Cell-Cell Interactions

Question 1

zonula occludens (tight junction)

Answer 1

prevents passage of fluids between cells. like a water-tight seal.

the only way things flow is across the plasma membranes

no tube, an impermeable layer (useful for thing that store fluids, like the bladder, intestines, or kidneys)

Question 2

gap junction

Answer 2

A tunnel, allows the flow of extracellular fluids between the two cells, also for electrical activity/coupling

“the gap in London (the Tube)”

allows for the transport of water and ions to and from connecting cells; they also spread electrochemical signals produced by action potentials (neuron, heart)

Question 3

macula adherens (desmosome)

Answer 3

think skin and intestines (places of high stress and need high flexibility)

a protein junction between two cells, not tight enough to prevent the flow of extracellular fluids like water and solutes

hold the cells together (connected to the scaffolding of the cell, the cytoskeleton)

do not allow fluids from one cell to enter another

Question 4

intercalated discs

Answer 4

link cardiac cells together, allow of ions to pass between cells

Question 5

steps of signal transduction through a common G-protein coupled receptor

Answer 5

1. formation of ligand-receptor complex, undergoes conformational change
2. G-protein acquires GTP
3. dissociation of G-protein subunits (the alpha subunit leaves)
4. alpha subunit regulates target protein (target protein can relay a signal via 2nd messenger)
   (4. 1. GTP is hydrolyzed)
5. intracellular phosphorylation cascade

Question 6

receptor tyrosine kinase

Answer 6

acts as an enzyme to its intracellular substrate

a type of enzyme-linked receptor

an integral membrane protein that relays a message from the extracellular side to the intracellular side

on activation, RTK dimerizes and phosphorylate tyrosine residues on each other’s tails

has enzymatic activity (see the kinASE – phosphorylates a substrate)

Question 7

intracellular receptor

Answer 7

on the inside of a cell membrane

a small, nonpolar molecule must be able to pass through the membrane. a steroid can also pass

Question 8

growth hormone

Answer 8

a large peptide hormone that cannot pass through a membrane and act as a ligand for an intracellular receptor

Question 9

membrane receptor protein (MRP)

Answer 9

an integral protein that communicates with the outside environment

includes G protein-coupled receptors and RTK

activated by a specific ligand to form the ligand-receptor complex (this is called signal transduction)

Question 10

G protein-coupled receptor (GPCR)

Answer 10

unique to eukaryotes; humans have over 1000 types; 30-50% of modern medicines act of this; ranging from light-sensitive compounds, odors, pheromones, hormones, and neurotransmitters

regulate the immune system, growth, sense of smell, taste, mood

7 transmembrane alpha helices

do not have enzymatic activity

Question 11

activated RTK

Answer 11

can cross-phosphorylate, resulting in a dimer with several phosphorylated tyrosines that serve as docking sites for a variety of proteins (a single ligand can activate multiple signal transduction pathways)

Question 12

ligand-gated ion channel

Answer 12

a receptor (such as that found on a neuron), when a ligand (e.g. acetylcholine) binds to it, ions (e.g. Na+, K+, Cl-, Ca2+) rushes into and out of a cell. basically, the ion gate opens and the permeability changes dramatically

produces an intracellular electrical response

Question 13

voltage-gated ion channel

Answer 13

open when a significant electrical potential difference has formed across a membrane (membrane potential)

Question 14

nicotinic and muscarinic receptors

Answer 14

channel proteins

both targets of acetylcholine

Question 15

secondary messenger

Answer 15

small, non-protein, water-soluble molecules or ions (cAMP)

Question 16

steroids act on…?

Answer 16

intracellular receptors

they usually activate a transcription factor, so that it enters the nucleus and initiates a transcription of certain genes

Question 17

three types of endocytosis

Answer 17

1. phagocytosis - eating a virus
2. pinocytosis (very unspecific) - bring undissolved, insoluble molecules (particles, solutes) inside the cell
3. receptor-mediated endocytosis (very specific)

Question 18

types of junctions

Answer 18

1. gap junctions
2. tight junctions
3. desmosomes

Question 19

ligand

Answer 19

something that binds to a protein to send a signal

can be a neurotransmitter, hormone

Question 20

3 main types of signal transduction

Answer 20

1. ligand-gated ion channel (fast - neuron)
2. G-protein coupled receptor (GPCR)
3. enzyme-linked receptor

LG-G-E

Question 21

stretch-activated

Answer 21

deformation of the cell membrane

Question 22

G protein

Answer 22

ability to bind GTP and GDP

composed of alpha, beta, and gamma (all on the inner side of the membrane), alpha and gamma attached to lipids by lipid anchors

bind GTP when active

Question 23

epinephrine

Answer 23

binds to the G-coupled protein receptor, induces a conformational change, the alpha subunit has a GTP instead of GDP; the alpha subunit of the G protein activates the adenylate cyclase (another protein in the inner membrane), which converts ATP to cAMP (takes away two phosphates), cAMP becomes a secondary messenger - this increase HR, dilates skeletal muscle blood vessels, break down glycogen

Question 24

enzyme linked receptor (ELR)

Answer 24

also called catalytic receptors

functions as an enzyme (catalyst), after binding of a signaling (chemical) molecule