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The Cell: Basic Unit
of Life
Discovery of Cells
• Discovered in 1665 by Robert Hooke,
English scientist and inventor of the light
microscope
Cell Theory
• Cells are the building blocks of living
organisms and the basic unit of life
• All cells come from other cells
• Cells contain hereditary information which
control all cell function
• All metabolism (the chemical reactions of
life) occurs within the cell
Biological size and cell diversity
Cell Size
• Some cellular processes depend on the
surface area for efficiency. Ex: Diffusion
depends on surface area. The greater the
surface area, the greater the rate of diffusion.
• Other cellular processes depend on volume.
Ex: the making of large proteins requires
greater volume in the cell
• Therefore the Surface Area to Volume
Relationship is important in living organisms
Cell Surface Area-to-Volume Ratio
• For a 1 cell organism such as a bacterium,
getting its oxygen would be through simple
diffusion. However, simple diffusion cannot
satisfy the requirements for larger organisms—
it would take several years!!!
• The plasma membrane of cells must be large
enough relative to cell volume to regulate
passage of materials
• Cell size and shape are related to its function!!!
Cell Surface Area-to-Volume Ratio
Technologies Used To Study Cells
1. Light Microscope: referred to as
compound microscope, used by most
students
• Two features determine how clearly an
object is viewed
1. Magnification
2. Resolution
•
Light microscope has 500 times more
resolution than human eye
Technologies Used To Study Cells
2. Electron Microscope
• Developed in the 1950s
• Allows study of the ultrastructure of cells
• 10,000 times more resolution than human eye
• Types of Electron Microscopes:
1. Transmission Electron Microscope (TEM)
•
Used to see the internal structure (ultra structure) of cells
2. Scanning Electron Microscope (SEM)
•
Used to produce 3D images of surfaces
Comparing Light & Electron Microscopy
TEM: Tongue With Taste Bud
SEM: Human Embryo at Day 3
SEM: Human Embryonic Stem Cells
SEM: Tooth Plaque
SEM: Cluster of Breast Cancer Cells
SEM: Osteoporosis Bone
SEM: Red Blood Cells
SEM: Nerve Cells
SEM: Blood Clot
SEM: Lung Cancer Cells
SEM: Isabela Implanting onto the
wall of the uterus
SEM: Split Human Hair
Technologies Used To Study Cells
3. Freeze-Fracturing
• Living material is plunged into liquid nitrogen
(-196 ºC) and pushed against a blade in a
precise way
• Frozen tissue splits along lines of weakness,
often in the middle of a membrane
• The fractured surfaces are “etched” with a heavy
metal so that they can be seen using TEM
• Used to determine function of organelles
Freeze Fractioning
Freeze Fractioning: Blood Vessel
in a Melanoma
Types of Cells
Prokaryotic Cells
• DNA is not enclosed by a nucleus
• Bacteria
Eukaryotic Cells
• DNA is enclosed by a nucleus
• Highly organized membrane-enclosed
organelles
• Animal, plant, fungi & protists
Intro To Cell Membranes
Functions of cell membranes:
• Divide the cell into structures that carryout
specialized activities, Organelles:
Mitochondion
Endoplasmic reticulum
Ribosomes
Vacuoles
Golgi Complex
Chloroplasts
Nucleus
Nucleolus
• Interacting membranes form endomembrane
system
• Vesicles transport materials between
compartments
Diagram of
a plant cell
Diagram of
an animal cell
Cell Organelles
Nucleus
• Contains the cell’s DNA
• Bounded by
– Nuclear envelope
– Double membrane perforated with nuclear pores
• DNA forms chromatin, which is organized into
chromosomes
Nucleolus
• Located inside the nucleus
• Its purpose is to make ribosomes
The cell
nucleus
Cell Organelles
Plasma Membrane
• Physically separate cell interior from
extracellular environment
• Regulates passage of materials
• Participates in biochemical reactions
• Receives information about environment
• Communicates with other cells
The Fluid Mosaic Model of the
Plasma Membrane
• It consist of a fluid Phospholipid Bilayer with a
“mosaic” pattern of numerous proteins such as
structural proteins and transport proteins
• The Phospholipid Bilayer is Amphipathic
because it contains both:
• Hydrophobic regions
• Hydrophilic regions
Phospholipid Bilayer
Fluid Mosaic Model of the Plasma Membrane
Cell Organelles
Endoplasmic Reticulum (ER)
• Network of folded internal membranes in the
cytoplasm
• Two Types of ER:
1. Smooth ER
• Site of lipid synthesis
• Site of detoxifying enzymes
• Does not have Ribosomes attached to its surface
2. Rough ER
• Has Ribosomes attached to its surface
• Ribosomes manufacture proteins
• Proteins may be moved into the ER lumen
Endoplasmic
Reticulum (ER)
Cell Organelles
Golgi Complex
• Membrane complex that processes, sorts, and
modify proteins
• In animal cells, Golgi complex also
manufactures lysosomes (sacs which contain
enzymes that breakdown materials)
• Golgi Complex modifies carbohydrates and
lipids and packages into vesicles, which are
then transported out of the cell.
Golgi Complex
Cell Organelles
Lysosomes
• break down worn-out cell structures,
bacteria, and other substances
Peroxisomes
• Involved in lipid metabolism and
detoxification
• Contain enzymes that produce and
degrade hydrogen peroxide
Lysosomes
Cell Organelles
Mitochondria “The Powerhouse of the Cell”
• Responsible for the brake down of nutrients
and the transfer of energy from the nutrients
to ATP through a process called Cellular
Respiration.
• As a by-product of Cellular Respiration,
Carbon Dioxide & Water are produced
• Most metabolic reactions within the cell take
place in the Mitochondia
Mitochondria
Cell Organelles
Chloroplasts
• Place where Photosynthesis occurs
• During Photosynthesis, Chlorophyll traps
light energy
• Light energy is converted to chemical
energy (ATP) to make Glucose
• As a by product of Photosynthesis,
Oxygen is produced
Chloroplast
Cellular Respiration and Photosynthesis
Cell Organelles
Cytoskeleton
• Internal framework of fibers made of:
– Microtubules
– Intermediate filaments
– Microfilaments
• Provides structural support for the cell
• Involved with transport of materials in the
cell
The
Cytoskeleton
Cell Organelles
Cilia
– Thin, movable structures that project
from cell surface
– Function in movement
Flagella
– Tail-like projections
– Function in movement
Cilia
Flagella