1. Chapter 12: DNA- The Molecule of Heredity

2. DNA determines the structure of proteins
All living things contain proteins
Provide complete instructions for making proteins
Made up of nucleotides

3. History of DNA Griffith (1928)
Tried to figure out how bacteria causes pneumonia
Experiment:
1st: injected mice with disease-causing bacteria (all died) and again with harmless bacteria (no sickness)
He heated the disease-causing bacteria to kill them and injected it into mice (mice lived)
2nd: mixed heat-killed bacteria with live, harmless bacteria and injected into mice (all died)

5. Conclusion: transformation  1 strain changed into another
Genes control changes to organisms

6. History of DNA Avery (1944) Repeated Griffith’s work
Experiment: Made an extract from heat-killed bacteria and treated it with enzymes (destroyed organic compounds)
Transformation still occurred
Repeated using enzymes to break down DNA
Transformation did not occur
Conclusion: DNA stores and transmits genetic info

7. Hershey and Chase (1952)
Did experiments using radioactive viruses to infect bacteria (bacteriophages)
Used radioactive markers to determine what actually entered a bacterial cell
Conclusion: Discovered DNA was the genetic material of all living things

8. Franklin and Wilkins (1950’s)
Experiment: Used X-ray diffraction on DNA
Conclusion: strands in DNA are twisted around each other (helix)

9. Watson and Crick (1953) No experiment
Conclusion: Discovered the structure of DNA
Made up of 2 chains of nucleotides held together by nitrogen bases
Double helix (twisted ladder)

10. Chapter 12 Scientist Review:
Match the scientist with the description of his or their conclusions:
Griffith Avery Hershey &Chase
_____ concluded that the genetic material of a bacteriophage is DNA
_____ concluded that DNA was the factor that caused one bacterium to transform into another
_____ concluded that bacteria could be transformed from harmless to disease-causing by an unknown factor

11. DNA in Cells Located in the nucleus of cells as chromosomes
Packed tightly
Consists of more than 30 million base pairs
Complimentary DNA strands
Can use 1 strand to make a copy of the other strand using base pairing

12. Nucleotides Make up DNA 3 parts to a nucleotide:
A simple sugar called Deoxyribose
A phosphate group
A nitrogen base

13. Nitrogen Bases 4 possible nitrogen bases: Adenine (A) Guanine (G)
Cytosine (C)
Thymine (T)

14. Adenine (A) and Guanine (G)
Double-ringed nitrogen bases
Called purines

15. Thymine (T) and Cytosine (C)
Single-ringed nitrogen bases
Called pyrimidines

16. Chargaff % of Guanine and Cytosine are equal
% of Adenine and Thymine are equal

17. Nucleotides join together to form long chains of complimentary base pairs
Adenine always pairs with Thymine (A-T or T-A)
Guanine always pairs with Cytosine (G-C or C-G)

18. Structure of DNA
Nitrogen bases of the nucleotides hold 2 strands of DNA together with weak hydrogen bonds
Twisted DNA  double helix

19. Sides of the ladder:
alternating phosphate groups and sugar molecules
Rungs of the ladder:
pairs of nitrogen bases
joined by weak hydrogen bonds

20. DNA Replication Making a copy of DNA
DNA is copied before cell division
Takes 6 hours in humans
During the S phase of interphase
DNA will separate into 2 strands
Carried out by the enzyme DNA polymerase
Unzips DNA by breaking hydrogen bonds to unwind the double helix
Each strand acts as a template or model to make new DNA strands
Makes new complimentary strands through base-pairing

21. Example:
TACGTT – Old DNA strand
ATGCAA – New DNA strand
After DNA is replicated, DNA will have 1 old strand and 1 new strand

23. Chapter 12 Bell Ringer #1:
The structure of a DNA molecule can be described as a _____.
During DNA replication, the DNA molecule ______ into two strands.
DNA looks like a twisted ladder. Which parts of a twisted ladder represent the hydrogen bonds and the sugar-phosphate backbones?

24. The Genetic Code DNA controls protein synthesis
Proteins have chains of amino acids
A code is needed to convert messenger RNA (mRNA) into a protein
20 amino acids
Codon: a group of 3 Nitrogen bases that code for a specific amino acid
64 possible combinations of codons
Some code for amino acids
Some code for making proteins
More than 1 codon can code for the same amino acid

25. There is 1 start codon (amino acid methionine)
DNA  TAC
RNA  AUG
There are 3 stop codons
Code for no amino acids

27. The sequence of nucleotides (N-bases) is the code for what controls the production of all proteins

28. Transcription Occurs in the nucleus
Making an RNA copy of a part of DNA
Makes messenger RNA (mRNA)
Requires RNA polymerase
Binds to and separates DNA
Strands of DNA used as a template
Binds to DNA regions called promoters

29. 4 Steps:
RNA polymerase unzips the DNA
Free RNA nucleotides floating in the cytoplasm base pair with nucleotides on DNA strand (makes mRNA)
mRNA strand breaks away and DNA strands go back together
mRNA leaves nucleus and goes out to the cytoplasm
Result of transcription: formation of 1 single-stranded RNA molecule

