Amino Acids Overview

Amino Acids

• The basic building blocks of proteins
• Contain an amino group (NH2), a carboxyl group (COOH), a hydrogen atom (H), and a side chain (R group)
• Side chains determine chemical properties
• Side chain properties include polarity, hydrophobic/hydrophilic, acidic/basic
• Amino acid properties determine how they behave within a polypeptide chain

Amino Acid Properties

• Non-polar hydrophobic (water-hating): glycine, alanine, valine, leucine, isoleucine, methionine, proline, phenylalanine, tryptophan
• Polar hydrophilic (water-loving): serine, threonine, tyrosine, cysteine, asparagine, glutamine
• Basic (positive charge): lysine, arginine, histidine
• Acidic (negative charge): aspartic acid (aspartate), glutamic acid (glutamate)

Additional Amino Acid Characteristics

• Small amino acids: glycine and alanine
• Branched amino acids: valine, leucine, isoleucine
• Sulfur-containing amino acids: cysteine and methionine
• Amino acid found at a bend in a protein: proline
• Amino acids that can be phosphorylated: serine, threonine, tyrosine
• Amino acids that can be glycosylated: asparagine, serine, threonine
• Amino acid that can be nitrosylated: cysteine

Essential vs. Non-essential Amino Acids

• Essential amino acids cannot be synthesized in the body and must come from the diet: methionine, arginine, threonine, tryptophan, valine, isoleucine, leucine, phenylalanine, histidine
• Non-essential amino acids can be synthesized by the body: alanine, aspartic acid, asparagine, cysteine, glutamic acid, glycine, proline, serine, tyrosine, lysine, glutamine

Protein Structure

• Four levels: primary, secondary, tertiary, quaternary

Primary Structure

• Linear sequence of amino acids linked by peptide bonds
• Peptide bonds are formed between the carboxyl group of one amino acid and the amino group of the next.
• Chain has direction: amino terminus (N terminus) to carboxyl terminus (C terminus)

Secondary Structure

• Regular, repetitive folding pattern stabilized by hydrogen bonds
• Two main types: alpha helix and beta pleated sheet
• Examples: alpha helix - collagen, keratin (hair), beta sheet - silk

Tertiary Structure

• Further folding of the polypeptide chain to form a globular structure.
• Stabilized by various bonds and interactions between side chains: disulfide bonds, hydrophobic interactions, ionic bonds, hydrogen bonds
• Determines the unique 3D structure and biological function of the protein

Quaternary Structure

• Arrangement of multiple polypeptide chains (subunits) in a multi-meric protein
• Subunits can be identical or different
• Held together by non-covalent interactions, inter-chain disulfide bonds
• Example: Hemoglobin

Native Conformation

• The functional, fully folded three-dimensional structure of a protein
• Determined by primary, secondary, tertiary, and sometimes quaternary structure
• Determines biological function: catalysis, protection, regulation, signal transduction, storage, transport

Denaturation

• Loss of the native conformation of a protein, leading to loss of function
• Can be caused by heat, pH changes, detergents, or heavy metals

Post-translational Modifications (PTM)

• Chemical modification of a protein after translation
• Involved in increasing protein diversity and function
• Examples: phosphorylation (addition of phosphate), glycosylation (addition of sugar), acylation (addition of fatty acid), ubiquitination (addition of ubiquitin), nitrosylation (addition of nitric oxide)

Carbohydrates

• Molecules made up of carbon (C), hydrogen (H), and oxygen (O) atoms
• Classified based on the number of monosaccharide units: monosaccharide (single unit), disaccharide (two units), oligosaccharide (few units), polysaccharide (many units)
• Can be associated with proteins (glycoproteins) or lipids (glycolipids)

Monosaccharides

• Simple sugar units with the empirical formula (CH2O)n, where n represents the number of carbon atoms.
• Can be classified based on the number of carbon atoms: triose (3 carbons), pentose (5 carbons), hexose (6 carbons)
• Polyhydroxy aldehydes (aldoses) or ketones (ketoses)
• Examples of hexoses: glucose, fructose, galactose, mannose

Glucose

• An aldose (aldehyde)
• Major source of energy in the body
• Found in fruit juices, starch, glycogen, lactose, maltose, and cane sugar

