Transcript Bacteria, virus, immune

Bacteria
 Bacteria (bacterium, singular), microorganisms
that lack a nucleus (prokaryote) and have a cell
wall
 Bacteria are the most common organisms on
earth but they can not be seen.
 However, colonies of bacteria, such as those
found on a laboratory culture plate, can be
viewed easily without a microscope.
Bacteria Structure
Bacteria
 Placed in two domains, 1) Domain Bacteria (typical
bacteria) and 2) Archae (ancient bacteria).
 Bacteria are placed in these domains depending on
the make up of their cell membrane and cell wall.
Bacteria
 Bacteria are often classified on the basis of their
physical shapes:
 bacteria can be spherical (cocci),

rod-shaped (bacilli),
 or corkscrew-shaped (spirochetes).
 Prefixes may be used:
 diplo means two
 staphlo means clusters
 strepto means chains
Bacteria
This scanning electron micrograph shows
disease-causing Streptococcus bacteria,
commonly found in the human mouth, throat,
respiratory tract, bloodstream, and wounds.
Often airborne in hospitals, schools, and other
public places, Streptococcus bacteria are
responsible for infections such as strep throat,
scarlet fever, and some types of pneumonia.
"Streptococcus Bacteria," Microsoft®
Encarta® Encyclopedia 99. © 1993-1998
Microsoft Corporation. All rights reserved.
Bacteria
 Another classification system divides bacteria into
gram-negative or gram-positive according to the
composition of their cell walls, a distinction identified
by a staining technique called the Gram stain.
 Bacteria that require oxygen are called aerobic
bacteria, or aerobes.
 Bacteria that live without oxygen are called
anaerobic bacteria, or anaerobes.
Bacteria: Reproduction
http://www.wwnorton.com/college/biology/mbio/animations/dna_replication.asp
 A bacterium reproduces by means of a process
called binary fission.
 Like all cells, bacteria contain genetic material
known as deoxyribonucleic acid (DNA).
 However, the DNA of bacteria is arranged in a
single circular chromosome. Bacteria also often
have additional DNA in the form of smaller rings
called plasmids.
 In binary fission, the single chromosome is
replicated, the bacteria divides into two cells, and
each cell receives one chromosome.
 The two cells are thus genetically identical.
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Bacteria: Genetic Diversity
 Bacteria shuffle DNA between cells by several
processes, including transformation, conjugation,
and transduction to gain genetic diversity.
 Through mixing genetic material, bacteria
develop new traits, including the ability to
withstand changes in acidity and temperature,
and resistance to antibiotics.
Bacteria: Genetic Diversity
 In transformation, bacteria take up fragments of DNA
released into the soil or water as dead bacteria are
decomposed.http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_1.html
 In conjugation, a donor bacterium attaches itself to a
recipient bacterium, generates a tube called a pilus,
and transfers fragments of plasmid DNA to the
recipient.http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_3.html
 Transduction involves the transfer of DNA fragments
between bacteria cells by a bacteriophage, a virus
that infects bacteria.
http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter13/animation_quiz_2.html
http://learn.genetics.utah.edu/content/begin/cells/scale/
Virus
 Virus, infectious agent found in virtually all life
forms, including humans, animals, plants, fungi,
and bacteria.
 Viruses consist of genetic material—either
deoxyribonucleic acid (DNA) or ribonucleic acid
(RNA)—surrounded by a protective coating of
protein, called a capsid.
 Viruses are between 20 and 100 times smaller than
bacteria.
 Viruses are not considered free-living, since they
cannot reproduce outside of a living cell.
 They have evolved to transmit their genetic
information from one cell to another for the
purpose of replication.
 Although many infectious diseases, such as the
common cold, are caused by viruses, there are no
cures for these illnesses.
 Individual viruses, or virus particles, also called
virions, contain genetic material, or genomes, in one
of several forms.
 The most elaborate viruses are the bacteriophages,
which use bacteria as their hosts.
Virus
http://highered.mcgraw-hill.com/olc/dl/120088/micro41.swf
Viral Replication
http://www.cellsalive.com/phage.htm
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Immune System
 Immune System, group of cells, molecules, and
organs that act together to defend the body
against foreign invaders that may cause disease,
such as bacteria, viruses, and fungi.
 The disease resistance provided by these systems
is called immunity.
 There are two types of immunity: innate and
adaptive.
 Innate, or nonspecific, immunity is the body’s first,
generalized line of defense against all invaders.
Innate Immunity
 Innate immunity is furnished by 1)barriers such
as skin, tears, mucus, and saliva
 2)the rapid inflammation of tissues that takes
place shortly after injury or infection.
 When an injury occurs, chemical messengers
called histamines are released.
 Histamines increase blood flow to the area and
increase permeability of the surrounding
capillaries, allowing more white cells into the
area.
Adaptive Immunity
 If an invader gets past this first line of defense, the
immune system develop specifically tailored
defenses against the invader.
 The immune system can call upon these defenses
whenever this particular invader attacks again in the
future.
 These specifically adapted defenses are known
as adaptive, or specific, immunity.
Adaptive immunity
 Adaptive immunity has four distinguishing
properties:
 1) It responds only after the invader is present.
 2) It is specific, tailoring each response to act only on
a specific type of invader.
 3) It displays memory, responding better after the first
exposure to an invader, even if the second exposure is
years later.
 4) It does not usually attack normal body components,
only those substances it recognizes as nonself.
White blood cells:macrophage
 White blood cells play an important role in the
immune system.
 Some white blood cells, known as macrophages
and neutrophils, play a function in innate
immunity by surrounding, ingesting, and
destroying invading bacteria and other foreign
organisms in a process called phagocytosis
(literally, "cell eating"), which is part of the
inflammatory reaction.
Immune Responses: Two Kinds
 Adaptive immune responses are actually
reactions of the immune system to structures on
the surface of the invading organism called
antigens.
 There are two types of adaptive immune
responses:

