Cells Lecture IV

1. Cells Lecture IV DNA and Protein Synthesis

2. Biology Standards Covered • 1d ~ students know the central dogma of molecular biology outlines the flow of information from transcription of ribonucleic acid (RNA) in the nucleus to translation of proteins on ribosomesin the cytoplasm

3. The Structure of DNA • DNA is a long molecule made up of nucleotides • Each nucleotide is made up of three parts: • 5-carbon sugar called deoxyribose • Phosphate group • Nitrogen Base

4. The Nucleotides Nitrogen Bases A- adenine G- guanine C- cytosine T- thymine Adenine Guanine Cytosine Thymine (Deoxyribose) 5-Carbon Sugar Phosphate group

5. Chargaff’s Rules • According to Erwin Chargaff: • Adeninealways pairs with Thymine • Cytosinealways pairs with Guanine

6. The Double Helix Nucleotide • base pairing-hydrogen bonds forming only between certain “base pairs” Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine(C) Guanine (G)

7. DNA Arranged in a Chromosome

8. Central Dogma • The term central dogma is used in science to describe the “making of proteins” from instructions coded in the DNA • An equation to remember for Central Dogma would be: DNA mRNA Amino Acid Chain Transcription Translation

9. Transcription inside the Nucleus Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNApolymerase DNA RNA

10. Transcription • Promoters – specific sites where the enzyme-protein RNA Polymerase binds to the strand of DNA to begin transcription

11. Central Dogma • Proteins are assembled into polypeptides • These are long chains of amino acids • There are 20 different types of amino acids • The properties of proteins are determined by which order these amino acids are joined

12. Central Dogma • Each of these amino acids that mRNA “codes” for recognizes the three base pair sequence • A codon consists of “three nucleotides in a row” that code for a single amino acid • AUG codes for the amino acid Methionine

13. The (20) Amino Acids Methionine is the universal “start codon” for all proteins

14. Central Dogma • Along with the twenty amino acids there are “special” base pair sequences that “code for” startand stopcodons • Stop codons are like the “period at the end of a sentence”. • They signify the end of a polypeptide (amino acid chain)

15. The (20) Amino Acids

16. Translation • The term central dogma is used in science to describe the “making of proteins” from instructions coded in the DNA • An equation to remember for Central Dogma would be: DNA mRNA Amino Acid Chain Transcription Translation

17.  Translation Nucleus mRNA Lysine tRNA Phenylalanine Methionine Transfer RNA Ribosome Start codon mRNA

18. Translation • Each strand of mRNA is separated into three base pairs called codons • AUG —- UUC --- AAA (mRNA) • This is where transfer RNAcomes in (tRNA)

19. Translation • tRNA is responsible for getting the right anticodon with each of the mRNA codons • An amino acidis attached to each anticodon Lysine (Amino Acid) tRNA Ribosome mRNA

20. Translation The Polypeptide “Assembly Line”The ribosome joins the two amino acids & breaks the bond between the tRNA & it’s amino acid Growing polypeptide chain Ribosome tRNA Lysine tRNA mRNA Completing the Polypeptide The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain. mRNA Ribosome Translation direction