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The genetic code is like a universal language for life, translating DNA into proteins. It's nearly identical across organisms, with a few exceptions, hinting at a shared origin for all living things on Earth.

Protein synthesis is a complex process involving initiation, elongation, and termination. It's similar in prokaryotes and eukaryotes, but with key differences in ribosome structure, location, and antibiotic sensitivity.

The Genetic Code and Its Universality

Universality of genetic code

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  • Set of rules that defines how information encoded in genetic material (DNA or mRNA sequences) is translated into proteins
  • Nearly universal across most living organisms
    • Common evolutionary origin for all life on Earth
  • Deviations from standard genetic code exist in some organisms and organelles
    • Mitochondria and some protozoans may have slight variations

Protein Synthesis (Translation) Process

Key steps in protein synthesis

  1. Initiation
  2. Elongation
    • Aminoacyl-tRNA synthetases attach appropriate amino acids to corresponding tRNAs
    • Ribosome moves along mRNA, reading codons and facilitating binding of appropriate aminoacyl-tRNAs
    • Peptide bonds form between amino acids carried by tRNAs, growing polypeptide chain
    • Ribosome translocates to next codon, process repeats
    • GTP hydrolysis provides energy for various steps in elongation
  3. Termination
    • Ribosome reaches stop codon (UAA, UAG, or UGA), release factors bind to ribosome
    • Release factors trigger hydrolysis of bond between polypeptide chain and final tRNA
    • Completed polypeptide chain is released, ribosomal subunits dissociate from mRNA

Prokaryotic vs eukaryotic translation

  • Initiation differences
    • Prokaryotes: Shine-Dalgarno sequences help recruit ribosome to mRNA
    • Eukaryotes: 5' cap and poly-A tail on mRNA help with ribosome recruitment and binding
  • Ribosome structure varies
    • Prokaryotic ribosomes: 70S (30S and 50S subunits)
    • Eukaryotic ribosomes: 80S (40S and 60S subunits)
  • Antibiotic targeting
    • Some antibiotics (streptomycin) specifically target prokaryotic ribosomes, exploiting differences
  • Localization differs
    • Prokaryotes: Transcription and translation are coupled, occurring simultaneously in cytoplasm
    • Eukaryotes: Transcription occurs in nucleus, mRNA transported to cytoplasm for translation

Ribosome structure and function

  • A site (aminoacyl-tRNA site): Accepts incoming aminoacyl-tRNA
  • P site (peptidyl-tRNA site): Holds tRNA with growing peptide chain
  • E site (exit site): Holds deacylated tRNA before it exits the ribosome
  • tRNA anticodon base-pairs with mRNA codon in A site, ensuring correct amino acid incorporation

Key Terms to Review (67)

