Biomolecules: Carbohydrates and Protein

Biological Polymers

Carbohydrates, nucleic acids, and lipids are polymers built from monomer units. They are synthesized through dehydration synthesis and broken down by hydrolysis, with enzymes aiding both processes.

Monosaccharides

Single sugar molecules with carbon backbones, carbonyl, and hydroxyl groups (e.g., glucose, fructose). In water, they form ring structures; glucose is the main fuel for cellular respiration.

α-glucose vs β-glucose

In α-glucose, the OH group on carbon-1 is below the ring (digestible by animals). In β-glucose, the OH is above the ring (indigestible by animals, more durable).

Polysaccharides

Long chains of monosaccharides linked by glycosidic bonds. Examples: starch, glycogen, cellulose, and chitin.

Starch and Glycogen

Both made of α-glucose; helical, energy storage polysaccharides. Starch (plants) and glycogen (animals) are easily digested.

Cellulose

Structural polymer of β-glucose; forms microfibrils in plant cell walls. Linear, strong hydrogen bonding; indigestible by most animals.

Chitin

Polymer of β-glucose with nitrogen groups; forms exoskeletons of arthropods and fungal cell walls; hydrophobic and strong.

Energy Storage vs Structure (Animals vs Plants)

Energy storage: Glycogen (animals), Starch (plants). Structure: Chitin (animals), Cellulose (plants).

Blood Group Antigens

Carbohydrate-based cell surface markers that identify self vs foreign cells; essential for matching blood types.

Glycolysis

Universal 10-step pathway using the same 10 enzymes in all eukaryotes to metabolize glucose.

Disaccharides

Two monosaccharides joined via dehydration forming a glycosidic linkage (e.g., maltose, sucrose, lactose).

Protein Functions

Enzymatic – catalyze reactions; Defensive – antibodies; Storage – amino acids; Transport – hemoglobin; Hormonal – insulin; Receptor – nerve signals; Contractile/Motor – cilia/flagella; Structural – keratin/collagen.

Amino Acids

Monomers with an amino group, carboxyl group, hydrogen atom, and R-group (side chain). R-groups can be nonpolar, polar, or charged (acidic/basic).

Polypeptides

Chains of amino acids linked by peptide bonds. The polypeptide backbone is formed through dehydration synthesis.

Protein Shape and Function

Function depends on 3D shape determined by amino acid sequence. Proteins can be globular (spherical) or fibrous (elongated).

Primary Structure

Linear amino acid sequence determined by genetic information. Dictates all higher protein structure.

Secondary Structure

Coils and folds from hydrogen bonding in the backbone; forms α-helices and β-pleated sheets.

Tertiary Structure

Overall 3D shape from side-chain interactions: hydrophobic interactions, hydrogen bonds, ionic bonds, disulfide bridges.

Quaternary Structure

Association of two or more polypeptides. Examples: Collagen (triple helix) and Hemoglobin (4 subunits with heme groups).

Chaperone Proteins

Assist folding by creating a hydrophilic environment for proper 3D shape formation.

Leventhal’s Paradox

There are ~10^300 possible protein conformations; proteins fold spontaneously to their lowest energy state.

Misfolded Proteins

Lead to diseases like Alzheimer’s and Cystic Fibrosis when folding goes wrong.

Sickle Cell Mutation

Single amino acid change (glutamic acid → valine) in hemoglobin changes structure, causing red blood cells to clump and reduce oxygen flow.