Chapter 22
Cytology: 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
•
•
•
•
•
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.
Cell Processes
Chapter 22
Part 2
The Life and Work of Cells
• A living cell must maintain a stable
environment – homeostasis
Conditions for Homeostasis
• Osmotic Pressure – correct concentration of
water in and out of the cell
• Proper pH – A proper combination of acids and
bases
• Food and wastes – Cell regulate the amount of
nutrients and wastes in its cytoplasm
• Maintenance and repair – the cell is constantly
taking old proteins out of service and replacing
them
Energy Requirements of Cells
• A cell requires a lot of energy
• The primary task of all cells is to obtain
energy to do work
Photosynthesis and
Cellular Respiration
• Storing Energy – Photosynthesis - It is this
process by which nearly all autotrophs
transform solar energy into chemical
energy (sugar)
• Releasing Energy – Cellular respiration –
the breakdown of chemical substances to
release energy
This energy makes ATP
Active Transport by Cells
• Some molecules and materials just move
back and forth across the membrane.
• Most things must be actively transported
across
• The cell must use energy (ATP) for this
process
• Example: Sodium pumps
Endocytosis
• The cell can bring particles larger than
molecules into and out of itself:
• Types of endocytosis:
1. Phagocytosis – “Cell Eating” –
Engulfing large substances
2. Pinocytosis – Cell Drinking” –
Taking in liquids
3. Exocytosis – Elimination of waste
Cell Movement
• Many cells are equipped
with appendages that
allow it to move..
• Flagella – a tail-like
structure
• Cilia – hair-like structures
• Both are made of
microtubules and
proteins…
The Cell Cycle and Mitosis
• Living cells can reproduce!
• The reproduce through the process of
mitosis
The Cell Cycle and Mitosis
Cytologists have divided the cell cycle into 5
parts:
1. Interphase
2. Prophase
3. Metaphase
4. Anaphase
5. Telophase
The Cell Cycle and Mitosis
• Interphase
– The cell spends most of its life cycle here
– Chromosomes are copied
– There are two copies of each chromosome by
the time prophase begins
The Cell Cycle and Mitosis
• Prophase
– Chromosomes are bunched up into bundles
– The chromosomes (in pairs) are now called
chromatids
– Each chromatid is connected in the middle by
a centromere
– Centrioles form at the ends of the cell
The Cell Cycle and Mitosis
• Metaphase
– Spindle fibers appear to connect to the
chromosomes
– The chromatids line up in the middle of the
cell
– The paired chromatids begin to separate
The Cell Cycle and Mitosis
• Anaphase
– The separated chromatids move toward the
centrioles at each end of the cell
– A groove appears in the center of the cell
The Cell Cycle and Mitosis
• Telophase
– A new nucleus forms around the
chromosomes at each end of the cell
– Chromosomes uncoil
– The cell pinches in half and two daughter cells
are formed
Cell Death
• Every cell will eventually die
• According to the “Second Law of
Thermodynamics” all systems eventually
break down and decay.