3.1.5 Nucleic acids

Question 1

Draw the structure of a nucleotide

Answer 1

Phosphate group
Pentose sugar
Nitrogenous base

Question 2

Name the pentose sugars in DNA and RNA

Answer 2

DNA: Deoxyribose
RNA: 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 of polypeptides
Genetic information determines inherited characteristics = influences structure and function of organisms

Question 4

State the role of RNA in living cells

Answer 4

mRNA: Complementary sequence to 1 gene from DNA with introns spliced out. Codons can be translated into a polypeptide by ribosomes
rRNA: Component of ribosomes
tRNA: Supplies complementary amino acid to mRNA codons during translation

Question 5

How do polynucleotides form

Answer 5

Condensation reactions between nucleotides form strong phosphodiester bonds
between phosphate group and deoxyribose

Question 6

Describe the structure of DNA

Answer 6

Double helix
H bonds between complementary base pairs on opposite strands (A-T C-G)

Question 7

How many hydrogen bonds between each base pair

Answer 7

2 between A and T
3 between C and G

Question 8

Name the complementary base pairs in RNA

Answer 8

Adenine and uracil
Guanine and cytosine

Question 9

Relate the structure of DNA to its functions

Answer 9

Helix is compact for storage in nucleus
Double stranded for semiconservative replication
Long molecule stores lots of information
Base sequence of triplets codes for amino acid

Question 10

Describe the structure of mRNA

Answer 10

Contains uracil instead of thymine
Single stranded and linear
Codon sequence is complementary to exons of 1 gene from 1 DNA strand

Question 11

Relate the structure of mRNA to its functions

Answer 11

Long - breaks down quickly so no excess polypeptide forms
Single stranded and linear - ribosomes can move along strand and tRNA can bind to exposed bases

Question 12

Describe the structure of tRNA

Answer 12

Single strand
Folded into clover shape
Anticodon in one end, amino acid binding site on other

Question 13

Why did scientists initially doubt that DNA carried the genetic code

Answer 13

Chemically simple molecule with few components

Question 14

Why is DNA replication described as semi conservative

Answer 14

Strands from original DNA molecule act as a template
New DNA molecule contains 1 old strand and 1 new strand

Question 15

Outline the process of semiconservative DNA replication

Answer 15

1. DNA helicase breaks H bonds between base pairs, unwinds helix
2. Each strand acts as a template
3. Free DNA nucleotides join to complementary base pairings AT CG
4. DNA polymerase forms the new strands by forming phosphodiester bonds
5. Replication is semiconservative
6. Each of the DNA molecules formed has one old and one new strand