General Biology Review Sheet: Key Concepts and Definitions

Biological Molecules and Structures

Polysaccharides

Polysaccharides are large carbohydrate molecules formed by the linkage of multiple monosaccharide units. They serve structural and energy storage roles in cells.

• Cellulose: The most abundant polysaccharide; provides structural support in plant cell walls. Composed of β-glucose linkages.

Amino Acids and Proteins

Amino acids are the building blocks of proteins, each with a unique side chain that determines its properties.

• Aspartic acid side chain: -CH2COOH; acidic, negatively charged at physiological pH.

• Amino acids with charged side chains: 3 (one with a negative charge, two with positive charges).

Protein Structure

Proteins have hierarchical structures that determine their function.

• Primary structure: Sequence of amino acids.

• Secondary structure: Alpha helices and beta sheets stabilized by hydrogen bonds.

• Tertiary structure: Overall 3D shape formed by side-chain interactions.

• Quaternary structure: Assembly of multiple polypeptide chains.

Protein Interactions

• Cooperativity: Binding at one site increases affinity at others (e.g., hemoglobin).

• Allosteric inhibition: Regulation by binding at a non-active site.

Enzyme Function

• Induced fit: Enzyme changes shape to fit substrate.

• Rough ER: Organelle that synthesizes and modifies proteins.

Cellular Structures and Functions

Double-Membrane Organelles

Some organelles are surrounded by two membranes, which compartmentalize cellular functions.

• Nucleus, mitochondria, chloroplasts

Organelle Functions

• Nucleus: Stores DNA, site of transcription.

• Endoplasmic reticulum (ER): Protein and lipid synthesis.

• Golgi apparatus: Protein modification and packaging.

• Lysosome: Digestion of macromolecules.

• Peroxisome: Oxidation reactions.

• Mitochondria: ATP production via cellular respiration.

• Chloroplast: Photosynthesis in plants and algae.

Membrane Transport

• Channel proteins: Allow passage of molecules across membranes.

• Carrier proteins: Transport specific molecules by changing shape.

Cell Junctions

• Gap junctions: Channels for communication between animal cells.

Cell Membrane and Cell Wall

Membrane Properties

• Fluidity: Maintained by cholesterol; stabilizes at high temperatures, prevents solidification at low temperatures.

• High temperature in membrane: Increases fluidity.

• Rough ER: Studded with ribosomes, site of protein synthesis.

Cell Wall

• Not a steroid: Histidine (amino acid).

• Not in membrane: Maintains fluidity; cholesterol stabilizes at high temps, prevents solidification at low temps.

Cell Theory and Endosymbiosis

Endosymbiont Theory

This theory proposes that mitochondria and chloroplasts originated from engulfed prokaryotes.

• Mitochondria: Derived from aerobic bacteria.

• Chloroplasts: Derived from photosynthetic bacteria.

Biochemical Reactions

Dehydration and Hydrolysis

• Dehydration reactions: Build polymers by removing water; opposite of hydrolysis.

• Hydrolysis: Breaks polymers by adding water.

Spontaneous Reactions

• Spontaneous reaction: Negative ΔG; exergonic.

Phosphorylation

• Phosphorylation: Addition of phosphate group to a molecule.

ATP Synthesis

• ATP: Adenosine triphosphate; main energy currency of the cell.

• ATP synthesis: $\text{ADP} + \text{Pi} \rightarrow \text{ATP}$

Genetics and Nucleic Acids

DNA and RNA Structure

• DNA bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).

• RNA bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G).

• Base pairing: A-T, C-G in DNA; A-U, C-G in RNA.

DNA Replication

• Replication: DNA is copied before cell division.

Gene Expression

• Transcription: DNA to RNA in the nucleus.

• Translation: RNA to protein in the cytoplasm.

Cellular Respiration and Photosynthesis

Glycolysis and Cellular Respiration

• Glycolysis: Glucose is split into pyruvate, producing ATP.

• Cellular respiration: Complete oxidation of glucose to produce ATP.

Photosynthesis

• Photosynthesis: Conversion of light energy to chemical energy in chloroplasts.

Cell Division

Mitosis and Meiosis

• Mitosis: Produces two identical daughter cells.

• Meiosis: Produces four genetically unique gametes.

Cellular Structures

Stroma and Matrix

• Stroma: Fluid inside chloroplasts.

• Matrix: Fluid inside mitochondria.

Thylakoids and Cristae

• Thylakoids: Membranous sacs in chloroplasts; site of light reactions.

• Cristae: Folds in the inner mitochondrial membrane; increase surface area for energy production.

Osmosis and Tonicity

Tonicity

• Isotonic: Equal solute concentration; no net change in water movement.

• Hypotonic: Lower solute concentration outside; water enters cell.

• Hypertonic: Higher solute concentration outside; water leaves cell.

Thermodynamics in Biology

Second Law of Thermodynamics

• Entropy: Disorder increases in spontaneous processes.

Summary Table: DNA and RNA Bases

Type	Bases	Base Pairing
DNA	A, T, C, G	A-T, C-G
RNA	A, U, C, G	A-U, C-G

Summary Table: Organelle Functions

Organelle	Main Function
Nucleus	Stores DNA, transcription
Mitochondria	ATP production
Chloroplast	Photosynthesis
Golgi apparatus	Protein modification and packaging
Lysosome	Digestion of macromolecules
Peroxisome	Oxidation reactions

Additional info:

• Some brief points were expanded for clarity and completeness.

• Scientific terms were defined and context provided for exam preparation.