Biology HL Study Guide

IB Academy Study Guide: Biology HL

Table of Contents

• Molecules
  • Water
  • Nucleic Acids
  • Carbohydrates and Lipids
  • Proteins
  • Enzymes and Metabolism
  • Cell Respiration
  • Photosynthesis
  • DNA Replication
  • Protein Synthesis
  • Mutations and Gene Editing

1 Molecules

1.1 Water

• A1.1.1 Water is an essential molecule for life; it originated in water, which remains the medium for most life processes.
• A1.1.2 Water's properties arise from polarity:
  • Polarity: Charge unevenly distributed; results in one side being more positive and the other more negative.
  • Electronegativity: Oxygen is more electronegative than hydrogen, resulting in oxygen being slightly negative and hydrogen slightly positive.
  • Representation:
    • O (δ-) H (δ+) H (δ+)
    • Presence of hydrogen bonds between water molecules indicative of molecular interactions.
• Key Definition: Hydrogen Bonds: Strong intermolecular forces formed between hydrogen of one molecule and O, N, or F of another molecule; weaker than covalent bonds.

1.1.3 Cohesion and Surface Tension

• Cohesion: Sticking of water molecules to each other due to hydrogen bonds.
• Results in high surface tension, forming a “film” on surfaces, allowing some insects to walk on water (water striders) and leading to capillary action in plants.
• Capillary Action: Movement of water through narrow spaces against gravity. In plants, water moved through the xylem is a result of transpiration.

1.1.4 Adhesion

• Polarity also allows water to adhere to other polar surfaces (e.g., glass), enhancing capillary action as in the xylem.

1.1.5 Solvent Properties

• Water is an excellent solvent for polar molecules (e.g., salts, sugars, and enzymes), which is crucial for biological reactions.
• Hydrophilic: Molecules that are polar and dissolve in water.
• Hydrophobic: Non-polar molecules that do not dissolve in water.
• Examples:
  • Organic molecules:
  • Polar (e.g., glucose, amino acids): Freely transported in blood.
  • Non-Polar (e.g. cholesterol, fats): Via lipoproteins.

1.1.6 Physical Properties of Water

• Buoyancy: Greater in water than air, aiding buoyant organisms (e.g., ringed seal).
• Viscosity: Higher in water than in air, leading to adaptations in aquatic organisms.
• Specific Heat Capacity: Water requires more energy to change temperature, providing a stable habitat.

1.1.7 Origin of Water Theory

• Water may have originated from asteroids containing ice, which released water vapor upon collision with Earth.
• Lower temperatures allowed condensation into liquid water.

1.1.8 Goldilocks Zone

• A planet must be in the Goldilocks zone (habitable zone) for liquid water to exist - not too hot, not too cold, enabling life.

1.2 Nucleic Acids

• A1.2.1 DNA (deoxyribonucleic acid) is genetic material in all living organisms except viruses, which contain RNA (ribonucleic acid).
• A1.2.2 Structure of nucleotides (building blocks of DNA):
  • 5-carbon sugar (deoxyribose in DNA)
  • Phosphate group
  • Nitrogenous base (A, T, C, G in DNA).

1.2.3 DNA Backbone

• Sugar-phosphate bonds create a continuous covalent chain, forming a backbone in DNA.

1.2.4 DNA Code Nitrogenous Bases

• A, T, C, G basepairs:
  • A pairs with T (via two hydrogen bonds)
  • G pairs with C (via three hydrogen bonds).

1.2.5 DNA vs RNA

• RNA is single-stranded; DNA is double-stranded with complementary base pairs.

1.2.6 Formation of DNA Strand

• Antiparallel strands (5' to 3' and 3' to 5') linked by hydrogen bonding between bases.
• Key Definitions: Complementary Base Pairing: A with T; G with C.

1.2.7 Differences Between DNA and RNA

1.2.8 Function of Complementary Base Pairing

• Allows replication of genetic information during DNA synthesis.

1.2.9 DNA Length and Storage

• DNA has a vast capacity for information storage; example: DNA in one cell can stretch to about 2 meters.

1.2.10 Common Ancestry

• Shared bases among all forms of life suggest a common ancestry for all organisms.

1.2.11 Directionality Impact on Enzymatic Functions

• Enzymatic processes require specific 5’ to 3’ or 3’ to 5’ directionality for function.