31. Example: DNA mRNA A G C T

32. Example: DNA mRNA
Name of amino acid: A G C T U C G A

33. Two Types of Nucleic Acids: RNA and DNA

34. In nucleus and cytoplasm
DNA
RNA
(3 types)
Sugar
Deoxyribose
Ribose
Bases
G, C, A, T
G, C, A, U (uracil)
Structure
Double-stranded
Single-stranded
Location in a Cell
Only in the nucleus
In nucleus and cytoplasm
Base Pairing
C-G and A-T
C-G and A-U

35. Messenger RNA (mRNA)
Brings instructions from DNA out of the nucleus and into the cytoplasm
Moves toward the ribosomes

36. Ribosomal RNA (rRNA) Makes up ribosomes Binds to messenger RNA
Uses the instructions from DNA to put amino acids in the correct order

37. Transfer RNA (tRNA)
Delivers the amino acids to the ribosomes to be made into a protein

38. RNA Editing DNA has introns (sequences of nucleotides)
Edited out before they become functional
Not involved in coding for proteins
Exons: code for proteins
Remaining pieces of DNA  put together with cap and tail = final RNA molecule

39. DNA Controls Protein Synthesis
What are proteins?
Long chains of amino acids (polypeptides)
Key structures and regulators of cell functions
Help with structural parts
Enzymes  chemical reactions
Help in transport through cell membrane

40. Making Proteins Protein production is similar to building car
DNA provides workers with instructions for making proteins
Workers build proteins (RNA)
Other workers bring parts (amino acids) to the assembly line

41. Translation Process of building proteins from mRNA
Takes place in the ribosomes
Transfer RNA (tRNA) brings amino acids to the ribosomes
Attaches to only 1 type of amino acid
Amino acid will become bonded to 1 side of the tRNA
The other side of the tRNA has 3 nitrogen bases called an anticodon
Pairs up with mRNA codon

42. Amino acids are joined by peptide bonds
Anticodon bind to the codon of mRNA through base pairing
Example: Codon: CGA
Anticodon: GCU
A chain of amino acids form until a stop codon is reached
Translation will end
Amino acid strand is released from the ribosome to become proteins

44. Chapter 12 Bell Ringer #2:
The 3 main types of RNA are ___, ___, & ___.
2. Copying part of a nucleotide sequence of DNA into a complementary sequence in RNA is called ____.
3. During the process of _____, the information carried by mRNA is used to produce proteins.
4. Each tRNA molecule contains 3 unpaired bases, called the _____, which ensure that amino acids are added in the correct sequence.

45. Mutations Any change in the sequence of DNA
Can be caused by errors in:
DNA replication
Transcription
Cell division
External agents

46. Mutations in Reproductive Cells: Birth Defects
Within the egg or sperm cells
Can produce new traits
Can result in proteins that do not work (can kill organism)
Could have positive effects
Faster
Stronger
Important in the evolution of a species

47. Mutations in Body Cells
Not passed on to offspring
May impair cell function
Can affect genes that control cell division (cancer)

48. Point Mutation (substitution)
Change in 1 N-base in DNA
Example: CGATTACGC (normal DNA) CGATTTCGC
(mutated DNA)
Albinism
Inability to produce pigments
Lethal to plants

49. Frameshift Mutation 1 N-base is added or deleted
Changes all codons from that point on
Example: CGATTACGC CGAATTACGC (N-base added)
Example: CGATTACGC CGTTACGC (N-base deleted)
May cause no problems or can be severe
More dangerous than point mutations

50. Chromosomal Mutations
Involve many genes
Usually very bad
Can change location of genes or number of copies
Involve changes in number or structure of chromosomes

51. 4 types:
Deletions  taking away
Insertions  adding
Inversions  switching parts (ex: ab ba)
Translocations  breaking off
Many occur from improper separation during meiosis

52. Causes of Mutations Source of genetic variation
Spontaneous or random mutations
Mutagens (things that cause mutations)
Radiation, X-Rays, UV light, chemicals
Carcinogens
Source of genetic variation

53. Gene Regulation
Certain DNA sequences serve as promoters (binding sites for RNA polymerase)
Ex: E. coli
Group of 3 genes that are turned on and off together (called an operon)
E. coli uses lactose as food
Genes must be expressed  called lac operon

54. Lac genes turned off by repressors (binds to operator)
Prevents transcription of its genes
Lac genes turned on by presence of lactose
Binds to repressor, allowing RNA polymerase to transcribe genes
Operons generally not found in eukaryotic cells

55. Eukaryotic cells (more complex)
Has short region of DNA (TATA box)
30 base pairs long
Helps RNA polymerase position itself
Hox genes
Series of genes that controls organs and tissues that develop in embryos
Determine basic body plan
Mutations can change organs
Ex: fruit fly
Expressed genes are transcribed into RNA
Genes are expressed with help from DNA-binding proteins

56. Chapter 12 Bell Ringer #3:
Genetic information is altered when changes in the DNA sequence, called ____ occur.
2. Changes in the DNA sequence of a single gene are called _____.
3. What causes the lac genes in E. Coli to turn off?
4. What causes the Lac genes in E. Coli to turn on?