Protein Synthesis Flashcards
Protein Synthesis
1)The sequence of bases in DNA contains the genetic code for making all the proteins in a cell
2)The transfer of information from gene (DNA sequence) to protein (polypeptide sequence or primary sequence) requires two process
-Transcription
-Translation
What is Transcription?
Transcription is the process of copying of a gene to form a RNA molecule
Transcription properties
1)Genes that encode for a protein are transcribed into mRNA
2)Genes that encode for other functional RNA are transcribed into transfer RNA (tRNA), ribosomal RNA (rRNA), micro RNA (miRNA) etc.
3)mRNA, tRNA, rRNA play key roles in protein synthesis
-Proteins will in turn regulate celluar activites
Messenger RNA (mRNA)
Information that will be translated into a protein sequence
Ribosomal RNA (rRNA)
Forms part of ribosomes which is responsible for protein synthesis
Transfer RNA (tRNA)
Carries specific amino acid to the ribosomes
Micro RNA (miRNA) - regulate, control
regulate/control
Process of Transcription
1)During Transcription, the protein (Helicase) unwinds the double-stranded DNA
2)RNA polymerase (together with many proteins) uses the unwound DNA strand as a template, and copies (or transcribes) a complementary RNA strand (mRNA) using monomeric ribonucleotides
3)The transcribed region contains the leader sequence, coding region as well as the tail region
4)After transcription is complete, the helicase and RNA polymerase (and other proteins involved in transcription) detach from the DNA
5)The unwound DNA region is rewound (reanneled)
6)RNA leaves the nucleus and enter the cytosol to be translated by the ribosomes
7)Despite the tightly packed an organized structure of DNA, the regions containing the relevant genes must be accessible to the transcriptional machinery
8)-The mRNA is complementary (in sequence) to the DNA template
-For every ‘A’ (adenine) on the DNA, the complementary nucleotide on the mRNA is ‘U’ (Uracil)
9)The challenge now is to translate the genetic information (in the form of mRNA sequences into a protein (in the form of amino acid sequences)
-The system must ensure the same nucleotide sequence will always be translated into the same protein
What is Translation?
Translation is the reading of the mRNA by ribosomes so as to synthesize the corresponding protein
Properties of Translation
1)In eukaryotes, translation occurs in the cytosol
2)Key players:
-mRNA, tRNA
-Ribosomes (made up of rRNA and proteins)
-Amino acids monomers (carried by tRNA), key proteins
-ATP
3)Messenger RNA (mRNA)
(i)Only the translated region will be ‘read; by ribosomes
(ii)Every 3 nucleotides on the translated region forms a codon (1 codon= 3 bases)
(iii)The codons do not overlap
-The first ‘AUG’ sequence moving from 5’ to 3’ usually from the first codon
-Each codon specifies (code) for a specific amino acid
4)Ribosome
-Cellular organelles made up of RNA and proteins (=ribonucleoprotein) and is responsible for converting the codon sequences in mRNA into amino acids sequences on a polypeptide
-Found in prokaryotes and eukaryotes
-Made up of 2 subunits
5)Transfer RNA (tRNA)
1)RNA molecule that carries covalently bound amino acids to the ribosome and transfers it to a growing polypeptide a=chain in translation
2)Has an anticodon sequence that binds to it’s complementary codon sequence on mRNA
3)The amino acid that each tRNA carries is dependent on the anticodon sequence
4)Each type of tRNA can only carry one type of amino acid
5)Plays a crucial role in translating codon (genetic) information into amino acid information
6)Process of translation
1)Ribosome binds to a 5’ UTR of mRNA and moves along the mRNA
2)Translation starts when it encounters a specific AUG codon (the start codon), which codes for methionine
3)tRNA that carries methionine will have an anticodon sequence that is complementary to ‘AUG’
4)The methionine tRNA will bind to the AUG codon via the anticodon sequence
5)The next codon is translated and the appropriate tRNA binds (carrying the 2nd amino acid
6)The first amino acid methionine is detached from its tRNA and forms a peptide bond with the incoming second amino acid. Process is repeated
7)Translation stops once the ribosome encounters a stop codon (UAG, UGA or UAA)