Fructose

• A ketose (ketone)
• Found in fruit juices, honey, and cane sugar

Monosaccharide Cyclisation

• Monosaccharides tend to form ring structures
• Cyclisation involves the reaction of the carbonyl group (C=O) with a hydroxyl group (OH) within the same molecule
• In aldoses, the carbonyl carbon (C1) becomes the anomeric carbon after cyclisation
• In ketoses, the carbonyl carbon (C2) becomes the anomeric carbon after cyclisation
• Anomeric carbon has two possible configurations: alpha (α) and beta (β) based on the position of the hydroxyl group

Disaccharides

• Two monosaccharide units linked together by a glycosidic bond

Glycosidic Bond

• A covalent bond between monosaccharides
• Formed via a condensation reaction involving the hydroxyl group of one monosaccharide and the anomeric carbon of another
• Named based on the numbers of the connected carbons and the position of the anomeric hydroxyl group (α or β)
• Example: Lactose - β-galactose + glucose, linked by a β(1→4) glycosidic bond

Polysaccharides

• Polymers consisting of many monosaccharide units linked together by glycosidic bonds
• Classified based on the type of glycosidic bond and branching patterns
• Example: Amylopectin, a branched polysaccharide with α(1→4) and α(1→6) glycosidic bonds

Polysaccharide Functions

• Storage: starch (in plants) and glycogen (in animals)
• Structure: cellulose (in plants) and chitin (in invertebrates)

Lipids

• A diverse group of water-insoluble (hydrophobic) organic molecules
• Major source of energy, structural components of cells and organelles, involved in cellular signaling

Classification of Lipids

• Fatty acids and their derivatives: prostaglandins, leukotrienes
• Lipids containing glycerol: neutral lipids (mono-, di-, tri-acylglycerol or triglycerides), charged lipids (phospholipids)
• Lipids not containing glycerol: steroids, sphingolipids, terpenoids
• Lipoproteins and lipopolysaccharides

Fatty Acids

• Long-chain carboxylic acids
• Classified based on chain length, saturation (presence or absence of double bonds), and position of double bonds
• Example: 18:1(Δ9) - oleic acid (18 carbons, one double bond at carbon 9 relative to the carboxyl carbon)

Acylglycerides (Triglycerides)

• Esters of glycerol with one, two, or three fatty acids
• Major form of energy storage in the body
• Commonly known as fat

Phospholipids

• Lipids with a phosphate group attached to a glycerol backbone
• Important components of cell membranes

Sphingolipids

• Lipids based on the sphingosine backbone
• Found in cell membranes and involved in signal transduction

Steroids

• Lipids with a characteristic four-ring structure
• Examples: cholesterol, sex hormones, and corticosteroids

Lipoproteins

• Complexes of lipids and proteins
• Involved in the transport of lipids in the blood

Arachidonic Acid

• Arachidonic acid is a 20-carbon chain fatty acid with four double bonds at carbons 5-6, 8-9, 11-12, and 14-15.
• Classified as an omega-6 (ω-6) fatty acid due to the terminal double bond being located six bonds from the omega carbon.

Essential Fatty Acids

• Essential fatty acids (EFAs) cannot be synthesized by our bodies and must be obtained from the diet.
• Linoleic acid (ω-6) is an EFA with the chemical formula CH3(CH2)4(CH=CHCH2)2(CH2)6COOH and is 18:2(n-6).
• α-Linolenic acid (ω-3) is another EFA with the chemical formula CH3CH2(CH=CHCH2)3(CH2)6COOH and is 18:3(n-3).
• EFA deficiency can lead to:
  • Scaly dermatitis (ichthyosis)
  • Visual and neurological abnormalities

Signaling Fatty Acids

• Eicosanoids are a group of signaling molecules derived from 20-carbon polyunsaturated fatty acids (PUFAs).
• Prostaglandins (PG) are an eicosanoid family synthesized from arachidonic acid via cyclooxygenase (COX).
  • Short half-life (seconds)
  • Involved in inflammation and platelet homeostasis.
• Leukotrienes are another eicosanoid family synthesized from arachidonic acid via lipoxygenase (LOX).
  • Longer half-life (up to 4 hours)
  • Multiple roles, including inflammatory responses and neutrophil adhesion.

