1. History of DNA

2. History of DNA Chromosomes are made of coiled DNA and protein
Experiments on bacteriophage viruses by Hershey & Chase proved that DNA was the cell’s genetic material

3. DNA Structure
Rosalind Franklin took diffraction x-ray photographs of DNA crystals
In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays- double helix

4. DNA Structure

5. DNA Two strands coiled called a double helix
Sides made of a pentose sugar Deoxyribose bonded to phosphate groups
Center made of nitrogen bases bonded together by weak hydrogen bonds

6. DNA Double Helix “Rungs of ladder” Nitrogenous Base (A,T,G or C)
“Legs of ladder”
Phosphate &
Sugar Backbone

7. DNA Nucleotide O O=P-O N CH2 O C1 C4 C3 C2 Phosphate Group
Nitrogenous base
(A, G, C, or T)
CH2 O C1 C4 C3 C2 5
Sugar
(deoxyribose)

8. Pentose Sugar Sugars are numbered clockwise 1’ to 5’ CH2 O C1 C4 C3 C2
(deoxyribose)

9. Chargaff’s Rule Adenine must pair with Thymine
Guanine must pair with Cytosine
The bases form weak hydrogen bonds T A G C

10. Nitrogenous Bases Double ring PURINES Adenine (A) Guanine (G)
Single ring PYRIMIDINES
Thymine (T)
Cytosine (C)
A or G
T or C

11. DNA P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A

12. Antiparallel Strands One strand of DNA goes from 5’ to 3’ (sugars)
The other strand is opposite in direction going 3’ to 5’ (sugars)

13. Question: DNA 5’-CGTATG-3’
What would be the complementary DNA strand for the following DNA sequence?
DNA 5’-CGTATG-3’

14. Answer:
DNA 5’-GCGTATG-3’
DNA 3’-CGCATAC-5’

15. DNA and Genes

16. DNA DNA contains genes, sequences of nucleotide bases
These Genes code for polypeptides (proteins)
Proteins are used to build cells and do much of the work inside cells

17. Polypeptides
Amino acid chains are called polypeptides

18. DNA Begins the Process DNA is found inside the nucleus
Proteins, however, are made in the cytosol of cells by organelles called ribosomes
Ribosomes may be free in the cytosol or attached to the surface of rough ER

19. Starting with DNA
DNA ‘s code must be copied(transcription) and taken to the cytosol
In the cytosol, this code must be read(translation) so amino acids can be assembled to make polypeptides(proteins)
This process is called PROTEIN SYNTHESIS

20. RNA

21. RNA Differs from DNA RNA has a sugar ribose
DNA has a sugar deoxyribose

22. Other Differences RNA contains the base uracil (U) DNA has thymine (T)
RNA molecule is single-stranded
DNA is double-stranded
DNA

23. .
Types of RNA
Messenger RNA (mRNA) copies DNA’s code & carries the genetic information to the ribosomes
Transfer RNA (tRNA) transfers amino acids to the ribosomes where proteins are synthesized
Ribosomal RNA (rRNA)

24. Messenger RNA Long Straight chain of Nucleotides Made in the Nucleus
Copies DNA
Contains the Nitrogen Bases A, G, C, U ( no T )
Sequence of 3 bases called codon

25. Transfer RNA (tRNA) Clover-leaf shape
Single stranded molecule with attachment site at one end for an amino acid
Opposite end has three nucleotide bases called the anticodon

26. Codons and Anticodons
The 3 bases of an anticodon are complementary to the 3 bases of a codon
Example: Codon ACU
Anticodon UGA
UGA
ACU

27. The Genetic Code A codon designates an amino acid
An amino acid may have more than one codon
There are 20 amino acids, but 64 possible codons

28. The Genetic Code
Use the code by reading from the center to the outside
Example: AUG codes for Methionine

29. Transcription and Translation

30. Transcription
The process of copying the sequence of one strand of DNA, the template strand
mRNA copies the template strand
Requires the enzyme RNA Polymerase
Occurs in the nucleus

31. Template Strand

32. Question:
What would be the complementary RNA strand for the following DNA sequence?
DNA 5’-GCGTATG-3’

33. Answer:
DNA 5’-GCGTATG-3’
RNA 3’-CGCAUAC-5’

34. Translation
Translation is the process of of decoding the mRNA into a polypeptide chain
Ribosomes read mRNA three bases or 1 codon at a time and construct the proteins
Occurs in the cytoplasm

35. Transcription Translation
Transcription occurs when DNA acts as a template for mRNA synthesis. Translation occurs when the sequence of the mRNA codons determines the sequence of amino acids in a protein.
Translation