DNA

Question 1

What are the monomers that make up DNA called?

Answer 1

• Nucleotides.

Question 2

What are the 3 components of a DNA nucleotide?

Answer 2

1.) Deoxyribose (pentose sugar.)
2.) Nitrogen- containing base.
3.) One phosphate group

Question 3

What is the name of the pentose sugar that makes up DNA?

Answer 3

• Deoxyribose sugar.

Question 4

What are the 4 different nitrogen- containing/ organic bases in DNA?

Answer 4

1.) Guanine.
2.) Cytosine.
3.) Adenine.
4.) Thymine.

Question 5

What is the function of DNA?

Answer 5

• DNA holds genetic information/ codes for sequence of amino acids in primary structure of protein.

Question 6

What is the general structure of DNA molecule like?

Answer 6

• The DNA **(polymer of nucleotides) **is a double- helix with two polynucleotide chains held together by hydrogen bonds between specific complementary base pairs.

Question 7

How are polynucleotides formed?

Answer 7

• Formed by condensation reactions between deoxyribose sugar (on one nucleotide) and phosphate group (on another nucleotide) , forming phosphodiester bond.

Question 8

True or False

Phosphodiester bonds, in DNA, between deoxyribose sugar and phosphate group are weak.

Answer 8

• False.
• Phosphodiester bonds are strong covalent bonds. This helps to ensure the genetic code isn’t broken down.

Question 9

How many bases code for 1 amino acid?

Answer 9

3 bases code for 1 amino acid.

Question 10

What is the “back- bone” of a polynucleotide?

Answer 10

• Sugar- phosphate backbone.
• Descirbing strong covalent bonds between sugar and phophate groups (ie. phosphodiester bonds.)

Question 11

Finish the sentence

A ……. reaction between two ……… forms a ………… bond.

Answer 11

• Condensation.
• Nucleotides
• Phosphodiester bond.

Question 12

How is the double- helix structure of DNA formed?

Answer 12

• DNA polymer occurs in pairs, these pairs are joined by hydrogen bonds (between the complementary bases.)

Question 13

What are the complementary base pairs in DNA?

Answer 13

• Guanine and cytosine (ie. guanine can only form hydrogen bonds with adenine.)
• Adenine and thymine (ie. adenine can only form hydrogen bonds with thymine.)

Question 14

How many hydrogen bonds form between adenine and thymine (complementary base pairs?)

Answer 14

• 2 hydrogen bonds form between these complementary base pairs.

Question 15

How many hydrogen bonds form between cytosine and guanine (complementary base pairs?)

Answer 15

• 3 hydrogen bonds form between these complementary base pairs.

Question 16

Why is complementary base pairing important?

Answer 16

• Important to help maintain order of genetic code when DNA replicates.

Question 17

Finish the sentence

DNA and RNA are important ………. …….. molecules.

Answer 17

• information
• carrying

Question 18

How is DNA’s structure suited to its function of being genetic information- carrier molecule/ very stable molecule?

6 main ways.

Answer 18

1.) Stable due to sugar- phosphate back- bone (strong covalent bonds) in double helix.
2.) Double stranded (replication can occur by using strands as templates.)
3.) Weak hydrogen bonds for easy unzipping of 2 strands during replication.
4.) Large molecule: carries/ stores a lot of information.
5.) Complementary base pairing allows identical copies to be made in DNA replication.
6.) Helical so can compact, large amount of genetic material in small space.

Question 19

Although DNA is large, why is it said to be “compact?”

Answer 19

• DNA coiled around proteins (called histones) - so, a lot of information can be stored in a small space in the molecule.

Question 20

Why did scientists doubt that DNA carried a genetic code?

Answer 20

• Due to the relative simplicity of the DNA molecule, many scientists doubted that it carried a genetic code.

Question 21

What is the full name of DNA?

Answer 21

• Deoxyribonucleic acid.

Question 22

Specimen Paper 1

During DNA replication, two DNA strand separate and each acts as a template for production of new strand. As new DNA strands are produced, nucleotides can only be added in 5’ to 3’ direction.
Use your understanding of enzyme action and DNA replication to explain why new nucleotides can only be added in 5’ to 3’ direction.

Answer 22

• DNA polymerase
• Active site of DNA polymerase is specific.
• Active site of DNA polymerase ONLY complementary to 5’ end of DNA.
• Shapes of 5’ and 3’ end of DNA are different.