AP Bio - Unit 4 Cell Communication and Cell Cycle

reception

the target cell's detection of a signal molecule coming from outside the cell. First stage of cell communication

transduction

The conversion of the signal to a form that can bring about a specific cellular response. Second stage of cell communication

response

the specific cellular response to the signal molecule. Third and final stage of cell communication

ligand

signal molecule that bonds specifically to a receptor site of another molecule

intracellular receptors

inside the plasma membrane in the cytoplasm or the nucleus. The ligand must travel through the cell membrane, so it is hydrophobic, like testosterone or nitric oxide (NO).

plasma membrane receptors

receptors that bind to water-soluble ligands

G-protein receptor

(GCPR) largest class of membrane receptors that works with the help of a G-protein. Has 7 transmembrane alpha helices
-Ligand binds to GCPR. Conformational change occurs that changes GCPR so it can bind to inactive G protein, causing GTP to displace GDP. This actives G protein.
-Then, G protein binds to enzyme and activates it. The enzyme can trigger the next step in pathway, with 2nd messengers.
EX: epinephrine

receptor tyrosine kinase

A type of enzyme linked receptor (catalytic receptor)
-Ligand binds and causes formation of dimer (always in pairs). In the dimer, each tyrosine kinase adds a phosphate from an ATP.
-Activated receptor protein initiates unique cell response for each phosphorylated tyrosine. Can activate multiple cell responses with one ligand.

ligand-gated ion channel

causes membrane to open or close, regulating the flow of specific ions.
-

phosphorylation cascade

-sequence of events where one enzyme phosphorylates another, causing a chain reaction leading to the phosphorylation of thousands of proteins
-It greatly enhances the signal, allowing for a large cellular response.

second messengers

-Molecules inside a cells that act act to transmit signals from a receptor to a target
-can initiate a phosphorylation cascade resulting in a cellular response
EX: Calcium ions and cyclic AMP

apoptosis

"cell suicide" - when the cell is systemically dismantled and digested. This protects neighboring cells from damage that would occur if a dying cell merely leaked out its enzymes
EX: Operation of immune system and formation of human hands and feet

cell cycle

the life of a cell from the time it is first formed from a divided parent cell until its own division into two cells

genome

a cell's endowment of DNA, aka its genetic information

somatic cells

all body cells except for gametes
divide using mitosis
diploid cells with 46 chromosomes in humans

gametes

sperm and egg cells
haploid cells with half the number of diploids
23 chromosomes in humans
divide using meiosis

mitosis

the division of the cell's nucleus (DOES NOT INCLUDE CYTOKINESIS!)

cytokinesis

the division of the cell's cytoplasm
cell plate in plants
cleavage furrow in animals

interphase

a newly formed cell with DNA molecules in a form called chromatin. the cell performs all normal functions (produce RNA and synthesize proteins)
90% of the cell cycle

G1 phase

when the cell grows while carrying out normal cell functions unique to its cell type
cell synthesizes all proteins needed for DNA replication (like histones)

S phase

when the cell carries out function, but also duplicates the chromosomes.

G2 phase

additional organelles are produced in prep for cell division
enzymes check for errors in DNA
centrioles form and appear
the gap after the chromosomes have been duplicated and just before mitosis

prophase

Chromatin becomes more tightly coiled into discrete chromosomes. Nucleoli disappear. Mitotic spindle (microtubules from centrioles) begins to form in the cytoplasm.

metaphase

spindle fibers attach to the kinetochore of each chromatid
chromosomes line up along the midline of the cell

anaphase

Cohesion breaks down. Sister chromatids being to separate, being pulled apart by motor molecules in the kinetochore. Cell elongates. At the end, opposite ends of the cell both contain complete and equal sets of chromosomes.

telophase

The nuclear membranes reform at opposite ends of the cell. Nucleolus forms. The chromatin fiber becomes less condensed.

cell cycle control system

System that moves the cell through its stages by a series of checkpoints, during which signals tell the cell either to continue dividing or to stop.

G1 phase checkpoint

-Seems to be most important, leads into the S phase
-If the cell does not get the "go-ahead" to divide, it enters G0
-CDK4-cyclin D complex phosphorylates retinoblastoma protein (RB) so it can no longer inhibit DNA replication

G2 checkpoint

CDK1-Cylcin B complex (aka mitosis promoting factor MPF)
-activates proteins that dissolve nuclear membrane, condense chromosomes, and form spindle fibers and kinectochores

G0 phase

non-dividing phase

kinase

something that has the ability to transfer phosphorus molecules, usually from high energy substance like ATP

cyclin-dependent kinases

(CDK) - enzymes that only function when cyclins are attached (always present in cell)

density dependent inhibition

the process in which crowded cells stop dividing

anchorage dependency

when normal cells must be attached to a substratum, like the extracellular matrix, in order to divide

tumor

a mass of abnormal cells within otherwise normal tissue

benign tumor

when abnormal cells remain at the original site

malignant tumor

invasive abnormal cells that impair the functions of organs.
Metastasis

quorum sensing

regulatory process by which bacteria ensure that there is a sufficient cell density before a specific gene product is made. Helps accomplish task they couldn't do alone
"bacteria communication"
evidence for evolution

autoinducers

chemical signaling molecules produced, released and detected by quorum sensing

local signaling

cell releases molecules that travel short distances and influence nearby cells
EX: synaptic signaling in nerve cells (paracrine signaling)

long distance signaling

both plants and animals use hormones
EX: endocrine system

hormone

(type of ligand) a chemical released by a cell in one part of the body, that sends out messenges that affect cells in other parts of the organism

nuclear response

a pathway that regulates transcription y activating proteins (transcription factors) that turn genes on and off

cytoplasmic response

a pathway that leads to the regulation of cytoplasmic activities
EX: epinephrine starts breakdown of glycogen in muscle and liver cells
EX: Apoptosis

blocked signal transduction

-conditions where signal transduction is blocked by a molecule, or when a molecule in a pathway goes bad
-can be deleterious or preventative
-EX: neurotoxins, poisons, antihistamines, birth control, caffeine

cyclin

proteins in a cell that accumulate through the cell's life. Once they get to a certain concentration, the cell knows to divide. They are used in cell cycle control.

mitogens

extracellular molecules, usually proteins called growth factors, that stimulate cell growth and differentiation
EX: platelet-derived growth factor and epidermal growth factor

Platelet-derived growth factor

protein released by platelets that tells the blood vessel to repair itself (angiogenesis)

epidermal growth factor

protein released by cells to be picked up by the cell itself or by other cells to stimulate growth

p53

-protein with many roles in cell control: prevents uncontrolled growth (tumor suppressor protein), can initiate repair of DNA, and can trigger apoptosis
-over half of human cancers are caused by the mutation of this gene

why cells divide

to reproduce, growth, and for repair and renewal

cohesion

protein that holds chromatids together

kinetochore

protein that binds to centromere and connects to spindle fibers during cell division

shmooing

process by which opposite mating type haploid yeast cells grow towards each other in order to fuse together to form a diploid

MPF

What triggers the cell's passage past the G2 checkpoint into mitosis?