BIOL 103 Study Guide - Final Guide: Aids, Memory T Cell, Antigen-Presenting Cell

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24 Jul 2016
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Immunity and Cancer
Cancer cells are:
Immortalized
Transformed
May undergo metastasis
Causes of cancer:
Inherited mutation (e.g. retinoblastoma, some breast cancers)
Environmental causes (e.g. mutagenic chemicals)
Genome alterations (e.g. rearrangements of DNA, increases in gene copy number, “jumping genes”
aka transposable elements) or alterations in chromosome-associated proteins such as histones
oGenomic rearrangements necessary for the proper assembly of the immunoglobulins
makes immune system vulnerable to several cancers
Oncogenic (cancer causing) viruses (can contain single stranded DNA or RNA)
Retrovirus: RNA virus that can integrate into the host DNA
How do retroviruses cause cancer:
1. Integration of the provirus near a gene important for cell growth and division (e.g. some
leukemias, mouse mammary cancer)
2. Retroviruses can carry a gene for cell growth and division as a passenger in their genome (e.g.
sarcomas, lung and colon carcinomas)
Immunity and HIV: exhausting the immune system
Human immunodeficiency virus (HIV) and acquired immune deficiency syndrome (AIDS)
Spread by transfer of white blood cells from one infected person to another
HIV enters helper T cells, using CD4 proteins as receptors
Once glycoproteins on envelope (gp120) bind to CD4, conformational change allows gp120 to
interact with chemokine co-receptors, gp120 enters host cell and two membranes (viral and host
cell) fuse
HIV also enters other cells such as antigen presenting cells, cells lining digestive tract and
microglial cells
Life Cycle:
1. Virus fuses with cell’s plasma membrane, capsid proteins are removed releasing viral proteins and
RNA
2. Reverse transcriptase catalyzes synthesis of DNA strand complementary to viral RNA, also second
DNA strand complementary to first
3. Double stranded DNA is incorporated as a provirus into the cell’s DNA
4. Proviral genes are transcribed into RNA molceules, serve as genomes for next viral generation and
as mRNA’s for translation into viral protein
a. Viral proteins include capsid proteins and reverse transcriptase (made in cytosol) and
envelope glycoproteins
5. Capsids are assembled around viral genomes and reverse transcriptase molecules
6. New viruses bud from host cell
After HIV infection:
Meanwhile the patient makes antibodies to HIV’s gp120s and is now considered HIV+
HIV proviruse can ‘hide’ in target cells including memory T cells
Helper T cells are destroyed by
oHIV virulent (lytic stage)
oNatural killer cells
oKiller T cells
oSyncytium formation
Helper T population can decline to ~5% of normal values
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