1. BIOLOGY CHAPTER 12 DNA AND RNA modified from PowerPoint by Mrs. Fisch
SECTION 1. DNA

2. QUESTIONS OF THE EARLY 1900s:
How do genes work?
What are genes made of?
Are they single molecules or many molecules?
Biologists began to search for the chemical nature of genes.

3. FREDERICK GRIFFITH’S EXPERIMENTS
British bacteriologist
Wanted to figure out why bacteria made people sick
1928: experiment on mice and bacteria that cause pneumonia
Two strains of the bacteria that can be grown in the laboratory:
type S = causes severe pneumonia
type R = relatively harmless

4. GRIFFITH’S EXPERIMENTS
First he injected living type S bacteria into mice. The mice died.

5. Second, he heated type S to kill the bacteria, and injected the dead bacteria into the mice. The mice lived.
Conclusion: the disease was not caused by a poison produced by the bacteria.

6. Next, he injected living type R bacteria
The mice did not get sick.

7. Finally, he injected a mixture of living type R and dead type S.
The mice died.

8. The dead mouse tissue showed living type S bacteria.
There must have been a factor, transferred from the dead bacteria, containing the information needed to turn type R cells to type S.
The factor probably contained genes.

9. We now know that genes are made of DNA.
Transformation - bacteria take up DNA from the surroundings and incorporate it into their own DNA
In this case, type S incorporated the DNA from the dead type R bacteria, getting the information needed to cause disease.

10. Built on Griffith’s results.
OSWALD AVERY
Built on Griffith’s results.
To see what type of chemical contained genetic information, he extracted material from heat-killed bacteria and treated it with enzymes to destroy the transformation factor.

11. Treatment of the extract with enzymes that break down protein, carbohydrates, and RNA did not affect the transforming ability of the extract.
However, treatment with an enzyme that breaks down DNA destroyed the transforming activity.
Therefore DNA appears to be the molecule that carries genetic information.

12. AVERY’S EXPERIMENT
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13. CONFIRMATION OF THE ROLE OF DNA
By 1952, scientists still were not convinced that hereditary material was DNA; it seemed too simple a molecule (its structure was not known yet).
Many thought that genes were made of proteins.

14. CONFIRMATION OF THE ROLE OF DNA
Alfred Hershey and Martha Chase provided definitive evidence for the role of DNA.

15. They used a bacteriophage (a virus that attacks bacteria) to prove that DNA was the genetic material.

16. A bacteriophage is made of a protein coat and DNA.
Hershey and Chase grew viruses in cultures containing radioactive isotopes of phosphorus (which is in DNA, but hardly at all in protein) and sulfur (which is in protein, but not in DNA).

17. When the viruses infected bacteria with their genetic material, the cells were found to have radioactive P but not radioactive S.
This shows that DNA but not protein had carried the genes of the virus.

19. Building blocks of DNA and RNA. Composed of:
NUCLEOTIDES
Building blocks of DNA and RNA.
Composed of:
5-carbon sugar (deoxyribose in DNA)
Phosphate group
Nitrogenous base

20. FOUR KINDS OF NITROGEN BASES IN DNA
Purines:
adenine
guanine
Pyrimidines:
cytosine
thymine
Mnemonics:
“Pure As Gold”;
“Cut The PYe”

21. Discovered by Erwin Chargaff
CHARGAFF’S RULES
Discovered by Erwin Chargaff
For different samples of DNA, the relative amounts of adenine and thymine are equal (A = T).
The relative amounts of cytosine and guanine are equal (C = G)

23. The results indicated that DNA had a helical (spiral) structure.
ROSALIND FRANKLIN
Used the technique of X-ray diffraction to get information about the structure of DNA.
The results indicated that DNA had a helical (spiral) structure.

24. Discovered in 1953 by James Watson and Francis Crick
STRUCTURE OF DNA
Discovered in 1953 by James Watson and Francis Crick
Known as the double-helix model
Made use of Franklin’s X-ray results

25. STRUCTURE OF DNA

26. What is a nucleotide?
What are the three parts of a nucleotide?
How many different nitrogenous bases are in DNA? Name them.

