Biochemistry Lecture: Lipids and Cell Membranes

Flashcards covering the key concepts from the lecture on lipids and cell membranes in biochemistry.

What are the common features of biological membranes?

Define cells and organelles, formed by lipid bilayers, include proteins, are fluid, semi-permeable, asymmetric, non-covalent structures.

What are the four different nomenclatures for fatty acids?

Saturated (12:0), One double bond (12:1), Two double bonds (12:2), Position of the double bond (Δ#).

What are the three types of lipids?

Phospholipids, Glycolipids, Cholesterol.

What is the basic structure of phosphoglycerides?

Glycerol-based with C1 and C2 esterified with fatty acids and C3 esterified with phosphate.

What characterizes sphingolipids?

Sphingosine-based, with one tail fixed and another attached to an amine, can be phosphorylated or glycosylated.

What are glycolipids?

Sugar-containing lipids that are always on the extracellular side of the membrane, derived from sphingosine.

What is the role of cholesterol in membranes?

Interferes with close packing of fatty acids and contributes to the formation of rigid lipid rafts.

What do micelles and liposomes represent in lipid structures?

Micelles are formed by fatty acids, while liposomes are formed by lipids; both are examples of spontaneous self-assembly.

What are the types of membrane proteins?

Integral, peripheral, and lipid-linked proteins.

What is membrane fluidity and what factors influence it?

Fluidity affects transport across membranes, influenced by temperature and lipid composition.

What are lipid rafts?

Regions made of sphingosine-containing glycolipids and cholesterol that are more rigid and act as scaffolds in membranes.

Why are membranes structurally and functionally asymmetric?

Because they have different lipid components and enzymatic activities on each layer.

What is the transferrin receptor cycle?

The process includes iron-bound transferrin, iron-free transferrin, and involves clathrin-coated pits.

What technique can be used to detect single channel proteins?

Planar bilayers.

What does the fluid mosaic model describe?

The lateral movement of lipids and proteins in membrane structures.

A researcher discovers a new organelle enclosed in a structure held together by non-covalent interactions that is asymmetric and semi-permeable. What is the most likely classification of this structure?

A biological membrane formed by a lipid bilayer.

Options:

• A) Cell Wall
• B) Protein Scaffold
• C) Biological Membrane
• D) Nucleic Acid Shell

A laboratory technician synthesizes a fatty acid labeled as (18:2 \Delta^{9,12}). What does this specific nomenclature indicate about the molecule's chemical structure?

The molecule contains (18) carbons and (2) double bonds, with the double bonds located at the (9^{th}) and (12^{th}) positions.

Options:

• A) 18 carbons, 2 double bonds at positions 9 and 12
• B) 18 double bonds, 2 carbons at positions 9 and 12
• C) 18 carbons, 0 double bonds
• D) 9 carbons, 12 double bonds

While analyzing a cell membrane extract, you identify phospholipids, glycolipids, and cholesterol. Which of the following is NOT a primary lipid type found in biological membranes?

Triglycerides (Triacylglycerols).

Options:

• A) Phospholipids
• B) Glycolipids
• C) Triglycerides
• D) Cholesterol

You are examining a lipid with a glycerol backbone where C1 and C2 are esterified with fatty acids and C3 is esterified with a phosphate group. How would you classify this lipid?

Phosphoglyceride.

Options:

• A) Sphingolipid
• B) Phosphoglyceride
• C) Glycolipid
• D) Cholesterol

A lipid is identified as having a sphingosine base, with one fixed tail and another attached via an amine group. If it is further glycosylated, what does it become?

A Glycolipid (specifically a glycosphingolipid).

Options:

• A) Phosphoglyceride
• B) Micelle
• C) Glycolipid
• D) Cholesterol

If you treat a cell with an enzyme that only cleaves sugars from the extracellular fluid, which membrane component is most likely to be altered?

Glycolipids, because they are sugar-containing lipids found exclusively on the extracellular side of the membrane.

Options:

• A) Cholesterol
• B) Phosphoglycerides
• C) Glycolipids
• D) Integral Proteins

A patient has a condition where their cell membranes are overly fluid. How would increasing the concentration of cholesterol help stabilize the membrane at physiological temperatures?

It interferes with the close packing of fatty acids and contributes to the formation of more rigid regions (lipid rafts).

Options:

• A) It increases the number of double bonds
• B) It interferes with close packing and aids rigid raft formation
• C) It removes all proteins
• D) It promotes micelle formation

In a lab experiment, pure fatty acids are placed in an aqueous solution and form small spherical clusters. What are these structures called?

Micelles. (Note: Liposomes are typically formed by complex lipids, while micelles are formed by simpler fatty acids).

Options:

• A) Liposomes
• B) Micelles
• C) Bilayers
• D) Rafts

Which type of membrane protein can only be removed by using detergents that disrupt the hydrophobic interactions of the lipid bilayer?

Integral membrane proteins.

Options:

• A) Peripheral proteins
• B) Lipid-linked proteins
• C) Integral proteins
• D) Cytoskeletal proteins

A deep-sea fish moves from cold Arctic waters to a warmer current. To maintain optimal membrane fluidity, what change should occur in its membrane composition?

An increase in saturated fatty acids or a decrease in unsaturated fatty acids to prevent the membrane from becoming too fluid.

Options:

• A) Increase unsaturated fatty acids
• B) Increase saturated fatty acids
• C) Decrease cholesterol
• D) Increase protein content

A specific region of the plasma membrane is found to be highly enriched in sphingosine-containing glycolipids and cholesterol. What is the functional term for this region?

Lipid rafts, which act as rigid scaffolds for signaling molecules.

Options:

• A) Micelles
• B) Fluid Mosaic
• C) Lipid rafts
• D) Clathrin pits

Biochemical assays show that the inner and outer leaflets of a erythrocyte membrane have totally different lipid compositions and enzymatic activities. This is an example of what membrane property?

Structural and functional asymmetry.

Options:

• A) Fluidity
• B) Asymmetry
• C) Permeability
• D) Non-covalent assembly

During the transferrin receptor cycle, how is iron-bound transferrin internalized into the cell?

Through clathrin-coated pits.

Options:

• A) Simple diffusion
• B) Active transport pumps
• C) Clathrin-coated pits
• D) Planar bilayers

A biophysicist wants to measure the electrical current passing through a single ion channel protein. Which experimental setup would be most appropriate?

Planar bilayers.

Options:

• A) FRAP (Fluorescence Recovery)
• B) Planar bilayers
• C) Centrifugation
• D) Chromatography

A researcher uses a laser to bleach a fluorescent dye on a cell surface and observes that the spot eventually refills with color. This experiment provides evidence for which model?

The Fluid Mosaic Model, specifically demonstrating lateral movement of lipids and proteins.

Options:

• A) Rigid Shell Model
• B) Protein Scaffold Model
• C) Fluid Mosaic Model
• D) Static Bilayer Model