Unit 7 - Bacteria, Viruses and the Immune System Flashcards
Capsid
The protein shell containing the viral genenome of a virus. The capsid is made of protein subunits called capsomeres
lymphocytes
A type of white blood cell that mediates immune responses. The two main classes are B cells and T cells. B cells make antibodies, which provide humoral immunity. Cytotoxic T cells destroy body cells that are infected by a pathogen or cancer cells. Helper T cells activate both B and T cells.
Phagocyte
Phagocytes ingest invading fungal and bacterial microbes. Two typse of phagocytes called neutrophils and macrophages go to the infected site. Neutrophils release chemical messengers to try to break down pathogens. Macrophages engulf large numbers of microphages.
Phagocytosis
a type of endocytosis in which large particulate substances or small organisms are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophpages, neutrophils, and dendritic cells)
Primary response
This is the first exposure to a foreign antigen. It takes a longer time for the specific antibodies to be produced.
Secondary response
The secondary is more rapid and more intense than the primary immune response, due to immunological memory. The antigens are recognized, which leads to a more rapid production of antibodies.
Specific Defense
Relies on B lymphocytes and T lymphocytes, which arise from stem cells in bone marrow. Involves recognition of antigens, activation of B and T cells, and humoral response (B cells produce antibodies), and the cell-mediated response (cytotoxic T cells kill infected body cells).
T cells (= T lymphocytes)
T lymphocytes form in the bone marrow and mature in the thymus gland. They fight pathogens in the cell-mediated immune response. The activation process begins when T cell antigen receptors recognize and bind to antigens. T cells form T clones. Some become effector cells, and the others become memory cells that respond to exposure to the same antigen later. Memory cells are responsible for immunological memory. The two types of T cells are helper T cells and cytotoxic T cells. Helper T cells direct the immune response. Cytotoxic T cells attack and klil body cells infected with pathogens as well as cancer cells, in cell-mediated immune response. They release perforin.
Vaccination (=immunization)
A vaccine contains dead or live viruses or enough of the oute rcoat of a virus to stimulate a full immune response and to impart lifelong immunity. It leads to active immunity as the individual makes his/her own antibodies after being given an immunization/vaccination.
MHC (major histocompatibility complex molecules)
These cell surface markers identify a cell as self. There are class I and class II MHC molecules. Class I are found on the surfaces of every nucleated body cell. Class II are found on specialized cells, like macrophages, B cells, dendritic cells, and activated T cells.
APCs (Antigen-presenting cells)
They present an antigen (an epitope) to the immune system. APCs include a macrophage or dendritic cell. Either the APC becomes infected with the antigen or it engulfs it. The MHC with the fragment of the antigen are displayed on the outside of the cell. Other cells become activated if they bind with the exposed antigen.
What is clonal selection?
Clonal selection is when a particular lymphocyte that matches a specific antigen or epitope is activated. Lymphocytes are activated, and they divide rapidly to form a population of clones that develop into effector and memory cells.
What are autoimmune diseases?
Autoimmune diseases are caused when the immune system cannot distinguish between self and nonself. Examples include lupus, MS, arthiritis, and juvenile diabetes. The immune system perceives several structures in the body as nonself and attacks them. In MS, the immune system attacks the myelin sheath, leading to the degeneration of nerve impulses.
What are allergies? Why do they occur?
Allergies are hypersensitive immune responses to certain substances called allergens. They involve the release of histamine, an anti-inflammatory agent which causes blood vessels to dilate. Sometimes anaphylactic shock can result in death.
How do macrophages work?
Macrophages are part of the nonspecific defense. They migrate to an infected site. They are developed from monocytes. Macrophages extend pseudopods and engulf huge numbers of microbes after a long period of time. They digest these microbes using lysozyme and two toxic forms of oxygen: superoxide anion and nitric oxide.
What is the role of the T-suppressor gene?
T-suppressor cells stop the immune response after the invading organisms are destroyed.
How do T-helper cells undergo positive feedback?
Positive feedback enhances an already existing process. When helper T cells are activated by a class II MHC molecule, it releases interleukin-I & II (cytokines), which stimulate B and T cells. SO, interleukin-I enhances the activity of the Th cells, stimulating them until their activation is maximized.
Bacteriophage
Viruses that infect bacteria. Also called a phage. Bacteriophages have complex capsids.
Host Range
Each virus can infect only a limited number of host species. This results from evolution go recognition systems by the virus. Viruses usually identify hosts by a lock and key fit between viral surface proteins and receptor molecules outside the cell.
Lytic Cycle
A phage replicative cycle that culminates in the death of the host cell. The host lyses, breaks open, and releases the phages that were produced inside the host. These phages can then go and infect a heathly cell.
Lysogenic Cycle
Allows replication of the page genome without destroying the host cell. The phage DNA is incorporated into the hosts DNA.
HIV (Human Immunodeficiency Virus)
A retrovirus that contains two identical molecules of single-stranded DNA and two molecules of reverse transcriptase. The reverse transcriptase transcribes and RNA template into DNA. This DNA is then incorporated int the hosts DNA HIV causes AIDS
Transposon
DNA segments that can move from one location to another within the cells genome. They are mobile genetic elements Transposons are candidates for the original source of viral genomes.
Transduction
A process in which phages carry bacterial DNA from one bacterial cell to another. When these two cells are members of different species, transduction results in horizontal gene transfer.
What is the purpose of a viral envelope?
A virus with an envelope is able to enter the host cell more easily. Glycoproteins on the viral envelope bind to receptors on the host cell
Provirus
The integrated viral DNA that occurs in the lysogenic cycle. The integrated DNA never leaves the hot’s genome.
What is the structure of a virus?
Viruses are made up of nucleic acid enclosed in a protein coat, or capsid. Commons structures of viruses are rod shaped, icosahedral, circular due to an outer envelope, or and icosahedral head with a tail apparatus.
What molecular processes could be blocked to combat an HIV infection?
Binding of the virus to the cell, reverse transcriptase function, integration into the host cell chromosome, genome synthesis, and, assembly of the virus inside the cell.
Describe the basic features of prokaryotic cells.
Most prokaryotes are unicellular. They typically have a diameter of .5 to 5 um. Common shapes are spherical, rod, and spiral.
How does Gram Staining work?
Samples are first stained with crystal violet dye and iodine, then rinsed in alcohol, and finally stained with a red dye. Gram-positive bacteria, have simpler and thicker walls, this traps in the violet dye leaving the bacteria purple. Gram-negative bacteria, are more complex and have a thinner layer between the plasma membrane, this allows for the violet to be washed out and the cell appears red from the second dye
