AP Bio unit 4

what is cell to cell communication critical for?

The function and survival of cells.

what is cell to cell communication responsible for?

the growth and development of cells

what does cell to cell communication involve?

the transmission of a signal from a sending cell to a receiving cell

how do cells communicate?

1. direct contact

2. local or long distance signaling

what is direct contact?

communication by cell-cell contact

what types of structures make cell to cell contact possible?

direct channels of communication

where do signaling substances exchange?

directly between the cytoplasms of two adjacent cells via channels

what do animal cells use to initiate direct contact?

gap junctions (formed by connexons)

what do plant cells use to initiate direct contact?

plasmodesmata

what can complementary cell surface molecules between adjacent cells do? What is an example of this?

they can interact and bind with each other, an example of this is receptor/antigen interaction in immune system

what is paracrine signaling?

When a signaling cell releases chemical messaging (local regulators/ligands) that travel a short distance through the extracellular fluid and cause a response in a nearby target cell

what is an example of paracrine signaling?

upon exposure to allergens, mast cells release histamine that signal for an inflammatory response in nearby cells

where does synaptic signaling occur? what is it a type of?

synaptic signaling occurs in animal nervous systems, is a special type of paracrine signaling

what do neurons secrete?

neurotransmitters

where do neurons diffuse across?

the synaptic cleft (space between the nerve cell and target cell)

what do neurons bind to? What does this cause?

Neurons bind to receptors, causing a chemical change inside the receiving cell

where does a cell signal to in autocrine signaling?

itself

what does the cell release in autocrine signaling? what does this bind to and initiate?

the cell releases a ligand that binds to receptors on the same cell to initiate signaling

what does autocrine signaling allow?

it allows the cell to regulate itself through positive and/or negative feedback

what is an example of autocrine signaling?

macrophage cells release cytokines that can signal to the macrophage itself to regulate activity

name all types of local signaling.

paracrine, synaptic, and autocrine signaling.

what is a hormone an example of?

a long distance signaling molecule

what do plants and animals use hormones for?

plants and animals use hormones to produce a response in target cells that may be too far from the signaling cell

where do hormones released by plants travel?

in the plant vascular tissue (xylem and phloem) or through the air to reach target tissues

what type of hormone signaling do animals use?

endocrine signaling

what do specialized cells release in long distance signaling? where is this material released? what will it do?

specialized cells release hormones into the circulatory system where they reach target cells

what is an example of hormone signaling? describe it.

Insulin, it is released by the pancreas into the bloodstream where it circulates through the body and binds to target cells.

what does cell signaling begin with?

an interaction between a ligand and a receptor

what are ligands?

chemical messengers, can be a peptide (protein) or small molecules (hormones, gasses, neurotransmitters)

what is a receptor?

a protein that recognizes and binds to specific chemical messengers (ligands)

what can binding initiate?

a signaling cascade

receptor-ligand bonding is ________

highly specific

where can receptors be found?

embedded in the plasma membrane (cell surface receptors) or inside the cell (in the cytoplasm or nucleus)

what are the most common types of receptors involved in signal pathways?

cell surface receptors

what types of ligands do cell surface receptors bind to?

ligands that are polar, water soluble and large

provide examples of cell surface receptors.

1. G protein coupled receptors (GPCRs)

2. ligand-gated ion channels

how many domains do surface receptors have?

Three.

1. the ligand bonding domain

2. the transmembrane domain

3. the intracellular domain

what is the ligand-binding domain?

the area that interacts with the ligand

what is the transmembrane domain?

a hydrophobic region that spans the plasma membrane

what is the intracellular domain?

the region inside the cell that transmits a signal

where are intracellular receptors found?

in the cytoplasm or nucleus of the target cell

what do intracellular receptors bind to?

ligands that can pass through the plasma membrane (small, hydrophobic molecules) such as steroid hormones and gasses

what do most intracellular receptors function as?

transcription factors

how many domains do intracellular receptors have?

two.

1. the ligand bonding domain

2. the DNA binding domain

what is the ligand bonding domain?

the area that interacts with the regions of target genes

how many stages can cell-to-cell signaling be divided into?

3: reception, transduction and response

what happens during the reception stage of cell-to-cell bonding?

The ligand binds to the receptor and a signal is detected.

what happens during the transduction stage of cell-to-cell signaling?

The extracellular signal is converted into an intracellular response.

what happens during the response stage of cell-to-cell signaling?

a cell process is altered

how does the ligand travel during the reception stage in intracellular receptors?

The ligand (usually a steroid hormone) diffuses across the plasma membrane and binds to intracellular receptors (either in cytosol or nucleus).

what does the transduction stage cause in intracellular receptors?

It causes the DNA binding domain of the receptor to change (activate)

what does the response stage allow in intracellular receptors?

the response stage allows for the ligand receptor complex to bind in order to control regions of target genes in the nucleus. It can turn genes on or off and alter cell activity.

what does the ligand do during the reception stage of cell-surface receptors? Name qualities that can describe these ligands during this stage.

