CELL SIGNALLING

By: Khuram Aziz M.phill Biochemistry

Overview of All lectures that you have learned

Its brief description and animations

Cells also communicate by direct contact.

1. Cell Junctions

Signaling substances dissolved in the cell can pass freely from one cell to another

2. Direct Contact

Through molecules on the surface of the cell

(embryonic development and the immune system)

COMMUNICATION BY DIRECT CONTACT WITH CELLS.

Local Chemical Signaling

Paracrine

Secreting cell acts on nearby target cell by discharging molecules into the extracellular fluid

Synaptic

Nerve cell releases neurotransmitter into synapses

DISTANT CELL COMMUNICATION

Hormones signal target cells at much greater distances.

Secreted into the body fluids, they reach all parts of the body.

Only specific target cells are recognized and respond

LOCAL & DISTANT CELL COMMUNICATION IN ANIMALS

Local and Distant Cell Communication In Animals.

THE THREE STAGES OF CELL SIGNALING

For a chemical signal to elicit a specific response, the target cell must possess a signaling system for the signal.

1. Reception

2. Transduction

3. Response

OVERVIEW OF CELL SIGNALING.

Reception – signal (ligand) binds to a specific cell surface protein.Transduction – binding results in conformation change of receptor. This initiates transduction (one or many steps)Response – almost any cellular activity

Many signal molecules cannot pass freely through the plasma membrane

Receptors are located on the plasma membrane

These families are called:

- G-protein linked receptors

- tyrosine kinase receptors

- ion channel receptors

Overview of the 3 Main Signal Transduction

Pathways:

e.g., neurotransmission

e.g., cAMP mediated flight or fight response (glycogen breakdown, muscle contraction)

e.g., regulation of many genes

A LIGAND-GATED ION-CHANNEL RECEPTOR.

(important in nervous system)

1. large or very polar extracellular ligand (e.g., hormone)

1. large or very polar extracellular ligand (e.g., hormone)

•changes in enzyme activity

Signal Transduction Themes:•intracellular 2nd messengers•Protein phosphorylation

3. intracellular 2nd messengers

4. protein phosphorylation

•changes in cytoskeletal organization

•changes in ion permeabilty

•activation of replication

•regulation of transcription

2. cell surface receptor2. cell surface receptor

•Membrane depolarization

STEROID HORMONES: ACTION

Figure 7-7

Most hydrophobic steroids are bound to plasma protein carriers. Only unbound hormones can diffuse into the target cell.

Translation produces new proteins for cell processes.

Some steroid hormones also bind to mem-brane receptors that use second messenger systems to create rapid cellular responses.

Steroid hormone receptors are typically in the cytoplasm or nucleus.

The receptor-hormone complex binds to DNA and activates or represses one or more genes.

Activated genes create new mRNA that moves into the cytoplasm.

Cellmembrane

Interstitialfluid

Cytoplasmicreceptor

Endoplasmicreticulum

Nucleus

Nuclear receptor

DNA

Translation

Rapid responses

Transcriptionproduces mRNA

Steroidhormone

Bloodvessel

Proteincarrier

Newproteins

Cell surface receptor

2

3

1

4 5

2a

1

2

2a

3

45

STEROID HORMONES: ACTION

Figure 7-7, step 1

Most hydrophobic steroids are bound to plasma protein carriers. Only unbound hormones can diffuse into the target cell.

Cellmembrane

Interstitialfluid

Nucleus

Bloodvessel

Proteincarrier

1

1

STEROID HORMONES: ACTION

Figure 7-7, steps 1–2

Most hydrophobic steroids are bound to plasma protein carriers. Only unbound hormones can diffuse into the target cell.

Steroid hormone receptors are typically in the cytoplasm or nucleus.

Cellmembrane

Interstitialfluid

Cytoplasmicreceptor

Nucleus

Nuclear receptor

Steroidhormone

Bloodvessel

Proteincarrier2

1

1

2

STEROID HORMONES: ACTION

Figure 7-7, steps 1–2a

Most hydrophobic steroids are bound to plasma protein carriers. Only unbound hormones can diffuse into the target cell.

Some steroid hormones also bind to mem-brane receptors that use second messenger systems to create rapid cellular responses.

Steroid hormone receptors are typically in the cytoplasm or nucleus.

