Fatty Acids, Lipids, and Membrane Structure: Key Concepts for Biology

What is the notation for the saturated fatty acid Palmitic acid?

16:0

What is the notation for the saturated fatty acid Stearic acid?

18:0

What is the notation for the monounsaturated fatty acid Oleic acid?

18:1

How does increasing unsaturation affect the melting point of fatty acids?

The melting point decreases because the kinks in the chains make them harder to pack together.

How does increasing saturation (or chain length) affect the melting point of fatty acids?

The melting point increases because the straight chains are easier to pack together.

What is the primary function of triacylglycerols?

They serve as a highly efficient way to store metabolic energy.

In what cells and locations are triacylglycerols synthesized?

They are synthesized in adipocytes, located in subcutaneous and abdominal cavities.

What is the basic structure of a glycerophospholipid?

A glycerol backbone with two fatty acid chains, and a phosphate group attached to a polar head group.

The action of Phospholipase C (PLC) on a membrane lipid produces what important signaling molecule?

Diacylglycerol (DAG).

What enzyme hydrolyzes the carboxyl ester bond at the C2 position of a glycerophospholipid?

Phospholipase A2.

The signaling molecule Diacylglycerol (DAG) is derived from membrane lipids and activates _____.

protein kinase

What molecule forms the backbone of sphingolipids?

Ceramide, which consists of sphingosine and an N-acyl fatty acid.

What are the two common head groups found on sphingomyelin?

Phosphocholine and phosphoethanolamine.

What is a key structural difference between cerebrosides and other phospholipids like sphingomyelin?

Cerebrosides have no phosphate group and are nonionic.

What defines a ganglioside?

They are complex glycosphingolipids with an oligosaccharide head group containing at least one sialic acid residue.

What percentage of brain lipids are composed of gangliosides?

Approximately 6%.

What is the characteristic fused ring structure of steroids, as seen in cholesterol?

A rigid structure of four fused rings (three 6-carbon rings and one 5-carbon ring).

Cholesterol is a metabolic precursor for what class of signaling molecules?

Steroid hormones.

How are insoluble steroid hormones transported through the blood?

They bind to carrier proteins.

What is the function of glucocorticoids, such as cortisol?

They are involved in carbohydrate, lipid, and protein metabolism.

What is the function of mineralocorticoids, such as aldosterone?

They regulate salt and water balance in the kidneys.

What is the function of androgens and estrogens?

They are involved in sexual development and function.

How is Vitamin D initially synthesized in the skin of animals?

Through the non-enzymatic, photolytic action of UV light on a sterol derivative.

What is the most potent active form of Vitamin D, and what is its function?

Calcitriol; it increases the absorption of Ca2+ and its deposition in bones and teeth.

What is a potential negative consequence of excessive Vitamin D?

Calcification of soft tissues and kidney stones.

Ubiquinone is another name for what important isoprenoid?

Co-enzyme Q.

What is the function of Vitamin A (retinol)?

It is oxidized to retinal, which acts as a photoreceptor in low light conditions.

What is the crucial function of Vitamin K?

It is required for the carboxylation of glutamate residues in proteins involved in blood clotting.

What is the most abundant member of the Vitamin E family?

$\alpha$-tocopherol.

What C20 fatty acid is the most important precursor for eicosanoids like prostaglandins?

Arachidonic acid.

What are two physiological roles of prostaglandins?

They are involved in producing pain and fever, and in regulating blood pressure.

Glycerophospholipids and sphingolipids, with their two hydrophobic tails, spontaneously form _____ in aqueous solution.

bilayers

What polymer is often used to coat liposomes to help them circulate longer in the blood for drug delivery?

PEG (polyethylene glycol).

How fast is lateral diffusion of lipids within a membrane leaflet?

It is rapid, allowing the membrane to act as a two-dimensional fluid.

How fast is the 'flip-flop' (transverse diffusion) of lipids from one membrane leaflet to the other?

It is very slow and rare.

What is the physical state of a lipid bilayer below its transition temperature?

It is in an ordered, gel-like state with stiffened tails.

What is the physical state of a lipid bilayer above its transition temperature?

It is in a disordered, liquid crystal state.

