Chapter 7 A View of the Cell
Cell Theory • CD-ROM • Before microscopes, people thought diseases were caused by curses and supernatural spirits • They had no idea microorganisms, such as bacteria and viruses existed • When the microscope was invented, scientists discovered cells exist • Cells are the basic units of living organisms
Cell Theory • Anton van Leeuwenhoek (Dutch) used the first simple light microscope in the 1600s • It had one lens (page 1064) • Gradually, lenses got better • Compound light microscopes use a series of lenses to magnify objects in steps • Can magnify up to 1500 times • The microscopes we use in the lab
Cell Theory • Robert Hooke (1600s, English) used a compound light microscope to study cork, the dead cells of oak bark • He saw small, geometric shapes that reminded him of the small rooms monks lived in called cells • Cells are the basic units of all living things
Cell Theory • Matthias Schleiden (1830s, German) discovered that all plants are made of cells • Theodor Schwann (German) discovered that all animals are made of cells • Rudolf Virchow discovered that all cells come from existing cells • All these scientists (plus others) contributed ideas that are now summed up in what we call the cell theory
Cell Theory • All organisms are composed of one or more cells. • The cell is the basic unit of structure and organization of organisms. • All cells come from preexisting cells.
Electron Microscopes • Electron Microscopes let us see a much greater magnification than light microscopes • They use beams of electrons to produce images • Scanning Electron Microscope • Used for scanning 3-D surfaces
Electron Microscopes • Transmission Electron Microscope • Used for scanning interior structures of cell
Types of Cells • Organelles are small, specialized structures within cells • Many, but not all are surrounded by membranes • Prokaryotes are organisms that do not have membrane-bound organelles (biology.arizona.edu) • Kingdom Monera ( now split into Eubacteria & Archaebacteria) • Eukaryotes are organisms that do have membrane-bound organelles • Kingdoms Animalae, Plantae, Fungi, Protista
Types of Cells • Robert Brown (Scottish) observed that eukaryotic cells have a prominent structure, the nucleus • the nucleus manages cellular functions • Rudolf Virchow concluded that this prominent structure was responsible for cell division
Section 1 Review • How has the history of microscopes influence the study of cells? • What are the three parts of the cell theory? • What is the difference between a light microscope and an electron microscope? • What is the difference between a prokaryote and a eukaryote?
The Plasma Membrane • Cells must maintain proper conditions within itself to function • The plasma membrane is a flexible boundary between the cell and its environment • It allows a steady supply of nutrients into and out of the cell at the appropriate levels • The plasma membrane is selectively permeable • This means that it allows some molecules to pass through while keeping others out. • Like a screen in a window
The Plasma Membrane • Phospholipids • The “head” is polar, or slightly charged • It is hydrophilic (likes water) • The “tail” is nonpolar, or not charged • It is hydrophobic (repels water) • The phospholipids arrange themselves form a bi-layer with the fatty acid tails forming the interior and the heads facing the watery environments outside and inside the cell
Plasma Membrane • The plasma membrane is called a phospholipid bilayer • Arranged in this manner, a barrier is created that is water-soluble at its outer surfaces and water-insoluble in the middle • Keeps out both water soluble and water insoluble molecules
Plasma Membrane • The current model of the plasma membrane is called the fluid mosaic model. • The phospholipids actually move around like a fluid. • The other components of the membrane (proteins, carbohydrates, cholesterol, etc.) move around as well
Plasma Membrane • Cholesterol helps to stabilize the phospholipids by preventing their fatty acid tails from sticking together • Transport proteins move span the membrane and move needed substances or waste materials through the plasma membrane • Other proteins and carbohydrates that stick out help cells to identify surface signals and other cells • These proteins play an important part in protecting cells from infection
Section 2 Review • What is a phospholipid? • Why is the cell membrane a bilayer? • What does polar and nonpolar mean? • What are the specialized parts of the cell membrane? • Why is the cell membrane referred to as fluid mosaic?
Cell Wall • Fairly rigid structure located outside the plasma membrane of some cells that provides additional support and protection • Plants, fungus, most bacteria • The cell wall is very porous, made of a tough mesh of fibers • Like framing of a house
Nucleus • Membrane-bound (called nuclear envelope) organelle that contains the directions to make proteins • Nuclear pores allow passage through the nuclear envelope • Chromatin - uncondensed strands of DNA • When cell is dividing, DNA condenses into chromosomes • Nucleolus - organelle within the nucleus that make ribosomes
Organelles • Ribosomes are the sites where the cell produces proteins according to the directions of DNA • One organelle without a membrane • Cytoplasm is the clear, gelatinous fluid inside the cell • Acts as a medium for things to move around in the cell • “Organelles can’t fly”
Organelles • The endoplasmic reticulum (ER) is arranged in a series of highly folded membranes suspended in the cytoplasm • In general, ER is involved in the movement of materials throughout the cell • Rough ER has ribosomes, which is where protein synthesis takes place • Smooth ER has no ribosomes and is involved in numberous biochemical activities, including the production and storage of lipids
Organelles • The Golgi apparatus is a flattened stack of tubular membranes that modifies the proteins • The Golgi sorts proteins into packages and packs them into membrane-bound structures called vescicles for later transport (like UPS)
Organelles • Vacuoles are membrane-bound compartments for temporary storage of materials • Store food, enzymes, water, waste • Plant cells have one very large vacuole
Organelles • Lysosomes are organelles that contain digestive enzymes • Digest old organelles, food, viruses, bacteria, etc. • Can fuse with a vacuole to dump waste or give enzymes • Lysosomes digest a tadpole’s tail
Organelles • Plastids are a group of organelles used for storage • Named for the color or pigment they contain • Chloroplasts are organelles that capture light energy and convert it to chemical energy (photosynthesis occurs here) • Plastid containing chlorophyll, which actually traps the light and gives plants green color
Organelles • Mitochondria are membrane-bound organelles in plant and animal cells that transform stored chemical energy into a usable form for the cell (ATP) • Has an outer and inner highly folded membrane • ATP produced on inner folds
Organelles • The cytoskeleton forms a framework for the cell • A network of tiny rods and filaments • Cytoskeleton is constantly changing its shape • Microtubules are thin, hollow cylinders made of protein • Microfilaments are smaller, solid protein fibers • Give support for cell • Provide “highway system” for organelles to move throughout cell
Organelles • Centrioles are organelles made up of microtubules that play a part in cell division • In animals and most protists • Cilia are short, numberous projections that look like hairs • Made of microtubules and help organelles move and feed • Flagella are longer projections that move in a whip-like motion • Made of microtublules - help with movement • Cells usually only have 1 or 2
Section 3 Review • How are highly-folded membranes an advantage for the functions of cellular parts? • Name an organelle that has highly-folded membranes. • If a cell synthesizes large quantities of protein molecules, which organelles might be numerous in that cell? • A cell’s digestive enzymes are enclosed in a membrane-bound organelle. How can these molecules function in the cell? • Compare and contrast the functions of a cell wall to the functions of a plasma membrane. • What are the functions of the cytoskeleton? • Why are mitochondria and chloroplasts referred to as energy transporters?