1) humoral

2) cell mediated.
White blood cells:Lymphocytes
 Lymphocytes are specialized white blood cells
whose function is to identify and destroy invaders.
 All lymphocytes begin in the bone marrow, the soft
tissue that fills most bone cavities, but they mature in
two different places (bone marrow or thymus gland.
 Lymph nodes are located throughout the body and
contain large numbers of white blood cells.
 They filter pathogens (disease-causing agents).
 and expose them to white blood cells.
 The spleen, an organ behind the stomach, filters
pathogens from the blood.
White blood cells: T Cells
 Helper T lymphocytes, regulate the immune
system by controlling the strength and quality of
all immune responses.
 Each lymphocyte, as it matures, makes an
antigen receptor—that is, a specific structure on
its surface that can bind with a matching
structure on the antigen like a lock and key.
Immune Responses: Humoral
 Humoral immune responses resist invaders that
act outside of cells, such as bacteria and toxins
(poisonous substances produced by living
organisms).
 Humoral immune responses can also prevent
viruses from entering cells.
White blood cells:B Cells
 Some lymphocytes mature in the bone
marrow and are called B lymphocytes.
 During humoral immune responses, B
lymphocytes, or B cells, make antibodies,
which circulate through the blood and
other body fluids, binding to antigens and
helping to destroy them.
Humoral Immune Response
 First, macrophages take up some of the antigen and
attach it to transport molecules, which then present
the antigen to T helper cells.
 The interleukins in turn activate any B lymphocytes
that have also bound the antigen.
 The activated B cells then divide and differentiate
into plasma cells which secrete antibodies.
 Finally, the secreted antibodies bind the antigen
and help destroy it.
Antibodies
 Antibodies are Y-shaped proteins.
 The antibody binds to the antigen at the
ends of the arms of the Y.
 Antibodies can sometimes stop an antigen’s
disease-causing activities simply by
neutralization—that is, by binding the
antigen and preventing it from interfering
with the cell’s normal activities.
 Antibodies also help destroy antigens by
preparing them for ingestion by
macrophages.
White blood cells:T Cells
 Other lymphocytes, called T lymphocytes, or T cells,
mature in the thymus, a small glandular organ
located behind the breastbone.
 Some T lymphocytes, called cytotoxic (cellpoisoning) or killer T lymphocytes, generate cellmediated immune responses, directly destroying
cells that have specific antigens on their surface
that are recognized by the killer T cells.
 Suppressor T cells help to shut down the immune
response after the pathogen is cleared from the
body.
 When the body is first exposed to an antigen,
several days pass before the adaptive immune
response becomes active.
 Immune activity then rises, levels off, and falls.
 During following exposures to the same antigen,
the immune system responds much more quickly
and reaches higher levels.
 This is because Memory Cells remain in the body.
 Memory cells will recognize the pathogen and
begin to divide rapidly, eliminating the pathogen
before it can produce disease.
 This complete resistance to disease is called
immunity and may be achieved through either
active or passive immunization.
 Active immunization occurs when a person’s own
immune system is activated and generates a
primary immune response.
 Active immunization can be triggered in two
ways, either by natural immunization or by
vaccination.
Natural immunization
 In natural immunization, the body contracts a
disease and recovers.
 After having had the disease once, a person is no
longer susceptible to it.
Vaccination
 Vaccination is intentional immunization against a
particular disease by the use of vaccines,
substances that are structurally similar to the
actual disease-producing agents but that do not
produce disease themselves.
 The first type of vaccine, contains chemically
killed bacteria or other pathogenic organisms.
 The other type, such as the oral polio vaccine,
contains weakened forms of living organisms that
have been genetically selected so they do not
produce disease.
Passive immunization
 Passive immunization does not engage the
person’s own immune system.
 Instead, the individual receives antibodies that
were created in another person or animal.
 This is temporary immunity.
Immune System Disorders
 Disorders of the immune system can range from the
less serious, such as mild allergy, to the life
threatening, such as more serious allergy, transplant
rejection, immune deficiencies, and autoimmune
diseases.
Allergic Reactions
 Allergy, sometimes called hypersensitivity, is
caused by immune responses to some antigens.
 Antigens that provoke an allergic response are
known as allergens.
Allergic Reactions
 These immediate hypersensitivity reactions result
from the production of antibodies when a person
is first exposed to an allergen.
 The antibodies become attached to mast cells—
white blood cells containing histamine, the
chemical that causes the familiar allergic
symptoms of runny nose, watery eyes, and
sneezing.
Allergic Reactions
 Mast cells are particularly abundant in the lungs
and intestine.
 If the antigen-binding sites of mast cells become
filled with an allergen, the mast cells release
histamine.
Organ Transplant
 The immune system recognizes and attacks anything
different from the substances normally present within
an individual, even substances that are only slightly
different, such as transplanted tissues and organs.
Organ Transplant
 To minimize the chances of transplant rejection,
physicians seek transplant donors who share as
many genes as possible with the transplant recipient.
 Even then, most transplant recipients are given drugs
to suppress their immune response and prevent
rejection of the transplant.
Immune Deficiencies
 Deficiencies in immune function may be either
inherited or acquired.
 An infectious agent resulting in fatal immune
deficiency is the human immunodeficiency virus
(HIV).
 This virus causes acquired immune deficiency
syndrome (AIDS) by infecting and eventually
destroying helper T cells.
Autoimmune Disease
 Autoimmunity is the immune response of the
body turned against its own cells and tissues.