Eukaryotic Cell Structure and Function: Inside the Cell (Chapter 7.4–7.5)

Eukaryotic Cell Structure

Overview of Eukaryotic Cell Components

Eukaryotic cells possess a variety of specialized structures, called organelles, that work together to maintain cellular function. The collaboration of these internal structures is essential for the emergence of life's properties.

• Organelles: Membrane-bound compartments within eukaryotic cells, each with specific functions.

• Cellular collaboration: Organelles interact to support metabolism, growth, and division.

• Main organelles: Nucleus, mitochondria, chloroplasts (in plants and algae), endoplasmic reticulum, Golgi apparatus, lysosomes, and cytoskeleton.

Mitochondria

Structure and Function

Mitochondria are the primary site of ATP production in eukaryotic cells, often referred to as the "powerhouse" of the cell. Their unique structure supports efficient energy conversion.

• ATP (Adenosine Triphosphate): The main energy currency of the cell, produced by mitochondria through cellular respiration.

• Double membrane:

  • Outer membrane: Defines the organelle's surface.

  • Inner membrane: Highly folded into sac-like structures called cristae, increasing surface area for energy production.

• Mitochondrial matrix: The solution enclosed within the inner membrane, containing enzymes for the citric acid cycle.

Dynamic Morphology and Genetics

Mitochondria are dynamic organelles capable of changing shape and number within cells.

• Fusion and fission: Mitochondria can merge (fusion) or split (fission), forming networks or individual organelles.

• Mitochondrial DNA (mtDNA): Mitochondria contain their own circular DNA, inherited maternally.

• Independent division: Mitochondria grow and divide independently of the cell cycle.

• Ribosomes: Mitochondria manufacture their own ribosomes for protein synthesis.

Chloroplasts

Structure and Function

Chloroplasts are organelles found in plant and algal cells, responsible for photosynthesis—the process of converting light energy into chemical energy.

• Three membranes:

  • Outer and inner membranes: Enclose the organelle.

  • Innermost membrane: Contains thylakoids, which are flattened sacs.

• Thylakoids: Arranged in stacks called grana, where the light-dependent reactions of photosynthesis occur.

• Stroma: The fluid surrounding thylakoids, containing enzymes for the Calvin cycle (sugar production).

Genetics and Origin

Chloroplasts share several features with mitochondria, including their own DNA and ribosomes.

• Chloroplast DNA: Encodes some of the organelle's proteins.

• Independent division: Chloroplasts grow and divide independently of cell division.

• Endosymbiosis theory: Proposes that mitochondria and chloroplasts originated as free-living bacteria engulfed by ancestral eukaryotic cells, leading to a mutually beneficial relationship.

Summary Table: Key Eukaryotic Cell Organelles

Organelle	Main Function	Key Features
Mitochondria	ATP production (cellular respiration)	Double membrane, cristae, matrix, own DNA/ribosomes
Chloroplasts	Photosynthesis	Three membranes, thylakoids/grana, stroma, own DNA/ribosomes
Nucleus	Genetic information storage and processing	Double membrane (nuclear envelope), nuclear pores
Endoplasmic Reticulum (ER)	Protein and lipid synthesis	Rough (ribosome-studded) and smooth regions
Golgi Apparatus	Protein modification and sorting	Stacked cisternae, dynamic structure
Lysosomes	Digestion and recycling	Acidic interior, hydrolytic enzymes

Additional info:

• The endosymbiosis theory is supported by the presence of double membranes and similarities between organelle and bacterial DNA.

• ATP production in mitochondria involves the electron transport chain and oxidative phosphorylation.

• Photosynthesis in chloroplasts consists of light-dependent reactions (in thylakoids) and the Calvin cycle (in stroma).