Metabolism and Synthesis | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Metabolism and Synthesis of Proteins

Protein Digestion in Non-Ruminants:

• Proteins in the digestive tract of non-ruminants are broken down into amino acids by proteolytic enzymes.

Role of Microbiological Processes in Ruminants:

• In cattle and sheep, protein nutrition is mainly influenced by microbiological processes in the rumen.

Utilization of Amino Acids in the Body:

• Amino acids absorbed into the bloodstream are utilized by tissues, especially during growth periods.
• These amino acids are used for building body proteins, including muscle, bone, blood, enzymes, and hormones.
• Excess amino acids beyond the body's requirements are broken down as they cannot be stored.

Metabolism of Amino Acids:

• The metabolism of proteins essentially involves the metabolism of amino acids.
• Amino acids are used to synthesize new body proteins through a process of breaking down and building up polypeptides.

Deamination and Transamination

Deamination Process: 

• Deamination is a rapid metabolic process that occurs in the liver and kidneys, leading to the production of ammonia and nitrogen-free acids from amino acids like alanine and pyruvic acid.
• These resulting acids can enter the carbohydrate or fat cycle based on their type, making amino acids either glucogenic (producing glucose) or ketogenic (producing ketone bodies). 
• This process contributes to glucogenesis or fat synthesis within the Tricarboxylic acid cycle, generating energy and forming glycogen and fatty acids.

Transamination Process: 

• Transamination involves transferring amino groups from one amino acid to another compound without releasing ammonia. 
• Organs like the liver and kidneys facilitate this process by transferring amino groups to form compounds like glutamic acid from a-ketoglutaric acid or aspartic acid from oxaloacetic acid. 
• Transamination can lead to the synthesis of various amino acids necessary for protein formation.

Biosynthesis of Protein

Protein Manufacturing Process: 

• Protein synthesis is a complex cellular process heavily reliant on enzymes, RNA, and DNA. 
• RNA and DNA consist of purine or pyrimidine bases, a 5-carbon sugar (ribose or deoxyribose), and a phosphate residue. 
• The classification of nucleic acids as RNA or DNA is based on the type of sugar present. 
• The synthesis of proteins is a fundamental cellular activity requiring intricate molecular mechanisms involving RNA and DNA.By elaborating on the processes of deamination, transamination, and protein biosynthesis, we gain a better understanding of how our bodies metabolize amino acids and synthesize proteins essential for various biological functions.

Protein Synthesis Overview

Role of RNA and DNA in Protein Synthesis: 

• DNA in the nucleus contains information for amino acids. 
• RNA acts as a messenger between DNA and ribosomes in the cytoplasm. 

Ribosomes and Protein Synthesis: 

• Ribosomes in the cytoplasm synthesize proteins using amino acids. 
• Amino acids are activated using ATP and combined with tRNA specific for each amino acid. 

mRNA and Protein Synthesis: 

• mRNA carries the message from DNA to ribosomes for protein synthesis. 
• Codons on mRNA match with tRNAs carrying specific amino acids to form proteins. 

Enzymes and Protein Synthesis: 

• Enzymes are essential for each step of protein synthesis. 
• Energy from ATP is required for linking amino acids in the correct sequence. 

Essential and Non-essential Amino Acids: 

• Essential amino acids must be obtained from the diet. 
• Non-essential amino acids can be synthesized by the body. 

Variations in Amino Acid Requirements: 

• Different species have varying essential amino acid requirements. 
• Ruminants can produce essential amino acids internally. 

Non-Protein Nitrogenous Substances: 

• Various nitrogenous compounds are present in feeds. 
• These compounds play important roles in nutrition and metabolism. 

Protein Digestion and Metabolism in the Rumen: 

• Rumen microorganisms break down proteins into amino acids and peptides. 
• Ammonia and CO₂ are utilized by rumen bacteria for synthesizing microbial proteins.

Ruminant Digestion Process:

• When ruminants consume food, a significant portion of the ammonia produced is absorbed through the rumen wall into the portal blood. This ammonia is then transported to the liver, where it undergoes conversion into urea.
• The majority of the urea is excreted in the urine, while a portion of it is either returned to the rumen through saliva or the ruminal wall. Within the rumen, ruminal fluid acts on urea, breaking it down into ammonia and carbon dioxide.

Microbial Protein Synthesis in the Rumen:

• The synthesis of microbial protein within the rumen is crucial for evaluating ruminant feed quality. There exists a direct correlation between the energy available to microorganisms and their protein synthesis rates, with this energy sourced from anaerobic fermentation.
• For optimal production, the quality of protein in ruminant diets is essential. It is now understood that microbial proteins synthesized in the rumen lack sufficient sulfur-containing amino acids for high productivity, particularly in scenarios like wool production in sheep where cystine, making up 11% of the protein, is crucial.

Non-Protein Nitrogen Utilization in Ruminants:

• Dating back to 1879, Weiske noted that non-protein nitrogenous substances could effectively serve as protein substitutes for ruminants. Loosli et al in 1919 further demonstrated that essential amino acids are synthesized in the rumen by microbes from non-protein nitrogenous sources.
• This process allows for the conservation of valuable protein resources that are more beneficial for human consumption. As a result, urea is commonly employed as a protein supplement for cattle. In the rumen, urea is hydrolyzed into ammonia and carbon dioxide by the enzyme urease, which is secreted by microorganisms.