3.1.5 Nucleic acids are Important Information-Carrying Molecules

Question 1

Basic function of DNA and RNA

Answer 1

DNA is to store genetic information

RNA transfers information to ribosomes

Question 2

Components of a nucleotide

Answer 2

Phosphate group

Penrose sugar (for DNA, deoxyribose and for RNA, ribose)

Nitrogen containing carbon base (for DNA, A,T,G,C and for RNA, A,U,G,C)

Question 3

Explain 5’3’ prime direction

Answer 3

• Phosphate binds to 5th carbon of penrose sugar
• Next nucleotide joins to 3rd carbon of penrose sugar
• Condensation recation occurs
• Phosphodiester bond is formed
• Appropriate enzyme, DNA/RNA polymerase

Question 4

How many hydrogen bonds form between base pairs A,T and A,U

Answer 4

2 hydrogen bonds

Question 5

How many hydrogen bonds form between base pairs G,C

Answer 5

3 hydrogen bonds

Question 6

Describe the structure of ribonucleic acid (6)

Answer 6

• Polymer of nucleotides
• Pentose sugar is ribose
• Organic bases are A,U,G,C
• mRNA = single stranded, linear polynucleotide, it’s a single stranded copy of a gene and takes information to the ribosome
• tRNA = single stranded polynucleotide coded into cloverleaf shape, brings amino acids to ribosome during protein synthesis
• rRNA = found in the ribosomes along with protein

Question 7

Provide the function of: sugar phosphate backbone

Answer 7

• Provides strength and stability
• Protects information coded in bases and hydrogen bonds

Question 8

Provide the function of: DNA being a longer molecule

Answer 8

Holds lots of information

Question 9

Provide the function of: DNA having a helix structure

Answer 9

Compact

Question 10

Provide the function of: DNA having a base sequence

Answer 10

Codes for amino acids and therefore proteins

Question 11

Provide the function of: DNA being double stranded

Answer 11

Allows SCR - each strand acts as a template

Question 12

Provide the function of: DNA having complementary base pairing

Answer 12

Accurate replication

Question 13

Provide the function of: DNA having weak hydrogen bonds between bases

Answer 13

Easily broken in SCR

Question 14

Provide the function of: DNA having many hydrogen bonds

Answer 14

Strong and stable

Question 15

The double helix

Answer 15

2 polynucleotide chains held together by hydrogen bonds between complementary base pairs

Question 16

The structure of the double helix is _______________

Answer 16

Antiparallel

Question 17

Describe the structure of DNA (6)

Answer 17

• Polymer of nucleotides
• Each nucleotide contains one deoxyribose, one phosphate group and one organic nitrogen base
• Phosphodiester bonds between then nucleotides
• Double helix - weak hydrogen bonds between complementary base pairs
• Organic bases: A,T,G,C

Question 18

Explain semi-conservative replication

Answer 18

1. 2 strands separated by breaking hydrogen bonds between complementary base pairs with DNA helicase
2. Separate strands act as template for replication and determine order of nucleotide bases. Free nucleotides within the nucleus are attracted and exposed to complementary base pairs on template strands
3. Hydrogen bonds form between these
4. DNA polymerase joins nucleotides in 5’3’ prime directions through condensation reactions forming phosphodiester bonds
5. 2 DNA molecules are formed, each with one original and one new strand

Question 19

Explain Meelson Stahl experiment

Answer 19

See notes

Question 20

Which scientists discovered the structure of DNA?

Answer 20

Watson and Crick

Question 21

Why do nucleotides only join in the 5’3’ prime direction?

Answer 21

• DNA polymerase
• Specific
• Only complementary with 3’ end
• 5’3’ ends are different and anti parallel

Question 22

Name the protein associated with DNA in a chromosome (1)

Answer 22

Histone (protein)

Question 23

Describe the role of two named enzymes in the process of semi-conservative replication of DNA (3)

Answer 23

1. DNA helicase breaks hydrogen bonds
2. DNA polymerase joins nucleotides
3. Form(s) phosphodiester bonds

Question 24

Give four structural differences between a DNA molecule and an mRNA molecule (4)

Answer 24

1. DNA has deoxyribose, mRNA has ribose;
2. DNA has thymine, mRNA has uracil;
3. DNA long, mRNA short;
4. DNA is double stranded, mRNA is single stranded

Accept ‘double helix’ for ‘double stranded’ and ‘single helix’ for ‘single stranded’

5. DNA has hydrogen bonds, mRNA has no hydrogen bonds

OR

DNA has (complementary) base pairing, mRNA does not;

Must be comparisons

Ignore splicing/introns

Question 25

Outline the similarities in, and the differences between, the structures of DNA and RNA molecules (6)

Answer 25

Similarities
1. Polymers of nucleotides;
2. (Nucleotide has) pentose, (nitrogen-containing
organic) base and a phosphate (group);
3. Cytosine, guanine and adenine (as bases);
4. Have phosphodiester bonds;

Differences
5. Deoxyribose v ribose;
6. Thymine v uracil;
7. Long v short;
8. Double helix/stranded v single stranded;

1. Accept ‘chain’ for
   polymer
2. Accept in correct
   context
   ‘ribose/deoxyribose’
   for pentose
3. Accept DNA longer
4. Ignore ‘large’ and
   ‘small’