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Chapter 4 – A Tour of the Cell
And comparison to viruses
State Standards
Standard 1.c. – Prokaryotic cells, eukaryotic cells (including those
from plant and animals), and viruses differ in complexity and general
Standard 1.e. – The endoplasmic reticulum and Golgi apparatus play
a role in the secretion of proteins
The Microscopic World of Cells
• Organisms are either:
– Single-celled, such as
most bacteria and
– Multicelled, such as
plants, animals, and
most fungi
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The Microscopic World of Cells
The human body is made up of trillions of cells many of which are
Muscle cells, Nerve cells, & blood cells…
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The Cell Theory
• Cells were first discovered in 1665 by Robert Hooke.
• The accumulation of scientific evidence led to the cell theory
- All living things are composed of one or more cells
- All cells are formed from previously existing cells
Microscopes provide windows to the
world of the cell
The Light Microscope
 Light passes through the
 Lenses enlarge, or magnify,
the image
Magnification – the increase
in the specimen’s apparent
Resolving power – the ability
to show 2 objects as being
Microscopes provide windows to the
world of the cell
The Electron Microscope
 Uses a beam of electrons
 Resolving power is higher
than the light microscope
 Can magnify up to
Microscopes provide windows to the
world of the cell
Scanning Electron
Microscope (SEM)
 Used to study the details of
the surface of the cell
 Produces a 3D image
 Used to study cell and
organelle surfaces
Microscopes provide windows to the
world of the cell
Transmission Electron
Microscope (TEM)
 An electron beam is aimed
through a thin section
 Used to explore the
internal structures of the
The Two Major Categories of Cells
The Two Major Categories of Cells
• There are 2 major categories of cells
- Prokaryotic cells
- Eukaryotic cells
• Both cells
- Are surrounded by a plasma membrane
- Consist of cytoplasm and organelles and contain DNA
• Prokaryotic and eukaryotic cells differ in several ways
The Size of Cells
 Most cells are 10-100
micrometers in size
 Cell size and shape are
related to their function
 Ex: red blood cells, nerve
cells, eggs
The Size of Cells
• The lower limit of cell size is determined by the fact that a cell
must be large enough to house the parts (DNA, organelles) it
needs to survive and reproduce.
• The maximum size of a cell is limited by the amount of surface
needed to obtain nutrients from the environment and dispose of
Prokaryotic Cells
Smaller than eukaryotic cells
(2-8 um)
Enclosed by a plasma
membrane that is usually
surrounded by a rigid cell wall
The cell wall may be covered by
a sticky capsule
DNA is found inside the cell
but it is not housed in a nucleus
Ribosomes (70S) are present
Internal structures surrounded
by membranes are not present
Structures of the Prokaryotic Cell
Nucleoid region – area where DNA is coiled in the cytoplasm. DNA
is in direct contact with the rest of the cell
Plasmid – smaller circular DNA molecules
Ribosomes – where proteins are made
Plasma membrane – encloses the cytoplasm of the prokaryotic cell
Structures of the Prokaryotic Cell
Cell wall – rigid, composed of lipids, carbohydrates and protein.
Protects the cell and maintains its shape
Cell Wall components determine if bacteria is classified as
• gram positive (+)
• or gram negative (-)..In
general more toxic and resistant to
Structures of the Prokaryotic Cell
Capsule – sticky outer coat that surrounds some prokaryotes.
Protects the cell surface. Helps bacteria attach to surfaces
Pili – short surface projections found in some prokaryotes. Helps
attach bacteria to surfaces
Flagella – long whiplike extensions found in some prokaryotes.
Propel cell through liquid environments
The Role of Bacteria in the Nitrogen Cycle
Eukaryotic Cells
 Larger than
prokaryotic cells
(10-100 um)
More complex in
DNA housed in the
Ribosomes (80S)
Membrane bound
Comparing Animal and Plant Cells
 Animal cells contain
centrioles, lysosomes,
 Plant cells contain a central
vacuole, cell wall,
Comparing Eukaryotic and Prokaryotic
Comparing Eukaryotic and Prokaryotic
Cells- Differences in parallel statements
Prokaryotic Cells
Eukaryotic Cells
 Date back at least 3.5 BYA
 Descended from ancient prokaryotes 2.1 BYA
 Ex include: Bacteria & Archaeabacteria
 Ex organisms: plants, animals, fungi, protists
 Simpler Structure (all single celled
 More Complex Structure (mostly multicellular
 Naked DNA (not wrapped around histone proteins)
 Circular Chromosomes
 DNA in cytoplasm (nucleoid region)
 70S ribosomes
 No internal membrane compartments
(no membrane bound organelles)-ex: no
mitochondria, no Rough ER
organisms but some single celled organism)
 DNA associated with histone proteins
 Chromosomes linear
 DNA separated from cytoplasm (in nucleus)
 80S ribosomes
 Internal membrane compartments
(membrane bound organelles) –ex: yup
mitochondria and Rough ER
Comparing Eukaryotic and Prokaryotic
CellsCommonalities: Prokaryotes & Eukaryotes
 Smallest units of Life (therefore has the characteristics of life Chapter 1!)
 Requires energy (to run metabolic reactions of life)
 Grows and develops
 Independently reproduce
DNA stores genetic information
 Can evolve over generations
 Order: internal organization
 Responds to environmental stimuli
 Ribosomes build proteins for the cells
 Contains plasma membrane to regulate what enters and leaves the cell
 Filled with cytosol (fluid)