Lecture 21 - DNA I

Question 1

What is the central dogma ? (Definition)

Answer 1

States how genetic information is stored, replicated and read

Question 2

What is the central dogma ? (Example form)

Answer 2

DNA makes RNA makes protein

Question 3

What is the definition of a gene ?

Answer 3

Unit of inheritance

Question 4

What is the lecturers definition of a gene ?

Answer 4

Life forms reproduce themselves and use energy

Question 5

What is the lecturers definition of a gene ?

Answer 5

Life forms reproduce themselves and use energy

Question 6

What are genes made of ?

Answer 6

DNA

Question 7

What did Avery, McCarty and MacLeod discover ?

Answer 7

That genes are made of DNA not protein

Question 8

What are the four things that DNA must do ?

Answer 8

1. Replicate faithfully
2. Have the coding capacity to generate the proteins required for cellular functions
3. Be transmitted from parent cell to daughter cell
4. Orchestrate many functions in organisms

Question 9

How much DNA does a diploid human cell contain ?

Answer 9

More than 2 meters

Question 10

Where are genes located in Eukaryotic cells ?

Answer 10

In chromosomes, in the nucleus

Question 11

Why was there a race to understand the structure of DNA ?

Answer 11

It would go a long way toward understanding the diversity and evolution of life forms

Question 12

What is the atomic composition of DNA ?

Answer 12

1. Carbon
2. Hydrogen
3. Oxygen
4. Phosphorus
5. Nitrogen

Question 13

What are the components of a nucleotide ?

Answer 13

1. Phosphate
2. Sugar - deoxyribose
3. Nitrogenous base

Question 14

What is the subunits of DNA ?

Answer 14

Nucleotides

Question 15

How many nitrogenous bases are there ?

Answer 15

4

Question 16

What are the four nitrogenous bases ?

Answer 16

1. Adenine
2. Guanine
3. Cytosine
4. Thymine

Question 17

Which nitrogenous bases are purines ?

Answer 17

1. Adenine

2. Guanine

Question 18

What nitrogenous bases are pyrimidines ?

Answer 18

1. Cytosine

2. Thymine

Question 19

How would you explain what type of structure is DNA ?

Answer 19

A polymer

Question 20

How would you explain what type of structure is a nucleotide ?

Answer 20

A monomer

Question 21

What are the four types of nucleotide ?

Answer 21

1. dAMP
2. dGMP
3. dCMP
4. dTMP

Question 22

What is the 5’ end of a DNA strand ?

Answer 22

Phosphate end

Question 23

What is the 3’ end of of a DNA strand ?

Answer 23

Hydroxy end

Question 24

Does the DNA strand have polarity ?

Answer 24

Yes

Question 25

What is the DNA’s strand directionality/polarity based on ?

Answer 25

The different end groups of the terminal nucleotides

Question 26

How is the sugar-phosphate backbone formed ?

Answer 26

Monomers linking together

Question 27

What is a rule concerning the monomer link to form the sugar-phosphate backbone ?

Answer 27

The link can only be made between the 5’ phosphate of one nucleotide and the 3’ hydroxyl of another

Question 28

How was the 3D structure of DNA determined ?

Answer 28

X-ray crystallography and model building

Question 29

What provides the fibres for X-ray crystallography ?

Answer 29

Addition of a solution of ethanol

Question 30

What seen on Rosalind Franklin’s B51 X-ray image of DNA ?

Answer 30

A helical repeat unit of 10 stacked base pairs

Question 31

What four things did X-ray analysis and model building reveal about the DNA structure ?

Answer 31

1. DNA is a 2-stranded helical structure with the sugar-phosphate backbones on the outside
2. The bases are stacked on the inside, perpendicular to the helix axis
3. Helical repeat unit = 34A (10bp per helix turn)
4. DNA double helix is about 20A wide

Question 32

How many strands does DNA have ?

Answer 32

2

Question 33

Where are the sugar-phosphate backbones found ?

Answer 33

On the outside of the DNA helical structures

Question 34

Where are the nitrogenous bases found on the DNA strands ?

Answer 34

On the inside of the strands, perpendicular to the helix axis

Question 35

What is the helical repeat unit ?

Answer 35

34A (10 base pairs per helix turn)

Question 36

How wide is the DNA double helix ?

Answer 36

20A

Question 37

How are the four types of bases arranged within the DNA double helix ?

Answer 37

Base composition and base ratio

Question 38

What form do the bases exist in ?

Answer 38

Normally keto not enol form

Question 39

What are tautomers ?

Answer 39

Structural isomers that differ from one another based on the position of protons and double bonds

Question 40

What is Chargaff’s rule of base composition ratio’s ?

Answer 40

Any species of any organism should have a 1:1 stoichiometric ratio of purine and pyrimidine bases, more specifically, that the amount of guanine should be equal to cytosine and the amount of adenine should be equal to thymine

Question 41

What are the key proposals of Watson and Crick ?

Answer 41

1. The only base pairs permitted are adenine paired with thymine and guanine paired with cytosine
2. Implications of base pairing for DNA replication
3. The DNA strands are in anti-parallel orientation

Question 42

How does replication occur ?

Answer 42

Via templating

Question 43

Why is the replication process called templating ?

Answer 43

A parent strand acts as a template on which the daughter strand is synthesised

Question 44

What does the sequence of bases on one strand determine ?

Answer 44

The sequence of bases on the other strand