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Summary Nucleic acids and their functions
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Cell cycle cell division
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Nucleic acids and their functions(a) the structure of nucleotides
Nucleotides are made up of a pentose sugar (deoxyribose in
DNA/ribose in RNA), phosphate group and nitrogenous base.
(b) the structure of ATP
Adenosine triphosphate is also a nucleotide; it has a ribose sugar,
three phosphate groups, and an adenine base.
(c) the central role of ATP as an energy carrier and its use in the liberation of
energy for cellular activity
When the high-energy bond between the second and third phosphate group is broken via
hydrolysis by the enzyme ATPase, 30.6kJ of energy is released for use in the cell, and
adenosine diphosphate is formed. This reaction is reversible, requiring energy from
respiration to reform the bond.
ATP -> ADP + Pi + 30.6kJ
(d) chemical energy in biological processes
Advantages of ATP:
Energy is released quickly from a one-step reaction involving just one enzyme (hydrolysis of
glucose takes many steps)
Energy is released in small amounts, 30.6kJ where it is needed. By contrast to the 1880kJ in
glucose wouldn’t be safe.
It is ‘universal energy currency’, i.e. It’s a common source of energy for all reactions in all
living things.
Roles of ATP in cells:
Used in anabolic reactions, e.g. DNA + Protein synthesis
Active transport
Muscle contraction
Nerve impulse transmission
(e) the structure of nucleic acids: DNA bases: purines-adenine and guanine,
pyrimidines-cytosine and thymine; complementary base pair rule; hydrogen
bonding and the double helix; antiparallel strands
DNA consists of two polypeptide strands that are arranged into a double helix.
First a dinucleotide is formed when a condensation reaction occurs between two
nucleotides: The 5th carbon of a deoxyribose sugar is joined to the 3 rd
deoxyribose sugar molecule above it, via the phosphate molecule.
This continues building a single strand of DNA in the 5’-3’ direction,
made up of phosphodiester bonds.
DNA forms a double-stranded molecule from 2 strands: one strand
runs the opposite direction to the other (anti-parallel).
Both strands are held together by hydrogen bonds forming between
complementary bases, the double strand twists creating a double
helix. Bases between both strands pair up in a certain way called the
complementary base pairing rule: Adenine-Thymine (2 H-bonds) and
Guanine-Cytosine (3 H-bonds). The H bonds are weak but altogether
very strong.
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