27. Nitrogenous bases act as the “rungs” joining the strands.
THE DOUBLE HELIX
A twisted ladder with two long chains of alternating phosphates and sugars
Nitrogenous bases act as the “rungs” joining the strands.
Bases held together by hydrogen bonds

28. COMPLEMENTARY BASE PAIRS
Hydrogen bonds can only form between certain bases.
Adenine pairs with thymine.
Cytosine pairs with guanine.
Explains Chargaff’s rules (A=T, C=G)

29. Phosphate
Nitrogen Bases
Sugar
Hydrogen
Bonds

30. In DNA, what does adenine pair with? What does cytosine pair with?
Who discovered the relationships between the above pairs?
Who discovered that DNA carries genetic information, not proteins?
Who used x-rays to determine the structure of DNA?

31. SECTION 2. CHROMOSOMES AND DNA REPLICATION How long is the DNA molecule?

32. DNA STRUCTURE IN PROKARYOTES
Approximately 5 million base pairs, 3,000 genes
Chromosome
E. coli bacterium
Bases on the chromosome
Bacteria usually have a single circular chromosome.
Found in cytoplasm (no nucleus)

33. DNA STRUCTURE IN EUKARYOTES
Packaged into chromosomes
Humans have approximately 3 billion base pairs (1 m long), with about 20,000 protein-coding genes.

34.
If the diameter of the DNA (2 nanometers) were as wide as a fishing line (0.5 millimeters) it might stretch as far as 21.2 km (or 13.6 miles), which would all have to be packed into a nucleus, the equivalent size of 25 cm in diameter. That is some packaging!

35. The nucleus of one human cell contains approximately one meter of DNA.
CHROMOSOMES
The nucleus of one human cell contains approximately one meter of DNA.
Chromosomes are made of chromatin, tightly packed DNA and protein.
Histones: proteins that DNA is coiled around in chromatin
Nucleosome: beadlike structure of DNA and histone molecules

36. NUCLEOSOME
thebiology.org

37. CHROMOSOME STRUCTURE

38. Process by which the cell duplicates DNA before it divides
DNA REPLICATION
Process by which the cell duplicates DNA before it divides
A new cells needs a copy of the information in order to grow.

39. Since the bases on the two strands are complementary, each strand contains enough information to recreate the entire DNA molecule.
CCBC Faculty Web

40. DNA unzipping (carried out by DNA helicase) – hydrogen bonds are broken and the two strands unwind.
DNA polymerase – principal enzyme involved in DNA replication
Unwound strands serve as a templates for new DNA.

41. disastergirrl.tumblr.com

42. After the DNA molecule comes apart, DNA polymerase joins nucleotides whose bases pair with their complementary bases.
DNA polymerase “proofreads” the new strands making sure the new bases are paired correctly.

43. SEMICONSERVATIVE REPLICATION
Each new DNA molecule will contain one of the original strands, and one newly synthesized strand with complementary bases.
This is referred to as semiconservative replication (semi- = half).

44. STARTING POINTS AND DIRECTIONS OF DNA REPLICATION
In prokaryotes, DNA replication begins at a single starting point and usually proceeds in both directions.
Because eukaryotic chromosomes are so much larger, there are many starting points on each chromosome, and replication also proceeds in both directions.

45. DIRECTIONS OF DNA REPLICATION

46. What is the principal enzyme involved in DNA replication?’
Why does a cell need to duplicate DNA?
Where is DNA found in prokaryotes? In eukaryotes?

47. RNA (ribonucleic acid)
SECTION 3. RNA AND PROTEIN SYNTHESIS
RNA (ribonucleic acid)
Long chain of nucleotides like DNA
Exceptions:
Ribose is the 5-carbon sugar (instead of deoxyribose)
Usually single-stranded
Uracil (U) replaces thymine (T)
and is complementary to adenine (A)

49. RNA THAT IS NOT SINGLE-STRANDED
Some types of RNA can fold back on itself and base pair for short sections (as in transfer RNA)
Some viruses have double-stranded RNA as their genetic material.

