DNA Notes Section 12.3

Transcription DNA is copied into a complementary strand of RNA Transferring info from DNA to mRNA

Occurs in the nucleus Why is this significant? DNA cannot leave the nucleus, so mRNA must carry the code to the ribosome

RNA RNA Polymerase Enzyme that attaches to DNA  separates DNA Synthesizes (builds) a mRNA strand Binds at the Promoter – a site that RNA recognizes

A combination of 3 nucleotides of mRNA is called a codon Each codon specifies a particular amino acid to be placed in the polypeptide chain

AUG = start codon  codes for methionine Stop codon = has no tRNA  does not code for an amino acid, so the chain is finished

1 strand (single) Ribose A, U, C, G U = Uracil 2 strands (double) RNA DNA 1 strand (single) Ribose A, U, C, G U = Uracil 2 strands (double) Deoxyribose A, T, C, G T - Thymine

Transcribe DNA: mRNA: A T T C G A G U A A G C U C

Translation Changing or decoding a mRNA molecule into producing a polypeptide Message is being translated from the language of nucleic acids to the language of amino acids (proteins)

To produce a protein, need: mRNA: messenger RNA tRNA: transfer RNA  carries amino acid to the ribosome rRNA: ribosomal RNA ribosome: site of protein synthesis

Fig. 12.

tRNA will bind to mRNA  the anticodon on tRNA will bind to the codon on mRNA

 Always use the mRNA codon with this chart! Use the chart (p. 338) to find what amino acids these codons “code” for:  Always use the mRNA codon with this chart!

UAC GAU 1) UCG 2) 3) ACU 4) ________ Codon (mRNA) Amino Acid Anticodon (tRNA) UAC GAU 1) UCG 2) 3) ACU 4) ________

AGC UAC UGA GAU 1) UCG 2) AUG 3) ACU 4) CUA Serine Methionine Codon (mRNA) Amino Acid Anticodon (tRNA) AGC UAC UGA GAU 1) UCG 2) AUG 3) ACU 4) CUA Serine Methionine Threonine Leucine

The Process of Translation The ribosome always has 2 spots for tRNA tRNA leaves when it is empty Stop = amino acid chain is finished

Peptide bond is the covalent bond that joins together two amino acids The polypeptide chain continues to grow until the ribosome reaches a stop codon on the mRNA

Conclusion: A section of DNA – a gene – directs the synthesis of a protein

Q: Why are proteins so important? *** Do so many different things! Most enzymes are proteins Control biochemical pathways in the cell Direct the synthesis of lipids, carbohydrates, nucleotides Responsible for cell structures & movement