A Tour of the Cell

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A Tour of the Cell
www.probes.com
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History of the Cell
? Cells were first discovered in 1665 by Robert
Hooke
From Micrographia
? The accumulation of scientific evidence led to
the cell theory (1) All living things are
composed of cells (2) All cells form from
previously existing cells
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• Cells are the building blocks of all life forms

• Organisms are either

? Single-celled, such as most bacteria and
protists ? Multicelled, such as plants, animals,
and most fungi
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Cells are made up of MACROMOLECULES

• Nucleic Acids
• (2) Proteins
• (3) Lipids
• (4) Carbohydrates

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The Two Major Categories of Cells

• Prokaryotic cells
• ? Eukaryotic cells

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Prokaryotes Vs. Eukaryotes
Prokaryotic cell
Nucleoid region
Eukaryotic cell
Nucleus
Organelles
Figure 4.4
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Prokaryotic cells

• Are much smaller than eukaryotic cells
• Lack internal structures surrounded by membranes
• ? Lack a nucleus

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A Detailed View of Prokaryotic Cells
Prokaryotic flagella
Nucleoid region (DNA)
Ribosomes
Plasma membrane
Cell wall
Capsule
Pili
Figure 4.5
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A Detailed View of Eukaryotic Cells
? An idealized animal cell
Centriole
Ribosomes
Not in most plant cells
Lysosome
Flagellum
Cytoskeleton
Plasma membrane
Nucleus
Mitochondrion
Rough endoplasmic reticulum (ER)
Smooth endoplasmic reticulum (ER)
Golgi apparatus
Figure 4.6A
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A Detailed View of Eukaryotic Cells
? An idealized plant cell
Not in animal cells
Cytoskeleton
Mitochondrion
Central vacuole
Nucleus
Cell wall
Rough endoplamsicreticulum (ER)
Chloroplast
Ribosomes
Plasma membrane
Smooth endoplasmic reticulum (ER)
Plasmodesmata
Golgi apparatus
Figure 4.6B
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Antony van Leeuwenhoek (1632-1723) Microscope
Maker
? Identified and termed animalcules
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Microscopes as Windows to Cells
? The light microscope is used by many scientists
(1) Light passes through the specimen (2)
Lenses enlarge, or magnify, the image
(a) Light micrograph (LM) of a white blood cell
(stained purple) surrounded by red blood cells
Figure 4.2A
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Microscope Terminology
Magnification An increase in the specimens
apparent size
Resolving power The ability of an optical
instrument to show two objects as separate
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The Electron Microscope
? Uses a beam of electrons instead of light

• Has a higher resolving power than light
  microscopes
• (can magnify up to 100,000X)

? The power of electron microscopy reveals many
details of cellular components
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Scanning Electron Microscopy
(b) Scanning electron micrograph (SEM) of a white
blood cell
Figure 4.2B
? for studying external cellular structures
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Transmission Electron Microscopy
(c) Transmission electron micrograph (TEM) of a
white blood cell
Figure 4.2C
? for studying internal cellular structures
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Power and Scale of Microscopy
Human height
Length of some nerve and muscle cells
Chicken egg
Unaided eye
Frog eggs
Plant and animal cells
Light microscope
Nucleus
Most bacteria
Mitochondrion
Electron microscope
Smallest bacteria
Viruses
Ribosomes
Proteins
Lipids
Small molecules
Figure 4.3
Atoms
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MEMBRANE STRUCTURE AND FUNCTION
The plasma membrane separates the living cell
from its nonliving surroundings and regulates
what goes in and out.
Organelles are surrounded by membranes to
separate them as distinct compartments of the
cell with specialized functions.
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The Fluid Mosaic Model of Membranes
? Membranes are composed of lipids AND proteins
and are highly dynamic (fluid)
? Membranes of the cell have selective
permeability (04-07a-MembraneStructure.mov)
(1) They allow some substances to cross more
easily than others (2) They block passage of
some substances altogether (3) The traffic of
some substances can only occur through transport
proteins (like glucose)
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The LIPID Component
? The lipids belong to a special category called
phospholipids
? Phospholipids form a two-layered membrane, the
phospholipid bilayer
Outside cell
Hydrophilic head
Hydrophobic tail
Cytoplasm (inside cell)
(a) Phospholipid bilayer of membrane
Figure 4.7A
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Phospholipids in Membranes
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The PROTEIN Component
? Most membranes have specific proteins embedded
in the phospholipid bilayer
Hydrophilic region of protein
Phospholipid bilayer
Hydrophobic region of protein
(b) Fluid mosaic model of membrane
Figure 4.7B
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FUNCTIONS of Membrane Proteins
Cytoplasm
Fibers of extracellular matrix
c
Enzymatic activity
b
Cell signaling
a
Attachment to cytoskeleton and extracellular matri
x
e
Intercellular joining
f
Cell-cell recognition
d
Transport
Cytoplasm
Cytoskeleton
Figure 4.8
04-08-ReceptorProtAnim.mov
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EVOLUTION CONNECTIONThe Origin of Membranes
? Phospholipids were probably among the organic
molecules on the early Earth
? When mixed with water, phospholipids
spontaneously form membranes
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THE NUCLEUSGENETIC CONTROL OF THE CELL
? The nucleus is the manager of the cell
Genes in the nucleus store the information
necessary to produce proteins, which perform
cellular functions
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Structure and Function of the Nucleus
? The nucleus is bordered by a double membrane
called the nuclear envelope