It binds to the specific cell surface receptors on the target cell. ligands can be polar (charged, hydrophilic) or large molecules.

what happens during the transduction stage in cell-surface receptors?

the receptor will activate (via a conformational change) when a ligand bonds to it. This activated receptor will initiate the fist step in a series of reactions, known as signaling. enzymes and second messenger will relay and amplify the signal.

what are protein kinases?

enzymes that relay and amplify the message by transferring a phosphate group from ATP to a protein (temporary).

how will the addition of a negative phosphate group affect protein kinases?

the addition of a negative phosphate group to the protein kinase will change its shape and alter its activity.

what are protein phosphates?

enzymes that remove phosphate groups from proteins.

what will protein phosphates do?

They will return the protein back to a baseline or non-phosphorylated state. They will also regulate protein kinase activity and can shut off pathways.

what changes in proteins? what does this do?

shape and function changes in proteins, which can increase activity, inactivate the protein or signal for it to be broken down.

what can activated kinases in each step do? what does this cause?

activated kinases in each step can act on many other proteins/enzymes (often other kinases). Then, each of those ho on to activate more, and so on (generally, the more steps in a pathway the greater the amplification).

what do many pathways use

second messangers

what is are examples of second messengers?

small, non-protein molecules and ions that relay and amplify the first message (ligands)

how do second messengers travel across the cell?

they rapidly diffuse across the cell.

what do second messengers in pathways pass?

signal to signaling proteins or target proteins

what do some second messengers regulate?

specific enzymes, like protein kinases

name 2 examples of second messengers.

Cyclic AMP (cAMP) and Ca2+ (calcium ion with a 2+ charge).

what is cyclic AMP (cAMP)? What does it activate?

Cyclic AMP (cAMP) is a small molecule made from ATP. It activates protein kinases (which then go on to activate target proteins).

How does Ca2+ (calcium ion with 2+ charge) enter the cell?

In pathways that use calcium as a messenger, a ligand binds to a calcium ion channel, allowing calcium ions to flow into the cell

What does Ca2+ do?

it can bind to some proteins (including kinases) changing their shape and activity

What is the response stage in a cell surface receptor?

When the final molecule in the signaling pathway converts the signal to a response that will alter a cellular process.

Name 3 examples of the response stage in a cell surface receptor.

1. cell growth

2. secretion of molecules

3. genes are turned on or off

are pathways always straightforward? How do pathways often communicate?

Pathways aren’t always striaghfoward and reality, and they often communicate with each other in what’s called crosstalk.

provide an example of a protein kinase using crosstalk.

a protein kinase in one pathway may phosphorylate proteins in another pathway as well

what does gene transcription sometimes require?

2 signals

what can signal transduction pathways influence?

how a cell responds to its environment

what changes can signal transduction pathways cause in the cell?

changes in gene expression and cell function

what can signal transduction pathways alter or result in?

they can alter phenotypes or result in cell death

what will mutations to receptor proteins or to any component of the signaling pathway result in?

a change to the transduction of the signal

how many types of important cell surface receptors are there in eukaryotic organisms?

2, GPCRs ( G coupled protein receptors) and ion channels (ligand gated ion channels)

what is the largest category of cell surface receptors?

GPCRs

what are GPCRs important in?

Animal sensory systems

What do GPCRs activate?

a group of regulatory proteins known as G proteins

Until when are the GPCR and G protein inactive?

They are inactive until ligand binding to GPCR on the extracellular side

what activates GPCR? what does this cause?

Ligand binding activates GPCR, which causes a conformational change

what activates G proteins? How?

receptor activates G proteins by causing GDP to release and GTP to bind

where can part of the activated G protein bind to after activation?

an effector downstream

what does the effector produce?

second messengers

what do second messengers activate? what does this trigger?

protein kinases, this triggers a cellular response

where are ligand gated ion channels located?

in the plasma membrane

where are ligand gated channels important?

in the nervous system

what do receptors in ligand gated ion channels act as?

gates for ions

what happens in ligand gated ion channels when a ligand binds to the receptor? What does this initiate?

the gate opens or closes, allowing the diffusion of specific ions. This initiates a series of events that leads to cellular response

what must the body be able to monitor?

internal conditions at all times

what are set points?

values for various physiological conditions that the body tries to maintain

what does the set point have?

a normal range for which it can fluctuate, e.x body temperature

what is the set point and normal range for body temperature?

set point: 98.6 degrees Fahrenheit

normal range: 97-99 degrees Fahrenheit

what is homeostasis?

the state of relatively stable internal conditions

what do organisms detects and respond to?

A stimulus, this response helps maintain balance

what does the body maintain homeostasis through?

feedback loops

how many types of feedback loops are there? what are they named?

2, negative and positive