Only a portion of each mRNA can be translated; The protein-coding region of the mRNA consists of an ordered series of 3-nt-long units called codons(密码子)that specify the order of amino acids;
• Only a portion of each mRNA can be translated; • The protein-coding region of the mRNA consists of an ordered series of 3-nt-long units called codons (密码子）that specify the order of amino acids;
1-1 polypeptide chains are specified by ORF The protein coding region of each mRNA is composed of a contiguous,non-overlapping string of codons called an opening reading frame(ORF)(可读框)； Each ORF begins with a start codon(起始密码子) and ends with a stop codon(终止密码子)； The mRNA is readed in a 5'->3'direction during protein translation; 5 3 AUGAAAGCAAUUUUCGUACUGAAAGGUUGGUGGCGCACUUCCUGA stop
1-1 polypeptide chains are specified by ORF • The protein coding region of each mRNA is composed of a contiguous, non-overlapping string of codons called an opening reading frame (ORF) （可读框）; • Each ORF begins with a start codon （起始密码子） and ends with a stop codon（终止密码子）; • The mRNA is readed in a 5’ → 3’ direction during protein translation;
The start codon -the first codon of an ORF; In bacteria:AUG(90%),GUG(8%),or UUG(1%)(5'-3); In eukaryotic cells:5'-AUG-3'; Functions: 1.Specifies the first amino acid to be incorporated into the growing polypeptide chain; 2.Defines the reading frame for all subsequent codons;
The start codon —the first codon of an ORF; In bacteria : AUG(90%), GUG(8%), or UUG (1%) (5’→3’); In eukaryotic cells: 5’-AUG-3’; Functions: 1. Specifies the first amino acid to be incorporated into the growing polypeptide chain; 2. Defines the reading frame for all subsequent codons;
5 3 AUGAAAGCAAUUUUCGUACUGAAAGGUUGGUGGCGCACUUCCUGA stop 5 3 AUGAAAGCAAUUUUCGUACUGAAAGGUUGGUGGCGCACUUCCUGA stop stop 5 31 AUGAAAGCAAUUUUCGUACUGAAAGGUUGGUGGCGCACUUCCUGA )N (FR A (H Three possible reading frames of the E.coli trp leader sequence; Copyright2004 Pearson Education,Inc.publishing as Benjamin Cummings
Three possible reading frames of the E. coli trp leader sequence;
Prokaryotic mRNA(polycistron,多顺反子) RBS start stop RBS start stop RBS start stop 5PPP 3 5-9 bases 000000000000000 000000000000000 000000000000000 start stop 5 AUG ☐AAAAA3' 5'cap 0000000000000000000000000090000000000 Eukaryotic mRNA(monocistron,单顺反子)
Prokaryotic mRNA (polycistron，多顺反子) Eukaryotic mRNA (monocistron ，单顺反子)