AP Bio Unit 4

intercellular signaling

Communication between cells

intracellular signaling

communication
within a cell

signaling cell

cell that releases signal molecules that allow communication with another cell

ligand

molecule produced by a signaling cell that binds with a specific receptor, delivering a signal in the process

signaling molecule

target cell

cell that has a receptor for a signal or ligand from a signaling cell

cells that are affected by chemical signals

receptor

protein in or on a target cell that bind to ligands

3 Stages

1. Reception

2. Transduction

3. Response

Reception

Ligands are released and hit a receptor

Intracellular

Transduction

chain reaction between molecules to send the signal to target molecules

Phosphorylation cascade

a series of enzyme-catalyzed phosphorylation reactions commonly used in signal transduction pathways to AMPLIFY a message

protein modification

proteins can change shape which changes the reception site which changes the signal it receives

second messengers

small (often nonpolar) molecules that relay signals received by transmembrane receptors to the final target

kinase

enzyme that attaches a phosphate group

phosphatase

enzyme that removes a phosphate group

Response

ex. protein synthesis, changes in metabolism, cell division and growth, nerve stimulation

Transcription Factors

protein that binds to the DNA to convert or transcribe it into RNA, which influences transcription of a gene and gene expression

apoptosis

programmed cell death

cell shrinks and ‘blebs’ to protect neighboring cells

autocrine signal

signal that is sent and received by the same or similar nearby cells

paracrine signal

signal between nearby cells that is delivered by ligands traveling in the liquid medium in the space between the cells

juxtacrine signal

signal between cells that are in direct contact through gap junctions

plasmodesma in plant cells

tight junctions, adherens, desmosome, hemidesmosome in animal cells

endocrine signal

long-distance signal that is delivered by ligands (hormones) traveling through an organism's circulatory system from the signaling cell to the target cell

internal receptor

(also, intracellular receptor) receptor protein that is located in the cytosol of a cell and binds to ligands that pass through the plasma membrane

Many intracellular receptors are transcription factors that interact with DNA in the nucleus and regulate gene expression.

cell-surface receptor

cell-surface protein that transmits a signal from the exterior of the cell to the interior, even though the ligand does not enter the cell

There are 3 types:

• G-protein-linked receptors

• Ion channel-linked receptors

• Enzyme-linked receptors

quorum sensing

method of cellular communication (using auto inducers) used by bacteria that informs them of the abundance of similar (or different) bacteria in the environment

positive feedback

uses a stimuli to start or ramp up a cellular process, usually moving farther away from homeostasis temporarily

intensifies a change in the body’s physiological condition, produces a greater response

positive feedback examples

• childbirth: hormones are released to increase the frequency and intensity of contractions until the baby is born

• blood clotting: Platelets in the blood start to cling to the injured site and release chemicals that attract additional platelets until the clot is large enough to stop the bleeding.

negative feedback

uses a stimuli to trigger a response bringing an organism back to homeostasis

reverses a deviation, maintains body parameters within their normal range

negative feedback examples

• blood sugar levels: when blood sugar increases or decreases, the pancreas releases insulin or glycogen to counteract

• body temperature: When the brain’s temperature regulatory center receives data that body temperature is lower or higher than the setpoint, it sets into motion the responses to counteract

set point

the physiological optimum value, a set value around which the normal range fluctuates

amplification

an increase in the intensity of a signal through networks of intracellular interactions

homeostasis

process by which internal variables are kept within a range of values appropriate to the system

the condition in which a system such as the human body is maintained in a more-or-less steady state

feedback inhibition

inhibitor binds to enzyme and changes the active site so no reaction occurs

Mitosis

a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth

Parts of Interphase

G1

S

G2

G1

a period of intense growth and activity

S

used to stand for the synthesis of DNA. The DNA is replicated so the cell now has two sets of the same DNA

G2

the cell continues to grow in order to finish cell division.

G0

a phase where a cell never divides, rests

Steps for Mitosis

1. prophase

2. metaphase

3. anaphase

4. telophase

Prophase

the first phase of mitosis. In prophase, the nuclear membrane begins to disintegrate, chromosomes condense, and the spindle begins to form

metaphase

chromosomes begin to line up in the middle of the cell. Also, the centrosomes move to the ends of the cell

anaphase

when the centromeres finally separate. The spindle pulls apart the now sister chromosomes (identical copies)

telophase

begins when the chromosomes move to opposite ends of the cell. The chromosomes begin to uncoil and return to their threadlike shape

Cytokinesis

when the cytoplasm is divided

• For plant cells, a cell plate

• For animal cells, a cleavage furrow

cell plate

A plate that develops at midline of dividing plant cell during cytokinesis, eventually becoming the cell wall for each of the two daughter cells.

Cleavage furrow

The cleavage furrow is a shallow groove in the cell membrane where cytoplasmic division will occur. It's the first sign of cytokinesis during cell division in an animal cell.