Monoacyl, Diacyl, and Triacylglycerols

• Monoacylglycerol is a breakdown product of triacylglycerol (TAG) during fat digestion.
• Diacylglycerol (DAG) is a potent intracellular signaling molecule involved in calcium mobilization.
• Triacylglycerol (TAG) is the primary storage form of energy in the body.
  • Composed of three fatty acids and glycerol.
  • Stored in adipose tissue.

Phospholipids and Sphingolipids

• Phospholipids, also known as phosphoglycerates, are major components of cell membranes.
  • Example: Lecithin

Steroids

• Steroids contain a characteristic fused ring system with a hydroxyl or keto group on carbon 3.
• Major steroid classes:
  • Cholesterol (27 carbons)
  • Bile acids (24 carbons)
  • Progesterone and adrenocortical steroids (21 carbons)
  • Androgens (19 carbons)
  • Estrogens (18 carbons)
• Functions of cholesterol:
  • Metabolic precursor to:
    • Vitamin D
    • Bile acids
    • Steroid hormones.
  • Plays a vital role in membrane structure.
  • A constant supply of cholesterol is needed.

### Lipoproteins

• Spherical particles found in plasma that transport lipids, including cholesterol.
• Have a hydrophobic core of triacylglycerols and cholesteryl esters surrounded by a phospholipid layer.

Amino Acids & Protein Structure

• The basic structure of an amino acid consists of a central carbon atom bound to an amino group, a carboxyl group, a hydrogen atom, and a side chain (R group).
• R groups vary in composition and properties, affecting the amino acid's polarity, hydrophobicity/hydrophilicity, and charge at neutral pH.
• Amino acid properties determine how they will behave within a polypeptide.

Amino Acid Characteristics

• Non-polar, hydrophobic: Glycine, Alanine, Valine, Leucine, Isoleucine, Methionine, Proline, Phenylalanine, Tryptophan
• Polar, hydrophilic: Serine, Threonine, Tyrosine, Asparagine, Glutamine, Cysteine
• Basic, positively charged: Lysine, Arginine, Histidine
• Acidic, negatively charged: Aspartic acid (Aspartate), Glutamic acid (Glutamate)

Essential vs. Non-Essential Amino Acids

• Essential amino acids: Cannot be synthesized by the body and must be obtained from the diet (e.g., Methionine, Arginine, Threonine, Tryptophan, Valine, Isoleucine, Leucine, Phenylalanine, Histidine, Lysine).
• Non-essential amino acids: Can be synthesized by the body (e.g., Alanine, Aspartic acid, Asparagine, Cysteine, Glutamic acid, Glycine, Proline, Serine, Tyrosine, Glutamine).

Protein Structure

• Primary structure: Linear sequence of amino acids linked by peptide bonds.
• Secondary structure: Regular, repetitive folding patterns stabilized by hydrogen bonds (e.g., alpha helix, beta pleated sheet).
• Tertiary structure: Further folding of the polypeptide chain into a globular shape, stabilized by various bonds and interactions between side chains (e.g., disulfide bonds, hydrophobic interactions, ionic bonds, hydrogen bonds).
• Quaternary structure: The arrangement of multiple polypeptide chains (subunits) in a multimeric protein, held together by non-covalent interactions and disulfide bonds.

Native Conformation & Post-Translational Modifications

• Native conformation: The functional, fully folded protein structure with a unique 3D shape, determined by the primary, secondary, and tertiary (and sometimes quaternary) structure.
• Post-translational modifications (PTMs): Chemical modifications of a protein after translation, resulting in a change in protein function (e.g., phosphorylation, glycosylation, acylation, ubiquitination, nitrosylation).

Abnormal Protein Aggregates and Disease

• Misfolding of proteins can lead to the formation of amyloid fibrils.
• Amyloid deposition in different tissues can cause diseases (e.g., Alzheimer's Disease).

Carbohydrates (Saccharides)

• Molecules containing carbon, hydrogen, and oxygen atoms.
• Monosaccharide: Single sugar unit (e.g., glucose, fructose, galactose).
• Disaccharide: Two monosaccharides linked together (e.g., lactose, maltose).
• Oligosaccharide: A few linked monosaccharides.
• Polysaccharide: Many monosaccharides linked together (e.g., cellulose, glycogen).

