1.5 Nucleic Acid + 1.6 ATP

Question 1

Draw the structure of a nucleotide

Answer 1

Slide 4

Question 2

Name the pentose sugars in DNA & 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 our inherited characteristics influencing structure and function of organisms

Question 4

State the role of RNA in living cells

Answer 4

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

rRNA is component of ribosomes (along with proteins)

tRNA: supplies complementary amino acid to mRNA codons during translation

Question 5

How do polynucleotide 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 purine and pyrimidine base pairs on opposite strands

Adenine + thymine
Guanine + cytosine

Question 7

Which bases are purine and which are pyrimidine?

Answer 7

A and G 2 ring purine bases

T and C and U 1 ring pyrimidine bases

Question 8

Name the complementary base pairs in DNA

Answer 8

2 H-bonds between adenine and thymine

3 H-bonds between guanine and cytosine

Question 9

Name the complementary base pairs in RNA

Answer 9

2 H-bonds between adenine and uracil

3 H-bonds between guanine and cytosine

Question 10

Relate the structure of DNA to its function

Answer 10

Sugar-phosphate backbone and many H-bonds provide stability
Long molecule storing 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 strands separate for replication

Question 11

Describe the structure of messenger RNA (mRNA)

Answer 11

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

Question 12

Relate the structure of messenger RNA (mRNA) to its functions

Answer 12

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

Question 13

Describe the structure of transfer RNA (tRNA)

Answer 13

single strand of about 80 nucleotides, folded into clover shape(some 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 14

Order DNA,mRNA and tRNA according to increasing length

Answer 14

tRNA

mRNA

DNA

Question 15

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

Answer 15

Chemically simple molecule with few components

Question 16

Why is DNA replication described as ‘semi conservative’?

Answer 16

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

Question 17

Outline the process of semiconservative DNA replication

Answer 17

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

Question 18

Describe the meselson-stahl experiment

Answer 18

1.Bacteria were grown in a medium containing heavy isotope 15N for many generations

2. Some bacteria were moved to a medium containing light isotope 14N. Samples were extracted after 1 & 2 cycles of DNA replication
3. Centrifugation formed a pellet. Heavier DNA (bases made from 15N) settled closer to bottom of tube

Question 19

Explain how the Meselson-stahl experiment validated semiconservative replication

Answer 19

Slide 40

Question 20

Describe the structure or adenosine triphosphate(ATP)

Answer 20

Nucleotide derivative of adenine with 3 phosphate groups

Slide 42

Question 21

Explain the role of ATP in cells

Answer 21

ATP hydrolase catalyses ATP —> ADP + Pi

Energy released is coupled to metabolic reactions

Phosphate group phosphorylates compounds to make them more reactive

Question 22

How is ATP resynthesised in cells?

Answer 22

ATP synthase catalyses condensation reaction between ADP and Pi

During photosynthesis and respiration

Question 23

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

Answer 23

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