25 Questions
What is the function of the peptidyl (P) site on the ribosome?
To bind peptidyl-tRNA
What is the central dogma of molecular biology?
One gene – one protein
What is the primary function of messenger RNA (mRNA)?
To serve as a genetic coding template for translation
What is the difference between transcription and translation?
Transcription is the synthesis of RNA, while translation is the synthesis of proteins
What is the role of ribosomal RNA (rRNA)?
To form the ribosomes and engage mRNA
In what type of cells can translation of mRNA begin before transcription has finished?
Prokaryotic cells
What is the primary function of aminoacyl-tRNA synthetases in protein biosynthesis?
To attach the correct amino acid to the correct tRNA
What is the significance of the AUG start codon in protein synthesis?
It initiates protein synthesis in bacteria
What is the outcome of the activation of amino acids in protein biosynthesis?
The attachment of an amino acid to a tRNA
How do aminoacyl-tRNA synthetases recognize the correct tRNA for a given amino acid?
Through other parts of the tRNA molecule
What is the energy source required for the activation of amino acids?
ATP
What is the result of the attachment of an amino acid to a tRNA?
The tRNA is said to be 'charged'
What binds to the initiation codon in eukaryotes?
Methionine tRNA
What is necessary for the initiation of translation in prokaryotes?
The Shine-Dalgarno sequence
What is the role of IF-3 in the initiation of protein synthesis in prokaryotes?
Combining with the starting factor 30S subunit
What is the location of the Shine-Dalgarno sequence in the mRNA?
Anywhere within the mRNA, but not at the start codon
What is the purpose of GTP hydrolysis in the initiation of protein synthesis in prokaryotes?
To add the 50S subunit to the complex
What is the location of fMet-tRNA in the initiation complex?
In the P site
What happens to the GTP bound to IF-2 in step 3 of the initiation process?
It is hydrolyzed to GDP and Pi, which are released from the complex
What is the role of eIF4A in eukaryotic initiation complex formation?
It has an RNA helicase activity
What is the result of peptide bond formation between the amino acids in the A and P sites?
The amino acid in the P site is joined to the amino acid in the A site
What is the function of the eIF4G protein in eukaryotic initiation?
It binds to the poly(A) binding protein
What happens to the tRNA in the P site during translocation?
It is released from the ribosome
What is the role of eIF4F complex in eukaryotic initiation?
It binds to the 5' cap of the mRNA
What is the result of translocation during elongation?
The ribosome moves one codon towards the 3' end of the mRNA
Study Notes
Protein Synthesis
- The Central Dogma: One gene – one protein
-
Protein Synthesis: The process of utilizing the genetic code to create proteins, consisting of two steps:
- Transcription: The synthesis of RNA using information in DNA, producing messenger RNA (mRNA)
- Translation: The synthesis of a polypeptide, using information in the mRNA, which occurs on ribosomes
The Components
-
The Ribosome:
- Site of protein synthesis
- Composed of two subunits (smaller and larger)
- Reads mRNA in 5’->3’ direction
- Has three tRNA binding sites:
- Exit (E) site: Spent tRNA exits ribosome here
- Peptidyl (P) site: Binds peptidyl-tRNA (tRNA attached to growing oligopeptide)
- Aminoacyl (A) site: Binds aminoacyl-tRNA (tRNA bound to amino acid)
Translation
-
Types of RNA:
- Messenger RNA (mRNA): Genetic coding templates used by translational machinery to determine amino acid order in a polypeptide
- Transfer RNA (tRNA): Forms covalent attachments to individual amino acids and recognizes encoded sequences of mRNAs
- Ribosomal RNA (rRNA): Assembled with ribosomal proteins to form ribosomes, which engage mRNAs and form a catalytic domain
-
The Genetic Code:
- Each codon specifies the amino acid to be placed at a corresponding position along a polypeptide
- Redundant (more than one codon may specify a particular amino acid) but not ambiguous (no codon specifies more than one amino acid)
-
Protein Biosynthesis: Occurs in 5 stages:
-
Activation of Amino Acids:
- Two chemical requirements must be met:
- The carboxyl group of each amino acid must be activated to facilitate peptide bond formation
- A link must be established between each new amino acid and the information in the mRNA that encodes it
- Attaching the right amino acid to the right tRNA is critical, occurring in the cytosol using Mg2-dependent activating enzymes (aminoacyl tRNA synthetases)
- Two chemical requirements must be met:
- Initiation
- Elongation
- Termination
- Folding and Posttranslational Processing
-
Activation of Amino Acids:
Initiation
-
Formation of the Initiation Complex:
- In prokaryotes: Initiating factors (IF 1, IF 2, IF 3), 30S ribosomal subunit, mRNA, and N-formyl methionyl-tRNA
- In eukaryotes: Initiating factors (elF 1, elF 2, elF 3, eIF 4, eIF 5), 40S ribosomal subunit, mRNA, and methionyl-tRNA
- The Shine-Dalgarno Sequence: A ribosome binding site necessary for initiation of translation, located 5-10 nucleotides upstream of the AUG start codon
Elongation
-
Steps:
- Incoming Aminoacyl-tRNA binds to the A site of the ribosome, matching anticodon to codon
- Peptide bond is formed between the 2 amino acids bound by their tRNAs to the A and P sites on the ribosome
- Translocation: The ribosome moves one codon towards the 3’ end of the mRNA, shifting the P-site tRNA to the E site where it exits, and the A site tRNA now sits in the P site
Understand the process of protein synthesis, including the central dogma, transcription, and translation. Learn about the components involved, such as ribosomes and their role in protein synthesis.
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