Microscope and Cells Chapter 4

I. The Cell Theory Schwann, Schleiden and Virchow are credited with coming up with the basics of the cell theory 3 components: 1.All living organisms are made up of cells 2.Cells are the basic units of structure and function in living organisms. 3.All cells come from cells that existed before them by cellular reproduction. http://www.youtube.com/watch?v=AeygTtDx2W8

Every cell has the following main characteristics: Cell membrane Cytoplasm DNA Ribosomes

II. The Compound Light Microscope Antone von Leeuwenhoek assembled the first microscope that was useful for scientific research. Compound light microscopes reflect light through a set of lenses and the specimen to magnify the specimen. See handout for the parts of the microscope – you must know it. http://www.youtube.com/watch?v=3emmlXcV-MU&feature=related

II. The Compound Light Microscope 1. Base: Part on which the microscope rests 2. Mirror/Light source: Reflects light through objective lens into barrel of microscope 3. Stage: Surface on which the slide is placed. 4.Arm Part by which microscope is carried

II. The Compound Light Microscope 5. Fine adjustment Used for fine, detailed focusing of microscope 6. Coarse adjustment Used for initial focusing of microscope 7. eyepiece Tube containing lens through which you look into microscope 8. body tube Tube extending from eyepiece to objectives

III. The Compound Light Microscope 9. Nosepiece Revolving circular structure containing objectives 10. High power objective Objective used for focusing minute details on microscope slide 11. Low power objective First objective used for focusing microscope slide 12. clip Used to hold slide on stage 13. diaphragm Controls amount of light that goes through stage into objective lens.

Two important characteristics that determine the quality of a light microscope: Magnification – an increase in the apparent size of an object. We calculate magnification by the following: Magnification of eyepiece x magnification of objective lens = total magnifying power Resolution – the measure of clarity of an image. As the magnification increases, the resolution of the image decreases.

III. Electron Microscopes Some microscopes use beams of electrons for magnification instead of light and are thus called electron microscopes. Two types: Scanning Electron Microscope (SEM) Transmission Electron Microscope (TEM)

III. Electron Microscopes Transmission Electron Microscope (TEM) Scanning Electron Microscope (SEM)

III. Electron Microscopes Scanning electron microscope (SEM) – used to study the detailed architecture of the surface of the object. Forms a 3D image, but does not show the inside of the object. Cholera Bacteria- Scanning Electron Microscope

III. Electron Microscopes Transmission electron microscope (TEM) – used to provide a detailed 2D image of the inside structure of the object that is viewed. Organelles in a pollen grain of tobacco (Nicotiana tabacum; AF = Actin filaments; G = Golgi apparatus; Mi = Mitochondrion; Mt = Microtubule- Transmission Electron Microscope

III. The Size of Cells http://www.cellsalive.com/howbig.htm Cells are microscopic, they are visible only with light microscopes. Most of their size ranges from 1-100 µm. Cells are small, because they have to be able to carry materials from one side of the cell to the next in a short period of time. Cells must have a large enough surface area to be able to take in nutrients and oxygen and release waste quickly.

IV. Prokaryotic Cells Prokaryotic cells – small cells (about 1-10 µm) that do not have a nucleus and membrane-bound organelles Found in bacteria and archaebacteria

Nucleoid region – Cell membrane – Cell wall – Capsule – Prokaryotic Cell Organelles: Nucleoid region – part of the prokaryotic cell where the DNA is found Cell membrane – innermost covering of the cell Cell wall – outside of cell membrane, made up of a special mix of polysaccharides and proteins (antibiotics break it down) Capsule – outside of the cell wall, protective covering (not all bacteria have it)

Prokaryotic Cell Organelles: Flagella (sing. Flagellum) – long, whiplike structure that moves bacteria Pili – short, hair-like projection used to stick to other surfaces and for conjugation (exchange of genetic materials between bacteria) Cytoplasm – jelly-like fluid that dissolves substances and holds organelles Ribosomes – organelles that make proteins in the cytoplasm

http://www.ted.com/talks/lang/eng/bonnie_bassler_on_how_bacteria_communicate.html