Monosaccharide Properties

• Empirical formula: (CH2O)n, where n = 3 (triose), 5 (pentose), or 6 (hexose).
• Structural components: Polyhydroxy aldehydes (aldoses) or ketones (ketoses).

Hexoses (C6H12O6)

• Isomers: Same chemical formula but different structures (e.g., glucose, fructose, galactose, mannose).
• Dietary sources: Glucose (fruit juices, starch, glycogen, lactose, maltose, cane sugar), Fructose (fruit juices, honey, cane sugar), Galactose (milk), Mannose (plants and gums).

Cyclisation of Monosaccharides

• Monosaccharides form rings in solution.
• Anomeric carbon: The carbon involved in ring formation.
• Alpha (α) configuration: The -OH group on the anomeric carbon is down (fish in the sea).
• Beta (β) configuration: The -OH group on the anomeric carbon is up (bird in the sky).

Disaccharides & Glycosidic Bonds

• Glycosidic bond: Covalent bond formed between two monosaccharides via a condensation reaction.
• The name/type depends on the connected carbons and anomeric configuration (alpha or beta).
• Example: Lactose = β-galactose + glucose, linked by a β(1→4) glycosidic bond.

Polysaccharides

• Oligosaccharides: 3-12 monosaccharides.
• Polysaccharides: Hundreds of monosaccharides.
• Structure: Chain length, branching, and glycosidic bond variations.

Polysaccharide Functions

• Storage: Glycogen (animals), Starch (plants).
• Structure: Cellulose (plants), Chitin (invertebrates).

Lipids

• Water-insoluble (hydrophobic) organic molecules.
• Major source of energy, structural components of cells and organelles, involved in cellular signaling.

Classification of Lipids

• Fatty acids and their derivatives: Prostaglandins, leukotrienes.
• Lipids containing glycerol: Neutral lipids (mono-, di-, tri-acylglycerols), Charged lipids (phospholipids).
• Lipids not containing glycerol: Steroids, sphingolipids, terpenoids.
• Lipoproteins and lipopolysaccharides: Complexes of lipids and proteins or carbohydrates, respectively.

Fatty Acid Structure

• Chain length: Number of carbons in the chain.
• Double bonds: Number and positions of double bonds relative to the carboxyl carbon.

The Fed and Fasting States: Creating Energy

• Lipids play a crucial role in energy production during both the fed and fasting states.
• They are a major source of energy for the body.### Arachidonic Acid
• 20 carbon chain with 4 double bonds between carbons 5-6, 8-9, 11-12, and 14-15
• Classified as an ω-6 fatty acid because its terminal double bond is 6 carbons in from the ω carbon

Essential Fatty Acids (EFAs)

• We cannot synthesize EFAs so they are nutritionally essential
• Linoleic acid (ω-6)
  • Chemical formula: CH3(CH2)4(CH=CHCH2)2(CH2)6COOH
  • Shorthand notation: 18:2(n-6)
• α-linolenic acid (ω-3)
  • Chemical formula: CH3CH2(CH=CHCH2)3(CH2)6COOH
  • Shorthand notation: 18:3(n-3)
• EFA deficiency (rare)
  • Can cause scaly dermatitis (ichthyosis), visual, and neurologic abnormalities

Signalling Fatty Acids

• Prostaglandins (PGs) and Leukotrienes are part of the eicosanoid family synthesized from 20-carbon polyunsaturated fatty acids (PUFAs)
• Eicosanoid synthesis:
  • Prostaglandins: synthesized from arachidonic acid via cyclooxygenase (COX)
    • Short half-life (seconds)
    • Multiple roles, including inflammation and platelet homeostasis
  • Leukotrienes: synthesized from arachidonic acid via lipoxygenase (LOX)
    • Longer half-life (up to 4 hours)
    • Multiple roles, including inflammation and neutrophil adhesion

Monoacyl, Diacyl, and Triacylglycerol

• Monoacylglycerol
  • Breakdown product of triacylglycerol (TAG) during fat digestion
• Diacylglycerol (DAG)
  • Potent intracellular signaling molecule
  • Involved in mobilization of calcium
• Triglycerides (Triacylglycerols: TAG)
  • Composed of 3 fatty acids and glycerol
  • The primary storage form of energy in the body
  • Stored in adipose tissue

