Cell Biology: The Cell Theory

Biology

• Biology: the scientific study of life.
• Explores life's structure, function, growth, origin, evolution, and distribution.
• Includes diverse sub-disciplines like Anatomy, Biochemistry, Botany, Cell Biology, Ecology, Evolutionary Biology, Genetics, Microbiology, Molecular Biology, Physiology, and Zoology.

Cell Biology

• Cell biology (cytology): A biology branch focused on cell structure, function, and behavior.
• The cell is examined as the basic unit of life.
• Encompasses the study of cells' physiological traits, structures, organelles, environmental interactions, life cycle, division, and death.
• Covers both prokaryotic and eukaryotic cells.
• Employs techniques such as microscopy, cell culture, and molecular biology.
• Cell biology improves progress in medicine, biotechnology, and agriculture.

The Cell Theory

• Living organisms consist of one or more cells.
• Cells form the structural and organizational foundation of organisms.
• Cells originate exclusively from pre-existing cells.

Cell Structure

• Cells contain diverse structures called organelles that perform distinct functions.
• The main types of cells are prokaryotic and eukaryotic.

Prokaryotic Cells

• Defined by the absence of a nucleus and other membrane-bound organelles.
• Typically smaller and less complex than eukaryotic cells.
• Bacteria and archaea are examples.
• Genetic material resides in a nucleoid region.
• Provide strength and protection through a cell wall.
• Contain ribosomes for protein synthesis.
• Certain prokaryotes use flagella for movement.

Eukaryotic Cells

• Cells containing a nucleus and additional membrane-bound organelles.
• Generally more complex than prokaryotic cells.
• Examples include protists, fungi, plants, and animals.
• The nucleus houses the cell's DNA.
• Feature organelles like mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes for specific tasks.

Key Organelles and Their Functions

• Nucleus: Encapsulates DNA and regulates cell activities.
• Mitochondria: Generate energy via cellular respiration.
• Endoplasmic Reticulum (ER): Participates in protein and lipid synthesis.
  • Rough ER: Features ribosomes for protein synthesis.
  • Smooth ER: Dedicated to lipid synthesis and detoxification.
• Golgi Apparatus: Modifies and packages proteins and lipids.
• Lysosomes: Use enzymes to break down cellular waste and debris.
• Ribosomes: Serve as the site of protein synthesis.
• Cell Membrane: The cell's outer barrier controlling substance passage.
• Cytoskeleton: Supports cell structure.

Cell Membrane

• Made of a phospholipid bilayer with proteins.
• Selectively permeable, regulates substance movement.
• Proteins function as channels, carriers, or receptors.

Cell Wall

• Offers support and protection to plant cells, bacteria, fungi, and algae.
• Composed of varied materials depending on the organism; for example, cellulose in plants and peptidoglycan in bacteria.

Cell Communication

• Chemical signals facilitate cell-to-cell communication.
• Signals travel locally or distantly.
• Receptor proteins on cell surfaces bind signaling molecules, triggering intracellular responses.

Cell Cycle

• The sequence includes growth, DNA replication, and division.
• Divided into interphase and mitosis/meiosis.
• Interphase: Cell growth and DNA replication occur.
• Mitosis: Cell divides into two identical daughter cells.
  • Prophase: Chromosomes condense.
  • Metaphase: Chromosomes align in the cell's middle.
  • Anaphase: Sister chromatids separate toward opposite poles.
  • Telophase: Chromosomes decondense, and new nuclear membranes develop.
• Cytokinesis: Cytoplasm divides creating two cells.
• Meiosis: Cell division producing gametes with half the chromosome number.

Cell Metabolism

• Metabolism refers to all the chemical reactions inside a cell.
• Catabolism: Breaks molecules down, releasing energy.
• Anabolism: Builds larger molecules, consuming energy.
• Enzymes: Proteins speeding up reactions.

Cellular Respiration

• Cells produce ATP using glucose and oxygen.
• Occurs in mitochondria.
• Includes glycolysis, the Krebs cycle, and the electron transport chain.

Photosynthesis

• Conducted by plants, algae, and some bacteria to transform light energy into glucose.
• Occurs in chloroplasts.
• Includes light-dependent reactions and the Calvin cycle (light-independent reactions).

Cell Transport

• Substances move across the cell membrane.
• Passive transport: Doesn't require energy; includes diffusion, osmosis, and facilitated diffusion.
• Active transport: Uses ATP to move substances against concentration gradients.

Cell Growth and Division

• Growth factors and nutrients regulate cell growth.
• Division is vital for growth, repair, and reproduction.
• Uncontrolled growth results in cancer.

Cell Specialization

• Cells differentiate into specialized types performing specific roles.
• Differentiation is controlled via gene expression.
• Examples include muscle, nerve, and blood cells.

Cell Death

• Apoptosis: Programmed cell death for tissue development and maintenance.
• Necrosis: Uncontrolled cell death from injury or disease.

Cell Signaling Pathways

• Cell communication pathways:
  • Endocrine: Hormones travel through the bloodstream to target cells.
  • Paracrine: Signals affect nearby cells locally.
  • Autocrine: Cells respond to their own signals.
  • Direct contact: Communication through physical contact.
• They regulate cell growth and differentiation.