1. Nucleic Acids and Protein Synthesis
Chapter 7

2. DNA
7-1

3. The Genetic Code
What is the structure that carries genetic information?
Scientists wondered this for years, and through many experiments, they figured out exactly what it was.

4. Griffith and Transformation
Frederick Griffith wanted to know how bacteria made people sick.
He isolated 2 separate strains of pneumonia bacteria from mice.
Only 1 of these caused pneumonia
The disease-causing strain of bacteria grew into smooth colonies (S-bacteria)
The harmless strain produced colonies with rough edges (R-bacteria)

5. The Experiment
Griffith injected mice with S-bacteria.
Mice died from pneumonia
Mice injected with R-bacteria
Mice never got sick
Heat-killed S-bacteria and then injected it into mice
Mice survived.
Mixed heat-killed S-bacteria with R-bacteria and injected them into mice.
Mice got sick and died.

6. The dead bacteria somehow passed on its disease-causing ability to the harmless bacteria.
Transformation: The process by which one strain of bacteria is changed by a gene or genes from another strain of bacteria.

7. Avery and DNA
Decided to repeat Griffith’s experiments, but also wanted to figure out which part of the bacteria was responsible for the transformation.
They had it down to being a protein, carbohydrate, or DNA.
Made a juice from heat-killed S-bacteria.
In different experiments, they introduced enzymes that destroyed proteins, carbohydrates, and DNA.
When the proteins and carbohydrates were destroyed, transformation occurred.
When DNA was destroyed, transformation did not occur
DNA is the structure that passes on genetic information.

8. Hershey-Chase Experiment
Scientists still doubted that DNA contained the genetic info. It was too simple.
They thought it was protein.
Hershey and Chase worked with viruses, specifically bacteriophages.
Bacteriophage: A virus that infects bacteria
A bacteriophage is made of only 2 things: DNA and Protein

9. To figure out which component was passed on, they tagged the viruses with phosphorus-32 and sulfur-35.
Proteins don’t contain phosphorus
DNA doesn’t contain sulfur.
If P32 was found in the bacteria, it’s the DNA that is transferred. If S35, it’s the protein.
Results: P32 was found in the bacteria.
DNA is definitely the genetic material.

10. The Structure of DNA What is the basic unit of a nucleic acid?
A nucleotide.
Made of 3 parts:
5-carbon sugar (deoxyribose)-Side of ladder
Phosphate Group- Side of ladder
Nitrogenous Base
There are 4 bases
Adenine (A), Cytosine (C), Guanine (G), Thymine (T)
These are placed into 2 groups:
Purines: 2 rings in the structure.
Adenine, Guanine
Pyrimidines: 1 ring in structure
Cytosine, Thymine

11. Chargaff’s Rules
Discovered that in DNA samples, percentages of guanine and cytosine are almost equal to one another. Adenine and Thymine percentages were also similar.
[A]=[T], [C]=[G]

12. X-Ray Diffraction
Rosalind Franklin used x-ray diffraction to get a general shape of the DNA molecule.
Aimed a powerful x-ray beam at concentrated DNA samples.
Results:
DNA is spring-shaped (helix)
Since it looked like an x, there are 2 helices (Double Helix)
Nitrogenous bases are in the middle

13. Making the Model
Watson and Crick used Chargaff’s rules and Franklin’s images to create a 3-D model.
It resembled a spiral staircase with nitrogenous bases in the middle.
Base-Pairing: Adenine goes with Thymine, Guanine goes with Cytosine.
Held together with hydrogen bonds
2 bonds between A and T
3 bonds between G and C

14. DNA and Chromosomes DNA length
The DNA in a single human cell measures out to between 1-2 meters.
The total length of all the DNA in a human is 2.0 x 1013 meters.
That’s 20,000,000,000,000 meters
At that distance, you would be able to travel to the sun and back almost 70 times.
Distance from Earth to the Sun = 93,000,000 miles.

15. Chromosome Structure Chromosomes are made of both DNA and proteins.
Chromatin: Consists of DNA tightly wound around proteins.
Histones: The proteins
When the DNA and several histones are wound together, a nucleosome is created.
Nucleosomes wind together to create chromosomes.

16. DNA Replication
Each strand of DNA can be used as a template to create another strand.
The strands are complimentary.
If you only had one strand, you could figure out the base sequence to the other side.
Practice: Construct the complimentary strand to the following base sequence:
ACCGATATGCAAT

17. In prokaryotes, DNA replication begins as a single point and then moves in both directions until replication is complete.
In Eukaryotes, replication occurs in hundreds of places on a single strand.

18. Replication Fork: The sites where separation and replication occur.
Duplicating DNA
Replication: The process of copying DNA

19. During DNA replication, the DNA molecule separates into 2 strands, and then produces 2 new complimentary strands following the rules of base pairing. Each strand of the double helix of DNA serves as a template, or model, for the new strand.

20. How DNA Replication occurs
DNA Helicase (an enzyme) “unzips” the DNA molecule.
Done by breaking the hydrogen bonds between the nitrogenous bases.
DNA Polymerase joins individual nucleotides to produce a DNA molecule.
Also, it proofreads each DNA strand to eliminate mistakes.
DNA Ligase binds the DNA strand back together.

