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, galactose).

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

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

Example: Glucose is a monosaccharide; sucrose is a disaccharide composed of glucose and fructose.

Stereoisomers, Optical Isomers, and Enantiomers

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

• Optical Isomers (Enantiomers): Molecules that are non-superimposable mirror images of each other.

• Chiral Carbon: A carbon atom attached to four different groups, resulting in chirality.

• Chiral vs. Achiral Compounds: Chiral compounds have at least one chiral carbon; achiral compounds do not.

Example: D- and L-glucose are enantiomers; their structures are mirror images and not superimposable.

Classification of Monosaccharides

Monosaccharides are classified by:

• Number of Carbon Atoms: Triose (3C), tetrose (4C), pentose (5C), hexose (6C), etc.

• Type of Carbonyl Group: Aldose (aldehyde group), ketose (ketone group).

• Combined Classification: e.g., aldotriose, ketotetrose.

Example: Glucose is an aldohexose; fructose is a ketohexose.

D and L Enantiomers of Monosaccharides

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

Haworth Projections and Anomers

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

• α (alpha) and β (beta) Anomers: Differ in the position of the -OH group on the anomeric carbon.

• Free Anomeric Carbon: If the anomeric carbon's oxygen is attached to a hydrogen, it is considered free (reducing sugar).

Important Monosaccharides

Important Disaccharides

Important Polysaccharides

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: No free anomeric carbon (e.g., sucrose).

Chapter 15: Lipids

General Properties of Lipids

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

Classification of Lipids

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

• Steroids: Lipids with a characteristic four-ring structure (e.g., cholesterol).

Fatty Acids

• Saturated Fatty Acids: No double bonds; straight chains; solid at room temperature.

• Monounsaturated Fatty Acids: One double bond.

• Polyunsaturated Fatty Acids: Two or more double bonds; essential fatty acids are polyunsaturated.

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

Example: Oleic acid is a monounsaturated fatty acid with a cis double bond.

Differences Between Saturated and Unsaturated Fatty Acids

• Saturated: Higher melting points, solid at room temperature, found in animal fats.

• Unsaturated: Lower melting points, liquid at room temperature, found in plant oils.

Triacylglycerols (Triglycerides)

Esters formed from glycerol and three fatty acids (triester). Both fats and oils are triacylglycerols.

• 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: Splitting with water to yield glycerol and fatty acids.

• Saponification: Hydrolysis with base to produce glycerol and soap (salts of fatty acids).

Steroids

Steroids have a core structure of four fused rings. Cholesterol is a key steroid, serving as a precursor for bile salts and steroid hormones.

• Cholesterol: Contains hydroxyl, alkyl, and double bond functional groups.

• Bile Salts: Derived from cholesterol; aid in fat digestion.

Comparison of Triacylglycerols, Fatty Acids, and Steroids

Chapter 16: Proteins

Amino Acids

Amino acids are the building blocks of proteins. Each contains a central (α) carbon attached to:

• Amino group (-NH2)

• Carboxyl group (-COOH)

• Hydrogen atom

• Variable "R" group (side chain)

Example: In glycine, the R group is a hydrogen atom.

Classification of Amino Acids by R Group

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

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

• Polar Acidic: Side chains with carboxyl 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 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: Formed 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: Found in collagen; three polypeptide chains wound together.

Hydrogen bonding is the main force stabilizing secondary structures.

Tertiary Structure

• Three-dimensional folding of a single polypeptide chain.

• Stabilized by interactions between R groups: hydrophobic, hydrophilic, ionic, hydrogen bonds, and disulfide bridges.

Quaternary Structure

• Association of two or more polypeptide chains (subunits).

• Difference from Tertiary: Tertiary is the 3D structure of one 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; most are 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 in DNA, ribose in RNA.

• Phosphoric Acid: Forms the backbone of nucleic acids.

Differences Between DNA and RNA

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 sequence is transcribed from DNA, replacing T with U.

Example: DNA: 5'-ATGC-3' pairs with 3'-TACG-5'; RNA transcript: 5'-AUGC-3'.

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.

• Each strand serves as a template for a new complementary strand.

RNA and Types of RNA

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

• tRNA (transfer RNA): Brings amino acids to ribosomes 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 using the genetic code.

Genetic Code: Triplet codons in mRNA specify amino acids.

Mutations

• Changes in the DNA sequence.

• Types: Substitution, insertion, deletion, frameshift, silent, missense, nonsense.