unit 4: cell communication and cell cycles Flashcards
What is a signal transduction pathway?
The chains of molecules that relay signals inside a cell
How does yeast mating serve as an example of a signal transduction pathway?
Yeast cells identify their sexual mates by chemical signaling. When exposed to each other’s mating factors, a pair of cells of opposite type change shape, grow toward each other, and fuse. The new cell contains all the genes of both original cells, a combination of genetic resources that provides advantages to the cell’s descendants.
Local signaling types
paracrine: signaling molecules are secreted by the signaling cell. some molecules only travel a short distance
synaptic: an electrical signal along a nerve cell that triggers the secretion of neurotransmitter molecules. nerve cell releases molecules into synapse and stimulates the target cell (mouse party)
long distance signaling
endocrine: specialized endocrine hormones into body fluids (often blood). specialized cells release circulatory travelling hormones. plant hormones/growth regulators sometimes travel in a vessel but often diffuse as gases (think ripening fruit gas)
Signal Transduction: Reception
a signal is detected when the chemical signl (or ligand) binds to a receptor protein on the surface of the cell or inside the cell
signal transduction: transduction
the transmission of molecular signals from a cell’s exterior to its interior
signal transduction: response
the cell’s response to their environment, communication with other cells, next steps, etc
ligans
a molecule that binds specifically to another molecule. generally causes a receptor protein to undergo a change in shape
G Protein-linked receptor
G proteins function as a molecular switch. When GDP is bound, the protein is inactive. With GTP bond, the protein is active and often works with another protein (usually an enzyme)
G Protein-Linked receptor process
ligand binds to receptor. receptor changes shape and activates G protein as GTP displaces the GDP molecule. the activated g protein dissociates from the receptor, diffuses across the membrane and binds to an enzyme. this changes the ENZYMES shape now and leads to a cellular response. G proteins also function as a GTPase enzyme. it turns GTP back to GDP and inactivates the G protein and enzyme once the protein has done its work.
A G protein is also a GTPase enzyme. Why is this important?
The GP hydrolyzes its bound GTP to GDP and Phosphorous base (step 4). This makes the GP inactive again and everything is available for reuse. The GTPase function allows the pathway to shutdown rapidly when the signaling molecule isnt present.
The second type of receptor described is receptor tyrosine kinase. Explain what a kinase enzyme does.
Kinase enzymes catalyze the transfer of a phosphate group from a donor ATP molecule to a substrate.
Explain what a kinase enzyme does.
Kinase enzymes catalyze the transfer of a phosphate group from a donor ATP molecule to a substrate.
- How does tyrosine kinase function in the membrane receptor?
They are membrane receptors that attach phosphates to tyrosine. They catalyze the transfer of a phosphate group from ATP to the amino acid tyrosine of a substrate protein.
Intracellular receptors are found in the cytoplasm or nucleus of the cell, where they bond to chemical messengers that are hydrophobic or very small, like nitric oxide.
Although cell-surface receptors represent 30% of all human proteins, they make up only 1% of proteins whose structures have been determined by x-ray crystallography.
Difference between first and second messengers
First messenger is the ligand while the second is any small non-protein component of a signal transduction pathway (such as Calcium ion or cAMP that relays a signal to a cell’s interior in response to a signaling molecule bound by a signal receptor.)
When cell signaling causes a response in the nucleus, what happens?
mRNA is transcribed and a protein is synthesized
