AP Bio Unit 4

What is cell communtication used for?

Coordinating their functions, maintaing homeostasis, and responding to their environment

What does cell communication involve?

recieving, processing, and responding to information

Different types of cell communication

Cell-to-cell contact, locally to nearby cells, over long distances

Ligand

Used to activate receptors on the recipient cell

Receptors

Receive the signal and can induce a pathway that leads to a response

Target cell

The cell that the ligand is trying to evoke a response from

Non-target cell

When there is a no receptor for ligand so a response can't be evoked

Relationship between ligands and receptors

The ligands and receptors are specfic towards each other

Autocrine

Occurs when cells communicate with themselves by releasing a ligand that binds to a receptor on the same cell

Target cell in autocrine

The cell itself

Apoptosis

When a virus infected cell forces itself to die which kills the virus and the cell

Juxtacrine

When cells communicate through direct contact with another cells

target cell in juxtacrine

A cell connected by gap junctions

Antigen-presenting cells

When the immune system directly presents an antigen (a type of ligand) to another immune cell signaling an immune system response

Gap junction

Allows for signaling molecules and other material to be exchanged between their cytoplasm

Where do gap junctions form?

Between the cell membranes in animal cells

Plasmodesmata

Allows for signaling molecules and other material to be exchanged between their cytoplasm

Where do plasmodesmata form?

Between the cell walls and cell membranes of plant cells

Paracrine

Allows communication between cells that are nearby but not directly touching each other

Target cell in paracrine

A nearby cell

Morphogen

Molecules excreted during embryonic development which signal cells to differentiate

Quorum sensing

When cells use chemical messengers when they are close to indicate their population density

What happens when population density is high enough in quorum sensing?

the cells will perform group behaviors like bioluminescence, forming biofilms, and attacking

Where does quorum sensing occur?

In bacterial cells

Synaptic Signaling

Where an electrical impulse in nerve cells signal the release of molecules (neurotransmitters) into a gap between cells

Where does synpatic signaling occur?

Nerve cells in animals

Endocrine

For communicating with cells that are far away and does so by secreting ligands into body fluids (like blood) so the message can be carried throughout the body

Target cells in endocrine

Far away cells

Hormones

Long distance signaling molecules used by plants and animals to communicate

Insulin

Protein-based hormone that it secreted by cells in the pancreas and signals cells throughout the body to regulate blood sugar

Ethylene

A small gas secreted by plants which promotes fruit ripening

Reception

A receptor on/in the target cell binds with the ligand

Where can receptors be located in a cell?

The surface of the cell, embedded within the cell membrane, or inside the cell within the cytoplasm or the nucleus

Transduction

After a signal is received, a series of steps convert the signal into an actual response

Signal Transduction Pathways

A sequence of molecular changes within a cell that transform the signal into a response

First step in signal transduction pathways

Reception: Ligand binds to the receptor

Second step in signal transduction pathways

Transduction: Singals are relayed from receptors to target cells and are amplified

Third step in signal transduction pathways

Response (cell growth, secretion, apoptosis, gene expression, etc.)

Secondary messengers

Intermediate chemicals that help transduce a chemical signal (Ca2+ and cAMP)

What can happen due to a change in structure of the receptor or ligand?

The signaling pathway is disrupted

What happens to the receptor when the ligand binds to it?

The receptor changes shape slightly

What begins the signal transduction pathway?

The receptors change in shape due to the ligand binding to it

What are the properties of transmembrane receptors?

Polar/hydrophilic

What happens when a ligand binds to a transmembrane receptor?

the receptor changes shape to relay information from the extracellular environment to the intracellular environment

G protein-couple receptor (GPCR)

A type of transmembrane receptor that work with the help of the G protein

What happens when a ligand binds to GPCR?

the receptor use GTP (an energy like ATP) which activates a G protein inside the cell, which can go activate another protein

Ligand-gated ion channels

Act as a gate for ions to pass into and out of the cell

What happens when a ligand binds to ligand-gated ion channels?

They open

What cells need ligand-gated ion channels?

cells, like in the nervous system, that use electrochemical signals to communicate

Intracellular receptors

Receptors that are found inside the cell, either in the cytoplasm or the nucleus

What are the properties of intracellular receptors?

