Chapter 4

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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

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

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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

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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.

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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.

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 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.

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

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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

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

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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

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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

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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)

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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.

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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

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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

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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

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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

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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.

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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

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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

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Hydrophobic interior of the bilayer is one reason membranes are selectively permeable.
Nonpolar, hydrophobic molecules are lipidsoluble 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

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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.

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Hydrophobic interior of the bilayer is one reason membranes are selectively permeable.
Nonpolar, hydrophobic molecules are lipidsoluble 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.

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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

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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.

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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

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

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Diffusion of a substance across a biological membrane
Diffusion is the movement of
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

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Osmosis
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◦ 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

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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

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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

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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.

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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

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

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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

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