Biochemistry Essentials

Biochemistry Cheatsheet

Biochemistry is the study of thechemical processes within and relating to living organisms. It focuses on four major classes of organicmolecules: carbohydrates, lipids, nucleic acids, and proteins.

I. The Foundation: KeyElements & Organic Chemistry

• Life's Essential Elements:

  • Carbon(C): 4 chemical bonds

  • Hydrogen (H): 1 chemical bond

  • Oxygen (O): 2 chemical bonds

  • Nitrogen (N): 3 chemical bonds

  These four elements form the vast majority of biological molecules.

• Biological Elements: Life utilizes 25 out of 92 naturally occurring chemical elements, with C, H, O, N being the most crucial.

• Isomers: The same atoms can arrange to form different molecules (e.g., ethanol vs. dimethyl ether, both ).

• Carbon's Versatility (Organic Chemistry):

  • Definition: Chemistry of molecules containing carbon.

  • Unique Property: Carbon is the only atom that can bond to itself numerous times, forming complex and varied structures.

  • Structures: Can form linear chains, branched chains (e.g., isobutane), and cyclic structures (e.g., cyclohexane).

  • Bond Types: Carbon can form single, double, or triple bonds (e.g., ethane , ethylene , acetylene ).

  • Complexity: A molecule with formula can have 62.5 million different structural isomers.

• Levels of Organization of Matter:

  1. Atoms

  2. Molecules

  3. Organelles

  4. Cells

  5. Tissues

  6. Organs

  7. Systems

  8. Organism

  9. Population

  10. Ecosystem

  Emergent Properties: New properties appear at each higher level of organization (the whole is greater than the sum of its parts).

II. The Moleculesof Life (Macromolecules)

Every living organism is composed of thousands of different molecules, grouped into four main families:

1. Carbohydrates (Sugars)

2. Lipids (Fats, Oils, Steroids)

3. Proteins

4. Nucleic Acids (DNA & RNA)

III. Carbohydrates (Sugars)

Divided into monosaccharides, disaccharides, andpolysaccharides.

• Monosaccharides (Simple Sugars):

  • Examples: Glucose, Galactose, Fructose (all , isomers of each other).

  • Role: Primary energy source.

• Disaccharides (Double Sugars):

  • Formation: Two monosaccharides linked together.

  • Examples:

    • Sucrose (Glucose-Fructose) table sugar.

    • Maltose (Glucose-Glucose) malt sugar.

    • Lactose (Glucose-Galactose) milk sugar.

• Polysaccharides (Complex Sugars):

  • Structure: Long chains of monosaccharides.

  • Examples & Roles:

    • Starch: Glucose storage in plants (abundant in grains, legumes, potatoes).

    • Glycogen: Glucose storage in animals (stored in liver and muscles).

      Regulation: Excess glucose glycogen synthesis; glucose deficiency glycogen breakdown.

    • Cellulose: Forms rigid plant cell walls (linear chains of glucose with beta linkages, making it indigestible for most animals).

  • Overall Roles of Carbohydrates:

    • Structure: Cellulose (plants), Chitin (fungi, arthropods).

    • Energy: Glucose is the primary "fuel" for cellular respiration.All carbohydrates can be converted into glucose for energy.

IV. Lipids (Fats, Oils, Steroids)

Diverse group of hydrophobic molecules.

• Main Types: Triglycerides, Phospholipids, Steroids.

• Fatty Acids:

  • Saturated Fatty Acids:

    • No double bonds between carbons.

    • Typicallyanimal fats.

    • Solid at room temperature.

    • Associated with cardiovascular problems.

    • Cannot add more hydrogen.

  • Unsaturated Fatty Acids:

    • One or more double bonds between carbons.

    • Typically vegetable fats (with exceptions).

    • Liquid at room temperature.

    • Can add hydrogen across double bonds (hydrogenation).

• Triglycerides:

  • Primary Role: Energy storage.

  • Efficiency: 1g of fat stores 2x more energy than 1g of carbohydrate.

  • Storage: Dietary surpluses of lipids, carbohydrates, or proteins can be converted into fat.

    Animal vs. Plant Storage: Animals store energy primarily as fat (more compact due to high energy density), while plants store it as starch.

