Jeopardy BB 450
Topic: Signaling Describe the steps of signaling through the beta-adrenergic receptor pathway. Bonus: What is the second messenger? What is the first messenger?
1) binding of hormone by receptor; 2) activation of G-protein by replacement of GDP by GTP in the alpha subunit; 3) binding of the alpha subunit (with GTP) by adenylate kinase; 4) production of cAMP by adenylate cyclase; 5) activation of protein kinase A by binding of cAMP; 6) phosphorylation of glycogen synthase (inactivates) and phosphorylase kinase (activates) by protein kinase A; 7) phosphorylation of glycogen phosphorylase by phosphorylase kinase (activates it); and 8) production of glucose-1-phosphate by action of glycogen phosphorylase on glycogen. Bonus: second messenger: cAMP; first messenger: hormone
Topic: final jeopardy The activity of chymotrypsin can be studied using an artificial substrate which, when cleaved by the enzyme, releases a yellow product. When the release of the colored substrate by the enzyme is studied, there is a VERY rapid release of the colored substrate. After that initial burst of activity, the remaining yellow color is released slowly. Explain this observation.
The reaction catalyzed occurs in two steps. The first step cleaves the bond to produce the yellow product, which is rapidly released. The other product of this reaction is the remainder of the substrate that is covalently linked to the enzyme. In order for the enzyme to bind another substrate molecule and release more yellow color, it must first release the covalently bound molecule. This step occurs slowly and explains why subsequent yellow molecules are released slowly - after the initial one is released, the enzyme must remove the covalently bound molecule, bind a new substrate, and cut the substrate and the continue the process repeatedly.
Topic: Mixed Bag What reaction does carbonic anhydrase catalyze? Bonus: What is the limiting step in carbonic anhydrase catalysis?
- Carboni anhydrase catalyzes the joining of carbon dioxide and water to form carbonic acid. - The limiting step in the act now carbonic anhydrase is the abstraction of the proton from water.
Topic: Proteases Chymotrypsin uses an active site serine to carry out its chemistry. Name two other categories or major classes of proteases. Bonus (+$200): Name a third category or major class of protease.
- Cysteine Proteases ex. Papain - Aspartyl Proteases ex. Renin - Metalloproteases ex. Thermolysin
Topic: Proteases Enzymes other than chymotrypsin, like trypsin and elastase, use an active site serine and catalytic triad. Why do their substrate specificities differ? Bonus: Describe this feature for one serine protease and how this corresponds to its specificity.
- Differ by the "specificity pocket (S1)" for binding their substrates. - Bonus: ex. Trypsin has a negatively charged amino acid at the bottom of its S1 pocket so it can favorably interact with positively charged amino acids arginine and lysine ( and as a result cuts after arginine and lysine)
Topic: Carbohydrates Define each of the following terms: - Enantiomers: (1) - Anomers:(2) - Diasteromers: (3) - Stereoisomers: (4) - Epimers: (5)
- Enantiomers: stereoisomers that are mirror images of each other - Anomers: sugars which differ only in the configuration of the anomeric carbon - Diastereomers: sugars which differ in stereoisomeric configuration - Stereoisomers: compounds which differ only in the spatial arrangement of their atoms - Epimers: sugars which differ in configuration of only one carbon
Topic: Regulation This hormone is generated during exercise or in a "fight or flight" situation. Bonus: What type of receptor does this hormone interact with?
- Epinephrine or adrenaline - Bonus: β-adrenergic receptor, a 7 Transmembrane receptor
Topic: Regulation Define feedback inhibition and give an example of feedback inhibition.
- Feedback inhibition: inhibition of an enzyme by ints product or a later product in its pathway (ex: The final product of a long pathway inhibits the first enzyme in the pathway) - CTP, the end product of pyrimidine biosynthesis, inhibits ATCase.
Topic: Regulation How is protein kinase-A regulated? Bonus: What is one pathway in which protein kinase-A is involved?
- Inactive form: R2C2 dimer - R= regulatory, C= catalytic - Active form: each R subunit binds 2cAMP, dissociates as R2 dimer, releasing the 2C domains to do their chemistry - Bonus: glycogen breakdown or β-adrenergic receptor signaling
Topic: Signaling What is the result of insulin signaling? Bonus: What kind of receptor does insulin bind to?
- Insulin signaling involves a kinase/phosphorylation cascade. Insulin results in the movement of the GLUT4 protein to the cell surface. GLUT4 is a glucose transport protein that transports glucose into cells. - Bonus: a receptor tyrosine kinase
Topic: Carbohydrates Where do N-linked and O-linked glycosylation occur on a protein and where do these occur in a cell?
- N-linked - attached to the R-group amine of asparagine, occurs in Golgi apparatus and ER - O-linked - attached to the R-group hydroxides of serine/threonine, occurs in Golgi apparatus
Topic: Proteases The ___________ is a specialized location in the active site of serine proteases that helps to stabilize the negative charge of the otherwise unstable tetrahedral intermediates. Bonus: (+$300) name one such enzyme that uses this feature.
