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DNA Flashcards

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1
Q

How is DNA found in eukaryotes?

A

It is found in the nucleus, as chromosomes which are a complex of DNA and histones. This complex is called chromatin.

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2
Q

How is DNA found in prokaryotes?

A

It is freefloating in the cytoplasm as supercoiled naked DNA.

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3
Q

What is the size of prokaryotes?

A

Up to 2 micrometers in diameter.

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4
Q

What is the size of eukaryotic cells?

A

About 20 micrometers.

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5
Q

How many chromosomes do humans have? What is the exception?

A

46, except for the gametes which have 23 each.

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6
Q

Which regions of chromosomes are condensed?

A

AT rich regions.

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7
Q

What is the genome of bacteriophages?

A

Around 5000 basepairs.

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8
Q

What is the genome size of humans?

A

3 billion base pairs.

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9
Q

How does the nr. of chromosomes reflect the complexity of an organism?

A

There is usually no correlation between the two.

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10
Q

What causes down syndrome?

A

3 copies of chromosome 21.

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11
Q

What causes turner syndrome in women?

A

They have only 1 X chromosome.

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12
Q

What causes chromic myeloid leukemia?

A

Translocation of material between chromosome 9 and chromosome 22.

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13
Q

What is the main cause of cystic fibrosis?

A

ΔF508 mutation where deletion of 3 nucleotides leads to loss of 1 phenylalanine.

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14
Q

What causes sickle cell disease?

A

A is changed to T at position 17 for the gene of the beta chain of haemogoblin which changes ammino acid from glutamate to valine.

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15
Q

What did the griffith experiment discover?

A

Genetic material can be transfered from dead cells to living cells.

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16
Q

What did the Avery experiment discover?

A

Genetic material was not transferred by RNase or proteases.

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17
Q

Detail the Hershey chase experiment. What did they discover?

A

A bacteriophage’s coat protein was labeled with S35. The same bacteriophage was also labelled with P32. When allowed to infect a bacteria, genetic material of infected bacteria only contained P32 labeled DNA.

This showed that DNA was responsible for the transfer of genetic material.

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18
Q

What does ceasium salt centrifugation rely on?

A

A substance’s density. It is also an equilibrium method.

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19
Q

What are the 3 main components of DNA?

A

The phosphate backbone, the sugar and the bases.

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20
Q

What positions are the OH groups on dioxyribose?

A

1’ 3’ and 5’.

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21
Q

What are the 4 bases and how can they be grouped?

A

Adenine, Thymine, Cytosine, Guanine. AG are purines and TC are pyrimidines.

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22
Q

At which positions does the phosphate backbone join with the sugar?

A

3’ and 5’.

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23
Q

What are Chargaff’s rules?

A

A=T and C=G, purines = pyrimidines.

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24
Q

What is the distance between nucleotides?

A

3.4angstrom.

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25
Q

How many H bonds between AT and CG?

A

2 between AT and 3 between CG.

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26
Q

What force is the separation of bases optimal for?

A

van der Waals forces.

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27
Q

What is the position of 1 DNA strand relative to its pairing strand?

A

Antiparalell. from 5’ to 3’.

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28
Q

What is the distance per turn of B-DNA. How many bases per turn. What is the diameter of 2 nucleotides?

A

3.4nm per turn. 10 base pairs per turn. 2nm in diameter.

29
Q

What causes the major and minor groove in DNA?

A

Asymetrical glycosidic bonds.

30
Q

What are the features of A-DNA, B-DNA and Z-DNA and how do they all form?

A

A-DNA is a right handed helix formed by the dehydration of B-DNA. B-DNA is the normal DNA and it is right handed. Z-DNA is formed by GC rich sequences at high salt concentrations. It is left handed.

31
Q

What wavelenght does DNA absorb maximally at?

A

260nm.

32
Q

Why do single strands of DNA have a higher melting point?

A

Bases are no longer stacked on each other.

33
Q

Why do GC rich sections of DNA have a higher melting point than AT rich regions?

A

Because they have more H bonds.

34
Q

How does salt concentration affect DNA melting?

A

It increases melting temp. as the salt positive counterion stabilizes the negative phosphate backbone,

35
Q

What are the main proteins in chromatin?

A

H1 H2A H2B H3 H4

36
Q

Which histones form the histone core?

A

All but H1.

37
Q

What is the role of H1?

A

Changes conformation to help compact DNA.

38
Q

What method does DNA replication use?

A

The semi conservative method.

