Chapter 9 biology 1610

What is a phosphorylation cascade? What is its purpose?

- A type of transduction system involving phosphorylation of kinases/ phosphatases - Acts to amplify the signal and allow for fine tuning of response

What are the 3 general types of membrane receptors?

- GPCR's, Tyr Receptor Kinases, gated ion channels

What is a transcription factor? What is its purpose?

- Protein that binds DNA and turns on (or off) specific genes to change cell function

What are the 3 main steps in signal transduction?

- Reception, transduction, response

Why can various types of cells receive the same signal but produce very different responses?

- The response of a particular cell to a signal depends on its particular collection of receptor proteins, relay proteins, and proteins needed to carry out the response. - different kinds of cells have different collections of proteins. - because different kinds of cells have different sets of activated genes.

How must two cells that respond differently to the same signal differ ?

- one or more of the proteins that handle and respond to the signal must be different.

ion channel receptors?

-Are ligand gated ion channels. -Receptors acts as a gate when the receptor changes shape

Receptor tyrosine kinases (RTKs)?

-Are membrane receptors that dimerize and phosphorylate each other -Can trigger multiple signal transduction pathways at once -Abnormal functioning of them can associate with many types of cancers

G protein-coupled receptors (GPCRs)?

-Are the largest family of cell surface receptors -Work with the help of G protein

G protein?

-Small protein that binds to GTP -Acts as an on/off switch

How can phosphorylation affect protein function?

-it can activate some enzymes -It can provide a site or location on some proteins for other proteins to bind -It serves as a ligand to activate some receptors

What type of ligands bind these R's?

-soluble -polar proteins

What are the three types of membrane receptors?

1-G protein-coupled receptors (GPCRs) 2-Receptor tyrosine kinases (RTKs) 3-ion channel receptors

How are signals amplified inside cells?

A signal may reach a cell in the form of a single hormone molecule. Inside the cell, the signal must be amplified so that the response is carried out multiple times rather than just be a single molecule. Amplification is built into the system. Any molecule that catalyzes a reaction can do so multiple times producing more than one product molecule. So each step in the signaling chain has the potential for amplification. If a signaling chain is several steps long then there is a great potential for amplification of the signal. For example if the membrane receptor can produce 10 second messengers and each second messenger can generate the transcription of 10 mRNA chains then the signal has been amplified one thousand fold.

This type of receptor is a transmembrane receptor. It has an extracellular domain that binds to ligand, and an intracellular domain that can directly phosphorylate other proteins. This is an example of a?

An enzymatic receptor

This type of receptor binds to hydrophobic ligands. This type of receptor is referred to as?

An intracellular receptor

Why are channels through membranes so important for nerve and muscle function?

Both nerves and muscles rely on the rapid transmission of information and of signals for movement. The diffusion of chemical signals over any significant distance would be too slow to cause muscle contractions quickly enough to deal with the challenges of moving a large body in a complex environment. Electrical signals travel much more rapidly and the direction of the signal can be more easily controlled. The mechanism for generating and controlling electrical signals is the movement of charged material (ions) across cellular membranes in a limited area. The control of ion movement requires gated channels through the membrane that are specific for certain ions and either open or close (depending on the ion) in response to a change in electrical charge. View the animation below, then complete the quiz to test your knowledge of the concept.

Why not have a separate signal for each response?

By sharing signaling molecules cells can minimize the number of proteins needed while maximizing the number of possible responses

How can one type of signal produce different responses in different cells? How is this possible?

Cell signaling pathways have many elements in common. G proteins and calcium channels are used in a number of different cell types to produce different responses. Different types of cells have different receptor proteins on their membranes. A liver cell will have different receptors from a muscle cell, for example. A liver cell will not respond to a ligand (external signal molecule) for a muscle cell because it lacks the appropriate receptor molecule. Even though other aspects of cell signaling may be similar in the two cells they can produce completely different reactions because the initial receptor molecule is different.

Autocrine signaling?

Cells signal to themselves

This type of receptor, once bound by ligand, can change conformation to allow specific substances to flow down their concentration gradient. What is this type of receptor referred to as?

Channel linked receptor

Paracrine signaling?

Communication between nearby cells, signals released into the extracellular space

Endocrine signaling?

Communication over long distances, signals released into the bloodstream, hormone

In apoptosis?

Components of the cell are chopped up and packaged into vesicles that are digested by scavenger cells • Apoptosis prevents enzymes from leaking out of a dying cell and damaging neighboring cells

This type of receptor is not an enzyme itself, but is bound to an enzyme that can hydrolyze GTP to GDP. What is this type of receptor reffered to as?

Coupled receptor

Are there any other types of receptors?

Cytosolic receptors ( for hydrophobic ligands)

Phosphatases?

Dephosphorylate

What are the effects of epinephrine?

Epinephrine is a hormone and a neurotransmitter. It is secreted in the medulla of the adrenal gland. The primary function of epinephrine is in the 'flight or fight' response to short term stress. Epinephrine has a variety of effects in different areas of the body including the breakdown of glycogen to glucose, the release of glucose into the body, increased heart rate, increased breathing rate, increased metabolic rate, increased flow of blood to the brain and skeletal muscles, and decreased flow of blood to the digestive system. All of these changes allow the body to respond quickly to any external danger.

Apoptosis?

Is programmed or controlled to cell suicide

Necrosis?

Is unexpected cell death due to damage or disease

Direct contact?

Receptors on one cell directly bind another/ adjacent cells

Protein phosphatases?

Remove the phosphates from proteins, a process called dephosphorylation

Why are calcium ions and cyclic AMP known as second messengers?

Second messengers are small, non-protein molecules inside cells that relay a signal to the cell's interior. The primary messenger is a signal protein that interacts with a receptor protein on the surface of the cell. The second messenger is the second molecule to carry the message. Calcium ions and cAMP are commonly used as second messengers for a variety of different signaling systems.

How does the structure of a signal molecule determine its function?

Signal molecules can interact with either intracellular or extracellular receptors. For a signal molecule to bind with an intracellular receptor it must be able to pass through the cellular membrane. Generally signal molecules that enter the cell are nonpolar and fat soluble. These signal molecules can pass through the lipid bilayer of the cell membrane. Signals that bind with extracellular receptors are proteins or other types of molecules that cannot readily pass through the membrane.

2nd messengers?

Small, nonprotein signal transduction molecules

Protein kinases?

Transfer phosphates from ATP to protein a process called phosphorylation

Most common 2nd messengers are?

cAMP, Ca 2+, DAG, IP3

Receptor protein?

molecule to which the receptor binds

synaptic signalling?

nerve signalling

Kinases?

phosphorylate

Ligand?

signaling molecule