Cell Physiology - Topic 3 Slides Flashcards
What are the two types of Intracellular communication?
Direct and Indirect
What is the Direct cell communication mechanism?
Gap Junctions
What is the Indirect cell communication mechanism?
Chemical messengers
What are the two types of chemical messengers?
Lipid soluble and lipid insoluble
What is Signal transduction?
The sequence of events between binding of messenger to receptor and the production of a cellular response
What are the Properties of Receptors?
- Specificity
- Saturation
- Affinity
Where are the two places Receptors can be?
- In the plasma membrane (transmembrane)
* Intracellular (cytosolic, nuclear)
What type of messengers do Intracellular membranes bind to?
Lipid soluble messengers like steroid hormones
Where do Intracellular receptors bind to receptors?
In the Cytoplasm or Nucelus
How do Intracellular receptors alter the transcription of mRNA?
By binding to the Response Element
What is the Response Element?
A specific sequence of DNA near the beginning of a gene that alters the rate of protein synthesis
What are Gap Junctions?
When transmembrane proteins form channels linking one cell to another
What do gap junctions allow for?
Ions and small molecules to move from one cell to another
What is Signal Transduction?
The sequence of events between the binding of messenger to its receptor and the production of the cellular response
Why don’t chemical messengers affect all cells?
Because they can only affect cells that have receptors to the messenger
How might the binding of a chemical receptor to two different messengers affect the response?
There will be two different cell responses depending on which receptor is bound to
Where will a chemical messenger bind if it is hydrophilic or lipid insoluble?
Receptors in the plasma membrane
What do water soluble chemical messengers bind to?
Receptors on the extracellular surface of the plasma membrane
What are some examples of water soluble chemical messengers?
Hormones, neurotransmitters, paracrine/autocrine compounds
What are membrane bone receptors usually linked to?
- A Channel
- An enzyme
- G-protein-linked receptors
What is the First Messenger?
Extracellular chemical messenger that binds to a specific membrane receptor
What is the Second Messenger?
Substance that enter or are generated in the cytoplasm of a cell in response to the binding of an extracellular messenger (first messenger) to receptor
What is Protein Kinase?
An enzyme that phosphorylates another protein
Where are G-proteins found?
The systolic surface of the plasma membrane
What do G proteins bind to?
Guanosine nucleotides (GDP and GTP)
What are the 3 subunits of G proteins?
α, β, γ
What does the alpha subunit of G protein bind to?
Guanosine nucleotides
What is the inactive form of G proteins?
G-GDP
What is the active form of G proteins?
G-GTP
What are the 3 types of G Proteins?
- Affect ion channels
- Stimulatory G proteins
- Inhibitory G proteins
What do G proteins that affect ion channels do?
Open or close channles
What do stimulatory G proteins do?
Activate enzymes
What do Inhibitory G proteins do?
Inhibit enzymes
What are Paracrine compounds?
Compounds released by one cell which act on neighboring cells near its secretion
What are Autocrine compounds?
Compounds secreted into the extracellular fluid and act on the cell that created it
What are the three types of receptors that water soluble chemical messengers bind to?
Channel, Enzyme or G-protein coupled receptors
What do second messengers do?
Diffuse throughout the cell to surface chemical relays from the plasma membrane to the biochemical machinery inside the cell
How do Protein Kinases phosphorylate other proteins?
By transferring a phosphate group to the protein from ATP
How does Phosphorylation affect a protein?
The phosphate group is negatively charged so it causes the conformation of the protein
What do G-protein coupled receptors activate?
Special membrane proteins called G proteins
Where are G proteins found?
On the intracellular side of the plasma membrane (cytosolic surface)
What do G-proteins function as a link between?
G protein coupled receptor and the effector protein
What is the target of the G protein?
The effector protein
What is the Effector protein?
The protein that the G protein will alter the activity of
What are the two things that an Effector protein usually is?
An ion channel or an enzyme
What do the Beta and Gamma subunit of G-proteins do?
Anchor the alpha subunit in the membrane
What does the alpha subunit of the G protein bind to in it inactive state?
GTP
What does the Alpha unit bind to in its active state?