Phospholipids (Phosphoglycerates) and Sphingolipids

• Glycerophospholipids
  • A major component of cell membranes
  • Example: Lecithin

Steroids

• Characterized by a fused ring system with a hydroxyl or keto group on carbon 3
• Major steroid classes:
  • Cholesterol: (27 carbons)
  • Bile acids: (24 carbons)
  • Progesterone and adrenocortical steroids: (21 carbons)
  • Androgens: (19 carbons)
  • Estrogens: (18 carbons)

Cholesterol Functions

• Metabolic precursor of vitamin D, bile acids, and steroid hormones
• Plays a vital role in maintaining membrane structure
• The body requires a constant supply of cholesterol

Lipoproteins

• Spherical particles found in plasma that transport lipids, including cholesterol
• Contain a hydrophobic core of triacylglycerols and cholesteryl esters
• A phospholipid layer surrounds the core

Amino Acid Classification

• The chemical properties of amino acids depend on the nature of their side chain (R group).
• R groups can be:
  • Polar
  • Hydrophobic/philic (water hating/loving)
  • Acidic (H+ Donor) -ve at neutral pH
  • Basic (H+ Acceptor) +ve at neutral pH
• Amino acid properties determine their behaviour in a polypeptide.

Amino Acid Side Chain Properties

• Non-polar (hydrophobic) - Aliphatic (hydrocarbon chain) or Aromatic (ring structure)
  • Glycine
  • Alanine
  • Valine
  • Leucine
  • Isoleucine
  • Methionine
  • Proline
  • Phenylalanine
  • Tryptophan
• Polar (hydrophilic) - Neutral, Basic (positive charge), Acidic (negative charge)
  • Serine
  • Threonine
  • Asparagine
  • Glutamine
  • Tyrosine
  • Cysteine
  • Lysine
  • Arginine
  • Histidine
  • Aspartic acid (Aspartate)
  • Glutamic acid (Glutamate)

More Amino Acid Characteristics

• Small Amino Acids: Glycine and Alanine
• Branched Amino Acids: Valine, Leucine, Isoleucine
• Sulphur-containing Amino Acids: Cysteine and Methionine
• Amino Acid found at a Bend in a Protein: Proline
• Amino Acids that can be Phosphorylated: Serine, Threonine, and Tyrosine
• Amino Acids that can be Glycosylated: Asparagine, Serine, and Threonine
• Amino Acid that can be Nitrosylated: Cysteine

Essential and Non-essential Amino Acids

• Essential Amino Acids - Amino acids cannot be synthesised in the body and must come from the diet.
  • Methionine
  • Arginine*
  • Threonine
  • Tryptophan
  • Valine
  • Isoleucine
  • Leucine
  • Phenylalanine
  • Histidine
  • Lysine
• Non-essential Amino Acids - Amino acids that can be synthesised from other amino acids or precursors.
  • Alanine
  • Aspartic acid
  • Asparagine
  • Cysteine
  • Glutamic acid
  • Glycine
  • Proline
  • Serine
  • Tyrosine
  • Glutamine*
  • *Conditionally essential in children

Levels of Protein Structure

• Primary Structure - Amino acids formed into a polypeptide chain.
  • Amino acids linked together with peptide bonds.
  • Peptide bond is formed between the carboxyl group of one amino acid and the amino group of the next amino acid.
  • Peptide bond = C(O) - NH
  • Chain has direction:
    • Start = amino terminus = N terminus
    • End = carboxyl terminus = C terminus
• Secondary Structure - Regular repetitive folding pattern controlled by amino acid sequence.
  • Stabilised by hydrogen bonds.
  • Examples:
    • Alpha (a) helix: collagen, keratin in hair
    • Beta (b) pleated sheet: silk
• Tertiary Structure - Further folding of the polypeptide chain into a globular form.
  • Compact folded structure:
    • Hydrophobic AAs (amino acids) on the inside
    • Hydrophilic AAs on the outside
  • Stabilised by interactions between side chains of amino acids:
    • Disulphide bonds (between 2 cysteines)
    • Hydrophobic interactions
    • Ionic bonds
    • Hydrogen bonds
• Quaternary Structure - Arrangement of protein subunits in a multi-meric protein.
  • 3D arrangement of more than one tertiary polypeptide.
  • Consist of 2 or more polypeptide chains - may be the same or different.
  • Held together by:
    • Non-covalent interactions
    • Inter-chain disulphide bonds
  • Example: Hemoglobin

