unit 5 - cell communication

Question 1

gap junctions

Answer 1

connect the cytoplasm of neighboring cells and allow passage of ions and small molecules between them. allows coordination of tissues (like cardiac muscle contraction)

Question 2

contact cell-cell signalling

Answer 2

signal is made through physical contact of signal and receptor molecules (glycoproteins and glycolipids) connecting on the 2 cells’ surfaces
examples:
- contact inhibition (cells dividing for growth or to heal wounds know to stop dividing when they touch another cell—means gap is filled)
- cortical reaction (egg builds wall to prevent multiple sperm from penetrating after the first sperm signal-touches)
- phagocytic cells recognize foreign microbes and form pseudopods to eat them
- cell specialization during embryonic development

Question 3

contact inhibition

Answer 3

mechanism of cell-cell signaling that is important in wound healing. cells divide in the absence of a cell-cell signal (gaps from damaged cells), and stop dividing when they come in contact with each other again

Question 4

paracrine signal

Answer 4

uses secretory molecules
“para” = nearby - signal molecules travel short distances
examples:
- immune cells and regulation of inflammation
- growth factors that regulate formation of blood cells from stem cells
- synaptic signalling

Question 5

autocrine signal

Answer 5

uses secretory molecules that bind to the outside of the same cell to trigger a reaction
examples:
- T cells in the immune system produce antigens to trigger their proliferation
- abnormal signalling can lead to the uncontrolled growth of cancer cells

Question 6

synaptic signal

Answer 6

uses secretory molecules
type of paracrine signalling, but specifically involving electrical signals in neurons

Question 7

endocrine signal

Answer 7

uses secretory molecules called hormones, come from endocrine glands
long-distance transport via blood and circulatory system

Question 8

what does the Delta signal do?

Answer 8

controls nerve cell differentiation in flies. touch receptor.
when a cell specializes as a neuron, it has Delta signal protein in the membrane. when this connects with the Notch receptor protein ona
neighboring cell, the Notch tail is cleaved and migrates to the nucleus to regulate appropriate gene transcription, preventing neighboring cells from also becoming neurons

Question 9

types of protein kinases

Answer 9

• serine/threonine kinases: phosphorylate proteins on serine or threonine amino acids
• tyrosine kinases: phosphorylate kinases on tyrosine amino acids

Question 10

G-proteins

Answer 10

proteins activated using GTP
* GTP: active
* GDP: inactive
*have intrinsic GTP-hydrolyzing (GTPase) activity–can regulated themselves

Question 11

G-protein-coupled receptors (GPCRs)

Answer 11

• found in plasma membrane
• evolutionarily old, found in bacteria also
• 1 polypeptide, spans plasma membrane 7x (7 membrane-spanning alpha-helices), large extracellular domain that binds the hormone
  
  • after the signal binds, the receptor undergoes a conformational change to attract and activate a G-protein in the cytosol
  • conformational change of alpha subunit, GDP disassociates and is replaced with GTP
  • activated alpha subunit separates from activated beta-gamma subunit
  • both activated subunits can then regulate target proteins/enzymes by activating them. target proteins act as secondary messengers and carry on the signalling cascade

Question 12

receptor protein-tyrosine kinase (RTKs)

Answer 12

transmembrane proteins that form dimers when activated, cytoplasmic domains act as enzymes that activate other proteins
* extracellular molecule bonds to a receptor, RTKs dimerize
* dimers autophosphorylate (one half adds phosphate groups to the tyrosine residue of the other half) becomes activated
* proteins with SH2 domains can recognize and dock at specific phosphotyrosine residues
* proteins are phosphorylated and propagate the signal further

Question 13

GPCR interference

Answer 13

• cholera: cholera toxin modifies alpha subunit of G-protein so it can’t hydrolyze its GTP and is perpetually active and opens too many Cl- channels, leading to diarrhea, dehydration, and death
• whooping cough: pertussis toxin lock the alpha subunit of a G-protein in inactive, GDP-bound state. Prolonged signal that stimulates coughing, interferes with normal functioning
• drugs used in treatment of nearly every major organ system
  
  • anti-clotting, high blood pressure, asthma, mental health medications

Question 14

adenylyl cyclase

Answer 14

membrane-bound enzyme that produces cAMP using ATP
* activated by the activated alpha subunit of a G-protein

