Essay
Importance of shapes fitting together in cells and organisms (25 marks)
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Accumulated 20/25 marks. Essay planning is essential to paper 3. Specific a-level terminology used.
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The importance of shapes of all organismsDNA is a polynucleotide characterised by a double helix structure composed of
two antiparallel strands, connected by hydrogen bonds. Within each nucleotide,
you'll find a phosphate group, a deoxyribose sugar, and a nitrogenous base
(either Adenine, Thymine, Cytosine, or Guanine). Complementary base pairs,
such as Adenine and Thymine, are bonded by two hydrogen bonds, while
Cytosine and Guanine are held together by three hydrogen bonds. The
significance of DNA's shape lies in the specificity of nitrogenous bases,
ensuring that each base pairs exclusively with its complementary base on the
adjacent nucleotide. Any alteration in this base shape disrupts complementarity,
rendering the DNA unable to carry genetic information during replication.
One example of DNA replication is semi-conservative replication, a process
vital for duplicating DNA before cell division, ensuring each new cell inherits a
complete set of genetic information. DNA helicase initiates replication by
breaking hydrogen bonds between complementary base pairs, causing the DNA
helix to unwind. Each original strand acts as a template for a new strand, with
exposed complementary bases joining together through a condensation reaction
catalysed by DNA polymerase. Hydrogen bonds form between bases in the
original and new strands, resulting in two identical DNA molecules. This
replication process is essential for interphase and ultimately dictates our
genotype.
Semi-conservative replication relies on enzymes like DNA polymerase, which
are biological catalysts that accelerate chemical reactions, such as metabolism.
Enzymes possess active sites that match specific substrates, allowing them to
form enzyme-substrate complexes that lower the activation energy required for
reactions. Enzymes are highly specific due to their complex tertiary structures.
For example, amylase catalyses the conversion of starch into maltose through
hydrolysis, a crucial step in digestion. Efficient digestion breaks maltose into
glucose, providing energy for aerobic respiration.
Enzymes are a type of protein with four structural levels: primary, secondary,
tertiary, and quaternary. The primary structure is a sequence of amino acids
linked by peptide bonds, dictated by DNA. Altering the primary structure affects
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