Lecture Notes: Microscopic Life
Last revised: Friday, November 29, 2002           Copyright 2002. Thomas M. Terry
Reading: Ch. 11 and 12 in text (skip material on plants)
Note: These notes are provided as a guide to topics the instructor hopes to cover during lecture. Actual coverage will always differ somewhat from what is printed here. These notes are not a substitute for the actual lecture!

Prokaryotes & Eukaryotes

prokaryote and eukaryote organization
Image drawn by Thomas M. Terry for The Biology Place. Used with permission.
  1. Prokaryotes
    • "pro" = before, + "karyos" = nucleus
    • Includes bacteria and cyanobacteria (formerly called blue-green algae and thought to be plants), as well as archaea (see below)
    • Simple architecture not understood until EM technology in 1940's
    • Typical sizes: 0.5-5 Ám (micrometer) diameter
  2. Eukaryotes
    • "eu" = true, + "karyos" = nucleus
    • Typically contain membrane-bounded organelles (e.g. mitochondria, lysosomes, endoplasmic reticulum, Golgi bodies)
    • Typical sizes: anywhere from 5 micrometers (yeast cells) to 50 or 100 micrometers. A few cells (such as bird eggs) are enormous, and some cells (such as animal nerve cells) can attain lengths of many meters, even though small in diameter.
    • Includes protists, fungi, animals and plants.

Classifying Life

What are microbes?

Bacteria: General characteristics

Bacteria and disease

Examples of Bacterial Diseases

Viruses: General characteristics

Some viral diseases

  1. "Cold" viruses. Many belong to rhinoviruses -- over 150 different species. Also cause foot-and-mouth disease
  2. Influenza virus
    • most lethal pathogen of 20th century. Epidemic of 1918-19 killed 20 million people!
    • Transmitted by person-to-person contact, mainly by droplets from coughing and sneezing.
    • Virus attacks mucous membranes of upper respiratory tract, sometimes lungs.
    • Symptoms: 3-7 days fever, chills, fatigue, headache, muscular aches. Most serious problems due to bacteria that invade while defences are weak. Death may occur in infants, elderly.

      Electron micrograph of papilloma virus. From "Virus Ultra Structure" by Linda Stannard
    • Virus particle (virion) has RNA, not DNA. No proofreading to correct errors, so much higher mutation rates than DNA viruses.
    • Antigenic shift occurs every few years. Viruses infect pigs and ducks as well as humans. Especially common in China. New virus strains evolve, human hosts no longer protected.
    • Vaccines not good for more than a few years because of new strains. Usually only recommend for those at most risk
  3. Human Immunodefiency Virus (HIV) and AIDS
    • Most lethal current human epidemic. Has caused over 2 million deaths worldwide, number of infected individuals is growing, especially in Africa and Southeast Asia.
    • Newest estimates are 33 million infected worldwide, 2/3 in Africa.
    • In some subsaharan countries in Africa, 25% of individuals between ages 15-24 are infected! Tremendous failure to provide information, prophylactics.
    • Transmission: sexual activity, especially with multiple sex partners. Also contaminated blood, needles, hospitals.
    • View 3-D diagram of HIV virion
    • View animated movie showing HIV virus uncoating and replication
    • AIDS lowers immune system's ability to respond to other infections, allows opportunistic pathogens to invade body. Most common infection is pneumonia (lung infection) caused by Pneumocystis (2/3 of all AIDS patients get this at some point).
    • Host cell for the virus is CD4 (T-helper) cell, needed to activate antibody production. In normal human, CD4 cells account for 70% of total T cells -- in AIDS, number decreases, may reach 0% of T cell pool.
    • Virus particle has RNA. Inside host cell, RNA is copied into DNA by unusual enzyme, reverse transcriptase (normal transcription is DNA RNA
    • DNA integrates into host chromosome
    • Virus DNA then transcribed & translated into viral proteins. RNA is packaged at cell membrane into new viruses by budding from cell
    • View TEM of HIV particles budding out of host cell
    • Progress of HIV infection only recently understood. Formerly thought that virus became latent. Now discover that virus is anythig but latent: during infected period (which can last 10 years), body is destroying ~ billion virions/day, and virus is killing about 100 million CD4 T cells a day. HIV virus continues replicating, and body rapidly replenishes lost T cells. Only when lymph nodes wear out does virus gain the upper hand.
    • Prognosis: with carefully selected treatments, better than before. Virtually every infected person dies sooner of later, usually within 10 years of infection. No cure known, no vaccine yet available. Virus mutates rapidly, many strain variations. Vaccines being tried, results mixed but preliminary.
    • Drugs: some types of drugs offer limited success. AZT (azidothymidine) reduces DNA synthesis in treated cells. But eventually, viral mutants resistant to drug arise. Also, long term use of drug can cause toxic side effects.
      Protease inhibitors: Like many viruses, HIV needs to cleave large protein product into smaller products, using viral protease protein. By inhibiting this enzyme, should block necessary stage in viral replication cycle. Still under development, but resistant viral mutants to these type of drugs have already been found.





Examples of Fungal Diseases

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