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Organic Chemistry
Table of Contents
Unit 28 Overview: Biomolecules
28.1 Nucleotides and Nucleic Acids
28.2 Base Pairing in DNA
28.3 Replication of DNA
28.4 Transcription of DNA
28.5 Translation of RNA: Protein Biosynthesis
28.6 DNA Sequencing
28.7 DNA Synthesis
28.8 The Polymerase Chain Reaction

🥼organic chemistry review

28.5 Translation of RNA: Protein Biosynthesis

Citation:

The genetic code is the language of life, translating mRNA into amino acids. It's read in triplets called codons, with 64 possibilities coding for 20 amino acids and stop signals. This universal code is the foundation for protein synthesis across nearly all organisms.

tRNA molecules are the cellular interpreters, matching codons to amino acids. With a specific structure and anticodon, they deliver amino acids to ribosomes during translation. This process builds proteins, the workhorses of cellular function, one amino acid at a time.

The Genetic Code and tRNA

Decoding of mRNA codons

  • The genetic code defines how information in mRNA translates into amino acids
  • mRNA is read 5' to 3' direction
  • Genetic code read in groups of three nucleotides (nucleotides) called codons
    • Each codon specifies an amino acid or stop signal
    • 64 possible codons ($4^3 = 64$, 4 different nucleotides)
      • 61 codons code for amino acids
      • 3 codons (UAA, UAG, UGA) serve as stop codons signaling end of polypeptide chain
  • Genetic code is degenerate meaning multiple codons can code for the same amino acid
    • UUU and UUC both code for phenylalanine
  • Genetic code nearly universal across all living organisms with few exceptions (mitochondria, some microorganisms)

Function of tRNA in translation

  • tRNA molecules serve as adapters between codons in mRNA and amino acids they represent
    • Each tRNA has an anticodon, three nucleotides complementary to specific codon in mRNA
    • Anticodon base-pairs with corresponding codon in mRNA during translation
  • tRNA molecules have specific three-dimensional structure
    • Anticodon located at one end of tRNA molecule
    • Other end of tRNA has attachment site for specific amino acid (amino acid)
      • Amino acid covalently bonded to 3' end of tRNA by aminoacyl-tRNA synthetase enzyme
  • tRNA with attached amino acid called aminoacyl-tRNA or charged tRNA
    • Aminoacyl-tRNA delivers amino acid to ribosome during protein synthesis

Protein Biosynthesis

Process of protein biosynthesis

  • Protein biosynthesis (translation) occurs in cytoplasm on ribosomes
    • Ribosomes composed of ribosomal RNA (rRNA) and proteins
    • Ribosomes have two subunits: large subunit and small subunit
  • Translation divided into three stages: initiation, elongation, termination
  • Initiation:
    1. Small ribosomal subunit binds to 5' end of mRNA (messenger RNA) at start codon (AUG)
      • Start codon codes for amino acid methionine
    2. Initiator tRNA carrying methionine base-pairs with start codon in P site of ribosome
    3. Large ribosomal subunit joins small subunit forming complete ribosome
  • Elongation:
    1. Next aminoacyl-tRNA enters A site of ribosome base-pairing with next codon in mRNA
    2. Peptide bond formed between amino acid on tRNA in P site and amino acid on tRNA in A site
      • Reaction catalyzed by ribosome (peptidyl transferase activity)
    3. Ribosome translocates moving tRNA in A site to P site and tRNA in P site to E site
      • tRNA in E site dissociates from ribosome
    4. Process repeats with next aminoacyl-tRNA entering A site until stop codon reached
  • Termination:
    1. When stop codon (UAA, UAG, UGA) encountered, release factor binds to A site instead of aminoacyl-tRNA
    2. Release factor catalyzes hydrolysis of bond between polypeptide chain and tRNA in P site
    3. Completed polypeptide chain released from ribosome
    4. Ribosomal subunits dissociate and can be used for another round of translation

Protein Synthesis Overview

  • Protein synthesis is the process of creating proteins from the genetic information in DNA
  • It involves transcription of DNA to mRNA, followed by translation of mRNA to a polypeptide
  • The resulting polypeptide chain folds into a functional protein structure

Key Terms to Review (27)

