WEEK 9 (DNA organisation)

Question 1

What are the four levels of complexity of DNA?

Answer 1

1. nucleotides form the repeating structural unit of nucleic acids
2. nucleotides are linked together in a linear manner to form a strand of DNA or RNA
3. two strands of DNA interact with each other to form a double helix
4. the three-dimensional structure of DNA results from the folding and bending of the double helix

Question 2

What is the name of the linkage in DNA/RNA strands?

Answer 2

Phosphodiester linkage

Question 3

What does the phosphodiester backbone consist of?

Answer 3

The phosphates and sugar molecules

Question 4

How many nucleotides in each strand are included in one full turn of the DNA double helix?

Answer 4

10 nucleotides

Question 5

Two strands of DNA form a right-handed ______________________

Answer 5

double helix

Question 6

The bases in opposite strands hydrogen bond according to which rule?

Answer 6

AT/GC rule

Question 7

The two strands are ____________ with regard to their 5’ to 3’ directionality

Answer 7

antiparallel

Question 8

What is the genetic term to say that the two sequences are complementary to each other?

Answer 8

the two sequences exhibit complementarity

Question 9

What does a Nucleosome “bead” consist of?

Answer 9

8 histone molecules + 146 base pairs of DNA

Question 10

Describe chromatin structure

Answer 10

• DNA exists in the condensed, chromatin form to fit into the nucleus
• DNA loops twice around a histone octamer to form a NUCLEOSOME
• H1 binds to the nucleosome and to “linker DNA” stabilising the chromatin fibre

Question 10

How many hydrogen bonds are between Adenine and Thymine

Answer 10

2 hydrogen bonds

Question 11

How many hydrogen bonds are between Cytosine and Guanine?

Answer 11

3 hydrogen bonds

Question 12

What charge do Phosphate groups give DNA?

Answer 12

a negative charge

Question 13

What charge does Lysine and Arginine give histones?

Answer 13

a positive charge

Question 14

What happens to DNA during mitosis?

Answer 14

DNA condenses to form chromosomes. DNA and histone synthesis occurs during S phase.

Question 15

Describe mitochondrial DNA

Answer 15

Mitochondria have their own DNA, which is circular and does not utilise histones

Question 16

What is the difference between Heterochromatin and Euchromatin?

Answer 16

Heterochromatin is condensed, appears darker on the electron microscope, transcriptionally inactive and has increased methylation and decreased acetylation.
(e.g Barr bodies)
[Heterochromatin = highly condensed]

Euchromatin is less condensed, appears lighter on the electron microscope, transcriptionally active and sterically accessible.
[Euchromatin is expressed]

Question 17

What are Polytene chromosomes?

Answer 17

Large chromosomes consisting of thousands of DNA strands derived from larval salivary gland cells of Drosophila

Question 18

What are lamp brush chromosomes?

Answer 18

a special form of chromosomes found in the growing oocytes (immature eggs) of most animals

Question 19

How do you calculate the map distance between two genes?

Answer 19

(New recombinants / Total offspring) X 100

Question 20

What is the smallest structure of a chromosome?

Answer 20

A nucleosome

Question 21

How many types of histones proteins are involved in the nucleosome?

Answer 21

4

Question 22

What are the types of histones proteins are involved in nucleosomes?

Answer 22

H2A
H2B
H3
H4

Question 23

How many codons code for amino acids?

Answer 23

64

Question 24

What are the start and stop codons?

Answer 24

Start codon is AUG (Methionine) and stop codon is UAG, UAA & UGA (no amino acid is coded)

Question 25

What is the Wobble position?

Answer 25

The wobble position of a codon refers to the 3rd nucleotide in a codon. This nucleotide has two major characteristics: Binding of a codon in an mRNA the cognate tRNA is much “looser” in the third position of the codon