1. Chapter Eight: From DNA to Proteins

2. Section One: Identifying DNA as the Genetic Material
Discovery of DNA
Oswald Avery said DNA must be the genetic material of the cell
Alfred Hershey and Marsha Chase provided definitive proof through studies of bacteriophages
Bacteriophage: a virus that takes over a bacterium’s genetic machinery and directs it to make more virus

3. Section Two: Structure of DNA
DNA Structure
Made of four nucleotides
Nucleotides: small units that make up DNA
Each nucleotide has 3 parts
Phosphate group
A ring shaped sugar called deoxyribose
Nitrogen containing base

4. Section Two: Structure of DNA
Nucleotides
There are four types of nucleotides that only differ in what base they possess.
Pyrimidines
Cytosine
Thymine
Purines
Adenine
Guanine

5. Section Two: Structure of DNA
DNA Shape
Watson and Crick said DNA was shaped like a double helix
Double helix: two strands of DNA wind around each other like a twisted ladder
Rosalind Franklin used x-rays to visualize DNA

6. Section Two: Structure of DNA
DNA Structure
DNA nucleotides are joined together in the center of the helix by base pairing
Base Pairing Rules
Thymine pairs with adenine
Guanine pairs with cytosine
Sugars and phosphates form the back bone

7. Section Three: DNA Replication
The process by which DNA is copied during the cell cycle
Carried out by proteins
DNA polymerases: a protein that bonds nucleotides together during DNA replication

8. Section Three: DNA Replication
DNA Replication Steps
Enzymes unzip the DNA double helix at the origin of replication
Free floating nucleotides pair, one by one, with the bases on the template strand, which forms a new complementary strand

9. Section Three: DNA Replication

10. Section Three: DNA Replication
DNA Replication Stages
3. Two identical DNA molecules are created. Each molecule has one strand from the original molecule and one new strand. This is why DNA replication is semiconservative.

11. Section Three: DNA Replication
Fast and Accurate
Many origins of replication allow many replications to happen at once
DNA has a built in “proofreading” function so it can correct any copying errors

12. Section Four: Transcription
Central Dogma of DNA
DNA replication, then transcription, then translation
Information flows from DNA to RNA to proteins
RNA: a single stranded chain of nucleotides that are is used to make proteins

13. Section Four: Transcription
The process of copying a sequence of DNA to produce a complementary strand of RNA
A gene is translated into RNA
RNA polymerases: enzymes bond together nucleotides in a chain to make a new strand of RNA

14. Section Four: Transcription
Transcription Steps
1. RNA polymerase recognizes the transcription start site of the gene. A transcription complex assembles on the DNA strand and begins to unwind it.

15. Section Four: Transcription
Transcription Steps
2.RNA polymerase make a complementary strand of RNA using the unwound DNA. Uracil instead of thymine binds with adenine. The DNA helix zips back together when the copying is done.

16. Section Four: Transcription
Transcription Steps
3. Once the entire gene has been copied into RNA, the RNA strand detaches from the DNA.

17. Section Four: Transcription
Involves 3 major types of RNA
Messenger RNA (mRNA): an intermediate message that is translated to form protein
Ribosomal RNA (rRNA): forms part of the ribosome, a cell’s protein factory
Transfer RNA (tRNA): brings amino acids form the cytoplasm to a ribosome to help make a growing protein

18. Section Four: Transcription
Transcription vs. DNA Replication
Similar
Both involve unwinding DNA
Both involve complementary base pairing
Both are highly regulated by the cell
Different
Transcription produces RNA
Replication produces DNA
Replication makes sure each cell has one copy of DNA
Replication occurs only once during the cycle, transcription occurs hundreds or thousands of times

19. Section Five: Translation
The process that converts an mRNA message into a polypeptide
One or more polypeptides make up proteins
The mRNA message is written using one of four nucleotides of RNA (cytosine, guanine, adenine, and uracil)
The polypeptides or proteins are made of amino acids
There are 20 amino acids

20. Section Five: Translation
Amino acids are recognized by there codons
Codon: a sequence of 3 nucleotides that code for an amino acid
Many amino acids are coded for by more than one codon

21. Section Five: Translation

22. Section Five: Translation
There are also stop and start codons that signal the end and the beginning of translation
Stop Codons: signal the end of the amino acid chain
UAA, UGA, UAG
Start Codons: signals the start of translation and the amino acid methionine
AUG

23. Section Five: Translation
For the mRNA code to be translated correctly, the codons must be read the correct way
The order in which they are read is called a reading frame
3 amino acids= 1 codon
There are no spaces between codons

24. Section Five: Translation
Translation Steps
Occurs in the ribosome
tRNA has an anticodon that matches the codon that allows it to pick up the correct amino acids
Anticodon: a set of 3 nucleotides that is complementary to an mRNA codon
For example: If the codon was CCC, the anticodon would be GGG

25. Section Five: Translation
Translation Steps
1. The exposed codon of the mRNA in the ribosome attracts a tRNA with the correct anticodon and amino acid.

26. Section Five: Translation
Translation Steps
2. The ribosome helps create a peptide bond between the two amino acids (the starting amino acid and the new one just added
3. The ribosome breaks the bond between the tRNA and the amino acid

27. Section Five: Translation
Translation Steps
4. The ribosome pulls the mRNA strand down one codon so that the tRNA is moved into the exit site and leaves the ribosome.
5. The first site is empty again so that a new amino acid can be added.

28. Section Six: Gene Expression and Regulation
Regulation of Gene Expression in Prokaryotes
Promoter: a DNA segment that allows a gene to start transcription
Operon: a region of DNA that includes the promoter, an operator, and one or more structural genes that code for a specific protein
Usually found only in prokaryotes or worms

29. Section Six: Gene Expression and Regulation
Regulation of Gene Expression in Eukaryotes
Transcription factors and regulatory DNA sequences help start transcription
RNA processing, the part that occurs after transcription, includes cutting out introns and putting together exons
Introns: nucleotide segments that occur between exons and do not code for proteins
Exons: nucleotide segments that code for part of a protein

30. Section Six: Gene Expression and Regulation

31. Section Seven: Mutations
A change in an organism’s DNA sequence
Mutations can be good or bad
Types of gene mutations
Point mutation: a mutation in which one nucleotide is substituted for another
Frameshift mutation: the insertion or deletion of a nucleotide to the DNA that changes the reading frame

32. Section Seven: Mutations

33. Section Seven: Mutations
Chromosomal Mutations
When chromosomes do not correctly align with each other during crossing over, the segments that result may be of a different size.
This could cause one chromosome to not have a particular gene and one chromosome to have two copies of one gene

34. Section Seven: Mutations
Chromosomal Mutations
Translocation: a mutation in which a piece of one chromosome moves to a non-homologous chromosome

35. Section Seven: Mutations
Mutations and Phenotype
Mutations may or may not affect phenotype
Chromosomal mutations have a large effect on genes and could cause a gene to no longer work or create a new hybrid gene with a new function
Gene mutations may effect enzyme functions, protein folding (which could inactivate a protein), or code for a premature stop codon

36. Section Seven: Mutations
Mutations and Offspring
Mutations in sex cells can affect offspring
They are the underlying source of genetic variation
Some can cause offspring to develop improperly or die before birth

37. Section Seven: Mutations
What causes mutations?
Replication errors
Mutagens: agents in the environment that can change DNA
Ex: UV rays, some industrial chemicals, cigarette smoke