Chapter 4

 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. 

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

 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. 

 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.

 Some microscopes use beams of electrons for magnification instead of light – 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.  Transmission electron microscope (TEM) – used to provide a detailed 2D image of the inside structure of the object that is viewed.

  Cells are microscopic, they are visible only with light microscopes.  Most of their size ranges from 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.

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

 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) ◦ 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

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

 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

 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)

 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.

 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 H 2 O 2 by-product  Vacuoles ◦ Digestion (like lysosomes); storage of chemicals, cell enlargement; water balance

 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

 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

 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

 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.

 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

 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

 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.

Phospholipid

 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.

 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.

 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

 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.

◦ Cell Membrane Proteins:  Integral proteins – act as ion channels or molecular channels  Peripheral proteins – act as receptors

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.

 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

 Passive ◦ Diffusion ◦ Osmosis ◦ Facilitated diffusion  Active  Bulk ◦ Endocytosis ◦ Exocytosis

 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 O 2 and CO 2

Simple Diffusion

 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

 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

 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

Osmosis

 Osmotic Pressure ◦ The pressure exerted by the flow of water through a semipermeable membrane separating two solutions with different concentrations of solute. ◦ Higher concentration of dissolved substances will result in lower osmotic pressure and in the movement of water into the area with more dissolved substances.

 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

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

 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.

 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.

Receptor-mediated endocytosis

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