V. Eukaryotic Cells Protists, Fungi, Plants, and Animals Have nucleus and membrane-bound organelles Much larger and more complex than prokaryotic cells. Reproduce sexually and asexually

Eukaryotic Organelles General Function: Manufacturing Nucleus Control center of cell; contains most of the cell’s DNA Nucleolus Location where ribosomes are synthesized Nuclear pore Allows RNA to move in and out of nucleus

Eukaryotic Organelles General Function: Manufacturing Ribosomes Protein synthesis Rough ER Comprised of a network of tubes and flattened sacs. Continuous with plasma membrane and nuclear membrane Site of protein synthesis (consists of ribosomes)

Eukaryotic Organelles General Function: Manufacturing Smooth ER Site of lipid and carbohydrate metabolism No ribosomes Golgi Apparatus Connected with ER; flattened disc-shaped sacs, stacked one on top of the other Modification, storage, and packaging of proteins. “tags” proteins so they go to the correct destination.

Eukaryotic Organelles General Function: Breakdown Lysosomes (in animal cells and some protists) Digestion of nutrients, bacteria, and damaged organelles; destruction of certain cells during embryonic development Peroxisomes Diverse metabolic processes with breakdown of H2O2 by-product Vacuoles Digestion (like lysosomes); storage of chemicals, cell enlargement; water balance

Eukaryotic Organelles General Function: Energy Processing Chloroplasts Conversion of light energy to chemical energy of sugars (site of photosynthesis) Mitochondria Conversion of chemical energy of food to chemical energy of ATP “Power House” of cell Bound by double membrane

Mitochondria

Eukaryotic Organelles General Function: Support, Movement, and Communication Cytoskeleton (including cilia, flagella, and centrioles in animal cells) Maintenance of cell shape; anchorage for organelles; movement of organelles within cells; cell movement; mechanical transmission of signals from exterior of cell to interior. Cell walls (in plants, fungi, and protists) Maintenance of cell shape and skeletal support; surface protection; binding of cells in tissues

Cell Transport We will be looking at: Cell Membranes Selective permeability of cell membranes The phospholipid bilayer that makes up cell membranes The model that describes cell membrane, the Fluid Mosaic Model Cell Transport Processes

Cell Membrane Functions Membranes provide the structural basis for metabolic order and surround the cell. Most organelle’s are made from membranes Semipermiability- Regulate the transport of molecules in and out of the cell Immune response Attaches cells to other cells or surfaces.

Selective Permeability Cell membranes control what goes in and out of the cell It allows some substances to cross more easily than others Cell membrane is amazingly thin

Phospholipid Bilayer Lipids, mainly phopholipids, are the main structural components of membranes Phospolipid has a phosphate group and only two fatty acids Head, with a charged phosphate group, is hydrophillic Fatty acid tails are nonpolar and hydrophobic Thus, the tail end is pushed away by water, while the head is attracted to water

Phospholipid Bilayer (continued)

Phospholipid Bilayer (continued) Phospholipids form a two-layer sheet called a phospholipid bilayer. Hydrophillic heads face outward, exposed to the water on both sides of a membrane Hydrophobic tails point inward, mingling together and shielded from water.

Phospholipid Bilayer (continued) Hydrophobic interior of the bilayer is one reason membranes are selectively permeable. Nonpolar, hydrophobic molecules are lipid- soluble can easily pass through membranes Polar molecules and ions are not lipid-soluble Ability to pass through membrane depends on protein molecules in the phospholipid bilayer.

