Nucleic acids

Question 1

Bases in DNA

Answer 1

adenine, guanine, cytosine, thymine

Question 2

Bases in RNA

Answer 2

adenine, guanine, cytosine , uracil

Question 3

Difference in base pairing in nucleic acids

Answer 3

Adenine - thymine or uracil form 2 hydrogen bonds between them

Guanine - cytosine form 3 hydrogen bonds between them

Question 4

Differences between DNA and RNA

Answer 4

In DNA, two long polynucleotide chains form a double helix, whereas in RNA is consists of one single helix short polynucleotide chain

RNA has uracil as a nitrogenous base rather than thymine

Question 5

What does semi conservative DNA replication mean and why is it important

Answer 5

One strand of one of the new DNA chain is from the original DNA, and the other is a newly synthesised strand

it ensures that the genetic code remains identical between generations of cells

Question 6

Whole process of semi-conservative replication

Answer 6

• DNA helicase will unzip the original DNA strand by breaking the H bonds between all the bases leaving two separate template strands
• New free DNA nucleotides will attach to the exposed bases on the template strands by complementary base pairing
• DNA polymerase will join adjacent nucleotides 5’-3’ to form phosphodiester bonds on the new strand of nucleotides

Question 7

Why is DNA antiparallel

Answer 7

as the sugar phosphate backbone runs 3’-5’ up one strand and 3’-5’ down the other strand

Question 8

What is the meselson-stahl experiment

Answer 8

Its evidence for semi-conservative replication

Added DNA of E coli in two separate test tubes in and grew them in 14n and 15n nitrogen isotopes.

then allowed DNA to replicate one generation to allow nitrogen isotopes to be incorporated into the DNA

then took a sample from each test tube and grew them together and allowed one generation of replication

then took all three tubes and spun in a centrifuge to allow DNA to form bands

14n showed a band at the high point

15n showed a band at a lower point

14n+15n showed a band in between, suggesting that the replication was semi conservative as both isotopes of nitrogen were incorporated into the DNA

Question 9

Structure of ATP

Answer 9

Adenine, ribose and 3 phosphates

adenosine triphosphate

Question 10

what is ATP broken into and how

Answer 10

ADP + Pi

its hydrolysed using the enzyme ATP hydrolase

Question 11

How is ATP synthesised

Answer 11

ADP + Pi = ATP

Condensation reaction to form a bond between to inorganic phosphates using the enzyme ATP synthase

Question 12

Adaptation of ATP (x2)

Answer 12

• it can be rapidly resynthesized after it has been broken down so can be recycled to be used in various functions in the body
• the inorganic phosphate can phosphorylate other compounds to make them more reactive

Question 13

Properties of ATP (x4)

Answer 13

-Releases small amounts of energy at a time to prevent cell death by heat as energy can be wasted through heat

• cannot leave the cell that it is synthesised in, so is constantly available for use in respiration
• it is an immediate source of energy as hydrolysis of ATP involves only 1 step
• Is soluble