Signal Transduction

exam 3

What do cells have to do in multicellular organisms?

Communicate with one another to coordinate activities

What is a signal transduction pathway?

a series of steps by which a signal reaching a cell’s surface is converted to a specific cellular response

What are symbionts?

any organism that lives in a close, long-term physical association with an organism of a different species

Signal transduction pathways are very similar in all

eukaryotes

How are signals grouped?

according to where the molecules originate and where they act

What are major categories of chemical signals in animals?

1. autocrine signals

2. paracrine signals

3. endocrine signals

4. neural signals

What are autocrine signals?

Signals that act on the same cell that secretes them

What are paracrine signals?

Signals that diffuse locally and act on nearby cells

What are endocrine signals?

Are hormones carries between cells by blood or other body fluids

What are neural signals?

signals that diffuse a short distance between neurons (neurotransmitters)

what is a chemical signal?

a molecule used by cells to communicate with one another and coordinate activities

Chemical signals can be

hydrophobic or hydrophilic

a cell will only respond to a signal if

it has the right kind of receptors

What are the three types of cell-surface receptors?

1. Ion channel linked

2. G-protein coupled

3. Enzyme linked

What is a cell-surface receptor?

specialized protein molecules embedded in the plasma membrane of a cell that responds to a signal molecule

How are cell surface receptors classified?

By what happens when the signal arrives

What happens when a signal arrives for an ion channel linked receptor?

allows a current to pass

What happens when a signal arrives for a g-protein receptor?

triggers activation of a G protein signal cascade

What happens when a signal arrives for an enzyme linked receptor?

usually phosphorylates itself and intracellular proteins

What enzyme is this?

Ion channel linked receptor

What enzyme is this?

G-protein coupled receptor

What enzyme is this?

Enzyme linked receptor

What are G proteins?

Small, peripheral membrane heterotrimers

What happens when a G-protein coupled receptor is activated?

Gα subunit swaps GDP for GTP and dissociate from the βγ subunits

What can Gα and Gβγ both react with?

downstream targets at the cell membrane

what do our senses rely on?

receptors

What does enzyme linked cell surface receptors activation frequently involve

phosphorylation-kinases or phosphatases

What do activated kinases do?

phosphorylate themselves and form a scaffold for various intracellular signaling proteins

What do phosphatases do?

remove phosphate

what does the presence of activated kinases do?

increases binding affinity

What are the three stages of signaling?

1. reception

2. transduction

3. response

what are second messengers?

non-protein molecules which relay and amplify signals from receptors on the cell surface to target molecules inside the cell. Diffuse quickly, can be removed quickly

What are protein kinases opposed by?

protein phosphatases

What is phosphorylation?

the process of adding a phosphate group to an organic molecule (PO₃^- or PO₄)

What does protein phosphorylation have a strong effect on?

enzyme activity

Is protein phosphorylation reversible?

yes-quickly

Signaling can be

slow or fast

What does fast signaling response usually do?

alter protein function

what does slow signaling response usually do?

alter gene expression

What is quorum sensing?

A process of cell-to-cell communication that allows bacteria to share information about their population density via autoinducers and adjust their gene expression accordingly

what are autoinducers?

small, chemical signaling molecules produced and secreted by bacteria, serves as the foundation for quorum sensing