Unit 1: Nucleic Acids

Question 1

what is a nucleic acid made up of?

Answer 1

nucleotides

Question 2

what are the differences between DNA and RNA

Answer 2

DNA - double stranded, deoxyribose sugar, bases A,T,C,G

RNA - single stranded, ribose sugar, bases A,U,C,G

Question 3

Why are hydrogen bonds important in base pairing?

Answer 3

A hydrogen bond is weak, this means that its relatively easy for these bonds to be formed and broken. This is very important if information is to be copied from a sequence of bases as in during DNA replication

Question 4

what is a nucleotide made up of?

Answer 4

nitrogen containing ring (base)
five carbon sugar (pentose)
phosphate

Question 5

what is attached to C1 in a nucleotide?

Answer 5

base

Question 6

what is attached to C2 in a nucleotide?

Answer 6

Hydrogen or Hydroxyl group

Question 7

what is attached to C3 in a nucleotide?

Answer 7

hydroxyl group

Question 8

what is attached to C5 in a nucleotide?

Answer 8

phosphate

Question 9

what are the two main types of bases called?

Answer 9

purines and pyrimidines

Question 10

what is a purine?

Answer 10

base that has a double ring structure - adenine and guanine

Question 11

what is a pyrimidine?

Answer 11

base that has a single ring structure - cytosine and thymine/uracil

Question 12

what is the trick to remember Purine and Pyrimidine?

Answer 12

Pure Agony

Question 13

what bond holds complementary base pairs together?

Answer 13

weak hydrogen bonds

Question 14

For the hydrogen bond to be stable, what must each base be?

Answer 14

the base pair must consist of one purine and one pyrimidine

Question 15

how are nucleotides joined together?

Answer 15

by condensation reaction between phosphate of one nucleotide and the hydroxyl group on the sugar of the next nucleotide. link by 5’ to 3’

Question 16

what is the bond between nucleotides called?

Answer 16

phosphodiester bond

Question 17

are the double strands in DNA, parallel or antiparallel?

Answer 17

antiparallel

Question 18

what is polymerase?

Answer 18

an enzyme capable of adding nucleotides to a DNA strand during replication or an RNA strand during transcription

Question 19

what is ligase?

Answer 19

an enzyme that catalyses the formation of phosphodiester bonds to join nucleotides together.

Question 20

what is the purpose of copying DNA?

Answer 20

for DNA replication during the S phase of the cell cycle

for transcription of DNA and RNA during protein synthesis

Question 21

what is the difference between replication and transcription?

Answer 21

new strand of nucleic acid can only happen in 5’ to 3’ direction because of the polymerase enzyme, so can only add on 3’
RNA - one strand
DNA - double strand so 5’ to 3’ and 3’ to 5’ need to be replicated

Question 22

what are the requirements for DNA replication?

Answer 22

DNA template
enzymes
four types of nucleotide
ATP

Question 23

DNA polymerase and RNA polymerase can only build in a what direction?

Answer 23

5’ to 3’

Question 24

What are the steps in DNA replication?

Answer 24

1. Enzymes open up a replication fork in the DNA double helix
2. the leading strand is synthesised complete in the 5’ to 3’ direction
3. replication starts with a short RNA primer, this is replaced with DNA later
4. DNA polymerase adds a new nucleotide to the 3’ end of the primer and so starts to build the new DNA chain
5. DNA polymerase matches free DNA nucleotides to their complementary bases on the template strand of DNA and then catalyses the formation of the phosphodiester bond between the end of the growing strand and the nucleotides
6. The phosphodiester bond is formed when the OH of the 5’ phosphate and the OH of the 3’ deoxyribose are involved in a condensation reaction
7. The other strand is called a lagging strand and is made in short 5’ to 3’ fragments (okazaki fragments)
8. as on the leading strand, the RNA primers are made first and DNA polymerase adds nucleotides to the 3’ end.
9. After the RNA primer has been replaced with DNA, DNA ligase links to 5’ to 3’ fragments of the lagging strand together and catalyses the formation of phosphodiester bonds between the nucleotides at the end of the fragments.

Question 25

what bond is between a phosphate and a sugar in a nucleotide?

Answer 25

phosphoester bond

Question 26

what is the difference between an Ribose and a Deoxyribose sugar?

Answer 26

RNA has an OH on carbon 2 whereas DNA has an H on carbon 2

Question 27

How many hydrogen bonds are there between cytosine and guanine?

Answer 27

3

Question 28

How many hydrogen bonds are there between adenine and thymine?

Answer 28

2