Basic Structure of a Cell
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Characteristics of organisms?
1. Made of CELLS
2. REPRODUCE (species)
3. Maintain HOMEOSTASIS
4. GROW and DEVELOP
5. EXCHANGE materials with surroundings
(water, wastes, gases)
6. RESPOND to environment
7. ORGANIZED
8. Require ENERGY (food)
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CELL THEORY
• All living things are made of cells
• Cells are the basic unit of structure
and function in an organism
• Cells come from the reproduction of
existing cells
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CELL SIZE
Typical cells range from 5 – 50 micrometers (microns) in
diameter
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First to View Cells
• In 1665, Robert
Hooke used a
microscope to
examine a thin
slice of cork (dead
plant cell walls)
• What he saw
looked like small
boxes
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Types of Microscopes
Light Microscope - Light passes through
several lenses
Electron Microscopes reveal details 1000 times
smaller than those visible in light microscopes
Scanning electron microscopes (SEMs) - Pencil like
beam of electrons is scanned over the surface of a specimen
making a 3-D image
Transmission electron microscopes (TEMs)
- Stream of electrons passes through thin specimen
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Cell Size and Types
• Cells, the basic units of organisms, can
only be observed under microscope
• Three Basic types of cells include:
Animal Cell
Plant Cell
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Bacterial Cell
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Which Cell Type is Larger?
Plant cell > _____________
Animal cell > ___________
bacteria
_________
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ENDOSYMBIOTIC THEORY
• some organelles within cells
were at one time free living
cells themselves
• organelles with their own
DNA
• Chloroplast and
Mitochondria
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Number of Cells
Although ALL living things are made of cells,
organisms may be:
• Unicellular – composed of one cell
• Multicellular- composed of many cells
that may organize into tissues, etc.
bacteria
butterfly
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Multicellular Organisms
• Cells in multicellular organisms often
specialize (take on different shapes &
functions)
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Specialized Plant cells
Guard Cells
Pollen
Xylem cells
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All Cells
– are surrounded by a barrier called
a cell membrane.
– contain DNA.
Bacteria
Animal cell
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Prokaryotes
• Simplest type of cell
• Nucleoid region contains the DNA
• Surrounded by cell membrane & cell wall
(peptidoglycan)
• ribosomes in their cytoplasm to make proteins
• Includes bacteria
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Eukaryotes
• More complex type of cells
• HAVE a nucleus and membrane-bound
organelles
• Cytoplasm with organelles
• Includes protists, fungi,
• plants, and animals
• “You are Eukaryotes”
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Two Main Types of
Eukaryotic Cells
Plant Cell
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Animal Cell
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Organelles
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•
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Little organs
Very small (Microscopic)
Perform various functions for a cell
Found in the cytoplasm
May or may not be membrane-bound
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Animal Cell Organelles
Ribosome (attached)
Ribosome (free)
Nucleolus
Nucleus
Cell Membrane
Nuclear envelope
Mitochondrion
Smooth
endoplasmic
reticulum
Rough
endoplasmic
reticulum
Centrioles
Golgi apparatus
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Plant Cell Organelles
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Cell or Plasma Membrane
• Composed of double layer of phospholipids and
proteins
• Surrounds outside of ALL cells
• Controls what enters or leaves the cell
• Living layer
Outside
of cell
Proteins
Carbohydrate
chains
Cell
membrane
Inside
of cell
(cytoplasm)
Protein
channel
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Lipid bilayer
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Phospholipids
• Heads contain glycerol & phosphate
and are hydrophilic (attract water)
• Tails are made of fatty acids and
are hydrophobic (repel water)
• Make up a bilayer where tails point
inward toward each other
• Can move laterally to allow small
molecules (O2, CO2, & H2O to
enter)
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The Cell Membrane is Fluid
Molecules in cell membranes are constantly moving
and changing
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GLYCOPROTEINS
Recognize
“self”
Glycoproteins have carbohydrate tails to act
as markers for cell recognition
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Cell Membrane in Plants