50. RNA THAT IS NOT SINGLE-STRANDED
wikispaces.psu.edu

51. protein synthesis – assembling amino acids into proteins
MAJOR FUNCTION OF RNA:
protein synthesis – assembling amino acids into proteins

52. THREE TYPES OF RNA:
1. Messenger RNA (mRNA) - carries code for the sequence of amino acids of proteins from DNA to rest of cell

53. 2. Ribosomal RNA (rRNA) - combines with proteins to form ribosomes

54. 3. Transfer RNA (tRNA) – transfers amino acid to ribosome as specified by mRNA
wikipedia

55. The central dogma of molecular biology explains the flow of genetic information within biological systems. Occurs in all cells.
DNA
RNA
Protein
Transcription
Translation
This process, in which genetic information is used to construct a protein, is called gene expression.

56. Transcription - converting genetic information from DNA to RNA

57. TRANSCRIPTION
When a secretary transcribes a speech, the language remains the same. However, the form of the message changes from spoken to written.
Similary, transcription of DNA to RNA is in the “language” of nucleotides and base pairing.

58. In eukaryotes, DNA is protected inside the nucleus.
TRANSCRIPTION
In eukaryotes, DNA is protected inside the nucleus.
RNA polymerase unzips DNA and makes the RNA.

59. mRNA carries the message of DNA into the cytoplasm to the ribosomes.
TRANSCRIPTION
One strand (the template or transcribed strand) serves as a template to make mRNA.
mRNA carries the message of DNA into the cytoplasm to the ribosomes.

60. Transcription doesn’t start just anywhere
Transcription doesn’t start just anywhere. It begins at special sequences called promoters.
Other signals tell the enzyme when to stop making the messenger RNA.

61. TRANSCRIPTION
RNA forms base pairs with DNA (A with T, U with A, C with G, G with C).
Primary transcript - length of RNA that results from the process of transcription

62. ACGAT ACCCT GACGAGCGTTAGCTATCG UGC UAU GGG ACU
TRANSCRIPTION
ACGAT ACCCT GACGAGCGTTAGCTATCG
UGC
UAU
GGG
ACU

63. If the DNA strand is:
G T A C C A G A T T A G C
What would the RNA strand be?

64. IF the DNA strand is:
G T A C C A G A T T A G C
What would the RNA strand be?
C A U G G U C U A A U C G

65. The initial RNA transcript is changed, or “edited,” before it is used.
RNA EDITING
The initial RNA transcript is changed, or “edited,” before it is used.
Large sections called introns are removed.
The remaining pieces, called exons, are used to code for proteins.

66. AFTER TRANSCRIPTION
Mature mRNA that was transcribed from DNA and edited leaves the nucleus through a nuclear pore.
It enters the cytoplasm and binds to a ribosome so that translation can begin.

67. TRANSLATION
To translate English into Chinese requires an interpreter who recognizes one language and converts it to another.
In the cell, the nucleotide language of RNA is converted to the amino acid language of proteins.

68. TRANSLATION
Involved in protein synthesis
Reading or “translating” the RNA code to form a chain of amino acids
Three nucleotides code for each amino acid.
Carried out by ribosome with mRNA attached
tRNA brings amino acids to the ribosome.

69. TRANSLATION

70. READING THE DNA CODE
A set of three DNA bases pairs with three mRNA bases.
Each group of three mRNA bases encodes a single amino acid.
This is called a codon.

71. There are 4 x 4 x 4 = 64 possible groups of three (codons).
READING THE DNA CODE
There are 4 x 4 x 4 = 64 possible groups of three (codons).
There are only 20 types of amino acids, so there can be more than one codon for each.
One codon is used to signal the starting amino acid, and three are “stop” signals.

73. ACGA TAC CCT GAC GAG CGT TAG CTA
UGCU
AUG
GGA
CUG

74. Lines up amino acids using mRNA code
TRANSFER RNA (tRNA)
Lines up amino acids using mRNA code
Attached to amino acid on one end
Anticodon – three letter complement to mRNA codon

75. A second tRNA, with its amino acid attached, binds.
PEPTIDE SYNTHESIS
After tRNA binds to the first codon, the ribosome moves and exposes the next codon.
A second tRNA, with its amino acid attached, binds.
A peptide bond is created between the two amino acids, and the first tRNA is released.