Question 15

second messengers

Answer 15

small, water soluble molecules/ions that diffuse through the cell and relay an extracellular signal to the interior of the cell
* most common: cAMP and IP3/Ca2+

Question 16

protein kinase A

Answer 16

enzyme that uses ATP to phosphorylate proteins, including transcription factors in the nucleus to regulate gene expression
* 4 subunits, 2 regulatory and 2 catalytic
* activated by cAMP, which binds to the regulatory subunits
* catalytic subunits can detach and enter the nucleus

Question 17

IP3 and DAG

Answer 17

• second messenger molecules that help activate protein kinase C
• products of PIP2, a type of phospholipid in the cell membrane

produced when:
1. activated alpha-subunit of a G-protein activates phospholipase C-beta
2. phospholipase C-beta phosphorylates and hydrolyzes PIP2 into two molecules, IP3 and DAG

• IP3 diffuses into the cytosol, binds to calcium channels in the membrane of the smooth ER
• calcium acts as a second messenger to activate protein kinase C
• DAG remains in the membrane and also helps activate protein kinase C
• protein kinase C can then cause a phosphorylation cascade or regulate gene trascription

Question 18

main functions of cAMP

Answer 18

activating protein kinase A, which can cause a phosphorylation cascade or activate gene transcription

cell responses can include increase in heart rate, glycogen or fat breakdown, or cortisol secretion

Question 19

calmodulin

Answer 19

• most common Ca2+ responsive protein, present in the cytosol of all eukaryotic cells
• dumbell shape- two globular ends and a long flexible alpha-helix. 2 Ca binding sites
• Ca2+ binds, calmodulin changes conformation and wraps around various target proteins to regulate their activity
  -Ca2+/calmodulin-dependent protein kinases, usually control gene transcription

Question 20

signals that can bind intracellular receptors

Answer 20

steroid and thyroid hormones
* cortisol, estradiol, testosterone, thyroxine
dissolved gases, only act locally
* nitric oxide

Question 21

malfunctioning receptor in sex determination

Answer 21

androgen insensitivity syndrome
* SRY gene on Y chromosome produces testes which produce testosterone
* AR gene contains the testosterone receptor. if mutated, body develops testes but female sex characteristics despite XY chromosomes

Question 22

function of NO as a molecular signal

Answer 22

induces vasodilation to increase blood flow
* nerve cells secrete acetylcholine that binds to GPCRs in endothelial cells on the interior of blood vessels, stimulating arginine residues to produce nitric oxide
* NO diffuses out of endothelial cells into smooth muscle cells with NO receptors, which relax in response
guess which silly little pill uses nitric oxide……..to increase blood flow……

Question 23

three chemical classes of hormones

Answer 23

1. lipid/steriod hormones - bind intracellular receptors in the cytosol or nucleus
2. gas (NO) - diffuses across plasma membrane, major paracrine signaling molecule in circulatory system
3. peptides and protein hormones - bind to extracellular receptors, the widest variety of signaling molecules

Question 24

Signaling by the steroid hormone estrogen is an example of _______ signaling

Answer 24

endocrine

Question 25

When activated, T lymphocytes secrete chemical factors that lead to their own growth and proliferation. This is an example of _______ signaling.

Answer 25

autocrine

Question 26

Which signal molecule diffuses through the plasma membrane to ultimately bind nuclear receptors and influence transcription?

Answer 26

estrogen

Question 27

Steroid hormones usually act via receptors that...

Answer 27

bind to DNA. they act as transcription regulators

Question 28

Nitric oxide is a signal molecule that can

Answer 28

diffuse across cell membranes and directly alter the activity of intracellular enzymes.

Question 29

The medical usage of nitroglycerine in heart disease is based on its

Answer 29

conversion to NO, which stimulates blood vessel dilation. treats patients with angina.

Question 30

The G protein that activates adenylyl cyclase is a

Answer 30

heterotrimeric G protein that separates into a and βγ subunits

Question 31

Cholera toxin inhibits the ability of the a subunit of G protein to split GTP. If you treated cells with cholera toxin, the resulting effect would be _______ of adenylyl cyclase

Answer 31

stimulation

Question 32

A major function of cAMP in animal cells is to activate

Answer 32

protein kinase A

Question 33

During the odorant response in the cilia of olfactory neurons, the second messenger _______, leads to the opening of ion channels in the plasma membrane of olfactory neurons and the production of a nerve impulse.