Amino acid: Amino acids are organic compounds that serve as the building blocks of proteins, each containing an amino group (-NH2), a carboxyl group (-COOH), and a unique side chain (R group) attached to the central carbon atom. They play critical roles in various biological functions, including cellular structure, function, and regulation.
Ribosomal RNA (rRNA): Ribosomal RNA (rRNA) is a type of RNA that, together with proteins, forms the structure of ribosomes, the cellular "machines" that assemble proteins based on the instructions from messenger RNA (mRNA). It plays a crucial role in the process of translating genetic information from mRNA into protein sequences during transcription.
Peptide bond: A peptide bond is a covalent chemical bond formed between two amino acid molecules when the carboxyl group of one molecule reacts with the amino group of another molecule, releasing a molecule of water (a condensation reaction). This bond is integral in forming the primary structure of peptides and proteins.
Translation: In the context of organic chemistry, particularly within the study of biomolecules and nucleic acids, translation is the process by which the genetic code carried by messenger RNA (mRNA) is decoded to produce a specific sequence of amino acids in a polypeptide chain, leading to protein biosynthesis. It occurs in the ribosome, where tRNA molecules match amino acids to the corresponding codons on the mRNA strand.
Initiation: Initiation is the first and critical step in various processes, marking the beginning of a sequence of events or reactions. This term is particularly relevant in the contexts of radical additions to alkenes, radical halogenation of alkanes, transcription of DNA, and translation of RNA during protein biosynthesis.
Peptide Bond: A peptide bond is a covalent chemical bond formed between the carboxyl group of one amino acid and the amino group of another amino acid, resulting in the creation of a peptide chain. This bond is crucial in the formation and structure of proteins, which are essential macromolecules for life.
Methionine: Methionine is an essential amino acid that plays a crucial role in protein synthesis and various metabolic processes within the human body. As one of the 20 standard amino acids, it is a fundamental building block for proteins and is involved in the translation of genetic information into functional proteins.
Amino Acid: Amino acids are organic compounds that serve as the fundamental building blocks of proteins. They consist of a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a unique side chain that determines the specific properties of each amino acid.
Polypeptide: A polypeptide is a long, linear chain of amino acids linked together by peptide bonds. It is the basic structural unit of proteins, which play crucial roles in the structure, function, and regulation of biological systems.
Nucleotide: A nucleotide is the basic structural unit of nucleic acids, such as DNA and RNA. It consists of a nitrogenous base, a five-carbon sugar, and a phosphate group. Nucleotides are essential in various biological processes, including DNA replication, transcription, and translation.
Codon: A codon is a sequence of three consecutive nucleotides in a molecule of messenger RNA (mRNA) that specifies the amino acid to be inserted at that position during protein synthesis. Codons are the fundamental units that direct the translation of genetic information from mRNA into the primary structure of a polypeptide chain.
TRNA: Transfer RNA (tRNA) is a type of RNA molecule that plays a crucial role in the process of protein synthesis within cells. tRNA acts as an adapter molecule, translating the genetic code stored in messenger RNA (mRNA) into the specific sequence of amino acids that make up a protein.
Anticodon: The anticodon is a sequence of three nucleotides on a transfer RNA (tRNA) molecule that is complementary to the codon on a messenger RNA (mRNA) molecule. It plays a crucial role in the translation process, where it binds to the corresponding codon to ensure the proper amino acid is incorporated into the growing polypeptide chain.
Ribosome: A ribosome is a complex molecular machine found within all living cells that is responsible for the synthesis of proteins, which are essential for the structure, function, and regulation of the body\'s tissues and organs. Ribosomes are central to the process of translation, where the genetic information encoded in messenger RNA (mRNA) is used as a template to direct the assembly of amino acids into polypeptide chains, ultimately forming functional proteins.
Charged tRNA: Charged tRNA, also known as aminoacyl-tRNA, is a critical component in the process of protein synthesis during translation. It refers to the tRNA molecule that has been covalently bonded to its corresponding amino acid, preparing it for incorporation into the growing polypeptide chain.
Peptidyl Transferase: Peptidyl transferase is an essential enzyme involved in the process of protein synthesis, specifically during the translation of RNA into polypeptide chains. It catalyzes the formation of the peptide bond between the growing polypeptide chain and the incoming amino acid, allowing for the sequential addition of amino acids to create a functional protein.
Translocation: Translocation is the process by which the ribosome moves along the mRNA, decoding the genetic code and synthesizing a polypeptide chain during the translation stage of protein biosynthesis.
Messenger RNA (mRNA): Messenger RNA (mRNA) is a single-stranded molecule that carries the genetic instructions from the nucleus to the ribosomes, where protein synthesis takes place. It serves as a template for the production of specific proteins in the cell.
Elongation: Elongation is a crucial process that occurs during both the transcription of DNA and the translation of RNA into proteins. It refers to the step-by-step extension of the growing nucleic acid or polypeptide chain as additional subunits are added to the sequence.
Genetic Code: The genetic code is the set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins. It is the universal language that allows living organisms to convert the digital information stored in genes into the functional molecules that carry out life's processes.
Release Factor: The release factor is a protein involved in the termination of protein synthesis during the translation process. It recognizes specific stop codons in the mRNA sequence and facilitates the release of the newly synthesized polypeptide chain from the ribosome.
Protein Synthesis: Protein synthesis is the process by which cells construct proteins, the essential building blocks of life. It involves the transcription of genetic information from DNA to messenger RNA (mRNA) and the subsequent translation of that mRNA into a functional protein molecule.
Aminoacyl-tRNA Synthetase: Aminoacyl-tRNA synthetases are a class of enzymes responsible for attaching specific amino acids to their corresponding transfer RNA (tRNA) molecules. These enzymes play a crucial role in the process of translation, where the genetic code is decoded to produce proteins.
RRNA: rRNA, or ribosomal RNA, is a type of RNA that is a crucial component of ribosomes, the cellular organelles responsible for protein synthesis. rRNA is essential for the structure and function of ribosomes, which are the sites where the genetic information encoded in mRNA is translated into proteins, a process known as translation.
Stop Codon: A stop codon is a sequence of three nucleotides in messenger RNA (mRNA) that signals the end of the coding sequence and the termination of protein synthesis during translation. These codons do not specify any amino acid and instead indicate that the ribosome should release the completed polypeptide chain and dissociate from the mRNA.
Start Codon: The start codon is a specific sequence of three nucleotides in messenger RNA (mRNA) that signals the translation machinery to begin synthesizing a protein. It marks the initiation site for protein synthesis during the process of translation.
Termination: Termination is the final step in a radical reaction mechanism where reactive radicals are converted into stable products, effectively stopping the chain reaction. This process is crucial in both synthetic organic chemistry and biological systems, as it ensures that the chain reactions do not continue indefinitely, leading to uncontrolled product formation or cellular damage.