Chapter 11 Terms Flashcards
Apoptosis
A type of programmed cell death, which is brought about by activation of enzymes that break down many chemical components in the cell.
cyclic AMP (cAMP)
Cyclic adenosine monophosphate, a ring-shaped molecule made from ATP that is a common intracellular signaling molecule (second messenger) in eukaryotic cells. It is also a regulator of some bacterial operons.
diaclyglycerol (DAG)
A second messenger produced by the cleavage of the phospholipid PIP2 in the plasma membrane.
hormone
In multicellular organisms, one of many types of secreted chemicals that are formed in specialized cells, travel in body fluids, and act on specific target cells in other parts of the body, changing the target cells’ functioning. Hormones are thus important in long-distance signaling
inositol trisphosphate (IP3)
A second messenger that functions as an intermediate between certain signaling molecules and a subsequent second messenger, Ca2+, by causing a rise in cytoplasmic Ca2+ concentration.
local regulator
A secreted molecule that influences cells near where it is secreted.
protein kinase
An enzyme that transfers phosphate groups from ATP to a protein, thus phosphorylating the protein.
protein phosphatase
An enzyme that removes phosphate groups from (dephosphorylates) proteins, often functioning to reverse the effect of a protein kinase.
second messengers
A small, nonprotein, water-soluble molecule or ion, such as a calcium ion (Ca2+) or cyclic AMP, that relays a signal to a cell’s interior in response to a signaling molecule bound by a signal receptor protein.
Communication between mating yeast cells
- Exchanging of mating factors: Each cell type secretes a mating factor that binds to receptors on the other cell types.
- Mating: Binding of the factors to receptors induces changes in the cells that lead to their fusion.
- New a/alpha cell: The nucleus of the fused cell includes all the genes from the a and alpha cells
Communication by direct contact between the cells
- Cell junctions
- Cell-cell recognition
Local signaling
- Paracrine signaling
- Synaptic signaling
Long-distance signaling
Endocrine (hormonal) signaling
Overview of cell signaling
- Receptor
- Transduction
- Response
A phosphorylation cascade
- A relay molecule activates protein kinase 1.
- Active protein kinase 1 transfers a phosphate from ATP to an inactive molecule of protein kinase 2, thus activating this second kinase.
- Active protein kinase 2 then catalyzes the phosphorylation (and activation) of protein kinase 3.
- Finally, active protein kinase 3 phosphorylates a proton that brings about the cell’s response to the signal.
- Enzymes called protein phosphatases (PP) catalyze the removal of the phosphate groups from the proteins, making them inactive and available for reuse.
A phosphorylation cascade
- A relay molecule activates protein kinase 1.
- Active protein kinase 1 transfers a phosphate from ATP to an inactive molecule of protein kinase 2, thus activating this second kinase.
- Active protein kinase 2 then catalyzes the phosphorylation (and activation) of protein kinase 3.
- Finally, active protein kinase 3 phosphorylates a proton that brings about the cell’s response to the signal.
- Enzymes called protein phosphatases (PP) catalyze the removal of the phosphate groups from the proteins, making them inactive and available for reuse.
Steroid hormone interacting with an intracellular receptor
- The steroid hormone testosterone passes through the plasma membrane.
- Testosterone bonds to a receptor protein in the cytoplasm, activating it.
- The hormone-receptor complex enters the nucleus and binds to specific genes.
- The bound protein acts as a transcription factor, stimulating the transcription of the gene into mRNA.
- The mRNA is translated into a specific protein.
Calcium and IP3 in signaling pathways.
- A signaling molecule binds to a receptor, leading to activation of phospholipase C.
- Phospholipase C cleaves a plasma membrane phospholipid called PIP2 into DAG and IP3.
- DAG functions as a second messenger in other pathways.
- IP3 quickly diffuses through the cytosol and binds to an IP3-gated calcium channel in the ER membrane, causing it to open.
- Calcium ions flow out of the ER (down their concentration gradient), raising the Ca2+ level in the cytosol.
- The calcium ions activate the next protein in one or more signaling pathways.
Nuclear responses to a signal: the activation of a specific gene by a growth factor (11.4)
The initial signaling molecule, a local regulator called a growth factor, triggers a phosphorylation cascade. Once phosphorylated, the last kinase in the sequence enters the nucleus and there activates a gene-regulating protein, a transcription factor. This protein stimulates transcription of a specific gene (or genes). The resulting mRNA then directs the synthesis of a particular protein in the cytoplasm.
Cytoplasmic response to a signal: the stimulation of glycogen breakdown by epinephrine
In this signaling system, the hormone epinephrine acts through a G protein-coupled receptor to activate a succession of relay molecules, including cAMP and two protein kinases. The final protein activated is the enzyme glycogen phosphorylase, which uses inorganic phosphate to release glucose monomers from glycogen in the form of glucose 1-phosphate molecules. This pathway amplifies the hormonal signal: One receptor protein can activate about 100 molecules of G protein, and each enzyme in the pathway, once activated, can act on many molecules of its substrate, the next molecule in the cascade. The number of activated molecules given for each step is approximate.
