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27 Cards in this Set

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  • Back
What are the four ways a protein can be regulated by change in structure?
(a) Allosteric Control
(b) Multiple forms of same Enzyme/Protein (Isozymes)
(c) Reversible Covalent Modification
(d) Proteolytic Cleavage
Why regulate protein structure/function?
So reponding to environmental stimuli is possible
So biological systems can be turned on and off
Why are changes in protein structure particularly effective for regulating biological processes?
Proteins/enzymes are the direct effectors of most functions in the cell.
Describe how allosteric control is used to regulate processes?
What special property do these proteins have?
Allosteric proteins have regulatory sites and/or multiple functional sites which are distinct from active site, which bind small molecules that change the protein's conformation, which is transmitted to the active site. Allosteric proteins have the cooperativity property, activity at one functional site affects the activity at others.
Describe how Isozymes - multiple forms of same protein - are used to regulate
Provide ability to regulate at distinct locations/times. Expressed in different tissues or at different stages in development. (Forms may be slightly more or less active that others?)
Describe how proteolytic activation is used to regulate
Proteins activated by hydrolysis of few or one peptide bond in an inactive precursor protein. (eg apoptosis, blood clotting...defects in mechanism cause emphysema and hemophilia).
What does the binding of Ca to Calmodulin cause?
changes in the protein's structure, creating an alpha helix, which serves as binding site for CaM Kinase1.
What happens when calmodulin binds CaM kinase 1?
kinase is activate and phosphorylates targets.
What are the allosteric effectors in the example with Ca and Calmodulin?
Ca2+ is an allosteric effector of
calmodulin, and the Ca2+ bound form of calmodulin is an allosteric effector of CaM Kinase1.
what function do STAT5 proteins play in the cell?
What form of STAT5 is needed to bind?
regulate gene expression by binding to DNA, only bind as a dimer. STAT5 exists as monomer if unmodified.
How is STAT5 modified?
kinase phophorylates STAT5, allowing it to form a dimer with another phosphorylated STAT5 by binding to special domain (SH2), can only bind if phosphorylated.
what kind of regulation by modification is STAT5 an example of?
STAT5 regulation is an example of regulation by reversible covalent modification
What component of hemoglobin and myoglobin actually binds the oxygen?
nonprotein component called heme, which contains iron molecule that oxygen binds to
Where is myoglobin found? hemoglobin? how are they used in these places?
Muscle: skeletal and cardiac, serves as storage site for oxygen in these tissues
In red blood cells, acts to transport oxygen through circulatory system.
What occupies the fifth and sixth coordination positions of the iron group?
What kind of ring is the iron found in, within the heme group?
A proximal histidine and oxygen

protoporphyrin ring
Why does the heme group need a protein component?
In water, iron is oxidized and oxygen is reduced to hydrogen peroxide, which is toxic to cells. The sequestering in a protein prevents this rxn.
Why doesn't myoglobin bind CO?
The distal histidine allows CO to bind only at an angle,
decreasing the affinity of CO approximately 125x. Oxygen is unaffected by this nearby distal heme.
How do Mb and Hb differ in their oxygen affinity?
Mb has higher affinity for oxygen than Hb.
The binding curve for Hb is sigmoidal, but its hyperbolic for Mb. Mb is half saturated at much lower concentrations of oxygen.
Cooperative binding - the first molecule of oxygen binding enhances binding of the second, etc. on Hb, creating the sigmoidal behavior.
Why would Mb not be an effective oxygen transporter?
its affinity for oxygen is too high to enable unloading, much better for storage.
How is DPG related to Hb?
What are characteristics of DPG?
Cooperative binding require DPG diphosphoglycerate, binds only deoxyHb (no oxygen bound), so stabalizes the T state of Hb. DPG promotes offloading of oxygen, so decreases Hb binding affinity.
What are the different polypeptides of Hb held together by?
What happens to the binding affinity of Hb and conc of oxygen increases?
Non-covalent bonds.
Binding affintiy increases.
How are blood transfusions adapted to deal with DPG?
DPG in blood decreases if its stored, no/low DPG can compromise oxygen delivery. DPG doesn't cross red cell membrane, so it can't be added to blood, but inosine, a precursor of DPG readily crosses and is converted to DPG.
What is different about Hb in fetal circulation?
What type of protein activity regulation is this?
Fetal Hb has gamma chains, not beta chains, which bind DPG less readily, so oxygen affinity of fetal Hb is higher, which enables oxygen transfer from maternal to fetal Hb. Example of the use of isozymes in regulating activity of protein during development.
How is binding affinity affected by H+ and CO2?
both associate with Hb and lower the oxygen affinity of Hb, causing unloading of oxygen in rapidly metabolizing tissues, which need the oxygen.
What kind of interaction are those between Hb and DPG, H, and CO2?
allosteric interactions.
what are the two states of the Hb tetramer?
What does binding of oxygen to Hb in T state cause?
T state - Hb deoxygenated
R-state- Hb oxygenated
converts to R state, making it easier for other sites to bind oxygen
What changes does binding of oxygen cause in the Hb molecule in the T-state?
salt bridges are broken and reformed, oxygen binding move the iron into the plane of the ring in the heme group, pulls the proximal histidine with it which causes the breaking of salt bridges.