Cellmembrane

Interstitialfluid

Cytoplasmicreceptor

Nucleus

Nuclear receptor

Rapid responses

Steroidhormone

Bloodvessel

Proteincarrier

Cell surface receptor

2

1

2a

1

2

2a

STEROID HORMONES: ACTION

Figure 7-7, steps 1–3

Most hydrophobic steroids are bound to plasma protein carriers. Only unbound hormones can diffuse into the target cell.

Some steroid hormones also bind to mem-brane receptors that use second messenger systems to create rapid cellular responses.

Steroid hormone receptors are typically in the cytoplasm or nucleus.

The receptor-hormone complex binds to DNA and activates or represses one or more genes.

Cellmembrane

Interstitialfluid

Cytoplasmicreceptor

Nucleus

Nuclear receptor

DNA

Rapid responses

Steroidhormone

Bloodvessel

Proteincarrier

Cell surface receptor

2

3

1

2a

1

2

2a

3

STEROID HORMONES: ACTION

Figure 7-7, steps 1–4

Most hydrophobic steroids are bound to plasma protein carriers. Only unbound hormones can diffuse into the target cell.

Some steroid hormones also bind to mem-brane receptors that use second messenger systems to create rapid cellular responses.

Steroid hormone receptors are typically in the cytoplasm or nucleus.

The receptor-hormone complex binds to DNA and activates or represses one or more genes.

Activated genes create new mRNA that moves into the cytoplasm.

Cellmembrane

Interstitialfluid

Cytoplasmicreceptor

Nucleus

Nuclear receptor

DNA

Rapid responses

Transcriptionproduces mRNA

Steroidhormone

Bloodvessel

Proteincarrier

Cell surface receptor

2

3

1

4

2a

1

2

2a

3

4

STEROID HORMONES: ACTION

Figure 7-7, steps 1–5

Most hydrophobic steroids are bound to plasma protein carriers. Only unbound hormones can diffuse into the target cell.

Translation produces new proteins for cell processes.

Some steroid hormones also bind to mem-brane receptors that use second messenger systems to create rapid cellular responses.

Steroid hormone receptors are typically in the cytoplasm or nucleus.

The receptor-hormone complex binds to DNA and activates or represses one or more genes.

Activated genes create new mRNA that moves into the cytoplasm.

Cellmembrane

Interstitialfluid

Cytoplasmicreceptor

Endoplasmicreticulum

Nucleus

Nuclear receptor

DNA

Translation

Rapid responses

Transcriptionproduces mRNA

Steroidhormone

Bloodvessel

Proteincarrier

Newproteins

Cell surface receptor

2

3

1

4 5

2a

1

2

2a

3

45

17-22

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THE STRUCTURE OF A G-PROTEIN –LINKED RECEPTOR.

RECEPTORS THAT ACTIVATE G PROTEINS

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ANOTHER RECEPTOR – G PROTEIN CYCLE

CAMP AS A SECOND MESSENGER.

c-AMP: a second messenger

OVERVIEW- GENERAL STRUCTURE

Lyase Enzyme that converts ATP to cAMP Interacts with g proteins and receptors 1064-1353 amino acids long 120-150 kilodaltons

GENERAL STRUCTURE CONT’D

10 mammalian isoforms All membrane bound 60% similarity 50%-90% in cytoplasmic regions

PRIMARY STRUCTURE

The main structural features of mammalian adenylyl cyclases

M1/M2: 2 sets 6 transmembrane spans C1a/C1b: large cytoplamic domains (360-390 amino

acids) C2a/C2b: large cytoplasmic domains (255-330 amino

acids) Most highly conserved sequence in all isoforms 50% similar; 25% identical

N terminus and C terminus

ROLE OF CYCLIC AMP

Step 1: activates protein kinasesStep 2: protein kinases phosphorylate substrate proteinsStep 3: activated substrate proteins regulate hormone production

G-protein Mediated cAMP synthesis

bga

GTP

GDP

a

GTP

ATP

cAMP +PPi

bg a

GTP

ATP

cAMP +PPi

GDPPi

When the [hormone] drops…

GDP

GTP

RECEPTORADENYLYL CYCLASE

G PROTEINS THAT INTERACT WITH ADENYLATE CYCLASE

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WHAT DOES IT DO?