• Lies immediately
against the cell
wall in plant cells
• Pushes out
against the cell
wall to maintain
cell shape
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Cell membrane
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Cell Wall
• Nonliving layer
• Supports and protects cell
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•
•
•
Cell wall
Made 0f;
cellulose in plants
peptidoglycan in bacteria
chitin in Fungi
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Cytoplasm
• Jelly-like substance
• Provides a medium for
chemical reactions to
take place
• Contains organelles
• Found in ALL cells
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cytoplasm
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Nucleus
Control center
Contains the DNA
Has a nuclear membrane with pores
Has a fixed number of chromosomes
that carry genes
• Genes control cell characteristics
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Nuclear Envelope
• Double membrane surrounding
nucleus
• Also called nuclear membrane
• Contains nuclear pores for
materials to enter & leave nucleus
• Connected to the rough ER
Nuclear
pores
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Inside the Nucleus The genetic material (DNA) is found
DNA is spread out
And appears as
CHROMATIN
in non-dividing cells
DNA is condensed &
wrapped around proteins
forming
as CHROMOSOMES
in dividing cells
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Nucleolus
• Inside nucleus
• Disappears when
cell divides
• Makes ribosomes
that make
proteins
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Ribosomes
• “Protein factories” for cell
• Join amino acids to make proteins
• Process called protein synthesis

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Cytoskeleton
• Helps cell maintain cell shape
• Also help move organelles
around
• Made of proteins
• Microfilaments are threadlike
Microtubules are tubelike
MICROTUBULES
MICROFILAMENTS
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Centrioles
Found only in animal cells
Paired structures
Made of bundle of microtubules
Appear during cell division forming
mitotic spindle
• Help to pull chromosome pairs
apart to opposite ends of the cell
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Mitochondria
• “Powerhouse” of the cell
• Generate cellular energy (ATP)
• active cells like muscle cells have
MORE mitochondria
• In both plants & animal cells
• Surrounded by a DOUBLE
membrane
• Folded inner membrane -CRISTAE
•
Has its own DNA
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What do mitochondria do?
“Power plant” of
the cell
Respiration:
Burns glucose to
release energy (ATP)
Stores energy as ATP
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Endoplasmic Reticulum - ER
• Network of hollow membrane tubules
• Connects to nuclear envelope & cell membrane
• Functions in Synthesis of cell products & Transport
Two kinds of ER ---ROUGH & SMOOTH
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Rough Endoplasmic Reticulum (ER)
• Has ribosomes on its surface
• Makes proteins for EXPORT out of cell
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Ribosomes
Can be attached to
Rough ER
OR
Be free
(unattached)
in the
cytoplasm
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Smooth Endoplasmic Reticulum
• Smooth ER lacks
ribosomes on its surface
• Is attached to the ends
of rough ER
• Makes cell products that
are USED INSIDE the
cell
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Golgi Bodies
Look like a stack of pancakes
Modify, sort, & package molecules
from ER for storage
OR transport out of cell
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Lysosomes
• Contain digestive enzymes
• Break down food, bacteria, and worn out cell
parts for cells
• Programmed for cell death (AUTOLYSIS)
• Lyse (break open) & release enzymes to break
down & recycle cell parts)
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Cilia & Flagella
• for cell movement
• Cilia are shorter and
more numerous on
cells
Flagella are longer and
fewer
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Vacuoles
Fluid filled sacks for storage
Small or absent in animal cells
Plant cells have a large Central Vacuole
No vacuoles in bacterial cells
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Contractile Vacuole
• Found in unicellular protists like
paramecia
• Regulate water intake by
pumping out excess
(homeostasis)
• Keeps the cell from lysing
(bursting)
Contractile vacuole animation
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Chloroplasts
Found in plants
Photosynthesis – food making process
Contains its own DNA
Contains enzymes & pigments for Photosynthesis
Never in animal or bacterial cells
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Chloroplasts
• Surrounded by DOUBLE
membrane
• Outer membrane smooth
• Inner membrane modified
into sacs called Thylakoids
• Thylakoids in stacks called
Grana & interconnected
• Stroma – gel like material
surrounding thylakoids
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