What class of membrane proteins associates tightly with the membrane via hydrophobic interactions and can only be separated by agents that disrupt the membrane?

Integral membrane proteins.

What structural motif, composed of 19-23 hydrophobic residues, often spans the lipid bilayer to anchor an integral protein?

An $\alpha$-helix.

The transmembrane domains of proteins are rich in _____ amino acids.

hydrophobic (nonpolar)

What is a $\beta$-barrel?

A transmembrane structure formed from antiparallel $\beta$-sheets, common in the outer membranes of bacteria, mitochondria, and chloroplasts.

How do peripheral membrane proteins associate with the cell membrane?

Loosely, through electrostatic and hydrogen bonding interactions with the surface.

Cytochrome C, which shuttles electrons in the mitochondria, is an example of what type of membrane protein?

A peripheral membrane protein.

Term: Prenylation

Definition: The covalent attachment of a lipid anchor derived from isoprene units to a protein.

What type of reversible protein lipidation on the cytoplasmic face of the plasma membrane is involved in transmembrane signaling?

Palmitoylation.

What protein constitutes about 75% of the erythrocyte's membrane skeleton, forming a dense meshwork?

Spectrin.

A deficiency in spectrin can lead to erythrocyte lysis and a condition called _____.

Hereditary Spherocytosis (HS)

What is the function of the protein Ankyrin in the erythrocyte membrane?

It anchors the spectrin skeleton to an integral membrane ion channel protein.

Glycolipids and glycosphingolipids are predominantly found on which leaflet of the plasma membrane?

The outer (extracellular) leaflet.

Membrane proteins are synthesized by ribosomes on the _____.

Rough Endoplasmic Reticulum (RER)

What is the function of a flippase enzyme?

It facilitates the movement of phospholipids across a bilayer, helping to equilibrate their distribution.

What type of enzyme uses ATP hydrolysis to move phospholipids from a low to high concentration across a membrane, establishing asymmetry?

A phospholipid translocase.

In the secretory pathway, what particle recognizes the signal peptide on a new polypeptide and halts synthesis?

The Signal Recognition Particle (SRP).

After binding the SRP receptor on the RER, the ribosome-polypeptide complex is passed to a channel-forming protein complex called the _____.

translocon

In the membrane Transport and synthesis, After synthesis in the ER, where are proteins further folded, modified with carbohydrates, and sorted?

In the Golgi apparatus.

What type of coated vesicle is responsible for transporting material from the extracellular space into the cell (endocytosis)?

Clathrin-coated vesicles.

What type of coated vesicle mediates retrograde transport from the Golgi back to the ER?

COPI-coated vesicles.

What is the general function of SNARE proteins?

They mediate the fusion of a vesicle with a target membrane.

In the SNARE complex, the R-SNARE is typically found on the _____ and the Q-SNARE is found on the _____.

vesicle; target membrane

What is 'hemifusion' in the process of vesicle fusion?

The initial stage where the outer leaflets of the vesicle and target membrane fuse together.

After the SNARE proteins 'zip up' and pull the membranes together, what structure is formed that allows contents to be released?

A fusion pore.

The cholesterol molecule shown has a polar head group (the _____ group) and a nonpolar hydrocarbon body.

hydroxyl (-OH)

The chemical structure shown with four fused rings (labeled A, B, C, D) is characteristic of a _____.

steroid

The movement of a phospholipid within one leaflet of the bilayer, shown as 'Rapid', is known as _____.

lateral diffusion

The movement of a phospholipid from one leaflet to the other, shown as 'Very slow', is known as _____.

transverse diffusion or flip-flop

According to the diagram, a protein that passes completely through the phospholipid bilayer is called an _____ membrane protein.

integral

According to the diagram, a protein that is loosely associated with one surface of the membrane is called a _____ membrane protein.

peripheral

Proteins that are covalently attached to lipids embedded within the cell membrane are called _____ proteins.

lipid-anchored

The structure of clathrin, which forms polyhedral cages around vesicles, is a three-legged protein complex called a _____.

triskelion

The process where R-SNARE and Q-SNARE proteins begin to intertwine, drawing a vesicle towards a target membrane, is called _____.

zipping or docking

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