6B Microorganisms and immunity Flashcards
Virus structure
Capsid protein coat
Nucleic acid core
Some carry proteins
Envelope stolen from host cell cell membrane
Attachment proteins
How is HIV transmitted
Through infected bodily fluids coming into contact with mucosal surfaces, damaged tissue or the bloodstream.
HIV replication
GP120 on the virus binds to CD4 receptors on the cell surface membrane of the T helper cell
Viral envelope fuses with cell membrane
The capsid is released into the cell and uncoats, releasing RNA into the cytoplasm.
Reverse transcriptase is used t make a complementary strand of DNA from the RNA template
Double stranded DNA is made and inserted into the human DNA
Host cell enzymes make viral proteins from the viral DNA
Proteins are assembled into new viruses which bud from the cell, killing it
developing AIDS
Initial HIV infection causes flu like symptoms
After a few weeks HIV antibodies are detected in the blood meaning they are HIV positive
Enter latency period with no symptoms
AIDS failing immune system , T helper cell count drops below a certain level or opportunistic infections occur due to the weakened immune system
Tuberculosis
Mycobacterium tuberculosis transmitted through inhalation of droplets containing bacteria into the lungs.
Bacteria engulfed by a phagocyte but survive due to their waxy coat. sealed in tubercles and lay dormant until they are reactivated eg weakened immune system due to AIDS
Symptoms: fever, coughing, lung damage, coughing up tissue, spread to the rest of the body
Pathogens routes of entry
Cuts in the skin
Digestive system
Respiratory system, inhalation
Mucosal surfaces
Barriers to prevent infection
Stomach acid HCL
Skin physical barrier
Gut and skin flora- harmless microorganisms outcompete pathogens for space and nutrients
Lysozyme- Mucosal surface secretions contain lysozyme which causes lysis in bacteria
Non-specific immune response
Inflammation- histamines, vasodilation and permeability
Interferons- inhibit replication, activation and promotion
Phagocytosis and lysozyme action- engulfment and lysis
Inflammation
recognition of foreign antigens cause immune system cells to release histamines, which cause vasodilation and increase permeability of blood vessels.
This brings more immune system cells to the site of infection and allows them to move out of vessels into infected tissue.
Interferons
When infected by a virus cells produce interferons, proteins which
Inhibit viral protein production and therefore replication
Promote inflammation
Activate cells involved in the specific immune response to kill infected cells
Phagocytosis
White blood cell identifies antigens on pathogen and engulfs it as the cytoplasm moves round the pathogen, containing it in a phagocytic vacuole
Lysosome fuses with the vacuole releasing lysozyme that kills the pathogen
Phagocyte presents pathogens antigens to activate immune system cells
Specific immune response
T lymphocytes bind to antigen presenting cells eg macrophage with specific receptors. When a complimentary antigen is found it binds and activates the t cell to divide by mitosis + differentiate
T helper cells- Release cytokine to activate B lymphocytes
T killer cells- bind to and destroy infected cells perforin
T memory cells- Remain in the blood to enable a quicker immune response to the same pathogen
B lymphocytes activate when their specific antibodies bind to a complementary antigen and substances from T helper cells are detected, to divide by mitosis and differentiate
Plasma/ be effector cells- produce complementary antibodies
B memory lymphocytes- remain in the blood to allow faster immune response to the same pathogen
Antibodies
Form antigen-antibody complexes
Variable region- form specific antigen binding sites
Constant region- allows binding to receptors on immune system cells
Hinge region- allows for flexibility when antigen-antibody complex is formed
Disulfide bonds- hold the polypeptide chains together (quaternary structure)
Agglutinate pathogens: clump pathogens together to allow phagocytosis all at once
Neutralise toxins: bind to toxins preventing them from affecting human cells until they are phagocytosed
Block cell surface receptors on pathogens: prevent binding with human cells and infection
Post- transcription mRNA modification
mRNA strands containing introns and exons are called pre-mRNA.
Introns are removed by splicing in the nucleus, along with some exons in alternative splicing. splicosome
This means more than one amino acid can be coded for by one gene
What is immunity
The presence of specific B and T memory lymphocytes which allows for a stronger and faster secondary immune response.
