BIOC 2300 Lecture Notes - Lecture 26: Cholesteryl Ester, Lipid Bilayer, Ester

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oliveminnow466

26 Mar 2019

School

Dalhousie University

Department

Biochem & Molecular Biology

Course

BIOC 2300

Professor

David Byers

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**2 questions on this lecture for the midterm *: transport of lipids in the circulation: lipoproteins, triacylglycerol synthesis, triacylglycerol degradation, fatty acid oxidation. Membrane-forming lipids and lipids that intercalate into membranes. Phospholipids are amphipathic, with hydrophobic tails, and little hydrophilic heads. This structure of the phospholipids allows them to intercalate within the membrane and form the lipid bilayer. Note: phospholipids are not used as energy substrates. Cholesterol is a structural lipid, and to some extent, amphipathic, due to the hydroxyl group. Fatty acids are shown in the diagram in the unesterified form. However, they are usually esterified to a cholesterol, or another molecule. Fatty acids make micelles and they intercalate in membranes as well: fully hydrophobic lipids. Cholesterol + fatty acid esterified = cholesteryl ester. Triacylglycerides are the key energy stores in the adipose tissues. Fat you need triacylglycerol and some cholesterol (less). Cholesterol does not generate energy, whereas triglycerides do.

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Cholesterol is transported in the bloodstream in lipoproteinparticles. There are several classes of lipoprotein particles, butone of the most important classes is called Low-densitylipoproteins (LDL). LDL particles are composed of a single moleculeof a large protein called apolipoprotein, as well as thousands ofcholesterols molecules and phospholipids. Part of theapolipoprotein forms the surface of the particles and faces theaqueous phase, while other parts face the hydrophobic interior ofthe particle where they interact with cholesterol and thehydrophobic tails of the phospholipids. When cells need additionalcholesterol, they produce a receptor protein on the surface oftheir plasma membrane that binds to the apolipoprotein andinitiates the uptake of LDL particles into the cell via a processcalled endocytosis.

1. What is the likely reason that LDL particles are used totransport cholesterol in the blood stream?

a. Cholesterol in LDL particles easily inserts into lipidbilayers

b. Cholesterol id largely insoluble in aqueous solutions

c. Cholesterol is synthesized within LDL particles

d. LDL particles can form lipid rafts in the lipid bilayer

2. What is the most likely location of phospholipids in LDLparticles?

a. Bound to the hydrophilic domain of apolipoprotein

b. In the lipid bilayer that surrounds LDL particles

c. On the surface interacting with the aqueous environment aswell as interacting with the hydrophobic core of the particle

d. Within the hydrophobic core of the particle

3. What best describes the class of protein that apolipoproteinbelongs to?

a. Amphipathic proteins

b. Cell surface proteins

c. Membrane associated protein

d. Multipass membrane proteins

4. What kind of molecule on the surface of the cell would bemost likely to serve as a receptor for LDL particles?

a. a cholesterol binding protein

b. a glycolipid

c. a phospholipid

d. trans membrane protein

5. What conditions would be most likely to trigger increaseduptake of LDL particles by cells?

a. increased glycolipid synthesis

b. increased plasma membrane growth

c. increased protein secretion

d. increase protein synthesis

BIOC 2300 Lecture Notes - Lecture 26: Cholesteryl Ester, Lipid Bilayer, Ester

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