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Human ageing

Cross-linking theory of aging

Old couples Image credit goes to Cellinsight Everything about human ageing and related diseases Cross-linking theory The cross-linking theory of aging was proposed in 1942 by Johan Bjorksten. According to this theory Collagen and other proteins undergoing structural changes due to molecular cross linkage (collagen is an important body proteins comprising 30℅ of body proteins) . In the presence of oxygen glucose molecules binding to to proteins and this cross-linked proteins causing damage to cells and tissues resulting in aging. This theory is also called as glycosylation theory of aging.  # Wrinkle and skin changes The cross-linked skin protein collagen  is responsible for wrinkles and skin changes during aging # Tendon stiffening An increased cross-linked collagen is the reason behind tendon stiffening, tendons are connective tissues which connect muscles to bones. a stiff tendon can pass more mechanical energy from muscles to bone but it lose it's elastic prop

The free radical theory of aging

The free radical theory of aging

Dr.Denham Herman a scientific researcher who proposed the 'free radical theory of aging' in the year 1956.according to this theory the process of aging is due to oxidative damage of cell organelles and other cytoplasmic contents by free radicals. intially it was assumed that the free radicals such as ROS(reactive oxygen species) produced during normal respiratory process.The free radical theory got more attention when researchers studied the cause of cancer ,Alzheimer disease,and heart diseases .This theory realises that old age is just another disease,our old age is starting when mitochondrial DNA (mtDNA) get damaged by free radicals.1970s many scientist involved in Reserch related to this theory and in 1980 J.Miquel clearly explained the mitochondrial involvement in the production of free radicals,the theory is known as mitochondrial theory of free radicals.
Animal cell structure
Cell structure
                   Animal cell,inrenal view (mitochondria distributed incytoplasm)


Mitochondria are tiny cellular organelles which are freely distributed in cytoplasm,they are covered with two membranes.The outer membrane is a double phospholipid layer,it covers and protects the inner part of the organelle and the inner one folded many times and forms structures called cristae,the fluid filled inner space of the organelle is called matrix.mitochondria has its own DNA(mtDNA)and ribosomes. mitochondria are often called as power houses of cell,they produce energy and stored in it.The energy that released from metabolic activities are using to convert ADP(adenosine diphosphate)to ATP(adenosine triphospate),when energy utilised ATP will change to ADP.More mitochondria are present in such cells which need more energy,for example muscle cells contain more mitochondria because it needed more energy for muscular activities,the Neuron has the least numer of mitochondria because it's function is to conduct electric impulses to and fro from central nervous system and deferent parts of the body,it need not much energy to work,and RBC( red blood corpacells)has no mitochondria because it need no extra energy to perform it's function,it work as oxygen carriers,the haemoglobin present in the RBC capable of doing the work.Most of the metabolic process is done inside mitochondria with the help of oxygen,this process is also called cellular respiration.
The free radical theory of aging
internal view

Free radicals

Free radicals are atoms or molecules with one unpared electron,in other words they are charged atoms or molecules.They are unstable and highly reactive,it pull out an electron from adjacent atoms or molecule to attain stability,the atom or molecule where the free radical pulled out electron became unstable and act as free free radical it will attack another and this process will continue,finally the whole cell may damage this process is called chain reaction.Initially ROS (reactive oxygen species)is termed as free radicals but later RNS(reactive nitrogen species) radicals are also found involving in oxidatative damage to cells and tissues.Both species consist of a number of free radicals and non radicals,non radicals also make damage to our body,some of the radicals and non radicals are giving below,
Super oxide....................O2*-
Pyroxyl...........................ROO* (general code),eg;(HOO*)
Hydrogen peroxide.........H2O2
Hypoclorous acid............... Hocl
Nitric oxide........................NO*(RNS)
Nitrosyl anion......................NO-
Nitrosil cation......................NO+
Nytryl chloride ....................NO2cl
Nitrous acid.....................HNO2

Peroxynitric acid..................ONOOH

The antioxidants

Antioxidants are substances that are able to neutralise free radicals by donating an electron,eg ; vitaminC, vitaminE,beta-carotene,etc.
Age related mascular degeneration can be treated by vitaminC,beta-carotene, and zinc to some extent,complete relief is not shows that skin cancer patients get significant reduction in cancer when treated with selinium.Anti oxident rich food such as fruits and vegetables can diminish oxidative stress and increase life span.once Dr.Denham Herman said 'accept the fact that you are not going to live fore ever but there is possibility if you work at it,you might make 100'. Herman used to eat vitamin rich diets and he died at the age of 98.

Oxidative stress

Oxidative stress is an imbalence of free radicals and antioxidants in the body,body produced a small amount of antioxidants the rest is absorbed from food,vegetables and fruits are good sources of antioxidants and also the regular excersice is good for avoiding oxidative stress,but it increases the formation of free radical the result is temperaly oxidative stress,however the free radical formed in muscles stimulate the production of antioxidants in the tissue.


√ our immune system producing free radicals,WBC producing free radicals that used to kill micro organisms that enter in our body.
√ scientist considered the free radical theory as one of many reasons of aging.
√ scientists compared the life span of parrots with same sized birds the quails,the ROS production in heart,liver,erythrocytes, muscle etc are very similar in both birds species,but parrots live 5_7 times more than the quails,feeding habit of both birds are different,parrots eat fruits,seeds etc,while quails eat grains insects etc 80% of its food is carbohydrate. If you  give same meals for both birds,the result is same,the parrots live longer,this experiment cannot explain on the basis of oxidative stress theory


The free radical theory failed in a number of scientific observation and even some sources said the theory is flavoured.however the cause of many degenerative diseases such as cancer,old age heart diseases, Alzheimer,atherosclerosis, and other chronic conditions found on the basis of this theory.Diet restriction can increase life span,this is scientifically proved and nobody question about it.There are many limitation to conduct experiment on this theory,the free radicals formed in our body will disappear within fraction of seconds,it will react with other molecules or atoms.Only way is to check the oxidative damage of DNA,proteins, lipids, connective tissues etc,there are  various testing tool kits available in the market for this purpose.
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