RNA and Transcription

1. RNA and Transcription DNA and Protein Synthesis

2. Coding for Genes • Gene are coded DNA instructions that control the production of proteins within the cell • The first step is to copy a part of the nucleotide sequence from DNA into RNA

3. RNA • RNA  ribonucleic acid, nucleotide • Sugar  Ribose • Single stranded • Contains the nitrogenous base Uracil (U) rather than Thymine

5. Types of RNA • Main job is Protein Synthesis the assembly of amino acids into proteins • Messenger RNA • Ribosomal RNA • Transfer RNA

6. Most genes contain instructions for assembly amino acids into proteins and messenger RNA carries copies of those instructions Messenger RNA (mRNA)

7. Proteins are assembled on ribosomes Ribosomes contain rRNA Ribosomal RNA (rRNA)

8. Transfers each amino acid to the ribosome as it is specified by coded messages of mRNA Transfer RNA (tRNA)

9. Transcription • RNA molecules are produced by copying part of the nucleotide sequence of DNA into a complementary sequence of RNA. This process is called Transcription • Requires RNA Polymerase (enzyme) • RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA

11. Transcription • RNA polymerase will only bind to certain spots on the DNA molecule, called promoters. (have a specific base sequence) • Promoters are signals in DNA that indicate to the enzyme where to bind to make RNA

12. RNA editing • RNA molecules require some editing before they can be used • DNA of eukaryotic genes contain sequences of nucleotides called introns, that are not involved in coding for proteins • The DNA sequences that code for proteins are called exons because they are “expressed”.

13. RNA editing

14. RNA editing • When RNA molecules are formed from the copied DNA, introns are cut out of the RNA while in the nucleus. • The remaining exons are spliced together to make the final mRNA

15. Genetic Code • Proteins are made by joining amino acids into long chains called polypeptides. • Each polypeptide contains a combination of any or all of the 20 different amino acids. This is how the properties of proteins are determined.

16. Genetic Code • RNA contains the bases, A U C G (letters) and this is what the “code” consists of. • The genetic code is read three letters at a time, so that each “word” of the coded message is three bases long. • Each three-letter “word” in mRNA is known as a codon.

17. A codon consists of 3 consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide. Codons

18. Example: UCGCACGGU UCG-CAC-GGU Ser- Hist- Gly Codons

19. Codons • AUG  Methionine or “START” codon • UAA, UAG, UGA  “STOP” codons, that signify the end of a polypeptide

20. Practice • T A C C C A T T G G A G T C G A T T • A U G G G U A A C C U C A G C U A A • AUG – GGU- AAC – CUC – AGC - UAA • MET – GLY – ASP – LEU – ARG - STOP

21. YOU TRY!! • DNA: T A C C C G T A C A A G T G C A C T