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Comprehensive Study Notes: Carbohydrates, Lipids, Proteins, and Nucleic Acids

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  • ense.Chapter 13: Carbohydrates

    Types of Carbohydrates

    Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They are classified based on the number of sugar units present.

    • Monosaccharides: Simple sugars containing a single sugar unit (e.g., glucose, fructose).

    • Disaccharides: Composed of two monosaccharide units joined by a glycosidic bond (e.g., sucrose, lactose).

    • Polysaccharides: Large molecules formed by the polymerization of many monosaccharide units (e.g., starch, cellulose).

    Example: Glucose (monosaccharide), maltose (disaccharide), amylose (polysaccharide).

    Stereoisomers and Chirality

    Stereoisomers are compounds with the same molecular formula and sequence of bonded atoms, but different three-dimensional orientations.

    • Optical isomers (enantiomers): Non-superimposable mirror images due to the presence of a chiral carbon.

    • Chiral carbon: A carbon atom attached to four different groups.

    • Achiral compound: A molecule that is superimposable on its mirror image.

    Example: D- and L-glucose are enantiomers.

    Classification of Monosaccharides

    • By number of carbons: Triose (3C), tetrose (4C), pentose (5C), hexose (6C), etc.

    • By carbonyl group: Aldose (aldehyde group), ketose (ketone group).

    • Combined: Aldotriose (e.g., glyceraldehyde), ketotetrose (e.g., erythrulose).

    D and L Enantiomers

    Monosaccharides exist as D- and L- forms, based on the configuration around the chiral carbon farthest from the carbonyl group. Only D-sugars are commonly found in nature.

    Haworth Projections and Anomers

    Haworth projections represent the cyclic structure of monosaccharides. The anomeric carbon is the carbon derived from the carbonyl group during ring formation.

    • α-anomer: The OH group on the anomeric carbon is trans to the CH2OH group.

    • β-anomer: The OH group on the anomeric carbon is cis to the CH2OH group.

    • Free anomeric carbon: If the anomeric carbon's OH is not involved in a glycosidic bond, it is considered free.

    Important Monosaccharides

    Name

    Carbons

    Chiral Carbons

    Aldose/Ketose

    D/L

    Glucose

    6

    4

    Aldose

    D

    Fructose

    6

    3

    Ketose

    D

    Galactose

    6

    4

    Aldose

    D

    Important Disaccharides

    Name

    Monosaccharide Components

    Glycosidic Bond

    Reducing/Nonreducing

    Maltose

    Glucose + Glucose

    α(1→4)

    Reducing

    Lactose

    Glucose + Galactose

    β(1→4)

    Reducing

    Sucrose

    Glucose + Fructose

    α,β(1→2)

    Nonreducing

    Important Polysaccharides

    Name

    Monosaccharide Component

    Glycosidic Bond

    Branched?

    Digestible?

    Amylose

    Glucose

    α(1→4)

    No

    Yes

    Amylopectin

    Glucose

    α(1→4), α(1→6)

    Yes

    Yes

    Glycogen

    Glucose

    α(1→4), α(1→6)

    Yes (more than amylopectin)

    Yes

    Cellulose

    Glucose

    β(1→4)

    No

    No (humans lack cellulase)

    Reducing and Nonreducing Sugars

    • Reducing sugars: Contain a free anomeric carbon capable of acting as a reducing agent (e.g., glucose, maltose, lactose).

    • Nonreducing sugars: Both anomeric carbons are involved in glycosidic bonds (e.g., sucrose).

    Chapter 15: Lipids

    General Properties and Classification

    Lipids are a diverse group of hydrophobic, nonpolar molecules, insoluble in water but soluble in organic solvents.

    • Fatty acids: Long, straight-chain carboxylic acids with an even number of carbons.

    • Steroids: Lipids with a characteristic four-ring structure.

    Fatty Acids

    • Saturated fatty acids: No double bonds; straight chains (e.g., stearic acid).

    • Monounsaturated fatty acids: One double bond (e.g., oleic acid).

    • Polyunsaturated fatty acids: Two or more double bonds (e.g., linoleic acid).

    • Geometric isomerism: Naturally occurring unsaturated fatty acids are usually cis-isomers.

    • Essential fatty acids: Polyunsaturated fatty acids that must be obtained from the diet (e.g., linoleic acid, α-linolenic acid).

    Triacylglycerols (Triglycerides)

    • Esters formed from glycerol and three fatty acids.

    • Fats: Solid at room temperature, higher in saturated fatty acids.

    • Oils: Liquid at room temperature, higher in unsaturated fatty acids.

    Chemical Properties of Triacylglycerols

    • Hydrogenation: Addition of hydrogen to unsaturated bonds, converting oils to fats.

