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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
What happens in the G2 phase of the cell cycle?
Double-checking/repair of the DNA
26
What is the G0 phase of the cell cycle?
Cell cycle arrest
27
Which enzyme catalyses the extension of the DNA nucleotide sequence in DNA replication? In which direction does it always work and extend the chain?
DNA polymerase | Reads in the 3'->5' direction, producing a new 5'->3' strand
28
What are the 3 stages of DNA replication?
Initiation Elongation Termination
29
Which enzyme provides the 'kick-start' for DNA replication? What does it do?
Primase | Synthesises a short RNA primer to begin DNA replication
30
What is the name given to the fragments that make up the lagging strand? Which enzyme joins these fragments?
Okazaki fragments | DNA ligase
31
Which enzyme unwinds the DNA double helix?
DNA helicase
32
What causes DNA replication to stop?
When the two replication forks come together
33
What stages make up the interphase of the cell cycle?
G1, S, G2
34
What is cytokinesis? When does it occur?
Division of the cytoplasm. After telophase.
35
How does DNA wrap around histones?
Loops around 8 histones twice to form a nucleosome
36
Further packaging of the dna by forming coils of nucleosomes produces what? What happens to these chromatin fibres in mitosis?
Chromatin fibres Condense into chromosomes
37
What are some clinical applications of nucleosides as drugs?
Often used as antiviral/anti cancer drugs
38
Why are nucleosides often used instead of nucleotides as drugs?
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
What is an example of an antiviral nucleoside based drug? How does it work?
AZT | Lacks carbon-3 OH- group, no phosphodiester bonds formed, no dna elongation
40
What are exonucleases?
Enzymes that cleave nucleotides from the END of a polynucleotide chain
41
What are endonucleases?
Enzymes that cleave the polynucleotide chain at any point other than the end 2
42
How does DNA polymerase repair mismatched nucleotides discovered during proofreading?
Using its exonuclease 3'->5' proofreading domain
43
What is the function of the enzyme topoisomerase?
Releases tension in the DNA helix as the helix is unwound
44
When does replication slippage occur in dna replication?
When there is respective sequences of DNA
45
What is replication slippage? What can it result in?
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
By which method are single strand DNA breaks repaired?
Base excision repair
47
Double stranded DNA breaks are the most dangerous type of DNA damage. How do mutations in the BRCA gene affect the repair of DSBs?
Can result in the persisting DSBs and defect in repairing ---> cancer
48
What gene is responsible for Huntington's? In what way is this gene inherited?
HTT Gene | Autosomal Dominant
49
Which mutation results in Huntington's?
A triplet repeat expansion (CAG - glutamine)
50
What is the normal amount of CAG repeats and the disease amount of CAG repeats?
``` Normal = 6-39 Disease = 35-121 ```
51
High levels of DNA damage result in either...
Cancer or Ageing
52
Mutations in which gene are often seen as the final step between pre-malignant to malignant cancer?
P53 mutations
53
What is the result of Werner Syndrome? What inheritance does it show?
Premature ageing | Autosomal recessive
54
What are the differences between the histone proteins in heterochromatin and euchromatin?
``` Heterochromatin = histones are deacetylated Euchromatin = histones are acetylated ```

MCBG (15 decks)

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