2.5 Cells Contain Four Major Types of Organic Molecules

Cells Contain Four Major Types of Organic Molecules

• Organisms primarily consist of water and organic molecules containing carbon and hydrogen.

• Autotrophs (like plants) produce their own organic molecules, while heterotrophs (like humans) must obtain them from food.

• Organic molecules exhibit vast diversity, with methane (CH4) being the simplest.

• Carbon's ability to form four covalent bonds allows for complex structures (chains, branches, rings).

• Major organic molecules: carbohydrates, proteins, nucleic acids, lipids. This similarity suggests common ancestry across all life forms.

Large Organic Molecules Are Composed of Smaller Subunits

Polymers and Monomers

• Proteins, nucleic acids, and some carbohydrates are polymers, chains of smaller units called monomers.

• Similar to railcars in a train, these monomers connect via small groups of atoms (e.g., hydroxyl, carboxyl, amino, phosphate groups).

• Dehydration Synthesis: A chemical reaction that links monomers into polymers by removing water and forming covalent bonds.

• Hydrolysis: The reverse process, breaking down polymers into monomers using water.

Major Types of Organic Molecules

1. Carbohydrates

• Composed of C, H, O in a 1:2:1 ratio, they serve as energy sources and structural components.

• Types include:

  • Simple Sugars (Monosaccharides): 5-6 carbon sugars (e.g., glucose, fructose).

  • Disaccharides: Two monosaccharides (e.g., sucrose, lactose) formed by dehydration synthesis.

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

2. Proteins

• Comprised of polymers of amino acids.

• Amino Acid Structure: Central carbon, hydrogen, carboxyl group, amino group (-NH2), and variable R group.

• Folds into four structures: primary (sequence), secondary (folds/loops), tertiary (3D shape), and quaternary (multiple polypeptides).

• Proteins perform various functions including enzymes, structural roles, transport, and storage.

3. Nucleic Acids

• Polymers of nucleotides, including DNA (stores genetic info) and RNA (transmits info).

• Each nucleotide includes a sugar (ribose in RNA, deoxyribose in DNA), phosphate groups, and nitrogenous bases (A, T, C, G for DNA; A, U, C, G for RNA).

4. Lipids

• Hydrophobic organic compounds including triglycerides (fats), phospholipids (cell membrane constituents), and steroids (cholesterol).

• Triglycerides: Composed of three fatty acids and glycerol, formed via dehydration synthesis which produces water.

• Fatty Acids: Saturated (no double bonds, solid at room temp) vs. unsaturated (double bonds, liquid at room temp).

• Cholesterol is vital for cell membranes and serves as a precursor for steroid hormones.

Summary of Organic Molecules:

Carbohydrates

• Simple Carbohydrates: Monosaccharides (e.g., glucose) and disaccharides (e.g., sucrose).

• Polysaccharides: Cellulose (structural), chitin (in fungi), starch (energy storage in plants), glycogen (energy storage in animals).

• Example Functions: Provide energy, structural support, critical for digestion.

Proteins - Structure & Function

• Primary Structure: The sequence of amino acids.

• Secondary Structure: Localized folds/stabilization via hydrogen bonds.

• Tertiary Structure: 3D shape due to hydrophobic interactions and bonds.

• Quaternary Structure: Assembly of polypeptide subunits into a functional protein (e.g., hemoglobin).

Denaturation of Proteins

• Proteins can lose their functional shape due to heat, pH changes, or salt concentration leading to loss of function.

• Example: Cooking an egg leads to protein denaturation, changing it from liquid to solid.

Nucleic Acids Structure

• DNA: Double helix structure (sugar-phosphate backbone and nitrogenous base pairing).

• Function: Stores genetic information dictating amino acid sequences for proteins.

Lipids Overview

• Triglycerides: Composed of fatty acids and glycerol; energy reserve, insulating properties.

• Saturated Fats: Typically solid at room temperature; can contribute to cardiovascular issues.

• Unsaturated Fats: Typically liquid at room temperature; healthier option.

• Cholesterol: Integral for cell membrane structure and precursor to microbial functions.