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Polypeptides are assembled from _____; name these building blocks.

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Polypeptides are assembled from amino acids; these are the building blocks that form the primary structure of proteins.

To understand how polypeptides are formed, let's go through the process step by step:

1. Amino Acid Structure: Each amino acid has a central carbon atom (the alpha carbon) to which an amino group \((NH_2)\), a carboxyl group \((COOH)\), a hydrogen atom, and a variable side chain (R group) are attached. The R group varies among different amino acids and determines the chemical nature of the amino acid.

1. Amino Acid Structure: Each amino acid has a central carbon atom (the alpha carbon) to which an amino group \((NH_2)\), a carboxyl group \((COOH)\), a hydrogen atom, and a variable side chain (R group) are attached. The R group varies among different amino acids and determines the chemical nature of the amino acid.

2. Peptide Bond Formation: Polypeptides are formed by the linkage of amino acids through peptide bonds. A peptide bond is a covalent bond that is formed between the carboxyl group of one amino acid and the amino group of another. This reaction is a condensation reaction, as it releases a molecule of water \((H_2O)\).

3. Ribosomes and mRNA: The assembly of polypeptides occurs in the ribosome, a cellular machine that reads the sequence of the messenger RNA (mRNA) to determine the order of amino acids in the polypeptide. The mRNA is transcribed from DNA and carries the genetic information that encodes the protein.

4. tRNA and Aminoacyl-tRNA Synthetases: Transfer RNA (tRNA) molecules bring the correct amino acids to the ribosome. Each tRNA has an anticodon that pairs with a complementary codon on the mRNA. Aminoacyl-tRNA synthetases are enzymes that charge the tRNA with the appropriate amino acid.


5. Initiation of Translation: The process begins with the initiation phase, where the small ribosomal subunit binds to the mRNA and the first charged tRNA. The start codon on the mRNA is typically AUG, which codes for methionine.

6. Elongation of the Polypeptide Chain: During elongation, the ribosome moves along the mRNA, and new amino acids are added one by one to the growing polypeptide chain. Each new amino acid is added as the tRNA anticodon pairs with the next codon on the mRNA.

7. Termination of Translation: The process ends when the ribosome reaches a stop codon on the mRNA (UAA, UAG, or UGA). These codons do not code for any amino acid and signal the termination of polypeptide synthesis.

8. Post-Translational Modifications: After the polypeptide chain is synthesized, it may undergo various modifications, such as folding into its three-dimensional structure, cleavage of certain amino acids, or the addition of other biochemical groups.

The general reaction for the formation of a peptide bond can be represented as follows: $$\text{Amino acid 1} + \text{Amino acid 2} \rightarrow \text{Dipeptide} + H_2O$$

In chemical terms, the reaction is:

$$\text{NH}_2\text{-R}_1\text{-COOH} + \text{H}_2\text{N-R}_2\text{-COOH} \rightarrow $$ $$ \text{NH}_2\text{-R}_1\text{-CO-NH-R}_2\text{-COOH} + H_2O $$

Where R1 and R2 represent the side chains of the respective amino acids.

In summary, polypeptides are linear chains of amino acids linked by peptide bonds, and their assembly is a fundamental process in the synthesis of proteins within cells.

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