Unit3Slides1

Major Types of Lipids

  • Fatty Acids

    • Components of other lipids and serve as signaling molecules

    • Commonly feature cis double bonds; trans bonds are rare in organisms

    • Inclusion of trans double bonds results in better alignment of fatty acid chains, leading to increased melting temperature and more solid-like behavior.

  • Triacylglycerols (Triglycerides)

    • Primary energy storage molecules in organisms

    • Composed of three fatty acids linked to glycerol

  • Glycerophospholipids

    • Major component of the cell membrane in eukaryotes and bacteria

  • Sphingolipids

    • Present in cell membranes and function as signaling molecules

Concept Questions

Fatty Acids

  • Statements:

    • A. Fatty acids are often used as building blocks for more complex lipids.

    • B. Fatty acids can be saturated, unsaturated, or polyunsaturated.

    • C. Double bonds in fatty acids are usually cis.

    • D. All of the above.

    • E. None of the above.

  • Answer: D. All of the above.

Triacylglycerols

  • Statement:

    • A. The modern name is triglycerides.

    • B. Three fatty acids are linked by glycerol.

    • C. All triacylglycerols are fats.

    • D. All of the above.

    • E. None of the above.

  • Answer: D. All of the above.

Glycerophospholipids

True or False Statements

  1. An alternate name is phospholipid.

    • True

  2. The two fatty acids are usually the same length and degree of saturation.

    • False (These can vary in saturation and length.)

  3. These are the primary components of cellular membranes.

    • True

Sphingolipids vs Glycerophospholipids

  • Sphingolipids:

    • Found predominantly in neurological tissue.

    • Built from sphingosine and may include saccharides as polar groups.

  • Glycerophospholipids:

    • Primarily composed of glycerol.

Isoprenoids and Steroids

  • Isoprenoids:

    • Composed of C5 isoprene units.

    • Include fat-soluble vitamins and hormones.

    • Heavily modified by oxidation/reduction processes.

  • Steroids:

    • Characterized by four fused rings.

    • Cholesterol, a key steroid, enhances the rigidity in cell membranes by being less flexible compared to fatty acids.

    • Note: While all steroids are isoprenoids, not all isoprenoids are steroids.

Lipid Classification for Vitamins

  • D Vitamins are classified as:

    • A. Fatty acid

    • B. Triacylglycerol

    • C. Glycerophospholipid

    • D. Steroid

    • E. Isoprenoid

    • F. They are not lipids

  • Correct classification would need to be confirmed based on specific vitamin structures, typically as isoprenoids.

Lipid Bilayers and Cell Membranes

  • Structure:

    • Lipid bilayer formed from glycerophospholipids and sphingolipids via the hydrophobic effect.

    • Cholesterol integrates into existing membranes affecting structure.

    • Not symmetric; inner and outer layers have distinct lipid compositions with different functions.

Fluid Mosaic Model of Membranes

  • Membranes are fluid, allowing lipid mobility.

  • Fluidity is influenced by saturated vs unsaturated fatty acids.

  • Lipid Rafts:

    • Clusters formed by covalent crosslinks or localized high cholesterol concentrations, influencing protein localization and interactions.

Regulation of Membrane Fluidity

  • Above T m (melting temperature), membranes exhibit liquid-crystalline properties.

  • Below T m, membranes become gel-like, leading to rigidity which can be detrimental to cell function.

  • Increased cis double bonds lower T m, enhancing fluidity; cholesterol modulates rigidity and transition range.

  • Cold-blooded animals adjust membrane lipid composition to ambient temperature changes.

Detergents and Membrane Interaction

  • Detergents disrupt bilayer organization by interacting with non-polar materials, leading to the formation of micelles around hydrophobic molecules.

  • Soap historically derived from treating triacylglycerols with sodium hydroxide, maintaining similar principles in modern formulations.

Monosaccharides: Structure and Classification

  • Monosaccharides are sugars that contain 3 to 6 carbons, a carbonyl group, and hydroxyl groups.

  • Types:

    • Aldoses: contain an aldehyde carbonyl.

    • Ketoses: contain a ketone carbonyl.

    • Epimers differ at only one stereocenter.

Cyclic Saccharides

  • In biological environments, 5- and 6-carbon sugars primarily exist in cyclic forms due to internal reactions with alcohols attacking carbonyls.

  • Conversion between linear and cyclic forms occurs, with β-d-glucose being the most stable configuration due to favorable equatorial positions of hydroxyl groups.

Modifications to Saccharides

  • Saccharides can be subjected to various modifications: reduction, oxidation, amination, and phosphorylation.

  • Formation of glycosides can prevent isomerization at the anomeric carbon position.

Disaccharides and Polysaccharides

  • Oligosaccharides typically use anomeric carbons to form glycosidic bonds.

  • Discern between reducing (free anomeric carbon) and non-reducing sugars.

  • Synthesis involves condensation reactions powered by UTP.

Structural Polysaccharides

  • Cellulose:

    • Composed of β-D-glucose polymers, providing structural supportvia hydrogen bonding.

  • Chitin:

    • Similar in structure to cellulose, found in the exoskeletons of invertebrates.

Energy Storage Polysaccharides

  • Starch:

    • Composed of α-linkages, easily accessible to digestive enzymes for rapid energy release.

    • Forms a more open structure compared to cellulose.

  • Glycogen:

    • α(1->6) branched polymer in animals, facilitated to rapid glucose release.

Nucleotides and Nucleic Acids

  • Nucleotides consist of three units: nitrogenous base, sugar (ribose or deoxyribose), and phosphate group.

  • Phosphate groups exist in mono, di, or tri configurations and are typically weak acids that are usually deprotonated.

  • Nucleic acids, built via phosphodiester bonds, are either DNA or RNA, distinguished by the sugar component.

DNA Structure and Function

  • DNA typically adopts a double helix structure.

  • Base pairing follows Watson-Crick rules: A pairs with T and C pairs with G.

  • The sequence of nucleotides is directional (5' to 3').

  • The stability of the double helix is enhanced by π-π interactions of stacked base pairs.

RNA Functions

  • RNA molecules serve multiple roles that vary from mRNA to tRNA and rRNA, aiding in translation and gene expression.

  • RNA has more functions than DNA due to its diverse structures and roles as carriers of information and functional molecules.

RNA Interference (RNAi)

  • A mechanism to silence genes, particularly in plants and other eukaryotic organisms, can be used for genetic engineering and therapeutic advancements.

  • Involves cleaving double-stranded RNA into small interfering RNA (siRNA), which subsequently targets mRNA for degradation.

Polymerase Chain Reaction (PCR)

  • PCR amplifies specific DNA sequences using DNA polymerase derived from thermophilic archaea, enabling the isolation of genes or specific DNA segments.

  • Mutations can be introduced in DNA sequences using primers with modified bases.

Peptides and Proteins

  • Peptide bonds form between amino acids through condensation reactions, leading to polypeptides and ultimately proteins characterized by specific functions.

  • Directionality of chains is vital, with sequences written from N-terminus to C-terminus.

Amino Acid Side Chains

  • Amino acids with specific side chains are classified as polar, non-polar, charged, and neutral.

  • The charge states of amino acids can change based on pH, influencing their behavior in biological systems.

  • Nomenclature for amino acids includes both three-letter and one-letter abbreviations to simplify references in biochemical contexts.