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76 Cards in this Set

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  • Back
302. What is the acyl carrier in fatty acid elongation systems?
Co-A (not ACP)
303. What is an important precursor for eicosanoids?

304. What are the two essential long chain FA's?

Why are they essential?
Linoleate & Linolenate

-They are essential because we cannot make them ourselves
305. Which omega 3 FA's correspond to linoleate and linolenate?
Linolenate: omega 3 fatty acids

Linoleate: omega 6 fatty acids
306. What is used to add double bonds in FA synthesis?
Fatty acyl-CoA desaturase
307. What is fatty acyl-CoA desaturase?
A mixed function oxidase that makes unsaturated FA's
308. How does the reaction of adding doubles bond work?

Three things...
1. Reduction of dioxygen oxidizes 2 different molecules
(a fatty acyl-CoA and NADPH)

2. Two e- come from the fatty acid and two e- come from NADPH
(unusual that you use e- to oxidize)

3. O2 is e- acceptor
309. What are the two enzymes that use oxygen as an e- acceptor?
1. Oxidases

2. Oxygenases
310. What do oxidases do?

Two things...
1. Use O2 just to dump e- on

2. O2 is not incorporated into the oxidized product
311. What is an example of an oxidase?
cytochrome oxidase
312. What are the two types of oxygenases?
1. Monooxygenases

2. Dioxygenases
313. What are monooxygenases?
They are mixed function oxygenases that add only 1 oxygen molecule to the substrate
314. What are dioxygenases?
They add both oxygen molecules (O2) to the substrate
315. What are the energetics of FA synthesis for one molecule of palmitate?
1 acetyl-CoA
7 malonyl-CoA

1 palmitate
7 CO2
14 NADP+
8 CoA
6 H2O
316. How many ATP are needed for FA synthesis?
42 ATP!
(expensive and chunky synthesis)
317. How is FA biosynthesis regulated?
Through phosphorylation of acetyl-CoA carboxylase
318. Under what conditions do you make fat?

Five things...
1. High blood glucose (ate)
2. Increased insulin levels
3. Activate phosphatase (dephosphorylate acetyl-CoA carboxylase; ACC)
4. ACC activated
5. Acetyl-CoA is converted to malonyl-CoA
319. Under what conditions do you burn fat?

Four things
1. Low blood glucose (starving)

2. Increased glucagon levels

3. Activate PKA (phosphorylate ACC)

4. ACC is inactivated
320. What two things allosterically regulate FA degradation?
1. Carnitine acyltransferase I

2. Malonyl-CoA

*elevated levels repress
321. What are eicosanoids and what are they derived from?
They are potent signaling molecules

Family of short range signaling lipids

They are derived from arachidonic acid
322. What are three types of eicosanoids?
1. Prostaglandins

2. Thromboxanes

3. Leukotrienes
323. What do prostaglandins do?
Cause inflammation
324. What do thromboxanes do?
cause blood vessel constriction
325. What do leukotrienes do?
cause smooth muscle contraction
326. What is required for synthesis of eicosanoids?

Two things...
1. Arachidonic acid

2. Dioxygenase
327. How is thromboxanes and other prostaglandins synthesized?

Three steps...
1. Form arachidonate

2. Use cyclooxgenase to put on peroxide

3. Modifications
328. What is arachidonate derived from?
329. What is cyclooxgenase (COX)?
A key enzyme in forming eicosanoids and causes human discomfort
330. What are most of our common medicines?
COX inhibitors
331. What are the two isozymes of COX?
Cox-1: required for secreting the mucin that lines and protects your stomach

Cox-2: required for inflammation
332. What does aspirin inhibit?

What does this result in?
-It inhibits both isoforms of COX

-It causes stomach irritation
333. Why have we developed specific COX-2 inhibitors (Vioxx and Celebrex)?

What's bad about them though?
-To eliminate to unhappy side effect of stomach irritation

-They have the unpleasant side effect of increasing the risk of heart attacks
334. What are cholesterol, steroids, and isoprenoids based on?

*used to make a vast number of other products
335. What are three important points about cholesterol?
1. It has a four ring fused nucleus

2. It has a hydroxyl group

3. Start with acetate to synthesize it
336. What is the order of events in steroid synthesis?
1. Acetate to Mevalonate

2. Mevalonate to Activated Isoprene

3. Activated Isoprene to Squalene

4. Squalene to Cholesterol
337. What happens in converting acetate to mevalonate?

Two things...
1. Condense two acetyl-CoA which then condenses with third acetyl-CoA to form 6 C compound

2. Reduction of HMG-CoA to mevalonate is rate-limiting step
338. What is the key enzyme in the regulation of steroid synthesis?

What does it catalyze?
HMG-CoA reductase is key enzyme that regulates steroid synthesis

It catalyzes reduction of HMG-CoA to mevalonate through a 4 e- reduction using 2 NADPH (NADPH -> NADP+)
339. What do drugs used to reduce cholesterol level inhibit?
They are competitive inhibitors of HMG-CoA reductase
340. How does squalene form?
Through successive condensations of activated isoprene
341. How is squalene converted into cholesterol?
Form an epoxide using an oxidase whose cofactor is NADPH

Then, cyclize the epoxide to the steroid nucleus using the enzyme cyclase
342. What activates and deactivates HMG-CoA reductase?

