BIOL1008 Study Guide - Quiz Guide: Human Microbiota, Gram-Negative Bacteria, Cell Membrane
10 Jun 2018
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PRACTICAL 5: Daily Defense
Our Immune system is really three lines of defense – two we are born with and one we acquire
throughout our lives. Our inborn ability to defend against pathogens is called innate or
nonspecific immunity. The most obvious of our innate defenses is our skin, which along with
mucous membranes and secretions (sebum, lysozyme, gastric juices, vaginal secretions and
saliva) are referred to as our first line of defense.
The Eye
While the cornea does not have a vascular supply bringing antibodies, it is protected from
infection largely as a result of antimicrobial substances secreted by the surrounding eye
tissues. The chief among these is lysozyme, a relatively small enzyme that is found in
perspiration, tears, saliva, nasal secretions and tissue fluids. Lysozymes are particularly active
against Gram positive bacteria. Gram positive bacteria have a very thick cell wall made of a
polymer of amino acids and sugars called peptidoglycan. The thick peptidoglycan layer
surrounds the plasma membrane of the bacteria. In contrast, Gram negative bacteria have a
very thin peptidoglycan layer that is sandwiched between an inner plasma membrane and
outer membrane.
The Skin
Skin is an excellent barrier to infection. It is composed of layers of cells which constantly
slough off from the outside and are replaced from the inside. Even the minute opening of the
sweat and sebaceous glands are protected by chemical substances secreted by the host cells
and are not ordinarily invaded.
1. THE SKIN
Three genera of bacteria that are predominant among the normal flora of the skin
- Micrococcus
- Staphylococcus
- Coryne bacterium
What conditions are present on the skin are considered to be responsible for the maintenance
of the normal flora?
- Low pH
- Dry (the Gram negative bacteria dies)
- Salts
2. INTRODUCTION TO CELL DIVISION
Cell Division
One of the basic concepts of biology is that all organisms (plants, animals, fungi and micro-
organisms) are composed of cells. All cells come from pre-existing cells through the process
of cell division. It is at the cellular level that the anatomy and physiology of an organism are
determined.
In cells capable of dividing, the cell cycle is the period from the beginning of one mitotic
division to the beginning of the next. The cell cycle is traditionally divided into four distinct
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Document Summary
Our immune system is really three lines of defense two we are born with and one we acquire throughout our lives. Our inborn ability to defend against pathogens is called innate or nonspecific immunity. The most obvious of our innate defenses is our skin, which along with mucous membranes and secretions (sebum, lysozyme, gastric juices, vaginal secretions and saliva) are referred to as our first line of defense. While the cornea does not have a vascular supply bringing antibodies, it is protected from infection largely as a result of antimicrobial substances secreted by the surrounding eye tissues. The chief among these is lysozyme, a relatively small enzyme that is found in perspiration, tears, saliva, nasal secretions and tissue fluids. Lysozymes are particularly active against gram positive bacteria. Gram positive bacteria have a very thick cell wall made of a polymer of amino acids and sugars called peptidoglycan. The thick peptidoglycan layer surrounds the plasma membrane of the bacteria.
