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MCBG > Introduction To DNA > Flashcards

Introduction To DNA Flashcards

1
Q

Why is the euchromatin (beads on a string) DNA expressed as genes whereas heterochromatin is not?

A

Euchromatin has a more open structure so can be accessed for transcription

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2
Q

What are the minor and major grooves of a DNA molecule?

A

Major grove = where the backbones are far apart

Minor groove = where the backbones are close together

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3
Q

What is a nucleosome?

A

A length of dna coiled around a histone

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4
Q

What is the diameter of a solenoid fibre?

A

30nm

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5
Q

Are genes expressed when DNA is in the chromosome form? Give a reason for your answer.

A

Chromosomes - genes not expressed, DNA very tightly wound

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6
Q

How many genes are there roughly in the human body?

A

~25000

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7
Q

What is a genome?

How many chromosomes is the human genome?

A

The entire dna sequence of an organism

24 chromosomes (22 autosomes, 2 sex chromosomes)

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8
Q

Give two examples of nucleic acids

A

DNA

RNA

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9
Q

What is a nucleotide? What is a nucleoside?

A 
Nucleotide = phosphate + sugar + base
Nucleoside = sugar + base
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10
Q

What is a similarity between the sugars that make up DNA and RNA?

A

They are both pentose sugars

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11
Q

What is the sugar in a DNA nucleotide?

A

2-deoxyribose

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12
Q

What is the sugar of an RNA nucleotide?

A

Ribose

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13
Q

At which carbon does the nitrogenous base of a nucleotide connect to the sugar?

A

Carbon-1

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14
Q

To which carbon is the phosphate group of a nucleotide connected to the sugar?

A

Carbon-5

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15
Q

What are the two classes of nitrogenous bases?

A

Purines and pyrimidines

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16
Q

What are the two purines?

A

Adenine, guanine

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17
Q

What are the two pyrimidines (+ 1 in RNA)?

A

Thymine, cytosine (and uracil)

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18
Q

How are nucleotides joined to one another?

A

By phosphodiester bonds between Carbon-3 and Carbon-5

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19
Q

Why can nitrogenous bases form hydrogen bonds?

A

The =O of the base is delta-ve

The -NH2 of the base is delta+ve

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20
Q

What type of helix is shown by DNA?

A

A right-handed double helix

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21
Q

In what way do the two strands of a DNA molecule run?

A

Antiparallel, one 5’-3’ and one 3’-5’

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22
Q

What are the 5 stages of the cell cycle?

A

G1, S, G2, Mitosis (and G0)

23
Q

What happens in G1 of the cell cycle?

A

Cell content replication, e.g. Increase in organelle no.

24
Q

What happens in the S phase of the cell cycle?

A

DNA Replication

25
Q

What happens in the G2 phase of the cell cycle?

A

Double-checking/repair of the DNA

26
Q

What is the G0 phase of the cell cycle?

A

Cell cycle arrest

27
Q

Which enzyme catalyses the extension of the DNA nucleotide sequence in DNA replication? In which direction does it always work and extend the chain?

A

DNA polymerase

Reads in the 3’->5’ direction, producing a new 5’->3’ strand

28
Q

What are the 3 stages of DNA replication?

A

Initiation
Elongation
Termination

29
Q

Which enzyme provides the ‘kick-start’ for DNA replication? What does it do?

A

Primase

Synthesises a short RNA primer to begin DNA replication

30
Q

What is the name given to the fragments that make up the lagging strand? Which enzyme joins these fragments?

A

Okazaki fragments

DNA ligase

31
Q

Which enzyme unwinds the DNA double helix?

A

DNA helicase

32
Q

What causes DNA replication to stop?

A

When the two replication forks come together

33
Q

What stages make up the interphase of the cell cycle?

A

G1, S, G2

34
Q

What is cytokinesis? When does it occur?

A

Division of the cytoplasm. After telophase.

35
Q

How does DNA wrap around histones?

A

Loops around 8 histones twice to form a nucleosome

36
Q

Further packaging of the dna by forming coils of nucleosomes produces what?

What happens to these chromatin fibres in mitosis?

A

Chromatin fibres

Condense into chromosomes

37
Q

What are some clinical applications of nucleosides as drugs?

A

Often used as antiviral/anti cancer drugs

38
Q

Why are nucleosides often used instead of nucleotides as drugs?

A

Nucleosides can be phosphorylated in the cell anyway and don’t carry the -ve charge that a phosphate group has making them able to pass through the plasma membrane more easily

39
Q

What is an example of an antiviral nucleoside based drug? How does it work?

A

AZT

Lacks carbon-3 OH- group, no phosphodiester bonds formed, no dna elongation

40
Q

What are exonucleases?

A

Enzymes that cleave nucleotides from the END of a polynucleotide chain

41
Q

What are endonucleases?

A

Enzymes that cleave the polynucleotide chain at any point other than the end 2

42
Q

How does DNA polymerase repair mismatched nucleotides discovered during proofreading?

A

Using its exonuclease 3’->5’ proofreading domain

43
Q

What is the function of the enzyme topoisomerase?

A

Releases tension in the DNA helix as the helix is unwound

44
Q

When does replication slippage occur in dna replication?

A

When there is respective sequences of DNA

45
Q

What is replication slippage? What can it result in?

A

Results in the looping out of the strand and in the next S phase there will be an extra or omitted nucleotide

Can lead to the expansions/contractions of the DNA sequence

46
Q

By which method are single strand DNA breaks repaired?

A

Base excision repair

47
Q

Double stranded DNA breaks are the most dangerous type of DNA damage. How do mutations in the BRCA gene affect the repair of DSBs?

A

Can result in the persisting DSBs and defect in repairing —> cancer

48
Q

What gene is responsible for Huntington’s? In what way is this gene inherited?

A

HTT Gene

Autosomal Dominant

49
Q

Which mutation results in Huntington’s?

A

A triplet repeat expansion (CAG - glutamine)

50
Q

What is the normal amount of CAG repeats and the disease amount of CAG repeats?

A 
Normal = 6-39
Disease = 35-121
51
Q

High levels of DNA damage result in either…

A

Cancer or Ageing

52
Q

Mutations in which gene are often seen as the final step between pre-malignant to malignant cancer?

A

P53 mutations

53
Q

What is the result of Werner Syndrome? What inheritance does it show?

A

Premature ageing

Autosomal recessive

54
Q

What are the differences between the histone proteins in heterochromatin and euchromatin?

A 
Heterochromatin = histones are deacetylated 
Euchromatin = histones are acetylated

MCBG (15 decks)

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