Inheritance and the Structure of DNA

1. Inheritance and the Structure of DNA

2. Deoxyribonucleic Acid

3. DNA Discovery Timeline • 1928-Frederick Griffith • transforming factor (material carrying genetic info) • 1944-James Watson and Francis Crick • discovered that DNA was the transforming factor  • 1952-Rosalind Franklin and Maurice Wilkins • took x-ray photographs of the DNA molecule • 1953-Watson and Crick • created a three-dimensional 3-D model of DNA  • 1962-Watson, Crick, and Wilkins • received the Nobel Prize in Medicine

4. What is DNA? • Genetic material used to express traits • Nucleotide units • Deoxyribose (sugar) • Phosphate • Base • Purines (double ring) • Thymine ( T ) • Cytosine ( C ) • Pyrimidine (one ring) • Adenine ( A ) • Guanine ( G )

5. Complementary Strands • Order of bases on the nucleotides in one strand of DNA complements the order of bases on the opposite strand • Anti - parallel • 5’ -> 3’ • Refers to where sugar & phosphate attach • Direction which new DNA is made • Sugar and phosphate alternate • Make up the sides • base sequence (ATGC) • attach to sugar

6. DNA Replication/Synthesis pg200 • DNA stores and transmit information • tells cells which proteins to make and when to make them • DNA located in the nucleus and cannot leave. • Replication is duplication or making more of DNA • Occurs during S phase of interphase • 2 main enzymes involved DNA Helicase and DNA Polymerase

8. DNA Helicase and DNA Polymerase Helicase unzips the DNA by breaking the hydrogen bonds between the two strands Binding proteins stabilize the strands keeping them open Nucleotide units are added from a 3’->5’direction(5’->3’ newcomplementary strand direction), this leading edge is continuous

9. 4. On the other strand of DNA, the 2nd strand called the lagging strand) • nucleotides are added from the 5’ end; creating a complementary strand of 3’->5’sporadically • since polymerase moves in a 5’->3’ it will move around to find location on the original strand that it can match up with to create segments on the new complementary DNA • this leaves gaps (called Okazaki fragments) that are later filled by the enzyme ligase 5. DNA Polymerase proof reads each strand sealing the molecules

10. RNA (Ribonucleic Acid) • RNA differs from DNA • Sugar is ribose • The nitrogen base THYMINE is replaced by URACIL • RNA U bonds with DNA A • RNA is single-stranded • There are three types of RNA • Messenger RNA (mRNA) • Transfer RNA (tRNA) • Ribosomal RNA (rRNA)

11. RNA (created from DNA) • Messenger RNA (mRNA) • copies the information from the DNA in the nucleus • Transfer RNA (tRNA) • reads the information from mRNA • carries amino acids to the ribosome • Ribosomal RNA (rRNA) • Links up with mRNA to read the “message” from DNA and to reveal codons for tRNA

12. Transcription vs Translation pg 206 • Transcription • DNA information to mRNA, tRNA, rRNA • Occurs in nucleus • Translation • mRNA to tRNA and rRNA • Polypeptide bonds are created between amino acids • Twist and turn of these chains create specific proteins • Result in phenotypes of organisms • in cytoplasm

13. Transcription pg 206 • Reading the gene • occurs on only one strand of DNA • RNA polymerase • Transcribed information has created a complementary strand of mRNA from DNA • A=U, C=G

14. Transcription illustration

15. Transcription • RNA polymerase, binds to the promotor • Promoter is particular sequence of DNA that RNA polymerase binds • DNA molecule unwinds and strands separate • RNA polymerase adds free nucleotides on one of the DNA strands • Complementary bases (AUGC) • As polymerase moves over DNA the strands rewind • RNA polymerase reaches termination signal indicated by sequence of bases • Releases DNA and RNA (mRNA,tRNA,rRNA)

16. Transcription

17. Genetic Code pg 207 • Gene Expression • Amino acids are created from instructions found in the nucleotide sequence on mRNA • Genetic Code term used to describe how the sequence of nucleotide units (bases) corresponds to a particular amino acid • Three letter (bases) word is referred to as a codon • mRNA has the codon

18. Codons in mRNA • Each sequence of 3 bases on mRNA encodes for either an amino acid or stop/start signal • Some amino acids will have 1,2,or 3 different codons • No codon codes for more than one amino acid • 64 mRNA codons • There are special codons that act as start and stop to the sequence • For example, AUG acts as a start codon codes for the amino acid Methionine • Others like (UAA, UAG, or UGA) are stop codons that don’t code for amino acids but are the end of the translating sequence • Reading the mRNA table pg 207, let’s try a few

19. Translation • RNA molecules (tRNA, rRNA, and mRNA) take information from DNA to proteins • Translates the sequence of bases found in the gene into material that the body can “read” (visible traits) • Occurs in Cytoplasm

20. RNA molecules

21. How it comes together in cytoplasm

22. Translation pg207 • Revisit Protein structure pg 208 • Polypeptides • 20 different types amino acids • Twist and fold into 3-D structure • Shape critical for function

23. Steps of Translation • rRNA, mRNA, and tRNA join together • Enzyme attaches amino acid to one end of tRNA • Other end of tRNA (anticodon) attaches to complementary bases on mRNA • AUG (methionine) begins the sequence • mRNA continues to “read” mRNA codons • tRNA brings the appropriate amino acids • Starting from the 1st codon, tRNA brings in the start amino acid (methionine) • Then as the 2nd tRNA attaches it’s amino acid to the 1st amino acid (creating a peptide bond) the 1st tRNA leaves • This process continues until the stop codon is reached

24. Textbook pg 208 Initiation and Elongation

25. Polypeptide chain continues to grow as the rRNA “reads” the codons on mRNA • rRNA reaches the stop codon (UAA, UAG, or UGA) • New polypeptide chain is released • The components of translation come apart

26. Elongation, Termination, Disassembly

27. Another view of Protein Synthesis

28. FYI - Deoxyribose vs Ribose sugars • 2-Deoxy-Ribose in DNA is replaced by Ribose in RNA. • The difference is a hydroxy group ( -OH ) in RNA versus a single proton ( -H ) in DNA. • The extra -O- in the ribose backbone prevents formation of stable double-helices in RNA.