protein synthesis: background
Done through 2 major processes:
- Transcription: mechanism by which the information coded in nucleic acids of DNA is copied into the nucleic acids of RNA
- Translation: mechanism by which the information coded in the nucleic acids of RNA is copied into the amino acids of proteins
mRNA
- mRNA transcribes the genetic code from DNA into a form that can be read and used to make proteins. mRNA carries genetic information from the nucleus to the cytoplasm of a cell.
- rRNA is located in the cytoplasm of a cell, where ribosomes are found. rRNA directs the translation of mRNA into proteins
- Like rRNA, tRNA is located in the cellular cytoplasm and is involved in protein synthesis. tRNA brings or transfers amino acids to the ribosome that correspond to each three-nucleotide codon of rRNA. The amino acids then can be joined together and processed to make polypeptides and proteins.
the dna & rna alphabet
- DNA alphabet = A, T, G, C
- RNA alphabet= A, U, G, C
- Although there are only four bases, there are 20 amino acids.
- These 4 bases are used in combinations of at least 3 to provide the capacity to code for 20 amino acids
Therefore the genetic code is a 3 letter code
–For example AUG specifies for the amino acid methionine, it is usually the first codon translated in any mRNA, there AUG is a start or initiator codon
–They act as periods of indicating the end of a polypeptide-encoding sequence.
–Once reached, polypeptide synthesis stops and the new polypeptide chain is released form the ribosome
- Each 3 letter combination (or code) is know as a codon
- Of the 64 codons (4^3), 61 specify for amino acids.
–For example AUG specifies for the amino acid methionine, it is usually the first codon translated in any mRNA, there AUG is a start or initiator codon
- These 3 codons do not specify for amino acids, UAA, UAG, UGA. They are known as stop codons (AKA: nonsense codons or termination codons)
–They act as periods of indicating the end of a polypeptide-encoding sequence.
–Once reached, polypeptide synthesis stops and the new polypeptide chain is released form the ribosome