BIOLOGY_FLIPBOOK: MOLECULES OF LIFE & CELL STRUCTURES AND FUNCTIONS

Set E Questions

i. State the main types of molecules of life. [5 marks]
ii. Compare and contrast between DNA and RNA. [19

marks]
iii. Explain how to calculate the percentage of cytosine

if a DNA molecule contains 24% thymine. [5 marks]
iv. Both prokaryotic and eukaryotic cells contain DNA.

Differentiate the DNA in prokaryotic and eukaryotic
cells. [6 marks]

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i. State the main types
of molecules of life.

Molecules of
life

Water Carbohydrates Lipids Proteins Nucleic acid
(DNA & RNA)

ii. Compare and contrast between DNA
and RNA.

DNA RNA

Similarities:

Both DNA and RNA are nucleic acids made up of monomers called
nucleotides
Both DNA and RNA contain a phosphate group, pentose sugar and
nitrogenous base
Both DNA and RNA have their nucleotides linked to each other by
phosphodiester bond between sugar and phosphate group.

Both DNA and RNA can undergo change, or mutation
Both DNA and RNA are essential for heredity in all living cells

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Differences: DNA RNA 5
Structure
Pentose sugar Double stranded (anti-parallel) Single stranded
Nitrogenous bases Deoxyribose Oxyribose
Adenine, thymine, guanine and Adenine, uracil, guanine and
Base pairs cytosine (A,T,G,C) cytosine (A,U,G,C)
Adenine and thymine pair (A-T) Adenine and uracil pair (A-U)
Size Guanine and cytosine pair (G-C) Guanine and cytosine pair (G-C)
Larger Smaller

Differences: DNA RNA
Reactivity
Ratio of nitrogenous bases More stable/ permanent Less stable/ non-permanent
Ratio of A to T and G to C is one Ratio of A to U and G to C varies

Type Has only one type of DNA Has three types of RNA
(mRNA, rRNA, tRNA)

Function Stores genetic information in Transfer genetic information to
chromosomes ribosomes for translation
Location in cell Nucleoid and plasmids Nucleoid, plasmids and ribosomes
(prokaryotes)
Location in cell Nucleus, mitochondria and Nucleolus and ribosomes
(eukaryotes) chloroplast (in plants)
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iii. Explain how to calculate the
percentage of cytosine if a DNA
molecule contains 24% thymine.

adenine: [A] thymine: [T] [A] + [T] = 24 + 24

guanine: [G] cytosine: [C] = 48%

According to Chargaff’s rule, Therefore, [G] + [C] = 100 – 48

amount of purines = amount of pyrimidine = 52%

[A] + [G] = [T] + [C] Since [G] = [C],

adenine [A] is paired to thymine [T], [A] = [T] [C] = 52 ÷ 2

guanine [G] is paired to cytosine [C], [G] = [C] = 26%

Given that: Percentage of cytosine = 26%

a DNA molecule contains 24% thymine,

[T] = 24%

Thus, [A] = 24% 7

iv. Both prokaryotic and eukaryotic cells contain
DNA. Differentiate the DNA in prokaryotic and
eukaryotic cells.

Diagram of Shape Size Location Number Presence of DNA replication
cells Circular Small Single histone protein occurence
Not enclosed by
DNA in nuclear envelope, Not associated DNA replication
prokaryotic lies freely in with histone occurs in
cell cytoplasm, located protein (naked cytoplasm
in nucleoid DNA)

DNA in Linear Large Enclosed in nuclear Multiple Associates with DNA replication
eukaryotic envelope, within histone protein occurs within
cell nucleus nucleus

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Thank you!

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