1. The Central Dogma of Molecular Biology DNA → RNA → Proteins Biology II D. Mitchell

2. The Central Dogma of Molecular Biology Reverse Transcription

3. DNA DNA-Deoxyribonucleic Acid The discovery of DNA’s structure clarified how DNA could serve as the genetic material.

4. Contributions of Scientists Hershey and Chase ◦ Confirmed that DNA carries the genetic information Erwin Chargaff ◦ The same four bases found in the DNA of all organisms ◦ the amount of adenine = the amount of thymine; the amount of guanine = the amount of cytosine.

5. Wilkins and Franklin ◦ Developed X-ray diffraction photographs of DNA ◦ X-rays revealed that DNA resembled a tightly coiled helix composed of two or three chains of nucleotides.

6. Watson & Crick ◦ Used the information from Chargaff, Franklin, and Wilkins ◦ Built a model of DNA with the configuration of a double helix, a “spiral staircase” of strands of nucleotides twisted around a central axis.

7. Structure of DNA Is a molecule that is a double helix -two strands twisted around each other. Each strand is composed of nucleotides. ◦ Nucleotides are made of three parts: a phosphate group, a sugar, and a nitrogen base. five-carbon sugar : deoxyribose nitrogen bases : adenine, thymine, guanine, and cytosine

8. Connecting the DNA molecule Rails of the DNA ladder are alternating sugar & phosphates Rungs are composed of pairs of bases Strands of nucleotides are held together by hydrogen bonds between bases.

9. Base Pairing Rules Rule: Rule: a purine on one strand of DNA always pairs with a pyrimidine on the opposite strand. Adenine and Guanine are purines. Thymine and Cytosine are pyrimidines. Adenine always pairs with Thymine Guanine always pairs with Cytosine

10. Purines are 2 ringed: Adenine or Guanine

11. Pyrimidines are 1 ringed: Thymine or Cytosine

12. The strictness of the base pairing results in two complementary strands. The sequence of bases on one strand determines the sequence of bases on the other strand. Example: TCGAACT AGCTTGA

13. DNA Complementary Strand Practice

14. Replication of DNA Replication - the making of an exact copy of the DNA molecule  Replication occurs whenever a cell divides  The copy must be 100% accurate (errors = death possibly)

15. Stages in replication (basic) 1. DNA molecule is split in two at the end by the work of the enzyme DNA polymerase. 1. DNA unzips slightly 1. New nucleotides attach to the free ends 1. Process continues until completed

16. Results of Replication results in two (2) double strands of DNA each strand is 50% new and 50% old DNA

17. Replication Practice

18. RNA Ribonucleic Acid

19. RNA Function: protein synthesis Location: found in ribosomes and the nucleolus Structure: Single helix composed of nucleotides Nitrogenous Bases: Adenine, Uracil, Guanine, and Cytosine 5-Carbon Sugar: Ribose

20. Three types of RNA: rRNA = ribosomal RNA - carries protein building instructions. Goes from the DNA in the nucleus to the ribosome ◦ mRNA = messenger RNA - is the message from DNA for the construction of the new protein molecule ◦ tRNA = transfer RNA - delivers amino acids to the ribosomes. Has an anticodon specific to the amino acid.

21. DNA→RNA→Protein DNA is TRANSCRIBED to messenger RNA (mRNA) mRNA carries the message to transfer RNA (tRNA) tRNA is TRANSLATED to an amino acid chain, which makes up proteins

22. Transcription The copying of one side of the DNA molecule that results in a single strand of RNA During transcription, a DNA strand provides a template for the synthesis of a complementary RNA strand. Transcription of a gene produces a messenger RNA (mRNA) molecule. ◦ mRNA carries the message from the nucleus to the ribosomes

23. Transcription Practice

24. Translation The reading of the RNA code to make proteins or polypeptides. (protein synthesis) The nucleotide sequence of mRNA determines the amino acid sequence that codes for a SPECIFIC protein. ◦ Translation occurs at ribosomes.

25. mRNA Codon Charts mRNA codon Charts are used for translation.

26. The genetic code consists of 64 triplets or codons of nucleotides. ◦ groups of three bases on a mRNA strand With three exceptions, each codon encodes for one of the 20 amino acids used in protein synthesis.

27. Processes In Eukaryotes And Prokaryotes The basic mechanics of transcription and translation are SIMILAR. Because bacteria lack nuclei, transcription and translation are coupled. In a eukaryotic cell, almost all transcription occurs in the nucleus and translation occurs mainly at ribosomes in the cytoplasm.