Nucleic Acids, DNA & ATP

Question 1

What are nucleotides?

Answer 1

Monomers that are the building blocks of DNA.

Question 2

What is the basic structure of a nucleotide?

Answer 2

• ribose sugar (joined to…)
• phosphate group
• nitrogenous base

Question 3

What are the 5 different bases?

Answer 3

• Guanine (G)
• Thymine (in DNA) / Uracil (in RNA) (T)
• Adenine (A)
• Cytosine (C)

Question 4

What are purines?

Answer 4

Larger bases with double rings of C and N - cytosine, thymine / uracil.

Question 5

What are pyrimidines?

Answer 5

Smaller bases with single rings of C and N - adenine, guanine.

Question 6

What are DNA and RNA both examples of?

Answer 6

Nucleic acids

• DNA is deoxyribonucleic acid as it’s ribose sugar is dexoyribose.
• RNA is ribonucleic acid as it’s ribose sugar is ribose.

Question 7

What are DNA and RNA?

Answer 7

They are both long chain polymers made up of many individual nucleotides.

Question 8

What are the main other differences between DNA and RNA?

Answer 8

• DNA is a double stranded molecule, RNA is single stranded
• DNA has hydrogen bonding, RNA does not
• DNA has a complementary base pairing, RNA does not

Question 9

How are DNA and RNA chemically different?

Answer 9

Deoxyribose sugar has one less oxygen than ribose sugar. It has a H atom attached to it, where ribose sugar has a hydroxyl (OH).

Question 10

How do nucleotides join?

Answer 10

Nucleotides join via a condensation reaction to form a phosphodiester bond. They are attached between the sugar of one nucleotide and the phosphate of another.

The chain of sugars and phosphates is known as the sugar-phosphate backbone.

Question 11

How are polynucleotides broken back down?

Answer 11

They are broken back into nucleotides by breaking the phosphodiester bonds in a hydrolysis reaction.

Question 12

How does a DNA molecule’s double helix work?

Answer 12

The two strands of the double helix are held together by hydrogen bonds between the bases. Each strand has a phosphate group at one end and a hydroxyl group at the other.

They are arranged so they run in opposite directions and are said to be “antiparallel”.

Question 13

What are the complementary base pairings in DNA?

Answer 13

Adenine and Thymine / Uracil
Cytosine and Guanine

Question 14

Why does adenine form a complementary base pairing with thymine / uracil?

Answer 14

They are both able to form two hydrogen bonds.

Question 15

Why does cytosine form a complementary base pairing with guanine?

Answer 15

They are both able to form three hydrogen bonds.

Question 16

What do complementary base pairings mean?

Answer 16

DNA always has equal amounts of adenine + thymine, and cytosine + guanine.

Small pyrimidine bases always bind to larger purine bases, resulting in parallel polynucleotide chains.

Question 17

How does the structure of DNA relate to it’s function?

Answer 17

• sugar-phosphate backbone - DNA is strong and stable
• many hydrogen bonds - provides strength and stability
• weak hydrogen bonds - strands can be separated during DNA replication
• double stranded - bases are protected and replication can be semi-conservative
• long polymer - can store lots of genetic information
• double helix - compact
• bases in sequence - allows accurate DNA replication

Question 18

What is DNA replication?

Answer 18

DNA copies itself before cell division so that each new cell has the full amount of DNA.

Question 19

Why is DNA replication important?

Answer 19

• making new cells for growth and repair
• passing on important between generations (reproduction)
• DNA replicate must be an exact copy to form two sister chromatids

Question 20

What does DNA helicase do?

Answer 20

DNA helicase attaches to the DNA molecule and causes the hydrogen bonds between complementary bases to break. This separates two polynucleotides.

Question 21

How does a new DNA strand form?

Answer 21

Free activated nucleotides line up with their complimentary bases on the DNA. They are only held in place by hydrogen bonds and not by phosphodiester bonds.

Question 22

Why are free nucleotides “activated”?

Answer 22

They contain three phosphates as opposed to one.

Question 23

What does DNA polymerase do?

Answer 23

DNA polymerase moves down the strand, catalysing the formation of phosphodiester bonds between activated nucleotides.

The extra two phosphate groups leave the nucleotides to provide energy for the reaction.

Question 24

What is meant by semi-conservative replication?

Answer 24

The new DNA strand contains one original strand and one new strand.

Question 25

What happens when copying is incorrect?

Answer 25

Incorrect copying can be random and spontaneous, which can lead to genetic mutations.

Question 26

What is ATP?

Answer 26

Adenosine Triphosphate

Question 27

What is the structure of ATP?

Answer 27

• ribose sugar
• nitrogenous base adenine
• 3 phosphate groups

This makes ATP a nucleotide

Question 28

What does ATP do?

Answer 28

It allows for energy from glucose to be transferred in smaller, more useful amounts.

Question 29

Why are ATP molecules useful for transferring energy?

Answer 29

A very small amount of energy is needed to break the covalent bonds between the phosphate groups, but they release a large amount of energy.

This is a hydrolysis reaction.

Question 30

What is the reaction for the hydrolysis of ATP?

Answer 30

ATP + water –> ADP + Pi + energy

Question 31

What is ADP?

Answer 31

Adenosine Diphosphate

Question 32

What does the “i” mean in the phosphate group?

Answer 32

It means the phosphate group is inorganic as it does not contain carbon.

Question 33

What enzyme catalyses ATP hydrolysis?

Answer 33

ATPase / ATP hydrolase

Question 34

What is ATP needed for?

Answer 34

• active transport
• muscle contraction
• forming larger molecules in anabolic reactions

Question 35

What is meant by phosphorylated reaction?

Answer 35

ADP and the phosphate are recycled back to ATP during respiration and photosynthesis.

It is a condensation reaction catalysed by ATP synthase.

Question 36

What are the three key parts of DNA purification?

Answer 36

• breaking (lysing) the cells and disrupting the nuclear membranes to release the DNA
• using enzymes to denature and remove associated proteins
• precipitating the DNA using an organic solvent

Question 37

Describe the process of DNA purification (1):

Answer 37

1. Place ethanol in a freezer 24 hours before starting - must be ice cold.
2. Cut onion into small pieces (5mm x 5mm).
3. Add 10cm3 washing up liquid to 90cm3 tap water in a beaker. Add some of the onion pieces.
4. Place water in a 60°C water bath for 15 minutes.
5. Cool mixture in ice water bath for 5 mins and stir continually - important in preventing breakdown of DNA. Constant stirring ensures the whole mixture has cooled.

Question 38

Why does the sample need to be placed in a 60°C water bath?

Answer 38

The detergent and heat disrupt the cellular membranes’ phospholipid bilayer - DNA is released.

The heat also denatures enzymes released by the cell.

Question 39

Describe the process of DNA purification (2):

Answer 39

6. Blend mixture for 5 seconds - further breakdown of membranes but does not break DNA.
7. Use filter paper to filter into another beaker - removes cell debris and membrane fragments. The filtrate contains DNA and associated proteins.
8. Pour 10cm3 into a test tube and add protease - denatures and removes proteins.
9. Add ice cold ethanol and wait 2-3 minutes - nucleic acids insoluble in ethanol so DNA forms a precipitate at the top of the mixture.