!!!Biological Molecules: Nucleic Acids

Question 1

What are nucleic acids?

Answer 1

Information carrying polymers

Question 2

What are the monomers of nucleic acids?

Answer 2

Nucleotides

Question 3

What are all individual nucleotides made of?

Answer 3

• a pentose sugar
• a phosphate group
• a nitrogen containing organic base

Question 4

For purines what is there basic structure and what bases do they consist of?

Answer 4

They have a double ring structure (check biology camera roll) and the bases are Guanine and Adenine

Question 5

For pyrimadines, what is their basic structure and what bases do they consist of?

Answer 5

They have a single ringed structure (check biology camera roll) and the bases are cytosine and either thymine or uracil depending if the molecule is DNA or RNA

Question 6

What is the formula of deoxyribose?

Answer 6

C5H10O4

Question 7

What bond holds together each nucleotide in a polynucleotide chain? Where do these bonds form? How do they form?

Answer 7

The phosphodiester bond which forms between the 3’ of the hydroxyl group of the pentose sugar and the the 5’ of the phosphate group as a result of a condensation reaction

Question 8

What are RNA molecules involved in?

Answer 8

The transfer of coded information in DNA to the amino acid sequence of proteins

Question 9

What are the three types of RNA

Answer 9

mRNA
ribosomal RNA
tRNA

Question 10

Give three points that are significant to RNA’s structure

Answer 10

• its a relatively short single stranded polynucleotide chain
• contains a pentose sugar which is always ribose
• the bases are A, U, C and G

Question 11

Give four points about the structure of DNA

Answer 11

• its a very long double helix structure made of two polynucleotide chains
• the polynucleotide strands in a DNA molecule are anti parallel
• the pentose sugar is ALWAYS deoxyribose
• the bases are A, T, C and G

Question 12

How are the polynucleotide chains in DNA anti parallel?

Answer 12

One is going from 5’-3’ of carbon and the other is going from 3’-5’ of carbon

Question 13

In DNA, what holds the polynucleotide chains together?

Answer 13

The hydrogen bonds between the complementary base pairs

Question 14

In DNA how many hydrogen bonds are there between each complementary base pair?

Answer 14

There are 2 between A-T and 3 between C-G

Question 15

Why would a higher proportion of C-G pairs make a DNA molecule more stable?

Answer 15

Because C-G have 3 hydrogen bonds while A-T only have 2 strengthening the whole DNA molecule as there are more hydrogen bonds

Question 16

Give three points that suggest DNA is a stable molecule

Answer 16

• the phosphodiester backbone protects the bases inside the double helix from physical and chemical forces
• the bases on each strand are linked by H bonds forming bridges between the deoxyribose phosphate backbone
• as a collective the hydrogen bonds between the complementary base pairs can be strong as many hydrogen bonds together become strong

Question 17

What is semi conservative DNA replication?

Answer 17

Where two strands are separated and each strand can act as a template

Question 18

How is DNA polymerase specific?

Answer 18

Because it only elongates in the direction of the 5’ to 3’

Question 19

What are the two main stages Cell division in eukaryotic cells and define them

Answer 19

• nuclear division = the process by which the nucleus divides and there are two types being mitosis and meiosis
• cytokineses = the process by which the whole cell divides

Question 20

What must happen before a cell nucleus divides?

Answer 20

The DNA must be replicated to ensure all daughter cells have the genetic information to produce the required enzymes and proteins

Question 21

State the steps of semi conservative DNA replication

Answer 21

1. The enzyme DNA helicase causes the two strands of the DNA to separate by breaking the hydrogen bonds that join the complementary bases together
2. Free activated nucleotides bind specifically to their complementary bases in the now separate strands from the DNA
3. Once the active nucleotides are bound, they are joined together by DNA polymerase which forms phosphodiester bonds between the deoxyribose phosphate backbone
4. The complete polynucleotide chains are formed producing two identical strands of DNA which each contain one polynucleotide chain from the original DNA strand and one new polynucleotide chain

Question 22

What are the 4 requirements for semi conservative replication to take place?

Answer 22

• the four nucleotides each with their bases of adenine, thymine, cytosine and guanine must be present
• both strands of the DNA molecule acting as a template for the attachment of these nucleotides
• the enzyme DNA polymerase
• a source of chemical energy to drive the process

Question 23

Describe how meselsohn and stahl proved Watson and cricks theory of DNA being semi-conservative

Answer 23

1. They had 3 theories which were dna being dispersive, conservative or semi conservative.
2. They grew bacteria in N15 (heavy) and after found that both strands of DNA were heavy.
3. Then they grew bacteria in the N14 (light) and found there was one heavy strand and one light strand in all the 1st generation DNA disproving the conservative theory because that would require only one type of nitrogen in the strands
4. This meant the scientists now had to determine wether DNA was dispersive or semi conservative
5. The bacteria was then grown in the N14 medium and after the second generation, two of the strands had both heavy and light and 2 of the strands were completely light which showed that one strand came from the original DNA and the other strand was new proving the semi conservative theory to be correct

Question 24

How is DNA adapted to its function?

Answer 24

• its a very stable structure allowing it to pass from one generation to the other without changing (rarely mutates)
• its two strands are held together by hydrogen bonds allowing them to be separated during DNA replication and protein synthesis for the genes to be read
• its a very large molecule so can carry the huge amount of genetic info
• the base sequence of a genes determines the structure and function of the protein it codes for