Cell Theory, Types and Structures

• Cell theory is a key principle that guides biologists' understanding of living things
• Cell theory: cells make up all living things, new cells arise from preexisting cells, and a cell is the smallest unit of life

Cell Types

• Prokaryotic cells are structurally simple, small, and lack membrane-bound organelles; examples include bacteria and Archaea
• Eukaryotic cells are structurally complex, large, and have membrane-bound organelles; examples include plants, animals, fungi, and protists

Surface-to-Volume Ratio

• As a cell increases in size, its surface area increases much more slowly than its volume

Microtubules

• Microtubules consist of the protein tubulin, responsible for the structure and movement of cilia and flagella
• Cilia are short, numerous cell extensions that move back and forth
• Flagella are longer than cilia and move in an undulating manner

Plasma Membrane

• The plasma membrane maintains cell's structural integrity.
• Lipids, proteins, and carbohydrates are the building blocks of the plasma membrane
• The structure of the plasma membrane is described as a fluid mosaic
• The plasma membrane is selectively permeable, controlling substance movement in and out of the cell
• Glycoproteins mediate cell recognition
• Receptors provide communication between cells
• Cell adhesion molecules stick cells together to form tissues and organs
• Phospholipid bilayer: composed of hydrophilic ("water-loving") heads and hydrophobic ("water-fearing") tails
• Extracellular fluid: watery solution outside cells.
• Cytoplasm is the jellylike solution inside the cell

Passive Transport

• Passive transport doesn’t require energy for movement across the membrane
• Simple diffusion moves a substance from high to low concentration
• Facilitated diffusion moves a substance from high to low concentration with the help of a membrane protein
• Osmosis is the movement of water molecules from high to low water concentration

Tonicity

• Hypertonic solution: higher solute concentration compared to inside the cell
• Isotonic solution: has the same solute concentration as inside the cell
• Hypotonic solution: has a lower solute concentration than inside the cell

Active Transport

• Active transport requires energy for movement across the membrane
• Endocytosis engulfs materials by the plasma membrane and draws them into the cell in a vesicle

Endocytosis Types

• Phagocytosis engulfs large particles or bacteria
• Pinocytosis engulfs droplets of fluid
• Exocytosis: a membrane-bound vesicle fuses with the plasma membrane, releasing its contents outside the cell

Nucleus

• The nucleus contains most of the cell's DNA
• The nuclear envelope is a double membrane that facilitates communication through nuclear pores
• Communication between the nucleus and cytoplasm occurs through nuclear pores
• Chromosomes are threadlike structures of DNA and associated proteins
• Nucleolus: a region within the nucleus forms and disassembles during the cell cycle, producing ribosomal RNA (rRNA)
• Ribosomal RNA is a component of ribosomes, where protein synthesis begins

Endoplasmic Reticulum (ER)

• The endoplasmic reticulum (ER) is a network of channels connected to the nuclear envelope
• Rough endoplasmic reticulum (RER) contains ribosomes for production of cell products
• Smooth endoplasmic reticulum (SER): lacks ribosomes, but is involved in the production of phospholipids and detoxification
• The Golgi complex consists of interconnected, flattened membranous sacs

Lysosomes

• Lysosomes contain about 40 digestive enzymes that break down macromolecules, old organelles, and invaders

Asbestos

• Asbestos is a group of naturally occurring, carcinogenic, and fibrous silicate minerals
• Inhalation of asbestos can cause lung cancer

Mitochondrion

• Mitochondrion are the location of cellular respiration, providing energy to the cell through the breakdown of glucose to produce ATP

Cytoskeleton

• The cytoskeleton is a network of fibers traversing the cytoplasm
• Microtubules are straight, hollow rods made of the protein tubulin
• Centrioles function in cell division and forming cilia and flagella
• Microfilaments are solid rods made of the protein actin
• Intermediate filaments maintain cell shape and anchor organelles

Cell Metabolism

• Cell metabolism includes all chemical reactions in a cell
• Cellular respiration and fermentation are catabolic pathways that break down complex molecules, releasing energy
• Anabolic pathways build molecules from simpler ones, consuming energy
• Cellular respiration is an oxygen-requiring pathway that breaks down glucose
• Product: material at the end of a chemical reaction
• Substrate: the material on which an enzyme works

Glycolysis

• Glycolysis splits glucose into pyruvate, generates 2 ATP, and does not require oxygen
• Transition reaction: pyruvate reacts with an enzyme to produce acetyl CoA, a high-energy fuel molecule
• Citric Acid (Krebs) Cycle: yields high-energy electron carriers (NADH, FADH2), 2 ATP, and releases CO2 as waste
• Electron Transport Chain: requires oxygen, transfers electrons from FADH2 and NADH to oxygen, releasing 32 ATP molecules

Fermentation

• Fermentation breaks down glucose without oxygen in the cytoplasm, resulting in 2 ATP
• Lactic acid fermentation occurs in the human body during strenuous exercise