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nucleic Acid And DNA Replication Flashcards

1
Q

What is the genetic material of all living things ?

A

Nucleic acid DNA

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2
Q

What is The Central dogma of the molecular biology ?

A

Process which
1. genetic information carried by DNA is transmitted through generations through DNA replication
2. Within a cell, genetic information of genes is used to make proteins through the process of transcription and translation

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3
Q

What is the process where DNA is converted into RNA ?

A

Transcription

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4
Q

What is the process where RNA is converted into proteins ?

A

Translation

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5
Q

What are the two types of nucleic acids ?

A

Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)

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6
Q

What are the monomers that make up nucleic acids called?

A

Nucleotides

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7
Q

What are the three components of a nucleotide ?

A

Pentose sugar (5C) - ribose (RNA) or deoxyribose (DNA)
Inorganic phosphate group
Nitrogenous base

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8
Q

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

A

Ribose has -OH group on carbon 2 while deoxyribose has -H (both projecting downwards)

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9
Q

Where is the inorganic phosphate group attached to on the pentose sugar ?

A

Carbon 5 (not part of the ring)

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10
Q

What gives rise to the negative charge on the nucleotides ?

A

The inorganic phosphate group

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11
Q

Is teh nitrogenous base hydrophobic or hydrophilic ?

A

Hydrophobic

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12
Q

What bonds are formed in complementary base pairing ?

A

hydrogen bonds

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13
Q

What are the two groups of nitrogenous bases ?

A

Purines and pyrimidines

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14
Q

Which of the two types of nitrogenous bases are bigger in size ?

A

Purines

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15
Q

How many ring structures does purines have ?

A

Two

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16
Q

How many ring structures do pyrimidines have ?

A

One

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17
Q

Which nitrogenous bases are purines ?

A

Adenine (A)
Guanine (G)

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18
Q

Which nitrogenous bases are pyrimidines ?

A

Thymine (T)
Cytosine (C)
Uracil (U)

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19
Q

What reaction do the components of nucleotide undergo to form the nucleotides ?

A

Condensation reaction

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20
Q

What is the bond formed between the nitrogenous base and pentose sugar called ?

A

Glycosidic bond

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21
Q

Which carbon of the pentose sugar is the nitrogenous base joined to ?

A

Carbon 1

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22
Q

What is the bond between the inorganic phosphate group and the pentose sugar in a single nucleotide called ?

A

Phosphoester bond

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23
Q

Which carbon is the inorganic phosphate joined to ?

A

Carbon 5

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24
Q

How many condensation reactions occur in the formation of one nucleotide ? And where ?

A

Two - one between nitrogenous base and pentose sugar, another between inorganic phosphate and pentose sugar

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25
Q

How many water molecules are removed in the formation of a nucleotide ?

A

Two

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26
Q

What do the nucleotides naturally occur as ?

A

Nucleoside triphosphates in the cytosol - three phosphates attached

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27
Q

How are nucleotides formed from a nucleoside triphosphate ?

A

By hydrolysis of the two terminal phosphate molecules of each nucleoside triphosphate molecule

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28
Q

Where does the energy used to link nucleotides together come from?

A

Energy released from the hydrolysis of the two terminal phosphate groups on a nucleoside triphosphate

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29
Q

What bond is formed between two nucleotides ?

A

Phosphodiester bond

30
Q

What is the phosphodiester bond formed between ?

A

Between carbon 5 of one nucleotide and carbon 3 of another nucleotide

31
Q

What is the phosphodiester bond made from ?

A

The inorganic phosphate of one of the nucleotides linking the two pentose sugars together

32
Q

What is the 5’ end of the polynucleotide strand ?

A

One end of the polynucleotide where there is a free phosphate group attached to the 5’ carbon of the pentose sugar on the terminal nucleotide

33
Q

What is the 3’ end of a polynucleotide strand ?

A

The end where there is a free hydroxyl group attached to the 3’ carbon of the pentose sugar of the terminal nucleotide

34
Q

What is the direction of every polynucleotide strand ?

A

5’ to 3’

35
Q

What are the features of DNA ?

A
  1. Double stranded
  2. Double helix
  3. Base pairing is very specific
  4. Purine pair with pyrimidine - constant width
  5. Antiparallel
36
Q

Which bases pair with which ? number of H bonds formed ?

A

Adenine (purine) pairs with thymine (pyrimidine) - 2 H bonds
Guanine (purine) pairs with cytosine (pyrimidine) - 3 H bonds

37
Q

Concentration of which bases are equal ?

A

Thymine equals to adenine
Cytosine equals to guanine
Pyrimidines and purines

38
Q

What is the constant width of a DNA strand ?

39
Q

How far apart are base pairs ?

40
Q

What is the length of a complete turn of the double helix (aka 10 base pairs) ?

41
Q

What is the criteria of a molecule to be able to act as genetic material ?

A
  • have means of coding for and storing genetic information
  • must be able to make exact copies of itself (replicate accurately)
42
Q

What are the principles of semi-conservative replication ?

A
  • there is unwinding and separation of the 2 DNA strands
  • each unwound strand act as template for synthesis of new daughter strand via complementary base pairing
  • results in 2 daughter DNA molecules which each consists of one original DNA strand and one newly synthesised DNA strand
43
Q

Where does DNA replication begin ?

