Genes and Chromosomes (Part 1)

Question 1

Describe the common structure of all nucleotides.

Answer 1

A phosphate group linked by a phosphoester bond to a pentose (a 5 carbon sugar molecule) that in turn is linked to an organic base.

Question 2

What type of bond links the pentose sugar to the phosphate ester of a nucleotide?

Answer 2

The phosphate is esterified to the C5’ of the pentose sugar by means of an ester bond (phosphoester bond)

Question 3

What type of bond links the heterocyclic base to the pentose sugar?

Answer 3

The N-glycosidic bond attaches the base to the 1’ position of the sugar in both DNA & RNA

Question 4

Which nitrogenous bases are purines?

Answer 4

adenine and guanine

Question 5

Which nitrogenous bases are pyrimidines?

Answer 5

• cytosine,
• thymine (DNA),
• and uracil (RNA)

Question 6

What forms phosphodiester bonds?

Answer 6

• DNA/RNA Polymerase

- DNA Ligase (Condensation rxn)

Question 7

In relation to nucleotides, where do phosphodiester bond forms?

Answer 7

The 5’ CH2 group of one residue becomes linked to the 3’ OH group of the next.

Question 8

Which bases interact with one another in the interior of the double helix of DNA, and how many H bonds do they form?

Answer 8

A2T

C3G

Question 9

The bases on opposite strands of the DNA are held together by?

Answer 9

Hydrogen bonds

Question 10

If a sample of DNA contains 35% adenine, what is % of the other nucleotides?

Answer 10

A = 35%; T = 35% C = 15%; G = 15%

Question 11

What are the differences between bacterial and human mRNA?

Answer 11

Bacterial: used and degraded within minutes.
Human: used and degraded within hours to days

Question 12

What are the post-transcriptional modifications of mRNA in Eukaryotes?

Answer 12

1) Transcription by RNA Polymerase II
2) Addition of 5’ cap structure
3) Addition of 3’ poly-A tail

Question 13

What is the first step in the capping of eukaryotic 5’ mRNA by addition of a 7-methyl- guanosine (7-Me G)?

Answer 13

A phosphatase removes one phosphate group from the 5’ end of the nascent RNA.

Question 14

In regards to the formation of the 7-Me-G’ mRNA cap, what happens after a phosphatase removes one phosphate group from the 5’ end of the nascent RNA.

Answer 14

Guanylyl transferase: adds a GMP in a reverse linkage (5’ to 5’ instead of 5’ to 3’).

Question 15

In regards to the capping of mRNA, what happens after Guanylyl transferase adds a GMP in a reverse linkage (5’ to 5’ instead of 5’ to 3’)?

Answer 15

Guanine-7-methyl transferase: adds a methyl group to the 7 position of the terminal guanine.

Question 16

In regards to mRNA capping, what happens after Guanine-7-methyl transferase adds a methyl group to the 7 position of the terminal guanine.

Answer 16

2’-O-methyl transferase: adds a methyl group to the 2’-O position to the next to last base on the 5’ end
(only some mRNAs)