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3) Genetics > Chapter 8: DNA: The Chemical Nature of the Gene > Flashcards

Chapter 8: DNA: The Chemical Nature of the Gene Flashcards

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1
Q

What are the three key characteristics of genetic material?

A
  • Must contain complex information
  • Must replicate faithfully
  • Must encode the phenotype
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2
Q

When was the DNA molecule discovered?

A
  • In 1869

- Prior to Watson and Crick

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3
Q

Why was the tetranucleotide theory dismissed at first?

A

Because many viewed it as too simple

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4
Q

What happens when virulent bacteria was injected into a mouse?

A

Mouse dies, and virulent bacteria was recovered

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5
Q

What happens when heat-killed bacteria was injected into a mouse?

A

Mouse lives, and no virulent bacteria recovered

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6
Q

What happens when a mixture of non-virulent bacteria and heat-killed bacteria was injected into a mouse?

A
  • Mouse dies, and virulent bacteria was recovered
  • Thus, an extract from dead bacterial cells (virulent) genetically transformed the non-virulent cells, causing the mouse’s death
  • Example of bacterial TRANSFORMATION
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7
Q

How was the nature of the transforming substance uncovered?

A
  • The mixture was treated with RNAse, DNAse, and proteases

- Only DNAse destroyed the transforming substance

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8
Q

What did the Hershey and Chase experiment demonstrate?

A

That DNA carries the genetic information in bacteriophages

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9
Q

Where would radioactive sulfur be integrated? Where would radioactive phosphorus be integrated?

A
  • Sulfur: protein (sulfuric amino acids)

- Phosphorus: DNA

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10
Q

Describe the Hershey and Chase experiment.

A

1) Infected cells with the phage in a solution containing 35S or 32P
2) Blender was used to centrifuge the cells, allowing the protein coat to leave
3) Solely the progeny phages from 32P are radioactive, indicating that DNA has been transmitted to the progeny phages

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11
Q

What method did Watson and Crick utilize to uncover the 3D structure of DNA?

A

X-Ray diffraction

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12
Q

Describe the X-Ray diffraction method.

A

1) Crystals of a substance are bombarded with X-rays, which are diffracted (bounce off)
2) The space of the atoms within the crystal determines the diffraction pattern, which appears as spots on a photographic film
3) The diffraction pattern provides information about the structure of the molecule

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13
Q

Which sugar is present in RNA? Which is present in DNA?

A
  • Ribose: RNA

- Deoxyribose: DNA

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14
Q

What is the main difference between a ribose and deoxyribose sugar?

A
  • DNA contains a hydrogen atom on the second carbon (2’)

- RNA contains a hydroxyl (OH-) on the second carbon (2’)

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15
Q

Why are RNA molecules more readily degraded?

A

As the hydroxyl molecules on ribose sugars are reactive, while deoxyribose sugars provide stability

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16
Q

Differentiate purine and pyrimidine bases.

A
  • Purine: two rings

- Pyrimidine: single ring

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17
Q

What are the two purines?

A

Adenine and Guanine

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18
Q

What are the three pyrimidines?

A

Cytosine, Thymine (DNA), Uracil (RNA)

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19
Q

What group provides the negative charge of DNA?

A

The phosphate group

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20
Q

Where is the phosphate group attached? Where is the base attached?

A
  • Phosphate: 5’

- Base: 1’

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21
Q

Which helices can DNA form? Which are the most common?

A
  • A (under specific conditions)
  • B (most common)
  • Z (only sometimes)
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22
Q

Is the DNA helix left- or right-handed?

A

Right-handed

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23
Q

Which structures of DNA are on the inside of the helix, and which are on the outside?

A
  • Inside: bases

- Outside: sugars and phosphates

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24
Q

Does every gene product become a protein?

A
  • No, certain genes generate RNA that is only functional at the RNA-LEVEL, meaning that there is no protein generated
  • RNA molecules may provide a regulatory role, and never produce protein
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25
Q

What special secondary structures may DNA and RNA form?

A

A stem and loop

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26
Q

What is the function of the special secondary structure in RNA?

A
  • May possess specific functions as an RNA molecule

- Normally, they are regulatory functions, but they may also be catalytic

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27
Q

DNA consists of ________ strands.

A

polynucleotide

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28
Q

A phosphodiester bond forms between what?

