Nucleic Acids

Question 0

What has to happen to DNA before it can read in to proteins?

Answer 0

DNA had to be copied into RNA

Question 1

What is DNA used for?

Answer 1

Storing information.

Question 2

What are nucleic acids made up of?

Answer 2

Nucleotides

Question 3

What makes up DNA?

Answer 3

A phosphate, a sugar and a nitrogenous base.

Question 4

How is the phosphate attached to the sugar?

Answer 4

Phosphoester bond.

Question 5

What is the sugar in DNA and RNA?

Answer 5

DNA deoxyribose, RNA ribose.

Question 6

What is the difference between the two sugars?

Answer 6

The H and OH attached to Carbon 2 (2’).

Question 7

The bases come in two different forms what are these?

Answer 7

Purines are adenine and guanine (they are double ringed) and pyrimidines are cytosine, uracil and thymine (they are single ringed).

Question 8

What are the nucleotides on DNA and RNA?

Answer 8

Both have guanine, cytosine and adenine but DNA has thymine and RNA uracil.

Question 9

What is a double helix?

Answer 9

Were to strands of nucleotides are twisted together to make a twin spiral or double helix.

Question 10

What are the strands made up of?

Answer 10

A backbone made of deoxyribose sugars linked to phosphates by phosphodiester bonds.

Question 11

What does the phosphodiester bond link?

Answer 11

The phosphate of carbon 5 (5’) to carbon 3 (3’) of the next nucleotide. This means that strands of nucleotides have polarity with 5’ at one end and 3’ at other.

Question 12

Why is the 5’ to 3’ polarity important?

Answer 12

As the two strands of the double helix run in opposite directions they are antiparrallel.

Question 13

What links the two strands?

Answer 13

By ‘rungs’ made of a pair of bases, one from each strand. The bases in each pair are linked by hydrogen bonds.

Question 14

How many hydrogen bonds do each set of base pairs have?

Answer 14

A+T=2

C+G=3

Question 15

Explain RNA?

Answer 15

The nucleotide strand had a 5’ at one end and 3’ at other. The strand may be looped back on itself to form based-paired regions, but it is still a single strand of nucleotides.

Question 16

What is nucleic acid synthesised for?

Answer 16

DNA replication during S phase of the cell cycle

Transcription of DNA to RNA during protein synthesis.

Question 17

How does synthesis of the new strand happen?

Answer 17

Synthesis of a new strand of nucleic acid can only happen in the 5’ to 3’ direction because the polymerase enzyme can only add new nucleotides on to the 3’ end of a nucleotide. The transcription of RNA only requires one strand to be made, so RNA polymerase can start at one point and build a 5’ to 3’ messenger RNA strand. But DNA replication requires both strands to be copied (one going 5’ to 3’, the other going 5’ to 3’), so something special had to happen.

Question 18

How does DNA replication start?

Answer 18

Enzymes open up a replication fork in the DNA double helix. Then the leading strand is synthesised complete in the 5’ to 3’ direction as the fork opens. Replication starts with the synthesis of a short RNA primer; this is replaced with DNA later. DNA polymerase as new DNA nucleotide to the 3’ end of the primer and so starts to build the new DNA chain. DNA polymerase marches free DNA nucleotides to their complementary bases on the template strand of DNA and the catalyses the formation of the phosphodiester bond between the end of the growing strand and the new nucleotide. This phosphodiester bond is formed when the OH of the 5’ phosphate and OH of the 3’ of deoxyribose are involved in the condensation reaction.

Question 19

What happens on the lagging strand?

Answer 19

It is made in short 5’ to 3’ fragments (Okazaki fragments). As on the leading strand, RNA primers are made first and DNA polymerase adds nucleotides on to the 3’ end. After the RNA primer has been replaced with DNA, then DNA ligase links the 5’ to 3’ fragments in the lagging strand together by catalysing the formation of phosphodiester bonds between the nucleotides at the end of the fragments.