Lecture 8: Cell-Cell Communication

Question 1

Cells can respond to signals

Answer 1

inside and outside the body

Question 2

why do cells need signals

Answer 2

• Need to respond to a changing environment
o Ex: increased availability of glucose, cells want to take it in. Need to increase their expression of glucose transporters
o Insulin signaling controls the response
• Cells need to communicate with each other for their own and the organism’s needs
o Cell-cell communication
o Muscle cell releases vasodilator when it needs more glucose/oxygen

Question 3

other uses for signaling

Answer 3

• Communication btw organisms who cannot communicate verbally (yeast bacteria, insects)
o Find mates
o Communicate danger
o Ants

Question 4

very local distance

Answer 4

: two cells are connected by gap junctions (animal; what happens in one cell happens to the other); surface proteins of two cells interact

Question 5

local distance

Answer 5

secreted molecules and/or contact

Question 6

long distance

Answer 6

secreted molecules that diffuse or are carried (by the bloodstream) throughout organism

Question 7

autocrine signaling

Answer 7

a cell secretes a molecule that effects itself

Question 8

paracrine siganling

Answer 8

a cell secretes a molecule that effects neighboring cells

Question 9

endocrine signaling

Answer 9

a molecule is secreted into the bloodstream

Question 10

targets

Answer 10

cells receiving the signal

Question 11

is a receptor required

Answer 11

yes

Question 12

ligand

Answer 12

secreted molecule for the receptor

Question 13

gap junction

Answer 13

used for direct intercellular signaling

Question 14

contact dependent signaling

Answer 14

target cell; membrane bound signaling molecule

Question 15

stages of signaling

Answer 15

• Receptor activation: signal binds to receptor molecule on target cell surface
o Binding of a signaling molecule causes a conformational change in a receptor that activates its function
• Signal Transduction: the binding of the signaling molecule changes the receptor protein in some way; converting the signal to bring about a cellular response
o Amino acids are changed
o When proteins bind their ligand, they undergo shape changes
o Activated receptor stimulates a series of proteins that forms a signal transduction pathway
• Cellular Response: some cellular activity is triggered
o Signal transduction pathway affects the functions and/or amounts of cellular proteins, thereby producing a cellular response

Question 16

reception

Answer 16

o Polar signaling molecules cannot enter the cell, so their receptors are found embedded in the membrane

Question 17

3 major types of receptors

Answer 17

• enzyme-linked receptors
• G protein coupled receptors (GPCRs)
• Ligand gated ion channel receptors
• Make up 30% of the human body

Question 18

enzyme linked receptors

Answer 18

o Found in all living species
o Extracellular domain binds signal
o Causes intracellular domain to become functional catalyst
o Most are protein kinases

Question 19

protein kinases

Answer 19

an enzyme that catalyzes the transfer of phosphate group (from ATP onto a protein)

• Exist as monomers, ligand binding triggers dimerization and phosphorylation
• New conformation allows recognition by relay molecules
• Triggers downstream signaling events

Question 20

what happens when you add a phosphate group

Answer 20

you change the shape of the protein which then changes the function

Question 21

GPCR

Answer 21

o Ex: yeast mating signals, epinephrine, many hormones and neurotransmitters, embryonic development, sensory reception
o Many diseases wreak havoc by interfering with GPCR signaling (cholera, pertussis)
o 60% of all current prescription drugs work by influencing GPCR signaling
o receptor is associated with G protein
o G protein is inactive
o Ligand binds to receptor, receptor changes shape and binds G protein, activating it
o G protein, now activated, releases from receptor and diffuses along mb, activating nearby enzyme

Question 22

ion channel receptors

Answer 22

o Ex: neurotransmitters and their receptors
o Ion channel is closed
o Ligand binds
o Channel opens
o Ions flow from one side of membrane to the other, changing the polarization

Question 23

polar molecule receptors need to be on the ________ in order to diffuse across the membrane

Answer 23

outside

Question 24

intracellular receptors

Answer 24

o Nonpolar signaling molecules can enter the cell, so their receptors are found in the cytoplasm or nucleus
• Steroid hormones, thyroid hormone, nitric oxide (bc of size not polarity)
o These signaling molecules enter ALL cells of the body, but only trigger reactions in those with receptors
o These signaling molecules often initiate gene transcription

Question 25

transduction

Answer 25

o Often a chain of protein kinases phosphorylate each other until a downstream target is phosphorylated and activated
o Each of these kinases must be dephosphorylated by protein phosphatases and returned to the inactive state

Question 26

Second messengers

Answer 26

o Not all components of signaling pathways are proteins
o Non-protein small molecuels can be activated by GPCRs or protein kinases and act as second messengers
• Ca^2+ ions
 GPCR act
• Cyclic AMP

Question 27

Why have so many levels of signaling

Answer 27

o Levels of control: being able to inhibit different levels of pathways allows for fine tuned control over responses
o Amplification: one molecule of ligand binds to the GPCR, but the activated enzyme can convert many molecules of ATP to cAMP
o Different responses by different cells

Question 28

Apoptosis

Answer 28

o Programmed organized cell death
o A cell orchestrates its own destruction and cleans up after itself as it dies
o Necessary for
• Development
• Cancer prevention
• Neurological prioritizing
• Protection against viral and bacterial infection
• Cells stuff everything in their lysosomes before death
o Can be autonomous or regulated by other cells (immune)

Question 29

Hormones

Answer 29

o Chemical messengers that travel in blood
o Have the potential to reach all cells of the body
o Only cells with receptors will bind and respond
o Widespread communication
o Different cells can have different receptors and produce different responses