Ageing
ROS is DNA oxidation. It happens when a hydroxyl molecule reacts with a guanine base to form 8- hydroxylamine (figure 4). This will break up the hydrogen bonds formed between the guanine and adenine bases which result in DNA mutation. All these effects will lead to an imbalance between cell death and cell growth in our body. Therefore, it accelerates the rate of ageing. 14
Figure 4: Skeleton formula of guanine and 8-hydroxyguanine
Although the concept of free radical theory has been very useful in the explanation of oxidative damage to our body, there are still some studies which show the limitation of this theory. So, whether oxidative damage is the answer to ageing is undetermined. 15
Cross-linked theory, suggested by Johan Bjorkten in 1942, also mentioned another environmental factor that could affect the rate of ageing. The theory states the incidence of glycation increases, with glucose and protein being covalently linked in the presence of oxygen. These covalent bonds will disturb the basic functioning of protein molecules like collagen, which might lead to the stiffening of blood vessels, delayed wound healing and a change in the eye lens. Also, it was believed that these cross- links occur more when the blood contains a high concentration of sugar, as diabetics often have two to three more times cross-linked proteins in the body than non-diabetics. This might prove that food with a high glycemic index will speed up the rate of ageing if the cross-linked theory is right. 16
14 Cadet , J. et al. (2017) ‘ Formation and repair of oxidatively generated damage in cellular DNA ’, Free Radic Biol Med . 107:13-34. doi:10.1016/j.freeradbiomed.2016.12.049. 15 Gladyshev, V. (2014) ‘ The Free Radical Theory of Aging Is Dead. Long Live the Damage Theory! ’ Antioxid Redox Signal . 20.4:727-731. doi:10.1089/ars.2013.5228. 16 Stammers, M.et al. (2020) ‘ Age-related changes in the physical properties, cross-linking, and glycation of collagen from mouse tail tendon ’, Journal of Biological Chemistry 295.31:10562-10571. doi:10.1074/jbc.RA119.011031
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