Chap 5 Cell Interaction and Signaling Flashcards
Why do cells communicate?
- To carry out one or more specific functions
- Coordinate behavior/activities
- To accomplish biological processes - To enable body t function as a whole
Explain the 3 stages of cell signaling.
- Reception
- Chemical signal binds to receptor,(cellular protein) typically at the cell surface. (can be in cell as well) - Transduction
- Binding leads to change in the receptor that riggers a series of changes along a signal transduction pathway and the signal is amplified. - Response
- The transduced signal triggers a specific cellular activity
How does epinephrine trigger the breakdown of glycogen to glucose?
- The hormone epinephrine is released by the kidney’s adrenal glands and can bind to receptors on liver cells. Upon binding to liver cells, the receptor undergoes a conformational change which triggers G protein to trigger the formation of cAMP. cAMP activates a cascade of protein kinase which in turn activates lipase (phosphorolayse b) to break down glycogen into glucose.
R-Epinephrine binding to receptors on liver cell
T-Causes series of changes inside the cell including activation of enzymes
R-Leads to activation of enzyme (phosphorolayse b) that leads to the breakdown of glycogen.
Where are 3 places receptors can be located? (Give examples if possible)
- On the cell surface (e.g. plasma membrane, GPCRs)
- In the nucleus
- In the cytoplasm (thyroid and steroid hormone receptors)
What mechanism do receptors use to bind to ligands?
Lock and Key mechanism
Why are G proteins named as such?
They are name G proteins as they bind to guanine nucleotides GDP and GTP.
Why are G proteins heterotrimers?
They are made of 3 different sub units alpha,beta,gamma.
How do GPCRs link the receptor to the G protein?
A cytosolic loop links the 5th and 6th alpha helices of the receptor to the G protein.
How does the receptor of NO act as an enzyme in smooth muscle cells? (Explain the process from NO formation to response)
A stimulus causes the production of NO by activating NO synthase. NO then diffuses out of the cell it was generated in and travels to its target cells (smooth muscle cells), and diffuses through the plasma membrane. NO binds to the receptor guanylyl cyclase an intracellular receptor which then acts an enzyme to produce produce cGMP from GTP. (cGMP is a secondary messenger). cGMP in turn causes release of neurotransmitters that cause smooth muscle relaxation, dilating blood vessels and increasing blood flow.
NO can either act within the cell it is produce in or penetrate the cell membrane to affect adjacent cells.
What are 6 types of signaling molecules (ligands)?
- Hormones
- Amino Acids
- Neurotransmitters
- Proteins
- Steroids
- Nitrous Oxide
Why are cell surface receptors required for some signaling molecules?
Some signaling molecules that are hydrophillic are unable to cross the cell membrane on their own and require receptors on the surface to receive the signal.
How do hydrophobic molecules bind to intracellular receptors.
Hydrophobic molecules are able to diffuse through the membrane which allows them to bind with receptors either inside the cytoplasm or nucleus.
Why do small hydrophobic molecules require the use of carrier proteins?
As small hydrophobic molecules are insoluble in aqueous solutions, they are transported through the blood stream or other extracellular fluids by binding to carrier proteins from which they disassociate from before entering the target cell.
What is the difference between steroid hormones and non steroid hormones? (Give examples for steroid and non steroid hormones)
Steroid hormones being hydrophobic can pass through the plasma membrane while non steroid hormones being hydrophillic cannot pass through the membrane and thus bind to cell surface receptors.
(e. g. Cortisol,Testosterone,Estrogen,Progesterone) Steroid
(e. g. Epinephrine,Glucagon) Non-steroid
What are some responses to a signal?
- Regulation of intracellular enzyme activity
- Changes in transcription (gene regulation,gene expression)
- turning a gene on or off
Define gene expression and gene regulation.
Gene regulation is the process of turning on or off a gene.
Gene expression is the flow of information from gene to protein (effect of turning on/off a gene)
Explain how a hydrophobic signaling molecule regulates the production of a protein. (intracellular receptor in cytoplasm) (give examples)
The signaling molecule being hydrophobic, diffuses through the plasma membrane into the cytoplasm where it binds to cytoplasmic receptor.Upon binding to the receptor, a conformational change causes DNA binding sites on the receptor to be exposed. The receptor ligand complex moves to the nucleus and binds to a specific regulatory region of the chromosomal DNA,promoting initiation of transcription either leading to a protein being produced or production to stop. (e.g. Steroid Hormones,Vitamin D,Thyroid Hormone)
Explain how a hydrophillic signal molecule causes a protein to be produced. (Give example)
Hydrophilic signal molecule first binds to cell surface receptors on the target cell. This triggers the signal transduction pathway which in turn leads to the activation of transcription factors. This transcription factor enters the nucleus and binds to DNA, switching on the gene which later results in transcription on an mRNA eventually leading to translation and formation of a protein. (e.g. Beta islet cells in the pancreas that release insulin in response to high blood glucose levels after a meal)
How does a signaling cascade amplify a signal?
At each step of the cascade, the signaling intermediate persists for long enough to stimulate the production of many molecules required for the next step in the cascade, thus multiplying the effect of a signal receptor ligand interaction.Thus small quantities of ligands are usually able to elicit a response from the target cells.
Explain direct contact/direct intracellular signaling. (Draw diagram)
Cells in direct contact send signal molecules through gap junctions. (cells are connected)
Explain contact dependent signaling. (Draw diagram)
Membrane bound signals and receptors on adjacent cells bind to trigger a response.
Explain the nature of paracrine signaling. (Give example)
Signals released by a cell acts on neighboring cells that are not in contact. These signals are usually short lived as it gets destroyed quickly by extracellular enzymes after it is released thus giving it a short range. (e.g. Important in early development as it coordinates the activities of clusters of neighboring cells.)
Explain autocrine signaling.
Cells release signaling molecules that affect itself and neighboring (nearby) target cells.
Explain endocrine signaling.
Signaling molecules (hormones) are secreted by specialized endocrine cells and carried through the circulation to act on target cells at distant body sites.
