DNA and nucleic acids

Question 1

What is the difference between the roles of DNA and RNA?

Answer 1

DNA stores and preserves genetic information. RNA plays a big role in protein synthesis.

Question 2

What does a nucleotide of DNA and RNA all contain?

Answer 2

A sugar (deoxyribose or ribose), a phosphate and a base

Question 3

What element do bases contain?

Answer 3

Nitrogen

Question 4

What are the two classes of the bases?

Answer 4

Purine and pyrimidine

Question 5

Which bases are purines?

Answer 5

Adenine and Guanine

Question 6

Which bases are pyrimidines?

Answer 6

Thymine, Cytosine (and Uracil in RNA)

Question 7

What type of bonds hold nucleotides together?

Answer 7

Phosphodiester bonds

Question 8

In which direction are phosphodiester bonds read?

Answer 8

A DNA template is read in the direction of 3’ to 5’. A newly synthesised DNA strand is read in 5’ to 3’. Complementary strands run in antiparallel.

Question 9

Is DNA a single stranded or double stranded structure?

Answer 9

It is a double stranded helix

Question 10

Complementary base pair rules

Answer 10

Purine base pairs with a pyrimidine

• Adenine bonds to thymine (uracil in RNA)
• Guanine bonds to cytosine

Question 11

What type of bonds hold together the complementary base pairs?

Answer 11

Hydrogen

Question 12

How many hydrogen bonds are between

• adenine and thymine
• guanine and cytosine

Answer 12

• 2 Hydrogen bonds

- 3 Hydrogen bonds

Question 13

What is important about the base sequence in DNA?

Answer 13

It carries the information for protein synthesis

Question 14

Is the sequence of bases in DNA constrained?

Answer 14

No the sequences of bases along a polynucleotide is not restricted as long as complementary base pair rule is satisfied

Question 15

What are the templates for RNA synthesis?

Answer 15

The templates for RNA synthesis are DNA molecules and the template for protein synthesis are RNA molecules

Question 16

What is the function of messenger-RNA (m-RNA)?

Answer 16

mRNA is made on the chromosome and carries genetic information to ribosomes for synthesis of particular protein

Question 17

What is the function of transfer-RNA (t-RNA)?

Answer 17

The transfer-RNA carries a specific amino acid from the cytoplasm to the ribosome

Question 18

What is the function of ribosomal-RNA (r-RNA)?

Answer 18

This is the central part of the ribosome and it functions to decode the messenger RNA

Question 19

What are plasmids?

Answer 19

Plasmids are non-chromosomal, self-replicating DNA segments. Plasmids can easily move in and out of cells. They are often used in genetic engineering. They are usually found in prokaryotes but they are found in eukaryotes too.

Question 20

What are the three categories of microogranisms based on their carbon source?

Answer 20

• Heterotrophs use organic compounds e.g. carbohydrates, lipids, hydrocarbons
• Autotrophs - use carbon dioxide as a carbon source
• Mixotrophs - grow under both heterotrophic and autotrophic conditions

Question 21

The two categories of nutrients

Answer 21

• Macronutrients - they are present in concentrations larger than 10-4 M e.g. C, N2, O2, K+, Mg 2+
• Micronutrients - they are present in concentrations less than 10-4 M e.g. Zn 2+, Cu 2+

Question 22

What are the two categories of growth media?

Answer 22

• Defined media contain specific amounts of pure chemical compounds with known chemical compositions
• Complex media contain natural compounds whose chemical composition is not exactly known

Question 23

Important note about thermodynamic equilibrium?

Answer 23

The constant effort of the cell to assimilate what it needs and get rid of what it doesn’t need is really a constant effort to maintain itself away from thermodynamic equilibrium. Thermodynamic equilibrium is death.