Nucleotides And Nucleic Acids

Question 1

What pentose sugars are in DNA & RNA

Answer 1

DNA - Deoxyribose
RNA - Ribose

Question 2

How are polynucleotide strands formed ?

Answer 2

Condensation reactions between nucleotides which form strong phosphoiester bonds

Question 3

How are polynucleotides broken down ?

Answer 3

Hydrolysis reactions which use a molecule of water to break the bonds

Question 4

What is the strcuture of DNA ?

Answer 4

Molecules twist to from double helix of 2 deoxyribose polynucleotide strands. Creating a sugar phosphate backbone. Hydrogen bonds form between complementary bases (AT & GC)

Question 5

Name the complementary base pairs in DNA and RNA ?

Answer 5

DNA - 2 H-bonds between Adenine and Thymine
RNA - 2 H-bonds between adenine and Uracil
Both - 3 H-bonds between guanine and Cytosine

Question 6

Why is DNA replication described as semiconservative ?

Answer 6

The strand of original DNA molecule act as templates
(New DNA molecule contains 1 old & 1 New strand)

Question 7

What is the role of DNA helicase in semiconservative replication ?

Answer 7

Breaks hydrogen bonds between base pairs to form 2 single strands, each of which can act as a template

Question 8

How is a new strand formed during Semi conservative replication ?

Answer 8

Free nucleotides attach to exposed bases by complementary base pairing
DNA polymerase joins the nucleotides in a 5-3 direction via condensation reactions forming phosphodiester bonds
Hydrogen bonds reform

Question 9

What are the features of the genetic code ?

Answer 9

Non-Overlapping - Each triplet is only read once
Degenerate - More than one triplet codes for the same amino acids
Universal - Same bases and sequences used by all species

Question 10

How does a gene determine the sequence of amino acids in a protein ?

Answer 10

Consist of base triplets that code for a specific amino acid

Question 11

How can DNA be purified by precipitation

Answer 11

Add ethanol & salt to aqueous solution. Nucleic acids precipitate out of solution
Centrifuge to obtain pellet of nucleic acid. Wash the pellet with ethanol and centrifuge again

Question 12

What does transcription produce and where does it occur ?

Answer 12

Produces mRNA
Occurs in the nucleus

Question 13

What is the process of transcription ?

Answer 13

• DNA Helicase breaks hydrogen bonds between complementary bases pairs, DNA Uncoils
• One of the DNA strands is used as a template to make a mRNA molecule
• Free Nucleotides line up by complementary base pairing, RNA Polymerase bonds adjacent nucleotides by phosphodiester bonds
• Single strand of mRNA formed

Question 14

What happens after a strand of mRNA is transcribed ?

Answer 14

• RNA polymerase detaches
• H bonds reform & DNA Recoils
• mRNA then leaves the nucleus through nuclear pores and attaches to a ribosomes to undergo translation

Question 15

What does Translation produce and where does it occur ?

Answer 15

Produces Proteins
Occur in ribosomes or cytoplasm

Question 16

Outline the process of translation ?

Answer 16

• MRNA attaches to a ribosome and tRNA collects amino acids from the cytoplasm and carries them to the ribosome
• Ribosomes moves along mRNA until a ‘Start’ Codon
• tRNA anticodons attaches to complementary bases on mRNA (2 a time)
• Condensation reactions between amino acids on tRNA form peptide bonds
• Process continues until ‘Stop’ Codon is reached

Question 17

What is a mutation ?

Answer 17

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

Question 18

Draw the structure of a nucleotide

Answer 18

Refer to GoodNotes

Question 19

Name the Purine bases and refer to structure

Answer 19

Two-ring molecules
- Adenine (C5H5N5)
- Guanine (C5H5N5O)

Question 20

Name the pyramiding bases and describe their structure

Answer 20

• Thymine (C5H6N2O2)
• Cytosine (C4H5N3O)
• Uracil (C4H4N2O2)