Molecular Genetics - Protein Synthesis Flashcards
What is transcription
the mechanism by which information coded in nucleic acids of DNA is copied into the nucleic acids of mRNA. Occurs in the nucleus
What is translation
the mechanism by which information coded in nucleic acids of RNA is copied into the amino acids of proteins. Takes place in ribosomes in the cytosol.
What are the steps of transcription
Initiation, Elongation, Termination
What are the steps of translation?
Initiation, Elongation, Termination
Transcription - Initiation
RNA polymerase binds to the promoter and unwinds DNA. It transcribes only 1 strand, the antisense or template strand.
Transcription - Elongation
pre-mRNA is formed complimentary to the template strand in the 5’ to 3’ direction
Transcription - Termination
RNA polymerase reaches the termination sequence and it detaches, forming the double helix.
Post Transcriptional Modifications
Capping - 7 G’s to the 5’ end which makes an attachment point for the ribosomes.
Tailing - 50-250 adenines added to the 3’ end by the poly-a-polymerase to make it more stable
mRNA splicing - snRNPs bind to the introns and loop them outwards so that exons can be joined together. The loop is called an active splicesome.
What is alternative splicing
increases the number and variety of proteins because exons can be joined in different combinations
Genetic Code is redundant meaning
multiple codons code for the same amino acid
What is amino acylation
adding an amino acid to tRNA
Translation - Initiation
methionine tRNA forms a complex with the small ribosomal subunit. It binds at the 5’ cap and moves along until it reaches AUG. The large ribosomal subunit binds to complete the ribosome. Initiation ends when met-tRNA is in the P-site.
Translation - Elongation
a second tRNA binds to the a-site. Peptidytransferase cleaves the amino acid from the p site and forms a polypeptide bond with the amino acid on the a site. The ribosome moves along the mRNA to the next codon which frees the a-site.
Translation - Termination
occurs when the a-site arrives at a stop codon. a proton release factor binds here instead of tRNA. The polypeptide chain is released and the ribosome detaches from the mRNA.
What is a polysome
multiple ribosomes translating at the same time.
