Download chapter 7 a view of the cell

Chapter 7
A view of the cell
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The Cell Theory
• Microscope invented by Anton van
Leeuwenhoek
• First person to see a cell (in cork)
Robert Hooke
• Matthias Schleiden found that all
plants have similar structures
• Theodore Schwann found the same
situation with animals
• Hence, the cell theory was born
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The Light Microscope
• Uses light and lenses
• The Simple light
Microscope used one lens
and natural light
(Leeuwenhoek)
• The Compound light
microscope: Uses
multiple lenses
– Magnifies up to 1500 times
The Electron Microscope
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Invented in the 1940s
Uses a beam of electrons
Magnifies up to 500,000 times
Two Kinds:
– Scanning electron microscope
(SEM): Scans the surface of
cells.
– Transmission electron
microscope (TEM): Allows for
study of structures inside cells.
The Electron Microscope
SEM
TEM
• Cell theory
–All organisms are composed of
one or more cells
–The cell is the basic unit of
organization of organisms
–All cells come from pre-existing
cells
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Two Basic Cell Types
• Prokaryotes: Cells lacking internal membrane-bound
structures
• Eukaryotes: Cells containing internal membrane-bound
structures
– The membrane-bound structures are called organelles
– Contains a nucleus: organelle that manages cellular function. First
observed by Robert Brown. Rudolf Virchow concluded that it was
responsible for cell division.
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• Organelles – membrane-bound
structures within eukaryotic
cells
– Each organelle has a specific
function for cell survival (ie.
Nucleus)
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7.2 The Plasma Membrane
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• Plasma Membrane – the
boundary between the cell and
its environment
– Responsible for allowing
nutrients into and out of the cell
– Allows waste and other products
to leave the cell
– Maintains homeostasis
• Water freely enters the cell
through the membrane
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• Certain particles (Na+ ions & Ca+ ions)
must be allowed in the cell only at
certain times, in certain amounts,
and through certain channels
• Selective Permeability keeps a
proper balance by allowing only
certain molecules to cross the
membrane
• Homeostasis – the process of
maintaining the cells environment
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Structure of the Plasma Membrane
• Composed of a
phospholipid bilayer.
– A Lipid with a phosphate
group attached
– Has only 2 fatty acid tails
– Forms a sandwich
• The phosphate group
forms the polar head
• The fatty acid tails form
the nonpolar tail
Plasma Membrane Structure
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Phospholipids
• Lipids with a phosphate group
attached
• Hydrophobic tails inside and
hydrophilic heads on outside
• The bilayer is a barrier that is
water-soluble at the outer surface
and water-insoluble in the middle
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• Water-soluble molecules will not
easily move through the membrane;
they are stopped by the waterinsoluble middle
• The polar phosphate group allows
the cell membrane to interact with
its watery environment
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Fluid Mosaic Model
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Fluid Mosaic Model
• The membrane is fluid: It is flexible and
phospholipids can move in the membrane like
water in a lake.
• The membrane is mosaic: There are proteins
embedded in the membrane that also move (like
boats in the lake)
Components of Membrane
• Cholesterol – helps stabilize the
phospholipids
– Prevents the fatty acid chains of the
phospholipids from sticking together
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• Transport Proteins – span the
entire membrane, creates a
selectively permeable membrane
– Regulates which molecules enter and
leave a cell
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Other components
• Other Proteins and carbohydrates on the
external surface: Helps with identification.
• Proteins on internal surface: Provides
flexibility by attaching the plasma membrane
to the cell’s internal structure.
7.3
Eukaryotic Cell Structure
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Cellular Boundaries
• Plasma membrane surrounds
the cell
• In plants, fungi, most bacteria
and some protists, the cell
wall surrounds the plasma
membrane
– Fairly rigid
– Provides support and
protection
– Made up of the
carbohydrate cellulose
– Has pores to allow
molecules through
Nucleus and cell control
• The Nucleus is the
leader of the cells
– Gives directions for
the making of
proteins
• The master set of
directions is in
chromatin
• During cell division,
chromatin
condenses to form
chromosomes.
• Chromatin – strands of genetic
material, DNA
– Condenses to form chromosomes
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Nucleus and Cell Control
• Inside the nucleus there is also the
nucleolus
– Makes ribosomes
• Ribosomes
– Assemble enzymes and proteins
– Get instructions from DNA
– Leave nucleus and enter cytoplasm in
order to make proteins
Nucleolus
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Ribosomes
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Cytoplasm
• Clear, gelatinous fluid inside a cell
• Majority of chemical reactions
take place
• Suspends cells organelles
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Assembly and Transport
• The endoplasmic reticulum: A series of
highly folded membranes
– Where cellular chemical reactions take
place
– Like a large workspace
– Smooth ER
• No Ribosomes attached
• Involved in production and storage of lipids
– Rough ER
• Ribosomes attached
• Involved in production of proteins
Assembly and Transport
• Proteins made in the
Rough ER may:
– form part of the
plasma membrane
– be released from the
cell
– transported to other
organelles
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Assembly and Transport
• The Golgi apparatus:
flattened system of
tubular membranes and
vessicles
– Modifies proteins
– Sorts and packages
proteins
• It’s kind of like the post
office: Sorts the mail
and sends it to the right
place
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• Vacuoles – membrane-bound spaces
used for temporary storage of
materials
– Store food, enzymes, waste products
• Plant cells usually have one large
vacuole, animal cells have many
smaller cells
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• Lysosomes – organelles that
contain digestive enzymes
– Digest organelles, food particles,
and engulfed viruses or bacteria
– Can fuse with vacuoles and
dispense enzymes into vacuole
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Lysosomes and recycling
• Lysosomes are organelles that
contain digestive enzymes
– digest food particles, organelles
and engulfed viruses or bacteria
• Membrane prevents digestive
juices from destroying the cell
• Can fuse with vacuoles and
digest the contents.
• Can also digest cells that
contain them.
– i.e. tadpole’s tail
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Energy Transformers
• For all the cellular processes to
happen, energy is needed
• Two organelles provide that energy:
– Choloroplasts (in plants)
– Mitochondria (in animals and plants)
Chloroplasts
• cell organelles that capture light
energy and produce food to store
for later
– Belongs to a group of plant organelles
called plastids which are used for
storage
– Located in cells of green plants and
some protists
– Double membrane
– Folded inner membrane forms stacks
of grana/thylakoids
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Chloroplasts
• In the thylakoid
membrane there is
the green pigment
called Chlorophyll
– Traps light energy
– Gives leaves and
stems their green color
• Plastids
– Starch
– Lipids
– Chlorophyll
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• Mitochondria – membrane-bound
organelles in plant and animal cells
– Transform energy for the cell
– Highly folded inner membrane
• Energy storing molecules produced in
inner folds
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Structures for Support and Locomotion
• Cytoskeleton: forms the
framework of the cell
– Maintains shape
– Assist organelles in moving
from place to place
– Composed of:
• Microtubules: thin hollow
cylinders made of protein
• Microfilaments: thin,
solid protein fibers
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Structures for Support and Locomotion
• Cilia and flagella : Structures
that aid in locomotion and
feeding.
– Composed of pairs of
microtubules, with a central pair
surrounded by 9 additional
pairs.
– Cilia are short, numerous, hairlike projections that move in a
wavelike motion
– Flagella are longer projections,
move in a whip-like motion.
Cilia
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Flagella
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The End
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