3.1 Biological Molecules - DNA, RNA

Question 1

what does DNA stand for?

Answer 1

deoxyribonucleic acid

Question 2

what does RNA stand for?

Answer 2

ribonucleic acid

Question 3

what is the role of DNA?

Answer 3

stores genetic information

Question 4

what is the role of RNA?

Answer 4

to transfer genetic information from DNA to ribosomes

Question 5

what are ribosomes made of?

Answer 5

RNA and proteins

Question 6

what are DNA and RNA polymers of?

Answer 6

nucleotides

Question 7

what are the elements of a nucleotide?

Answer 7

a pentose sugar, a nitrogenous base and a phosphate group

Question 8

what are the 5 bases?

Answer 8

adenine
thymine
guanine
cytosine
uracil

Question 9

which 4 bases are found in DNA, what are there complementary pairs and how many H bonds are formed between them?

Answer 9

adenine and thymine are complementary and 2H bonds form between them
guanine and cytosine are complementary and 3H bonds form between them

Question 10

what do all nitrogenous bases contain?

Answer 10

carbon
hydrogen
oxygen
nitrogen

Question 11

which bases are classed as pyramidines (single carbon ring)?

Answer 11

cytosine
thymine
uracil

Question 12

which bases are classed as purines (double carbon ring)?

Answer 12

guanine
adenine

Question 13

which 4 bases are found in RNA, what are there complementary pairs?

Answer 13

adenine is complementary to uracil
guanine is complimentary to cytosine

Question 14

how are dinucleotides formed?

Answer 14

from a condensation reaction between 2 nucleotides forming a phosphodiester bond between the phosphate group on 1 nucleotide and the C3 on the pentose sugar on the other

Question 15

what enzyme catalyses the reaction joining adjacent nucleotides through a phosphodiester bond in a condensation reaction?

Answer 15

DNA polymerase

Question 16

which has a relatively short polypeptide chain, DNA or RNA?

Answer 16

RNA

Question 17

describe the DNA structure

Answer 17

2 polynucleotide strands are antiparallel. 2 antiparallel strands twist to form a DNA double helix structure

Question 18

what does DNA do before cell division, why does it do this and what is this process called?

Answer 18

DNA replicates itself before cell division so each new cell has the full amount of DNA, this process is called semi-conservative replication

Question 19

what enzyme breaks the hydrogen bonds between bases in semi-conservative replication?

Answer 19

DNA helicase

Question 20

what is the first step in semi-conservative replication?

Answer 20

DNA helicase breaks the hydrogen bonds between bases on the 2 polynucleotide DNA strands causing the helix to unwind to form 2 single strands

Question 21

what is the second step in semi-conservative replication?

Answer 21

each original single strand acts as a template for a new strand, complementary base pairing means that free floating DNA nucleotides are attracted to their complementary exposed bases on each original template strand

Question 22

what is the third and final step in semi-conservative replication?

Answer 22

condensation reactions joint nucleotides of the new strand together catalysed by the enzyme DNA polymerase, hydrogen bonds form between the bases on the original and new strands

Question 23

what does each DNA molecule contain after semi-conservative replication?

Answer 23

one strand from the original DNA molecule and one new strand

Question 24

what is either end of a DNA strand called and why?

Answer 24

they are slightly different in structure, one end is called the 3’ end and one is the 5’ end, this depends on which end the pentose sugar is facing

Question 25

which end of the DNA strand is the active site of DNA polymerase complementary to?

Answer 25

the 3' end OF THE NEWLY FORMING DNA STRAND

Question 26

which direction is the newly forming DNA strand made?

Answer 26

from 5' to 3'

Question 27

which direction does the enzyme move on the template strand?

Answer 27

from 3' to 5'

Question 28

the DNA polymerase on one strand works in the opposite direction of the DNA polymerase on the other strand why?

Answer 28

because the strands in the double helix and antiparallel and DNA polymerase is only complementary to the 3' end and therefore works in a 5' to 3' direction

Question 29

which scientists determine the structure of DNA and the theory for semi-conservative replication?

Answer 29

Watson and crick

Question 30

what is conservative replication?

Answer 30

the original copy of DNA creates an 1 exact copy containing 2 original stands and one 1 copy containing 2 newly formed strands (2 daughter strands)

Question 31

what does the semi-conservative replication experiment by meselson and stahl prove?

Answer 31

that a strand of DNA replicates itself form 2 DNA structures each containing one original strand and one new strand (one parent strand and one daughter strand)

Question 32

describe the meselson and stahl experiment proving semi-conservative replication

Answer 32

1. Two samples of bacteria were grown for many generations: One in a medium containing the heavy isotope ¹⁵N. The other in a medium containing the lighter isotope ¹⁴N. 2. As the bacteria reproduced, they used the nitrogen from the medium to make nucleotides for new DNA. Over time, the nitrogen became part of the bacterial DNA. 3. A sample of DNA was taken from each group and spun in a centrifuge: DNA from the ¹⁵N bacteria settled lower in the tube (heavier). DNA from the ¹⁴N bacteria settled higher (lighter). 4. Bacteria originally grown in the ¹⁵N medium were then transferred to a medium containing only ¹⁴N. 5. The bacteria were allowed to undergo one round of DNA replication in the ¹⁴N medium. 6. Another sample of DNA was taken and spun in a centrifuge. 7. The DNA now settled in the middle of the tube, showing it contained a mixture of heavy and light nitrogen.

Question 33

describe what the result of the experiment would have been if DNA underwent conservative replication

Answer 33

the original heavy DNA -15N- would have still been together and would gave seated towards the bottom and the new light DNA would settle towards the top - there would be 2 lines