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m > Unit 1: Human Cells - Key Area 2 - Structure and replication of DNA > Flashcards

Unit 1: Human Cells - Key Area 2 - Structure and replication of DNA Flashcards

1
Q

What does DNA consist of?

A

Units called nucleotides

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2
Q

What are nucleotides made of?

A

Phosphate, deoxyribose sugar and a base

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3
Q

What forms the genetic code?

A

The base sequence

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4
Q

What holds each strand of DNA together?

A

Each individual strand of DNA is held together by a strong chemical bond between the phosphate of one nucleotide and the carbon 3 of the sugar, on another nucleotide.

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5
Q

What holds the bases in adjacent strands together together and what does this cause?

A

Weak hydrogen bonds hold the bases together and makes it coil into a double helix structure.

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6
Q

What does the 3’ end of a DNA strand have?

A

A deoxyribose sugar

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7
Q

What does the 5’ end of a DNA strand have?

A

A phosphate

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8
Q

What end can nucleotides only be added to?

A

The 3’ end.

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9
Q

How many different nucleotides are there and what causes them to be different?

A

There are 4 different nucleotides, depending on the base they have.

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10
Q

What are the 4 different bases?

A

Adenine, Cytosine, Guanine and Thymine

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11
Q

What do the 2 DNA strands have running in different directions?

A

Their phosphate backbone.

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12
Q

What is the double helix described as having?

A

The Double helix is described as having two anti - parallel chains of nucleotides because one side goes from 5’ to 3’ and the opposite side goes from 3’ to 5’.

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13
Q

What is DNA arranged in?

A

Tightly coiled chromosomes.

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14
Q

What is DNA polymerase and what is it’s function?

A

DNA polymerase is an enzyme that controls the formation of the sugar phosphate bonding of the nucleotides into the DNA strand. This enzyme can also add nucleotides to the 3’ end of a growing DNA chains, but only add nucleotides to a pre existing chain so for it to work a primer must be present.

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15
Q

What is a primer?

A

A short sequence of nucleotides at the 3’ end.

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16
Q

What strand has to be replicated in fragments?

A

The 5’ end.

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17
Q

What is the 5’ end also called and why is this?

A

The lagging strand as it has to be replicated in fragments and is slower than the 3’ end.

18
Q

What is the 3’ end also called?

A

The leading strand.

19
Q

What is ligase and what does it do?

A

Ligase is an enzyme that joins all the DNA fragments together once they are all in place.

20
Q

For DNA replication to occur, what must the nucleus contain?

A

Primers, DNA (Template), Enzymes(Ligase and DNA Polyemrase), ATP and Nucleotides (the 4 types).

21
Q

Where does DNA replication occur?

A

In the nucleus.

22
Q

What is the first thing that happens to the DNA molecule in the DNA replication process?

A

A DNA molecule unwinding.

23
Q

What happens to the DNA molecule after it has unwound in DNA replication?

A

The hydrogen bonds between the adjacent bases are broken and these bases act as a template for a new DNA strand to be made.

24
Q

What happens after the nucleotides are exposed in DNA replication?

A

Free floating nucleotides in the nucleus join on to their complementary bases. and this happens simultaneously along the DNA strand.

25
Q

Which end of the DNA can nucleotides be added to?

A

3’ end

26
Q

How do you know which end of a DNA strand is the 5’ end?

A

It is joined to a phosphate.

27
Q

Why is DNA replication important?

A

DNA replication is important so that When cells divide they have to have the correct genetic information they need to function properly and that no information is lost.

28
Q

Why is a primer needed in DNA replication?

A

A primer is needed in DNA replication because DNA polymerase can only add nucleotides to a pre existing chain.

29
Q

What is the function/ what does PCR do?

A

PCR amplifies DNA. ( It creates many copies of a piece of DNA in vitro (outside of the body)).

30
Q

What does the amplification of DNA involve the use of?

A

The amplification of DNA involve the use of primers. Each primer is a short strand of DNA complementary to a specific target sequence at the 3’ end of the strand to be replicated.

31
Q

What are the steps involved in PCR?

A

• DNA is heated to seperate/denature the DNA stands. • It is then cooled to allow the primers to bind to the target sequence of DNA. • Heat tolerant DNA polymerase then adds nucleotides to the primers (at the 3’ end of the original DNA strands). • Repeated cycles of heating and cooling amplify the region of DNA. • The first cycle of replication produces 2 identical; DNA molecules, the second produces 4 molecules and so on and in an hour a short length can become a million.

32
Q

What is the first process of PCR called which is carried out at 94 - 96 degrees celsius?

A

Denaturation/separation.

33
Q

What happens in the first stage of PCR?

A

The DNA is heated so it is denatured and the weak hydrogen bonds between the bases are broken to leave to single strands.

34
Q

What is the second process of PCR called where the temperature are cooler at around 68 degrees celsius?

A

Annealing

35
Q

What is the last process of PCR called which is carried out about 72 degrees celsius?

A

Elongation

36
Q

What are practical uses of PCR?

A

• Solve crimes - if not enough DNA is found to work on it can be amplified so the forensics people have more to work with (DNA profiling). • Diagnosing genetic disorder - testing for cystic fibrosis etc. • Settiling paternity disputes using (DNA profiling).

37
Q

What is the role of ligase?

A

Joins fragments of DNA at the 5’ end strand/ lagging strand.

38
Q

What is the role of DNA polymerase?

A

Adds nucleotides to the 3’ end of a strand when there is a pre existing chain and primer.

39
Q

The 5’ end is replicated in fragments, whilst the 3’ end strand is replicated continuously. Explain why the strands are replicated in different ways?

A

DNA polymerase can only add nucleotides at the 3’ end of a growing strand.

40
Q

As a result of DNA replication what happens to the DNA content of a cell?

A

It is doubled.

41
Q

What happens to the primers in the second stage of PCR?

A

The primers bind or anell to the target sequence of DNA.

42
Q

Why is the temperature raised again in the third process of PCR?

A

So the temperature is closer to the optimum temperature for DNA polymerase to add nucleotides to the primers.

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