21. RNA and Protein Synthesis
7-2, 7-3

22. Protein Synthesis is divided into 2 stages.
Gene: Coded DNA instructions that control the production of proteins within the cell.
Well how are proteins made from the genes?
Protein Synthesis is divided into 2 stages.
Transcription
Translation
The first step (transcription) is to copy part of the nucleotide sequence from DNA into RNA, which then makes the proteins
RNA= ribonucleic acid
The assembly of amino acids into proteins is controlled by RNA

23. The Structure of RNA Very similar to DNA structure, but 3 differences.
The sugar is Ribose
RNA is usually single-stranded
Instead of having Thymine, it has Uracil

24. Types of RNA
3 main types
mRNA
rRNA
tRNA

25. mRNA= messenger RNA Copies the instructions from genes in DNA.
Serves as the messenger from the DNA to the rest of the cell.

26. rRNA= ribosomal RNA Proteins are synthesized/assembled by ribosomes
Ribosomes are made of rRNA and other proteins.

27. tRNA= transfer RNA
Transfers amino acids to the ribosome to be assembled into proteins.

28. Transcription
Transcription: Process of copying part of the nucleotide sequence of DNA into a complimentary sequence of RNA.
Occurs in the nucleus.
Works very similarly to DNA replication.
RNA Polymerase works a lot like DNA Polymerase
RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses 1 strand of DNA as a template from which nucleotides are assembled into strands of RNA.

30. How does the RNA polymerase know where to start and stop copying?
RNA polymerase doesn’t bind to DNA just anywhere.
The enzyme only binds to a region called a promoter, which has a specific sequence or “start codon.”
Promoters: Signals in DNA that indicate to the enzyme where to bind to make RNA.
Similar signals in DNA cause transcription to stop.

31. RNA Editing
When RNA is made from DNA, there is a lot of editing that needs to be done.
RNA Polymerase incorrectly copies 1:10,000 nucleotides.
DNA contains sequences of nucleotide that do not code for proteins. (Introns)
The DNA sequences that do code for proteins are called Exons.
These are expressed in protein synthesis.
When the RNA is being created from DNA, both introns and exons are copied.
Introns must be cut out and then the exons are spliced together.
The information that is left from the exons can then be translated into a protein.

32. The Genetic Code
The properties/characteristics of proteins are determined by the order in which amino acids are joined together to make a polypeptide
Polypeptide= A long chain of amino acids.
The genetic code is read 3 letters at a time
Each 3-letter word is called a codon
Codon: consists of 3 consecutive nucleotides that specify a single amino acid.
64 possible codons.
1 start codon
3 stop codons

33. What is the start codon? Stop codons?
Crack the code:
UCGCACGGU

34. Translation
Translation: Process of decoding an mRNA message into a protein
Takes place on ribosomes

35. Step 1: messenger RNA
After transcription, mRNA leaves the nucleus and enters the cytoplasm.

36. Step 2: mRNA attaches to a ribosome.
mRNA moves through the ribosome’s AP site, the codon sequence is read, and tRNA brings in the matching amino acid, which is added to the polypeptide.

37. tRNA Each tRNA molecule carries only 1 kind of amino acid
Each tRNA has 3 unpaired bases, which are complimentary to an mRNA codon= anticodon

38. Step 3
Peptide bonds are formed between the amino acids in the AP site.
The ribosome moves on to the next codon, the first tRNA exits the ribosome, and the bond between the amino acid and the tRNA is broken.
A new tRNA enters the empty A site.

40. Step 4 Polypeptide chain grows until a stop codon is reached.
When this happens, translation ends and the polypeptide folds into a new, useable protein.

41. Summary DNA contains a code for the creation of proteins.
This happens through a series of steps.
DNA needs to be transcribed into a readable code
Transcribe: To write out in another language.
The newly transcribed code then needs to be translated, or interpreted, so a protein can be made.

43. Protein Synthesis Overview
Crash Course
The Hippies

44. Genetic Mutations

45. Genetic Mutations

46. Intro.
Cells sometimes make mistakes when they are copying their own DNA.
Mutation: An accidental change in the genetic material.
2 main categories for mutations:
Gene Mutations: Produce changes in a single gene.
Chromosomal Mutations: Produce changes in whole chromosomes.

47. Gene Mutations
Point Mutation: Involves changes in one or a few nucleotides.
Occur at a single point in the DNA sequence.
Types: Substitutions, Insertions, and deletions.

48. Substitutions are not that bad for the protein.
Ex: ATT CGT ACA GAT  ATT CGT ACC GAT
Insertions and deletions can ruin the protein by causing the entire sequence to shift, changing all of the amino acids.
Frameshift Mutation
Ex: ATT CGT ACT GAT  ATT CTA CTG AT (Deletion)
 ATT CGG TAC TGA T (Insertion)

49. Chromosomal Mutations

50. Significance of Mutations
Most mutations have no real affect on an organism.
When protein structure is altered, most of the time it is harmful
Cancer, fatality
Sometimes these are beneficial and lead to genetic variation and evolution.