Chapter 2 - Nucleic Acids

Question 1

What are nucleic acids - list the three examples and what they do.

Answer 1

• important info carrying molecules

1. DNA (deoxyribosenucleic) holds genetic information
2. RNA (ribonucleic) transfer genetic information from DNA to the ribosomes during protein synthesis.
3. Ribosomes formed from RNA and proteins

Question 2

What is the common structure of DNA and RNA?

Answer 2

• both polymers of nucleotides
  Formed from: a pentose (deoxyribose or ribose), a nitrogen containing organic base, and a phosphate group.

Question 3

What sort of bond is formed from the condensation of two nucleotides?
Describe the structure diagram

Answer 3

Phosphodiester bond

              O
              |
      -O - P = O
              |
              O

Question 4

Describe what DNA is like

Answer 4

• a relatively long double helix, with 2 polynucleotide chains held together by hydrogen bonds between specific complementary bases. (Pair up to form base pairs)
• it is double stranded, and the strands run anti parallel to each other.

E.G. ADENINE always with THYMINE, and, GUANINE always with CYTOSINE.

Question 5

Describe the role of sugar phosphate backbone, and hydrogen bonds in DNA

Answer 5

Makes molecule VERY stable
- Sugar phosphate backbone protects organic bases from chemical attack
- Hydrogen bonds between complementary bases HOLDS strands together (individually weak but collectively strong)

Question 6

What is RNA? What’s the difference in bases between RNA and DNA

Answer 6

• relatively short single stranded polynucleotide chain

In RNA: URACIL is used instead of THYMINE

Question 7

What does the term semi - conservative refer to?

Answer 7

• each strand of DNA acts as a template for replication
• so every DNA molecule is made of 1 original and 1 new strand

Question 8

Describe the process of semi - conservative replication of DNA [5]

Answer 8

1. The enzyme DNA HELICASE unwinds the double helix
2. DNA HELICASE then breaks hydrogen bonds between complementary bases of the polynucleotide strands. Strands then unzip
3. Free DNA nucleotides then attracted to exposed bases on template strands and complementary base pairing occurs via hydrogen bond formation.
4. Enzyme DNA POLYMERASE joins adjacent nucleotides via a condensation reaction = phosphodiester bonds + a new sugar-phosphate backbone
5. Allows new DNA strand to grow until complete

Question 9

How is DNA adapted for semi - conservative replication? [3]

Answer 9

• easily broken hydrogen bonds between bases allows strands to separate easily
• 2 strands so both act as templates
• complementary base pairing allows accurate replication

Question 10

What is ATP made up of?

Answer 10

Adenosine triphosphate (1 molecule of ribose, 1 molecule of adenine and 3 phosphate groups)

Adenine|
|
Ribose - p - p - p

Question 11

What are the differences between ATP and DNA?

Answer 11

ATP:
Sugar - ribose
3 phosphate groups
Base always adenine

DNA:
Sugar - deoxyribose
1 phosphate group
Base can be any

Question 12

Describe the hydrolysis of ATP.
E.g. what does it make, what enzyme catalysis it, what can the Pi do after?

Answer 12

Hydrolysis of ATP to ADP (adenosine diphosphate) and an inorganic phosphate ion (Pi)
- by the enzyme ATP hydrolase

• the phosphate ion can be used to phosphorylate other compounds, often making them more reactive.

Question 13

How is ATP resynthesised? Also what sort of reaction is it?

Answer 13

• by the condensation of ADP and Pi and is catalysed by the enzyme ATP synthase during PHOTOSYNTHESIS or RESPIRATION

ADP+PI —> ATP+ H2O (a rapid single step reaction)

Question 14

Why is ATP useful as an energy source?

Answer 14

• ATP hydrolysis releases energy in SMALL, MANAGEABLE amounts via a rapid, single step reaction.
• Ensures energy isn’t wasted via heat

Question 15

Why do humans synthesise such a large amount of ATP?

Answer 15

• ATP cannot be stored
  -only releases in small amounts of energy at a time / per ATP molecule