BioChem Chapter 10 Homework Questions

Which statement concerning phospholipid synthesis is true?

Addition of polar "head groups" to diacylglycerol usually involves CDP derivatives

This enzyme removes the first fatty acid from a triacylglycerol molecule, which produces diacylglycerol (DAG) and a free fatty acid. It is stimulated through binding to its cofactor, CGI-58.

Adipocyte triacylglycerol lipase

Where are triacylglycerols stored in humans under normal conditions?

Adipocytes

In one model of lipid droplet formation, neutral lipids _________

Aggregate between the lipid bilayers of the endoplasmic reticulum

Chylomicra are large due to a core of lipids formed from dietary fats and are coated with the apolipoproteins AI, CII, and B48. If blood is drawn after a high fat meal, what would be seen in the blood sample?

Chylomicra has a lower density than the rest of the blood sample and forms a "creamy" upper layer, whereas blood cells are dense forming a lower layer

Lipid storage diseases ______

Commonly are lysosomal disorders

What is the primary purpose of high-density lipoproteins (HDLs)?

HDLs transport excess cholesterol from circulation back to the liver for recycling and to prevent buildup in the arteries

In intestinal enterocytes, triacylglycerol _________

Production relies on ATP hydrolysis to product acyl-CoA

Lipid storage droplets are the only organelle known that is bound by a phospholipid monolayer. Why is there only a monolayer?

The droplet has a hydrophobic core

Coordination of phospholipid and triacylglycerol biosynthesis is meditated by ______

The enzyme lipin (phosphatide phosphatase)

Most important to efficient passage of dietary lipids into lymphatic circulation is _________

The prescene of bile

Which is NOT important to the decreased fluidity of lipid rafts?

They are mostly comprised of phosphatidylcholine with unsaturated fatty acids

In enterocytes, 2-monoacylglycerol is the source of the glycerol backbone for triacylglycerol synthesis.

True

Lingual and gastric lipases are active at acidic pH, whereas pancreatic lipase is active at alkaline pH. As food moves further down the digestive tract, the pH of the environment increases. Thus means lingual and gastric lipases lose activity, and pancreatic lipase becomes more active.

True

Liver tissue contains substantial amounts of glycerol kinase, which promotes the production of glycerol-3-phospahte, an intermediate in triacylglycerol synthesis.

True

Liver tissue synthesizes triacylglycerols de novo using acetyl-CoA from glycolysis as the starting molecule.

True

Pancreatic lipase can act on either triacylglycerol or diacylglycerol. Therefore, pancreatic lipase can degrade one molecule of triacylglycerol into two molecules of free fatty acids and one molecule of 2-monoacylglycerol.

True

Which of the following best describes the order for the conversion of glycerol-3-phosphate into a triacylglycerol?

2 acyltransferase reactions, 1 phosphatase reaction, then 1 acyltransferase reaction

Which is NOT true of lipoproteins?

Apolipoproteins within their coats hold beta sheet secondary structures

In what form is the energy needed for triacylglycerol biosynthesis provided?

CDP-DG

Which of the following statements about membrane lipids is FALSE?

Glycerophospholipids may have a sugar molecule as their polar head group (glycolipids)

Which of the following explains how phosphatidylserine is synthesized?

Serine displaces the ethanolamine from a phosphatidylethanolamine

When is the energy needed for triacylglycerol biosynthesis provided?

Synthesis of CDP-DG

If LDLr were deleted, LDL would accumulate on/in:

outside of the cell

If AP2 were deleted, LDL would accumulate on/in:

plasma membrane

Several enzymes, for example, hepatic lipase and lipoprotein lipase, can bind to lipoproteins. There are mutant viruses of these enzymes that bind lipoproteins but are not catalytically active. Cells expressing these mutants can still absorb cholesterol. What does that tell us about the functions of these proteins in cholesterol absorption?

All of the above

Excess dietary carbohydrates and amino acids ________

Are converted to triacyclglycerols in the liver

Which of the following best describes the sequence of events for the synthesis of phosphatidylcholine?

