That’s in our food?

Bacterial contamination in our food often makes the news. There are many bacteria present on raw food, especially raw meat. Campylobacter (pictured above), salmonella, and other microorganisms can be found, even after cooking if the meat has not been sufficiently exposed to the heat. Ionizing radiation can be used to disrupt the DNA-RNA-protein synthesis cycle that allows the bacteria to reproduce. Cobalt-60 is a common radiation source, as is cesium-137. But, just to be safe, order that burger well-done.

Effects of Radiation

In order to better understand how cellular radiation damage occurs, we need to take a quick review of how the cell functions. DNA in the nucleus is responsible for protein synthesis and for regulation of many cellular functions. In the process of protein synthesis, DNA partially unfolds to produce messenger RNA (mRNA).

Figure 1. DNA replication.

The mRNA leaves the nucleus and interacts with ribosomes, transfer RNA, amino acids, and other cellular constituents in the cytoplasm. Through a complex series of reactions, proteins are produced to carry out a number of specialized processes within the organism. Anything that disturbs this flow of reactions can produce damage to the cell.

The major effect of ionizing radiation on the cell is the disruption of the DNA strand. With the DNA structure damaged, the cell cannot reproduce in its normal fashion. Protein synthesis is affected, as are a number of processes necessary for proper cell function. One common effect is the generation of cancer cells. These cells have an abnormal structure due to the damaged DNA. In addition, they usually grow rapidly since the normal control processes regulating cell growth have been changed by the altered composition of the DNA. Tissue damage is also common in people with severe exposure to radiation.

Effects of Radiation on Humans

We can see two general types of effects when humans are exposed to radiation. Low-level exposure can lead to development of cancer. The regulatory processes regulating cell growth are disrupted, leading to uncontrolled growth of abnormal cells. Acute exposure can produce nausea, weakness, skin burns, and internal tissue damage. Cancer patients receiving radiation therapy experience these symptoms, but the radiation is targeted to a specific site in the body so that the damage is primarily to the cancer cells and the patient is able to recover from the exposure.

Summary

• Basic cellular processes leading to protein synthesis are described.
• Effects of ionizing radiation on protein synthesis are listed.
• The impact of ionizing radiation on human health is discussed.

Practice

View the presentation at the link below and answer the following questions:

http://www.wisc-online.com/Objects/ViewObject.aspx?ID=AP1302

1. How does the DNA prepare for the process of protein synthesis?
2. Where does the messenger RNA go after it is made?
3. What does the messenger RNA attach to in order to start protein synthesis?
4. What is a protein composed of?

Review

1. What is the major effect of ionizing radiation on the cell?
2. What are acute effects of radiation damage?
3. What are long term-effects of radiation damage?

Glossary