GTP
What alters the affinity of the Alpha sub unit for GDP?
The binding of an extracellular first messenger
How does the alpha subunit on the G protein change in response to the binding of a first messenger to the membrane?
It responds through a conformational change that decreases its affinity for GDP and increases its affinity for GTP
What occurs after the alpha subunit of the G protein binds to GTP?
The G protein is activated dissociates from the receptor and the GTP bound alpha subunit separates from the beta and gamma subunits
What occurs after the Alpha subunit separates from the Beta and Gamma subunits?
It moves to its target protein in the membrane called, the effector protein
What does Alpha subunit of G proteins move to after it has separated from the rest of the G protein?
The effector protein
What does the Alpha unit do to the Effector protein?
Alter the activity of this target protein to produce some sort of response in the cell
How does the Alpha subunit inactivate?
It hydrolyzes or breaks down GTP to GDP and inorganic phosphate
What happens to the Alpha subunit once GTP is converted back to GDP?
The alpha subunit recombines with the other two unit and the G protein combines with the receptor
Why does the Alpha Subunit not stay active for long?
Because it has intrinsic GTPase activity
What is the meaning of the Alpha subunits intrinsic GTPase activity?
It means that it also functions as an enzyme that hydrolyzes ot breaks down GTP
What are Stimulatory G proteins associated with?
Activation of an enzyme
What are inhibitory G proteins associated with?
Inhibition of an enzyme
Why is G protein activity slow?
Because it has many steps
What do G protein catalyzed enzymes do?
Catalyze the production of second messengers in the cell
What is the most common second messenger system found in the cells?
Cyclic AMP second messenger system
What enzyme does the G protein activate in the Cyclic AMP system?
Adenylyl cyclase
Where is the Catalytic site of Adenylyl Cyclase of the AMP messenger system located?
On the cytoplasmic surface of the plasma membrane
What happens once the Alpha subunit binds to Adenylyl Cyclase in the Cyclic AMP messenger system?
Adenylyl cyclase catalyzes the conversion of cytosolic ATP into cyclic AMP
What is the second messenger in the Cyclic AMP messenger system?
Cyclic AMP
What does Cyclic AMP do once converted?
It diffuses through the cytoplasm and binds to Protein Kinase A
What is another name for Protein Kinase A?
Cyclic AMP dependant protein kinase
What is needed to activate Protein Kinase A?
The second messenger Cyclic AMP
What does Protein Kinase A do?
Catalyzes the phosphorylation of proteins in the cell by transferring a phosphate group from ATP to cellular proteins
What happens once Protein Kinase A phosphorylates cellular proteins?
Their activity is altered resulted in a cellular response
How are the actions of Cyclic AMP terminated?
By the conversion of cyclic AMP to non cyclic AMP by the enzyme phosphodiesterase
What is an example of a first messenger that exerts its effects through beta adrenergic receptors?
Epinephrine in the heart
What receptors does Epinephrine act through?
Beta Adrenergic receptors
What occurs in an Inhibitory Cyclic AMP system?
An inhibitory G protein which reduces the activity of adenylate cyclase producing less Cyclic AMP in the cell
Where and how is calcium usually present?
In very low concentrations in the cytoplasm of cells (nanomolar range) and in higher concentrations in the extracellular fluid in the millimolar range
Which organelles in the cell store calcium?
The Endoplasmic reticulum
What is the normally low levels of calcium in the cytoplasm facilitated by?
Active transport systems found in the plasma membrane of the cell
When Calcium enters the cell what does it cause the release of?
More calcium from the endoplasmic reticulum
How does Calcium cause the release of more Calcium from the endoplasmic reticulum?
By binding to receptors on the endoplasmic reticulum causing ion channels to open
What is Calcium Induced Calcium release?
When calcium allowed into the cell bind with the endoplasmic reticulum causing more calcium to be released into the cytoplasm of the cell
What occurs once calcium levels are high enough in the cell?
Calcium acts as a second messenger and binds to Calmodulin, activating it
What does the Calcium calmodulin complex do?
Activates a Calmodulin dependent protein kinase which phosphorylates proteins in the cell leading to a cellular response
What is the Second messenger in the Calcium system?
Calcium