A

5’-phosphate to the 3’-OH group of a deoxyribose sugar

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29
Q

Differentiate the hydrogen bonding patterns between AT pairs and CG pairs.

A
  • AT: 2 hydrogen bonds

- CG: 3 hydrogen bonds

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30
Q

DNA strands are (parallel/antiparallel)

A

antiparallel

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31
Q

How do hydrogen bonds compare to phosphodiester bonds?

A

Hydrogen bonds are not as strong

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32
Q

Are RNA molecules single-stranded or double-stranded?

A

Normally single-stranded, but double-stranded molecules may exist

33
Q

What occurs in Prokaryotic organisms to allow for the organization of the DNA?

A
  • Supercoiling the DNA

- Binding the twisted loops of DNA with proteins (not histone proteins)

34
Q

Differentiate positive and negative supercoiling.

A
  • Positive: DNA is over-rotated (helix twists on itself)

- Negative: DNA is under-rotated (helix twists on itself in the opposite direction)

35
Q

What occurs in Eukaryotic organisms to allow for the organization of the DNA?

A

The production of histone proteins

36
Q

How do the histone proteins vary in size?

A
  • H1 is the largest

- H2A, H2B, H3, and H4 are approximately the same size

37
Q

What forms a nucleosome core?

A
  • 8 histone proteins
  • H2A (2)
  • H2B (2)
  • H3 (2)
  • H4 (2)
38
Q

How many base pairs encompass a single turn of a DNA strand around a nucleosome core?

A

146 base pairs

39
Q

What allows DNA to interact with the histone proteins?

A

DNA is negatively charged, while histone proteins are positively charged

40
Q

What is chromatin?

A

Refers to the DNA and histone protein complex

41
Q

What controls the accessibility of DNA?

A
  • The nucleosome
  • The more nucleosomes, the denser the chromosome, as the DNA is tightly packed
  • If the nucleosomes are removed, the DNA unravels (available for transcription)
  • Epigenetics
42
Q

The ______ is the fundamental repeating unit of chromatin.

A

nucleosome

43
Q

What is the histone tail?

A
  • The regions of the beginning and ends of histone proteins, which stick out of the nucleosome
  • They may be modified, which signals either the release or the tight binding of DNA
44
Q

What kind of DNA may be cut and digested by nuclease? What kind of DNA cannot?

A
  • Naked DNA may be cut

- DNA wound by histones cannot, as it is protected

45
Q

How may you identify genes that are important at a certain stage of development?

A
  • Through a nuclease treatment, you can identify the “naked” regions of DNA that are not bound by histone proteins
  • DNA that remains following the treatment is LESS important (as it is not active and is bound by histones)
46
Q

Why is gene accessibility said to be dynamic?

A

Because the accessible DNA is constantly changing due to environmental conditions, which affects epigenetics

47
Q

Where is DNA methylated in Eukaryotes? What does it form?

A
  • On cytosine

- Forms 5-methylcytosine

48
Q

How does DNA methylation differ from chemical modifications within a histone protein?

A

Modification on the DNA itself

49
Q

What is the consequence of DNA methylation?

A
  • Increases compaction of the DNA strand
  • Regions containing methylated DNA are ALWAYS SILENT
  • Methylation does NOT result in a difference in the genome
50
Q

What is euchromatin?

A
  • Accessible
  • Contains few nucleosomes
  • Contains genes that are actively expressed
51
Q

What is heterochromatin?

A
  • Contains multiple regions of DNA methylation

- Silent genes

52
Q

What is facultative heterochromatin?

A

Region that may jump from an open (euchromatin) to closed (heterochromatin) structure

53
Q

Does the structure of DNA change during development? What does this indicate?

A
  • Yes

- Indicates that chromatin structure changes during transcription

54
Q

How does a program control for the development of an embryo? When?

A
  • Through the alterations in the structure of chromatin

- During transcription

55
Q

What is the chromosomal puff in Drosophila?

A
  • Stack of different chromosomes in the gland that produces saliva in Drosophila
  • DNA is less dense in regions that are puffed, which means that genes are extremely solicited in this area, producing a variety of gene products
56
Q

What is the signature motif of centromeres in humans?

A
  • There is NO specific motif

- But, the structure is conserved (highly condensed heterochromatin)

57
Q

What is partly the reason behind aging? How?

