General Biology: Biomolecules, Cell Structure, and Function Study Guide

Biomolecules of Life

Major Classes of Biomolecules

Living organisms are composed of four major classes of biomolecules, each with distinct structures and functions.

• Carbohydrates: Organic molecules made of carbon, hydrogen, and oxygen. Monomers: Monosaccharides (e.g., glucose).

• Lipids: Hydrophobic molecules including fats, oils, and steroids. Monomers: Glycerol and fatty acids (for fats).

• Proteins: Polymers of amino acids that perform a wide range of functions. Monomers: Amino acids.

• Nucleic Acids: DNA and RNA, which store and transmit genetic information. Monomers: Nucleotides.

Example: Starch (a carbohydrate) is a polymer of glucose monomers.

Bond Formation and Breakdown

Chemical bonds in biomolecules are formed and broken through specific reactions:

• Dehydration (Condensation) Reaction: Joins monomers by removing a water molecule.

• Hydrolysis: Breaks polymers into monomers by adding a water molecule.

Example: Hydrolysis of a protein breaks peptide bonds, releasing amino acids.

Types of Bonds in Biomolecules

• Glycosidic Bonds: Link monosaccharides in carbohydrates.

• Peptide Bonds: Link amino acids in proteins.

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

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

Types of Lipids

Lipids are diverse in structure and function. The main types include:

• Triglycerides: Composed of glycerol and three fatty acids; main form of stored energy.

• Phospholipids: Contain a phosphate group; major component of cell membranes.

• Steroids: Four fused carbon rings; includes cholesterol and hormones.

Properties of Phospholipids and Cholesterol

• Phospholipids: Amphipathic molecules with hydrophilic heads and hydrophobic tails; form bilayers in membranes.

• Cholesterol: Maintains membrane fluidity; excess can lead to heart disease but is also a precursor for steroid hormones.

Saturated, Unsaturated, Cis, and Trans Fats

• Saturated Fats: No double bonds; solid at room temperature (e.g., butter).

• Unsaturated Fats: One or more double bonds; liquid at room temperature (e.g., olive oil).

• Cis Fats: Hydrogen atoms on the same side of the double bond; naturally occurring.

• Trans Fats: Hydrogen atoms on opposite sides; often artificially produced; associated with health risks.

Proteins and Amino Acids

Basic Structure of Amino Acids

Amino acids have a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable R group.

• General formula: $\text{H}_2\text{N}-\text{CHR}-\text{COOH}$

Five Major Types of Proteins

• Enzymes: Catalyze biochemical reactions.

• Structural Proteins: Provide support (e.g., collagen).

• Transport Proteins: Move substances (e.g., hemoglobin).

• Defensive Proteins: Protect against disease (e.g., antibodies).

• Signaling Proteins: Coordinate cellular activities (e.g., hormones).

Carbohydrates: Energy and Storage

Energy Use and Storage

• Glucose: Primary energy source for cells.

• Human Storage: Glycogen in liver and muscles.

• Plant Storage: Starch in plastids (e.g., amyloplasts).

Nucleic Acids: DNA and RNA

Similarities and Differences

• DNA: Double-stranded, deoxyribose sugar, bases A, T, C, G.

• RNA: Single-stranded, ribose sugar, bases A, U, C, G.

• Pyrimidines: Cytosine, Thymine (DNA), Uracil (RNA).

• Purines: Adenine, Guanine.

Transcription and Translation

• Transcription: DNA is transcribed to RNA.

• Translation: RNA is translated to proteins.

Monomers of Nucleic Acids and Proteins

• Nucleic Acids: Nucleotides (phosphate group, sugar, nitrogenous base).

• Proteins: Amino acids.

DNA to RNA and "Antiparallel"

• DNA forms RNA through transcription.

• Antiparallel: The two strands of DNA run in opposite directions (5' to 3' and 3' to 5').

Cell Structure and Function

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: No nucleus, no membrane-bound organelles, smaller (e.g., bacteria).

• Eukaryotic Cells: Nucleus, membrane-bound organelles, larger (e.g., plants, animals).

Plant vs. Animal Cells:

• Plant Cells: Cell wall, chloroplasts, large central vacuole.

• Animal Cells: No cell wall, no chloroplasts, small vacuoles.

Cell Theory

• All living things are composed of cells.

• Cells are the basic unit of structure and function in living things.

• All cells arise from pre-existing cells.

Major Features Found in All Cells

• Plasma membrane

• Cytoplasm

• Genetic material (DNA or RNA)

• Ribosomes

Organelles of the Cell: Location and Function

• Nucleus: Contains genetic material; controls cell activities.

• Mitochondria: Site of cellular respiration; produces ATP.

• Endoplasmic Reticulum (ER): Synthesizes proteins (rough ER) and lipids (smooth ER).

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

• Lysosomes: Digestive enzymes; break down waste.

• Chloroplasts (plants): Site of photosynthesis.

• Vacuoles: Storage of substances; large in plants.

Cell Membrane Structure and Properties

Phospholipid Bilayer

The cell membrane is primarily composed of a phospholipid bilayer, which provides a semi-permeable barrier between the cell and its environment.

• Structure: Two layers of phospholipids with hydrophilic heads facing outward and hydrophobic tails inward.

• Properties: Fluidity, selective permeability, presence of proteins and cholesterol.

Diffusion and Osmosis

• Diffusion: Movement of solutes from high to low concentration.

• Osmosis: Movement of water across a semi-permeable membrane from low solute to high solute concentration.

Equation for Osmosis:

$\Psi = \Psi_s + \Psi_p$

Where $\Psi$ is water potential, $\Psi_s$ is solute potential, and $\Psi_p$ is pressure potential.

Table: Comparison of Prokaryotic and Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Membrane-bound Organelles	Absent	Present
Cell Size	Small (1-10 μm)	Larger (10-100 μm)
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Key Terms to Know

• Monomer, Polymer, Dehydration, Hydrolysis, Glycosidic bond, Peptide bond, Triglyceride, Phospholipid, Steroid, Saturated fat, Unsaturated fat, Cis fat, Trans fat, Amino acid, Protein, Enzyme, Nucleotide, DNA, RNA, Pyrimidine, Purine, Transcription, Translation, Antiparallel, Prokaryote, Eukaryote, Organelle, Cell membrane, Diffusion, Osmosis.