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, self-

contained 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 Cells1. Nucleus: contains the genetic

code; serves as master control center

2. Cytoplasm: serves as the fluid medium for the molecules and organelles of the cell

3. 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

relaysand 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 FactoriesStructure 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 self-repairing

• 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.