Nucleic acids + ATP

Question 1

Name the pentose sugars in DNA & RNA

Answer 1

DNA: deoxyribose
RNA: ribose

Question 2

State the role of DNA in living cells

Answer 2

Base sequence of genes codes for functional RNA & amino acid sequence of polypeptide

Genetic information determines inherited characteristics = influences structure & function of organisms

Question 3

State the role of RNA in living cells

Answer 3

mRNA: Complementary sequence to 1 gene from DNA with introns (non-coding regions) spliced out. Codons can be translated into a polypeptide by ribosomes.

rRNA: component of ribosomes

tRNA: supplies complementary amino acid to mRNA codons during translation

Question 4

How do polynucleotides form?

Answer 4

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

Question 5

Describe structure of DNA

Answer 5

double helix of 2 polynucleotide strands (deoxyribose)

H-bonds between complementary purine & pyrimidine base pairs on opposite strands:
adenine (A) + thymine (T) + guanine (G) + cytosine (C)

Question 6

Which bases are purine and which are pyrimidine?

Answer 6

A & G = 2-rinng purine bases
T & C & U = 1-ring pyrimidine bases

Question 7

Relate structure of DNA to its functions

Answer 7

• sugar-phosphate backbone & many H-bonds provide stability
• long molecule stores lots 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 strand separate for replication

Question 8

Describe structure of messenger RNA (mRNA)

Answer 8

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

Question 9

Relate structure of messenger RNA (mRNA) to its functions

Answer 9

(functions in same order as structure)
- Breaks down quickly so no excess polypeptide forms
- Ribosome can move along strand & tRNA can bind to exposed bases
- Can be translated into a specific polypeptide by ribosomes

Question 10

Describe structure of transfer RNA (tRNA)

Answer 10

-Single strand of about 80 nucleotides
- Folded into clover shape (paired bases)
- 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 11

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

Answer 11

• Strands from original DNA molecule act as a template
• New DNA molecule contains 1 old strand & 1 new strand

Question 12

Outline the process of semi-conservative DNA replication

Answer 12

1. DNA helicase breaks H-bonds between base 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 new strand
5. H-bonds reform

Question 13

Describe structure of adenosine triphosphate (ATP)

Answer 13

Nucleotide derivative of adenine with 3 phosphate groups

Question 14

Explain role of ATP in cells

Answer 14

ATP hydrolyses catalyses ATP -> ADP + Pi

• Energy released is coupled to metabolic reactions
• Phosphate group phosphorylates compounds to make them more reactive

Question 15

Explain why ATP is suitable as ‘energy currency’ of cells

Answer 15

• High energy bonds between phosphate groups
• Small amounts of energy released at a time = less energy wasted as heat
• Single-step hydrolysis = energy available quickly
• Readily resynthesised