Chapter 3
Cytology Part I:
The Design and Function of Cells
Key Topics
• Cells as the structural and functional units of
living things.
• Variety in cells
• Complexity of cells
• Structure of a cell
• Life Processes of a cell
• Cell division
• Cell death
The Variety and Complexity of Cells
Cells are the units of structure and function of
living things.
The study of cells is known as the science of
cytology (cell biology)
Much of what we know about cells and their
function was unknown before 1980!
The Variety and Complexity of Cells
In recent years, the science of cytology has merged
with the science of molecular biology.
Molecular biology is the branch of science which seeks
to discover how the cellular mechanisms of living
things actually work.
Cell biology has exploded with new discoveries which
gives us a new appreciation for the design of God’s
living creation!
The Discovery of Cells
•
Robert Hooke first observed cells in sections of cork under a
microscope in 1665.
•
In 1838 and 1839 two scientists stated what is now known
as the cell principle.
The Cell Principle:
1. All living things are composed of living units
called cells and of cell products.
2. All cells come only from preexisting cells.
The Function of Cells
•
•
•
•
Cells do all the work that is done in an organism.
Cells manufacture materials that are used for life.
Cells work together and transport material.
Cells communicate to each other and respond to
different situations.
• Cells grow and reproduce to carry on the work they
were created to do.
How amazingly intricate is the design of cells by the
Creator God!!
Variety among Cells
• Variety in size
It is important to understand that while
there is variety in size, it is minimal and an organism
is larger due the number of cells and not the size of
the cells in the organism.
• Variety in number
• Variety in shape
The variety of size, shape, and number, combined with
magnificent architecture, make living cells
phenomenal creations of God.
The Complexity of Cells
• Until about 50 years ago, cells were all thought to be
simple bags of fluid or slime known as “protoplasm.”
• Scientists now know that a cell is a tiny, selfcontained city with its own power plant, chemical
factories, food warehouses, and waste disposal
facilities.
• The cell also has an extensive transportation
network.
• All activities of the cell are directed automatically by
the cell’s control center.
The Three Main Parts of Cells
1.
2.
3.
Nucleus: contains the genetic
code; serves as master control
center
Cytoplasm: serves as the fluid
medium for the molecules and
organelles of the cell
Cell Membrane: outer
boundary; separates cell from
environment
The Nucleus
• Contains the DNA
(deoxyribonucleic acid)
the blueprints for all
physical characteristics
of the organism
the blueprints for all
the cell’s machine
The Nucleus:
The Nuclear Envelope
• Resembles the cell membrane in
chemical structure
• It is a double membrane with a
narrow water-filled space
between the layers
• Nuclear Pores - large portholelike
proteins in the envelope serve as
“gates”
The pores regulate the
transport of large molecules into
and out of the nucleus
Small molecules are allowed
thru, but large proteins are
blocked unless they contain a
special “tag”
The Nucleus:
DNA Storage
• DNA storage and the
retrieval of the information
it contains is the main
function of the nucleus
• The human cell contains 4-6
feet of DNA
• The DNA is coiled on
protein “spools”
• The DNA and the protein
“spools” are referred to as
chromatin
The Nucleus:
The Nuclear Matrix
• A protein scaffolding
system that extends
throughout the nucleus
and is attached to the
nuclear envelope
• Houses the enzymes
and protein machinery
used to read and copy
the DNA
The Nucleus:
The Nucleolus
• Manufactures
ribosomes (the protein
factories of the cell)
Cytoplasm:
Fluid Mechanism of the Cell
•
•
•
•
Fluid medium of the cell
Contains the organelles (little organs)
Contains numerous dissolved molecules
Most of the activities of life occur within the
cytoplasm and its organelles
• Molecules of proteins, lipids, and carbohydrates
abound to be used as parts for other materials
manufactured by the cell
• Enzymes are present carrying our various functions
such as energy production
The Skeleton of the Cell:
A Cellular Framework
• The cell has an intricate
internal skeleton
• The cytoskeleton is
composed mostly of
microtubules
• The microtubules are
hollow and rod
like…they contain a
protein called Tubulin
The Skeleton of the Cell:
A “mass-transit” system
• The microtubules support
the cell…they also act as the
highway system for the cell.
• Proteins and other
materials are produced by
ribosomes and packaged
(vesicle) and placed on the
highway.
• Scientists have observed
vesicles traveling in
opposite directions along
the same microtubule, just
like a real “highway”.
Mitochondria:
Power Plant of the Cell
• A mitochondria “burns”
carbohydrates and fats and
uses the energy to produce
ATP…
• ATP is the energy molecule
of the cell
• ATP stands for adenosine tri
phosphate
• The more active a cell is the
more mitochondria it
needs.
Mitochondria:
Power Plant of the Cell
• Cardiac muscles require
great numbers of
mitochondria.
• The “waste” of the
mitochondria is in the
form of heat which
gives the organism its
operating temperature.
Chloroplasts in Plant Cells
• Chloroplasts also have
folded membranes used
in photosynthesis.
Ribosomes: Protein Factories
•
•
•
•
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The importance of
proteins:
Proteins are complex
Proteins serve as pumps
As chemical catalysts
As power generators
As communication
relays
and more…
Ribosomes: Protein Factories
How Proteins are made:
• Proteins are made by ribosomes
• Powered by ATP, ribosomes assemble amino
acids into complex proteins, guided by
“blueprints” from the nucleus.
• Some cells have more ribosomes than others.
Ribosomes: Protein Factories
Structure of Ribosomes:
• Ribosomes are composed of
two halves that fit together
like a clamshell.
• As a “blueprint” molecule is
fed through the ribosome,
the ribosome assemble
amino acids into a growing
protein chain.
• Ribosomes are the smallest
and most numerous of
organelles.
Endoplasmic Reticulum: A Purposeful
Network
• The ER is a system of folded membranes that
attaches to the outside of the cell’s nucleus
and extends throughout the cell.
Endoplasmic Reticulum: A Purposeful
Network
Purpose of the ER:
• The ER is moves the proteins that the
ribosomes make.
• The ER serves to break down toxins and waste
and manufactures fat molecules.
Endoplasmic Reticulum: A Purposeful
Network
Two Types of ER:
• ER near the nucleus is covered with thousands
of ribosomes...
it is called rough ER.
• ER farther away from the nucleus does not
have ribosomes…
it is called smooth ER.
The Golgi Complex:
The Shipping Center of the Cell
• It packages proteins made
in the Rough ER.
• Ships the packages to their
final destinations.
• The proteins are labeled
with “shipping tags.”
• The proteins are loaded into
a container called a vesicle.
Lysosomes:
Recycling Centers of the Cell
• Contains ion pumps
that make the interior
acidic.
• Also can be used to
attack bacteria.
Vacuoles:
Storage Containers
• More numerous in
plants.
Cell Membrane:
Structure
• Phospholipids – Two
layer of lipids called a
“lipid bilayer”
• The cell-membrane is
self-sealing and selfrepairing
• Membrane proteins –
embedded in the
membrane –carry on
processes and act as
“gates”
Cell Membrane:
Machinery of the Cell
• Ion pumps – allow the cell
to pump atoms like
potassium and sodium into
the cell
• Portals/gates – allow
various molecules in
• Sensors – inform the cell of
outside environment
• Identification tags – tell
other cells who the cell is
Cell Wall of Plants
Outside the cell
membrane in plants is
the rigid cell wall.
It stiffens the cell, allowing
a plant to stand upright.
The cell wall is made of
lignin and cellulose.