Fluid Mosaic Model Plasma membrane is described as a “Fluid Mosaic” Mosaic denotes a surface made of small fragments, like pieces of colored tile A membrane is considered “mosaic” because it has diverse protein molecules embedded in a framework of phospholipids. A membrane mosaic is “fluid” in that most of the individual proteins and phospholipids can can drift literally in the membrane

Fluid Mosaic Model (“Fluid”) Tails of phospholipids are kinked. Kinks make the membrane more fluid by keeping adjacent phospholipids from packing tightly together. In animal cells, the steroid cholesterol stabilize the phospholipids at body temperature and also keep the membrane fluid at lower temperatures. In a cell, phospholipid bilayer remains about as fluid as salad oil at room temperature.

Fluid Mosaic Model (“Mosaic”) Cell membrane carbohydrates bonded to proteins and lipids in the membrane: A protein with attached sugars is called a glycoprotein whereas a lipid with sugars is called a glycolipid. Function as cell identification tags that are recognized by other cells. Significant for cells in an embryo to sort themselves to tissues and organs. Also functions in the immune system to recognize and reject foreign cells.

Fluid Mosaic Model (“Mosaic”) Cell Membrane Proteins can be… Enzymes: catalyze the assembly of molecules Receptors: relay messages from other cells to the inside of the cell. Move substances across the membrane: like water and glucose

Fluid Mosaic Model (“Mosaic”) Cell Membrane Proteins also function to: Attach to the cytoskeleton and external fibers Form junctions between cell

Fluid Mosaic Model (“Mosaic”) Cell Membranes proteins may be located: Within the cell membrane: integral proteins Usually act as ion channels or molecular channels Outside the cell membrane: peripheral proteins Usually act as receptors

Fluid Mosaic Model

Cell Transport Transport means the movement of molecules from one side of the cell membrane to the other Transport is influenced by: The size of substances The polarity of substances The concentration of substances The permeability of the cell membrane

Types of Cell Transport Passive Diffusion Osmosis Facilitated diffusion Active Bulk Endocytosis Exocytosis

Passive Transport Diffusion of a substance across a biological membrane Diffusion is the movement of particles from high concentration to low concentration. Moves with a concentration gradient No energy input required Eventually reaches equilibrium Molecules continue to move back and forth, but no net change in concentration will occur Small, nonpolar molecules that easily diffuse across plasma membranes, such as O2 and CO2

Passive Transport Simple Diffusion

Passive Transport Osmosis the diffusion of water across the cell membrane. Especially important when the solute cannot move through the membrane. Tonicity: Describes the tendency of a cell in a given solution to lose or gain water. Isotonic, hypertonic, and hypotoni

Passive Transport Osmosis (continued): Isotonic solution Equal concentration of solvent inside and outside of cell; water goes in and out Cell’s volume remains the same; equilibrium Hypertonic solution Solute concentration is lower inside cell (solvent concentration is higher inside cell) ;Water goes out Cell shrivels Causes plasmolysis in plant cells

Passive Transport Osmosis (continued): Hypotonic solution Solute concentration is greater inside the cell (solvent concentration is lower inside the cell); water goes in Cell swells and may lyse Causes cytolysis in animal cells Refer to figure 5.17

Passive Transport Osmosis

Passive Transport Facilitated diffusion Many substances can’t diffuse freely across membrane because of their size, polarity, or charge Need the help of specific transport proteins in the membrane to move across the membrane

Active Transport Transport processes that can move substances from the lower concentration area to the higher by using energy. Energy is gained by using ATP molecules

Active Transport A type of active transport is the Na-K ion pump 3 sodium ions move out of the cell with the help of a transport protein, while 2 potassium ions move into the cell. This process requires energy in the form of ATP.

Active Transport

Bulk Transport Type of active transport that involves movement of large particles. Endocytosis – a process by which large particles can move into the cell by using membrane vesicles Types of endocytosis: Phagocytosis – engulfing solid particles Pinocytosis – engulfing liquids, solutions Receptor-mediated endocytosis – moving into the cell by first binding with receptor molecules on the cell’s surface.

Bulk Transport Receptor-mediated endocytosis

Bulk Transport Exocytosis – the process by which the cell releases large molecules via vesicles through its cell membrane

Summary of Cell Transport