Cell and Molecular Biology Exam 2: Cell Communication

What are the four major types of cell signaling?

endocrine (long distance), paracrine (local), neuronal (electrochemical), and contact-dependent (direct cell-cell)

what is endocrine signaling

hormones travel through bloodstream to distant target cells

what is paracrine signaling

local mediators act on nearby cells

what is contact dependent signaling

requires direct cell-to-cell contact via membrane-bound signals

what determines whether a cell responds to a signal

presence of the correct receptor

where are intracellular receptors located

inside the cell (cytosol or nucleus)

what type of molecules bind intracellular receptors

small hydrophobic molecules (like steroid hormone or nitric oxide)

what are the 3 types of cell surface receptors

ion-channel, G-protein, and enzyme-coupled

what do ion-channel-coupled receptors do

open/close ion channels in response to ligand bonding

what are GPCRs

7-pass transmembrane receptors that activate G proteins

what is the structure of a G protein

3 subunits: alpha, beta, gamma

what activates G protein

GDP —> GTP exchange on alpha subunit

what happens after activation

alpha separates from beta/gamma —> both can signal downstream

what are second messengers

small molecules that amplify signals inside the cell

examples of second messengers

cAMP, Ca2+, and DAG

what enzyme produces cAMP

adenylyl cyclase

what does RTK stand for

receptor tyrosine kinase

what activates RTKs

ligand binding —> dimerization —> phosphorylation

what happens after phosphorylation

recruitment of intracellular signaling proteins

what is Ras

a GTP-binding protein involved in growth signaling

what is proto-oncogene

a normal gene that can become cancer-causing

what happens in a gain-of-function Ras mutation

Ras is always active —> uncontrolled cell growth

what does MAP kinase pathway do

promoted cell growth and proliferation

what is a signaling cascade

a series of intracellular steps that relay a signal

why are cascades useful

signal amplification

what are fast responses

protein activity changes (seconds)

what are slow responses

gene expression changes (minuted to hours)

what is a loss-of-function mutation

protein is inactive

what is gain-of-function mutation

protein is always active

if upstream is LOF but downstream is GOF, what happens

signal still occurs