Unit 4: Lecture 16

Define quorum sensing.

Define quorum sensing.

The process that allows bacteria to sense population density through the concentration of signaling molecules

What are signal transduction pathways?

Cell communication

What do bacteria of all strains release?

A signal to note presence; less signal=less population=divide more; more signals= more population= divide less (as not enough food for more offspring)

What are the cell communication pathways in yeast (fungi, single celled)?

The yeast, S. cerevisiae, has two mating types, a and α; membrane surface of cell have different receptors that secrete a signal (a or α); one a cell mates with one α cell leading to a fusion into one cell that has both a and α

Are the molecular details of signal transduction in yeast and mammals similar?

Yes

What are similarities in multicellular organisms to quickly give a signal?

A gap junction or plasmodesmata in plants; cell-cell recognition

What macromolecules are receptors?

Protein

Define signal transduction pathway.

Series of steps by which a signal on a cell's surface is converted into a specific cellular response

What are the 3 steps of a signal transduction pathway?

1. Reception (receive a signal)

2. Transduction (to change from one form to another)

3. Response

What is the 1st step of a signal transduction pathway?

Reception- target cell detects a signaling molecule that binds to a receptor on the cell surface

What is the 2nd step of a signal transduction pathway?

Transduction- series of steps as various relay molecules are activated due to the binding of the signaling molecule altering the receptor; transactions often involve a cascade of protein phosphorylations

What is the 3rd step of a signal transduction pathway?

Response- A specific response in the target cell triggered by the transduced signal triggers

What is a ligand?

A signal that binds to a receptor (resulting in a change to a receptor):

-induces conformational change

-exposes active site on intracellular end

What are the two types of ligand?

1. Local Regulators- Signal molecules that travel a short distance as its response cell is nearby

2. Hormones- Signal that travels a long distance from the cell it is secreted from (chemicals used by plants and animals)

Where do signals come from?

Body, medication, heat, etc.

What are the three types of local signals?

1. Paracrine signaling (e.g. clotting factor; short-lived)

2. Synaptic signaling (neurons send signals to target cells)

3. Autocrine- a cell signaling to itself (e.g. white blood cell releases signal which triggers receptor of another WBC, helps WBC stay active)

What is an example of the first type of local signaling?

Paracrine signaling- Inside veins and arteries are RBC, WBC, and platelets; Outside of veins and arteries are proteins like collagens; Injury occurs-> platelet will sense collagen fibers and release signals (clotting factor) to cause other platelets to gather that also release clotting factors until the wound is healed

What are common synaptic signals?

Neurotransmitters

How do allergies occur (runny nose)?

Paracrine signaling- WBC on mast cells release histamine due to response to the allergen; histidine [amino acid]->(decarboxylation) histamine [signaling molecule]

What makes cells make the hormone signal?

Endocrine cell/gland

Where does the hormone travel through after it leaves the endocrine cell?

Bloodstream to a target cell far way

What are examples of endocrine signaling (hormones)?

Pancreas (gland/cell) produces insulin and glucagon (hormone), ovary produces estrogen and testosterone, adrenal glands produce cortisol, epinephrine, etc. (all these signals that stay in the body)

What are exocrine signals?

Signal that leaves the body (e.g. sweat)

What are the two types of hormones?

1. Peptide hormones (e.g. glucagon)

2. Lipid hormones (e.g. estrogen and testosterone)

What are the two types of receptors?

1. Cell-surface receptors

2. Intracellular receptors (within the cell)

Receptors are _________ _________ to the signal they bind to.

Highly specific

What is often the initial transduction of the signal?

Receptor shape change

What are the three main families of membrane receptors?

1. G protein-coupled receptors

2. Receptor tyrosine kinases

3. Ion channel receptors

What is the first main type of membrane receptors?

G protein-coupled receptors: plasma membrane that works with the help of a G protein; the largest family of all cell-surface receptor types. All very similar in structure but diverse in function

What is a G protein?

An on/off switch; if GDP is bound to the G protein, the G protein is inactive

What is the second main type of membrane receptors?

Receptor tyrosine kinases (RTK): membrane receptor (works only when it binds to a signal) that attach phosphates to tyrosines to activate transcellular pathway

What is the third main type of membrane receptors?

Ion-gated receptor: A signal bind to it causing the gate to allow specific ions through such as Na+ or Ca2+

What signals can interact with intracellular receptors?

Signals that can diffuse through the lipid bilayer (e.g. estrogen); steroid and thyroid hormones can readily cross the membrane

Where are intracellular receptor proteins found?

Cytosol or nucleus of target cells

What can act as a transcription factor?

An activated hormone-receptor complex (turning on specific genes)

What is the importance of the signal vitamin D?

Increases bone deposition (deposits calcium and phosphate from blood into bones) and reduces the action of parathyroid hormone (a hormone that increases calcium/phosphate levels in the bloodstream from bone)

What is Rickets?

A bone growth disorder often due to Vitamin D deficiency; common in dark-skinned children due to malnourishment (poverty-stricken areas) and that dark-skinned children don't absorb as much light to produce the Calcium

Define amplification.

One signal hits a receptor and causes 10 different responses

What are common players in transduction?

-Protein kinases: phosphorylate things

-Protein phosphatases: Takes a phosphate off (abundant and active)

Where do phosphate groups attach to?

Hydroxyl groups

What are four important things about protein phosphorylation?

1. It's fast

2. The substrate (ATP) is abundant and universal

3. Always energetically favorable

4. Phosphate is easy to remove (to turn off signal)

What are the major forms of protein kinases?

Serine/threonine kinases and tyrosine kinases

What are first messengers?

The extracellular signal (ligands)

What are second messengers?

Small, nonprotein, water-soluble molecules or ions that spread throughout a cell by diffusion

What are the most common types of second messengers?

1. Cyclic AMP (cAMP)

2. Ca+ ions

What type of messenger does transduction use?

Second messengers

How do different cells have different responses to the same signal?

Cells have different collections of proteins/receptors; signal transduction pathways

What results in a termination of a signal?

If ligand concentration falls, fewer receptors will be bound; unbound receptors revert to an inactive site

Define apoptosis.

Programmed or controlled cell suicide (a transduction pathway)

What happens during apoptosis?

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

What triggers apoptosis?

-an extracellular death-signal

-DNA damage in the nucleus

-Protein misfolding

-May be involved in diseases such as Parkinson's and Alzheimer's

-Interference with apoptosis may contribute to some cancers

Define necrosis.

Premature death of living cells

What happens in necrosis?

-Loss of membrane integrity

-results in inflammation

-potentially results in gangrene

-chain rxn (may lead to amputation)