5' Cap: The 5' cap is a modified guanine nucleotide added to the 5' end of a mature eukaryotic messenger RNA (mRNA) molecule. It plays a crucial role in the structure and function of RNA, as well as in the process of protein synthesis (translation).
A (aminoacyl) site: The A (aminoacyl) site on the ribosome is where the incoming aminoacyl-tRNA binds during protein synthesis. It plays a crucial role in translating mRNA into proteins by ensuring that the correct tRNA and its attached amino acid are added to the growing polypeptide chain.
A site: The A site, also known as the aminoacyl site, is a specific location on the ribosome where the incoming aminoacyl-tRNA (charged tRNA) binds during the process of protein synthesis, or translation. The A site is one of the three tRNA binding sites on the ribosome, along with the P site and the E site.
Amino Acid: Amino acids are the fundamental building blocks of proteins, which are essential macromolecules that perform a vast array of functions in living organisms. They are organic compounds composed 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.
Amino acids: Amino acids are organic molecules that serve as the building blocks of proteins. They play a crucial role in cellular processes and are essential for protein synthesis.
Aminoacyl tRNA synthetase: Aminoacyl tRNA synthetase is an enzyme that attaches the appropriate amino acid to its corresponding tRNA molecule. It plays a crucial role in translating mRNA codons into functional proteins by ensuring the correct amino acids are incorporated.
Aminoacyl-tRNA Synthetase: Aminoacyl-tRNA synthetases are a class of enzymes responsible for attaching specific amino acids to their corresponding transfer RNA (tRNA) molecules during the process of protein synthesis (translation). These enzymes play a crucial role in ensuring the accurate pairing of amino acids with their cognate tRNA, which is essential for the faithful translation of genetic information into functional proteins.
Anticodon: An anticodon is a sequence of three nucleotides in transfer RNA (tRNA) that pairs with a complementary codon in messenger RNA (mRNA) during protein synthesis. It ensures the correct amino acid is incorporated into the growing polypeptide chain.
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 facilitates the incorporation of the correct amino acid into the growing polypeptide chain.
Archaea: Archaea are a domain of single-celled microorganisms that are genetically distinct from bacteria and eukaryotes. They often inhabit extreme environments but can also be found in more common habitats.
CCA amino acid binding end: The CCA amino acid binding end is a specific sequence of three nucleotides (cytosine-cytosine-adenine) at the 3' end of tRNA molecules where an amino acid attaches during protein synthesis. This sequence plays a critical role in the translation process within cells.
Charged tRNA: Charged tRNA, also known as aminoacyl-tRNA, is a tRNA molecule that is covalently bonded to its corresponding amino acid. This charging process is essential for the addition of amino acids during protein synthesis.
Chloroplasts: Chloroplasts are organelles found in eukaryotic cells that conduct photosynthesis, capturing light energy to produce glucose and oxygen. They contain their own DNA and are believed to have originated from cyanobacteria through endosymbiosis.
Codon: A codon is a sequence of three nucleotides in mRNA that specifies a particular amino acid or a termination signal during protein synthesis. It is the basic unit of the genetic code.
Codon: A codon is a sequence of three nucleotides in a messenger RNA (mRNA) molecule that specifies the amino acid to be inserted at a specific position during protein synthesis. Codons are the fundamental units of the genetic code that direct the translation of mRNA into a polypeptide chain.
Cognate amino acid: A cognate amino acid is the specific amino acid that is attached to a tRNA molecule, allowing it to be incorporated into a growing polypeptide chain during translation. This precise pairing ensures that the genetic code is accurately translated into proteins.
Degeneracy: Degeneracy in the genetic code refers to the redundancy of the genetic code, where multiple codons encode for the same amino acid. This feature helps protect against mutations by minimizing their impact on protein function.
E (exit) site: The E (exit) site is a location on the ribosome where tRNAs, having donated their amino acids, are released from the ribosome. This site ensures the efficient progression of translation by making room for new tRNA molecules.
E site: The E site, or exit site, is a specific region on the ribosome where the deacylated transfer RNA (tRNA) molecule exits the ribosome after it has delivered its amino acid to the growing polypeptide chain during protein synthesis.
E. coli: Escherichia coli (E. coli) is a gram-negative, rod-shaped bacterium commonly found in the lower intestine of warm-blooded organisms. While most strains are harmless, some can cause serious food poisoning and infections.
Elongation: Elongation is the process of extending or lengthening a molecule or structure. In the context of molecular biology, it refers to the continuous addition of subunits to a growing polymer, such as DNA, RNA, or a polypeptide chain, during the processes of replication, transcription, and translation, respectively.
Elongation of translation: Elongation of translation is the process during protein synthesis where amino acids are sequentially added to a growing polypeptide chain. This phase occurs after initiation and before termination in translation.
Eukaryotic Ribosome: The eukaryotic ribosome is a complex molecular machine responsible for the synthesis of proteins within the cells of eukaryotic organisms, such as plants, animals, and fungi. It is the site where the genetic code is translated into functional proteins that carry out essential cellular processes.