    • Hydrolysis: Breakdown into glycerol and fatty acids (e.g., during digestion).

    • Saponification: Hydrolysis with a base to produce soap and glycerol.

    Steroids

    • Characterized by a four-fused ring structure.

    • Cholesterol: Contains hydroxyl, alkyl, and double bond functional groups; precursor to bile salts and steroid hormones.

    Comparison Table

    Type

    Structure

    Function

    Triacylglycerols

    Glycerol + 3 fatty acids (ester bonds)

    Energy storage

    Fatty acids

    Long hydrocarbon chain + carboxylic acid

    Building blocks, energy

    Steroids

    Four fused rings

    Hormones, membrane structure

    Chapter 16: Proteins

    Amino Acids

    • Contain a central (α) carbon attached to an amino group (–NH2), carboxyl group (–COOH), hydrogen atom, and an R group (side chain).

    • The R group determines the identity and properties of the amino acid.

    Classification of Amino Acids

    • Nonpolar: Hydrophobic side chains (e.g., leucine).

    • Polar neutral: Uncharged polar side chains (e.g., serine).

    • Polar acidic: Side chains with carboxylic acid groups (e.g., aspartic acid).

    • Polar basic: Side chains with amino groups (e.g., lysine).

    Essential Amino Acids

    • Cannot be synthesized by the body; must be obtained from the diet.

    • Complete foods: Contain all essential amino acids (e.g., eggs, meat).

    • Incomplete foods: Lack one or more essential amino acids (e.g., most plant proteins).

    Protein Structure

    • Primary structure: Sequence of amino acids linked by peptide (amide) bonds.

    • Peptide bond: Amide linkage between the carboxyl group of one amino acid and the amino group of another.

    • N-terminus: Free amino group at one end of the peptide chain.

    • C-terminus: Free carboxyl group at the other end.

    • Dipeptide, tripeptide, tetrapeptide: Chains of 2, 3, or 4 amino acids, respectively.

    Secondary Structure

    • α-helix: Right-handed coil stabilized by hydrogen bonds.

    • β-sheet: Sheet-like arrangement stabilized by hydrogen bonds.

    • Triple helix: Three polypeptide chains woven together (e.g., collagen).

    • Hydrogen bonding is the main stabilizing force.

    Tertiary Structure

    • Three-dimensional folding due to interactions between R groups:

      • Hydrophobic interactions

      • Hydrophilic interactions

      • Disulfide bonds

      • Salt bridges

      • Hydrogen bonds

    Quaternary Structure

    • Association of two or more polypeptide chains.

    • Difference from tertiary: Tertiary is the folding of a single chain; quaternary involves multiple chains.

    Denaturation of Proteins

    • Loss of secondary, tertiary, or quaternary structure without breaking peptide bonds (primary structure remains intact).

    Enzymes

    • Biological catalysts, usually proteins.

    • Have optimum temperature and pH for activity.

    Chapter 17: Nucleic Acids

    Components of DNA and RNA

    • Bases: Purines (adenine, guanine), pyrimidines (cytosine, thymine in DNA; uracil in RNA).

    • Sugars: Deoxyribose (DNA), ribose (RNA).

    • Phosphoric acid: Forms the backbone via phosphodiester bonds.

    Differences Between DNA and RNA

    Feature

    DNA

    RNA

    Sugar

    Deoxyribose

    Ribose

    Bases

    A, T, G, C

    A, U, G, C

    Strands

    Double

    Single

    Function

    Genetic storage

    Protein synthesis, regulation

    Nucleoside and Nucleotide

    • Nucleoside: Base + sugar.

    • Nucleotide: Base + sugar + phosphate group.

    Nucleic Acid Sequence

    • DNA strands are complementary: A pairs with T, G pairs with C.

    • RNA: A pairs with U, G pairs with C.

    • Given a DNA sequence, the complementary strand can be written by base pairing rules.

    3’ Hydroxy End and 5’ Phosphate End

    • Nucleic acid strands have directionality: 5’ end (phosphate group), 3’ end (hydroxyl group).

    DNA Replication

    • Process by which DNA makes a copy of itself before cell division.

    RNA and Types of RNA

    • mRNA (messenger RNA): Carries genetic code from DNA to ribosome.

    • tRNA (transfer RNA): Brings amino acids to ribosome during translation.

    • rRNA (ribosomal RNA): Structural and catalytic component of ribosomes.

    Transcription and Translation

    • Transcription: Synthesis of RNA from a DNA template.

    • Translation: Synthesis of proteins from mRNA sequence.

    • Genetic code: Triplet codons in mRNA specify amino acids.

    Mutations

    • Changes in the DNA sequence.

    • Types: Substitution, insertion, deletion, frameshift, silent, missense, nons

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