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Worksheet 9.1
Chapter 9: Cells and energy – fifteen summary facts
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There are four levels of protein organization:
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primary level – involves the sequence of amino acids
secondary level – involves hydrogen bonds between the carboxyl and amino groups of
separate amino acids
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tertiary level – involves interactions among R-groups of separate amino acids
quaternary level – involves multiple peptide chains which combine to form a single chain.
Not all proteins have quaternary level organization.
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Fibrous proteins produce long, narrow shapes; globular proteins are more three-dimensional in
shape. Fibrous proteins are usually insoluble in water; globular proteins are usually water soluble.
Actin is an example of a fibrous protein; haemoglobin is an example of a globular protein.
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Amino acids may be grouped according to the properties of their side chains (R-groups) into polar
and non-polar amino acids. Polar amino acids have hydrophilic properties and occur near the
exterior and interior of cell membranes. Polar and non-polar amino acids are important in
determining the specificity of an enzyme. Active sites of enzymes often involve polar and nonpolar amino acids in their make-up and this affects whether the substrate will ‘fit’ or not.
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Enzymes speed up both anabolic and catabolic reactions without being changed themselves. The
way they work is explained by the induced-fit model. This model is different from the lock-andkey model in that the enzyme’s active site and the substrate change shape once they are in contact
to bring about a closer fit for the lowering of the activation energy, which allows the reaction to
proceed more rapidly.
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Activation energy is the energy necessary to destabilize chemical bonds in a substrate in order to
bring about some change.
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In competitive inhibition, a molecule called a competitive inhibitor, competes directly for the
active site of an enzyme. In non-competitive inhibition, the inhibitor does not compete for the
enzyme’s active site. It combines with the allosteric site and brings about a change in
conformation of the active site, thus inhibiting the enzyme. End-product inhibition involves noncompetitive inhibition to stop a metabolic pathway.
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Oxidation and respiration are important to both cell respiration and photosynthesis. Oxidation
involves loss of electrons, gain of oxygen, loss of hydrogen and a compound with lower potential
energy. Reduction involves gain of electrons, loss of oxygen, gain of hydrogen, and a compound
with higher potential energy. If a compound is oxidized, another substance must be reduced thus
causing a redox reaction.
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Cell respiration includes glycolysis, anaerobic respiration and aerobic respiration. The link
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reaction, the Krebs cycle and oxidative phosphorylation occur in aerobic respiration within the
mitochondrion. Glycolysis and anaerobic respiration occur in the cytosol.
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The electron transport chain and chemiosmosis are the processes by which most ATPs are
produced. These processes occur on the inner mitochondrial membrane and on the membranes of
the cristae. FADH2 and NADH bring the energy-rich electrons to the electron transport chain.
Oxygen is the final acceptor of the chain’s energy-rich electrons to form ‘water of metabolism’.
10 The final ATP net gain of aerobic cellular respiration is 36 ATPs. The cell is most efficient at
breaking down the carbohydrate glucose; however, other organic compounds are commonly
broken down by respiration.
11 Photosynthesis occurs in the chloroplasts of autotrophic cells. The process of photosynthesis
involves light-dependent and light-independent reactions. Thylakoids have photosystems that
include chlorophyll a molecules, accessory pigments, and a protein matrix. Photosystem I and
photosystem II both operate to carry out the light-dependent reaction of photosynthesis.
12 Products of the light-dependent reaction are ATP, free oxygen, and NADPH. These products are
then used by the light-independent reaction to form glucose and ultimately complex carbohydrates.
13 The light-independent reaction involves the Calvin cycle and begins and ends with the compound
RuBP (ribulose bisphosphate). Triose phosphate (TP) is the pivotal compound of the Calvin cycle,
which produces glucose, disaccharides, polysaccharides, or RuBP.
14 The absorption spectrum of photosynthesis represents the wavelengths of light absorbed by the
pigments of the chloroplast. The action spectrum of photosynthesis represents the effectiveness of
different wavelengths of light in carrying out photosynthesis. There is a strong positive correlation
between the action spectrum and the absorption spectrum.
15 Many factors may affect the rate of photosynthesis. These include temperature, light intensity, and
carbon dioxide concentration. If any one of these factors is below a certain level and affects the
rate of photosynthesis, it is called a limiting factor.
© Pearson Education Ltd 2010. For more information about the Pearson Baccalaureate series please visit
www.pearsonbacc.com
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