Genetic code: The genetic code is a set of rules by which information encoded in DNA or RNA sequences is translated into proteins by living cells. It determines how sequences of nucleotides correspond to specific amino acids.
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 establishes the correspondence between the sequence of nucleotides in nucleic acids and the sequence of amino acids in proteins, allowing cells to synthesize specific proteins necessary for their structure and function.
GTP: GTP, or Guanosine-5'-triphosphate, is a high-energy nucleotide that plays crucial roles in both the catabolism of carbohydrates and the process of protein synthesis. As a key participant in various cellular processes, GTP serves as an essential energy currency and signaling molecule within the cell.
Initiation: Initiation is the critical first step in various biological processes, including DNA replication, RNA transcription, and protein synthesis. It marks the beginning of these fundamental mechanisms that are essential for cellular function and gene expression.
Initiation factors: Initiation factors are proteins that play a crucial role in the early stages of translation by facilitating the assembly of the ribosome and initiator tRNA on the mRNA strand. They ensure that the translation process begins accurately and efficiently.
Initiation of protein synthesis: Initiation of protein synthesis is the process where ribosomes assemble around the target mRNA to begin translating its code into a polypeptide chain. This step sets the stage for elongation and termination phases in protein synthesis.
Initiation of translation: Initiation of translation is the first phase of protein synthesis where the ribosome assembles around the target mRNA. This process requires initiation factors and a specific sequence on the mRNA called the start codon.
Initiator tRNA: The initiator tRNA is a specialized transfer RNA (tRNA) molecule that is responsible for starting the process of protein synthesis, or translation, in cells. It carries the amino acid methionine and binds to the start codon (AUG) on the mRNA molecule, marking the beginning of the polypeptide chain.
Large subunit: The large subunit is one of the two components of ribosomes, responsible for catalyzing peptide bond formation during protein synthesis. It works in conjunction with the small subunit to translate mRNA into a polypeptide chain.
Mitochondria: Mitochondria are membrane-bound organelles found in eukaryotic cells that generate most of the cell's supply of ATP, used as a source of chemical energy. They also play roles in other processes such as signaling, cellular differentiation, and cell death.
MRNA: mRNA (messenger RNA) is a type of RNA that carries genetic information from DNA to the ribosome, where proteins are synthesized. It acts as a template for protein synthesis during translation.
N-formyl-methionine: N-formyl-methionine (fMet) is a derivative of the amino acid methionine, with a formyl group added to its amino group. It serves as the initial amino acid incorporated during the synthesis of proteins in prokaryotes and in the mitochondria and chloroplasts of eukaryotes.
Nonsense codon: A nonsense codon is a sequence of three nucleotides in mRNA that signals the termination of protein synthesis. It does not code for an amino acid.
P (peptidyl) site: The P (peptidyl) site is one of three binding sites on the ribosome essential for protein synthesis. It holds the tRNA carrying the growing polypeptide chain during translation.
P site: The P site, or peptidyl site, is a specific location on the ribosome where the growing polypeptide chain is attached during the process of protein synthesis (translation). It is one of the three key sites on the ribosome that play a crucial role in the translation of mRNA into a functional protein.
Peptide Bond: A peptide bond is a covalent chemical bond that is formed between the carboxyl group of one amino acid and the amino group of another amino acid, resulting in the creation of a polypeptide chain. This bond is crucial for the structure and function of proteins, which are essential macromolecules in living organisms.
Peptidyl transferase: Peptidyl transferase is an enzyme that forms peptide bonds between adjacent amino acids during protein synthesis. It is a critical component of the ribosome's large subunit.
Poly-A Tail: The poly-A tail is a sequence of adenine (A) nucleotides added to the 3' end of a mature messenger RNA (mRNA) molecule. It plays a crucial role in the stability, translation, and export of mRNA during the process of protein synthesis.
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 are essential macromolecules that perform a wide variety of functions in living organisms.
Polyribosome: A polyribosome, or polysome, is a complex formed by multiple ribosomes simultaneously translating a single mRNA strand. This structure allows for efficient and rapid synthesis of multiple copies of a protein.
Polysome: A polysome, or polyribosome, is a complex formed by multiple ribosomes simultaneously translating an mRNA molecule. This structure allows for the efficient synthesis of multiple protein copies from a single mRNA strand.
Prokaryotic Ribosome: A prokaryotic ribosome is the cellular organelle responsible for the process of translation, where genetic information is used to synthesize proteins within prokaryotic cells such as bacteria and archaea. Prokaryotic ribosomes are distinct from their eukaryotic counterparts in terms of their structure and function.
Protein sequence: A protein sequence is the order of amino acids in a protein, determined by the sequence of nucleotides in the corresponding gene. This sequence dictates the protein's structure and function.
