Carbohydrates
Macromolecules that provide energy and structural support. Composed of carbon, hydrogen, and oxygen.
Subtypes
- Monosaccharides — simple sugars (glucose, fructose)
- Disaccharides — two sugars joined (sucrose, lactose)
- Polysaccharides — long chains (starch, glycogen, cellulose)
Key Functions
- Primary energy source (glucose)
- Structural support (cellulose in plants)
- Energy storage (glycogen in animals, starch in plants)
- Cell identity & communication (cell surface)
Monosaccharides
- Trioses — 3 carbon atoms
- Pentoses — 5 carbon atoms (ribose in RNA)
- Hexoses — 6 carbon atoms (glucose, galactose)
- Names typically end in -ose
Disaccharide Formation
- Dehydration reaction (water molecule released)
- Lactose = glucose + galactose (found in milk)
- Maltose = glucose + glucose (malt sugar)
- Sucrose = glucose + fructose (table sugar)
Key Definitions
Monosaccharide
The simplest form of sugar; cannot be broken down further by hydrolysis. Most common is glucose.
Dehydration Reaction
A chemical reaction that removes a water molecule (H₂O) to form a covalent bond between two monomers.
Polysaccharide
A long chain of monosaccharides linked by covalent bonds. May be branched or unbranched. Examples: starch, glycogen, cellulose, chitin.
Lipids
Hydrophobic molecules that store energy, form membranes, and serve as hormones. Insoluble in water.
Types of Lipids
- Fats (triglycerides) — energy storage
- Phospholipids — cell membrane structure
- Steroids — hormones, cholesterol
- Waxes — protective coatings (beeswax, leaf wax)
Fatty Acids
- Saturated — only single bonds, solid at room temp
- Unsaturated — one or more double bonds, liquid
- Chain length: 4–36 carbons (12–18 most common)
- Attached to glycerol via covalent bonds
Phospholipids
- Major component of plasma membrane
- Hydrophilic head (phosphate group)
- Hydrophobic tails (two fatty acid chains)
- Forms bilayer — tails face inward
Functions
- Long-term energy storage (fats)
- Insulation (thermal, electrical)
- Membrane structure (phospholipids)
- Hormone synthesis (steroids)
Key Definitions
Triglyceride
A fat molecule with a glycerol backbone and three fatty acid chains. Main form of energy storage in animals.
Hydrophobic
Water-repelling. Lipids are hydrophobic due to nonpolar carbon-carbon and carbon-hydrogen bonds.
Steroid
A lipid with four linked carbon rings. Examples include cholesterol and sex hormones. Hydrophobic despite not resembling other lipids.
Proteins
Most functionally diverse macromolecules. Polymers of amino acids with roles in structure, regulation, transport, and catalysis.
Protein Types
- Structural — collagen, keratin
- Enzymatic — catalyze chemical reactions
- Hormonal — insulin, regulates blood glucose
- Transport — hemoglobin carries oxygen
- Protective — antibodies (immune system)
Amino Acid Structure
- Central carbon atom
- Amino group (–NH₂)
- Carboxyl group (–COOH)
- Hydrogen atom
- R group — unique to each of 20 amino acids
Enzymes
- Biological catalysts — speed up reactions
- Break, rearrange, or form molecular bonds
- Example: salivary amylase breaks down starch
- Produced by living cells
Hormones
- Chemical signaling molecules
- Usually proteins or steroids
- Secreted by endocrine glands
- Regulate growth, metabolism, reproduction
Key Definitions
Amino Acid
The monomer of proteins. All 20 amino acids share the same fundamental structure but differ only in their R group.
Peptide Bond
The covalent bond formed between amino acids during protein synthesis (dehydration reaction).
Enzyme
A protein catalyst that speeds up biochemical reactions without being consumed. Highly specific to their substrate.
Nucleic Acids
Carry the genetic blueprint of life. DNA stores information; RNA transfers it to build proteins.
DNA vs RNA
- DNA — double helix, deoxyribose sugar, stores genes
- RNA — single strand, ribose sugar, transfers info
- DNA bases: A, T, G, C
- RNA bases: A, U, G, C (Uracil replaces Thymine)
Nucleotide Structure
- Nitrogenous base
- Pentose sugar (5-carbon)
- Phosphate group
- Nucleotides link to form polynucleotides
DNA Double Helix
- Two strands of nucleotides
- Strands bonded at bases via hydrogen bonds
- Phosphate-sugar backbone on the outside
- Coils into double spiral structure
Functions
- DNA — genetic information storage
- mRNA — carries instructions from DNA to ribosome
- tRNA — brings amino acids to ribosome
- ATP (adenosine triphosphate) — energy currency
Key Definitions
Nucleotide
The monomer of nucleic acids. Composed of a nitrogenous base, a pentose sugar, and a phosphate group.
Double Helix
The structure of DNA — two strands coiling around each other, held together by hydrogen bonds between complementary base pairs.
Complementary Base Pairing
A always pairs with T (in DNA) or U (in RNA); C always pairs with G.
Transport Mechanisms
How substances cross the plasma membrane — passive (no energy) or active (requires ATP).
Passive Transport (no ATP)
- Simple Diffusion — small nonpolar molecules
- Facilitated Diffusion — via channel/carrier proteins
- Osmosis — diffusion of water
- Moves from high → low concentration
Active Transport (needs ATP)
- Moves against concentration gradient (low → high)
- Requires protein pumps
- Na⁺/K⁺ pump — pumps 3 Na⁺ out, 2 K⁺ in
- Maintains electrochemical gradient
Endocytosis (into cell)
- Phagocytosis — "cell eating" (large particles)
- Pinocytosis — "cell drinking" (fluids)
- Receptor-mediated — specific ligand binding
- Forms vesicles from pinched membrane
Membrane Structure
- Phospholipid bilayer — selectively permeable
- Integral proteins — embedded in membrane
- Peripheral proteins — on inner/outer surface
- Hydrophobic core blocks polar molecules
Key Definitions
Concentration Gradient
The difference in concentration of a substance across a space. Molecules diffuse from high to low concentration.
Osmosis
The diffusion of water across a semipermeable membrane from a hypotonic (less solute) to hypertonic (more solute) solution.
Exocytosis
The process of vesicles fusing with the cell membrane to release contents outside the cell. Opposite of endocytosis.
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