Module 1 - DNA

Question 1

Three parts of nucleotides

Answer 1

Tri-phosphate group: α-group phosphate closest to sugar, β-group phosphate second-closest to sugar, γ-group phosphate furthest from sugar.

2’ deoxyribose (the second carbone is missing an oxygen)

Base: connected to the sugar with a β-N-glycosidic bond

Question 2

Bases - purine and pyrimidines

Answer 2

Purine - contain a double ring, Adenine and Guanine

Pyrimidine - contain a single ring, Thymine and Cytosine

Question 3

Glycosidic bond

Answer 3

Glycosidic bond means binding to a sugar.

β-N-glycosidic bond is what binds the base and the sugar in a nucleotide.

Every base contains a nitrogen which has one free bond and this is how the glycosidic bond is formed.

Question 4

Chargaff’s rule

Answer 4

The total number of purines is equal to the total number of pyrimidines (A=T and G=C)

Question 5

Bases - names of their nucleotides

Answer 5

Adenine = 2’ -deoxyadenosine, 5’ -triphosphate (dATP)

Thymine = 2’ -deoxythymidine, 5’ -triphosphate (dTTP)

Guanine = 2’ -deoxyguanosine, 5’ -triphosphate (dGTP)

Cytosine = 2’ -deoxycytidine, 5’ -triphosphate (dCTP)

Question 6

Nucleotide bonding

Answer 6

Occurs in the 5’ to 3’ direction (5’ is at the top, 3’ bonds with the next nucleotide)

Nucleotides are bonded by a phosphodiester bond (phospho - phosphate, diester - there are two oxygens the phosphate is linking with)

Question 7

Three types of DNA

Answer 7

A-DNA -> found rarely, only forms in dehydrating conditions.

B-DNA -> Most common form of DNA.

Z-DNA -> Found naturally along with B-DNA, although it is biologically active, it’s function is not clear yet.

Question 8

A-DNA:
Type of helix
Base pairs per turn
Distance between base pairs
Distance between complete turns
Diameter
Major groove
Minor groove

Answer 8

A-DNA:
Right-handed (normal)
11 (B < A < Z)
0.29nm (A < B < Z)
3.2nm (A < B < Z)
2.55nm (Z < B < A)
Narrow, deep
Wide, shallow

Question 9

B-DNA:
Type of helix
Base pairs per turn
Distance between base pairs
Distance between complete turns
Diameter
Major groove
Minor groove

Answer 9

B-DNA:
Right-handed (normal)
10 (B < A < Z)
0.34nm (A < B < Z)
3.4nm (A < B < Z)
2.37nm (Z < B < A)
Wide, deep
Narrow, shallow

Question 10

Z-DNA:
Type of helix
Base pairs per turn
Distance between base pairs
Distance between complete turns
Diameter
Major groove
Minor groove

Answer 10

Z-DNA:
Left-handed (not normal)
12 (B < A < Z)
0.37nm (A < B < Z)
4.5nm (A < B < Z)
1.84nm (Z < B < A)
Flat
Narrow, deep

Question 11

Major groove

Answer 11

Larger groove of the two that spiral around B-DNA

Question 12

Minor groove

Answer 12

Smaller groove of the two that spiral around B-DNA

Question 13

Measuring genes (units)

Answer 13

One megabase pair (1Mbp) = One thousand kilobase pairs (1000Kbp) = 1000000 base pairs (1x10⁶bp)

Question 14

Exons

Answer 14

Code for proteins. Human genes contain one more exon than introns.

Exons take up approximately 10% of a gene.

Question 15

Introns

Answer 15

Do not code for proteins.

Introns can take up to 90% of the space on a gene

Question 16

RNA - coding and non-coding

Answer 16

Coding RNA ~ 4% = mRNA

Non-coding RNA ~96% = rRNA, tRNA, snRNA, etc

Question 17

Genes - unique or family

Answer 17

Unique genes occur once and are not repeated or similar to any other genes in the species.

Family genes can be either simple or complex multigene families

Question 18

Simple multigene families

Answer 18

Contain the same gene repeated in high amounts.

Occurs mainly for rRNA genes as lots of ribosomes are needed.

Question 19

Complex multigene families

Answer 19

Contain similar but different genes,

Occurs mainly for things like globin genes.

Question 20

Globin genes

Answer 20

Are slightly different for different function.

Embryo and foetus haemoglobins bind to oxygen stronger than adult heamoglobins so that the embryo can take oxygen from the mother.

Question 21

Molecular clock

Answer 21

We can analyse the rate of mutation of a gene and then use this information to discover how distant two of the same genes are from each other.

The more differences between two of the same gene, the more distant they are from each other.

Question 22

Pseudogenes

Answer 22

Genes that have lost their function and therefore become inactive over time.