Transcription & Translation 11.2

DNA transcription to m-RNA The information in the “blueprint” of DNA is very important, so it never leaves the protection of the nucleus Instead, the DNA “message” is transcribed to messenger RNA, which is expendable m-RNA can then go out to the ribosomes with the information...

RNA (ribonucleic acid)  Three types (mRNA, tRNA, & rRNA)  Single-stranded in humans  Contains sugar/phosphate backbone and nitrogenous bases; just like DNA  The sugar this time is ribose  The bases are adenine, cytosine, guanine and uracil

mRNA (messenger)  Takes DNA ‘message’ out of the nucleus to the cytoplasm.  Starts with RNA polymerase (enzyme) that finds the gene to be transcribed from the DNA  Another enzyme ‘unzips’ that section of DNA to expose the bases for that gene

Transcription  RNA bases pair up with exposed DNA bases from a start signal code to a stop signal code  Each three nucleotides code for a protein; on mRNA this is called a codon  This process is called transcription

tRNA (transfer)  Involved in protein synthesis  There is one tRNA for every amino acid (twenty different amino acids = twenty different tRNA)  Three bases on a tRNA will bond with each codon on an mRNA; these bases are called the anticodon

Transcription  Where: Occurs in cell nucleus  Overview: - DNA molecule must separate - RNA molecules H bond with DNA strand via RNA polymerase. - * A (DNA) pairs with U (mRNA) instead of A-T bond. - T (DNA) pairs with A (mRNA)

 Codons – series of three nucleotides in m-RNA that correspond to an amino acid in translation (charts show codons)  Anti-codon – corresponding nucleotide triplet in t-RNA  Reading frames 3 nucleotide sequence. Messenger RNA

mRNA Overview Info.  mRNA codes for Amino Acids; it gets translated into polypeptides/proteins.  mRNA translation occurs in cell cytoplasm. Before leaving the nucleus RNA transcript is modified. Addition of extra nucleotides, G nucleotide cap, and “poly-A tail” These serve as protection from enzyme degradation during transport

DNA Strand: 5’- AAA TAA CCG GAC – 3’ mRNA codon: 3’ UUU AUU GGC CUG -5’ Amino Acid: Phe Ile Gly Leu tRNA anti-codon: AAA UAA CCG GAC

Transcription &Translation DNA is like a blueprint that contains the information to build proteins. Remember that proteins are specific because of the order of amino acids in them. DNA is ultimately responsible for giving the instructions for that amino acid order.

Translation  Pairing occurs while mRNA is attached to a ribosome (ribosomes read the codons and build the proteins)  tRNAs come to the ribosomes carrying an amino acid and attach to the corresponding codon

Translation  The amino acid is linked to the growing protein by a peptide bond  Then the ribosome will move down and read the next codon and wait for the next correct tRNA  This process is called translation since you are translating DNA code into a new language of proteins

Translation - 1 This is the same DNA as we looked at before... T A A A A G G C C C

Transcription - 2 T A A A A G G C C C Enzymes uncoil and separate the two sides of the molecule...

Transcription - 3 T A A A A G G C C C But this time, only one side of the DNA molecule is copied...

Transcription - 4 T A A A A G G C C C RNA poly- merase joins nucleo- tides in the proper positions... AUGCUUUCGG

Translation Now transfer- RNA’s line up with m-RNA t-RNA brings along specific amino acids AUGCUUUCGG A U C C C A trp G A A phe

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