1. DNA Notes
Section 12.3

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

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

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

5. 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

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

7. 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

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

9. 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)

10. 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

11. Fig. 12.

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

13.  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!

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

16. 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

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

19. 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

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

21. 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