A

A site known as the origin of replication (specific sequence of DNA nucleotides)

44
Q

Which enzyme separates the two DNA strands and how ?

A

Enzyme helicase
Breaks the H bonds between the complementary bases then unwinds and separates the strands

45
Q

How are the DNA strands kept separated ?

A

Binding of single-stranded DNA binding proteins which stabilise the separated strands

46
Q

Which direction does DNA replication occur in ?

A

Both directions

47
Q

When is a replication bubble formed ?

A

When the two strands separate

48
Q

What does enzyme primase do ?

A

Catalyses the synthesis of a RNA primer complementary to DNA nucleotide on template strand

49
Q

Why is synthesis of the RNA primer important ?

A

As DNA polymerase III cannot initiate DAN synthesis by joining the first nucleotides (cannot synthesise DNA from scratch), it can only add on new DNA nucleotides to to a pre-existing 3’ -OH end which the RNA primer provides

50
Q

What enzyme elongates the new strands and how ?

A

DNA polymerase III adds on free DNA nucleotides to the exposed bases on the parental DNA strand by complementary base pairing
It catalyses formation of phosphodiester bond between two adjacent DNA nucleotides, elongating new DNA strand

51
Q

Which direction does DNA polymerase III work in ?

A

5’ to 3’ direction with respect to the growing chain - new DNA nucleotides are only added to the exposed 3’ hydroxyl end of the growing strand

52
Q

Is DNA polymerase III capable of proofreading ?

53
Q

How does DNA polymerase III proofread ?

A

Once a DNA nucleotide is added, DNA polymerase III will proofread it against the template. It can remove an incorrectly paired DNA nucleotide then pairs it with the correct DNA nucleotide

54
Q

What are the two newly synthesised strands called ?

A

Leading strand
Lagging strand

55
Q

How is the leading strand elongated ? Direction ?

A

Elongated continuously in the 5’ to 3’ direction (elongating strand) and the DNA polymerase III moves towards the replication fork

56
Q

How is the lagging strand elongated ?

A

Elongated discontinuously through the synthesis of short fragments of nucleotides called Okazaki strands - each strand requires a RNA primer for DNA polymerase III to elongate it

57
Q

In which direction does DNA polymerase III move when synthesising the Okazaki fragments ?

A

Moves away from the replication fork

58
Q

What happens to DNA polymerase III when an Okazaki fragment is completed ?

A

It detaches from the template strand and reattaches itself to the newly exposed DNA template to synthesise the next Okazaki fragment

59
Q

What is the overall direction of replication of both strands ?

A

Towards the replication fork

60
Q

What does DNA polymerase I do ?

A

Replaces corresponding DNA nucleotides on newly synthesised strand when RNA primers are removed

61
Q

What does DNA ligase do ?

A

Seal up the gaps between the newly replaced DNA an teh existing fragments - catalyses formation of phosphodiester bond

62
Q

Why is replication called semi-conservative replication ?

A

Since the two daughter DNA molecules each consist of one parental DNA strand and one newly synthesised daughter DNA strand

63
Q

What is end replication problem ?

A

Failure to replace the RNA primer at the 3’ end of parental template strand with corresponding DNA nucleotides because there is no 3’ end available for DNA polymerase to add on new DNA nucleotides to the new strand
The newly formed daughter DNA strand will be shorter than parental strand and DNA continues to shorten with every replication, resulting in possible loss of critical genes after many rounds of replication

64
Q

Do prokaryotes have end replication problem ? Why ?

A

No as they have circular DNA

65
Q

What is strand slippage ?

A

When a newly synthesised strand loops out a bit resulting in addition of extra nucleotide base
OR
When the template strand loops out a bit resulting in deletion of a nucleotide base in the newly synthesised strand

66
Q

What are the three different hypothesis for replication of DNA ?

A

Conservative hypothesis
Dispersive hypothesis
Semi-conservative hypothesis

67
Q

What is the conservative hypothesis ?

A

Both strands of DNA molecule act as template for synthesis of entirely new DNA molecule
The two parental strands re-associate to form one of the daughter DNA molecules while the two newly synthesised DNA strands form other daughter strand

68
Q

What is dispersive hypothesis ?

A

Parental DNA molecule break up into short segments which act as templates for the synthesis of DNA
The segments are then joined together with each strand of both daughter molecules contain a mixture of old and newly synthesised parts

69
Q

What features of DNA allow it to be a good store of genetic information ?

A
  1. Able to carry coded information to direct cell activity
  2. Sufficiently stable so that heritable mutations occur rarely
  3. Capable of accurate replication
  4. DNA repair
  5. Mutations result in genetic variation
70
Q

How is DNA sufficiently stable ?

A
  • large number of H bonds between nitrogenous base pairs across the two strands of polynucleotides that make up the DNA double helix
  • strength of phosphodiester bond between DNA nucleotides
  • hydrophobic interactions between teh stacked bases
  • Low reactivity of DNA as there is no -OH bonded to carbon 2 (unlike RNA with ribose sugar)
  • in euk, DNA is wrapped around histone proteins reducing its acidic properties
71
Q

Why is DNA able to accurately replicate ?

A

Due to ability of DNA strands to base pair allow copies of the molecule to be made with no loss of information during DNA replication

72
Q

How is DNA repaired ?

A

Using the intact complementary strand as a template to guide the repair

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