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More signal transduction Cell-cell contact via gap junctions or plasmodesmata; signal molecule passes between cells Ce PowerPoint Presentation
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More signal transduction Cell-cell contact via gap junctions or plasmodesmata; signal molecule passes between cells Cell-cell recognition molecule binds to specific receptor; “receptor-ligand interaction”. These ligands are primary messengers What happens next?.

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Presentation Transcript
slide1

More signal transduction

Cell-cell contact

via gap junctions or plasmodesmata;

signal molecule passes between cells

Cell-cell recognition

molecule binds to specific receptor;

“receptor-ligand interaction”

slide4

When the ligand binds, other molecules are

produced within the cell

“second messengers” relay the signal from

interior of cell

May trigger cell activity and/or gene expression

slide5

Many different types of molecules can be ligands

Hydrophilic molecules bind to membrane

receptors. Receptor may be found on many

different cells.

Hydrophobic molecules bind to intracellular

receptors

steroids

retinoids

slide6

Families of membrane receptors

G-protein-linked receptors

tyrosine kinase receptors

ion-channels

intracellular

slide7

G protein-linked receptors

Have similar structures but different amino

acid sequences

Seven transmembrane -helices

N-terminus on extracellular side, C-terminus

on cytosolic side

slide10

Two major types of G proteins

Large heterotrimeric G proteins mediate

signal transductions

Small monomeric G proteins help regulate

the cytoskeleton

slide12

G is bound to GDP; complex is inactive

When a ligand binds it (G) releases GDP and

binds GTP

G separates from other subunits. These can

move freely along membrane and bind

to enzymes or other proteins, activating

them. Both the G and G can bind to and

activate different cellular proteins

G protein can hydrolyze the GTP and quickly

revert to inactive state

slide13

Many different types of G proteins can interact

with different cellular proteins

Vision

Smell

Acetylcholine receptors: one “family” are ion

channels (contraction), another are

G protein receptors (relaxation)

Developmental pathways

What does G protein activation accomplish?

Activation of second messenger system

cAMP

calcium

Levels are elevated

slide14

Tyrosine kinase pathways

(what is a kinase? Adds phosphate groups

to a particular amino acid)

Growth, proliferation, specialization

“cytoplasmic tail” portion of receptor has several

tyrosines. Proteins are found as separate

peptides in inactive form?

What activates it? You know by now!

slide15

Dimer forms upon aggregation. Tyrosines

are phosphorylated via ATP hydrolysis

“relay” proteins bind to tyrosines, become

activated

These can now move through the cell and

activate other pathways

slide18

Tyrosin kinases can activate many pathways

simultaneously

Think about it: growth, differentiation, etc.

require many different activities

G protein pathways are not as diffuse

slide19

Ion channels

Ligand gated

activated when a specific molecule binds

example: acetylcholine receptor

in postsynaptic cell

Voltage gated

stimulus is electrical, not chemical

Both important in neervous system activity

in

slide22

Intracellular receptors

In nucleus or cytosol

Ligand is small and hydrophobic

Promotes transcription or cell activation

slide24

Now that we have seen how the signal

activates the cell, how is the signal

actually transduced?