Inside the Cell – Organelles and Cell Structure

Chapter 7a: Inside the Cell – Organelles

Introduction

This chapter explores how the properties of life emerge from the collaboration of internal structures within a cell. It focuses on identifying the parts of the cell, understanding the differences between cell types, and examining how cellular components work together to support life.

Cell Structure Overview

Plasma Membrane

The plasma membrane is a fundamental feature of all cells, separating the cell's interior from its external environment.

• Structure: Composed of a phospholipid bilayer with embedded proteins.

• Function: Maintains a distinct internal environment by controlling the movement of substances in and out of the cell.

• Cytoplasm vs. Cytosol: The cytoplasm includes all contents within the plasma membrane except the nucleus, while the cytosol refers specifically to the fluid portion.

Example: The plasma membrane's selective permeability is essential for nutrient uptake and waste removal.

Ribosomes

Ribosomes are macromolecular machines found in all cells, responsible for protein synthesis.

• Composition: Made of RNA molecules and proteins.

• Function: Catalyze the formation of polypeptides from amino acids during translation.

• Ribozyme: Some ribosomal RNA molecules act as enzymes (ribozymes).

Example: Ribosomes can be free in the cytosol or attached to the endoplasmic reticulum in eukaryotic cells.

Classification of Cells and Organisms

Cell Types by Morphology

Cells are classified based on their structural features:

• Prokaryotes: Cells lacking a nucleus and membrane-bound organelles.

• Eukaryotes: Cells containing a nucleus and membrane-bound organelles.

Domains by Phylogeny

Organisms are grouped into three domains based on evolutionary relationships:

• Bacteria: Prokaryotic cells.

• Archaea: Prokaryotic cells with distinct molecular characteristics.

• Eukarya: Eukaryotic cells, including plants, animals, fungi, and protists.

Additional info: The domain system reflects genetic and biochemical differences among major groups of organisms.

Major Topics in Cell Structure

Roadmap of Chapter Topics

The chapter is organized into three main sections:

• 7.1 Prokaryotic Cell Structure: Examines the features and organization of prokaryotic cells.

• 7.2 Eukaryotic Cell Structure: Details the components and complexity of eukaryotic cells.

• 7.3 Integration of Cell Parts: Explores how organelles and structures work together as a system.

Example: The endomembrane system in eukaryotes coordinates protein and lipid processing.

Key Terms and Concepts

• Organelle: Specialized structure within a cell that performs a specific function.

• Phospholipid Bilayer: Double layer of phospholipids forming the basic structure of cell membranes.

• Translation: The process by which ribosomes synthesize proteins using messenger RNA as a template.

• Ribozyme: An RNA molecule capable of acting as an enzyme.

Summary Table: Cell Types and Domains

Cell Type	Key Features	Domains
Prokaryote	No nucleus, no membrane-bound organelles	Bacteria, Archaea
Eukaryote	Nucleus, membrane-bound organelles	Eukarya

Important Equations

• General formula for surface area of a sphere (cell):

$A = 4\pi r^2$

• General formula for volume of a sphere (cell):

$V = \frac{4}{3}\pi r^3$

Additional info: The surface area-to-volume ratio is critical for cell function, affecting nutrient uptake and waste removal.