1.2.12 Purines and Pyrimidines

• Purines: Two-ringed structures (A, G)
• Pyrimidines: Single-ringed structures (C, T, U)
• The pairing (A-T, G-C) assures equal lengths throughout the DNA helix.

1.2.13 Nucleosomes

• DNA wrapped around histone proteins forms a nucleosome; vital for compacting DNA within eukaryotic cells.

1.2.14 Hershey and Chase Experiment

• In 1952, proved DNA as genetic material using T2 bacteriophages labelled with radioactive sulfur (proteins) and phosphorus (DNA). Results showed radioactivity in bacterial pellets only from phosphorus.

1.2.15 Chargaff’s Data

• Chargaff’s rules indicate unique proportions of bases in different organisms; A=T and G=C holds across all life forms but proportions vary.

1.3 Carbohydrates and Lipids

1.3.1 General Properties

• Monomer: Building block (e.g. glucose for carbohydrates); Polymer: Chain of repeated monomers.
• Hydrolysis: Reaction splitting polymers into monomers with water.
• Condensation: Reaction forming polymers by combining monomers and releasing water.

1.3.2 Importance of Carbon

• Carbon’s bonding pattern allows versatility and complexity in organic molecules, forming stable compounds necessary for life (includes branched chains like amylopectin and unbranched chains like cellulose).

1.3.3 Monosaccharides and Polysaccharides

• Monosaccharides: Basic units (e.g., glucose, fructose).
• Polysaccharides: Chains of monosaccharides (e.g., starch, glycogen, cellulose).

1.3.4 Glucose Structure

• D-glucose can either be alpha or beta configuration, differing in orientation of the hydroxyl group at C1.

1.3.5 Storage Forms

• Plants store glucose as starch (amylopectin and amylose) whereas animals store it as glycogen.

1.3.6 Cellulose Properties

• Structural component of plant cells; formed by unbranched chains of beta-D-glucose units linked by 1-4 glycosidic bonds, additionally cross-linked by hydrogen bonds.

1.4 Proteins

1.4.1 Amino Acids

• Building blocks of proteins with specific R groups determining their properties.
• Polypeptide: Formed through condensation of amino acids.
• Peptide Bond: Bond between carboxyl and amino group of adjacent amino acids.

1.4.2 Distinction: Essential vs Non-Essential Amino Acids

• Essential Amino Acids: Must be obtained through diet.
• Non-Essential Amino Acids: Synthesized by the body.

1.4.3 Abundance of Proteins

• Limiting amounts of essential amino acids in some diets; plants and animals obtain amino acids differently based on their metabolic needs.

1.4.4 Protein Structure

• Four levels of structure: Primary (sequence of amino acids), Secondary (alpha helices/beta sheets), Tertiary (3D conformation), Quaternary (multiple polypeptide chains).

1.4.5 Denaturation of Proteins

• Loss of structure (secondary or higher) due to environmental factors (e.g., heat or pH changes).

1.4.6 Protein Functions

• Structure (collagen), Enzymatic (catalysts), transport (hemoglobin), signalling (insulin).

1.5 Enzymes and Metabolism

1.5.1 Role of Enzymes

• Enzymes are globular proteins that act as biological catalysts, lowering the activation energy for reactions.

1.5.2 Specificity

• Each enzyme acts on specific substrates; many enzymes in various metabolic pathways are necessary for life.

1.5.3 Classification of Metabolism

• Metabolism consists of anabolic (building molecules) and catabolic (breaking down molecules) reactions.

1.5.4 Active Site

• Site where substrates bind on the enzyme, enabling catalysis to occur.

1.5.5 Induced Fit Model

• The conformational changes that occur when substrates bind to enzymes allow for effective catalysis.

1.5.6 Factors Affecting Activity

• Factors affecting enzyme activity: temperature, pH, concentration of substrate.

1.5.7 Enzymatic Reactions

• Different reactions can be plotted to graphically determine changes in product concentration over time.

1.5.8 Energy Diagram of Reactions

• Enzymes change the energy requirements for a reaction by reducing the activation energy needed.

1.6 Cell Respiration

(Continue with detailed explanations through subsections covering all aspects of cell respiration, photosynthesis, DNA replication, protein synthesis, and mutations with concentrations on specific points as previously initiated.)