Answer 33

cAMP

Question 34

MAP kinase is an abbreviation for _______ protein kinase.

Answer 34

mitogen-activated

Question 35

Ras is a membrane-bound _______ when activated.

Answer 35

G-protein that binds GTP

Question 36

Hydrolysis of PIP2 by phospholipase C produces:

Answer 36

DAG and IP3

Question 37

G protein-coupled receptors are important molecules involved in signal transduction. Which statement about G protein-coupled receptors is true?

Answer 37

They generally contain seven membrane-spanning a helices.

Question 38

Which statement about G protein signaling is false?

Answer 38

The a subunit becomes deactivated when the hormone dissociates from the receptor.

Question 39

Cyclic AMP (cAMP) is synthesized from ATP by the action of

Answer 39

adenylyl cyclase

Question 40

Receptor tyrosine kinases represent critical molecules involved in growth and differentiation though phosphorylation of target substrates on tyrosine residues. Which structural feature is not common among all receptor tyrosine kinases?

Answer 40

a single polypeptide

Question 41

Which of the following is not a commonly observed consequence of the binding of a signaling molecule to its cell surface receptor?

Answer 41

increased synthesis of the receptor

Question 42

second messengers are:

Answer 42

small molecules and ions that relay signals received by cell-surface receptors

Question 43

SH2 domains are:

Answer 43

protein domains that bind phosphotyrosine-containing peptides

Question 44

mechanism of viagra

Answer 44

blocks enzyme that degrades cGMP. NO enters endothelial cells of penis blood vessels, activating guanylyl cyclase to convert GTP to cGMP, which activates PK-G and induces vasodilation continuous activation of PK-G

Question 45

types of cell responses

Answer 45

- Control the behavior of the cell - Opening or closing ion channels (send an action potential) - Altering cell metabolism (activate or inhibit metabolic enzymes) - Altering gene expression (turning on or off genes) - Altering shape and movement - Cell division - Cell differentiation

Question 46

mutations that lead to cancer

Answer 46

- abnormal autocrine signaling that produces continuous growth factors - overexpression of RTKs, spontaneous dimerization in the absence of growth signals, covalent linkages of the extracellular or tyrosine kinase domains that lead to perpetually dimerized receptors - production by cancer cells of dimerized proteins with tyrosine-kinase function - mutated Ras proteins can lead to uncontrolled cell division - activated MAP kinase

Question 47

how do steroid hormones regulate transcription?

Answer 47

bind intracellular receptors, then the receptor-hormone complex enters the nucleus and regulates gene activity by binding to regions of DNA and altering their level of transcription - each hormone binds a different receptor protein and each receptor acts at a specific regulatory site in the DNA example of dysfunction: intersex individuals that lack the receptors to express genes activated by testosterone

Question 48

how do signal transduction pathways work?

Answer 48

binding of a signalling molecule activates receptors --> receptors activate enzymes --> enzymes release second messengers --> protein producing the target cellular response is activated

Question 49

Ras proteins

Answer 49

- small GTP-binding protein, similar to alpha subunit of G-proteins, found on cytoplasmic side of the plasma membrane - activated by receptor tyrosine kinase, via an adaptor protein with an SH2 domain - promotes activation of phosphorylation cascade using Mitogen-activating protein kinases (MAP-kinase) - eventually alters gene trascription to stimulate cell proliferation, apoptosis inhibition, or cell differentiation

Question 50

mutated Ras proteins

Answer 50

- inhibited removal of GTP - perpetually active Ras leads to uncontrolled cell division (cancer)

Question 51

Akt protein kinase

Answer 51

- activated by IP3 - causes a phosphorylation cascade that inhibits apoptosis

Question 52

structure and mechanism of intracellular receptor gene transcription regulation

Answer 52

structure: transcription activating domain, DNA binding domain, signal molecule binding domain - in its inactive form, intracellular receptors are bound to an inhibitor protein that prevents the DNA-binding domain from interacting with DNA - lipid-soluble signal molecule (steroid hormones) binds to an intracellular receptor, causing the inhibitor to dissacociate and expose the DNA binding site - hormone-receptor complex moves into the nucleus and binds DNA to regulate transcription