nucleic acids and ATP

Question 1

structure of a nucleotide

Answer 1

phosphate group
pentose sugar
nitrogenous base

Question 2

role of DNA in living cells

Answer 2

base sequence of genes codes for functional RNA and AA sequence of polypeptides

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

Question 3

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 (along with proteins)

tRNA: supplies complementary AA to mRNA codons during translation

Question 4

how do polynucleotides form

Answer 4

condensation reaction between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone)

Question 5

structure of DNA

Answer 5

double helix- 2 polynucleotide chains (deoxyribose)

H-bonds between complementary purine + pyrimidine base pairs on opposite strands:
A+T
C+G

Question 6

which bases are purine and which are pyrmidine

Answer 6

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

Question 7

name the complemetary base pairs in DNA

Answer 7

2 H-bonds between A+T
3 H-bonds between G+C

Question 8

name the complementary base pairs in RNA

Answer 8

2 H-bonds between A+U
3 H-bonds between G+C

Question 9

relate the structure of DNA to its functions

Answer 9

sugar phosphate backbone+lots of H bonds = stability

long molecule= stores lots of info

compact helix= storage in nucleus

base sequence of triplets = codes for AA

double stranded= semi-conservative replication

complementary base pairing= accurate replication

weak H bonds= strands seperate for replication

Question 10

structure of mRNA

Answer 10

-long ribose polynucleotide (shorter than DNA)
-uracil not thymine
-single stranded and linear (no complementary base pairing)
-codon sequence complementary to exons of 1 gene from 1 DNA strand

Question 11

relate the structure of mRNA to its functions

Answer 11

-breaks down quickly so no excess polynucleotide forms
-ribosome can move along strand and tRNA can bind to exposed bases
-can be translated into a specific polynucleotide by ribosomes

Question 12

structure of tRNA

Answer 12

-single strand of about 80 nucleotides
-folded into clover shape (some paired bases)
-anticodon one one end, AA binding site on other
a) anticodon binds to complementary mRNA codon
b) AA corresponds to anticodon

Question 13

order DNA, mRNA, tRNA according to increasing length

Answer 13

tRNA
mRNA
DNA

Question 14

why did scientists initially doubt that DNA carried the genetic code

Answer 14

chemicallly simple molecule with few components

Question 15

why is DNA replication considered ‘semi-conservative’

Answer 15

-strands from original DNA molecule acts as template
-new DNA molecule contains 1 odd and 1 new strand

Question 16

process of semi-conservative replication

Answer 16

1) DNA helicase breaks H bonds between base pairs
2) each strand acts as a template
3) free nucleotides attatch 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 17

describe Meselson-Stahl experiment

Answer 17

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 pellet- heavier DNA (bases made from 15N) settled closer to bottom of tube

Question 18

explain how the Meselson-Stahl experiment validated semiconservative experiment

Answer 18

• growth in 15N
  1st division- all molecules have 1 strand 15N and 1 strand 14N
  2nd division- 50% have 2 strands 14N + 50% have 1 strand 15N and 1 strand 14N

Question 19

structure of ATP

Answer 19

ribsose sugar
adenine
3 phosphates

Question 20

role of ATP in cells

Answer 20

ATP hydrolase catalyses ATP to ADP and Pi
-energy released is coupled to metabolic reactions
-phosphate group phosphorylates compounds (make them more reactive)

Question 21

how is ATP resynthesised in cells

Answer 21

ATP synthase catalyses condensation reaction between ADP and Pi during photosynthesis and respiration

Question 22

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

Answer 22

-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