• The nucleus contains chromatin and
• the nucleolus

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Nuclear envelope
Ribosomes
Chromatic
Nucleolus
Pore
Figure 4.9
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How DNA Controls the Cell
? Genes encoded by DNA are copied to another
molecule, mRNA
DNA
1
Synthesis of mRNA in the nucleus
mRNA
?mRNA molecules representing genes are exported
from the nucleus into the cytoplasm
Nucleus
Cytoplasm
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mRNA
Movement of mRNA into cytoplasm via nuclear pore
? Ribosomes in the cytoplasm read the mRNA and
use the info to make a protein
Ribosome
3
Synthesis of protein in the cytoplasm
Protein
Figure 4.10
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The Central Dogma of Molecular Biology

• Transcription
• Translation

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Exceptions to the Central Dogma
Retroviruses
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Chloroplasts and Mitochondria Energy Conversion
? Cells require a constant energy supply to do
all the work of life
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Chloroplasts
Inner and outer membranes of envelope
? Chloroplasts are the sites of photosynthesis
the conversion of light energy to chemical energy
Granum
Space between membranes
Stroma (fluid in chloroplast)
Figure 4.17
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Mitochondria
? Mitochondria are the sites of cellular
respiration, the process of producing ATP from
food molecules
Outer membrane
Inner membrane
Cristae
Matrix
Space between membranes
Figure 4.18
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EVOLUTION CONNECTIONThe Origin of Organelles
? The Endosymbiont Theory eukaryotic organelles
evolved from prokaryotes that were engulfed by
other cells
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The CytoskeletonCell Shape and Movement
? The cytoskeleton is an infrastructure of the
cell consisting of a network of fibers
(1) Actin Fibers (structure movement OF the
cell) (2) Microtubules (structure movement
WITHIN the cell)
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Functions of the Cytoskeleton
? Provide mechanical support and structure to the
cell to give it shape
Figure 4.19A
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Functions of the Cytoskeleton
? The cytoskeleton can change the shape of a cell
for movement
Figure 4.19B
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Motile Appendages
? Flagella propel the cell in a whiplike motion
? Cilia move in a coordinated back-and-forth
motion
Figure 4.20A, B
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Non-moving cells have cilia and flagella, too
? The human windpipe is lined with cilia
Figure 4.20C
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The universal architecture of eukaryotic cilia
(a) Paramecium
(b) Cells from fallopian tube
(c) Cross section of cilium
Figure 1.9
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CELL SURFACESProtection, Support, and Cell-Cell
Interactions
? Most cells secrete materials that are external
to the plasma membrane (except those that have
cell walls!)
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Plant Cell Walls and Cell Junctions
? Plant cells are encased by cell walls
Walls of two adjacent plant cells
Vacuole
Plasmodesmata (channels between cells)
Figure 4.21
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Animal Cell Surfaces and Cell Junctions
? Animal cells lack cell walls

• They secrete a sticky covering called the
  extracellular matrix
• (2) This layer helps hold cells together to form
  tissues and organs and so on.

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Connections Between Animal Cells
Extracellular matrix
(a) Tight junctions
(b) Anchoring junctions
(c) Communicating junctions
Plasma membranes of adjacent cells
Extracellular matrix
Figure 4.22
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The Secretory System Manufacturing and
Distributing Cellular Products
? Many of the membranous organelles in the cell
belong to the secretory, or endomembrane, system
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The Endoplasmic Reticulum
? The endoplasmic reticulum (ER)
Nuclear envelope

• Produces an enormous variety of molecules
• (2) Is composed of smooth and rough ER

Ribosomes
Rough ER
Smooth ER
Figure 4.11
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Rough ER
? The roughness of the rough ER is due to
ribosomes that stud the outside of the ER membrane
? The functions of the rough ER include
(1) Producing proteins (2) Producing new membrane
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After the rough ER synthesizes a molecule it
packages the molecule into transport vesicles
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Transport vesicle buds off
Secretory protein inside transport vesicle
Ribosome
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Protein
1
Rough ER
2
Polypeptide
Figure 4.12
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Smooth ER
? The smooth ER lacks the surface ribosomes of ER
and produces lipids, including steroids
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The Golgi Apparatus
? Works in partnership with the ER ? Refines,
stores, and distributes the products of cells
Transport vesicle from ER
Receiving side of Golgi apparatus
Golgi apparatus
New vesicle forming
Transport vesicle from the Golgi
Shipping side of Golgi apparatus
Plasma membrane
Figure 4.13
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Lysosomes
? A lysosome is a membrane-enclosed sac

• It contains digestive enzymes
• (2) The enzymes break down macromolecules

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Digestive Functions of the lysosome
To fuse with food vacuoles to digest the food
Lysosome
Digestive enzymes
Plasma membrane
Digestion
Food
Food vacuole
(a) Lysosome digesting food
Figure 4.14a
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Digestive Functions of the lysosome
To break down damaged organelles
Lysosome
Digestion
Damaged organelle
(b) Lysosome breaking down damaged organelle
Figure 4.14b
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Vacuoles Membranous Sacs
? Two types are the contractile vacuoles of
protists and the central vacuoles of plants
Central vacuole
Contractile vacuoles
(a) Contractile vacuoles in a protist
(b) Central vacuole in a plant cell
Figure 4.15
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Summary of the Endomembrane System
Rough ER
Transport vesicle from ER
Golgi apparatus
Secretory vesicle from Golgi
Vacuole
Lysosome
Secretory protein
Plasma membrane
Figure 4.16
04-16-EndomembraneSysAnim.mov
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BIOLOGY AND SOCIETY Drugs That Target CELLS
? Antibiotics are one of the great marvels of
modern medicine
(1)Treatment with these drugs will kill invading
bacteria (2)The drugs dont harm the human cells
of the host
Figure 4.1
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BIOLOGY AND SOCIETY Drugs That Target CELLS
? Chemotherapy and Cancer

• Targets cells that are growing rapidly
• (2) The drugs dont affect most human cells, but