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SBI4U > Molecular Genetics > Flashcards

Molecular Genetics Flashcards

1
Q

Who were credited with deducing the structure of DNA?

A

James Watson and Francis Crick

They made this discovery in 1953.

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2
Q

What are the components of DNA?

A
  • Deoxyribose sugar
  • Phosphate group
  • Nitrogenous base

These components together form a nucleotide.

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3
Q

What is the structure of DNA?

A

A thread-like molecule twisted in a clockwise direction to form a double helix

DNA consists of two antiparallel strands of nucleotides.

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4
Q

What are the ends of a DNA strand called?

A

5’ end and 3’ end

The two strands run in opposite directions.
‘ means end

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5
Q

What terminates the 5’ end of a DNA strand?

A

Phosphate group

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6
Q

What is the significance of complementary base pairing in DNA?

A

Adenine pairs with Thymine (A-T) and Guanine pairs with Cytosine (G-C)

This pairing is crucial for the structure and function of DNA.

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7
Q

Fill in the blank: DNA is a ______ polymer.

A

nucleotide

This indicates that DNA is made up of repeating units called nucleotides.

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8
Q

True or False: DNA strands are parallel to each other.

A

False

The strands are antiparallel.

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9
Q

What type of molecule is DNA described as?

A

A nucleotide polymer

This means that it is composed of many nucleotides linked together.

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10
Q

What is the direction of the twist in the DNA double helix?

A

Clockwise

This twist is a key feature of the double helix structure.

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11
Q

What are the two types of nitrogenous bases?

A

Adenine and guanine are purines; cytosine and thymine are pyrimidines.

Purines have a double ring structure, while pyrimidines have a single ring structure.

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12
Q

What does complementary base pairing maintain in a DNA molecule?

A

A constant width.

This refers to the consistent distance between the two strands of DNA due to specific pairing of bases.

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13
Q

If the nucleotides of all chromosomes in a genome could be stretched out in one long double helix, how long would they measure?

A

1.8 meters.

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14
Q

What is a nucleosome?

A

A complex of histones supporting coiled DNA.

Nucleosomes are formed by wrapping DNA around histone proteins, facilitating DNA packing.

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15
Q

What is the role of histones in DNA structure?

A

Histones help to coil DNA into nucleosomes.

Histones are positively charged proteins that attract the negatively charged DNA.

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16
Q

What contributes to the molecular stability in a DNA molecule?

A

Three forces:
* Phosphodiester bonds
* Hydrogen bonds
* Hydrophobic interactions.

Each of these forces plays a critical role in maintaining the integrity and stability of the DNA structure.

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17
Q

What do phosphodiester bonds link in a DNA molecule?

A

The sugar-phosphate backbone of one nucleotide to another.

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18
Q

What stabilizes the inner core of the DNA molecule?

A

Hydrogen bonds.

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19
Q

Fill in the blank: The hydrophobic interactions cause bases to remain _______.

A

inside the structure.

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20
Q

True or False: The phosphate group and sugar are hydrophobic.

A

False.

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21
Q

What is the function of supercoiling in chromatin?

A

It helps maintain the compact structure of chromosomes.

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22
Q

What terminates the 3’ end

A

Nitrogenous base

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23
Q

What is the significance of the Meselson and Stahl experiment?

A

Proof of semiconservative replication of DNA

Conducted in 1957 to demonstrate how DNA replicates.

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24
Q

What organism was used in the Meselson and Stahl experiment?

A

E. coli

A type of bacteria used to study DNA replication.

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25
Q

What isotopes were used in the Meselson and Stahl experiment?

A

Heavy nitrogen (N) and regular nitrogen (N)

Heavy nitrogen has a higher atomic mass.

26
Q

What method was used to isolate DNA strands in the experiment?

A

Centrifugation

A technique to separate components based on density.

27
Q

What was the result of the test tube containing heavy DNA?

A

Produced one discrete band in the low region

Indicating the presence of heavy nitrogen-labeled DNA.

28
Q

What was the result of the test tube containing regular DNA?

A

Produced one discrete band

This band was in the region corresponding to regular nitrogen.

29
Q

In the experiment, what was produced after bacteria replicated once in normal nitrogen medium?

A

One discrete band intermediate between bands in tube 1 and tube 2

Indicated the formation of hybrid DNA.

30
Q

What was the outcome when bacteria from heavy nitrogen medium replicated twice in normal nitrogen medium?

A

Produced two discrete bands: one at intermediate level, one at regular N level

Demonstrated that the initial DNA served as a template.

