Cell Biology: Structure, Types, and Cell Theory

• Biology is the scientific study of life, examining the structure, function, growth, origin, evolution, and distribution of living organisms.
• Cell biology (also known as cytology) is a branch of biology studying the structure, function and behavior of cells.
• A cell is the basic unit of life and is responsible for all life's processes.

Cell Theory

• The cell theory states that all living organisms are composed of one or more cells.
• The cell theory states that the cell is the basic unit of structure and organization in organisms.
• The cell theory states that cells arise from pre-existing cells.

Cell Types

• There are two primary types of cells: eukaryotic and prokaryotic.
• Eukaryotic cells have a membrane-bound nucleus and other organelles.
• Prokaryotic cells do not have a nucleus or membrane-bound organelles.

Eukaryotic Cells

• Eukaryotic cells are more complex than prokaryotic cells.
• Eukaryotic cells are found in plants, animals, fungi, and protists.
• Eukaryotic cells contain organelles such as the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes.
• The nucleus contains the cell's genetic material (DNA) and controls the cell's growth and reproduction.
• Mitochondria are responsible for generating energy for the cell through cellular respiration.
• The endoplasmic reticulum (ER) is involved in protein synthesis and lipid metabolism. There are two types of ER: rough ER (with ribosomes) and smooth ER (without ribosomes).
• The Golgi apparatus processes and packages proteins and lipids.
• Lysosomes contain enzymes that break down cellular waste and debris.

Prokaryotic Cells

• Prokaryotic cells are simpler and smaller than eukaryotic cells.
• Prokaryotic cells are found in bacteria and archaea.
• Prokaryotic cells lack a nucleus and other membrane-bound organelles.
• The genetic material (DNA) in prokaryotic cells is located in the cytoplasm.
• Prokaryotic cells have a cell wall that provides structure and protection.
• Some prokaryotic cells have flagella for movement.

Cell Membrane

• The cell membrane (also called the plasma membrane) surrounds the cell and separates its contents from the external environment.
• The cell membrane is composed of a phospholipid bilayer with embedded proteins and cholesterol.
• The phospholipid bilayer is a barrier to the passage of water-soluble molecules.
• Membrane proteins perform various functions, including transport, signaling, and cell adhesion.
• Cholesterol helps to maintain membrane fluidity.

Cell Wall

• The cell wall is a rigid outer layer that provides support and protection to the cell.
• Plant cells have a cell wall made of cellulose.
• Bacterial cells have a cell wall made of peptidoglycan.
• Fungal cells have a cell wall made of chitin.

Cytoskeleton

• The cytoskeleton is a network of protein filaments that provides structural support to the cell.
• The cytoskeleton is involved in cell movement, cell division, and intracellular transport.
• The cytoskeleton is composed of three main types of filaments: microfilaments, intermediate filaments, and microtubules.
• Microfilaments are made of actin and are involved in cell shape, cell movement, and muscle contraction.
• Intermediate filaments provide mechanical strength to cells and tissues.
• Microtubules are made of tubulin and are involved in cell division, intracellular transport, and the formation of cilia and flagella.

Cell Communication

• Cells communicate with each other through chemical signals.
• Cell signaling is essential for coordinating cellular activities and maintaining homeostasis.
• Cells communicate through various signaling molecules, including hormones, neurotransmitters, and growth factors.
• Cell signaling involves three main steps: reception, transduction, and response.
• Reception: A signaling molecule binds to a receptor protein on the cell surface or inside the cell.
• Transduction: The receptor protein undergoes a conformational change that triggers a cascade of intracellular events.
• Response: The cell responds to the signal by altering its gene expression, metabolism, or behavior.

Cell Division

• Cell division is the process by which a cell divides into two or more daughter cells.
• Cell division is essential for growth, development, and repair.
• There are two main types of cell division: mitosis and meiosis.
• Mitosis is a type of cell division that results in two daughter cells, each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth.
• Meiosis is a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores.

Mitosis

• Mitosis is the process of cell division that produces two identical daughter cells.
• Mitosis is involved in growth, repair, and asexual reproduction.
• Mitosis consists of four main phases: prophase, metaphase, anaphase, and telophase.
• Prophase: The chromosomes condense, and the nuclear envelope breaks down.
• Metaphase: The chromosomes line up along the metaphase plate.
• Anaphase: The sister chromatids separate and move to opposite poles of the cell.
• Telophase: The chromosomes arrive at the poles, and the nuclear envelope reforms.

Meiosis

• Meiosis is the process of cell division that produces four genetically different daughter cells (gametes).
• Meiosis is involved in sexual reproduction.
• Meiosis consists of two rounds of cell division: meiosis I and meiosis II.
• Meiosis I separates homologous chromosomes.
• Meiosis II separates sister chromatids.
• Meiosis results in genetic variation through crossing over and independent assortment.

Cellular Respiration

• Cellular respiration is the process by which cells generate energy in the form of ATP.
• Cellular respiration involves the breakdown of glucose in the presence of oxygen.
• Cellular respiration occurs in three main stages: glycolysis, the Krebs cycle, and the electron transport chain.
• Glycolysis occurs in the cytoplasm and breaks down glucose into pyruvate.
• The Krebs cycle (also known as the citric acid cycle) occurs in the mitochondria and oxidizes pyruvate to produce carbon dioxide and high-energy electron carriers (NADH and FADH2).
• The electron transport chain occurs in the inner mitochondrial membrane and uses the high-energy electron carriers to generate ATP.

Photosynthesis

• Photosynthesis is the process by which plants and some other organisms convert light energy into chemical energy.
• Photosynthesis uses sunlight, water, and carbon dioxide to produce glucose and oxygen.
• Photosynthesis occurs in two main stages: the light-dependent reactions and the Calvin cycle.
• The light-dependent reactions occur in the thylakoid membranes of the chloroplasts and use light energy to produce ATP and NADPH.
• The Calvin cycle occurs in the stroma of the chloroplasts and uses ATP and NADPH to convert carbon dioxide into glucose.

Cell Specialization

• Cell specialization (also known as cell differentiation) is the process by which cells become specialized to perform specific functions.
• Cell specialization is essential for the development and function of multicellular organisms.
• Cell specialization is determined by gene expression. Not all genes are expressed in all cells.

Cell Growth and Death

• Cell growth is the increase in cell size and mass.
• Cell death is a normal part of development and tissue homeostasis.
• There are two main types of cell death: apoptosis and necrosis.
• Apoptosis is programmed cell death and is a controlled process.
• Necrosis is accidental cell death and is caused by injury or infection.

Cancer

• Cancer is a disease characterized by uncontrolled cell growth and division.
• Cancer cells can invade and destroy nearby tissues and organs.
• Cancer is caused by mutations in genes that control cell growth and division.
• Cancer can be treated with surgery, radiation therapy, chemotherapy, and immunotherapy.