Cell Biology: An Overview

Basic Characteristics of Cells

• Definition: Cells are the smallest living units of an organism.
• Common Features:
  • Cell Membrane: Separates the inside of the cell from the environment.
  • Cytoplasm: Jelly-like fluid inside the cell.
  • DNA: Genetic material of the cell.

Categories of Cells

Eukaryotic Cells

• Characteristics:
  • Have organelles, including a nucleus.
  • More advanced and complex.
  • Found in plants and animals.

Prokaryotic Cells

• Characteristics:
  • No nucleus or membrane-enclosed organelles.
  • DNA is not contained within a nucleus.
  • Always unicellular (e.g., bacteria).

Organelles and Their Functions

Nucleus

• Function: Control center of the cell, contains DNA.
• Components:
  • Chromatin: Spread-out form of DNA inside the nuclear membrane.
  • Chromosomes: Condensed structures of DNA when the cell is ready to divide.
  • Nucleolus: Structure where ribosomes are made.

Ribosomes

• Function: Synthesize proteins.
• Location:
  • Free-floating in the cytoplasm.
  • Attached to the endoplasmic reticulum (ER).

Endoplasmic Reticulum (ER)

• Types:
  • Rough ER: Has ribosomes attached.
  • Smooth ER: No ribosomes attached.
• Function: Transport materials such as proteins.

Golgi Apparatus (Golgi Body)

• Function: Customizes proteins into usable forms by folding them or adding other materials (e.g., lipids, carbohydrates).

Vacuoles

• Function: Store various materials.
• Plant Cells: Central vacuole stores water.

Lysosomes

• Function: Act as garbage collectors, taking in damaged/worn-out cell parts.
• Feature: Filled with enzymes to break down cellular debris.

Mitochondria

• Function: Powerhouse of the cell, produces ATP through cellular respiration.
• Note: Found in both animal and plant cells.

Cytoskeleton

• Function: Maintains cell shape.
• Components:
  • Microfilaments: Made of protein.
  • Microtubules: Thin, hollow tubes.

Chloroplasts

• Function: Site of photosynthesis in photoautotrophic organisms (e.g., plants).
• Feature: Contains green pigment chlorophyll.

Cell Wall

• Function: Shapes, supports, and protects plant cells (not found in animal cells).

Unique Structures in Some Cells

Cilia

• Function: Trap and expel inhaled particles in the respiratory tract.
• Feature: Microscopic hair-like projections.

Flagella

• Function: Aid in cell movement.
• Examples:
  • Found in some bacteria.
  • Present in human sperm cells.

Summary

• Eukaryotic Cells: Plant and animal cells with a nucleus and membrane-enclosed organelles.
• Prokaryotic Cells: Unicellular organisms without a nucleus or membrane-enclosed organelles.
• Common Features: All cells have a cell membrane, cytoplasm, and genetic material.
• Energy Organelles: Both plant and animal cells have mitochondria, but only plant cells have chloroplasts.