3.1.5 Nucleic acids are important information-carrying molecules

Question 1

What is DNA ?

Answer 1

DNA is the genetic material found in all living organisms, ranging from single-celled
bacteria to multicellular mammals

Question 2

Where is DNA found ?

Answer 2

Found in the nucleus of eukaryotes and in the
organelles, chloroplasts, and mitochondria. In prokaryotes, the DNA is not enclosed in a
membranous envelope

Question 3

What is the biological process RNA is involved in ?

Answer 3

protein synthesis

Question 4

What monomers are DNA and RNA made of ?

Answer 4

nucleotides

Question 5

What are the three components of a nucleotide ?

Answer 5

1. a pentose sugar (made with 5 carbon atoms)
2. a nitrogenous base
3. a phosphate group

Question 6

What sugar and bases does a DNA nucleotide have ?

Answer 6

Deoxyribose , adenine (A), thymine (T), cytosine (C), and guanine
(G).

Question 7

What sugar and bases does RNA nucleotide have ?

Answer 7

Ribose ,the base uracil (U) replaces thymine (T) A , C and G

Question 8

Compare DNA to RNA

Answer 8

DNA :
Deoxyribose sugar
Double stranded
Thymine

Similarities:
Nucleic acid
Adenine Phosphate
Guanine
Cytosine

RNA:
Ribose sugar
Single stranded
Uracil

Question 9

What is a polynucleotide ?

Answer 9

polymer of nucleotides

Question 10

How do nucleotides join together ?

Answer 10

Nucleotides join via a condensation reaction between the phosphate group of one
nucleotide and the sugar of another.

Question 11

What chemical bond forms between nucleotides ?

Answer 11

This forms a strong, covalent, phosphodiester bond (which consists of the
phosphate group and two ester bonds).

Question 12

What is the chain of sugars and phosphates known as ?

Answer 12

sugar-phosphate backbone

Question 13

Fill in the gaps
When a polynucleotide is formed, the __ phosphate of the incoming nucleotide
attaches to the _ hydroxyl group at the end of the growing chain.

Answer 13

When a polynucleotide is formed, the 5′ phosphate of the incoming nucleotide
attaches to the 3′ hydroxyl group at the end of the growing chain.

Question 14

What is the structure of DNA ?

Answer 14

DNA is made of two polynucleotide chains in a double-helix structure.

Question 15

What bonding joins the two polynucleotide chains in DNA ?

Answer 15

hydrogen bonding between
bases

Question 16

When each base can only pair with one particular partner what is this key term ?

Answer 16

complementary
base pairing

Question 17

How many hydrogen bonds do adenine and thymine form ?

Answer 17

2

Question 18

How many hydrogen bonds does cytosine and guanine form ?

Answer 18

Three

Question 19

In semi-conservative replication how many strands can be templates ?

Answer 19

2

Question 20

What is RNA ?

Answer 20

Short, single polynucleotide chain much shorter than DNA

Question 21

Why is DNA replication called semi-conservative ?

Answer 21

because half the strands in each new DNA
molecule come from the original DNA molecule

Question 22

Describe the process of semi-conservative replication

Answer 22

The DNA replication process
1. The enzyme DNA helicase breaks the hydrogen bonds between the base pairs on
the two polynucleotide DNA strands. This unwinds the helix to form two single
strands.
2. Each original single strand acts as a template for the new strand. Complementary
base pairing means that free-floating DNA nucleotides are attracted to their base
pair - A with T and C with G
3. Condensation reactions join the nucleotides of the new strands together using the
enzyme DNA polymerase as the catalyst. Hydrogen bonds form between bases on
the original and new strands
4. Each new DNA molecule contains one strand from the original DNA molecule and
one new strand

Question 23

Who proposed the semi conservative DNA replication theory and who validated it ?

Answer 23

Watson and Crick - proposed
Meseleon and Stahl - proved

Question 24

Describe the Meselon-Stahl experiment

Answer 24

Meselson and Stahl experimented with E. coli grown first in heavy nitrogen (15N)
then in 14N
‒ DNA grown in 15N (red band) is heavier than DNA grown in 14N (orange band), and
sediments to a lower level in cesium chloride solution in an ultracentrifuge
‒ When DNA grown in 15N is switched to media containing 14N, after one round of
cell division the DNA sediments halfway between the 15N and 14N levels, indicating
that it now contains fifty percent 14N.
‒ In subsequent cell divisions, an increasing amount of DNA contains 14N only.
‒ This data supports the semi-conservative replication model