Biology notes 1

Quaternary Structure

• Quaternary structure refers to the arrangement and interactions between multiple polypeptide chains, known as subunits.
• Interactions can involve disulfide bridges, salt bridges, and intermolecular forces.

Protein Folding

• Protein folding can occur spontaneously without assistance.
• Chaperone proteins can aid in correct folding.
• Denaturation may occur due to pH changes, high salt concentrations, organic solvents, or elevated temperatures.

Carbohydrates

• Monosaccharides, the basic units of carbohydrates, have the formula Cn(H2O)n and can be either aldoses or ketoses.
• Monosaccharides can cyclize to form hemi-acetals/hemi-ketals.
• Disaccharides consist of two linked monosaccharides via glycosidic bonds (e.g., sucrose = glucose + fructose).
• Polysaccharides are long chains of monosaccharides; starch serves as the primary energy storage in plants.
• Amylose is linear (α-(1-4) bonds), while amylopectin is branched (α-(1-4) and α-(1-6) bonds).
• Glycogen is a branched glucose polymer used for energy storage in animal muscles and liver.
• Cellulose, a linear glucose polymer with β-(1-4) bonds, provides structural support in plant cell walls.
• Chitin, made of N-acetylglucosamine, is found in fungal cell walls and arthropod exoskeletons.

Nucleic Acids

• DNA consists of deoxyribose sugar, and RNA consists of ribose sugar with bases A, C, G, T (for DNA) and A, C, G, U (for RNA).
• DNA has a right-handed double helix structure (B-form) with antiparallel, complementary strands held together by hydrogen bonds.
• Watson-Crick base pairing includes A-T (2 hydrogen bonds) and G-C pairs (3 hydrogen bonds).

Lipids

• Lipids are hydrophobic and insoluble in water, playing diverse roles in biological systems.
• Key lipid types:
  • Triglycerides for energy storage and insulation.
  • Phospholipids form cell membranes.
  • Cholesterol adds membrane fluidity and is a steroid precursor.
  • Steroids function as hormones.
  • Sphingolipids and prostaglandins play roles in cellular signaling and the nervous system.
  • Terpenes are involved in plant functions and cholesterol biosynthesis.

Fatty Acids

• Fatty acids are carboxylic acids with long hydrocarbon chains.
• Saturated fatty acids have no double bonds; unsaturated can have one (monounsaturated) or more (polyunsaturated).
• Triglycerides consist of three fatty acids bonded to glycerol and are stored in adipose tissue.

Phospholipids

• Phospholipids are crucial for cell membranes, being amphipathic with hydrophilic heads and hydrophobic tails.
• Unsaturated phospholipids enhance membrane fluidity due to loose packing.

Steroids and Cholesterol

• Cholesterol contributes to membrane fluidity and is a precursor for steroid hormones and bile.

Organelles

• Nucleus: Stores DNA, site of transcription, contains the nucleolus for rRNA synthesis.
• Ribosomes: Sites of protein synthesis, existing as free ribosomes or attached to the rough ER.
• Rough ER: Involved in glycoprotein synthesis and production of phospholipids and steroids.
• Smooth ER: Functions in detoxification, lipid synthesis, and carbohydrate metabolism.
• Golgi Apparatus: Modifies, sorts, and packages proteins for secretion or transport.
• Mitochondria: Powerhouse of the cell; ATP synthesis, fatty acid catabolism, contains its own DNA.
• Lysosomes: Digestive organelles that break down waste materials.
• Peroxisomes: Involved in fatty acid degradation and detoxification processes.
• Centrosomes and Centrioles: Microtubule-organizing centers critical for cell division.
• Vacuoles: Storage organelles, large central vacuole in plant cells maintains turgor pressure.
• Chloroplasts: Sites of photosynthesis in plant cells.

Plasma Membrane

• Composed of a phospholipid bilayer, follows the fluid mosaic model.
• Components:
  • Phospholipids and glycolipids for structure, affecting fluidity.
  • Cholesterol modulates membrane fluidity based on temperature.
  • Membrane proteins include peripheral, integral, and transmembrane proteins, with roles in transport and signaling.

Intercellular Junctions

• Gap Junctions: Allow nutrient exchange and communication between cells (e.g., cardiac muscle).
• Tight Junctions: Prevent leakage between cells (e.g., intestinal cells).
• Desmosomes: Provide mechanical strength and adhesion between cells.

Cytoskeleton

• Microfilaments: Comprised of actin, involved in cell movement and division.
• Intermediate Filaments: Provide structural support to the cell.
• Microtubules: Tubulin-based, serve as tracks for intracellular transport and are key components of mitotic spindles and cilia/flagella.

Membrane Transport

• Diffusion: Movement of solute from high to low concentration.
• Osmosis: Water movement across a membrane.
• Solutions categorized as hypertonic, hypotonic, or isotonic based on solute concentration differences.

Calvin Cycle

• Carbon fixation processes occur in three stages:
  • Carbon Fixation (using Rubisco to convert CO2 into 3-phosphoglycerate).
  • Reduction (produces glyceraldehyde-3-phosphate using ATP and NADPH).
  • Regeneration (converts glyceraldehyde-3-phosphate back into ribulose-1,5-bisphosphate, utilizing ATP).

Photorespiration

• Photorespiration occurs when Rubisco catalyzes the oxidation of ribulose-1,5-bisphosphate, competing with carbon fixation.
• Higher O2 concentrations and temperatures increase photorespiration, affecting overall photosynthesis efficiency.
• Stomata regulate gas exchange; closure under high temperatures limits CO2 uptake and increases O2, exacerbating photorespiration.

C4 Photosynthesis

• C4 plants utilize a different pathway for carbon fixation, allowing efficient functioning in high temperatures and light intensities.

This quiz explores the quaternary structure of hemoglobin, focusing on how multiple polypeptide chains interact to form functional proteins. Additionally, it covers the role of disulfide bridges, salt bridges, and intermolecular forces in protein stability and folding. Test your understanding of these critical concepts in biochemistry.