General Biology Study Notes: Macromolecules, Cells, and Membranes

Macromolecules

Definition and Types

Macromolecules are large molecules composed of smaller organic molecules called monomers. When monomers are joined together by covalent bonds, they form polymers.

• Monomers: Small, individual units of a macromolecule.

• Polymers: Large molecules, chains of monomers bonded together.

• Polymerization occurs via covalent bonding of monomers.

Polymer Principles

• Polymers are built from smaller units called monomers.

• Synthesis and breakdown of polymers usually involve water:

  • Dehydration (condensation) synthesis: Removes water to join monomers.

  • Hydrolysis: Adds water to break polymers into monomers.

• Many polymers can be built from a small set of monomers.

Carbohydrates

Overview

Carbohydrates are molecules built from monomer units with the chemical formula CH2O. They serve as energy sources and structural components.

• Three size categories: monosaccharide, disaccharide, polysaccharide.

Monosaccharides

• Smallest carbohydrates; serve as fuel and carbon sources.

• Often drawn as linear skeletons or ring forms in aqueous solutions.

• Examples: Glucose, Fructose.

Disaccharides

• Formed by joining two monosaccharides via dehydration synthesis.

• General reaction: $\text{Monosaccharide}_1 + \text{Monosaccharide}_2 \rightarrow \text{Disaccharide} + \text{H}_2\text{O}$

• Example: Sucrose (glucose + fructose).

Polysaccharides

• Result from many monosaccharides linked together.

• Serve as energy storage (e.g., glycogen, starch) or structural support (e.g., chitin, cellulose).

Storage Polysaccharides

• Starch: Plant storage, composed of glucose monomers.

• Glycogen: Animal storage, highly branched.

Lipids

Overview

Lipids are hydrophobic molecules, including fats, oils, and steroids. They store energy, provide insulation, and form cell membranes.

• Composed mainly of hydrocarbon chains.

• Types include triglycerides, phospholipids, and steroids.

Types of Lipids

• Triglycerides: Three fatty acids bonded to glycerol.

• Phospholipids: Major component of cell membranes; amphipathic (hydrophilic head, hydrophobic tail).

• Steroids: Four fused carbon rings; examples include cholesterol and hormones.

Saturated vs. Unsaturated Fatty Acids

• Saturated: Maximum number of hydrogen bonds; no double bonds.

• Unsaturated: One or more double bonds; can form more bonds.

Proteins

Amino Acids and Peptide Bonds

Proteins are polymers of amino acids. Amino acids are joined by peptide bonds formed via dehydration synthesis.

• Each protein has a unique combination of amino acids.

Levels of Protein Structure

• Primary: Sequence of amino acids.

• Secondary: H-bonds between amino and carbonyl groups; forms alpha helices and beta sheets.

• Tertiary: 3D folding due to R group interactions, disulfide bridges, ionic bonds, hydrophobic interactions.

• Quaternary: Multiple polypeptide subunits.

Denaturation

• Loss of protein's shape due to pH or temperature changes.

Nucleic Acids

Overview

Nucleic acids are polymers of nucleotides. They store and transmit hereditary information.

• Two major types: DNA and RNA.

Nucleotide Structure

• Phosphate group

• Sugar (ribose in RNA, deoxyribose in DNA)

• Nitrogenous base (purines and pyrimidines)

Polymerization

• Nucleotides are joined by phosphodiester linkages.

• Synthesis occurs from 5' to 3' direction.

DNA and RNA Structure

• DNA: Double helix, complementary base pairing (A-T, G-C).

• RNA: Single strand, uracil replaces thymine.

Cells

Definition and Types

Cells are the basic unit of life, containing all components necessary for chemical reactions. They are classified as prokaryotic or eukaryotic.

• Prokaryotic: No membrane-bound organelles; includes bacteria and archaea.

• Eukaryotic: Membrane-bound organelles; includes animals, plants, fungi, protists.

Cell Size

• Lower limit: All components must fit.

• Upper limit: Must regulate supplies adequately.

Plasma Membrane

• Selective barrier; composed of phospholipid bilayer.

Nucleus

• Control center; contains DNA.

• Double membrane system; contains chromatin and nucleolus.

Ribosomes

• Sites of protein synthesis.

• Free or bound to endoplasmic reticulum.

Endomembrane System

• Includes nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, plasma membrane.

• Components are connected or transfer materials via vesicles.

Endoplasmic Reticulum (ER)

• Rough ER: Protein synthesis (ribosomes attached).

• Smooth ER: Lipid synthesis, detoxification, carbohydrate metabolism.

Golgi Apparatus

• Finishes, sorts, and packages products of the cell.

• Cis face: Receives products from ER.

• Trans face: Ships materials to other parts of the cell.

Lysosomes

• Degrade "spent" organelles and food items; contain hydrolytic enzymes.

Vacuoles

• Storage areas for resources.

• Types: food vacuoles, contractile vacuoles (H2O), central vacuoles (plants).

Mitochondria and Chloroplasts

• Mitochondria: Site of most ATP synthesis.

• Chloroplasts: Site of carbohydrate synthesis in plants.

Cytoskeletal Elements

• Provide structural framework for the cell.

• Types: microfilaments, intermediate filaments, microtubules.

Organelles of Motility

• Flagellum: Moves the entire cell.

• Cilium: Moves things along the cell surface.

Extracellular Surfaces

• Composed of proteins, lipids, and sugars; form extracellular matrix for support, adhesion, movement, regulation.

Cell Communication

• Cells communicate via junctions:

  • Tight junctions: Prevent leakage.

  • Desmosomes: Fasten cells together.

  • Gap junctions: Provide cytoplasmic channels.

  • Plasmodesmata: Plant cell channels.

Membranes

What is a Membrane?

Membranes separate regions of a cell and maintain differing environments. The plasma membrane separates the internal and external environments.

Membrane Structure

• Lipids and proteins are the chief ingredients.

• Phospholipids form a bilayer with hydrophilic heads and hydrophobic tails.

• Proteins are embedded or attached to the bilayer.

Membrane Fluidity

• Maintained by hydrophobic/hydrophilic interactions.

• Phospholipids and proteins can move within the bilayer.

• Fluidity depends on chemical composition and structure.

Fluidity Influences Permeability

• Permeability: Movement of materials across a membrane.

• Hydrophobic portion is selectively permeable.

• Large polar molecules and charged molecules are repelled by the hydrophobic core.

Membrane Proteins

• May be fluid or anchored.

• Integral proteins span the bilayer; peripheral proteins reside on surfaces.

• Anchored proteins strengthen membranes.

Summary Table: Macromolecules

Macromolecule	Monomer	Bond Type	Main Function
Carbohydrate	Monosaccharide	Glycosidic	Energy, structure
Lipid	Fatty acid, glycerol	Ester	Energy storage, membranes
Protein	Amino acid	Peptide	Catalysis, structure, transport
Nucleic Acid	Nucleotide	Phosphodiester	Genetic information