Native Conformation

• Functional fully folded protein structure.
• Unique three-dimensional structure determined by:
  • Primary structure
  • Secondary structure
  • Tertiary structure
  • Sometimes quaternary structure
• Determines the biological function of the protein:
  • Catalysis
  • Protection
  • Regulation
  • Signal transduction
  • Storage
  • Transport

Denaturation and Post-Translational Modifications (PTM)

• Denaturation - Loss of protein shape and function due to environmental changes like:
  • Heat
  • pH change
  • Chemicals
• Post-Translational Modifications (PTM) - Chemical modification of a protein after translation.
  • Functional group is attached to an amino acid.
  • Results in a change in protein function.
• Some Common PTM of Proteins:
  • Phosphorylation: + phosphate on serine and/or threonine or tyrosine residue = phosphoprotein
  • Glycosylation: + sugar group on asparagine or serine or threonine residues = glycoprotein
  • Acylation: + fatty acid
  • Ubiquitination: + ubiquitin = death signal
  • Nitrosylation: + NO (nitric oxide)

Abnormal Protein Aggregates and Disease

• Misfolded proteins can aggregate into fibrils (amyloid).
• Over 20 different proteins can form amyloid.
• Amyloid deposition in different tissues is associated with disease.
• Presence of misfolded proteins in the brain is linked to Alzheimer's Disease.

Carbohydrates

• Molecules that contain Carbon (C), Hydrogen (H), and Oxygen (O) atoms.
• Monosaccharide: Single saccharide unit
• Disaccharide: 2 linked monosaccharides
• Oligosaccharide: A few linked monosaccharides - can be associated with proteins (glycoproteins) or lipids (glycolipids).
• Polysaccharides: Consists of many monosaccharides linked together, examples:
  • Cellulose
  • Glycogen

Monosaccharides

• Simple sugar units.
• Empirical formula = (CH2O)n where n = 3 - 7 carbons.
  • n = 3 carbons: triose
  • n = 5 carbons: pentose
  • n = 6 carbons: hexose
• They are poly-hydroxy aldehydes (aldose) or ketones (ketose).

Hexoses (C6H12O6)

• Isomers: Same chemical formula but different structures.
  • Examples:
    • Glucose: Aldo group - Fruit juices, starch, glycogen, lactose, maltose, cane sugar
    • Fructose: Keto group - Fruit juices, honey, cane sugar
    • Galactose: Found in milk (lactose)
    • Mannose: Found in plants and gums

Monosaccharide Cyclisation

• Aldoses: Cyclisation happens at carbon 1 (C1). C1 in a cyclised aldose = anomeric carbon.
• Ketoses: Cyclisation happens at carbon 2 (C2).
• Alpha (a) anomeric carbon: OH group is down (fish in the sea)
• Beta (b) anomeric carbon: OH group is up (bird in the sky)

Disaccharides & Glycosidic Bonds

• Bond between 2 sugars.
• Bond type depends on:
  • Connected carbon numbers
  • Position of the anomeric hydroxyl group
• Alpha (a) bond: OH group is in the alpha configuration.
• Beta (b) bond: OH group is in the beta configuration.
• Example: Lactose = b-galactose + glucose
  • Bond is between carbon 1 of b-galactose and carbon 4 of glucose: condensation event
  • Bond (linkage) is b (1→ 4) glycosidic bond

Polysaccharides

• Oligosaccharides: n = 3-12 monosaccharides
• Polysaccharides: n > 12 - hundreds of monosaccharides.
• Variations in chain structure can occur:
  • Monosaccharides
  • Glycosidic bonds
  • Branch points
  • Structure
• Example: Amylopectin
  • Branched every 24-30 residues
  • (1-4, 1-6)