Protein synthesis: Protein synthesis is the biological process by which cells generate new proteins. It involves transcription of DNA into mRNA and translation of mRNA into a polypeptide chain.
Pyrrolysine: Pyrrolysine is a rare, naturally occurring amino acid that is used in the ribosomal synthesis of proteins in some archaea and bacteria. It is encoded by the UAG codon, which is normally a stop codon.
Reading frame: A reading frame is a way of dividing the sequence of nucleotides in a nucleic acid (DNA or RNA) into a set of consecutive, non-overlapping triplets or codons. The correct reading frame determines which amino acids will be encoded by the gene.
Release Factor: The release factor is a protein involved in the termination of protein synthesis during translation in ribosomes. It recognizes the stop codon on the mRNA and triggers the release of the newly synthesized polypeptide chain from the ribosome, allowing it to fold and mature into a functional protein.
Ribosome: Ribosomes are molecular machines within cells that facilitate the translation of mRNA into proteins. They consist of rRNA and proteins, forming two subunits that join during protein synthesis.
Ribosome: A ribosome is a cellular organelle responsible for the synthesis of proteins within a cell. It is the site where the genetic information encoded in messenger RNA (mRNA) is translated into functional proteins, a process known as translation.
Ribozyme: A ribozyme is an RNA molecule capable of catalyzing specific biochemical reactions, similar to the action of protein enzymes. They play a crucial role in RNA processing and protein synthesis.
RRNA: rRNA, or ribosomal RNA, is a type of RNA that, together with proteins, makes up the ribosomes. Ribosomes are the cellular machinery responsible for protein synthesis.
Selenocysteine: Selenocysteine is a naturally occurring amino acid that is incorporated into certain proteins via a unique RNA sequence. It is often referred to as the 21st amino acid.
Shine-Dalgarno sequence: The Shine-Dalgarno sequence is a ribosomal binding site in bacterial mRNA, located upstream of the start codon. It helps align the ribosome with the start codon to initiate protein synthesis.
Small subunit: The small subunit is a component of the ribosome that binds to mRNA and initiates translation. It plays a crucial role in decoding the mRNA sequence into a polypeptide chain.
Start codon: A start codon is a specific sequence of nucleotides in mRNA that signals the beginning of protein synthesis. The most common start codon is AUG, which codes for the amino acid methionine.
Start Codon: The start codon is a sequence of three nucleotides in messenger RNA (mRNA) that signals the ribosome to begin the translation process of protein synthesis. It marks the location where the ribosome should start reading the genetic code and assembling amino acids into a polypeptide chain.
Stop codon: A stop codon is a nucleotide triplet within mRNA that signals the termination of translation. It instructs the ribosome to release the newly synthesized polypeptide chain.
Stop Codon: A stop codon, also known as a termination codon, is a sequence of three nucleotides in a messenger RNA (mRNA) molecule that signals the end of the protein-coding region. These codons instruct the ribosome to cease translation and release the completed polypeptide chain, marking the completion of protein synthesis.
Termination: Termination is the process by which a biological process or reaction is brought to an end. In the context of DNA replication, RNA transcription, and protein synthesis, termination refers to the specific mechanisms that signal the conclusion of these fundamental cellular processes.
Termination of translation: Termination of translation is the process by which a completed polypeptide chain is released from the ribosome after a stop codon is encountered. It marks the end of protein synthesis.
Translation: Translation is the process by which ribosomes synthesize proteins using mRNA as a template. It involves decoding the genetic information contained in mRNA to produce a specific polypeptide chain.
Translation: Translation is the process by which the genetic information encoded in messenger RNA (mRNA) is used to direct the synthesis of proteins, the fundamental macromolecules that carry out the majority of cellular functions. This process is a crucial step in gene expression, connecting the information stored in the genome to the functional molecules that enable life.
TRNA: tRNA (transfer RNA) is a type of RNA molecule that helps decode mRNA sequences into proteins. It carries specific amino acids to the ribosome during protein synthesis.
Wobble position: The wobble position is the third nucleotide in a codon, which can undergo non-standard base pairing. This flexibility allows for the same tRNA to recognize multiple codons.
5' Cap
See definition

The 5' cap is a modified guanine nucleotide added to the 5' end of a mature eukaryotic messenger RNA (mRNA) molecule. It plays a crucial role in the structure and function of RNA, as well as in the process of protein synthesis (translation).

Term 1 of 67

Key Terms to Review (67)

5' Cap
See definition

The 5' cap is a modified guanine nucleotide added to the 5' end of a mature eukaryotic messenger RNA (mRNA) molecule. It plays a crucial role in the structure and function of RNA, as well as in the process of protein synthesis (translation).

Term 1 of 67

5' Cap
See definition

The 5' cap is a modified guanine nucleotide added to the 5' end of a mature eukaryotic messenger RNA (mRNA) molecule. It plays a crucial role in the structure and function of RNA, as well as in the process of protein synthesis (translation).

Term 1 of 67



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© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.
Glossary
Glossary