Biochemistry Chapter on Lipids

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Questions and Answers

What is the primary structural characteristic of fatty acids?

They contain a single carbon atom with no functional groups.

They have a hydrophilic carboxylate group attached to a hydrocarbon chain. (correct)

They are composed entirely of carbon and oxygen without any hydrogen.

They contain a hydrophobic phosphate group.

What distinguishes saturated fatty acids from unsaturated fatty acids?

Saturated fatty acids contain a functional group known as a phospholipid head.

Saturated fatty acids have carbon atoms fully bonded with hydrogen. (correct)

Saturated fatty acids have a longer hydrocarbon chain.

Saturated fatty acids have at least one double bond in their structure.

Which of the following describes the term 'amphipathic' in relation to membrane lipids?

They have both hydrophilic and hydrophobic regions. (correct)

They are soluble in water and do not interact with hydrophobic substances.

They are completely hydrophobic and do not form structures in water.

They are primarily composed of sugars and proteins.

Heat production from fat oxidation mainly occurs in which type of adipose tissue?

Brown fat, which specializes in thermogenesis. Signup and view all the answers

What is the primary role of fats, or triacylglycerols, in animals?

They act as long-term energy storage molecules. Signup and view all the answers

Which statement about the structure of naturally occurring fatty acids is correct?

They typically have an even number of carbon atoms. Signup and view all the answers

What are adipocytes primarily responsible for in the body?

Storing energy in the form of fat. Signup and view all the answers

What is NOT a function of fat storage in animals?

Providing chemical signaling through steroids. Signup and view all the answers

What is true about the stereochemical numbering system in glycerophospholipids?

The pro-S carbon is assigned as C1. Signup and view all the answers

Which enzyme deficiency is related to the accumulation of GM2 ganglioside in Tay-Sachs disease?

Hexosaminidase A Signup and view all the answers

In which type of membrane lipid is the fatty acid linked via an amide bond?

Ceramides Signup and view all the answers

How does cholesterol affect membrane fluidity?

It decreases fluidity by reducing unsaturated bonds. Signup and view all the answers

Which statement about peripheral membrane proteins is correct?

They are associated with one side of the bilayer. Signup and view all the answers

What distinguishes glycosphingolipids from glycerophospholipids?

Glycosphingolipids possess a hydrophobic tail derived from sphingosine. Signup and view all the answers

What is the significance of the fluid mosaic model proposed by S.J. Singer and G.L. Nicolson?

It portrays membranes as a mixture of lipids and proteins that can move fluidly. Signup and view all the answers

Which molecular structure is essential to form ceramides in sphingolipid metabolism?

Sphingosine Signup and view all the answers

What occurs during the gel–liquid crystalline phase transition in a synthetic lipid bilayer?

The movement of chains becomes more dynamic. Signup and view all the answers

How does the lipid composition of a membrane affect its transition temperature (Tm)?

Longer saturated tails tend to increase the Tm. Signup and view all the answers

What effect does the addition of 20 mol % cholesterol have on the transition temperature of a membrane?

It broadens the transition without changing the transition temperature. Signup and view all the answers

What is the typical thickness of a cell membrane?

6 nm Signup and view all the answers

What characterizes the semi-fluid liquid crystalline state of biological membranes under physiological conditions?

Lipids can move more freely than in a solid state. Signup and view all the answers

What happens to the leaflets of a membrane concerning lipid composition?

Outer and inner leaflets usually differ in lipid composition. Signup and view all the answers

During the experimental demonstration of membrane fluidity, what occurs when cells with marked surface membrane proteins fuse?

The proteins gradually mix over the fused surface. Signup and view all the answers

What phase forms at cholesterol-to-phospholipid (C:PL) mole ratios above 0.9:1?

Two separate lamellar phases. Signup and view all the answers

What is the primary function of bacteriorhodopsin in bacterial cells?

Functions as a light driven proton pump Signup and view all the answers

Which structural feature characterizes glycophorin A?

A single, highly hydrophobic transmembrane helix Signup and view all the answers

What role does the translocon play in membrane protein insertion?

It facilitates the passage of protein segments through the lipid bilayer Signup and view all the answers

What does the 'inside positive' rule refer to in membrane protein orientation?

The alignment of transmembrane helices with their ends in the cytoplasm Signup and view all the answers

Which lipid molecule is primarily associated with cell membrane stability and signaling?

Phosphatidylinositol Signup and view all the answers

What structural characteristic is true for the transmembrane helices during their synthesis?

They insert into the membrane while still being synthesized Signup and view all the answers

What is identified as a feature of both the 'closed' and 'open' conformations of the SecY translocon?

It allows nascent peptides to access the membrane core Signup and view all the answers

What type of residues primarily accumulates in cytosolic loops of integral membrane proteins?

Small, polar residues Signup and view all the answers

What is the primary function of aquaporins in eukaryotic cells?

