My Exam 2 questions and answers

1. Lipitor leads to increased levels of LDL receptors on the surface of liver cells. 2. Lipitor stimulates the production of VLDL, which decreases levels of circulating cholesterol. 3. Lipitor inhibits the production of HDL, which increases levels of circulating LDL and VLDL. 4. Lipitor inhibits HMG-CoA reductase, which reduces intracellular cholesterol levels. 5. Lipitor decreases bile acid production by stimulating acyl-CoA cholesterol acyltransferase. 6. Lipitor binds to the NPC1L1 cholesterol transporter protein and inhibits cholesterol uptake.

1 and 4 only

Put the correct steps required for absorption of dietary fats into order.

1) Emulsification of fats 2) Lipase cleavage 3) Intracellular synthesis of triaglycerols 4) Chylomicron assembly 5) Export of lipoprotein particle 6) Entry into the circulatory system

Glycogen phosphorylase is regulated by phosphorylation, with the (1) T state / (2) R state being in the inactive dephosphorylated conformation. (3) Insulin / (4) Glucagon signaling stimulates the phosphorylation of glycogen phosphorylase, resulting in a shift to the (5) inactive / (6) active R state conformation. Glucagon signaling (7) stimulates / (8) inhibits the activity of glycogen synthase by (9) activating / (10) inhibiting protein kinase A (PKA).

1, 4, 6, 8, 9

Starting with glucose derived from the diet, how many ATP are required to incorporate this dietary glucose molecule into liver glycogen? Explain your responing.

2 ATP; one is needed to generate glucose-6-P (isomerized to G-1P), and another is used to regenerate UTP

Starting from a molecule of glucose imported from the blood, what is the energy cost for adding that molecule of glucose to a growing glycogen chain?

2ATP

Which of the following is a product from fatty acid oxidation of palmitate?

8 Acetyl-CoA

Sunflower oil has a melting temperature of -6C and beef tallow has a melting temperature of +45C. What contributes to the ~50C difference in melting temperature?

Beef tallow has ~40% palmitate and stearate combined, but sunflower oil only has ~10% combined.

Muscle glycogen phosphorylase is regulated by both allosteric effectors, such as AMP and ATP, and by hormonal signaling. Allosteric effectors bind to the phosphorylated and unphosphorylated forms of the enzyme and shift the equilibrium between the inactive T conformation and the active R conformation. In contrast, hormonal regulation involves activation of kinase and phosphatase enzymes, which modulate the phosphorylation status of glycogen phosphorylase.

Both forms of control are important because they work together to ensure maximum interconversion of glucose and glycogen so that liver cells can maintain safe blood glucose levels at all times. Allosteric regulation by AMP and ATP provides a way to quickly shift the activity of muscle glycogen phosphorylase between the active and inactive states before hormonal signaling is fully stimulated.

Put the correct steps required for absorption of dietary fats into order A Lipase cleavage B Intracellular synthesis of triacylglycerols C Emulsification of fats D Export of lipoprotein particle E Entry into the circulatory system F Chylomicron assembly

C, A, B, F, D, E

Order the following steps in glycogen particle synthesis. _A A branching enzyme adds α-1,6 linkages B The glycogen synthase activity of glycogenin uses UDP-glucose to extend the chain up to 7 residues. C The glycosyltransferase activity of glycogenin adds UDP-glucose to a tyrosine residue in glycogenin. D The glycogen synthase activity of glycogenin forms an α-1,4 glycosidic bonds that adds UDP-glucose to an O-linked glucose residue. E The glycogen synthase activity of glycogenin forms an α-1,4 glycosidic bond that adds UDP-glucose to an O-linked glucose disaccharide. F Glycogen synthase uses UDP-glucose to form α-1,4 glycosidic bonds that add to the glycogenin primer

C, D, E, B, F, A

In the elongation of glycogen, activated glucose units are attached to which hydroxyl of the terminal residue of the growing glycogen chain?

