Unit 1: human cells- Structure and replication of DNA Flashcards Preview

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Flashcards in Unit 1: human cells- Structure and replication of DNA Deck (25)
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What does DNA consist of?

Units called nucleotides.


What are nucleotides made of?

Phosphate, deoxyribose sugar and a base.


What forms the genetic code?

The base sequence.


What holds each strand of DNA together?

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.


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

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


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

A deoxyribose sugar.


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

A phosphate.


What end can nucleotides only be added to?

The 3' end.


What are the 4 different bases?

Adenine, Guanine, Cytosine and Thymine.


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

The phosphate backbone.


What is the double helix described as having?

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


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

DNA polymerase is an enzyme that controls the formation of the sugar phosphate bonding of the nucleotides into the DNA stand. This enzyme can also add nucleotides to the 3' end of a growing DNA chain.


What is a primer?

A short sequence of nucleotides at the 3' end.


What strand has to be replicated in fragments?

The 5' end.


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

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


What is the 3' end also called?

The leading strand.


What is ligase and what does it do?

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


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

Primers, DNA (template), enzymes ( DNA polymerase and ligase), ATP and nucleotides.


Where does DNA replication occur?

In the nucleus.


Why is DNA replication important?

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


Why is a primer needed in DNA replication?

A primer is needed in DNA replication because DNA polymerase can only add nucleotides to the 3' end.


What is the function of PCR/ what does PCR do?

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


What are the steps involved in PCR?

1) DNA is heated to break the hydrogen bonds and separate the strands.

2) it is then cooled to allow primers to bind to the target sequence of DNA.

3) Heat tolerant DNA polymerase then adds nucleotides to the primers ( at the 3' end of the original DNA strands).


What are practical uses of PCR?

- solve crimes ( if not enough DNA is found to work on, it can be amplified so the forensics people have more to work with i.e. DNA profiling)

- diagnosing genetic disorder

- paternity tests


What is the role of ligase?

Joins fragments of DNA at the 5' end of the lagging strand.