Cell Receptors and Signal Transduction

A lot of communication happens through____messengers

Chemical

Specialized areas of the cell membrane sensitive to chemicals and cause cell to change function when activated

Receptors

Most of the receptors are known as ______proteins

Transmembrane

Any molecule bound to a cell membrane protein

Ligand

Is ligand binding reversible or irreversible?

reversible

Do proteins have one or any bindingsites for ligands?

Multiple

What is the result of a ligand binding to a protein

Protein conformation is changed

Once the cell recieves the signal a _____system is required to covrert it to a meaningful response within cell

transduction

Step of signal transduction

Messenger attches to the binding site on the receptor

Protein shape changes

Response produced

Depends on strength of ligand protein binding

Affinity

All binding sites occupied

Saturation

More than one ligand binding one site

Competition

Name of the chemical messenger that transmits response of first messenger

Second messenger

4 Features of Ligand-protein binding

Specificty

Saturation

affinity

Competiton

Sitting Silent at church

First messenger binding site has particular shape into which only certain molecules fit (Another version of Specific)

Specificity

If one molecule elicits a strong response in specificity, related molecules may elicit___responses

Weak

Do unrelated molecules elicit a response at the receptor?

NO

The degree to which the receptors on the cell are occupied by messengers. If more receptos are occupied by messenger is the cellular response stronger or weaker? What happens if 100% of receptos are occupied

Saturation; Stronger; full saturation

The strength with which a chemical messenger binds to its receptor

Affinity

Different molecules with similar structures will compete for binding to the receptor

Competition

Chemical messenger that binds to a receptor and triggers normal response. Drugs Mimic action of normal messenger

Agonist

Molecule that binds to receptor but doesn’t elicit response

antagonist

The number of receptors in cell membrane is not constant and can change in response to stimulus over time is an example of _____regulation

Physiological

High extracellular concentration messenger and total number of receptors decreases

Down-regulation

Down regulation causes cells to develop_____sensitivity

example of negative feedback mechanism

decreased

Low extracellular concentration of messenger and total number of receptors increases

Up-regulation

Up-regulation causes cells to develop _____sensitivity

Increased

A sequence of events that start with receptor activation by messenger and leads to cellular response is a ______pathway

signal trannsduction

Steps of Signal Transduction

Messenger attaches to bind site of receptor

Protein shape changes

Cellular response produced

Examples of cellular response

electrical state or permeability of cell membrane

Metabolism of cell

Contractile activity of cell (Muscle cells0

The same type of ___can be used to produce very different responses in different cell type

Receptor

Location of receptors

Plasma membrane

4 main types of signal transduction pathways for plasma membrane receptors

Ion channels

Enzymes

Interaction with cytoplasmic enzymes

Interact with G-proteins(transmembrane proteins)

What happens and what is the result of a first messenger attaching to receptor

Ion channel opened. ions move in or out of cell

What changes after ions move in and out of the cell

electrical potential of membrane and intracellular concentration of ions changes: generates action potential

What activates the enzyme protein inside the cell?

When the first messenger(a growth factor) bind stocks the receptors that function as enzymes

leads to changes in gene expression, cell growth, cell proliferation or differentiation

Enzymatic activity resides in cytoplasmic enzymes which are closley linked to receptors that Interact with_____Enzymes

Cytoplasmic

when a first messenger attches to the receptor, a conformational chnage in the receptor leads to activation of the_____

Cytoplasmic enzyme

Leads to changes in gene expression, cell proliferation, immune response

What is ghe Largest category of receptors?

Receptors that Interact with G proteins

Is a receptor that interacts with G proteins a channel or enzyme?

NO; linked through G proteins to effector proteins such as channels or enzymes

How do G-rptein receptors work?

1.first messenger binds to receptor

2.prduces conformational change in receptor

3.G-protein dissociates, diffuses along inner surface of plasma membrane; bind sto effector protein

4. effector protein becomes activated to cause cellular response

5. Syste can use second messenger to amplify response

If effector protein is a channel, the G protein may cause that ion channel to ___or___

close, open

If effector protein is an enzyme, a second messenger is produced inside the cell; what does it then serve as?

A switch from the plasma membrane to biomechanical machinery inside cell

G-protein Coupled Receptors using Cyclic AMP Second Messenger System STEPS

1. first messenger attaches to receptor, receptor protein changes shape; activates G protein

2. G protein activates effector protein ADENYLATE CYCLASE

3. ADENYLATE CYCLASE catalyzes conversion of ATP to cyclic AMP and cAMP acts as second messenger

4. cAMP inside cell activates protein kinase; causes phosporylation of other proteins; leads to cellular responses; changes in electrical escitability and contractibility

What is a signal amplification?

More first messenger attaches to receptor, more second messenger is produced, and then there are stronger cellular responses

How can we control or turn off CYCLIC AMP Second Messenger System?

Reduce cAMP by breaking it down via the enzyme phosphodiesterase

changes in level of PDE will affect level of cAMP