77. The ribosome shifts to the next codon, and the process repeats.
When a stop codon is reached, the polypeptide and mRNA are released from the ribosome.
(see Fig in textbook)

78. Start codon

81. Amino acids within a polypeptide
anticodon
anticodon
anticodon
DNA
mRNA
Protein
Single strand of DNA
codon
codon
codon
mRNA
This diagram illustrates how information for specifying the traits of an organism is carried in DNA. The sequence of bases in DNA is used as a template for mRNA. The codons of mRNA specify the sequence of amino acids in a protein, and proteins play a key role in producing an organism’s traits.
Alanine
Arginine
Leucine
Amino acids within a polypeptide

83. genetic information encoded in DNA is copied onto messenger RNA
Transcription
Translation
Process
genetic information encoded in DNA is copied onto messenger RNA
information encoded in mRNA is used to assemble a protein
Occurs
in the nucleus
on a ribosome
Change
DNA mRNA
mRNA protein

84. Which process involves mRNA taking a message from DNA to a ribosome?
Which process involves mRNA being decoded on a ribosome and turned into proteins?
What is the process by which DNA unzips and is copied?

85. REVIEW: ORGANELLES INVOLVED IN PROTEIN SYNTHESIS
Ribosomes may be free or bound to endoplasmic reticulum
( = rough ER).
Proteins made on rough ER are for membranes or for export from cell.

86. Rough ER modifies proteins and packs them into vesicles.
Golgi further modifies proteins and sends them to various destinations (secretion or other membranes).
Secreted proteins are released by exocytosis.

88. What is a codon? Where is it found?
What carries the anticodon that corresponds to each codon?
Where does translation occur?
What is mRNA translated into?

89. Permanent changes in genetic material
SECTION 4. MUTATIONS
Permanent changes in genetic material
Can be inherited, if occurring in cells leading to gametes
A source of variation in a genetic sequence
Can involve either genes or chromosomes
Not all are bad. Some are beneficial; many have little or no effect.

90. DNA fails to copy properly
CAUSES OF MUTATIONS
DNA fails to copy properly
External influences – exposure to chemicals and radiation causes DNA damage

91. Small-scale changes in the DNA sequence, affecting single genes.
GENE MUTATIONS
Small-scale changes in the DNA sequence, affecting single genes.
Point mutation: a change in a single nucleotide in a sequence of DNA.
Silent mutation - the same amino acid is coded, so there is little or no effect.
Missense mutation - produces a codon for a different amino acid.
Nonsense mutation - produces a stop codon, so the protein is shortened.

93. Frameshift mutation: a nucleotide is added or deleted, causing a shift of the entire sequence one way or the other from that point on Usually results in a nonfunctional protein

94. Insertion – extra base pairs are added
Deletion – a section of DNA is deleted

95. CHROMOSOMAL MUTATIONS
Involve a changes in the number or structure of the chromosomes.
Deletion - a piece of a chromosome breaks off and is lost. Tens or hundreds of genes may be lost.
Duplication - a segment of a chromosome is repeated.

96. Inversion - segment of a chromosome is reversed.
Translocation - part of one chromosome breaks off and attaches to another.

97. CHROMOSOMAL DISORDERS
Will be discussed along with notes for Chapter 11, section 4
In text: pages
Most are due to nondisjunction (failure of chromosomes to separate during meiosis)

98. IMPORTANCE OF MUTATIONS
Mutations are the source of genetic variety within populations and species.
Many have little effect.
Some are harmful.
There are many human genetic disorders arising from mutations.
Mutations can lead to uncontrolled growth in cancer.

99. IMPORTANCE OF MUTATIONS
Some mutations are beneficial. When acted on by natural selection, the accumulation of beneficial mutations through evolution has led to the diversity of life on Earth.

100. What kind of gene mutation occurs when one nucleotide is switched with another?
What type of gene mutation occurs when one nucleotide is either added or removed?
What type of chromosomal mutation occurs when a part of a chromosome breaks off and attaches to another?