Protein digestion and metabolism: nutrition article 7

Welcome again to my course on nutrition and welcome to new medical article on our health topic (nutrition).
Let us go now to answer many healthy questions about protein digestion and metabolism.
Protein digestion is very wide health topic that we can handle in many medical articles but I will go into it very fast in my short medical article.
Proteins are digested by 3 main enzymes:
1.     Pepsin: is secreted by stomach cells mainly chief cells. It is secreted in inactive form called pepsinogen and activated by stomach acidity. It is the main enzyme to break down proteins.
2.     Trypsin: is secreted by pancreas in inactive form too called trypsinogen. It is activated by small intestine alkalinity. Its main function to hydrolyze proteins.
3.     Chymotrypsin: it is also secreted by pancreas. Its main function to proteolysis proteins by breaking amide bond.
Now going to metabolism, protein metabolism divided to two health topics first one is protein synthesis and second one is protein breakdown.
·        Protein synthesis: which takes the following steps:
                                      I.            Amino acid synthesis: is a process of forming amino acids from any other sources like forming amino acids from α-ketoacids by transamination.

                                   II.            Transcription (RNA synthesis): is the process of forming RNA strand from DNA strand by RNA polymerase enzyme. It works in steps that is shown in figure below (fig.1)
RNA transcription
                                      III.            Translation: is the process by which proteins are synthesized from RNA strands in 3 steps: (fig.2)
v Initiation: when ribosome assembly and first amino acid attach to start codon.
v Elongation: when successive attachments of amino acids to the complex take place.
v Termination: by releasing RNA strand, new protein and ribosome assembly.
DNA synthesis
·        Proteins break down:
                                      I.            Urea cycle: is process to change toxic ammonium to urea that can be excreted with urine or breath.
Urea cycle depends on combining CO2 with ammonium to form urea as shown in figure.3
Urea cycle

                                   II.            Energy from amino acids:
Amino acids take many pathways to enter krebs’ cycle according to their type. So they enter citric acid cycle in different parts as shown in figure.4.

After all those complex health information, we should remember that proteins are the corner stone of our body specially muscles so be sure that you eat balanced protein diet.
As medical advice you should eat 25-28% proteins in your main meal.
To more health information about proteins just go to this short medical article.
Good bye and good luck ^_^
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