PROTEIN SYNTHESIS TRANSCRIPTION AND TRANSLATION. TRANSLATING THE GENETIC CODE ■GENES: CODED DNA...
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Transcript of PROTEIN SYNTHESIS TRANSCRIPTION AND TRANSLATION. TRANSLATING THE GENETIC CODE ■GENES: CODED DNA...
PROTEIN SYNTHESISTRANSCRIPTION 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.