Lipid Chemistry and Biology

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Lipids

• Lipids are a type of biological molecule, including fats, waxes, and related compounds.
• Examples of lipids include syhenul, plau, and waxtslid.

Structure and Composition

• Lipids are composed of fatty acid chains, which are long chains of carbon atoms with hydrogens attached.
• The fatty acid chains can be single or double, with the double bonds forming a "kink" in the chain.
• Lipids can also have a glycerol backbone, which is a three-carbon molecule that serves as the central structure of the lipid.

Types of Lipids

• Waxes are a type of lipid that consist of a long-chain fatty acid and a long-chain alcohol.
• Fats are a type of lipid that consist of a glycerol backbone and three fatty acid chains.
• Plau lipids are a type of lipid that is found in plant cells.

Functions of Lipids

• Lipids serve as a source of energy for cells.
• They are also important for maintaining the structure and function of cell membranes.
• Lipids can act as hormones or signaling molecules, helping to regulate various cellular processes.

Other Important Concepts

• Lipids are non-polar molecules, which means they are insoluble in water.
• They are often stored in cells as droplets or as part of the cell membrane.
• Lipids can be broken down into smaller molecules, such as fatty acids and glycerol, through a process called lipolysis.

Phospholipids

• Phosphatidyl inositol is a phospholipid present on the interface of the membrane, concentrated in lipid rafts.
• Phospholipids are the major constituents of membranes and are responsible for the membrane being a bilayer.
• Phospholipids have a complex structure consisting of a molecule of glycerol, attached to two fatty acids, a phosphate, and usually one other small molecule (X).

Fatty Acids

• Most carbon-carbon bonds in fatty acids are single, but they may contain one, two, or more carbon-carbon double bonds.
• Double bonds in fatty acids are most often cis.
• For monounsaturated fatty acids, the double bond is usually between carbon atoms 9 and 10.

Triglycerides

• Triglycerides are not part of the cell membrane and aggregate into globules, stored as an energy source.
• Triglycerides are a component of oils and can be hydrolyzed to produce glycerol and three fatty acids.

Lipases

• Lipases hydrolyze triglycerides (fats) into their component fatty acid and glycerol molecules.
• Initial lipase digestion occurs in the lumen of the small intestine, where bile salts reduce the surface tension of the fat droplets, allowing lipases to attack the triglyceride molecules.

Glycerophospholipids

• Glycerophospholipids are the major constituents of membranes and are responsible for the membrane being a bilayer.
• Glycerophospholipids have a complex structure consisting of a molecule of glycerol, attached to two fatty acids, a phosphate, and usually one other small molecule (X).

Phospholipase Action

• Phospholipases are enzymes that cleave ester bonds within phospholipids.
• Phospholipases contribute to the stability and insulation of nerve cells.

Sphingolipids

• Sphingolipids are a type of lipid that contains a sphingoid base, a fatty acid, and a single sugar residue.
• Cerebrosides are a type of sphingolipid that contains a sphingoid base, a fatty acid, and a single sugar residue, commonly found in the nervous system.
• Gangliosides are the most complex sphingolipids, containing multiple sugar residues in addition to a sphingoid base and a fatty acid, predominantly present in the nervous system.

Sterols

• Sterols are a subgroup of steroids with a hydroxyl group at the 3-position of the A-ring.
• Sterols are amphipathic lipids synthesized from acetyl-coenzyme A via the HMG-CoA reductase pathway.
• The overall molecule is quite flat, with a hydroxyl group on the A-ring that is polar, while the rest of the aliphatic chain is non-polar.

Ceramides

• Ceramides are the simplest form of sphingolipids, composed of a sphingoid base and a single fatty acid linked by an amide bond.
• Ceramides serve as precursors for more complex sphingolipids and are involved in cellular signaling pathways related to apoptosis and stress responses.

