1. DNA and RNA
Honors Biology

2. The Discovery of the Gene
1928: Frederick Griffith
experiments on bacteria that caused pneumonia
He isolated 2 strains of bacteria (one harmful, one harmless)

3. His Experiments
Hypothesis: bacteria produced a toxin that caused the disease

4. Results
Griffith hypothesized that the “heat killed” bacteria passed “something” to the harmless strain
He called this process transformation
The offspring of the transformed bacteria passed the ability on to their offspring
The “something” is a gene

5. How could Avery’s goal be tested?
Next: Oswald Avery
He repeated Griffith’s experiment in 1944
His goal was to determine what molecule was involved in the transformation
How could Avery’s goal be tested?

6. He used various enzymes to destroy different molecules within the bacteria
He discovered that DNA contains the information that is passed from one generation to the next

7. Alfred Hershey and Martha Chase
Worked with Bacteriophages
“bacteria eaters”
Viruses that infect bacteria
Consist of a DNA or RNA core surrounded by a protein coat

8. They determined that it was the DNA that entered the bacteria
Hershey and Chase conducted an experiment to discover what part of the virus entered the bacteria
They grew viruses in cultures containing radioactive isotopes: phosphorus-32 and sulfur-35
This way they could trace the DNA (32P) and the protein coat (35S)
They determined that it was the DNA that entered the bacteria

10. The Viruses attach to bacteria and inject the genetic information
The viral genes then take over the bacteria and begin to produce new virus “parts”
The bacteria then splits open and hundreds of new viruses emerge to attach more cells

11. What is DNA made of? DNA is a polymer of subunits called nucleotides
3 parts of a nucleotide
5-C sugar = Deoxyribose
Phosphate group
Nitrogenous base

12. Nitrogenous Bases Purines: contain 2 carbon rings
Adenine
Guanine
Pyrimidines: contain 1 carbon ring
Thymine
Cytosine

13. What does DNA look like?
1950, Erwin Chargaff discovered that the percentages of Guanine and Cytosine were almost equal in any sample of DNA
The same was true for Adenine and Thymine
Chargaff’s rules
He had no clue why

14. Maurice Wilkins and Rosalind Franklin
In 1952, both scientists were working independently with X- ray Diffraction

16. James Watson and Francis Crick
Built a 3-D model of DNA
In 1953, using the work of Franklin and Wilkins they determined that DNA was a double helix

18. DNA Replication The structure of DNA makes it very simple to replicate
In eukaryotic chromosomes replication takes place in hundreds of places along the DNA in both directions= replication forks

19. Steps of Replication
Step 1: DNA is “unzipped” by the enzyme helicase which breaks the Hydrogen bonds in several locations called replication “bubbles”

20. Step 2: DNA polymerase then attaches to the old strands and “plugs” in the appropriate base pairs
Adds nucleotides from the 3’ to the 5’ end of the template strand
One daughter stand gets copied in one continuous piece (leading strand)
The other gets copied in fragments called Okazaki fragments (lagging strand)
These are later linked together by DNA Ligase

22. Step 3: another type of DNA polymerase then “proofreads” and corrects any mistakes
Error= 1 out of every billion pairs
Video

23. Telomeres: segments of non- coding DNA found at the ends of the strands
Prevents DNA from being lost or damaged
Telomerase is responsible for copying these segments
Often turned “off” in adults

24. Prokaryotes verse Eukaryotes
Replication in most prokaryotes starts from a single point and proceeds in 2 directions until the entire circular chromosome is copied

26. RNA Polymer made up of subunits called nucleotides
Nucleotide consists of:
5-C sugar ribose
phosphate group
nitrogenous base (Adenine, Cytosine, Guanine, Uracil)

27. How is rna different from dna?
Single stranded
Contains ribose instead of deoxyribose
Contains Uracil instead of Thymine

28. Types of Rna Messenger RNA (mRNA) Single stranded helix
Function: copies the “recipe” from the DNA so that proteins can be made

29. Transfer RNA (tRNA) Single stranded “hair pin” shaped
Function: “transfers” amino acids to the ribosomes during protein production

30. Ribosomal RNA (rRNA) Single stranded globular
Function: makes up ribosomes

31. Protein synthesis Transcription
Process by which mRNA “copies” the recipe from DNA
Takes place in the nucleus
RNA polymerase is responsible for creating the mRNA

32. RNA polymerase binds to the promoter
Specific sequence of nucleotides that marks the beginning of the recipe
It then plugs in the complimentary base pairs until the end sequence is reached.

33. Introns are non-coding sequences of DNA that are not part of the “recipe” and must be cut out
Exons are the coding sequences of DNA that are “expressed”

34. RNA processing

35. The Genetic code Proteins are made of 20 different amino acids
What make one protein different from another?
mRNA contains codons which “code” for a specific amino acid
A codon consist of 3 nucleotides
A codon chart is used to decipher the language of DNA

37. Translation
Process by which the tRNA “translates” the genetic code by delivering amino acids to the ribosome
Takes place on the ribosome

38. mRNA attaches to the P site of the small subunit of the ribsome How?
The tRNA have anticodons that pair up with the codons of the mRNA
AUG is the start codon that marks the beginning of the “recipe”
This allows the large subunit to attach making the ribosome functional

39. Another tRNA comes and attaches to the next codon at the A site
A peptide bond forms between the 2 amino acids
Then mRNA shifts over
The original tRNA is now free to leave the E site
This elongation process continues until a stop codon is reached
Video

41. How do cells determine which genes to express?
Example: E. coli (bacteria)
Operon: group of genes that work together
In E. coli there is a lac operon which must be expressed (turned on) in order for them to use lactose as food
When lactose is available the lac operon is “turned on” but when it is not available it is “turned off”

42. It is turned on by the presence of lactose
How do you turn it off?
The lac operon is turned off by repressors proteins which attach to the operator
Operator: sequence of nucleotides in front of the lac operon
How do you turn it on?
It is turned on by the presence of lactose
Lactose binds to the repressors which causes them to change shape and disconnect
This leaves room for RNA polymerase to attach and begin protein synthesis

43. Eukaryotic gene regulation
Do not have operons, instead genes are controlled individually
Instead they have a TATA box
sequence of about 30 nucleotides TATATA or TATAAA
The TATA box binds a protein that helps RNA polymerase attach to the promoter

44. Various DNA binding proteins called transcription factors attach to the TATA box to either turn the gene “on” or “off”(repressors)
Enhancer sequences help by looping DNA to bring transcription factors together

45. Transcription factors regulate gene expression in many ways
Attract RNA polymerase (on)
Block RNA polymerase (off)
Uncoil areas of DNA so that are accessible (on)
Bozeman

46. Eukaryotic gene regulation is much more complex than prokaryotic
Why? Multicellular with different genes being expressed in different types of cells

47. Genes can also be regulated by
controlling mRNA leaving the nucleus
Manipulating the stability of RNA
Breaking down proteins

48. RNA Interference (RNAI)
Small segments of RNA (small interfering RNA siRNA) that are cut into sections called microRNA (miRNA) by Dicer Enzymes
These miRNA destroy RNA with complementary sequence
Page 380
Video

49. Differentiation: During embryonic development cells become specialized
Controlled by master control genes called homeotic genes
Homeobox genes code for transcription factors that activate other genes (ie. Hox genes)
Mutations in these hox genes can cause mutations such as legs to grow on fruit flies where antennae should be

50. Differentiation also controlled by environment Ex: Metamorphosis
Can be sped up by cues such as drying pond, food availability, temperature, population size