Biomolecules

Amino Acids and Proteins

Amino acids are the building blocks of proteins, each consisting of a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group). Proteins are polymers of amino acids and perform a wide variety of functions in cells.

• Amino acid structure: Central carbon, amino group, carboxyl group, hydrogen, and side chain (R group).

• Peptide bond: Covalent bond formed between the amino group of one amino acid and the carboxyl group of another via dehydration synthesis.

• Protein structure: Four levels—primary (amino acid sequence), secondary (alpha helices and beta sheets), tertiary (3D folding), and quaternary (multiple polypeptide chains).

• Function: Enzymes, structural support, transport, signaling, and defense.

• Example: Hemoglobin is a protein that transports oxygen in the blood.

Nucleic Acids

Nucleic acids, such as DNA and RNA, store and transmit genetic information. They are polymers of nucleotides, each composed of a sugar, phosphate group, and nitrogenous base.

• Nucleotide: Building block of nucleic acids; consists of a pentose sugar, phosphate group, and nitrogenous base.

• DNA vs. RNA: DNA contains deoxyribose sugar and is double-stranded; RNA contains ribose sugar and is single-stranded.

• Base pairing: In DNA, adenine pairs with thymine, and cytosine pairs with guanine.

• Function: DNA stores genetic information; RNA is involved in protein synthesis and gene regulation.

Carbohydrates and Lipids

Carbohydrates are energy sources and structural components, while lipids serve as energy storage, membrane structure, and signaling molecules.

• Monosaccharides: Simple sugars (e.g., glucose).

• Disaccharides: Two monosaccharides joined by a glycosidic linkage (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, glycogen, cellulose).

• Lipids: Include fats, phospholipids, and steroids. Fats are composed of glycerol and fatty acids; phospholipids form cell membranes.

• Phosphodiester bond: Covalent bond in nucleic acids between the phosphate group and sugar.

Cell Structure

Eukaryotic Cell Organelles

Eukaryotic cells contain membrane-bound organelles that compartmentalize cellular functions.

• Nucleus: Contains genetic material (DNA).

• Endoplasmic reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids.

• Golgi apparatus: Modifies, sorts, and packages proteins and lipids.

• Mitochondria: Site of cellular respiration and ATP production.

• Lysosomes: Contain digestive enzymes for breaking down macromolecules.

• Chloroplasts: Site of photosynthesis in plant cells.

• Double membrane: Mitochondria and chloroplasts have two membranes, providing compartmentalization.

Cellular Compartments and Transport

Cells maintain distinct internal environments through compartmentalization and selective transport across membranes.

• Compartmentalization: Organelles create specialized environments for specific functions.

• Transport: Substances move between organelles via vesicles and across membranes by diffusion, facilitated diffusion, and active transport.

• Example: Proteins synthesized in the rough ER are transported to the Golgi apparatus for modification.

Cellular Respiration

Overview and Pathways

Cellular respiration is the process by which cells extract energy from organic molecules, primarily glucose, to produce ATP.

• Glycolysis: Occurs in the cytoplasm; breaks down glucose into pyruvate, producing ATP and NADH.

• Citric acid cycle (Krebs cycle): Occurs in the mitochondrial matrix; oxidizes acetyl-CoA to CO2, generating NADH, FADH2, and ATP.

• Electron transport chain (ETC): Located in the inner mitochondrial membrane; transfers electrons from NADH and FADH2 to oxygen, producing water and driving ATP synthesis.

• ATP synthase: Enzyme that synthesizes ATP using the proton gradient across the inner mitochondrial membrane.

• Fermentation: Anaerobic process that regenerates NAD+ by converting pyruvate to lactate or ethanol.

Key Equations:

• Overall cellular respiration:

• ATP synthesis (chemiosmosis):

Electron Carriers and Energy Yield

NADH and FADH2 are electron carriers that transfer high-energy electrons to the electron transport chain.

• NADH: Nicotinamide adenine dinucleotide; carries electrons from glycolysis and the citric acid cycle.

• FADH2: Flavin adenine dinucleotide; carries electrons from the citric acid cycle.

• Proton motive force: The electrochemical gradient generated by the ETC, used to drive ATP synthesis.

Gas Exchange

Principles of Gas Exchange

Gas exchange is the process by which oxygen and carbon dioxide are transferred between the environment and an organism's cells.

• Diffusion: Movement of gases from areas of high concentration to low concentration.

• Partial pressure: The pressure exerted by a single gas in a mixture; drives diffusion across respiratory surfaces.

• Respiratory surfaces: Must be moist, thin, and have a large surface area for efficient gas exchange.

• Examples: Alveoli in mammalian lungs, gills in fish, stomata in plant leaves.

Comparative Gas Exchange

Different organisms have evolved specialized structures for gas exchange, adapted to their environments.

• Alveoli: Tiny air sacs in mammalian lungs where gas exchange occurs.

• Stomata: Pores in plant leaves that regulate gas exchange and water loss.

• Cooperativity: Hemoglobin exhibits cooperative binding, increasing oxygen delivery efficiency.

Diagrams and Structures

Be Able to Draw and Label

• Amino acid structure: central carbon, amino group, carboxyl group, side chain (R group).

• Nucleotide structure: pentose sugar, phosphate group, nitrogenous base.

• Cellular organelles: nucleus, mitochondria, ER, Golgi apparatus, lysosome, chloroplast.

• Respiratory surfaces: alveoli, stomata.

Vocabulary

Key Terms and Definitions