Sphingomyelins

• Sphingomyelins consist of a sphingoid base, a fatty acid, and a phosphorylcholine or phosphorylethanolamine head group.
• Sphingomyelins are abundant in cell membranes, especially in myelin sheaths.

Waxes

• Waxes are esters made of long-chain alcohols and fatty acids.
• Waxes provide protection, especially to plants, in which wax covers the leaves of plants.

Fat-Soluble Vitamins

• Fat-soluble vitamins include vitamins A, D, E, and K.
• Fat-soluble vitamins play integral roles in a multitude of physiological processes, such as vision, bone health, immune function, and coagulation.

Lipid Bilayer and Membrane Fluidity

• The lipid bilayer is a 2D array of amphipathic molecules that forms spontaneously and is very fluid.
• The lipid bilayer is formed from glycerophospholipids and sphingolipids.
• Cholesterol is present in the lipid bilayer, which restricts lipid movement and serves as a fluidity buffer.

Lipid Bilayer Translocation

• Lipids move laterally easily while lipid movement between layers is less frequent.
• Lipid movement between layers may require protein for translocation.
• Interleaflet movement is essential for asymmetry.

Lipid Bilayer Asymmetry

• The two leaflets in the bilayer are not identical.
• Some lipids have to do with the orientation of lipid-synthesizing enzymes.
• Some lipids have to do with translocases or "flippases".
• The function of the membrane is more than just as a "cell sack".

Factors Affecting Melting Temperature

• The degree of saturation affects the melting temperature.
• The chain length affects the melting temperature.

Cellular Membranes

• Glucose transport works by a rocker mechanism.
• Glucose binds on one side, eliciting a conformational change, which exposes the molecule to the other side.
• Glucose transport moves in either direction and is an example of facilitated (passive) transport.

Primary and Secondary Active Transport

• Active transport requires energy input and moves against the gradient.
• The Na, K-ATPase reaction cycle hydrolyzes 1 ATP to pump 3Na+ ions out of the cell and 2 K+ ions inside the cell.

Secondary Active Transporter

• The piggyback mechanism uses an established gradient to transport material.
• Symporters can move glucose into the cell with Na+.
• The Na+ gradient is already established by the Na+/K+ ATPase.

ABC (ATP-Binding Cassette) Transporters

• ABC transporters are composed of two membrane-integral domains and two ATP-hydrolyzing domains.
• ABC transporters use ATP to transport material into the cell.
• ABC transporters transport material against its gradient.

Acetylcholine Release

• Acetylcholine (ACh) is a neurotransmitter stored in synaptic vesicles.
• When a nerve impulse reaches the axon terminal, Ca2+ ions from the ECF enter the cell, and ACh is released.

Polysaccharides

• Polysaccharides are common fuel-storage molecules.
• Polysaccharides can be joined in a variety of ways.
• Tremendous repertoire of complex molecules.

Glycoproteins and Glycolipids

• Glycoproteins and glycolipids are polysaccharides attached to proteins or lipids.
• Amylopectin is a polymer present in starch.
• Glycogen is a polymer that resembles amylopectin, but with branches every 12 residues.

Structural Carbohydrates

• Cellulose is a glucose polymer formed between #1 and #4C atoms.
• Cellulose is a rigid and strong structure that provides rigidity and strength for plant cell walls.

Disaccharides

• Disaccharides occur in nature most commonly as breakdown products of polysaccharides.
• Animals do not make cellulose and most cannot digest it.
• Microbes do, and normal microflora for ruminants.

O-Glycosylation

• O-glycosylation is a highly specific process that gives tremendous variety and specificity to molecules.
• O-glycosylation tends to be built one residue at a time in the Golgi apparatus.

Purpose of Glycosylation

• The purpose of glycosylation is to:
  • 1. Provide a specific signal for protein targeting
  • 2. Regulate protein function
  • 3. Modify the immune response
  • 4. Modulate cell-cell interactions
  • 5. Influence the degradation of proteins