Nucleotides and nucleic acids

Question 1

What is the structure of a nucleotide?

Answer 1

• Phosphate group
• 5 Carbon deoxyribose sugar
• Nitrogenous base

Question 2

What type of sugar is in a
1. DNA (deoribonucleic acid)
2. RNA (ribonucleic acid)

Answer 2

• DNA = deoxyribose
• RNA = ribose

Question 3

How does a polynucleotide strand formed and broken down?

Answer 3

• a condensation reaction between nucleotides which form stron phosphodiester bonds ( sugar-phosphate backbone
• Hydrolysis reaction use a molecule of water to break the bonds

Question 4

What is DNA?

Answer 4

• a polymer
• has phosphodiester bonds between the nucleotides
• consists of two phospodiester strands
• it has as sugar-phosphate back bone attached to complementary bases
• twisted in a double helix shape
• hydrogen bonds between complentary base pairs that run antiparallel

Question 5

What are the purines and the pyrimidine bases?

Answer 5

Purine - 2 ring molecules
* adenine
* guanine
Pyrimidines - one ring molecules
* cytosine
* thymine
* uracil

Question 6

What the complementary base pairs in DNA?

Answer 6

• 2 hydrogen bonds between A + T
• 3 hydrogen bonds between G + C

Question 7

What does the term semi-conservative mean in DNA replication?

Answer 7

• Strands from original DNA molecule act as templates
• New DNA molecule contains 1 old strand and 1 new strand (specific base pairing enables genetic enables genetic material to be conserved accuratly )

Question 8

Explain DNA replication

Answer 8

1. DNA untwists and unzips (hydrogen bonds are hydrolysed)
2. Free nucleotides in the nucleoplasm bind at the exposed complementary bases
3. Hydrolysis releases the extra phosphate groups from the nucleotides and supplies the energy to form the phosphodiester bonds between the sugar of one nucleotide and the phosphate of the adjancet nucleotide. This is cataylsed by the enzyme DNA polymerase
4. This occurs in the 5 to 5 and thte 3 to 3 direction
5. The leading strand is synthesised continuously as DNA polymerase keeps working in the 5 to 3 direction as new bases are exposed. The lagging strand is synthesised in fragments ( okazaki fragments) joined using ligase enzymes.

Question 9

What are features of the genetic code?

Answer 9

• universal - same bases and sequences used by all species
• Triplet -three bases code for one amino acid
• degenerate - more than one triplet codes for same amino acid
• **non overlapping **- each triplet is only read once

Question 10

how does a gene determine the sequence of amino acids ?

Answer 10

Consists of base triplets that codes for specific amino acids

Question 11

Describe how DNA can be purified and extracted?

Answer 11

1. Add dish soap , salt , fruit ( kiwi) in a ziplock bag and remove as much air as possible
2. Crush the fruit , and then sieve into a beaker then transfer to a boiling tube
3. Slowly and carefully , 5 ml of chilled ethanol down the side
4. There should be a separation of white preciptate

Question 12

Outline the process of transcription

Answer 12

mRNA is formed in the nucleus :
1. A section of the DNA unzips ( Hydrogen bonds between base pairs break )
2. Activated RNA nucleotides ( they have two extra phosphate groups ) for H bonds wirh complementary bases on template strand in the nucleolous
3. The enzyme RNA polymerase checks for mistakes and catalyses the formation of phosphodiester bonds between the mRNA nucleotides forming the sugar-phosphate backbone - checks for mistakes
4. The release of the phosphate backbone provides energy for bonding to adjacent nucleotides
5. At the stop triplet the mRNA breaks off and leaves th nucleus via a nuclear pore
6. In the cytoplasm, the mRNA strand attaches to a ribosomes

Question 13

Outline the process of translation

Answer 13

1. Ribosomes moves along mRNA until start codon
2. tRNA anticodon attaches to complementary bases on mRNA
3. A second tRNA anticodon joins to the second codon with is complementary anticodon
4. A condensation reaction takes place between the amino acids - this requires energy and ATP
5. This continues down the lendth od mRNA till a polypeptide chain until a stop codon is reached

Question 14

What is ATP and ADP?

Answer 14

1. adenosine triphosphate - 3 inorganic phosphate groups
2. adenosine diphospahte - 2 inorganic phosphate groups

Question 15

What is a mutation?

Answer 15

An alteration to the DNA base sequence . Mutations often arise spontaneously during DNA replication .

Question 16

What is tRNA?

Answer 16

• a single stranded polynucleotide folded into three hairpin loops
• one free end of unpaired bases joins to a specific amino acid
• at the opposite end there is a anticodon complementary codon

Question 17

What is DNA in eukaryotic cells?

Answer 17

• The majority of DNA in the nucleus
• Wound around the histone making chromosomes
• loops of DNA without histones

Question 18

What is DNA in prokaryotic cells?

Answer 18

• Loop within the cytoplasm
• naked - not wound around cytoplasm
• small loops called plasmids