2024 H2 BLCT Notes (Stu)

Page 30: Carbohydrates

Cellulose Structure and Function

  • Structure: Cellulose is a polysaccharide composed of long chains of beta-glucose units linked by β-1,4-glycosidic bonds. These chains form microfibrils that aggregate to create rigid structures.

  • Tensile Strength: The hydrogen bonds between hydroxyl groups in neighboring chains give cellulose its tensile strength, allowing it to provide structural support in plant cell walls.

Starch Structure

  • Structure: Starch is a polysaccharide composed of numerous alpha-glucose units. It exists in two forms: amylose (linear chains) and amylopectin (branched chains), both linked by α-1,4-glycosidic bonds (amylopectin also has α-1,6-glycosidic branches).

Glycogen Structure

  • Structure: Glycogen is a highly branched polysaccharide made up of alpha-glucose units, primarily linked by α-1,4-glycosidic bonds with branching occurring through α-1,6-glycosidic bonds. It is denser and more branched than starch, allowing for rapid energy mobilization due to the numerous ends available for enzymatic action.

Glycosidic Linkages in Starch and Cellulose

  • Distinction: Cellulose contains β-1,4-glycosidic linkages, while starch contains α-1,4-glycosidic linkages.

  • Biological Importance: This differentiation affects digestibility; humans can break down starch but lack enzymes to hydrolyze cellulose effectively. This is crucial for energy storage and structural roles in organisms.

Page 31: Lipids

Overview of Lipids

  • Definition: Lipids are a diverse group of hydrophobic biological molecules that are not considered true polymers.

  • Composition: Generally made of C, H, and O; characterized by low oxygen content and high hydrogen, with no generalized formula.

  • Tests: Ethanol emulsion test produces a cloudy white suspension, indicating the presence of lipids.

Classification of Lipids

  1. Simple Lipids

    • Triglycerides: Composed of glycerol and three fatty acids; solid at 20°C are fats; liquid are oils.

    • Waxes: Formed from fatty acids and long-chain alcohols (e.g., cuticle in leaves).

  2. Compound Lipids

    • Phospholipids: Composed of two fatty acids, one phosphate group, and glycerol.

    • Glycolipids: Composed of fatty acids and carbohydrate chains.

  3. Steroids: Characterized by a four-ring carbon skeleton; includes hormones like testosterone and cholesterol.

Page 32: Functions of Lipids

Functions of Lipids

  • Energy Source: Lipids provide a high-energy yield; triglycerides yield more energy per gram than carbohydrates.

  • Cell Structure: Integral for cell membranes and organelle membranes.

  • Insulation and Protection: Aid in thermal insulation and protect organs.

  • Biochemical Roles: Essential for fat-soluble vitamins and hormones.

Page 33: Triglycerides

Structure of Triglycerides

  • Composition: Made of one glycerol molecule linked to three fatty acids forming ester bonds through condensation reactions.

  • Types of Fatty Acids:

    • Saturated: No double bonds, straight chains, closely packed.

    • Unsaturated: One or more double bonds, kinked chains, packed less densely, leading to lower melting/boiling points.

Page 34: Triglyceride Functionality

Energy Storage and Other Functions

  • Energy Efficiency: High density of C-C and C-H bonds means greater energy storage capacity than carbohydrates.

  • Lightweight: Ideal for flying animals and seed dispersal.

  • Hydrophobic Structure: Insoluble in water, minimizes water potential impact in cells.

  • Metabolic Water Production: Provides metabolic water during oxidation, crucial for certain environmental adaptations.

Page 35: Phospholipids

Structure of Phospholipids

  • Composition: Two fatty acids, one phosphate group, and glycerol. Amphipathic nature due to hydrophilic phosphate head and hydrophobic fatty acid tails.

  • Behavior in Water: Form bilayers, positioning heads outward and tails inward, essential for membrane structure.

Page 36: Phospholipid Functionality

Role in Membranes

  • Cell Membrane Formation: Phospholipid bilayer structure allows selective permeability, crucial for cellular function and ion concentration maintenance.

  • Axonal Insulation: Forms myelin around nerve cells, increasing electrical resistance.

Page 37: Cholesterol

Structure and Function of Cholesterol

  • Composition: Hydrocarbon chain, four hydrocarbon rings, and a hydroxyl group; amphipathic due to polar and non-polar regions.