31
Q

What does the term ‘semiconservative replication’ mean?

A

Each new DNA molecule consists of one old strand and one new strand

This is the mechanism by which DNA replicates.

32
Q

True or False: The Meselson and Stahl experiment proved that DNA replication is conservative.

A

False

It proved that DNA replication is semiconservative.

33
Q

What type of replication does DNA undergo?

A

Semi-conservative

Each new strand is composed of one parental half and one newly synthesized daughter half.

34
Q

Who conducted experiments that confirmed the semi-conservative nature of DNA replication?

A

Meselson and Stahl

Their experiments provided key evidence for the semi-conservative model.

35
Q

What is the role of proteins at the initiation stage of DNA replication?

A

Bind to specific sites on DNA, blocking reformation of hydrogen bonds

This prevents the strands from re-annealing.

36
Q

What enzymes help relieve tension in DNA strands during replication?

A

DNA Gyrase and Topoisomerases

They cut and reseal DNA strands to allow untwisting.

37
Q

What is the function of DNA Polymerase III?

A

Builds complementary DNA strands

It synthesizes DNA in the 5’ to 3’ direction.

38
Q

What is required for DNA Polymerase III to start synthesizing DNA?

A

An existing starting point provided by an RNA primer

The RNA primer is inserted on the DNA template by the primase enzyme.

39
Q

What energy source does DNA Polymerase III use to join nucleotides?

A

Energy from breaking phosphate bonds

This energy is derived from the nucleotides themselves.

40
Q

What is the leading strand in DNA replication?

A

The strand that uses the 5’ to 3’ template strand and is synthesized continuously

It is synthesized in the direction of the replication fork.

41
Q

What is the lagging strand in DNA replication?

A

The strand using the 3’ to 5’ template strand, synthesized discontinuously in short fragments

These short fragments are called Okazaki fragments.

42
Q

Fill in the blank: DNA Polymerase III synthesizes DNA in the _____ direction.

A

5’ to 3’

This is the only direction in which DNA can be synthesized.

43
Q

True or False: The lagging strand is synthesized in the same direction as the replication fork.

A

False

The lagging strand is synthesized in the opposite direction of the replication fork.

44
Q

What is the function of DUA Polymerase I?

A

Removes RNA primers from the leading strand and fragments of the lagging strand and replaces them with the correct deoxyribonucleotide.

45
Q

What role does DNA ligase play in DNA replication?

A

Joins Okazaki fragments together via phosphodiester bonds.

46
Q

What happens as DNA strands are built during replication?

A

They automatically rewind to form a double helix.

47
Q

How do DNA polymerase III and I ensure accuracy in DNA replication?

A

They recognize whether hydrogen bonding has taken place between base pairs.

48
Q

What occurs if a mismatch is detected by DNA polymerase?

A

The polymerase excises the incorrect base and inserts the correct one.

49
Q

What are telomeres?

A

Long sequences of repetitive non-coding DNA.

50
Q

What is the function of telomeres in chromosomes?

A

They act as buffer zones at the ends of chromosomes, helping guard against loss of valuable genetic material during replication.

51
Q

Fill in the blank: DNA ligase joins Okazaki fragments together via _______.

A

phosphodiester bond

52
Q

What did Watson and Crick realize about the DNA molecule?

A

DNA strands must run anti-parallel for stability

This was a crucial insight into the structure of DNA.

53
Q

What did Rosalind Franklin discover about DNA?

A

DNA has a helical structure

Her work contributed significantly to understanding DNA’s shape.

54
Q

What key concept did Hershey and Chase demonstrate?

A

DNA is responsible for carrying genetic information

Their experiments with bacteriophages provided strong evidence for this.

55
Q

What did Avery, McCarty, and MacLeod discover?

A

DNA is a transforming substance

This finding was pivotal in identifying DNA as the genetic material.

56
Q

What were Chargaff’s findings regarding nitrogenous bases?

A

Nitrogenous bases occur in definite ratios

Specifically, adenine pairs with thymine and cytosine pairs with guanine.

57
Q

What did Chargaff discover about the quantities of thymine and adenine?

A

The quantities always matched

This observation was crucial for understanding base pairing in DNA.

58
Q

What role did Hammerling attribute to the nucleus?

A

Control center of the cell

His experiments with algae demonstrated the nucleus’s importance in heredity.

59
Q

What did Griffith discover about DNA

A

the transformation principle

60
Q

What did Meischer discover about DNA

A

DNA as the hereditary molecule

61
Q
A

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