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PROTEIN SYNTHESIS TRANSCRIPTION AND TRANSLATION TRANSLATING THE GENETIC CODE ■ GENES: CODED DNA INSTRUCTIONS THAT CONTROL THE PRODUCTION OF PROTEINS WITHIN THE CELL ■ FIRST STEP IN DECODING GENETIC MESSAGES IS TO COPY PART OF THE NUCLEOTIDE SEQUENCE FROM DNA TO RNA (RIBONUCLEIC ACID) ■ RNA MOLECULES CONTAINS CODED INFORMATION FOR MAKING PROTEINS STRUCTURE OF RNA ■ CONSISTS OF LONG CHAIN OF NUCLEOTIDES ■ – – – DIFFERENCES BETWEEN DNA AND RNA: SUGAR IN RNA IS RIBOSE AND NOT DEOXYRIBOSE RNA IS SINGLE STRANDED RNA CONTAINS URACIL INSTEAD OF THYMINE TYPES OF RNA ■ IN THE MAJORITY OF CELLS, RNA MOLECULES ARE INVOLVED WITH ONE JOB ---- PROTEIN SYNTHESIS ■ – – – THREE MAIN TYPES: MESSENGER RNA RIBOSOMAL RNA TRANSFER RNA TYPES OF RNA ■ messenger RNA (mRNA) – RNA MOLECULES THAT CARRY COPIES OF INSTRUCTIONS FOR ASSEMBLING AMINO ACIDS INTO PROTEINS – Serve as “messengers” from DNA to the rest of the cell ■ ribosomal RNA (rRNA) – RNA THAT ALONG WITH SEVERAL DOZEN PROTEINS THAT MAKE UP A RIBOSOME – Proteins are assembled on ribosomes ■ transfer RNA (tRNA) – TRANSFERS EACH AMINO ACID TO THE RIBOSOME AS IT IS SPECIFIED BY CODED MESSAGES IN mRNA TRANSCRIPTION ■ THE PROCESS THAT COPIES THE MESSAGE IN A GENE INTO A MESSENGER RNA (mRNA) MOLECULE THAT PROVIDES THE INSTRUCTIONS FOR MAKING A PROTEIN MOLECULE – REQUIRES AN ENZYME CALLED RNA POLYMERASE – RNA POLYMERASE: ■ BINDS TO DNA AND SEPARATES THE DNA STRANDS ■ USES ONE STRAND OF DNA AS A TEMPLATE THAT CAN BE ASSEMBLED INTO THE CORRESPONDING STRAND OF RNA RNA SPLICING ■ IN EUKARYOTES, THE mRNA TRANSCRIBED FROM A GENE IS MODIFIED OR PROCESSED BEFORE IT LEAVES THE NUCLEUS ■ INITIAL mRNA HAS STRETCHES OF NON-CODING NUCLEOTIDE SEQUENCES CALLED INTRONS ■ THE CODING REGIONS OF THE RNA TRANSCRIPT—THE PARTS OF A GENE THAT REMAIN IN THE mRNA AND WILL BE TRANSLATED, OR "EXPRESSED"—ARE CALLED EXONS ■ BEFORE THE RNA LEAVES THE NUCLEUS, THE INTRONS ARE REMOVED AND THE EXONS ARE JOINED TOGETHER, PRODUCING AN MRNA MOLECULE WITH A CONTINUOUS CODING SEQUENCE THE GENETIC CODE ■ THE LANGUAGE OF mRNA INSTRUCTIONS – CODE IS WRITTEN IN A LANGUAGE THAT ONLY HAS FOUR LETTER – READ THREE LETTERS AT A TIME, SO THAT EACH “WORD” OF THE CODED MESSAGE IS THREE BASES LONG ■ CODON: THE THREE CONSECUTIVE NUCLEOTIDES THAT SPECIFY A SINGLE AMINO ACID THAT IS TO BE ADDED TO THE POLYPEPTIDE THE GENETIC CODE ■ SINCE THERE ARE FOUR DIFFERENT BASES, THERE ARE 64 POSSIBLE THREE-BASE CODONS (4 X 4 X 4 = 64) ■ SOME AMINO ACIDS SPECIFIED BY MORE THAN ONE CODON ■ AUG IS THE “START” CODON – CODES FOR THE AMINO ACID METHIONINE ■ THERE ARE THREE “STOP” CODONS (UAA, UAG, UGA) – STOP CODONS DO NOT CODE FOR AN AMINO ACID TRANSLATION ■ DURING TRANSLATION, OR PROTEIN SYNTHESIS, THE CELL USES INFORMATION FROM mRNA TO PRODUCE PROTEINS. ■ Step 1: MESSENGER RNA TRANSCRIBED FROM DNA IN THE NUCLEUS AND RELEASED INTO THE CYTOPLASM. ■ Step 2: mRNA MOLECULE IN THE CYTOPLASM ATTACHES TO A RIBOSOME. AS EACH CODON OF mRNA MOVES THROUGH THE RIBOSOME, THE PROPER AMINO ACID IS BROUGHT IN BY tRNA. – EACH tRNA MOLECULE ONLY CARRIES ONE KIND OF AMINO ACID – IN ADDITION TO AN AMINO ACID, EACH tRNA MOLECULE HAS THREE UNPAIRED BASES CALLED ANTICODONS TRANSLATION ■ Step 3: RIBOSOME FORMS A PEPTIDE BOND BETWEEN THE FIRST AND SECOND AMINO ACIDS – RIBOSOME ALSO BREAKS THE BOND THAT HELD THE FIRST tRNA MOLECULE TO ITS AMINO ACID AND RELEASES THE tRNA – RIBOSOME THEN MOVES ON TO THE NEXT CODON ■ Step 4: POLYPEPTIDE CHAIN CONTINUES TO GROW UNTIL RIBOSOME REACHES A STOP CODON ON THE mRNA MOLECULE. – NEWLY FORMED POLYPEPTIDE CHAIN THEN RELEASED ALONG WITH mRNA MOLECULE VIDEO ■ https://www.youtube.com/watch?v=h5mJbP23Buo CENTRAL DOGMA OF BIOLOGY PRACTICE ■ A CERTAIN GENE HAS THE FOLLOWING SEQUENCE OF NUCLEOTIDES: – GACAAGTCCACAATC ■ FROM LEFT TO RIGHT, WRITE THE SEQUENCE OF THE mRNA MOLECULE TRANSCRIBED FROM THIS GENE. ■ READING THE mRNA CODONS FROM LEFT TO RIGHT, WRITE THE AMINO ACID SEQUENCE OF THE POLYPEPTIDE TRANSLATED FROM THE mRNA. ■ REPEAT STEP THREE, READING THE CODONS FROM RIGHT TO LEFT.