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Eukaryotic Cell Biology > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

Signal transduction pathway

A

When extracellular signal molecule binds to the receptor protein, it activates one or more intracellular signaling pathways or systems.

System depend on intracellular signaling proteins. Their function is to process the signal inside receiving cell and distribute to intracellular targets (effector proteins).

The effector protein is altered in some way by the signal and implement appropriate change in cell behavior.

Examples of effector proteins: transcription regulators, ion channels, components of metabolic pathway or parts of the cytoskeleton.

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2
Q

Contact-dependent signaling

A

Development of complex structured (eye, immune response)

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3
Q

Paracrine signaling

A

Secretion of local mediators rhat act on cells in the local environment.

Autocrine signaling (respond to its own signal). E.g. used to reinforce developmental decision. (Cancer cells)

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4
Q

Synaptic signaling

A

Limited to neurons

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5
Q

Endocrine signaling

A

Long-distance; distribution of hormones via bloodstream.

Hormones are a signaling molecule secreted by the endocrine cell.

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6
Q

Describe the two major classes of signaling molecules and how signal characteristics affect receptor location

A

Different signal characteristicd drive receptor type

Hydrophilic signals, unable to cross the PM, use Cell-surface receptors.

Small hydrophobic signals (steroid hormones) diffuse across the plasma membrane and can activate intracellular receptors

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7
Q

Binding specificity

A

The ability to distinguish closely related substances

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8
Q

Agonist

A

Drug that binds to a receptor and activates the receptor to produce a biological response

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9
Q

Antagonist

A

Drug that binds to receptor, does not induce a response: prevents a receptor activation

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10
Q

Binding affinity

A

Defines the strength of the interaction beteeen the ligand (signaling molecule) and its receptor

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11
Q

Kd

A

Equilibrium binding constant =Kd

Kd = dissociation constant

It is a measure of the affinity if the receptor for its lifand

Kd = [Rfree][Lfree]/[RL]

Kd is = the ligand concentration at 1/2 max binding

Lower the Kd, higher the affinity

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12
Q

Do cells need signals to survive?

A

Yes

If a cell has no signal it will go through apoptosis

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13
Q

What is special about acetylcholine relating to cell signaling?

A

Acrtylcholine can have different effects on different target cells

If they:
1. Use the same receptor
Or
2. Different receptors in use but they both have the signal binding domain

Remember: An extracellular signal has little information content

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14
Q

How are responses to a signal molecule programmed

A
  1. Through the receptors that the target cells carry

2. Through the internal machinery to which the receptors are coupled

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15
Q

What are the requirements fir a signal to bind to a cell-surface receptor

A

Must be a transmembrane protein

Must have both extracellular and intracellular domains

Binding to the extracellular domain must lead to a molecular change inside the cell that can be recognized

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16
Q

What are the 3 major classes of cell-surface receptors?

A
  1. Ion-channel coupled receptors
    - gated ion channels
  2. G-protein couples receptors.
    - work via trimerix G-proteins
    - associated with vision and smell
  3. Enzyme coupled receptors
    - enzyme = kinase
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17
Q

What are the 3 main types of molecular switches

A
  1. Ligand binding: allostery, allosteric proteins. (Structural change occurs = functional change)
  2. Phosphorylation
    - The protein kinase adds phosphate groups
    - The protein phosphatase removes phosphate groups
  3. GTP-binding proteins
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18
Q

What are the two main groups of protein kinases?

A

Serine/threonine kinases

Tyrosine kinases

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19
Q

What are the two major types of G proteins?

A

Large trimeric G-proteins: help relay signals from the G-protein receptors that activate them

Small monomeric G-protein: help relay signals from many classes of cell-surface receptors.

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20
Q

What is the function of Guanine nucleotide-dissociation inhibitors (GDIs)

A

Can hold G-protein inactive by inhibiting the release of a bound GDP

21
Q

Function of GTPase-activating proteins

A

Regulators of G protein signaling (RGS).

Promote dephosphorylation to GDP

22
Q

Function of Guanine nucleotide-exchange factors (GEFs)

A

Promote bonding of GTP

23
Q

Function of scaffolding proteins

A

Bring groups of interacting signaling proteins together.