Three things...
1. Insulin activates by promoting dephosphorylation of the reductase

2. Glucagon deactivates by promoting phosphorylation of the reductase

3. Cholesterol inhibits the reductase
343. Can lipids move in the blood stream freely?

Why or why not?
Lipids are too hydrophobic to move freely in the blood stream and need to be complexed to various proteins for transport
345. What two proteins do lipids bind to for transport?
1. Serum Albumin: bind/move FA's

2. Lipoproteins: bind/transport triacyglycerols and cholesterol
346. What are the four major classes of human plasma lipoproteins?
1. Chylomicrons

2. Very low density lipoprotein (VLDL)

3. Low-density lipoprotein (LDL)

4. High-density lipoprotein (HDL)
347. Which lipoproteins mostly carry FA's?

1. Chylomicrons

348. Which lipoproteins carry a significant amount of cholesterol?

1. LDL

2. HDL
349. Which lipoprotein is the biggest and which is the smallest?
The biggest is chylomicrons (lowest density)

The smallest is HDL
350. What do chylomicrons mostly transport?

To where?
Dietary lipids are packaged in chylomicrons

Most of their triacylglycerol content is released to adipose and muscle tissue during transport through the capillaries
351. What is LDL termed?
"Bad" cholesterol

*It raises level of cholesterol in the body
352. Where does LDL travel to?
It delivers cholesterol to peripheral tissue or returns to the liver
353. What is HDL termed?
"Good" cholesterol

*It reduces level of cholesterol in the body
354. Where does HDL travel to?
It takes excess cholesterol and goes to the liver for excretion
355. Why is too much cholesterol bad?
It plugs up the pumping (clogs arteries)

beefy chunkiness
356. Is there any was to reduce the LDL and raise the HDL? How?

Two ways
Yeah, Jimmy Jam

1. Eat monounsaturated fat (olive oil, canola oil-this is the best way)

2. Eat polyunsaturated fat (corn, soybeans)
357. What fat will raise both LDL and HDL?
Saturated fats (whole milk, butter, cheese)
358. What fat is the worst for and raises only LDL?
Trans fats (unnatural fats in fast food, chips, shortening)
359. How can you tell the types of fats apart to know if it's good or bad for you?

Three ways?
1. Monounsaturated and polyunsaturated fats are liquids

2. Saturated fats are solids

3. Trans fats are solid or semi-solid
360. What is the major path for nitrogen into biomolecules?

Two parts...
1. Nitrogen fixation (N2 -> NH4)

2. NH4 to glutamate/glutamine (glutamine synthetase)
361. What is the minor path for nitrogen into biomolecules?

Two parts...
1. Nitrogen fixation

2. NH4 to oxaloacetate/glutamate (glutamate dehydrogenase)
362. Where does organic nitrogen come from?
We are surrounded by nitrogen (80% of air is N2)
363. Can we use any of the N2 in the air? Why or why not?

The energy to dissociate N≡N is too high (930 KJ/mol to dissociate)
364. What is the source of nearly ALL organic nitrogen?

How is this done?
Nitrogen fixation

Only a few species of bacteria make the enzyme nitrogenase which converts N2 to ammonia in an 8 e- reduction
365. What is the biologically useful form of nitrogen?
366. What is the main place for NH4 to assimilate into the blood?
Glutamine through glutamine synthetase
367. How is NH4 assimilated into glutamine?
1. Glutamate is converted to L-glutamine

2. Glutamine synthetase is the enzyme used
369. What is glutamine synthetase?

Two points...
1. A major pathway for incorporating ammonia into biomolecules

2. Critical control point regulated by feedback inhibition
368. What does glutamine serve as?
It is a biosynthetic precursor of many biomolecules
370. What is feedback inhibition?
Where the final product of the pathway allosterically inhibits the first committed step of the pathway
371. Where is feedback inhibition common?

Two places
1. Regulation of amino acids

2. Nucleotide biosynthesis
372. What are three allosteric regulators for glutamine synthetase?
1. Feedback inhibition
2. Anything that uses glutamine is an allosteric regulator to this enzyme
3. End produces of glutamine metabolism
373. In what two ways can the nitrogen from glutamine (or glutamate) be transferred to other molecules?
1. Amidotransferase

2. Aminotransferase
373. What is done in amidotransferase?
Move the amide nitrogen from glutamine to other acceptor molecules
374. How does amidotransferase work?

Two things...
1. The ϓ-amido nitrogen of glutamine is released as NH3

2. The NH3 travels through a channel to the second active site where it reacts with an acceptor
375. What does aminotransferase do?
It can indiscriminately swap the α-amino groups between amino acids and ketoacids
376. What cofactor is used in all aminotransferases?
Pyridoxal Phosphate (PLP)
377. What is the common donor in aminotransferase?