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RECEPTORS THAT DIRECTLY ALTER THE ACTIVITY OF INTRACELLULAR MEDIATOR

17-38

SER

IP3 (inositol triphosphate)

Ca++

G-protein mediated signal transduction is mediated by several 2nd messengers:

DAG(diacyl glycerol) OH

protein kinase C

Ultimateeffects

cAMPprotein kinase A

Adenylate cyclase

Phospholopase C

2ND MESSENGERS: IP3 AND DAG

PLC- active

Phosphatidylinositol- 4,5 biphosphate=(PIP2)

PLC= Phospholipase C

is a membrane phospholipid cleaved into free IP3 and membrane bound DAG by phospholipase C. (Ch.7) (Ch.12)

HYDROLYSIS OF PIP2

phosphatidylinositol 4,5-bisphosphate

One of the most widespread pathways of intracellular signaling is based on

the second messengers derived form PIP2

LE 11-12_1

CYTOSOL

Ca2+Endoplasmicreticulum (ER)

IP3-gatedcalcium channel

IP3 (secondmessenger)

DAG

PIP2G-protein-linkedreceptor Phospholipase C

G protein

Signal molecule(first messenger)

EXTRACELLULARFLUID

GTP

LE 11-12_2

CYTOSOL

Ca2+Endoplasmicreticulum (ER)

IP3-gatedcalcium channel

IP3 (secondmessenger)

DAG

PIP2G-protein-linkedreceptor Phospholipase C

G protein

Signal molecule(first messenger)

EXTRACELLULARFLUID

GTP

Ca2+ (secondmessenger)

LE 11-12_3

CYTOSOL

Ca2+Endoplasmicreticulum (ER)

IP3-gatedcalcium channel

IP3 (secondmessenger)

DAG

PIP2G-protein-linkedreceptor Phospholipase C

G protein

Signal molecule(first messenger)

EXTRACELLULARFLUID

GTP

Ca2+ (secondmessenger)

Variousproteinsactivated

Cellularre-sponses

Ca2+ pool can be affected in 2 ways:

1. Ligand binding to a calcium ion channel

2. Activation of IP3 signaling pathway

G PROTEINS THAT OPEN CALCIUM ION CHANNELS

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ligand -gated (IP3)

ligand -gated (Ca2+ )

voltage -gated

P-type Ca2+ pump

P-type Ca2+ pump

HYDROLYSIS OF PIP2

phosphatidylinositol 4,5-bisphosphate

One of the most widespread pathways of intracellular signaling is based on

the second messengers derived form PIP2

Phospholipase C-mediated effects:

•Liver glycogen breakdown (vasopressin)•Pancreatic amylase secretion (acetylcholine)•Platelet aggregation (thrombin)

Protein kinase C effects include:

• neurotransmitter release• cell growth & division• cell differentiation • glycogen hydrolysis• fat synthesis

CALMODULINCalmodulin binds directly with calcium ions to regulate the activity of specific proteins.

Upon binding it undergoes a conformational change allowing binding of other proteins, activating or inactivating them

The protein Calmodulin with calcium binding.

Calcium: bluealpha-Helices: orangebeta-sheets: green.

CALCIUM/CALMODULIN

CA2+ ions

CALMODULIN

#6: THE CALCIUM CALMODULIN COMPLEX REGULATES ENZYME ACTIVITY

Ca+2 triggers

conformation change

CCC

(enzyme)

SIGNAL AMPLIFICATION

17-54

CYTOPLASMIC RESPONSE TO A SIGNAL.

Amplification

cAMP and the Fight-or-Flight Response; activation of PKA

cAMP

adrenaline

inactiveadenylylcyclase

inactiveactive protein kinase A

phosphorylase kinase

p

p glycogenphosphorylase

glycogen glucose-1-phosphate

Liver cell

amplification cascade

cAMP

activeATP

inactive

inactive

active

active

CAFFEINE KEEPS YOU AWAKE BECAUSE IT

1. Prevents the synthesis of cAMP.

2. Prevents the breakdown of cAMP.

3. Inactivates the enzyme protein kinase A.

4. Inhibits the enzyme glycogen phosphorylase

Caffeine inhibits the enzyme phosphodiesterase, which normally breaks down cAMP.

.

Thanks GOOd LUCK