BIOLOGICAL MOLECULES - nucleic acids and DNA, ATP, evidence for semi conservative replication

Question 1

draw the structure of a nucleotide?

Answer 1

phosphate-sugar-base

Question 2

name the pentose sugars in RNA and DNA?

Answer 2

RNA - ribose
DNA - deoxyribose

Question 3

state the role of DNA in living cells?

Answer 3

The base sequence of genes codes for functional RNA and amino acid sequence of polypeptides.
Contains genetic information which determines inherited characteristics which influences structure and function of organisms.

Question 4

State the role of RNA in living cells?

Answer 4

mRNA - carries the genetic code from the DNA to the ribosome, where it’s used to make a protein during translation.

rRNA -involved in synthesisising proteins and catalyses the peptide bond formation

tRNA- supplies complementary amino acids to mRNA codons during translation.

Question 5

How do polynucleotides form?

Answer 5

condensation reactions between nucleotides forming strong phosphodiester bonds ( sugar phosphate backbone)

Question 6

describe the structure of DNA

Answer 6

double helix of 2 polynucleotide strands
Hydrogen bonds between complementary purine and pyrimidine base pairs on opposite strands.

A and T
C and G

Question 7

which bases are purine and which bases are pyrimidine?

Answer 7

A and G - 2 ring purine bases
T and C - 1 ring pyrimidine base

Question 8

Name the complementary base pairs in DNA?

Answer 8

adenine thymine - 2 h bonds
cytosine guanine - 3 h bonds

Question 9

Name the complementary base pairs in RNA?

Answer 9

Adenine and Uracil - 2 h bonds
Guanine and cytosine - 3 h bonds

Question 10

relate the structure of DNA to its functions?

Answer 10

• sugar phosphate backbone and many hydrogen bonds provides stability
• long molecules stores a lot of information
• helix is compact for storage in nucleus
• base sequence in triplets codes for amino acids
• double stranded for semi- conservative replication
• complementary base pairing for accurate replication
• weak h bonds so strands separate for replication

Question 11

describe the structure of messenger RNA?

Answer 11

long ribose polynucleotide
shorter than DNA
contains uracil instead of thymine
single stranded and linear

Question 12

relate the structure of mRNA to its function?

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

why is DNA replication described as ‘semiconservative’?

Answer 13

• strands from original DNA act as a template
• new DNA molecule contains one old strand and one new strand

Question 14

outline the process of semiconservative DNA replication?

Answer 14

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

Question 15

describe the meselson-stahl experiment?

Answer 15

1. bacteria were grown in a medium containing heavy isotopes of 15-Nitrogen for many generations.
2. some bacteria were moved to another medium containing light isotope 14-N.
3. samples were extracted after 1 and 2 cycles of DNA replication
4. centrifugation formed a pellet. Heavier DNA (15N) settled closer to the bottom of the tube.

Question 16

describe the structure of adenosine triphosphate (ATP)

Answer 16

adenine
ribose sugar
3 phosphate groups

Question 17

explain the role of ATP in cells?

Answer 17

ATP hydrolase catalyses ATP —-> ADP +Pi
- Small and soluble so easily transported around the cell
-phosphate group phosphorylates compounds to make them more reactive

Question 18

how is ATP resynthesised in cells?

Answer 18

ATP synthase catalyses condensation reactions between ADP and Pi, during photosynthesis and respiration

Question 19

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

Answer 19

• high energy bonds between phosphate groups
• small amounts of energy is released at a time = less energy is wasted as heat
• single step hydrolysis = energy is available very quickly
• readily resynthesised