C-4

Which of the following is true concerning cholesterol and plasma membrane?

Cholesterol inserts into the membrane via its non-polar planar rings.

Which KEY enzyme catalyzes the ATP investment reaction required for oxidation of palmitate?

Fatty acyl-CoA synthetase

How does glycogen metabolism regulation differ between liver cells ans muscle cells?

Glucose is not exported from muscle cells because muscle cells lack glucose-6-phosphatase. Muscle cells are not sensitive to glucagon

How does glycogen metabolism differ between muscle and liver cells?

Liver cells contain glucose-6-phosphatase, which dephosphorylates glucose-6P to release glucose

What is the difference between the net number of ATP generated by glycolysis from glucose produced by the glycogen phosphorylase enzyme reaction as compared to glucose obtained from the diet?

One less net ATP is generated in glycolysis from dietary glucose as compared to glucose from glycogen.

Which of the following proteins is activated by phosphorylation during glycogen-activated fatty acid release from adipocytes?

Perilipin

Which type of phospholipid provides the fatty acid for lecithin-cholesterol acyltransferase to produce cholesterol esters?

Phosphatidylcholine

Why do plant root nodules in leguminous plants contain high levels of glutamine synthetase?

Root nodules assimilate NH4+ into glutamine

T F LDL particles are "bad" cholesterol because they are associated with increased heart disease. T F VLDL particles transport lipids from the intestines into the bile duct of the liver. T F HDL particles are "good" cholesterol because they are the smallest lipoproteins in serum. T F Lipoprotein lipase cleaves triacylglycerols in lipoproteins and releases chylomicrons. T F Statin drugs lower serum LDL levels by stimulating LDL receptor expression on liver cells.

T, F, F, F, T

Why is less ATP produced from the average carbon in a sugar molecule than from a carbon in a fat molecule?

The carbons in fatty acids are a more reduced form of carbon than those in sugars.

Partial hydrogenation, as used by the food industry, results in

The resulting products being less expensive than animal fats

How can the body easily adjust the relative levels of some amino acids using animotransferases?

Use common intermediates to interconvert between amino acids.

Why do fatty acids have to be sequestered by fatty acid binding protein (FABP4) within adipocytes before being exported to the circulatory system where they are bound to serum albumin protein? A correct answer is not provided. In the absence of FABP4, the free fatty acids would pack closely together and become crystalline. Free fatty acids are aromatic aliphatic molecules that will disrupt the assembly of intracellular pathways. At physiological pH, the carboxyl group on free fatty acids is deprotonated to form FABP4-palmitic acid. The FABP4 protein is similar to soap in that it provides a way for fatty acids to form

a correct answer is not provided

In addition to triacylglycerols, which other lipid synthesized in the liver is transported by VLDLs?

cholesterol

Which enzyme is responsible for assembly of palmitate from activated acetyl-CoA fragments?

fatty acid synthase

In the breakdown of glycogen by glycogen phosphorylase, the immediate predominant product is

glucose-1-phosphate.

The Haber process is 98% efficient. How does it achieve that level of efficiency?

high pressures and recycling nitrogen

Adenylylation of Try397 regulates glutamine synthetase by

inhibiting activity

What is the point of the pyruvate-->malate-> glyceraldehyde-3-P system?

it provides a source of NADH for gluconeogenesis via malate transport

What enzyme is activated by HDL to release cholesterol from the cell membranes of peripheral tissues?

lecithin-cholesterol acyltransferase

The water-soluble enzyme in the small intestine that hydrolyzes the acyl ester bonds in triacylglycerols is

lipase

The introduction of 14CO2 into a cell actively synthesizing fatty acids results in 14C labeled

malonyl-CoA.

In comparison with glycerophospholipids and sphingolipids, cholesterol contains a

steroid ring

Predict the fatty acid with the highest melting point.

trans 14:1 (delta7)

One disadvantage of using partial hydrogenation in the food industry is that

trans fats are formed during the process.