Viruses

1.         The structure of viruses is very different from living cells. They do not have any cell parts.

            a.         Viruses are made of a piece of DNA surrounded by a protein coat. The protein coat is called a capsid.

            b.         The capsid gives each virus a unique shape.

            c.         Some viruses have a membrane around the capsid.

2.         Viruses do not display most of the characteristics of living things. Most biologists classify them according to the host the virus infects.

            a.         There are three general types of viruses:

                        i.         Those that infect bacteria.

                        ii.        Those that infect plants.

                        iii.       Those that infect animals. Some animal viruses contain DNA while others contain RNA.

            b.         Each virus is quite specific about what it will infect.

                        i.         Usually a virus that infects a plant or a cow will not infect a human.

3.         Viruses cause serious diseases in humans and can be passed from one person to another.

            a.         They can:

                        i.         travel on dust or water in the air (e.g., measles, common cold)

                        ii.        travel on food or in drinking water (e.g., hepatitis)

                        iii.       spread by animal or insect bites (e.g., rabies, West Nile)

4.         When a virus infects a cell it takes over the cell organelles and uses them to make more viruses.

            a.         The viruses attaches to the cell.

            b.         The viruses injects its nucleic acid (DNA or RNA) into the cell. The capsid is left outside.

            c.         The nucleic acid directs the cell to make virus proteins and nucleic acid.

            d.         The newly made virus parts assemble to make more viruses.

            e.         These new viruses then escape from the cell and can infect other cells. Sometimes the cell is killed when the new viruses escape.

Bacteria

1.         Bacteria are simple, single-celled organisms.

2.         There are a few major differences between bacterial cells and other cells.

            a.         Bacteria do not have a membrane around the nucleic acid. This means they do not have a nucleus.

            b.         They do not have the organelles found in most other cells.

3.         Some bacteria are heterotrophs which means they must eat.

4.         Some are autotrophs which means they can make their own food (like plants).

5.         Bacteria are found in every habitat on the planet.

6.         Bacteria reproduce by a type of asexual reproduction called binary fission.

            a.         This means a bacterial cell simply divides into two new, identical cells.

            b.         Most bacteria divide quite quickly. The common bacterium E. coli can divide every 20 minutes under the right conditions.

            c.         A few bacteria can become many very quickly, making bacterial infections very dangerous.

7.         There are three shapes of bacteria.

            a.         Cocci - are spherical or egg-shaped.

                        i.         A common cocci bacterium is streptococci which causes strept throat

                        ii.        Others, called staphylococci grow on our skin and around us all the time.

                        iii.       They often cause food poisoning if food is not properly washed, cooked, or stored.

            b.         Bacilli are rod shaped like cylinders.

                        i.         One type of bacillus bacteria causes botulism, a deadly food poisoning that can occur in improperly canned food.

                        ii.        A bulging can is a sign of a contaminated can. The bacteria produce a gas which causes the can to bulge.

            c.         Spirilla are curved or spiral shaped.

                        i.         One spirilla bacterium causes cholera which kills about 130,000 people each year worldwide.

                        ii.        A spiral bacterium also causes syphilis, a sexually transmitted infection which can cause blindness, nervous disorders and death.

8.         Most bacterial infections can be treated using antibiotics. These are drugs which kill bacteria.

            a.         Because antibiotics are used so often, many bacteria have become resistant. New antibiotics have to be developed all the time to avoid this problem.

9.         Some are used to make foods like cheese, vinegar and yogurt.