• Phospholipids:

  • Structure: Glycerol backbone, two fatty acid tails, and a phosphate group head.

  • Amphipathic: Hydrophilic head (phosphate) and hydrophobic tails (fatty acids).

  • Main Function: Form cell membranes.

  • Self-Assembly in Water: Can formmicelles, liposomes, and lipid bilayers (plasma membranes).

• Steroids:

  • Structure: Characterized by a carbon skeleton of four fused rings (sterol nucleus).

  • Examples: Cholesterol (membrane component, precursor to other steroids), hormones (e.g., testosterone, estrogen).

V. Proteins

Represent ~50% of the dryweight of most cells and perform diverse functions.

• Building Blocks: Made up of 20 different amino acids.

• Protein Structure Hierarchy:

  1. Primary Structure: Linear sequence of amino acids (e.g., Lysozyme has 129 amino acids).

  2. Secondary Structure: Local folding into repeating patterns, mainly alpha () helices andbeta () pleated sheets, stabilized by hydrogen bonds.

  3. Tertiary Structure: Overall 3D shape of a single polypeptide chain, resulting from interactions between R-groups (hydrophobic interactions, hydrogen bonds, ionicbonds, disulfide bridges).

  4. Quaternary Structure: Assembly of multiple polypeptide subunits (e.g., Hemoglobin, ATP synthase).

  Folding: The specific 3D structureis crucial for function and is driven by different forces (e.g., hydrophobic interactions, hydrogen bonds, ionic bonds, disulfide bridges).

• Dietary Proteins & Amino Acids:

  • Our cells synthesize proteins from amino acids obtained through digestion.

  • Essential Amino Acids: 8 amino acids cannot be synthesized by the human body and must be obtained from diet.

  • Sources:

    • Animal proteins generally contain all 8 essential amino acids in suitableproportions.

    • Vegetable proteins can be deficient in one or two essential amino acids (requiring dietary complementation).

  • Dietary Implications:

    • Protein Deficiency: Bodydigests its own proteins (muscle, blood proteins) to obtain amino acids.

    • Excess Protein: Surplus amino acids are converted to fat.

    • Scenario: One can gain fat while losing muscle mass if consuming insufficient protein relative to caloric intake.

• Key Functions of Proteins:

  1. Structure: Keratin (hair, nails), Collagen (connective tissue).

  2. Regulation: Hormones (e.g., adrenaline).

  3. Movement: Actin and Myosin (muscle contraction).

  4. Transport: Hemoglobin (oxygen transport).

  5. Immunity: Immunoglobulins (antibodies).

  6. Receptors & Transporters: Membrane proteins (e.g., sodium-potassium pump).

  7. Metabolism: Enzymes (e.g., lactase).

• Prions:

  • Normal: Glycoprotein PrPC.

  • Altered: Infectious PrPSC (misfolded form).

  • Mechanism: When PrPC encounters PrPSC, PrPC transforms into PrPSC. These prions polymerize, resist protective enzymes, and accumulate, leading to neurodegenerative diseases.

  • Associated Diseases: Kuru, Bovine Spongiform Encephalopathy (Mad Cow Disease), Scrapie, Creutzfeldt-Jakob Disease.

VI. Nucleic Acids

Carry genetic information.

• Types: DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid).

• DNA:

  • Structure: Double helix.

  • Components (Nucleotide):

    • Phosphate group

    • Deoxyribose sugar

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

  • Base Pairing: A with T, C with G.

• RNA (Ribonucleic Acids):

  • Types: mRNA (messenger RNA), tRNA (transfer RNA), rRNA (ribosomal RNA), regulatory RNAs, guide RNAs.

  • Structure: Single helix (or single strand).

  • Differences from DNA:

    • Sugar: Ribose instead of deoxyribose.

    • Base: Uracil (U) instead of Thymine (T). (A with U, C with G).

VII. Vitamins

Essential organic compounds that humans cannot synthesize and must obtain from their diet.

• Total Required: Humans need 13 different vitamins.

• Minerals (from chart, example):

  • Vitamin A: Calcium, Magnesium, Zinc, Phosphorus

  • Vitamin B12: Calcium, Zinc, Phosphorus, Magnesium

  • Vitamin B13: Calcium, Zinc, Phosphorus, Magnesium