Protein Synthesis Flashcards
Transcription
The process of copying DNA into mRNA in the nucleus
Process of Transcription
RNAP binds to promotor site which separates DNA into 2 strands, and exposing DNA bases for pairing
Only 1 strand will be used for replication
RNAP slides along the template strand and synthesizes the new RNA strand by complementary base pairing
A = U, C = G
RNAP then links the nucleotides together through covalent bonds, then ends transcription when it reaches terminator region of the gene
RNA breaks away from the DNA template strand, and DNA strands rejoin to form a double helix, then the RNA strand diffuses through the nuclear pore into the cytoplasm
Differences with Coding and Non-Coding RNA
Coding is identical to RNA
Non-coding is complementary to RNA
Coding serves as a reference for mRNA formation
Non-coding doesn’t participate in protein synthesis
Coding is 5’ to 3’
Non-coding is 3’ to 5’
Transcriptome
The full range of RNA types made in a cell, and changes based off the activity of the cell
Genetic Code
A set of rules by which information encoded in mRNA sequences is converted into proteins
Amino Acid and Bases
There are 20 amino acids, and only 4 bases. Since the bases are read in groups of 3, this gives 4^3 or 64 combinations which is more than enough to code for 20 amino acids
Stop Codons
UAA
UAG
UGA
Types of Genetic Code
Linear: Read in one direction
Degenerate: More than one codon for an amino acid
Universal: The same base sequence always codes for the same amino acid
Punctuation: Start and Stop codons which initiate and end translation
Translation
The synthesis of polypeptides with a specific amino acid sequence that is determined by their base sequence on the mRNA molecule
Occurs in cytoplasm and requires tRNA, mRNA and ribosomes
Structure of Ribosomes
Made of proteins and rRNA
Has large and small subunit, large subunit has three binding sites for tRNA molecules (A, P, E). Small subunit has a binding site for mRNA
A, P, and E Sites
A Site: Aminoacyl site, where the new tRNA carrying an amino acid binds which adds amino acid to the growing polypeptide chain
P Site: Peptidyl site, which holds the tRNA during peptide bond formation
E Site: Exist site, where tRNA that lost their amino acid leaves the ribosome
Role of tRNA
Carries amino acids to the large subunit of the ribosome and matches them to the coded mRNA nucleotides to be assembled into proteins
Role of Ribosomes
Use the sequence of codons in mRNA to assemble amino acid into polypeptide chains
Role of mRNA
Has a site that can bind to the small subunit of the ribosome with a star and stop codon to indicate where translation begins and ends
Process of Translation
Consists of 3 stages: Initiation, Elongation, and Termination
Initiation is where the mRNA binds to the small subunit of the ribosome at the 5’ end, and slides across the mRNA to the start codon. The tRNA binds to the small subunit of the ribosome and binds to mRNA through complementary base pairing. Large ribosome then binds to smaller one.
Elongation is where the second tRNA pairs with the next codon at the A site. The two amino acids join by a peptide bond. This causes a shift, making the first tRNA go to the E site and exiting the ribosome, and the second tRNA to go to the P site. Another tRNA pairs with the mRNA at the A site, and the process continues and the polypeptide becomes longer until a stop codon is reached.
Termination is when a stop codon is reached, which triggers the termination of translation as no tRNA have a complementary anticodon. A protein called the release factor fills up the A site to forcefully shift the last tRNA into the E site thus releasing it, and the mRNA detaches from the small sub-unit, and the small and large sub-unit separate