- Oxyanion hole - Bonus: chymotrypsin
Topic: Regulation What reaction does phosphatase catalyze? Bonus: What reaction does kinase catalyze?
- Phosphatases are enzymes that catalyze the removal of phosphoryl groups attacked to proteins - Bonus: kinases catalyze the addition of phosphoric groups
Topic- Regulation How does caffeine give you a little bit of a "buzz"?
- Phosphodiesterase is inhibited by caffeine - Phosphodiesterase is responsible for converting cAMP back to AMP - Caffeine gives a small boost of blood glucose by keeping cAMP levels higher
Topic: Signaling Describe RAS and its role in signaling. Bonus: What are mutations in RAS often associated with?
- RAS is a protein that plays a role in the signaling process, a proto-oncogene. - RAS is involved in EGF signaling. The signaling complex that forms after EGF binding and activation of the EGF receptor activates RAS by causing it to release GDP and replace it with GTP. (When bound to GDP, it is inactive and when it binds to GTP, it is activated.) - Activation of RAS results in activation of transcription pathways that result in cell division. - Mutations to RAS result in RAS being left on (so cells continuously divide). Mutated RAS is the most common point mutation in cancer - found in 90% of pancreatic cancers and 20% of all cancers.
Topic: Signaling How is the β-adrenergic receptor signaling pathway turned off?
- Receptor: if the receptor gets stuck, it is phosphorylated by the G-protein receptor kinase which provides a binding site for arrestin. Arrestin prevents G-protein from interacting with the receptor, stopping signaling by the G-protein. - G-protein: auto-regulating, alpha subunit hydrolyzes GTP to GDP and re-binds to the beta and gamma units and no longer associates with adenylate cyclase (adenylate cyclase no longer activated) - cAMP: phosphodiesterase breaks down cAMP - PKA: breakdown of cAMP by phosphodiesterase has the effect of inactivating protein kinase A.
Topic: Proteases List the 4 types of proteases discussed in class. How do these differ in terms of their catalytic mechanisms?
- Serine protease: catalytic triad with a serine (activated to alkoxide ion), covalent intermediate- 2 steps (fast step and slow step) - Cysteine protease: catalytic triad with a cysteine, covalent intermediate- 2 steps (fast step and slow step) - Aspartyl protease: aspartic acids to activate a water molecule and align the peptide for attack, no covalent intermediate holds one of the peptides- 1 step - Metalloprotease: metal ion to activate a water molecule, no covalent intermediate holds one of the peptides- 1 step
Topic: Mixed Bag Name the three different zymogens discussed in class required for blood clotting. What are the names of their active and inactive form? Bonus: Which enzyme is inhibited by warfarin? Double Bonus: What is the very first signal to stimulate the blood clotting process?
- Thrombin: inactive: prothrombin, active: thrombin cleaves fibrinogen to make fibrin - Fibrin: inactive: fibrinogen, active: fibrin activated by thrombin - XIIIa aka transglutaminase: inactive: XIII, active: XIIIa activated by thrombin - Bonus: Vitamin K reductase is inhibited by warfarin. - Double bonus: exposure of collagen (connective tissue)
Topic: Mixed Bag Name the two types of subunits in ATCase. Bonus: How is ATCase allosterically regulated?
- Two types of subunit in ATCase: regulatory and catalytic - CTP binds ATCase, promotes T state, less reactive - ATP binds ATCase, promotes R state, more reactive
Topic: Mixed Bag What is the free energy change for coupling the synthesis of aTP to dephosphorylation of G6P?
-ATP + H2O ADP + Pi ΔG°' = -30.5 kJ/mol G6P + H2O glucose + Pi ΔG°' = -13.8 kJ/mol - Net reaction: ADP + G6P ATP + glucose -13.8 kJ/mol + 30.5 kJ/mol = 16.7 kJ/mol (this reaction will not proceed spontaneously)
Topic: Proteases Serine, aspartic acid, and histidine make up a group of residues in chymotrypsin known as a
catalytic triad
Topic: Signaling Describe the mechanism of activation of G protein
A change in shape of the receptor causes changes in the G protein. In the G protein, the α subunit binds GDP but when activated, GDP is exchanged for GTP; α subunit simultaneously dissociates from β and γ Activated G protein transmits signals by binding other proteins (here, adenylate cyclase)
Topic: Carbohydrates What distinguishes different blood types?
Composition of the sugars/glycosylation on the surface of red blood cells
Topic: Carbohydrates In what conformation are most biological sugars found?
D-conformation
Topic: Mixed Bag If there are 10 times as much ADP in Pi than ATP at equilibrium at 298K in water, what is the Keq ?
Keq = [ADP]eq[Pi]eq / [ATP]eq = (10)(10)/(1) = 100