Polysaccharide Functions

• Storage in animals:
  • Glycogen: A homopolymer of glucose. Branched every 12-14 residues (1-4, 1-6)
• Storage in plants:
  • Starch: A homopolymer of glucose:
    • Amylopectin (80-85%): Branched every 24-30 residues (1-4, 1-6)
    • Amylose (15-20%): Non-branched helical structure (1-4)
• Structure in plants:
  • Cellulose: Homopolymer of glucose. Long straight chains (β1-4)
• Structure in invertebrates:
  • Chitin: Homopolymer of n-acetyl-glucosamine

Lipids - General Properties

• Heterogeneous group of water-insoluble (hydrophobic) organic molecules.
• Functions:
  • Major source of energy in the body
  • Structural components of cells and organelles
  • Involved in cellular signaling events, e.g. steroids, prostaglandins, leukotrienes

Lipid Classification

• Fatty Acids and their Derivatives:
  • Prostaglandins
  • Leukotrienes
• Lipids containing glycerol:
  • Neutral lipids: mono-, di-, tri-acylglycerol (triglycerides)
  • Charged lipids: Phospholipids
• Lipids Not containing glycerol:
  • Steroids
  • Sphingolipids
  • Terpenoids
• Lipoproteins and lipopolysaccharides

Fatty Acid Chain Lengths

• Number before colon: Number of carbons in chain
• Number after colon: Numbers and positions of double bonds relative to carboxyl carbon
• Example:
  • 18:2 - 18 carbon chain with 2 double bonds
  • 16:0 - 16 carbon chain with 0 double bonds### Arachidonic Acid
• A 20-carbon chain fatty acid with 4 double bonds.
• Classified as an omega-6 fatty acid due to its terminal double bond being 6 bonds away from the omega carbon

Essential Fatty Acids (EFAs)

• Cannot be synthesized by the body, so they are essential for human health
• Linoleic acid (omega-6): 18:2(n-6); plays a key role in various bodily functions, including cell growth and development.
• Alpha-linolenic acid (omega-3): 18:3(n-3); crutial for brain function, vision, and cardiovascular health.
• EFA deficiency is rare but can lead to symptoms like scaly dermatitis and visual and neurological abnormalities.

Signalling Fatty Acids

• Prostaglandins (PG):
  • Part of the eicosanoid family synthesized from arachidonic acid.
  • Synthesized via cyclooxygenase (COX).
  • Short half-life (seconds)
  • Involved in inflammation, platelet homeostasis, and other important functions.
• Leukotrienes:
  • Also part of the eicosanoid family, synthesized from arachidonic acid.
  • Synthesized via lipoxygenase (LOX).
  • Longer half-life (up to 4 hours).
  • Play a variety of roles, including mediating inflammation and neutrophil adhesion.

Monoacyl, Diacyl, and Triacyl Glycerol

• Monoacyl glycerol:
  • A breakdown product of triglycerides during fat digestion.
• Diacylglycerol (DAG):
  • A potent intracellular signaling molecule involved in the mobilization of calcium.
• Triglycerides (Triacylglycerols: TAG):
  • Composed of three fatty acids and a glycerol molecule.
  • The primary form of energy storage in the body.
  • Stored in adipose tissue.

Phospholipids

• Major components of cell membranes.
• Glycerophospholipids:
  • A type of phospholipid, with lecithin being a common example.

Sphingolipids

• A class of lipids that play a role in cell signaling and membrane structure.

Steroids

• Characterized by a fused ring system with a hydroxyl or keto group on carbon 3.
• Major steroid classes:
  • Cholesterol:
    • Contains 27 carbon atoms.
    • Plays a crucial role in membrane structure and acts as a metabolic precursor for vitamin D, bile acids, and steroid hormones.
  • Bile acids:
    • Contain 24 carbons.
  • Progesterone and adrenocortical steroids:
    • Contains 21 carbons.
  • Androgens:
    • Contains 19 carbons.
  • Estrogens:
    • Contains 18 carbons.

Lipoproteins

• Spherical particles found in plasma that transport lipids, including cholesterol.
• Have a hydrophobic core of triacylglycerols and cholesteryl esters.
• A phospholipid layer surrounds the core and is associated with proteins.

Explore the fundamental building blocks of proteins through this quiz on amino acids. Learn about their structures, properties, and classifications, including polar, non-polar, acidic, and basic amino acids. This quiz will test your knowledge on the various characteristics and functions of amino acids in polypeptides.