SECTION 12-3

RNA AND PROTEIN SYNTHESIS

RNA STRUCTURE

SINGLE STRAND MADE OF A LONG CHAIN OF

NUCLEOTIDES RNA NUCLEOTIDE IS MADE OF A

NITROGEN BASE, A PHOSPHATE GROUP AND THE 5 CARBON SUGAR, RIBOSE

3 WAYS THAT RNA DIFFERS FROM DNA

5-CARBON SUGAR IS RIBOSE SINGLE-STRAND CONTAINS THE NITROGEN BASE URACIL

INSTEAD OF THYMINE (A PAIRS WITH U) 4 NITROGEN BASES ARE ADENINE,

URACIL, CYTOSINE & GUANINE

TYPES OF RNA

MESSENGER RNA mRNA TRANSFER RNA (tRNA) RIBOSOMAL RNA (rRNA) MESSENGER RNA – READS, COPIES AND

CARRIES THE INFORMATION IN DNA TRANSFER RNA – TRANSFERS EACH AMINO

ACID TO THE RIBOSOME AS SPECIFIED BY MESSENGER RNA

RNA

RIBOSOMAL RNA – PART OF THE STRUCTURE OF THE RIBOSOME

RIBOSOMES ARE THE SITE OF PROTEIN SYNTHESIS

TRANSCRIPTION

OCCURS IN THE NUCLEUS M RNA READS & COPIES INFO IN DNA; RNA POLYMERASE IS THE ENZYME

USED IN TRANSCRIPTION OCCURS VERY QUICKLY – PROCEEDS

AT A RATE OF 60 NUCLEOTIDES PER SECOND.

TRANSCRIPTION

RNA POLYMERASE BINDS TO DNA AT A PROMOTER-A SPECIFIC SEQUENCE OF DNA THAT ACTS AS A START SIGNAL FOR TRANSCRIPTION

RNA POLYMERASE SEPARATES THE DNA STRANDS

USING ONE STRAND OF DNA AS A TEMPLATE TO ASSEMBLE RNA NUCLEOTIDES INTO A STRAND OF MESSENGER RNA

TRANSCRIPTION

ENDS WHEN A TERMINATOR IS REACHED

THE NEW STRAND OF MESSENGER RNA LEAVES THE NUCLEUS AND MOVES TO THE CYTOPLASM

THE DNA MOLECULE REASSEMBLES ITSELF INTO THE DOUBLE HELIX

TRANSLATION STEP 2 OF PROTEIN SYNTHESIS

DURING TRANSLATION, THE INFORMATION IN MESSENGER RNA IS TRANSLATED INTO A PROTEIN BY USE OF THE GENETIC CODE.

THE GENETIC CODE

THE LANGUAGE OF MESSENGER RNA INSTRUCTIONS

CONTAINS THE AMINO ACIDS AND START AND STOP SIGNALS, OR CODONS, THAT ARE CODED FOR BY MESSENGER RNA.

MESSENGER RNA & THE GENETIC CODE

MESSENGER RNA CONTAINS CODONS WHICH ARE THE THREE-BASE SEQUENCES ONLY IN MESSENGER RNA.

THERE ARE 64 POSSIBLE THREE BASE CODONS.

VOCABULARY – GENETIC CODE

THE GENETIC CODE CONTAINS START AND STOP CODONS.

START CODON – AUG; TELLS TRANSLATION TO START

STOP CODON – UAA, UAG, UGA; TELLS TRANSLATION TO STOP

TRANSLATION

TAKES PLACE IN THE CYTOPLASM ON THE RIBOSOME

IS THE DECODING OF A MESSENGER RNA INTO A POLYPEPTIDE CHAIN

TRANSLATION

BEGINS WHEN A MESSENGER RNA MOLECULE ATTACHES TO THE RIBOSOME

AS EACH CODON OF M-RNA MOVES THROUGH THE RIBOSOME,THE CORRECT AMINO ACID IS ATTACHED TO THE GROWING POLYPEPTIDE CHAIN BY T-RNA

TRANSLATION

TRANSFER RNA CARRIES THE ANTICODON-THE 3-BASE SEQUENCE THAT IS COMPLEMENTARY TO THE M-RNA CODON

EXAMPLE: M-RNA – CUG; T-RNA IS GAC. THE ANTI-CODON SPECIFIES A SPECIFIC

AMINO ACID

TRANSLATION

CONTINUES UNTIL A STOP CODON IS REACHED ON THE M-RNA MOLECULE

NEWLY FORMED POLYPEPTIDE IS RELEASED INTO THE CYTOPLASM

POLYPEPTIDE = PROTEIN – A CHAIN OF AMINO ACIDS LINKED BY PEPTIDE BONDS.

TRANSLATION

THE RIBOSOMES AND TRANSFER RNA CAN BE USED IN THE MAKING OF ANOTHER PROTEIN;

THEY ARE RECYCLED.

NECESSARY VOCABULARY

PROTEINS – CHAINS OF AMINO ACIDS AMINO ACIDS – 20 DIFFERENT INDIVIDUAL

UNITS THAT FORM PROTEINS POLYPEPTIDE – LONG CHAINS OF PROTEINS CODONS – 3 BASE SEQUENCE IN MESSENGER

RNA THAT DETERMINES WHICH AMINO ACID IS ADDED TO THE POLYPEPTIDE

VOCABULARY

ANTI-CODON – 3 BASE SEQUENCE ON A TRANSFER RNA MOLECULE WHICH ARE COMPLEMENTARY TO ONE OF THE MESSENGER RNA CODONS.

START CODON – AUG; TELLS TRANSLATION TO START

STOP CODON – UAA, UAG, UGA; TELLS TRANSLATION TO STOP

GENES

CODED DNA INSTRUCTIONS THAT CONTROL THE PRODUCTION OF PROTEINS WITHIN THE CELL

MOST GENES CONTAIN LITTLE MORE THAN INSTRUCTIONS FOR ASSEMBLING PROTEINS