CDP-choline reacts with a diacylglycerol

Chylomicrons ______

Deliver fatty acids directly to adipose tissue and muscle

Where is the energy needed for triacylglycerol biosynthesis provided?

Endoplasmic reticulum

Adipose tissue contains substantial amounts of glycerol kinase, which promotes the production of glycerol-3-phosphate, an intermediate in triacylglycerol synthesis.

False

In contrast to pancreatic lipase, lingual and gastric lipases require colipase for optimal enzyme activity.

False

Triacylglycerols are synthesized in the liver and adipose tissue using 2-monoacylglycerol as the source of the glycerol backbone.

False

Why is fatty acid free bovine serum albumin (BSA) often included in lipase essays?

Fatty acid free BSA binds fatty acids

The synthesis of triacylglycerols involves the addition of acyl groups to glycerol-3-phosphate. What is the source of the acyl groups?

Fatty acyl-CoA

The removal of the second fatty acid during triacylglycerol breakdown is catalyzed by this enzyme, resulting in monoacylglycerol (MAG) and a second free fatty acid. It is activated through interactions with perilipin and must be phosphorylated by PKA for activity.

Hormone sensitive lipase

The rate of breakdown of TAGs in adipocytes is determined by the activity of which of the following enzymes?

Hormone-sensitive lipase

Caveolar rafts and coated pits are similar in that both _________ I. Form plasma membrane invaginations II. Form intracellular vesicles III. Incorporate the same plasma membrane proteins IV. May be involved in cell signaling via membrane proteins

I and IV

Sphinganine is an intermediate in the synthesis of which of the following? I. Ceramides II. Sphingomyelins III. Cerebrosides IV. Prostaglandins

I, II, III

Important to hormonal control of lipolysis is/are _________. I.G protein coupled receptors II. Cholesterol III. Perilipin IV.PKA

I, III, and IV

Which of the following lipids would NOT likely be found in a lipid raft? I. Glycosphingolipids II. Glycerophospholipids III. Cholesterol IV. palmitoleic acid

II and IV

Which of the following statements about lipolysis in adipocytes is TRUE?

It is increased in response to a glucagon signal

You would like to develop a new pharmacological agent to help specifically with weight loss. Which is most true in developing your drug?

It should stimulate perilipin

Atherosclerosis develops when _____ particles accumulate _____ within blood vessels.

LDL; between endothelium and smooth muscle

A phospholipid monolayer coating a core of triacylglycerols or cholesteryl esters describes _________

Lipid storage droplets

Which of the following terms is used to describe the breakdown of triacylglycerols into free fatty acids and glycerol?

Lipolysis

This enzyme cleaves the remaining ester, resulting in free glycerol and a third fatty acid molecule. It is cytosolic and is not thought to be regulated by other proteins.

Monoacylglycerol lipase

In phospholipid biosynthesis, CTP __________

all of the above

Below is the structure of pancreatic lipase. This structure consists of _______ and has two globular domains separated by a flexible hinge allowing movement of the domains. The larger of the domains is the amino-terminal _____ domain and the smaller is the carboxyl-terminal _____ domain. The _____ domain interacts with colipase.

both alpha helices and beta sheets, catalytic, regulatory, regulatory

Coated vesicles _____

contain receptor and adaptor proteins and clathrins

High-density lipoprotein (HDL) is produced in the ___ and has a very high ___ ratio of the lipoproteins

liver; protein-to-lipid

The chylomicra enter the _______ tissues by passing through capillary beds in those tissues. The endothelial cells in these beds contain _______, which degrade triacyclglycerols found in the chylomicra

muscle and adipose; lipoprotein lipase

If clathrin were deleted, LDL would accumulate on/in:

plasma membrane

If dynamin were deleted, LDL would accumulate on/in:

plasma membrane

Lingual and gastric lipases _____

produce glycerol + free fatty acids

Cholesterol ester is the storage form of cholesterol. Based on your knowledge of lipid metabolism, the synthesis of cholesteryl ester _____ energy and what is the source of that energy?

requires and Acyl-CoA