptors merge to activate the same response in the cell

What are some responses to cell signaling?

gene expression, increase in cellular metabolism, cell growth

Yeasts can communicate by releasing a signaling molecule called

mating factor

What does mating factor do?

it binds to cell-surface receptors in nearby yeast cells, initiating a cell signaling cascade

What is bacterial signaling known as?

quorum sensing

What is the key factor for signaling in bacteria?

population density

Quorum sensing utilizes molecules called

autoinducers