Bio 201 - Cell BiologyDr. Hutson

Lecture 20 – ReviewMarch 14, 2014

Review topics

• Motor proteins• Signal transduction all• Other

Signal transduction: what it is• How cells interpret (i.e. “transduce”) signals from other cells.• Involves ligand binding to a receptor, usually on the cell

surface.– High affinity– Specificity

• Conformational change in receptor is key to intracellular response.

• Intracellular response often involves complex, multi-step pathways

• Sometimes involves a second messenger: soluble molecule produced in response to ligand binding; responsible for activation of next step in pathway

“Modes” of signaling between cells

• Juxtacrine and Contact-dependent: very fast and specific to cells in immediate surroundings

• Paracrine: relatively fast, affects more cells• Endocrine: much slower, affects many

different cells throughout organism; good for coordinating cellular responses

Different ligands may bind to different types of receptors. Different receptors transduce qualitatively

different types of responses.GPCRs:

ACβ α

cAMP

ras

PKA

MAPK

Many different types of ligands

Growth factors

RTKs:

enzymes

txn

Response to ligand binding usually involves changes in enzyme activity• Relatively fast• Reversible• Response amplification

Response to ligand binding usually involves changes in transcriptional activity• Slower• Not necessarily reversible• b/c enzymes involved, amplification

Υ

Many different responses

Growth, proliferation

Different ligands may bind to different types of receptors. Different receptors transduce qualitatively

different types of responses.

Steroid hormones

txn

Steroid hormone Rs:

Response to ligand binding almost always involves changes in transcriptional activity• Slower• Not necessarily reversible• No amplification (no enzymes)

Many different responses, incl. growth, differentiation

The same ligand may have different effects on different types of cells. This is sometimes due to the fact that

different cells have different targets of Gα.Liver:

ACβ α

cAMP

PKA

Epinephrine

enzymes

Υ

Some blood vessels and sweat glands:

β α

Epinephrine

Υ PLC

IP3

Ca++

Contraction (some blood vessels); Secretion (sweat glands)

Glycogen breakdown

glucose

In other cases, it is due to the fact that different cells have different targets of PKA.

Liver:

ACβ α

cAMP

PKA

Epinephrine

Υ

Glycogen breakdown

glucose

Bronchial smooth muscle cells:Epinephrine

Bronchodilation

ACβ α

cAMP

PKA

Υ

Analyzing the effects of activators and inhibitors

ACβα

cAMP

PKA

Epinephrine ΥGTP

Glycogen breakdown glucose(and inhibition of glycogen production)

Motor proteins - MyosinFunction: Muscle contraction, actin retraction in amoeboid cellsInteracts with: actinDirection: + end directed

Myosin is anchored

+ -

+ -

ATP binds

+ -

Motor proteins - KinesinFunction: Organelle transportInteracts with: MicrotubulesDirection: + end directed

Kinesin is bound to vesicle or organelle (NOT anchored)

+ -

ATP binds

+ -

Motor proteins - DyneinFunction: Organelle transport; cilia and flagellaInteracts with: MicrotubulesDirection: - end directed

Mechanistically similar to kinesin, but going in the opposite direction.

Comparison of motor proteins