23. In the metabolic pathway, what will happen if you create a bacterium X that carries a mutation making enzyme III inactive? Assuming each bacterium only carries a single copy of the gene for each enzyme. Enzyme Enzyme Enzyme Enzyme A- B C IV X will require external source of C to survive. The culture medium of X will have a lot of molecule B C. Culture filtrate of X will allow another mutant with a defective enzyme II to grow. DX cannot make enzyme IV. X can still make E from A.

There have been recurring cases of mad-cow disease in the United Kingdom since the mid-1990s. Mad-cow disease is caused by a prion, an infectious particle that consists only of protein. In 1986, the media began reporting that cows all over England were dying from a mysterious disease. Initially, there was little interest in determining whether humans could be affected. For 10 years, the British government maintained that this unusual disease could not be transmitted to humans. However, in March 1996, the government did an about-face and announced that bovine spongiform encephalopathy (BSE), commonly known as mad-cow disease, can be transmitted to humans, where it is known as variant Creutzfeldt-Jakob disease (VCJD). As in cows, this disease eats away at the nervous system, destroying the brain and essentially turning it into a spongelike structure filled with holes. Victims experience dementia; confusion; loss of speech, sight, and hearing; convulsions; coma; and finally death. Prion diseases are always fatal, and there is no treatment. Precautionary measures taken in Britain to prevent this disease in humans may have begun too late. Many of the victims contracted it over a decade earlier, when the BSE epidemic began, and the incubation period is long (VCJD has an incubation period of 10 to 40 years). A recent study concluded that 1 in 2,000 people in Great Britain carry the abnormally folded protein that causes VCJD. In spite of these numbers, the death rate from VCJD remains low. It is not clear whether this means that the incubation period for the disease is much longer than previously thought, or whether they may never develop the disease. How can a prion replicate itself without genetic material?

Recently, scientists discovered that a rare disorder called polkadotism is caused by a bacterial strain, polkadotiae. Mice injected with this strain (P) develop polka dots on their skin. Heat-killed P bacteria and live D bacteria, a nonvirulent strain, do not produce polka dots when injected separately into mice. However, when a mixture of heat-killed P cells and live D cells were injected together, the mice developed polka dots. What process explains this result? Describe what is happening in the mouse to cause this outcome.

20. The image above reveals two bacterial cells in the process of A. cell lysis B. transduction C. conjugation D. transformation -NAM-NAG-NAM-NAG D-Glu D-Ala D/ Transpeptidase D-Ala DAP T 1 D-Ala D-Glu L-Ala NAG-NAM-NAG-NAM FYRET E. budding K 21. Modification of the enzyme pictured (above) might result in resistance to A. quinolone B. streptomycin C. chloramphenicol D. penicillin E. trimethoprim