Decoding Genetics: The Journey of Genes and Proteins

1. UNDERSTANDING HEREDITY PROTEIN SYNTHESIS

2. Genes & Proteins • Genes - sequences of nucleotide bases • Genes code for proteins • Proteins - amino acids linked together by peptide bonds • 20 different amino acids exist

3. Genes & Proteins • Amino acid chains are called polypeptides • So: Protein = polypeptide Ribbon Structure of Mouse Cholera Antibody

4. Starting with DNA • DNA - found inside the nucleus • Proteins are made in the cytoplasm of cells by organelles called ribosomes • Ribosomes may be free in the cytoplasm or attached to the surface of rough ER

5. Starting with DNA • DNA ‘s code must be copied and taken to the cytoplasm • In the cytoplasm, this code must be read so amino acids can be assembled to make proteins • This process is called protein synthesis

6. RNA

7. Roles of RNA & DNA • DNA = COOKBOOK • RNA = KITCHEN CREW

8. Roles of RNA & DNA • RNA is a disposable copy of a portion of DNA • It is used to construct a protein • Comparison of RNA and DNA

9. . Three Types of RNA • Messenger RNA - mRNA • Ribosomal RNA - rRNA • Transfer RNA - tRNA

10. Messenger RNA (recipe) • Long chain of nucleotides • Made in the nucleus • TranscribesDNA & leaves through nuclear pores • Carriesinformation for a specific protein to ribosome

11. Ribosomal RNA (head chef) • rRNA is a single strand 100 to 3000 nucleotides long • Globular in shape • Made in the nucleolus of a cell • Reads mRNA and assembles proteins

12. Transfer RNA (kitchen staff) • Clover-leaf shape • Single stranded molecule with attachment site at one end for an amino acid • Found out in the cytoplasm • Brings amino acid to ribosome

14. The Genetic Code • Codon - a set of three RNA bases • Codon - designates a specific amino acid • An amino acid may have more than one codon and there are 64 codons

15. Transcription and Translation

16. Protein Synthesis • The production or synthesis of polypeptide chains (proteins) • Two phases:Transcription & Translation • mRNA must be processed before it leaves the nucleus of eukaryotic cells

17. Transcription • The process of mRNAcopying the sequence of one strand of DNA • During transcription, RNA polymerasebinds to DNA and separates the DNA strands • RNA Polymerase then usesone strand of DNA as a template to assemble nucleotides into RNA

18. What would be the mRNA strand for the following DNA sequence? DNA 5’-GCGTATGAA-3’ mRNA 3’-CGCAUACUU-5’

19. STEPS OF TRANSCRIPTON: • RNA polymerase binds to DNA just before code for protein begins • Nucleotide bases are added to make strand of mRNA • RNA polymerase detaches from DNA and mRNA • Enzymes proofread the mRNA sequence before it leaves nucleus

20. mRNA Transcript • mRNAleaves the nucleus through its pores and goes to the ribosomes

21. Translation • Translation = the process of decoding the mRNA into a polypeptide chain • Ribosomesread mRNA three nucleotide bases or 1 codon at a time

22. STEPS OF TRANSLATION: • mRNA transcript start codon AUG attaches to the ribosome • Amino acids are brought to the ribosome by tRNA • tRNA plugs into the mRNA with an anticodon • The amino acids are attached like beads on a string • tRNA is released to cytoplasm; mRNA is disassembled • Stop codon tells ribosome to release protein

23. Summary of Protein Synthesis TranscriptionTranslation DNA mRNA tRNA amino acid protein code copy anticode assemble product

24. Mutations are Mistakes • Mistakes in gene code cause mistakes in the protein • These mistakes are called mutations • In protein synthesis mutations involving one base are called point mutations • Some mutations may do nothing to the final protein others may do serious damage