DNA Replication, Gene Expression, and Cell Structure

Introduction

This study guide covers foundational topics in general biology, focusing on DNA replication, gene expression, and the structure and function of cells. It includes key definitions, explanations of major biological processes, and comparisons of molecular and cellular structures.

Defining Life and Scientific Method

Characteristics of Life

• Definition of Life: Life on Earth is defined by a set of characteristics shared by all living organisms, including organization, metabolism, homeostasis, growth, reproduction, response to stimuli, and adaptation through evolution.

• Cell Theory: States that all living things are composed of cells, and all cells arise from pre-existing cells. This theory disproved the idea of spontaneous generation.

The Scientific Method

• Definition: A systematic approach to understanding the natural world through observation, hypothesis formation, experimentation, and analysis.

• Application: Used to further our understanding of biological processes by testing predictions and refining theories.

Cell Structure and Types

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles; DNA is located in the nucleoid region. Examples: Bacteria and Archaea.

• Eukaryotic Cells: Have a nucleus and various membrane-bound organelles (e.g., mitochondria, endoplasmic reticulum). Examples: Plants, Animals, Fungi, Protists.

• Compartmentalization: Eukaryotic cells use internal membranes to create specialized compartments, increasing efficiency and allowing for complex functions.

DNA and RNA Structure and Function

• DNA (Deoxyribonucleic Acid): Stores genetic information; double helix structure composed of nucleotides (adenine, thymine, cytosine, guanine).

• RNA (Ribonucleic Acid): Involved in protein synthesis; types include mRNA (messenger), tRNA (transfer), and rRNA (ribosomal).

• Functions: mRNA carries genetic code from DNA to ribosomes, tRNA brings amino acids, rRNA forms part of the ribosome.

Water and Biological Molecules

Properties of Water

• Polarity: Water is a polar molecule, allowing it to form hydrogen bonds.

• Cohesion and Adhesion: Cohesion allows water molecules to stick together; adhesion allows them to stick to other substances.

• Solvent Properties: Water dissolves many substances, facilitating chemical reactions in cells.

Covalent, Hydrogen, and Ionic Bonds

• Covalent Bonds: Atoms share electrons; strong and stable (e.g., bonds within water molecules).

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., between water molecules).

• Ionic Bonds: Formed by the transfer of electrons between atoms, resulting in charged ions (e.g., NaCl).

Macromolecules

• Four Major Classes: Carbohydrates, lipids, proteins, nucleic acids.

• Carbohydrates: Monosaccharides, disaccharides, polysaccharides (e.g., glucose, starch).

• Proteins: Polymers of amino acids; structure determines function.

• Lipids: Hydrophobic molecules, including fats, phospholipids, and steroids.

• Nucleic Acids: DNA and RNA; polymers of nucleotides.

Protein Structure and Function

Levels of Protein Structure

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Local folding (alpha helix, beta pleated sheet).

• Tertiary Structure: Overall 3D shape of a single polypeptide.

• Quaternary Structure: Association of multiple polypeptides.

Denaturation

• Definition: Loss of protein structure (and function) due to environmental changes (e.g., temperature, pH).

Cell Membranes

Phospholipid Bilayer

• Structure: Double layer of phospholipids with hydrophilic heads facing outward and hydrophobic tails inward.

• Function: Forms a selective barrier, controlling entry and exit of substances.

• Fluid Mosaic Model: Describes the membrane as a dynamic structure with proteins embedded in or attached to the bilayer.

Membrane Proteins and Transport

• Integral Proteins: Span the membrane; involved in transport and signaling.

• Peripheral Proteins: Attached to the membrane surface; involved in signaling and maintaining cell shape.

• Selective Permeability: Only certain molecules can cross the membrane freely.

• Transport Proteins: Facilitate movement of substances across the membrane.

• Receptors: Proteins that receive and transmit signals from outside the cell.

Diffusion and Osmosis

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

• Osmosis: Diffusion of water across a selectively permeable membrane.

Central Dogma of Molecular Biology

• Definition: Describes the flow of genetic information in the cell: DNA → RNA → Protein.

• Transcription: DNA is transcribed into mRNA.

• Translation: mRNA is translated into a protein at the ribosome.

Glossary of Key Terms

• Central Dogma

• Chromosome

• Gene

• Genome

• Nucleotides

• Amphipathic

• Hydrophobic

• Hydrophilic

• Double helix

• Alpha helix

• Beta pleated sheet

• Primary sequence

• Secondary structure

• Tertiary structure

• Quaternary structure

• Denature

• Osmosis

• Diffusion

• mRNA, rRNA, tRNA

• Genetic code

• Codon

• Start and stop codons

• Anticodon

• Transcription

• Translation

• Primary transcript

• RNA splicing

• Exons and introns

• RNA polymerase

• DNA polymerase

Comparison Table: Prokaryotic vs. Eukaryotic Cells

Example: Central Dogma in Action

• Gene Expression: The gene for hemoglobin is transcribed into mRNA, which is then translated into the hemoglobin protein in red blood cells.

Additional info:

• Some content was inferred and expanded for clarity and completeness, such as the detailed explanations of macromolecules and the structure/function of cell membranes.