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DNA and Protein Synthesis: Key Experiments and Basics

Explore the pivotal experiments and fundamental concepts of DNA and protein synthesis, including base pairing rules, double helix structure, replication, transcription, and translation processes.

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DNA and Protein Synthesis: Key Experiments and Basics

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  1. DNA and Protein Synthesis LH Biology 2011

  2. DNA Experiments • 1928; Griffith→ showed that some substance conveyed traits from heat-killed pathogenic bacteria to harmless bacteria; hypothesized that it was DNA, but was not supported • 1952; Hershey and Chase→ used a virus called T2 to show that it was DNA that infected the bacteria, not the protein

  3. Hershey and Chase • Showed that radioactive isotopes of sulfur (found only in proteins) were NOT transferred into new viral particles • However, radioactive phosphorus (only in DNA) were transferred • Therefore, it must have been the DNA that transferred the genes, not the protein

  4. More Scientists… • Rosalind Franklin→ used X-ray crystallography to find shape of DNA • Watson and Crick → discovered the double helix shape • Erwin Chargaff → found that amount of A = T and amount of C = G; this led to the discovery of how the bases matched up

  5. DNA - basics • Deoxyribonucleic Acid • Stores and transmits genetic info • Tells the cells which proteins to make and when to make them • Made up of nucleotides • Double helix structure

  6. Nucleotides • 3 parts: • Phosphate • Sugar • Deoxyribose – DNA • Ribose - RNA • Nitrogen Base

  7. Nitrogen Bases • 2 types: • Purines→ 2 carbon rings • Adenine and Guanine (A & G) • Pyrimidines → 1 carbon ring • Cytosine and Thymine (C & T)

  8. Base Pairing Rules • A always matches with T (2 H-bonds) • C always matches with G (3 H-bonds) • Bases are connected by WEAK hydrogen bonds • This is how the two strands of DNA are held together

  9. DNA Structure • Double Helix (twisted ladder) • Sides of ladder = sugar/ phosphate backbone • Rungs of ladder = nitrogen bases

  10. Protein Synthesis • 3 major processes: • Replication→ DNA copied to DNA • Transcription → DNA copied to RNA • Translation → building a protein according to RNA instructions • Uses mRNA, rRNA, and tRNA Nucleus Cytoplasm

  11. DNA Replication • Occurs in nucleus • DNA is copied • Process: • 2 strands separate • Enzyme helicase “unzips” strands by breaking H bonds • Point at which the strands separate is called the replication fork

  12. Helicase

  13. Complementary bases match up • Two new strands are formed • A with T • C with G • Enzyme DNA Polymerasehelps build the new strands from the 5’  3’ direction • Replication starts at many places simultaneously

  14. Accuracy of Replication • Very low mistake rate, because cells have enzymes (including DNA Polymerase) that proofread, recognize, and fix mistakes! • HOWEVER, mistakes can happen MUTATIONS

  15. What does DNA code for? • Each set of 3 bases is called a codon • Each codon codes for a specific amino acid • A chain of amino acids = a protein • Thus….DNA codes for proteins!

  16. Page 192 in bookLets Practice:CCAAGAGUGUGAAUG

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