Biochemistry (ATC)

Water's unique properties make life possible.

• Water is polar, allowing hydrogen bonding.
• It is the universal solvent for biological reactions.
• Cohesion, adhesion, and high heat capacity stabilize organisms.
• Its properties support transport and temperature regulation.

Proteins are built from amino acids and do most cellular work.

• Amino acids link by peptide bonds into chains that fold into shapes.
• Structure has four levels: primary, secondary, tertiary, quaternary.
• Enzymes are proteins that speed reactions by lowering activation energy.
• Enzyme function depends on shape and the active site.

Carbohydrates provide energy and structure.

• Built from monosaccharides (e.g., glucose) into di- and polysaccharides.
• Starch and glycogen store energy; cellulose provides structure.
• They are the body's quick energy source.
• Ratio of carbon, hydrogen, and oxygen defines them.

Nucleic acids store and express genetic information.

• DNA carries the genetic code as a double helix.
• Nucleotides (base, sugar, phosphate) are the building blocks.
• RNA helps translate genes into proteins.
• Base pairing (A-T, G-C) allows replication.

Lipids store energy and build membranes.

• Fats and oils are energy-dense (triglycerides).
• Phospholipids form the cell membrane bilayer.
• Steroids (e.g., cholesterol) serve as hormones and membrane components.
• Lipids are hydrophobic (water-fearing).

Membranes control movement in and out of cells.

• The phospholipid bilayer is selectively permeable.
• Passive transport (diffusion, osmosis) needs no energy.
• Active transport uses ATP to move against gradients.
• Membrane proteins act as channels and pumps.

Metabolism captures and uses energy.

• Catabolism breaks molecules down; anabolism builds them up.
• Cellular respiration converts glucose to ATP.
• Stages: glycolysis, Krebs cycle, and electron transport chain.
• ATP is the cell's energy currency.