Biology Lecture 5 - Cell Communication

cell communication

cells communicate to call on each other for help, signals to manage the body, detect and respond to environmental signals

quorum sensing

• bacteria can sense population density

• modulate gene expression accordingly

multicellular organisms coordinate their cells

to survive, grow and divide, differentiate, and die

apoptotic cell

dead cell

autocrine signals

act on the same cell that secretes them

paracrine signals

diffuse locally and act on neighboring cells

endocrine signals

are hormones carried between cells by blood or other body fluids

contact dependent signals

membrane bound signal molecule

neural signals

diffuse a short distance between neurons

neuroendocrine signals

are released from neurons but are carried by blood or other body fluids and act on distant cells

signal receptors

differnt cell types produce distinct sets of receptors, can be extracellular or cytoplasmic

cell surface receptors

external

intracellular receptors

internal

signal generation

another cell (or self)

signal reception

cytoplasmic or extracellular receptor

changes in cell signaling component

direct effect or signal amplification

mediate response

metabolism, cytoskeleton, transcription factor

extracellular reception and cytoplasmic resption process

1. generation - signal made, released

2. reception - receptor/ligand meet

3. changes in signaling component - movement of signal into cell

4. response

extracellular reception of signals

• large, hydrophilic signaling molecules

• relatively slow response to signal

• significant amplification of signal at each step

cytoplasmic reception of signals

• small, hydrophobic signals

• very fast signaling

• signla to transcription factor activation

changes in protein structure can dramatically alter protein function

• binding another protein

• binding to a small molecule

• phosphorylation

reversible activation of signaling components

on switch and off switch

secondary messengers

small non portein signaling molecules

adrenaline

signaling stimulates glycogen breakdown

Which statement about signal transduction in cells can be used to explain how specificity is achieved in a signal transduction pathway?

A receptor protein changes its conformation only when its binding site is occupied by a small molecule with a shape complementary to the site.

In designing a drug to bind to a receptor and block the binding of a natural ligand in the human body, a pharmaceutical chemist would focus on mimicking which aspect of the natural ligand?

Orientation of functional groups

Which statement about membrane receptors in a signal transduction pathway is true?

Ligands bind to the extracellular binding domain and do not enter the cell.

In order to respond to a signal, a cell must have a specific _______ that can detect the signal.

receptor

Paracrine signals bind to

receptors on neighboring cells.

Which statement about ligand‒receptor complexes is false?

After binding to a cell membrane receptor, a ligand participates in the cellular response.

A deer smells a predator as it passes by and quickly bounds to safety. Which sequence represents the correct order of steps in the signal transduction pathway that is involved?

Signal travels to target cell   receptor binds signal   conformational change occurs in receptor   signal is transduced within cell   effects from signal transduction occur

After a signal arrives at a target cell, the next step in a signal transduction pathway involves

receptor binding.

Signals that travel to distant cells through the circulatory system are

hormones.

Which statement about cyclic AMP is false?

It possesses enzymatic activity.

How does an external chemical signal initiate a response in a cell?

It causes a change in conformation of a receptor protein.

Acetylcholine is a compound released by one neuron that diffuses across a synapse to a nearby neuron, where it binds and initiates a response. How would you classify acetylcholine?

Paracrine signal

Autocrine signals bind to

receptors on the cell that produced them.

To respond to a signal, a cell must have a(n) _______ molecule that can detect the signal.

receptor

Which molecule acts as a second messenger in the cascade by which epinephrine stimulates the activation of the enzyme glycogen phosphorylase in liver cells?

Cyclic AMP

Aldosterone is a steroid compound synthesized in the adrenal glands that binds to receptors in kidney cells. How would aldosterone be classified?

Hormone

Which is the correct order of the steps in a generalized signal transduction pathway?

Signal molecule binds to receptor   molecules within cell transduce signal   cell responds

The concentration of cAMP in a cell is usually increased by activity of

adenylyl cyclase.

The major difference between a cell that responds to a signal and one that does not is the presence of a

receptor.

An entire cell signaling process is known as a signal _______ pathway.

transduction