Introduction to Cell Biology

Introduction to Cell Biology

• Cell biology studies cells, their structure, function, and internal mechanisms.
• Cells are the fundamental units of living organisms.
• Two main cell types exist:
  • Prokaryotic cells: Lack a nucleus and membrane-bound organelles, simpler structures.
  • Eukaryotic cells: Contain a nucleus and membrane-bound organelles, more complex structures.

Key Components of a Eukaryotic Cell

• Three main regions:
  • Plasma membrane: Outer boundary, selectively permeable.
  • Cytoplasm: Fluid-filled interior, contains organelles and cytosol.
  • Nucleus: Contains DNA, controls cellular activities, and protein synthesis.

Plasma Membrane

• A selective barrier, regulating what enters and exits the cell.
• Composed of lipids, proteins, and carbohydrates.

Cytoplasm

• A fluid-filled space within the cell, containing organelles and cytosol (the gel-like substance).
• Organelles are specialized structures with specific functions.

Nucleus

• Contains the cell's DNA.
• Controls cellular activities, including protein synthesis.
• Contains a nucleolus, site of ribosome assembly.

Function and Characteristics of a Prokaryotic Cell

• Smaller than eukaryotic cells, simpler structures.
• Lack a nucleus and membrane-bound organelles.
• Genetic material is usually a single, circular DNA molecule in the nucleoid region.
• Prokaryotes are self-sufficient; they can:
  • Multiply
  • Produce energy (e.g., ATP synthesis)
  • Send and receive signals
  • Move
• Microscopic in size and are the most abundant cell type.

The Importance of Cellular Compartmentation

• Compartmentation allows for efficient and specialized functions within cells.
• Eukaryotic compartmentalization increases cellular complexity and organization.

Cellular Components

• Organelles are organized compartments with specific functions.
• The nucleus directs cellular activities, including protein synthesis.
• The endoplasmic reticulum (ER) is involved in protein and lipid synthesis.
• Mitochondria produce energy via cellular respiration.
• Lysosomes break down cellular waste and debris.

Cell Theory

• All living things are made up of one or more cells.
• Cells are the fundamental units of life, possessing the characteristics necessary for life.
• New cells arise from pre-existing cells through cell division.
• Cells are the smallest units considered living.

Cell Division and the Cell Cycle

• Cell division is crucial for growth, repair, and reproduction.
• The cell cycle describes the events from cell formation to division.
• Four phases:
  • G1 (Gap 1): Cell growth, carrying out normal functions.
  • S (Synthesis): DNA replication occurs.
  • G2 (Gap 2): Preparation for cell division.
  • M (Mitosis): Cell division.

Importance of the Cell Cycle

• Enables growth and development in multicellular organisms.
• Allows repair of damaged tissues.
• Enables sexual reproduction.

Key Differences Between Prokaryotic and Eukaryotic Cells

• Nucleus: Prokaryotes lack, eukaryotes have.
• Organelles: Prokaryotes have few, eukaryotes have many.
• Genetic material: Prokaryotes have circular DNA, eukaryotes have linear DNA.
• Size: Prokaryotes are generally smaller than eukaryotes.

Cellular Composition

• Cells primarily consist of water, proteins, lipids, and carbohydrates.
• These molecules are organized into structures for specific functions.
• Amino acids create proteins with diverse cell functions.
• Lipids (phospholipids) form cell membranes.
• Carbohydrates provide energy and structural support.

Cellular Functions

• Cells perform crucial functions like:
  • Cellular respiration: Converting food into energy.
  • Protein synthesis: Creating proteins.
  • DNA replication: Copying DNA.
  • Cell signaling: Communicating between cells.

Cell Communication

• Cells communicate via signals.
• Signal transduction pathways transmit information between cells.
• Essential for coordinating cellular activities and tissue function.

Death of a Cell

• Apoptosis: Programmed cell death, crucial for development and removing damaged cells.
• Necrosis: Accidental cell death, caused by injury or insult.

Unicellular and Multicellular Organisms

• Unicellular organisms: Exist as a single, self-sufficient cell performing all life functions.
• Multicellular organisms: Consist of many specialized and interdependent cells.

Types of Multicellular Organizations

• Tissues: Groups of similar cells performing a shared function.
• Organs: Structures formed by different tissues working together.
• Organ systems: Groups of organs carrying out a complex bodily function.

The Importance of Studying Cell Biology

• Fundamentally understanding the basis of life.
• Developing new therapies for diseases.
• Advancing technologies like biotechnology.
• Investigating the origin of life.

Bacterial Shapes

• Bacteria can be spherical (coccus), rod-shaped (bacillus), or spiral (spirillum).

Essential Needs for Bacterial Survival and Multiplication

• Nutrients: Fundamental elements (carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur) for survival.
• Energy Source: Light (phototrophs) or chemical compounds (chemotrophs) power bacterial functions.
• Carbon Source: Bacteria need carbon to build organic molecules. Autotrophs synthesize organic compounds from inorganic materials. Heterotrophs obtain organic carbon from pre-existing organic matter.
• Growth Factors: Certain molecules (amino acids, vitamins, hormones) bacteria require but cannot synthesize.

Bacterial Classification Based on Temperature Tolerance

• Thermophiles: Thrive in high temperatures (40-55°C).
• Mesophiles: Prefer moderate temperatures (20-40°C).
• Psychrophiles: Thrive in cold temperatures (typically below 20°C).

Bacterial Classification Based on pH Tolerance

• Acidophiles: Prefer acidic environments (pH 4 or lower).
• Basophiles: Survive in alkaline environments (pH 8-11 or higher).
• Neutrophiles: Thrive in neutral pH environments (around 7).

Bacterial Classification Based on Oxygen Requirements

• Strict Aerobes: Require oxygen for survival.
• Anaerobes: Cannot tolerate oxygen.
• Microaerophiles: Require small amounts of oxygen.
• Facultative Anaerobes: Can thrive with or without oxygen.

Key Differences Between Animal and Bacterial Cells

• Cell Wall: Animal cells lack a cell wall; bacterial cells have one.
• Nucleus: Animal cells have a true nucleus; bacterial cells have a nucleoid region.
• Organelles: Animal cells have membrane-bound organelles; bacterial cells do not.
• Size: Bacteria are typically much smaller than animal cells.
• Reproduction: Bacteria reproduce asexually (binary fission); animal cells reproduce sexually (mitosis/meiosis).
• Genetic Material: Bacteria have a single, circular chromosome; animals have multiple, linear chromosomes.