Lecture 7

Question 1

· Name key components required for cell signaling and where they are usually located

Answer 1

Most signals bind to a receptor found on the outside of the membrane which leads to a signal transduction which releases secondary messangers that will amplify the signal and this will cause effector proteins to alter the cells behavior

Question 2

· Describe the four modes of cellular signaling

Answer 2

There are four basic categories of cell signaling, autocrine, paracrine, endocrine and by direct contact. Endocrine is signaling from one cell to another over long distances so the signaling molecule is often carried through the blood to reach the other cell receptor. Paracrine affect nearby cells and autocrine is when the cell sends signals to the outside of the cell but activates on it’s own receptors. Cells can also signal to other cells through direct contact in form of gap junctions for example.

Question 3

· Name the four receptor families with examples, and their respective subtypes

Answer 3

There are four receptors types. G protein-coupled receptors which are the most common, enzyme linked receptors, ionotropic receptors and nuclear receptors. G protein coupled receptors have 4 subtypes, Class A, B, C and Fizzled/ TAS2. Ligand gated ion channels have 3 subtypes, cys loop receptors, ionotropic glutamate receptors and ATP gated channels. Enzyme linked receptors have 6 subtypes, receptor tyrosine kinases, tyrosine-kinase associated receptors, receptor like tyrosine phosphatases, receptor serine/threonine kinases, receptor guanylyl cyclases, histidine-kinase associated receptors. Nuclear receptors have four subtypes, I, II, III and IV.

Question 4

· Describe the basic structure of the four receptor families and, in general terms, their mode of action

Answer 4

G protein coupled receptors are found in the cell membrane and can be activated with a signal molecule. As it is activated it changes shape and moves down the cell membrane to bind to the inactivated G protein and as a result activates it. GTP will then take the place of the GDP. The activated protein will then detach from the receptor and bind to the enzyme. The enzymes will then catalyze the intracellular response and the receptor and protein goes back to it’s previous form.

Enzyme linked receptors act slowly over hours and often catalyze reactions such as growth hormone for example and act over long periods of time. The receptors either function as enzymes or dissociate from enzymes. They often have their ligand binding site outside the cell membrane and their catalytic or enzyme binding site on the inside of the membrane.

Nucleus receptors act over hours and affect transcription thus affecting the cell very long term. The receptor is inside the nucleus so the signaling molecule enters the cell membrane and the nucleus to activate the receptor.

on channel-coupled receptors also known as channel linked receptors are ionotropic receptors are fast acting and can be found in nerve and muscle cells for example. They act through a small humber of neurotransmitter that open or close ion channels by binding to them,. temporarily changing the ion permeability of the cell membrane causing hyperpolarization and depolarization.

Question 5

· Name and describe the function of second messengers

Answer 5

Common secondary messengers involve cAMP and calcium ions. Ca2+ is a fast acting and potent messenger. Bring the message downstreams and amplify the reaction, one receptor can trigger thousands of secondary messangers.