1. Chapter 13
DNA, RNA and Proteins

2. DNA Pre-class question 4/27
If you were to take a chromosome, decompress it into chromatin, separate the nucleosomes and remove the histones, what would you have?
DNA
Homework – Due Tuesday (4/28)
Active Reading: The Structure of DNA

3. DNA is Genetic Material Found in Cells 3 Major Experiments
1. Griffith’s Discovery of Transformation
2 Bacteria Types
Rough (R), no capsule, broken down by the body’s immune system, does not cause pneumonia
Smooth (S), capsule, protected from the body’s immune system, causes pneumonia

4. Griffith’s Experiment Conclusions
Heat destroyed the capsule, but not the S bacteria.
S bacteria has the genetic code for making the capsule.
The genes of the S bacteria were taken up by the R bacteria, which then began to make the protective capsule.
The genetic code of the R bacteria had been transformed.

5. DNA, RNA or Protein? 2. Avery’s Experiment
Avery wanted to know what substance, DNA, RNA or protein, was causing the transformation in Griffith’s experiment.
When Avery treated the S heat killed bacteria with enzymes to destroy both RNA and protein, transformation still occurred.
When Avery treated the S heat killed bacteria with enzymes to destroy the DNA, transformation did not occur.

6. The Genetic Material in Viruses
2. Hershey Chase Experiment
Hershey and Chase worked with bacteriophages (viruses that infect bacteria, which in turn produce more viruses). Bacteriophages are made of DNA and protein. The scientists wanted to know which substance the genetic material in the bacteriophage was made of.

7. 3 Phases
Step 1
Proteins Contain Sulfur and DNA contain phosphorus. Two virus samples were incubated with either radioactive sulfur or radioactive phosphorus.
Step 2
The virus samples were then allowed to infect bacteria. Each mixture was then separated into two portions, one containing bacteria and the other containing only viruses.

8. Conclusion
Step 3
The infected bacteria contained radioactive phosphorus, but did not contain radioactive sulfur.
Because the Bacteria contained radioactive phosphorus, and phosphorus is a component of DNA, Hershey and Chase conclude that DNA was the genetic material in viruses.

9. Pre-Class Question 4/28
In the Hershey-Chase experiment, where DNA was found to be the component of bacteriophages responsible for “infecting” bacteria, what radioactive substance was found in the bacteria?

10. The Double Helix of DNA
Each strand of DNA is made of subunits called nucleotides
Each nucleotide is made of 3 parts:
A phosphate group
A 5 carbon sugar molecule
(Deoxyribose)
A nitrogen containing base

11. The Information in DNA Nitrogen Bases Purines
Adenine (A) and Guanine (G)
Pyrimidines
Cytosine (C) and Thymine (T)
On opposite strands, A always
pairs up with T and C always
pairs up with G. Base pairs
are held together with hydrogen
bonds. The strands are said to be
complimentary.

12. Discovering DNA’s Structure
Chargaff’s Observation
In every organism, the amount of thymine always equals the amount of adenine. Likewise the amount of cytosine always equals the amount of guanine.
Photographs of DNA
Rosalind Franklin and Maurice Wilkins
developed x-ray diffraction images of
strands of DNA.

13. Discovering DNA’s Structure, Cont.
Watson and Crick’s Model of DNA
By combining Chargaff’s observation and the photographs taken by Franklin and Wilkins, Watson and Crick created a 3-dimensional double helix model of DNA which won them the Nobel Peace Prize in 1962.

14. Replication of DNA
In DNA replication, the DNA molecule unwinds, and the two sides split. Then new nucleotide sequences are added to each side until two identical sequences result.
DNA replication occurs before cell division so that each new daughter cell has a complete copy of the parent DNA.

15. 3 Steps of DNA Replication
DNA helicases break the hydrogen bonds between base pairs and unwind the helix. As the strands separate, replication forks form
Step 1 – Unwinding and Strand Separation
Step 2 – Adding Complementary Bases
DNA polymerase forms the new DNA molecule by traveling along each single strand and adding complementary nucleotides.
Step 3 – Formation of Two Identical DNA Molecules
Two identical DNA molecules are produced, each consisting of one new strand

16. Prokaryotic and Eukaryotic Replication
Prokaryotic Replication
Eukaryotic Replication
Prokaryotes have circular DNA
Replication occurs at one site, producing 2 replication forks and proceeds in opposite directions
Eukaryotes have linear DNA
Replication occurs at many sites, producing 2 replication forks and proceeds in opposite directions.

17. Eukaryotic Replication
Because replication occurs at more than one site on the DNA, eukaryotic DNA can be replicated at a faster rate than prokaryotic DNA. An entire human chromosome can be replicated in about 8 hours.

18. Gene Expression and RNA
Stage I – Transcription
Takes place in the nucleus
RNA is made from DNA
Stage II – Translation
Takes place in the cytoplasm on ribosomes
Uses RNA to make proteins

19. How is RNA different from DNA?
RNA is single stranded
An RNA nucleotide contains ribose sugar, not deoxyribose.
RNA contains the nitrogenous base, Uracil, but does not contain Thymine.

20. 3 Types of RNA Messenger RNA (mRNA) Transfer RNA (tRNA)
DNA is transcribed into messenger RNA. Messenger RNA transports the genetic code to ribosomes for translation.
Transfer RNA (tRNA)
Transfer RNA reads the mRNA sequence and translates it into amino acids which are used to make proteins.
Ribosomal RNA (rRNA)
Ribosomes are comprised of ribosomal RNA and proteins/

21. Transcription (3 Steps)
Step 1 – RNA polymerase binds to a “promoter” gene or “start” location on the DNA.
Step 2 – RNA polymerase unwinds the DNA
Step 3 – RNA polymerase moves along the DNA adding complementary RNA bases (A-U, T-A, C-G, G-C)
As RNA base pairs are added, the DNA strands close up and reform the double helix. Eventually the polymerase reaches a stop signal in the DNA.

22. Transcription vs. Replication
In both processes, DNA is used as a template. However, transcription results in the formation of mRNA whereas replication results in the formation of DNA. During replication, both DNA strands are involved while only one DNA strand is involved in transcription.

23. Nitrogenous base (A,T,C,G,U)
Pre-class Question 5/11
Which part of a nucleotide contains genetic information?
Nitrogenous base (A,T,C,G,U)
Homework
Chapter 13 Vocab Quiz Wednesday
Chapter 13 Test Friday

24. The Genetic Code: Three-Letter Words
Each 3-nucleotide sequence is called a codon
Each codon contains the code to make 1 of 20 amino acids (building blocks of proteins).

26. Translation: RNA to Proteins
Step 1-Binding of tRNA to mRNA
The anti-codon of tRNA binds to the mRNA start codon at the ribosome. Each tRNA carries one amino acid. The amino acid carried by this tRNA is methionine.

27. Translation continued
Step 2 – Formation of peptide bonds
A second tRNA anti-codon binds to the next sequence of mRNA. As a peptide bond is formed between the two adjacent amino acids, the first tRNA is released from the ribosome.

28. Translation Continued
Step 3 –
The ribosome moves one codon down the mRNA. The mRNA and the tRNA move as a unit.
Step –
The process of translating mRNA into an amino acid chain continues until stop codon is reaced

29. The Final Step of Translation
The newly made polypeptide falls off the ribosome, the ribosome complex falls apart and the ribosome is then free to begin translation again with the same mRNA molecule or with a different transcript.