1.5 Nucleic Acids + 1.6 ATP

Question 1

What makes up a nucleotide

Answer 1

Phosphate group

Organic base

Pentose sugar

Question 2

Name Pentose sugars in DNA and RNA

Answer 2

Deoxyribose (DNA) and Ribose (RNA)

Question 3

State role of DNA in living cells

Answer 3

Base sequence of genes that code for functional RNA and amino acid sequence of polypeptides

Genetic info determines inherited characteristics= influences structure and function of organisms

Question 4

State role of RNA in living cells

Answer 4

mRNA: complementary sequence to 1 gene from DNA with introns spliced out. Codons can be translated into a polypeptide by ribosomes

rRNA: component of ribosomes, along with proteins

tRNA: supplies complementary amino acids to mRNA codons during translation

Question 5

How do polynucleotides form

Answer 5

Condensation reaction between nucleotides form strong phosphodiester bonds, sugar phosphate backbone

Question 6

Describe structure of DNA

Answer 6

Double helix of 2 polynucleotide strands (deoxyribose)

H-bonds between complementary purine and pyrimidine base pairs on opposite strands:

A+T, G+C

Question 7

Which bases are purine and/ or pyrimidine

Answer 7

A&G = 2 ring purine base

T&C&U = 1 ring pyrimidine base

Question 8

Name complementary base pairs in DNA

Answer 8

2 H-bonds between adenine and thymine

3 H-bonds between guanine and cytosine

Question 9

Name complementary base pairs in RNA

Answer 9

Same as DNA except instead of thymine it’s 2 H-bonds between adenine and uracil

Question 10

Relate structure of DNA to its functions

Answer 10

• sugar phosphate backbone and many H-bonds provide stability
• long molecule stores lots of info
• helix is compact for storage and functions
• 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 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 structure of 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 a specific polypeptide by ribosomes

Question 13

Describe 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 other:
a) anticodon bonds to complementary mRNA codons
b) amino acids 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 genetic code

Answer 15

chemically simple molecule with few compliments

Question 16

Why’s DNA replication described as semiconservative

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 process of semiconservative DNA replication

Answer 17

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 18

describe Meselson and Stahl experiment

Answer 18

1. Bacteria were grown in medium containing heavy isotope N¹⁵ for many generations
2. Some bacteria were moved to a medium containing light isotope N¹⁴. Samples were extracted after 1 and 2 cycles of DNA replication
3. Centrifugation formed a pellet. Heavier DNA (bases made from N¹⁵) settled closer to bottom of tube

Question 19

Explain how Meselson and Stahl experiment validated semiconservative replication

Answer 19

Grown in N¹⁵

1 division: all molecules have 1 strand of N¹⁵ and 1 strand of N¹⁴

2 division 50% has 2 strands N¹⁴, 50% has 1 strand N¹⁵ and 1 strand N¹⁴

Question 20

Describe structure of Adenosine Triphosphate (ATP)

Answer 20

Nucleotide derivative of adenine and 3 phosphate

Question 21

Explain role of ATP in cells

Answer 21

ATP hydrolyse catalyses into ADP and Pi

•energy released is coupled to metabolic reactions
•phosphate group phosphorylates compounds to make them more reactive

Question 22

How’s ATP resynthesised in cells

Answer 22

ATP synthase catalyses condensation reactions between ADP and Pi

During photosynthesis and respiration

Question 23

Explain why ATP is suitable as energy currency in cells

Answer 23

High energy bonds between phosphate groups

Small bursts of energy released at a time= less energy wasted as heat

Single step hydrolysis = energy available quickly

Readily resynthesised