Chapter 7 A View of the Cell. Cell Theory CD-ROM Before microscopes, people thought diseases were...
Transcript of Chapter 7 A View of the Cell. Cell Theory CD-ROM Before microscopes, people thought diseases were...
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Chapter 7
A View of the Cell
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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
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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
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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
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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
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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.
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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
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Electron Microscopes
• Transmission Electron Microscope– Used for
scanning interior structures of cell
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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
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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
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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?
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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
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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
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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
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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
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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
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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?
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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
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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
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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”
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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
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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)
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Organelles
• Vacuoles are membrane-bound compartments for temporary storage of materials– Store food,
enzymes, water, waste
– Plant cells have one very large vacuole
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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
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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
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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
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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
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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
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Animal Cell
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Plant Cell
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Section 3 Review1. How are highly-folded membranes an advantage for
the functions of cellular parts?2. Name an organelle that has highly-folded membranes.3. If a cell synthesizes large quantities of protein
molecules, which organelles might be numerous in that cell?
4. A cell’s digestive enzymes are enclosed in a membrane-bound organelle. How can these molecules function in the cell?
5. Compare and contrast the functions of a cell wall to the functions of a plasma membrane.
6. What are the functions of the cytoskeleton? 7. Why are mitochondria and chloroplasts referred to as
energy transporters?