AP Bio: Signal Transduction

signal transduction pathway

chemical reactions that lead to a cell's response to a signal, involves reception, transduction, and a response

specificity

only cells with the correct "specific" receptors will respond to the signal.

conformation change

A change in the shape of a receptor protein caused by binding of the ligand.

ligand

a signal molecule that bonds to a receptor that initiates a cellular response

ligand releases

results in the conclusion of a signal transmission

binding of ligand to receptor is reversible

non-covalent, binding is favored but it can be undone so that stimulation does not last forever

Step 1

Reception: A ligand binds to a receptor protein

3 kinds of plasma membrane receptors

1.ion channel receptors 2. protein kinase receptors 3. g linked protein receptors

ion channel receptors

gated ion channels are opened by a conformation change. Ex. ligand gated calcium channels

protein kinase receptor

receptors change shape upon binding., creating dimers that allow phosphorylation and in turn activates relay proteins.

protein kinase

catalyzes the breakdown of ATP to ADP. The addition of the removed phosphate to a protein, activates the protein

ATP + Protein ---> ADP + Phosphorylated protein

phosphorylation

adding/transferring a phosphate group to a molecule. Activates protein.

Phosphorylated protein= active

Dephosphorylated protein= inactive

g protein

A receptor protein with three polypeptide subunits that can bind to

1. the receptor

2. GDP.GTP

3. An effector protein

effector/ accessory protein

a protein in a g protein linked receptor signal transduction that can cause an effect in the cell

amplification

One ligand binding can result in many signaling cascades within the cell.

protein phosphatase

Enzyme responsible for the removal of phosphate from an active protein.

Step 2

Transduction: a series of molecular events, most commonly protein phosphorylation catalysed by protein kinases,

Step 3

Response: The final event occurring as a result of signal transduction.

secondary messenger

Released by the cell in response to binding of a ligand to a receptor. Messengers initiate components of intracellular signal transduction cascades. Examples: cyclic AMP, cyclic GMP, inositol trisphosphate, diacylglycerol, and calcium.

signal cascade

A series of chemical reactions within the cell as a result of reception of an external stimulus.

ATP

The source of phosphate in many signal pathways. Dephosphorylated molecule is ADP.

GTP

The source of phosphate in many signal pathways. Dephosphorylated molecule is GDP.

transcription

The initiation of the expression of a particular gene. Often the response of a cell to signal transduction.

protein kinase

a type of protein kinase responsible for phosphorylating proteins in RTKS.

G1 Phase

Primary growth phase of the cell

S Phase

Phase where DNA is replicated

G2 Phase

Growth stage in which the cell prepares for division; organelles replicate and spindle forms

Interphase

Collective name for G1, S, and G2 Phases

Mitosis (M)

Division of the nucleus

Cytokinesis (C)

Cytoplasm divides; forms 2 daughter cells

Chromosome

coiled DNA; visible

Spindle

Consists of fibers made of microtubules and associated proteins; location where chromosomes attach

Prophase

Chromatin fibers condense into chromosomes, mitotic spindle begins to form, centromeres move away from each other

Metaphase

Centrosomes at opposite poles of the cell, Chromosomes convene at metaphase plate

Telophase

Two daughter nuclei form in the cell, nuclear envelope forms

G1 Checkpoint

Most important checkpoint; if cell receives go-ahead signal, the the cell continues with the cell; in the absence of the go-ahead signal, cell exits the cell cycle and enter the G0 phase

M Checkpoint

Cell in mitosis receives a stop signal when any of its chromosomes are not attached to spindle fibers

Cancer

Uncontrolled dividing of cells

Undifferentiated

Description of a stem cell

Homologous

Describes a pair of chromosomes; one maternal and one paternal

Chromatin

uncoiled DNA; found during interphase

Diploid

A cell with two copies of each chromosome

Haploid

A cell with half the number of chromosomes

Meiosis

Process by which gametes are made

Crossing Over

Occurs during meiosis; increases genetic variation

Mutation

Any change in DNA

Binary Fission

The way in which bacteria reproduce; copy and split

G0 (G zero)

Resting state for cells not dividing

Density-Dependent Inhibition (Contact Inhibition)

Cells stop dividing when it's too crowded in an area

Cyclin

Protein that increases and decreases throughout the cell cycle and activates enzymes needed for division

2 Divisions

A description of the events in meiosis

1 Division

A description of the events in mitosis

46

Represents the number of chromosomes in a human somatic cell.

23

Represents the number of chromosomes in a human gamete.