BISC1111 - Chapter 11 - Cell and Membrane Signaling

Cell junctions

Neighboring cells in organs, tissues, etc that interact and communicate via direct contact

Plasmodemata

channels through cell walls, composed of plasma membranes, which connect two adjacent plant cells

Tight junctions

Membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid

Desmosomes

Anchoring junctions that provides structure and prevents cells from being pulled apart

Gap junctions

(communicating junctions) provide cytoplasmic channels between adjacent cells

How do cells communicate?

With signal molecules

Local signaling

Animal cells communicating via direct contact of surface molecules

What is local signaling useful for?

Embryonic development. Immune responses, and adult stem cell population

paracrine signaling

Signal released from a cell has an effect on nearby neighboring cells.

Synaptic signaling

a type of local signaling in nerve cells that releases neurotransmitters as a response to an electrical signal

Horomones

long-distance chemical signals in both plants and animals

Do cells respond to any type of signal?

No. They only respond if that have that signal's specific receptor

Endocrine signaling

Specialized cells release hormone molecules into vessels of the circulatory system, by which they travel to target cells in other parts of the body.

Reception

The target cell's detection of a signal molecule that binds to receptor proteins on the cell's surface

Transduction

Stage where binding of a signaling molecule alters the receptor and creates a signal transduction pathway

Cellular Response

Transducted signals triggering specific responses in the cell

Ligand

A molecule that binds specifically to a receptor, usually a larger one.

Where do most signal receptors reside?

On the plasma membrane. Although some are inside of the cell itself

G-protein couple receptors

Transmembrane receptors that work with G-proteins that bind with the energy in GTP to provide energy for enzymes

receptor tyrosine kinases

membrane receptors that catalyze the transfer if phosphate groups from ATP to other proteins

Ligand gated ion channel

Type of membrane receptor that has a region that can act as a "gate" when the receptor changes shape to allow specific ions to flow through it

Intracellular receptors

receptors located inside the cell's cytoplasm or nucleus rather than on its cell membrane

Which types of molecules easily pass through the membrane and activate receptors?

Small and hydrophobic ones

During transduction, what happens when receptors are activated?

They activate other proteins in a cycle until the protein producing the response is activated

Protein kinases

transfer phosphates from ATP to protein, a process called phosphorylation

Phosphorylation cascade

A series of enzyme-catalyzed phosphorylation reactions commonly used in signal transduction pathways to amplify and convey a signal inward from the plasma membrane.

protein phosphatases

Rapidly removes phosphates from proteins in a process called dephosphorylation

Second messengers

Small, non-protein water soluble molecules or ions that send messages throughout the cells by diffusion.

What are the two most common second messengers?

Cyclic AMP and Calcium

Cyclic AMP (cAMP)

A compound formed from ATP that acts as a second messenger.

adenylyl cyclase

Converts ATP to cyclic AMP in response to an extracellular signal.

What does cAMP activate?

Kinase A, which then activates other proteins

Output response

the cell's response to an extracellular signal. Occurs either in the nucleus or cytoplasm

What do cellular responses do?

regulates both the synthesis and activity of proteins and other enzymes by turning genes on and off in the nucleus. And cell division

What are the four aspects of signal regulation?

Amplification of the signal itself, products becoming more active than before with every step, specificity of the response, and efficiency of the response

Do signals have the same effect in every cell?

No. Their signal responses have different responses in cells with different proteins and pathways

Response type 1

Pathway leads to a single response

Response type 2 and 3

The pathway branches into two different outcomes

Response type 4

Two different cells on their own separate paths converge at one point, leading to a unified response

Response 5

Signals that had one effect in on cell go into a different receptor and have a different response

What happens if the concentration of external signaling molecules decreases?

Less receptors will bind, which will then cause them to revert to an inactive state

Apoptosis

programmed cell death

What happens in apoptosis?

Dead or infected cells are chopped up, put into vesicles, and then eaten by scavengers cells

Why is apoptosis important?

It prevents enzymes leaking out from dying cells and damaging neighboring cells

Ced-9

Master regulator of apoptosis in C. elegans. When death signals are received, it is activated and kills the cell

Proteases

enzymes that break down proteins in apoptosis

Nucleases

Enzymes that break down nucleic acids in apoptosis

caspase

A "killer enzyme" that plays a role in apoptosis, or programmed cell death

How many caspases that carry out apoptosis do humans have?

15

What are some potential causes of internal apoptosis triggering?

irreplaceable DNA damage and excessive protein folding

Apoptosis aids in....

Hand (human) and paw (formation)