B2 2.6-2.7

Question 1

Nucleic Acids

Answer 1

Very large molecules constructed by linking nucleotides to form a polymer.

Question 2

Nucleotide Structure

Answer 2

• A pentose sugar.
• A phosphate group (negatively charged, acidic).
• A base- contains nitrogen.

Question 3

How are nucleotides bonded?

Answer 3

Covalently

Question 4

How are nucleotides made into polymer chains?

Answer 4

• Covalent bonds form between the pentose sugar and the phosphate groups of the molecules.
• This creates a strong backbone of alternating sugars and phosphates, with a base on each one.

Question 5

How many types of nucleotides are there?

Answer 5

Four, one for each base.

Question 6

How many sequences of bases are possible along a DNA molecule?

Answer 6

Literally any sequence

Question 7

What does the base sequence do?

Answer 7

Stores information

Question 8

What do the Phosphates and Sugars do?

Answer 8

Support the structure of the base sequence.

Question 9

How are DNA and RNA different?

Answer 9

• DNA has 1 less Oxygen atom.

- DNA is double stranded, RNA single stranded.

Question 10

DNA bases vs RNA bases

Answer 10

Adenine
Cytosine
Guanine
DNA: Thymine
RNA: Uracil

Question 11

What does DNA consist of?

Answer 11

Two strands of antiparallel covalently bonded nucleotides.

Question 12

Why are the strands of DNA antiparallel?

Answer 12

Because they run in opposite directions to one another, one from 5’ to 3’, the other from 3’ to 5’.

Question 13

What is a word for DNA’s structure?

Answer 13

Double Helix structure.

Question 14

Complementary Base Pairing

Answer 14

Each specific base can only pair with one other:
Adenine + Thymine (Uracil)
Guanine + Cytosine

Question 15

How are the strands of DNA held together?

Answer 15

By hydrogen bonds between the bases.

Question 16

What are molecular models?

Answer 16

Current theories of the time.

They are a representation of an idea, and help to fabricate them physically.

Question 17

What was the first model for DNA structure?

Answer 17

• First model consisted of three-stranded DNA- a triple helix with bases on the outside and magnesium holding it together with ionic bonds to the phosphate groups.
• This was later rejected due to an inconsistency in magnesium levels.
• It also did not consider Chargaff’s Principle (also known as the base pair rule-bases should be in a 1:1 ratio).

Question 18

What did Crick and Watson do when the first DNA structure was rejected?

Answer 18

• They then used cardboard cut outs to realise how the different elements of DNA would fit together, creating the Double Helix structure.
• They then prepared a second model, which ‘just looked right’.
• This began a molecular biology revolution.

Question 19

When a cell divides…

Answer 19

… so do the strands of a double helix

Question 20

How does complementary base pairing work?

Answer 20

• The base strand on the old strand determines that of the new strand- only nucleotides with a complementary base to the next base on the old strand can be added, e.g. Adenine to an existing Thymine base.
• The H-Bonds in between them stabilize the structure.

Question 21

Who provided the first evidence for semi-conservative replication?

Answer 21

Meselson and Stahl in 1958- published evidence.