Biological molecules: Nucleic acids + ATP

Question 1

Draw the structure of a nucleotide.

Answer 1

Question 2

Name the pentose sugars in DNA and RNA

Answer 2

-Deoxiribose
-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 for polypeptides
-Genetic information determines inheritedd characteristics and influences structure and function of organisims

Question 4

State the role of RNA in living cells

Answer 4

-mRNA complementary sequence t one gene from DNA with introns spliced out.Codons can be translated into a polypeptide by ribosomes
-rRNA component of ribosome along with proteins
-tRNA supplies complementary amino acid to mRNA codons during translation

Question 5

How do polunucleotides form?

Answer 5

Condensation reactions between nucleotides form strong phospodiester bond(sugar phospate backbone)

Question 6

Describe structure of DNA

Answer 6

-Double helix of two polynucleotide strands
(deoxiribose)
-H-bonds between specific complementary (purine and pyrimidine) base pairs on opposite strands:
Adenine+ Thymine
Guanine+ Cytosine

Question 7

Which bases are purine and which bases are pyrimidine

Answer 7

A&G= two ring purine bases
T&C= one ring pyrimidine bases

Question 8

Name the complementray base pairs in DNA

Answer 8

2 hydrogen bonds between Adenine and Thymine
3 hydrogen bonds between Guanine and Cytosine

Question 9

Name the complementary base pairs in RNA

Answer 9

2 Hbonds between adenine and uracil
3 hydrogen bonds between Guanine and Cytosine

Question 10

Relate the structure of DNA to its functions

Answer 10

-Sugar phosphate backbone and many hydrogen bonds provide stabilty
-Long molcule stores lots of information
-Helix is compact for storage in nucleus
-Base sequence of triplets codes for amino acids
-Double stranded for semi-consrvative replication
-Complementary base pairing for accurate replication
-Weak hydrogen bonds break so starnds seperate for replication

Question 11

Describe structure of messenger RNA

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 one gene from one DNA strand

Question 12

Relate the structure of mRNA to its functions

Answer 12

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

Question 13

Describe the structure of tRNA

Answer 13

-Single strand of around 80 nucleotides
-Folded into clover shape(some paired bases)
-Anticodon on the other end amino binding site on the other
-Anticodon binds to complementary mRNA codon
-Amino acid corresponds to anticodon

Question 14

Order DNA tRNA and mRNA according to incresing length

Answer 14

tRNA
mRNA
DNA

Question 15

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

Answer 15

Chemically simple molecule with few components

Question 16

Why is DNA replication described as semiconservative?

Answer 16

-Strands fromoriginal DNA molecule act as a template
-New DNA molecule contains one old starand and one new strand.

Question 17

Outline the processes of semi conservative replication.

Answer 17

1DNA 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 adjecent nucleotides on a free strand
5. H-bonds reform

Question 18

Describe the Messon-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 containg light isotpe 14N.Samples were extracted after 1& 2 cycles od DNA replication
2. Centrifugation formed a pellet.Heavier DNA(bases made from 15N) settled closer to the bottom of the tube

Question 19

Explain how the Messon-Stahl experiment validated semi-conservative replication

Answer 19

Where the DNA settled show that the bacterial DNA had replicated semiconservatively

Question 20

Describe the structure of adenosine triphosphate (ATP)

Answer 20

Nucleotide derivative of adenine with three phosphate groups

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 resyntheisied in cells?

Answer 22

-ATP synthase catalyses condensation reaction between ADP&Pi
-During photosynthesis and respiration

Question 23

Explain why ATP is suitable as the enrgy currency of cells

Answer 23

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 resynthsised