Small and hydrophobic/nonpolar

Example of intracellular receptors

Steriod hormones

Steriod hormones

Intracellular receptor, released through diffusion (estrogene, testorone)

Protein hormones

Extracellular receptor, released through exocytosis (insulin)

What occurs during a signal transduction pathway?

The original signal is transferred within the cell AND amplified throughout the cell

What is the use of many molecules beneficial in signal transduction pathways?

They allow for more controlled changes in the pathway and it allows for the signal to be greatly amplified

Where does the amplification come from?

each relay molecule in a pathway that activates multiple other molecules

How are relay molecules activated?

Through a change in structure

Protein Kinase

An enzyme that's responsible for phosphorylating other proteins in turn changing their structure

How do protein kinases activate each other?

They transfer a phosphate group from ATP to a another protein kinase which activates it

Phosphorylation Cascade

The continuous movement of phosphate groups from ATP to protein kinases throughout signal transduction pathways

What step does the phosphorylation cascade occur in?

Transduction

How is a response amplified?

Through the phosphorylation cascade as protein kinase phosphorylates relay molecules which then goes on to phosphorylate more relay molecules

RElay molecules

Typically proteins that relay the message from on molecule to another molecule (causes amplification)

How can a protein go back to its inactive form?

Through dephosphorylation

Are all signal transduction molecules proteins?

No

Second Messengers

Small non-protein molecules that are activated after the original ligand (first messenger) and relay and amplify the signal

cAMP

A messenger inside the cell that carries a signal rom he membrane to the rest of the cell

What are the benefits of secondary messengers?

They are small and able to quickly and easily spread out throughout the cell which activates multiple protein kinases

What is a signal transduction pathway?

A series of steps that converts an exeternal signal into a specific cellular response through receptor activation and intracellular signaling

What's the last step in the signal transduction pathway?

Cell response

What does a signal transduction pathway result in?

some kind of regulation of cell activity

What is a signal transduction pathway's role in protein synthesis?

by acting as transcription factors which turn genes "on" or "off" in the nucleus

GPCR

A type of receptor protein in the cell membrane that helps cells respond to signals outside the cell

What does a cell do when it no longer needs to make a certain type of protein?

It turns those genes "off"

What does a cell do when it needs to make a certain type of protein?

It turns those genes "on" to synthesize the protein

What does regulating protein activty control?

movement, cell division, transport, apoptosis, etc.

Shmooing

When cells release pheromones in their local environment that signal other cells to undergo a structural change

What does the change in structure from shmooing allow?

The change in structure allows the yeast cells to undergo sexual reproduction

What causes the change in structure in shmooing?

changes in gene expression

What type of cell does shmooing occur in?

Yeast cells

Activation of the SRY gene

When the SRY genes are activated on the Y-chromosome that signals the baby in the womb to become a boy and activate testis development

What happens if the SRY is not activated?

the baby is a girl

What happens when there is a change in the signal transduction pathway?

The rest of the chain is altered

What happens if a receptor is blocked?

The signal cannot be received

What happens if molecules in this chain are altered?

the signal won't reach the point where the response is supposed to occur

What occurs with the addition of receptors?

This can enhance or amplify the response

Homeostasis

Maintaining a constant internal environment even when the outside environment changes

How does stimulus lead to a response?

Stimulus is detected by a receptor/sensor, the signal is conveyed through a pathway and the response is triggered

Negative feedback mechanism

Helps maintain homeostasis by reducing the original stimulus

What's the goal of a negative feedback mechanism?

Doing the opposite of the original stimulus in order to move an internal environment back towards homeostasis

What's more common, positive or negative feedback?

Negative feedback

What occurs in a negative feedback loop?

The final product of the chain will inhibit the orginal stimulus which decreasing the process

Positive feedback mechanisms

Moving further away from homeostasis to amplify a response

What's the goal of positive feedback?

 achieve a specific change by moving an internal environment away from homeostasis

What occurs in a positive feedback loop?

The final product is brought back to the orginal stimulus and amplifies it

In feedback diagrams, what does a pointed arrow mean?

that one step activates the on its pointing to

In feedback diagrams, what does a flat bar mean?

one step inhibits the one its pointing to

Cell division

The process in which the cells reproduce by preexisting cells dividing to produce new cells

Mitosis

Division of the nucleus