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11/20/2014
1
The Life of a Cell In 1665, Robert Hooke examined the
bark of an oak tree under an early
microscope. He thought he was looking
at something similar to the small rooms
of dormitories and prisons; hence the
name: cells.
Now, we know that Robert Hooke was
not looking at living cells, but the
remains of dead cell walls.
Some history… Life is Based on the Existence of Cells
The Cell Theory:
Living things are made of cells.
Cells are the basic unit of life.
Cells come from preexisting cells.
The study of cells is
called cytology.
Cells are diverse
• Even though cells are tiny,
they are very complex! • They vary in several ways:
– Size – Shape – Function (job)
Cell Shape
Shape relates to a cell’s function.
• A flat shape of dead skin cells is well suited for
covering the body surface.
• The long, thin, threadlike shape of nerve cells is
well suited for transmitting messages throughout
the body.
Why is there so much variety in cell shape? Cell Size: Why are cells so small?
1. Volume increases faster than surface area.
2. Surface area is too small for cell to receive materials fast enough.
3. As a result, the cell divides
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Surface Area = 96 mm2
Volume = 64 mm3
Ratio = 1.5 : 1
Surface Area = 192 mm2
Volume = 64 mm3
Ratio = 3: 1
4 m
m
4 m
m
4 mm 4 mm
Organisms are divided into TWO groups based on cell type:
1. Prokaryotic cells
2. Eukaryotic cells
Prokaryotic Cells
Lack a nucleus and membrane-bound organelles.
Unicellular.
Fossils date to 3.5 billion years ago.
Small, simple cells.
All prokaryotes are bacteria.
Eukaryotic Cells
Have a nucleus and membrane-bound organelles.
Some are unicellular, most are multicellular.
Fossils date to 1.7 billion years ago.
Large, highly organized cells.
Plants, animals, protists and fungi are eukaryotes.
Prokaryotes
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What are prokaryotic cells? Unicellular organisms that lack a nucleus.
PROKARYOTES
Archaebacteria “ancient” or extreme
Eubacteria “true” or common
Example of Prokaryotic Cells: Bacteria
In the space provided in your notes, write what you already know about bacteria.
What do bacteria look like?
• Bacillus: rod-shaped.
• Coccus: sphere-shaped.
• Spirilus: spiral- or helical-shaped.
Arrangement of Bacteria Where do bacteria live?
Can be found on most materials and surfaces
– Billions on and in your body right now
E. Coli O157:H7
can make you
very sick.
Streptococcus
can cause strep
throat.
This E. coli helps
you digest food.
Organization of a Bacterial Cell
Nucleoid (DNA)
Cell Wall
ribosomes
Plasmid (DNA)
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Some bacteria contain
• Flagella: used for movement
• Pilli: hair-like structures that anchor bacteria to a surface
• Capsule: outside layer that protect the bacteria from white blood cells.
Some bacteria contain
Endospore:
• Thick wall that encloses DNA
• Protects against harsh conditions (drought, harsh temperatures)
Bacteria Reproduce
1) Asexually Binary fission
Bacteria Reproduce
2) Sexually Conjugation
Bacteria exchange
plasmid DNA.
How can bacteria be helpful? • Bacteria play a large role in modern medicine,
agriculture, and ecology.
• Decomposers break down organic material.
• Fermentation (bread, dairy, beer).
• Genetic engineering (GMOs and antibiotics).
• Take nitrogen in atmosphere and turn it into something organisms can use
How can bacteria be harmful?
• Pathogens: Disease causing agents
Bacteria cause disease by destroying living cells or by releasing chemicals that harm the body.
• Examples of sicknesses caused by bacteria:
– Strep throat
– Ear infections
– Lyme disease
– Tetanus
– Tuberculosis
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Eukaryotes
Why do cells have organelles? Division of labor into separate compartments
(organelles) makes cell activities more ORGANIZED and EFFICIENT.
This is made possible by the presence of LIPID membranes that form boundaries around each organelle (membrane-bound organelles).
Nucleus
Control center because it contains DNA
Surrounded by the nuclear membrane
Nuclear membrane has pores to allow things to enter/leave nucleus
nucleus
DNA Exists in Two Different Forms
CHROMATIN
Loose, uncoiled DNA.
Stretched out so the cell can “read” the DNA.
Present during the normal, everyday life of the cell.
CHROMOSOMES
DNA is tightly wound and organized
Only during cell division
Plasma (Cell) Membrane Boundary of cell (mostly lipids)
Controls movement of materials in and out; maintains HOMEOSTASIS
outside of cell
inside of cell
Cell Wall
Rigid outer layer of plant cells
Made of cellulose
Gives plant cells strength and support.
Only in PLANT Cells
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Cytoplasm
Jelly-like material that fills cell
cytoplasm
Chloroplast (a type of plastid) Present in LEAF cells
Photosynthesis: Process of making food (glucose)
Contain chlorophyll (green pigment)
chloroplasts
Plastids (only in PLANT cells)
Store food or pigment molecules.
chromoplasts in red pepper cells Leucoplasts in potato cells
store starch
Mitochondria
The Powerhouse
Breaks down food
molecules (glucose) to release usable energy (ATP)
Vacuole
Fluid-filled storage area:
– Water
– Salts
– Enzymes
– Carbohydrates
PLANT cells have one large
vacuole; ANIMAL cells have
several small ones.
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Ribosomes
Small, round organelles that produce proteins
Can be scattered throughout the cytoplasm or bound to the Rough ER
ribosomes
Nucleolus
Circular structure inside the nucleus
Makes ribosomes
Nucleus
Nucleolus
Endoplasmic Reticulum (ER)
System of tubes and channels
Rough ER has ribosomes for protein production
Smooth ER produces lipids and also breaks down toxins
smooth ER
rough ER
Golgi Apparatus Packaging factory for newly made lipids, proteins, and
other molecules
Vesicles - Small, circular packages that ship materials
vesicles
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Lysosome
Contains DIGESTIVE ENZYMES to breakdown:
a) food
b) old cell parts
c) waste
d) invading viruses and bacteria
e) the cell itself
lysosomes
Cytoskeleton
Network of protein fibers that provide structure and support to the cell.
Anchors the organelles in the cytoplasm.
cytoskeleton
Centrioles
Pair of cylindrical structures that assist in cell reproduction (division)
Only in ANIMAL cells
Cilia and Flagella Cilia short hair-like
extensions on the surface of some cells.
Help move substances across the cell’s surface.
Flagella are longer than cilia and less numerous.
Whip-like motion moves a cell from place to place.
Plant vs. Animal Cell Plant Animal
Cell wall and cell membrane
1 large vacuole
No centrioles
Plastids
Chloroplasts
Square shape
Cell membrane only
Several vacuoles
Centrioles
No plastids
Variety of shapes (due to the flexible cell membrane)
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