DNA Structure Flashcards

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1
Q

What are the four bases found in DNA?

A

Adenine, Thymine, Cytosine and Guanine

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2
Q

Which two bases are the purines?

A

Adenine and Guanine are the larger purines

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3
Q

Which bases are the pyrimidines?

A

Cytosine and Thymine are the smaller pyrimidines (also Uracil in RNA)

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4
Q

How many rings do purines have?

A

Two

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5
Q

How many rings do pyrimidines have?

A

One

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6
Q

How many hydrogen bonds are formed between Cytosine and Guanine?

A

Three

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7
Q

How many hydrogen bonds are formed between Adenine and Thymine?

A

Two

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8
Q

Which form of chromatin stains lightly?

A

Euchromatin

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9
Q

Which form of chromatin stains dark?

A

Heterochromatin

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10
Q

What is a nucleosome?

A

A nucleosome consists of a length of DNA wrapped around a histone core

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11
Q

What is the ‘beads on a string’ structure?

A

This is where DNA is wrapped around 8 histones twice to form nucleosomes (euchromatin)

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12
Q

What is the solenoid stucture?

A

This is where the DNA is packaged as a 30nm fibre of chromatin as a result of the helical winding of nucleosomes (heterochromatin)

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13
Q

In which form of chromatin are genes expressed?

A

Euchromatin (beads on a string)

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14
Q

In which form of chromatin are genes not expressed?

A

Heterochromatin (solenoid)

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15
Q

How many chromosomes are in a human diploid cell?

A

46 chromosomes (23 pairs)

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16
Q

How many chromosomes are in a human haploid cell (gamete)?

A

23 chromosomes

17
Q

What is a gene?

A

A gene is a sequence of nucleotides that carries the code for proteins. They have a specific chromosomal location.

18
Q

What is the human genome?

A

The entire DNA sequence of a human

19
Q

How many chromosomes in the human genome?

A

24 (22 autosomes plus X and Y)

20
Q

What is a nucleotide?

A

Base + Sugar + Phosphate

21
Q

What is a nucleoside?

A

Base + Sugar (no phosphate)

22
Q

What are the two types of pentose sugars?

A

Ribose (in RNA) and Deoxyribose (in DNA)

23
Q

For example, what is the nucleoside and nucleotide associated with Adenine in RNA and DNA?

A

Nucleoside in RNA = Adenosine
Nucleotide in RNA = Adenosine monophosphate (AMP)

Nucleoside in DNA = Deoxyadenosine
Nucleotide in DNA = Deoxyadenosine monophosphate (dAMP)

24
Q

By what bonds are adjacent nucleotides joined?

A

Phosphodiester bonds

25
Q

The DNA chain has polarity. What are the two ends called?

A

It goes from 5’ to 3’. 5’ is the phosphate end and 3’ is the end with the OH

26
Q

Name two features of the two strands of DNA

A

Complementary and anti-parallel

27
Q

How long is DNA vs what is the size of a cell nucleus?

A

2 metres of DNA into a 6 micrometre cell nucleus

28
Q

What is the width of DNA?

A

2 nanometres

29
Q

What is the total length of DNA per cell?

A

2 metres

30
Q

What is on the 5’ end?

A

Phosphate

31
Q

What is on the 3’ end?

A

OH

32
Q

What is the difference between the major and minor groove?

A

The major groove occurs where the backbones are far apart, the minor groove occurs where they are close together.

33
Q

Which groove of the DNA is easier for proteins to bind to?

A

Major groove because the backbones are not in the way.

34
Q

How many base pairs in one complete turn?

A

10

35
Q

What is the space between the base pairs?

A

0.34nm

36
Q

In which groove are bases exposed?

A

Major