A
  • Telomeric sequences

- As every round of replication leads to shorter and shorter chromosomes

58
Q

Why was the discovery of the structure of DNA so important for understanding genetics?

A

Without knowledge of the structure of DNA, it was impossible to understand how genetic information was encoded or expressed

59
Q

What are Chargaff’s rules?

A
  • A = T

- C = G

60
Q

If Avery, MacLeod, and McCarty had found that samples of heat-killed bacteria treated with RNase and DNase transformed bacteria, but that samples treated with protease did not, what conclusion would they have made?

A) Protease carries out transformation
B) RNA and DNA are the genetic materials
C) Protein is the genetic material
D) RNase and DNase are necessary for transformation

A

C) Protein is the genetic material

61
Q

Could Hershey and Chase have used a radioactive isotope of carbon instead of 32P? Why or why not?

A

No, since carbon is contained in both protein and nucleic acids

62
Q

Why is DNA better suited to serve as the long-term carrier of genetic information?

A

Because the additional oxygen atom in RNA makes it more reactive and less chemically stable than DNA

63
Q

What is a nucleoside?

A

Sugar and a base

64
Q

Is DNA acidic or basic? Why?

A

Acidic, because of the negative charge of the phosphorus

65
Q

How do the sugars of RNA and DNA differ?
A) RNA has a six-carbon sugar; DNA has a five-carbon sugar
B) The sugar of RNA has a hydroxyl group that is not found in the sugar of DNA
C) RNA contains uracil; DNA contains thymine
D) DNA’s sugar has a phosphorus atom; RNA’s sugar does not

A

B) The sugar of RNA has a hydroxyl group that is not found in the sugar of DNA

66
Q

How do hydrogen bonds compare to phosphodiester bonds?

A

Hydrogen bonds are relatively weak compared with the covalent phosphodiester bonds

67
Q

The antiparallel nature of DNA refers to
A) Its charged phosphate groups
B) The pairing of bases on one strand with bases on the other strand
C) The formation of hydrogen bonds between bases from opposite strands
D) The opposite direction of the two strands of nucleotides

A

D) The opposite direction of the two strands of nucleotides

68
Q

How does Z-DNA differ from B-DNA?

A

B-DNA has a right-handed helix, while Z-DNA is a left-handed helix

69
Q

What enzyme does supercoiling rely on?

A

Topoisomerases, which add or remove rotations

70
Q

Most DNA found in cells is negatively supercoiled. What are the two advantages?

A

1) Makes the separation of the two strands of DNA easier during replication and transcription
2) Can be packed into a smaller space than relaxed DNA

71
Q

How does bacterial DNA differ from Eukaryotic DNA?

A

Bacterial DNA is not complexed with histone proteins and is circular

72
Q

Where do all chromosomes have heterochromatin?

A

At centromeres, telomeres, and other specific places

73
Q

Neutralizing their positive charges would have which effect on the histone proteins?
A) They would bind DNA tighter
B) They would bind less tightly to the DNA
C) They would no longer be attracted to each other
D) They would cause supercoiling of the DNA

A

B) They would bind less tightly to the DNA

74
Q

How does acetylation alter chromatin structure?

A

Reduces the positive charges that normally exist on lysine and destabilizes the nucleosome structure, so histones hold the DNA less tightly

75
Q

What is epigenetics?

A
  • Alterations of chromatin structure that are passed on to descendant cells
  • They do not include changes in the base sequence
76
Q

Which of the following is a characteristic of DNA sequences at telomeres?
A) One strand consists of guanine and adenine or thymine nucleotides
B) They consist of repeated sequences
C) One strand protrudes beyond the other, creating some single-stranded DNA at the end
D) All of the above

A

D) All of the above

77
Q 
Most of the genes that encoded proteins are found in 
A) unique-sequence DNA
B) moderately repetitive DNA
C) highly repetitive DNA
D) all of the above
A

A) unique-sequence DNA

78
Q 
How many copies of the H2B histone would be found in chromatin containing 50 nucleosomes?
A) 5
B) 10
C) 50
D) 100
A

D) 100

79
Q

Hairpins are formed in DNA as a result of
A) sequences on the same strand that are inverted and complementary.
B) sequences on the opposite strand that are complements.
C) sequences on the same strand that are identical.
D) sequences on the opposite strand that are identical.

A

A) sequences on the same strand that are inverted and complementary.

3) Genetics (16 decks)

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