Question

need help on biology

27. Oxidative stress:

A. Accelerates telomere shortening

B. Is mitigated by a diet rich in antioxidants

C. Is higher in individuals under a lot of psychological stress

D. All the above

Answer 1

Oxidative stress is caused by an imbalance between production of antioxidants and production of reactive oxygen species (ROS). ROS is majorly responsible for oxidative stress in an organism. Telomeres, which are non-tandem guanine rich DNA repeats at ends of the chromosome, protect the DNA from damage. Telomeres shorten by nearly 30-200 bp every replication cycle, thereby reducing the length on chromosomes.   As telomeres have high number of guanine residues, they are especially sensitive to oxidative damage. The telomeres will shorten due to double stranded breaks caused by the ROS species during oxidative damage. The single stranded regions generated will not be efficiently replicated in next replicative cycle. Thus, oxidative stress results in telomere shortening.

Antioxidants are chemicals that inhibit oxidation of compounds. ROS species are mainly responsible for generation of oxidative stress. They include superoxide radicals, hydrogen peroxide, single oxygen etc. Due to excess production of ROS, the balance between the production and destruction of ROS is affected. This leads to oxidative damage to enzymes as they cause a reducing environment. Antioxidants are molecules that reduce the oxidative damage as they prevent oxidation caused by ROS. Antioxidants will lower the ROS levels in cells and therefore reduce oxidative stress.

Chronic physiological stress is involved in aging. One of the mechanisms involved in via generation of oxidative damage during periods of physiological stress. Physiological stress is the response of body to a threat. Thus, in individuals under physiological stress, oxidative stress is higher. During stress, there is production of cortisol, a glucocorticoid hormone. Cortisol is known to stimulate the production of ROS and reactive nitrogen species. Both ROS and RNS will increase oxidative stress.

Right choice: D. all of the above.