This decreases the possibility of activating the wrong protein

24
Q

Function of modular interaction domains

A

They mediate interaction between intracellular signaling proteins

25
Q

Describe the major characteristics of a G-protein coupled receptor

A

Largest family of cell surface receptors
Examples: light, odorants, peptides (neurotransmitters), hormones

Structure is single polypeptide that is a multi pass transmembrane protein with 7 transmembrane domains

Activation of the receptor creates binding site for trimetic G-protein on intercellular side

Interaction of the G-protein with the receptor activates the G protein

26
Q

Describe the major characteristics of Trimeric G-Protein

A

Composed of 3 polypeptides (subunits) 

Function in a similar fashion to mono medic GTP-binding proteins

Covalently attached lipids found on both the alpha and y subunits

27
Q

Process of G-protein activation

A
  1. Ligand (signaling molecule) binds receptor activating it which causes conformational change that exposes a binding site for G-protein
  2. G-protein binds: Receptor acts as the GEF (GDP is ejected, GTP binds)
  3. GTP binding activated the alpha subunit causing it to dissociate from the Beta/gamma subunit. This activated the beta/gamma.
  4. Both subunits can activate target proteins
  5. GTPase activity of alpha subunit, hydrolyses GRP to GDP, inactivates alpha subunit, which reassociates with beta gamma subunit

Key concept: both alpha subunit and beta/gamma subunit can relay a signal

28
Q

I’m GPCR pathways, effector proteins are either….

A

Enzymes that catalyze the formation of second messengers or ion channels

29
Q

Describe the role of Adenylyl Cyclase

A

It is an effector protein. An enzyme that catalyzes formation of 2 messengers

Produces cAMP

Membrane bound enzyme

Converts ATP into cAMP which is a ubiquitous intercellular messenger (2nd messenger)

cAMP works as a ligand to activate other target proteins

In order to function as a messenger cells need to be able to quickly change its concentration therefore rapid synthesis and rapid degradation can occur

30
Q

What mediates the effects of cAMP

A

Protein Kinase A (PKA)

Tetramers: 2 regulatory and 2 catalytic domains

Binding of cAMP causes dissociation of the two catalytic domains

Unmasks the active sites: activated

Binding of cAMP to the regulatory subunits is cooperative. Binding of the first cAMP lowers the Kd for binding of the second!

This means that small changes in level of cytosolic cAMP can cause proportionately large changes in the amount of active PKA

31
Q

PKA

A

is a serine/threonine Kinase

Will phosphorylate different proteins in different cell types

32
Q

Characteristics of signal that binds to cell surface receptor

A

Transmembrane
Extra cellular and intracellular domain
Causes molecular change that can be recognized inside cell

33
Q

The 3 major classes of cell surface receptors

A

Ion channel receptor
G protein coupled receptor
Enzyme coupled receptor

34
Q

GPCR

A

Single poly peptide
Transmembrane multi pass
Activation of it creates binding site for trimeric G protein
Interaction of the G protein with receptor activated the G protein

35
Q

Trimeric G protein

A

3 polypeptides (alpha subunit and beta/gamma sub unit)

Covalently attached lipids found on both the alpha and gamma subunits

36
Q

Effector proteins of GPCR pathways

A

Enzymes that catalyze formation of second messengers or ion channels

37
Q

Adenylate Cyclase

A

Produces cAMP
Membrane bound
Converts ATP into cAMP

38
Q

cAMP

A

2nd messenger

Works as ligand to activate other target proteins

39
Q

PKA

A

binding of cAMP causes dissociation of the two catalytic domains: becomes active

Small changes in level of cAMP can cause large changes in amount of active PKA

PKA is a regulator of cAMP

40
Q

Phospholipase C

A

Enzyme that cleaves PI 4,5 biphosphate to produce IP3 and DAG

41
Q

IP3 and DAG

A

2nd messengers

IP3 opens Ca++ channels

DAG activates protein kinase C

42
Q

Ca++

A

Acts as an allosteric effector (ligand)

43
Q

Calmodulin

A

Enzymes
ION pumps
Protein kinases

44
Q

Dark adapted cells

A

Have open channels that are depolarized

Increased levels of cGMP

45
Q

RTKs

A

Important in responses to signals that promote growth

Signal binding (activation) causes the receptors to dimerize. Diners can cross-phosphorylate

Phosphorylated tyrosines are docking sites for proteins with SH2 and PTB

SH3 domains: protein/protein

46
Q

Adaptor proteins

A

Composed almost entirely of SH2 and SH3

47
Q

Explain how Ras is activated (RTK)

A

Active when bound to GTP

activation of RAS by RTK

The activated receptor is bound by Grb2 (adaptor protein)
grb2 is bound by the RAS-gef (sos)
SOS activates RAS

48
Q

RAS can activate MAPkinase modules

A

Mitogens are signals that stimulate cell proliferation

Kinase cascades allow signal amplification

49
Q

Akt

A

Critical for cell proliferation and survival

Eukaryotic Cell Biology (2 decks)

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