Week 1 (DNA structure)

Question 1

What are phosphate groups commonly joined to?

Answer 1

C5 (5’) hydroxl of the ribose or deoxyribose sugar

Question 2

Define genome

Answer 2

The complete store of information in an organisms DNA

Question 3

What does a nucleotide consist of?

Answer 3

• Nitrogen containg base
• A 5 carbon sugar
• 1 or more phosphate groups

Question 4

How are nucelotides joined together?

Answer 4

By a phosphodiester linkage between a 5’ C and a 3’ C

Question 5

Draw the structure of complementary base pairs

Answer 5

Question 6

What is the difference between nucleoside and nucleotide?

Answer 6

Base + Sugar = Nucleoside

Base + Sugar + Phosphate = nucleotide

Question 7

energy

Name other functions of nucleotides

Answer 7

1. Carry energy in their easily hydrolised phosphoanhydride/ phosphodiester bonds
2. Combine with other groups to from co-enzymes
3. Act as specific signalling molecules in the cell

Question 8

What gives a DNA strand chemical polarity?

Answer 8

The way in which the nucleotides are linked together. This polarity in a DNA chain is indicated by referring to one end as the 3ʹ end and the other as the 5ʹ end

Question 9

List the nucleoside of each base

Answer 9

Question 10

Draw cytosine thymine and uracil

Answer 10

Question 11

What is the difference between the sugar used in ribose and in deoxyribose?

Answer 11

Question 12

Why do organisms differ from one another?

Answer 12

Organisms differ from one another because their respective DNA molecules have different nucleotide sequences and, consequently, carry different biological messages

Question 13

How are nucleotides linked together and how does this affect polarity?

Answer 13

The nucleotides are linked together covalently by phosphodiester bonds:

a covalent bond is formed between the 5’ phosphate group of one nucleotide and the 3’-OH group of another

Thus, each polynucleotide strand has a chemical polarity; that is, its two ends are chemically different. The 5ʹ end of the DNA polymer is by convention often illustrated carrying a phosphate group, while the 3ʹ end is shown with a hydroxyl.

Question 14

Explain the structure of DNA

Answer 14

1. Two long polynucleotide chains composed of four types of nucleotide subunits. Each of these chains is known as a DNA chain, or a DNA strand.
2. The chains run antiparallel to each other
3. Hydrogen bonds between the base portions of the nucleotides hold the two chains together
4. Nucleotides are composed of a five-carbon sugar to which are attached one or more phosphate groups and a nitrogen-containing base. I
5. In the case of the nucleotides in DNA, the sugar is deoxyribose attached to a single phosphate group (hence the name deoxyribonucleic acid), and the base may be either adenine (A), cytosine (C), guanine (G), or thymine (T). 6. The nucleotides are covalently linked together in a chain through the sugars and phosphates, which thus form a “backbone” of alternating sugar–phosphate–sugar–phosphate. These same symbols (A, C, G, and T) are commonly used to denote either the four bases or the four entire nucleotides—that is, the bases with their attached sugar and phosphate groups.

Question 15

What are the two types of bases?

Answer 15

Pyrimidines and purines

Question 16

How could information in DNA be duplicated and copied from generation to generation?

Answer 16

The double-stranded nature of the structure: because each strand of DNA contains a sequence of nucleotides that is exactly complementary to the nucleotide sequence of its partner strand, each strand can act as a template, or mold, for the synthesis of a new complementary strand

Question 17

How does th 3D structure of DNA arise?

Answer 17

From the chemical and structural features of its two polynucleotide chains. Because these two chains are held together by hydrogen-bonding between the bases on the different strands, all the bases are on the inside of the double helix, and the sugar-phosphate backbones are on the outside

This complementary base-pairing enables the base pairs to be packed in the energetically most favorable arrangement in the interior of the double helix. In this arrangement, each base pair is of similar width, thus holding the sugar-phosphate backbones a constant distance apart along the DNA molecule. To maximize the efficiency of base-pair packing, the two sugar-phosphate backbones wind around each other to form a right-handed double helix, with one complete turn every ten base pairs

Question 18

Draw adenine and guanine

Answer 18

Question 19

What carbon of the sugar does the base link to?

Answer 19

C1

Question 20

What is the difference between ribose and deoxyribose?

Answer 20

Ribose has an OH attached to its 2’ C

Deoxyribose has a H attached to its 2’ C