AP Biology Cell communication - signal reception

Cell Communication - Signal Reception

Ch. 11Section 11.2

Whiteboards please

How cells “hear” the call

• The target cell has a receptor protein that recognizes the chemical signal Recognition happens when

the signal molecule binds to the receptor

They fit together like lock and key

signal specificity The same signal

molecule can generate different responses in different cells

Each type of cell may contain different types of proteins, thus they will respond to the same signal molecule differently

Signal SpecificitySignal Specificity

Different types of Different types of cells contain different cells contain different proteins and so proteins and so respond differently to respond differently to signal moleculessignal molecules

Why does epinephrine cause a livercell to metabolize glycogen, but cause a muscle cell to contract??

QUICK THINKQUICK THINKExplain why cells can respond differently to the same signal

molecule

Critical Vocab!!

• Signal molecule = ligand

Signal Reception

• Ligand binds to receptor • Receptor protein changes shape• This starts the transduction pathway• Leads to cell response

Quick Think

•How do cells “hear” the message from other cells?

Ligands – 2 types

Large and/or Polar Ligands• Proteins• Ions• Cannot pass

through cell membrane

• Bind to protein receptor on exterior of cell membrane

Non-polar Ligands• Lipids –

Steroid Hormones

• Can pass through cell membrane

• Bind to receptor protein inside cell

Testosterone - a steroid signal molecule

• Testosterone is a hormone, a steroid, secreted by the testis

• It travels through the blood stream• It enters all kinds of cells• But the only cells that can “hear” it

are the target cells that have the right receptor molecule inside the cell

• Once inside, testosterone binds to the receptor and helps turn on genes that control male sex characteristics

Example Cell Response

• Many ligands are transcription factors

• Direct the cell to DNA mRNA protein

Quick Think

• Where are intracellular reception proteins?

• Why can their chemical signals pass into the cell?

Quick Think

• Nerve Growth Factor (NGF) is a water-soluble signal molecule. Would you expect the receptor for NGF to be intracellular or in the cell membrane? Why?

Most signal receptor proteins are in the cell membrane

• There are 3 main types of cell membrane signal receptors G-protein-linked

receptors Receptor tyrosine

kinases Ion-channel receptors

G-protein linked receptors

• Made up of a receptor protein + a G protein

• They have 7 helices

The G-protein part

• The G-protein part is like an on/off switch for the receptor protein

• When GDP (cousin of ATP) is bound to it, the G protein is inactive

G-Protein Linked Receptors 1.Ligand attaches to receptor protein2.G-protein activated3.G protein activates an enzyme4.Transduction & cell response

The G-protein

• G-protein receptor systems are really common and play a role in lots of different cell processes Development of embryos Vision & Smell

• Lots of diseases involve G-proteins Bacterial infection like botulism

and cholera interrupt G-protein function

Most drugs (medicines) work by influencing a G-protein pathway

Quick Think

•How does a G-protein linked receptor function?

Tyrosine-kinase receptors

• Best when the cell needs to trigger several cell responses at once

Tyrosine-kinase receptors

• kinase - enzyme that catalyzes the transfer of phosphate groups

• So it is an enzyme that functions to transfer a phosphate group from ATP to tyrosine

Tyrosine-kinase receptors

• Has 3 parts: Extracellular (outside

the cell) signal-binding site

1 helix An intracellular

(inside the cell) tail with a bunch of tyrosines on it

Tyrosine-kinase receptors

• Once 2 signal molecules binds to 2 tyrosine-kinase receptors, they pair up to form a dimer

Tyrosine-kinase receptors

• Once this happens, this causes the tyrosine-kinase part of the receptor to take phosphate from ATP and add it to the tyrosine tail

• This makes the receptor protein “fully activated”

Tyrosine-kinase receptors

• Once the tyrosine-kinase receptor is fully activated, it is recognized by other proteins in the cell

• Each tyrosine-kinase receptor may activate many different proteins that may lead to many different cell responses

1. 2 ligands bind to 2 receptor proteins

2. 6 Pi (from 6 ATP) added to receptor protein tails

3. Each Pi can activate a different cell response

Quick Think

•Summarize how a tyrosine-kinase receptor functions.

Ligand-gated ion channel protein

• Receptor protein that acts as a gate for entry into the cell

• When a signal molecule binds to the receptor protein, the gate opens to allow specific ions (like sodium or calcium) to flow through it

Ligand-ion-gated channel protein

1. ligand binds & protein channel opens

• ions flow through

• ligand dissociates & gate closes

Ligand-gated-ion channel protein

• Important in the nervous system Neurotransmitter binds as a

ligand Ion-channel proteins open Ions flow into cell Triggers an electrical signal

that moves down the length of the cell

Quick Think

•Summarize how a Ligand-gated ion channel functions.

Cell Communication Research• Create an infographic about a disease or drug that

disrupts cell communication