RNA

1. RNA and the business of making proteins

2. RNA structure • RNA is the principle molecule that carries out the instructions coded in DNA • RNA is a nucleic acid • RNA is different than DNA in three ways • Sugar is ribose • RNA is single stranded • RNA contains uracil instead of thymine • Thymine forms H bonds with adenine

3. Transcription • This is the process by which RNA molecules are made • Part of the nucleotide sequence of DNA is copied into RNA • Enzyme responsible is called RNA polymerase • “Start” sequences in DNA tell RNA polymerase where to start copying • “Stop” sequences tell RNA polymerase where to stop

4. Forms of RNA • Section of DNA code for three different kinds of RNA •  Messenger RNA (mRNA) • Serves as a temple for the assembly of the protein • It’s a long chain of RNA • Ribosomal RNA (rRNA) • Makes up the organelle where proteins are assembled (remember?????) • Transfer RNA (tRNA) • Carries specific single amino acids to the site of protein assembly (one tRNA for every type of amino acid)

5. Genetic Code (1) • Proteins are made of polypeptides, which are made of amino acids • There are 20 different amino acids • The order of the amino acids determines the properties of the protein • The order of the nucleotides in DNA controls the order of the amino acids in the finished protein. • This is called the genetic code

6. Genetic Code (2) • The language is written in only 4 letters (AUCG) • Nucleotides in mRNA are read in groups of 3 letters • The group of 3 nucleotides is called a codon

7. Genetic Code (3) • The language is written in only 4 letters (AUCG) • Nucleotides in mRNA are read in groups of 3 letters • The group of 3 nucleotides is called a codon

8. Genetic Code (4) • For example: m RNA sequence AAACACGGU • Is read like this: AAA CAC GGU • Which translates as: Lysine-Histidine-Glycine

9. Genetic Code (5) • The start signal is AUG, which stands for the amino acid methionine • Thus methionine is usually the first amino acid in all proteins • Sometimes enzymes cut this off after the complete protein is made •  There are three stop signals that do not code for any amino acid • UAA, UAG, UGA

10. Genetic Code (6) • Translation is the process in which mRNA is decoded into an amino acid sequence • Ribosomes match up the appropriate tRNA with the sequence on the mRNA • Every tRNA has a three nucleotide anti-codon which matches up with the mRNA codon

11. Genetic Code (7) • The ribosome binds two codons at a time • When a tRNA binds its amino acid to the polypeptide chain it is released from the ribosome to bind to another one of its specific amino acid • The ribosome moves along the mRNA reading two codons at a time until it comes to one of the three stop codons. The result is a protein, which is released from the ribosome

12. Mutations • Inheritable change in genetic information • Gene mutations • Substitution (no effect on codon) • Insertion or deletion (effects codon) • Chromosome mutations • Deletion, duplication, inversion, translocation

13. Effects of mutations • So what’s the big deal? • Some have little or no effect • Some produce beneficial variation • Some negatively affect gene function