Facilitating rapid water transport Signup and view all the answers

What characteristic structure do aquaporins contain that is critical for their function?

Tetramer of identical monomers Signup and view all the answers

In the structure of gramicidin A, what conformation do the molecules adopt to form an ion pore?

Helical conformation Signup and view all the answers

Which feature of the aquaporin water channel contributes to ion selectivity?

The geometry of chelating groups in ion channels Signup and view all the answers

What specific motif is conserved in the helices of aquaporins?

N-terminal Asn-Pro-Ala Signup and view all the answers

What element of the aquaporin structure limits the passage of H3O+ ions?

Electrostatic repulsion due to dipoles Signup and view all the answers

What advantage do cells gain from using aquaporins for water transport over passive diffusion?

Faster transport of water molecules Signup and view all the answers

Which characteristic of the heptamer structure of a-hemolysin distinguishes its dimensions?

10 nm in diameter and 10 nm in length along the sevenfold axis Signup and view all the answers

What initiates the formation of a clathrin-coated vesicle?

Formation of a coated pit Signup and view all the answers

Which component primarily determines the resting potential of a nerve fiber?

Concentration of K+ ions Signup and view all the answers

What is the primary role of Schwann cells in neural transmission?

To insulate the axon with myelin Signup and view all the answers

What occurs during the action potential generation?

Voltage-gated channels open allowing ion flow Signup and view all the answers

What characterizes the nodes of Ranvier along an axon?

They contain numerous Na+ ion channels Signup and view all the answers

During the process of bulk transport across membranes, which vesicle formation is associated with cholesterol?

Caveolae Signup and view all the answers

How is electrical impulse conduction generally initiated in neurons?

Through changes in membrane potential Signup and view all the answers

What does the resting axon voltage typically read, assuming specific ion concentrations?

60 mV Signup and view all the answers

Study Notes

Biochemistry I - CHM219

Course instructor: Assist. Prof. Dr. Esra Aydemir
Topic: Lipids, Membranes, and Cellular Transport

Lipids

Lipid molecules tend to be insoluble in water but can associate to form water-soluble structures (micelles, vesicles, bilayers)
Amphipathic lipids have a hydrophilic (polar) head group and a hydrophobic (nonpolar) tail.
Fatty acids are the simplest lipids, with a hydrophilic carboxylate group at one end and a hydrocarbon chain at the other. Fatty acids typically have 12 to 24 carbons.
Saturated fatty acids have single bonds between carbons, while unsaturated fatty acids have one or more double bonds. Examples include stearic acid (saturated, C18) and oleic acid (unsaturated, C18).
Fatty acids can be ionized (e.g., stearate ion, oleate ion).
Membrane lipids are amphipathic.
Most naturally occurring fatty acids contain an even number of carbon atoms.
Unsaturated fatty acids usually have cis configuration.
Fats (triacylglycerols) are triesters of fatty acids and glycerol and are the major energy storage molecules in many organisms.

Membrane Structure and Properties

Cell membranes are primarily composed of a phospholipid bilayer.
Phospholipids are amphipathic.
The major classes of membrane-forming lipids are glycerophospholipids, sphingolipids, glycosphingolipids, and glycoglycerolipids.
Membrane structure is characterized by a hydrophobic core and hydrophilic head groups facing outward.
The bilayer is about 6 nm thick.
Cholesterol is a component of many animal membranes, influencing membrane fluidity.
Membrane proteins (peripheral, integral, and glycoproteins).

Transport Across Membranes

The rate of nonmediated transport is proportional to the diffusion and partition coefficients and inversely proportional to membrane thickness.
Facilitated transport (pores, permeases, carriers) increases the rate of diffusion significantly, and often depends on concentration differences.
Cotransport: coupled transport of molecules (e.g., sodium and glucose).
Transport by modification: a substance that has diffused through a membrane is modified so that it cannot return (e.g., phosphorylation of sugars).
Active transport moves substances against a concentration gradient using energy from ATP hydrolysis. The Na+-K+ pump is an example of active transport.

Excitable Membranes, Action Potentials, and Neurotransmission

Neurons conduct electrical impulses via membrane potential changes.
The resting potential is determined by permeabilities of the membrane to ions (e.g., K+ leak channels).
An action potential is generated and propagated by voltage-gated channels (e.g., sodium and potassium).
Neurotoxins can block ion channels, affecting nerve function.

Techniques for Studying Membranes

Electron microscopy (EM) is important for visualizing membrane structure within cells.
Freeze-fracture technique allows observation of membrane bilayer leaflets.
Vesicles (e.g., liposomes) and bilayers can be prepared and reconstituted to study membrane functions.

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Description

Test your knowledge on the structural characteristics and functions of lipids, including fatty acids and their roles in biological membranes. This quiz covers various topics like saturated vs unsaturated fats, adipocytes, and the functions of membrane lipids. Ideal for students studying biochemistry or related fields.