  • Role: Regulates membrane fluidity, aids in bile salt formation, and serves as a precursor for hormones.

Page 38: Lipid Checklist

Review Questions

  1. Define hydrophilic, hydrophobic, and amphipathic.

  2. Describe triglyceride formation.

  3. Differentiate saturated and unsaturated fats.

  4. Compare triglycerides and phospholipids structurally.

  5. Discuss cholesterol structure and biological importance.

Page 39: Nucleic Acids

Overview of Nucleic Acids

  • Function: Serve as genetic material; encode genetic information across living organisms.

  • Composition: Comprised of C, H, O, N, P; exist as DNA and RNA in cells.

Page 40: Nucleotide Structure

Components of Nucleotides

  • Composition: Each nucleotide contains a pentose sugar, phosphate group, and nitrogenous base.

  • Types: DNA nucleotides (deoxyribonucleotides) and RNA nucleotides (ribonucleotides) differ in their sugars and bases.

Page 41: Nitrogenous Bases

Types of Nitrogenous Bases

  • Purines: Adenine (A) and Guanine (G); consist of two rings.

  • Pyrimidines: Cytosine (C), Thymine (T; DNA only), Uracil (U; RNA only); single ring structure.

Page 42: Nucleoside and Phosphate Variations

Nucleoside Forms

  • Descriptive Forms: Nucleoside, nucleoside monophosphate, diphosphate, triphosphate (linked to energy transport and transfer in cells).

Page 43: Phosphodiester Bonds

Formation of Polynucleotides

  • Reaction: Nucleotides form polynucleotides through condensation reactions creating phosphodiester bonds with the release of pyrophosphate and water.

  • Directionality: Synthesized in the 5’ to 3’ direction, resulting in a sugar-phosphate backbone.

Page 44: DNA Structure

DNA Macromolecular Structure

  • Composition: DNA consists of two polynucleotide strands coiling into a double helix, anti-parallel orientation, with base pairing (A with T and G with C).

  • Stability Factors: Maintained by hydrogen bonding and hydrophobic interactions, ensuring structural integrity.

Page 45: DNA Characteristics

Structural Characteristics of DNA

  • Groove Orientation: Major and minor grooves enable protein interaction.

  • Function: Stores genetic information and facilitates replication through base pairing.

Page 46: Discovery of DNA Structure

Historical Contributions

  • Key Figures: Watson and Crick developed the 3D structure, building on previous discoveries from Miescher, Levene, Avery, Chargaff, Franklin, and Wilkins.

Page 49: RNA Structure

Characteristics of RNA

  • Single-Stranded Nature: Differentiates it from DNA; participates in protein synthesis.

  • Types: Messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA); each has unique roles in gene expression.

Page 50: mRNA Function

mRNA Overview

  • Function: Acts as a messenger carrying genetic instructions from the nucleus to ribosomes for protein synthesis.

  • Codons: Base sequences read in triplets, each specifying an amino acid.

Page 51: tRNA Structure and Function

tRNA Overview

  • Structure: Single-stranded but folds into a cloverleaf shape due to intramolecular base pairing.

  • Functionality: Transfers specific amino acids to ribosomes during translation, possessing specific sites for attachment and codon matching.

Page 52: rRNA Structure and Function

rRNA Overview

  • Role: Comprises the structural component of ribosomes, essential for protein synthesis. Also possesses catalytic activity during peptide bond formation.

Page 56: Proteins Overview

General Characteristics

  • Definition: Proteins are composed of one or more polypeptide chains folded into specific structures for biological functions.

  • Biuret Test: Detects proteins by changing the biuret reagent from blue to violet, indicating peptide bonds.

Page 57: Amino Acids Structure

Components of Amino Acids

  • General Structure: Central carbon, amine group, carboxylic acid group, hydrogen atom, and variable side chain (R group).

  • Properties: Physical and chemical properties dictated by the R group; solubility varies depending on charge or polarity.

Page 59: Protein Structure Bonds

Types of Bonds in Proteins

  • Peptide Bonds: Strong covalent bonds linking amino acids; form primary structure.

  • Disulfide Bonds: Formed from cysteine oxidation; stabilize 3D structure of proteins.

  • Ionic Bonds: Generated between charged R groups; sensitive to pH changes.