Biology Exam 2 Lecture 8: Cell-Cell communication

What is cell-cell communication?

The process of cells detecting and responding to signals in the extracellular environment

How do signals lead to a response inside the cell?

By changing the conformation of a receptor

What is apoptosis?

Programmed cell death

Give an example of cell-cell communication with phototrpism

Phototropism in plants, which allowed ultimate cells to change shape bending the peat in a coordinated way. The signaling molecule responsible for phototropism is auxin which is inhibited by light and transmitted from cell to cell

True or false: cell-cell communication occurs between adjacent cells only

False, they can also occur between cells that are long distances too

What are the 5 ways cell -cell communication signals are relayed

1. Direct intercellular signaling

2. Contact dependant signaling

3. Autcrine signaling

4. Paracrine signaling

5. Endocrine signaling

(1) what is direct intercellular signaling?

Cell junctions allow signaling molecules to pass from one cell to another

(2) what is contact dependant signaling

Molecules bound to the surface of cells serve as signals to cells coming in contact with them

(3) autocrine signaling

Cells secrete signaling molecules that bind to their own cell surface or similar neighboring cells

(4) what is paraccrine signaling?

Signaling does not affect originating cell, but does influence nearby cells

(5) endocrine signaling

Signals called hormones travel long distance and are usually longer lasting in effect

What are the 3 stages of cell signaling? (RSC)

1) receptor activation

• signaling molecules bind to a receptor

2) signal transduction

• activated receptor stimulates a sequence of changes- a signal transduction pathway

3) cellular response

• different responses possible

• Change enzyme activity

• Change function of structural proteins

• Change gene expression via transcription factors

(1) what is receptor activation?

• Ligand signaling molecule

• Binds NONCOVALENTLY to receptor with high specificity

• Binding and release between receptor and ligand relatively rapid

• Ligand binding changes receptor structure – this conformational change transmits the signal across the membrane

• Once a ligand is released, the receptor reverts and is inactive again

(Basically, receptor protein get activated, a signaling molecule is binded, and a conformational change happens in the receptor, which sends the message across the membrane!!

Then, the ligand is released, and the receptor reverts and is inactive again.)

What are most signaling molecules/ligands?

They are

A. Too small and hydrophilic,

B. or too large to pass through the plasma membrane

• so that’s why they have to bind to the activated receptor protein and the protein sends on the message

What are the 3 cell surface receptor types? (EGL)

1. Enzyme linked rejectors

2. G protein coupled receptors

3. Ligand gated ion channels

In an enzyme linked receptor, what domain binds the signal? What domain becomes a functional catalyst that promotes a reaction (often a kinase)?

1. The extracellular domain

2. The intracellular domain (kinase means adding a phosphate group)

What do most enzyme linked receptors function as?

Protein kinases

• transfer a phosphate from atp to a specific amino acid

In a protein kinase receptor, how do you make an unphosphorylated protein a phosphorylation one?

One phosphate is removed from ATP t(makes adp), and the phosphate is added to the amino acid/protein

Where are G protein coupled receptors found?

In all eukaryotes and are common in animals

How many trans membrane segments do GPCRs have?

7 transmemnbrane segments

What happens in a G protein coupled receptor?

1. The signaling molecule links to the gcpr, and that makes it link to the G protein

2. The protein exchanges gdp for g3p, ain’t the G protein separates and separates into active alpha subunit and beta gamma dimer

3. The signaling molecule eventually dissociates from the receptor and the subunit hydrolyzes gdp into gdp+ pi (phosphate) then the a subunit and by dimer reassociate

(Basically, signaling molecule gets linked and then G protein links too, then the G protein separates into the two parts, then alpha subunit hydrolyzed g3p into gdp+pi, and beta gamma dimer reassociate.)

Where are ligand gated ion channels found?

Fungal, plant and animal cells

• they’re also called iconographic receptors

What happens in a ligand gated ion channel?

• ligand binding causes ion channels to open and ions to flow through the membrane

• In animals, these transmit synaptic signals between neurons and muse les or between two neurons

(Basically,when the signaling. Molecule binds the channel opens up)

Whats an example of an intracellular receptor?

• some receptors are inside the cell, and these ligands diffuse through the membrane

An example of this is estrogen, where the hormone passes through cell membrane and into the nucleus where it binds estrogen receptor

The estrogen receptor complex binds dna and regulates gene transcription

What does the estrogen receptor complex do ?

It binds dna and regulates gene transcription,

• estrogen is an example of an intracellular receptor

How does estrogen make its way through the plasma membrane?

Since its hydrophobic its able to diffuse (its a type of lipid). It can enter by itself all the way to the nucleus. Then it binds with the receptors, and it causes transcription.

What is a receptor tyrosine kinase

• a category of enzyme linked receptors found in animals

• Recognize various types of signaling molecules

What is a growth factor?

Hormone that acts to stimulate growth cell or division

• such as efg, epidermal growth factor, one function is to stimulate epidermal cells to divide, and they fu cotton in many different contexts.

• It’s an example fo signal transduction and cellular response via an enzyme linked receptor.

What is a protein kinase cascade?

Relay proteins activate additional proteins in the signal transduction pathway, and each kinase can activate multiple proteins.

• an advantage is signal amplification and greater cellular response

• Basically, a series of reactions that transmit a signal to intracellula proteins through protein phos.

Whats the significance of choanocyte cells?

• they come from choanoflagellates, (spomges) that wave flagella to move food through the sponge.

• Genome data shows that singes arose from chanoflagelates

• Rtks, which are enzyme linked receptors, are found in all animals and choanocytes, but not in other eukaryotes or bacteria or archaea

• Rtks may have been a important for the evolution of complex animal structures

Example of signal transduction a cellular response via a gpcr? (Second messenger)

Camp!!

• this is an example of a second messenger

• After the alpha subunit is freed after the signal binding to occur activates a G protein to bind gtp, then

• A subunit binds to adenyly Cyclase enzyme which makes Camp!!

How does a signal transduction pathway in which a G protein coupled receptor make itself recognize Adrenalin

• ephinephrine binds to gcpr, and a subunit dissacoiates from G protein

• A subunit activates adenylyl cyclase, which catalyzes camp production from atp

• Camp then activates protein kinase A

• Activated catalytic pea sunk its phosphorylation specific cellular proteins

• And then the message is sent on to the other cells!!

What are the pka targets?

• enzymes

• Structural proteins

• Trancsrtiptuion factoes

When signaling molecules are no longer produces, eventually effects of pika are reversed