PROTEIN SYNTHESIS THE FORMATION OF PROTEINS USING THE INFORMATION CODED IN DNA WITHIN THE NUCLEUS AND CARRIED OUT BY RNA IN THE CYTOPLASM

PROTEIN STRUCTURE n ORGANISMS ARE COMPOSED OF FROM SEVERAL HUNDRED TO SEVERAL THOUSAND DIFFERENT PROTEINS n EACH PROTEIN IS A POLYMER KNOWN AS A POLYPEPTIDE n EACH POLYPEPTIDE CONSISTS OF A SPECIFIC SEQUENCE OF AMINO ACIDS n ONLY 20 AMINO ACIDS ARE USED n EACH PROTEIN MAY BE COMPOSED OF THOUSANDS OF INDIVIDUAL AMINO ACID RESIDUES n AMINO ACIDS MUST BE ARRANGED IN A SPECIFIC SEQUENCE TO INSURE PROPER FUNCTION n SEQUENCE DETERMINES THE SHAPE -- SHAPE DETERMINES FUNCTION

GENETIC CODE n TRANSFERS INFORMATION n BUILT INTO DNA ARRANGEMENT OF NITROGEN BASES n TRANSFERRED TO RNA DURING TRANSCRIPTION DNA IS TEMPLATE n REQUIREMENTS OF A CODE MUST BE ABLE TO CODE FOR 20 AMINO ACIDS ONE BASE = 4 CODONS TWO BASES = 16 CODONS THREE BASES = 64 CODONS

CODONS n IS A THREE BASE SEQUENCE OF NITROGEN BASES ON mRNA n EACH CODON IS SPECIFIC FOR A SINGLE AMINO ACID n ATTRACTS A COMPLIMENTARY SEQUENCE OF BASES ON tRNA n INITIATION AND TERMINATION CODONS START AND STOP TRANSLATION

64 CODONS FOR 20 AMINO ACIDS n EACH AMINO ACID HAS SEVERAL CODONS DIFFER FROM EACH OTHER ONLY IN THE THIRD BASE n SOME CODONS DO NOT CODE AMINO ACIDS (INITIATION AND TERMINATION) n CODE IS UNIVERSAL - USED BY ALL LIVING THINGS

RNA n mRNA CARRIES CODON SEQUENCE FORMED FROM DNA SEQUENCE DURING TRANSCRIPTION DETERMINES ORDER OF AMINO ACIDS IN PROTEIN n tRNA TRANSPORTS AMINO ACID TO mRNA SPECIFIC AMINO ACID SITE AT ONE END THREE BASE COMPLIMENTARY ANTICODON AT THE OTHER END

TRANSLATION THE PROCESS OF ASSEMBLING PROTEINS FROM THE INFORMATION CODED IN THE mRNA

AMINO ACID SITE ANTICODON tRNA HYDROGEN BONDS

EACH tRNA IS SPECIFIC FOR A CERTAIN AMINO ACID TRANSPORTS AMINO ACIDS TO RIBOSOME FOR PROTEIN SYNTHESIS THE ANTICODON END BONDS TO THE mRNA

ASSEMBLY OF A POLYPEPTIDE n BEGINS WHEN RIBOSOME ATTACHES TO THE AUG CODON n AUG CODON PAIR WITH THE UAC ANTICODON ON A tRNA CARRYING METHIONINE (ALWAYS FIRST) n METHIONENE IS LATER REMOVED n TRANSLATION OCCURS SIMULTANEOUSLY AT MANY RIBOSOMES USING THE SAME mRNA (ASSEMBLY LINE FASHION) n THE RIBOSOME MOVES ALONG THE STRAND EACH CODON IS PAIRED WITH ITS COMPLIMENTARY ANTICODON AND AN AMINO ACID IS ADDED TO THE CHAIN n AN ENZYME IN RIBOSOME CATALYZES THE BONDING BETWEEN AMINO ACIDS FORMING PEPTIDE BONDS n CONTINUES UNTIL THE RIBOSOME REACHES A TERMINATION CODON THEN THE mRNA IS RELEASED n POLYPEPTIDE IS COMPLETE

PROTEIN ASSEMBLY ON THE RIBOSOMES

OVERVIEW OF PROTEIN SYNTHESIS n ORDER OF AMINO ACIDS IS DETERMINED BY ORDER OF BASES IN mRNA n ORDER OF BASES IN mRNA IS DETERMINED BY ORDER OF COMPLIMENTARY BASES IN DNA n THE REGION OF DNA WHICH CODES FOR THE SEQUENCE OF AMINO ACIDS IN A SINGLE POLYPEPTIDE IS CALLED A GENE n MANY GENES MAY BE REQUIRED TO FORM A SINGLE PROTEIN

Primary Structure of a Protein The primary structure of a protein is its amino acid sequence, formed when a peptide bond joins the carboxyl group (one Carbon atom, two Oxygen atoms, and a Hydrogen atom) of one amino acid to the amino group (N) of another. A long chain forms from many amino acids, with one molecule of water given off with the formation of each peptide “link.” Microsoft Illustration