Cells, Organelles, & Biomolecules

Introduction

This study guide covers the fundamental concepts of cell structure, organelle function, and biomolecules, as outlined in Chapters 3 and 4. Understanding these topics is essential for grasping the basics of cellular biology and the molecular foundations of life.

Cell Structure and Microscopy

Methods for Studying Cells

• Light Microscopy: Uses visible light to observe cells, often with stains to highlight structures. Suitable for viewing living or fixed cells.

• Electron Microscopy: Employs beams of electrons for much higher resolution, allowing visualization of subcellular structures. Includes transmission and scanning electron microscopy.

• Fluorescence Imaging: Uses fluorescent dyes or proteins to label specific cell components, enabling detailed study of molecular localization and dynamics.

Example: Electron micrographs can reveal the intricate internal membranes of prokaryotic cells or the compartmentalization in eukaryotic cells.

Major Lineages of Life and Cell Types

Domains of Life

• Bacteria

• Archaea

• Eukarya

These domains represent the major evolutionary lineages, each with distinct cellular characteristics.

Types of Cells

• Prokaryotic Cells: Found in Bacteria and Archaea. Characterized by lack of a nucleus and membrane-bound organelles.

• Eukaryotic Cells: Found in Eukarya. Possess a nucleus and various membrane-bound organelles.

Prokaryotic Cells

Structure and Features

• Size: Typically 1–10 μm in diameter; much smaller than eukaryotic cells.

• Cell Wall: Provides structural support and protection.

• Cell Membrane: Regulates transport of substances in and out of the cell.

• Ribosomes: Sites of protein synthesis.

• Cytoskeleton: Maintains cell shape and aids in division.

• Genetic Material: Single circular chromosome; may contain 1–100 plasmids (small, circular DNA molecules).

• Internal Membranes: Infoldings of the plasma membrane can house photosynthetic machinery (e.g., chlorophyll, photosystem proteins).

Example: Bacteria such as Escherichia coli have a cell wall, circular chromosome, and may possess plasmids conferring antibiotic resistance.

Eukaryotic Cells

Structure and Features

• Size: Typically 10x larger than prokaryotic cells (10–100 μm).

• Compartmentalization: Contains specialized organelles (e.g., nucleus, mitochondria, endoplasmic reticulum).

• Complex Cytoplasm: Divided into distinct regions and compartments for various cellular processes.

Example: Plant cells have a large central vacuole, chloroplasts, and a rigid cell wall, while animal cells lack these structures.

Organelles and Their Functions

• Nucleus: Stores genetic material (DNA) and coordinates cellular activities.

• Mitochondria: Site of cellular respiration and energy production.

• Endoplasmic Reticulum (ER): Synthesizes proteins and lipids; rough ER has ribosomes, smooth ER does not.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or use within the cell.

• Vacuole: Large organelle in plants, fungi, and protists; functions in storage of proteins, pigments, toxins, and water balance.

Example: Vacuoles in plant cells store pigments (for flower color), proteins (in seeds), and toxins (e.g., nicotine, alkaloids).

Distinguishing Prokaryotic and Eukaryotic Cells

Key Differences

• Presence of Nucleus: Eukaryotes have a nucleus; prokaryotes do not.

• Chromosome Structure: Prokaryotes have circular chromosomes; eukaryotes have linear chromosomes.

• Organelles: Eukaryotes possess membrane-bound organelles; prokaryotes do not.

• Cell Wall: Present in most prokaryotes and some eukaryotes (plants, fungi).

Example: The presence of a circular chromosome is a distinguishing feature of bacterial cells.

Origin of Cells

Hypotheses for the Origin of Life

• Reducing Atmosphere Hypothesis: Proposed by Alexander Oparin and J.B.S. Haldane in the 1920s. Suggests that complex organic compounds formed from simple molecules in a reducing atmosphere (rich in H2, CH4, NH3, H2O) with energy from lightning or UV radiation.

• Deep Sea Vent Hypothesis: Suggests that life originated at hydrothermal vents, where heat and dissolved gases (H2, CO2, NH3) reacted in mineral-rich environments, catalyzing the formation of organic molecules.

Example: Laboratory experiments simulating early Earth conditions have produced amino acids and other organic molecules, supporting the chemical evolution hypothesis.

Biomolecules and Macromolecules

Carbon Skeletons

• Organic Compounds: Contain carbon, hydrogen, oxygen, and nitrogen.

• Valence Electrons: The number of unpaired electrons in the valence shell determines the number of covalent bonds an atom can form.

• Types of Carbon Skeletons: Can be straight chains, branched chains, or rings.

Example: Glucose has a ring structure, while fatty acids have long, unbranched chains.

Functional Groups

Functional groups are specific groups of atoms within molecules that confer characteristic chemical properties.

Disulfide Bridge: A covalent bond between two sulfur atoms, often linking different molecules or regions of the same molecule, important in protein structure.

Hydrophilic vs. Hydrophobic Molecules

• Hydrophilic: Molecules with polar functional groups (e.g., hydroxyl, carboxyl) that interact with water.

• Hydrophobic: Non-polar molecules that do not interact well with water.

Example: Ethanol (with a hydroxyl group) is hydrophilic, while hydrocarbons (e.g., H–C–C–H) are hydrophobic.

Additional info:

• Exam procedures and announcements are not included in the study notes, as they pertain to course logistics rather than biology content.

• Some content inferred from context and standard biology curriculum.