1.6-Nucleic Acids + 1.7-ATP

Question 1

Draw the structure of a nucleotide

Answer 1

Phosphate group, pentose sugar and nitrogen-containing base.

Question 2

Name the pentose sugars in DNA and RNA.

Answer 2

DNA: Deoxyribose
RNA: Ribose

Question 3

State the role of DNA in living cells

Answer 3

• Base sequence of genes codes for functional RNA and
  amino acid sequence of polypeptides.
• Genetic information determines the inherited
  characteristics = influences structure and function of
  organisms.

Question 4

State the role of RNA in living cells.

Answer 4

mRNA: Complementary sequence to 1 gene from DNA with introns (non-coding regions) spliced out. Codons can be translated into a polypeptide by ribosomes.
tRNA: Supplies complementary amino acid to mRNA codons during translation.
rRNA: Component of ribosomes (along with proteins).

Question 5

How do polynucleotides form?

Answer 5

Condensation reaction between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone).

Question 6

Describe the structure of DNA

Answer 6

Double helix of 2 polynucleotide strands (deoxyribose).
H-bonds between complementary bases: A+T, G+C.

Question 7

Name the complementary base pairs in DNA.

Answer 7

2 hydrogen bonds between A and T.
3 hydrogen bonds between G and C.

Question 8

Name the complementary base pairs in RNA.

Answer 8

2 hydrogen bonds between A and U.
3 hydrogen pairs between G and C.

Question 9

Relate the structure of DNA to its functions.

Answer 9

• Sugar-phosphate backbone and many H-bonds provide
  stability.
• Long molecule so stores a lot of information.
• Helix is compact for storage in nucleus.
• Base sequence of triplets codes for amino acids.
• Double-stranded for semi-conservative replication.
• Complementary base pairing for accurate replication.
• Weak H-bonds break so strands separate for replication.

Question 10

Describe the structure of mRNA.

Answer 10

• Long ribose polynucleotide but shorter than DNA.
• Contains uracil instead of thymine.
• Single-stranded and linear so no complementary base
  pairing.
• Codon sequence is complementary to exons of 1 gene
  from 1 DNA strand.

Question 11

Relate the function of mRNA to its function.

Answer 11

• Breaks down quickly so no excess polypeptide forms.
• Ribosome can move along strand and tRNA can bind to
  exposed bases.
• Can be translated to a specific polypeptide by
  ribosomes.

Question 12

Describe the structure of tRNA.

Answer 12

• Single strand of about 80 nucleotides.
• Folded into a clover shape (some bases are paired).
• Anticodon on one end, amino acid binding site on the
  other:
  a) anticodon binds to complementary mRNA codon.
  b) amino acid corresponds to anticodon.

Question 13

Order DNA, tRNA and mRNA according to increasing length.

Answer 13

tRNA
mRNA
DNA

Question 14

Why did scientists initially doubt that DNA carried the genetic code?

Answer 14

It was a chemically simple molecule with few components.

Question 15

Why is DNA replication described as ‘semi-conservative’?

Answer 15

• Strands from the original DNA acts as a template.
• New DNA molecule contains 1 old strand and 1 new
  strand.

Question 16

Describe the process of Semi-Conservative Replication.

Answer 16

1. DNA helicase breaks the H-bonds between these pairs.
2. Each strand acts as a template.
3. Free nucleotides from nuclear sap attach to exposed
   bases by complementary base pairing.
4. DNA polymerase catalyses condensation reactions that
   join adjacent nucleotides on a new strand.
5. H-bonds reform.

Question 17

Describe the structure of ATP

Answer 17

Adenine, ribose and 3 phosphate groups.

Question 18

Explain the role of ATP in cells.

Answer 18

ATP hydrolase catalyses ATP+Water -> ADP + Pi
- Energy released is coupled to metabolic reactions.
- Phosphate group phosphorylates