39
Q

What was the Meselson Stahl experiment and what did it show?

A

They grew bacteria on N15 untill all DNA was N15. They Then Monitored the percentage of N15 after each gen. grew on N14.

1st: mix of both
2nd: 50/50
3rd: 75% N14 25% N15.

This proved the semiconservative method.

40
Q

What disproved the dispersive method of DNA replication?

A

Even denatured DNA maintained the ratios suggested by the semiconservative method.

41
Q

How can DNA replication be described

A

bi-Directionsal

42
Q

What is the replication fork and how does it work?

A

A DNA strand is opened up by helicase. DNApolymerase attached to each strand. Synthesis of DNA ONLY OCCURS IN THE 5’ TO 3’ direction.

DNApolymerase then forms a new strand of matching DNA on one side and matching fragments on the other hand called the lagging strand. This is because the DNApolymerase can only build up DNA 5’ to 3’.

43
Q

What are okazaki fragments joined by?

A

DNAligase.

44
Q

What is required for DNA replication?

A

An RNA primer made by primase.

45
Q

What is the Sanger method of DNA sequencing?

A

DNA is denatured to form single strands. A primer is laid down. To it, all the required nucleotides are added along with a small conc. of the ddNTP of the base you want to sequence. This ddNTP lacks a 3’ OH which will break DNA synthesis at every point that base is encountered.

This is done with every base untill all the DNA is sequenced.

46
Q

What is used to separate all the fragments after sanger sequencing?

A

electrophoreses.

47
Q

What is the main difference between old and new sequencing methods?

A

New method uses a reversible terminator to sequence the DNA after the addition of each dNTP. The different bases are all phosphorescent.

48
Q

What is PCR (polymerase chain reaction)?

A

It is a way of replicating DNA quickly.
DNA is denatured. A primer is then laid down. This is annealed to the DNA by lowering the temp. DNA polymerase along with the required dNTPs are added.

49
Q

What type of DNApolymerase is used in PCR and why?

A

Taq. Because it is thermally stable.

50
Q

What is the base that gets substitutes in RNA?

A

T gets replaced with U.

51
Q

What is the difference in the sugar part of RNA?

A

There is an extra OH at the 2’ position.

52
Q

What is mRNA used for?

A

It is the template for protein synthesis.

53
Q

What is rRNA?

A

Ribosomal RNA. Major component of ribosomes.

54
Q

What is tRNA?

A

It carries the activated form of amminoacids to the ribosome.

55
Q

What is snRNA?

A

Participates in RNA splicing.

56
Q

What is miRNA?

A

Inhibits translation of certain parts of the RNA.

57
Q

What is not required for RNA synthesis?

A

A primer.

58
Q

What is the process for forming RNA?

A

RNApolymerase unwinds DNA and binds to it. The starting sequence is marked by promoter regions. Transcription then beggins in the 5’ to 3’ direction.

The termination signal tells the polymerase when to stop. One of this is a kink formed in the new RNA containing a bent GC region followed by a flat AT region. This destabilizes the polymerase and kicks it off.

59
Q

What are RNA promoter regions in prokaryotes?

A

An AT rich region at around -10 (Pribnow box)

A TTGACA sequence at -35

60
Q

What is the difference in transcription and translation between eukaryotes and prokaryotes?

A

They cannot happen at the same time in eukaryotes because RNA synthesis happens in the nucleus.

61
Q

What do RNApolymerase 1 2 and 3 produce?

A

1 produces rRNA, 2 produces mRNA and 3 produces tRNA and 5S rRNA.

62
Q

How is eukaryotic pre-mRNA processed?

A

A polyA tail is added at the 3’ end to specify export to the cytoplasm and increase stability.

A cap is added to the 5’ end in the form of a 5’-5’ phosphate link to 7-methyl G.

63
Q

What are introns?

A

Non-coding regions of RNA

64
Q

What are exons?

A

Coding regions in RNA

65
Q

What is splicing and what is its purpose.

A

Splicing cuts out all the introns and joins togheter the exons.

66
Q

What performs splicing?

A

spliceosome.

67
Q

What precent of genetic diseases are linked to splicing errors?

A

15%

68
Q

How is transcription regulated in prokaryotes?

A

Prokaryotes can encode the formation of multiple proteins in a single strand of RNA. They can regulate their formation by using a repressor protein which prevents the translation of certain proteins.

69
Q

What does polycystronic mean?

A

it means a single RNA strand can encode multiple proteins.

DNA (1 decks)

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