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Topic 2 – Molecular Biology

Molecules to Metabolism
Metabolism is the web of all the enzyme-catalysed reactions in an organism
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Catabolism is the
breakdown of complex molecules from simpler molecules including the hydrolysis of macromolecules
into monomers
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There are now examples of organic molecules which can be
artificially synthesised, such as urea, which falsifies the theory of vitalism
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There is a
difference in charge from one side of the molecule to the other
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These bonds give water its cohesion
properties
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Adhesion refers to the
binding between different polar molecules
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This means that more energy is stored and a lot of heat is needed to
warm it up
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It is
used as a coolant in sweat because it has high heat vaporisation so it can evaporate from the skin
quickly
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Monosaccharides are small and soluble and may be joined together to make larger carbohydrates by
condensation reactions
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From left to right: α glucose, β glucose, and ribose
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Fructose is found in the fruit and berries of a plant
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Disaccharides consist of two monosaccharides joined together by a condensation reaction
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Maltose is formed by two glucose
molecules, lactose is formed by glucose and galactose molecules,
and sucrose is formed by glucose and fructose molecules
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Starch and glycogen are
examples of polysaccharides formed by the condensation of α glucose
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Glycogen is found in the liver and muscles of animals and
provides energy as a short term energy store
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It is found in plants and gives support and strength
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Glycogen has shorter chains and is more highly branched because
animals have a higher rate of respiration
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Both are insoluble so they don’t
attract water molecules and affect the water potential
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Cellulose is not an energy store because it gives strength
and support
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The R group in a fatty acid is always a hydrocarbon chain
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Unsaturated fats have at least one double bond, and
saturated fats have a straighter chain
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Trans fats are formed when liquid oils are hydrogenated and
converted into solid fats
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Triglycerides form when a condensation reaction joins three fatty acids and one molecule of glycerol
together
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The bond between the glycerol and
the fatty acid is called an ester bond
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Lipids are suitable for long-term
energy storage because one gram of fat gives twice as much energy as one
gram of carbohydrates
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Add an equal amount
of Benedict’s reagent and heat
in a boiling water bath for 5
minutes
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Pour the mixture into water
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Positive Result
The sample should turn orange
and there should be an
orange/red precipitate
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The sample should turn dark
blue/black
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There are
twenty different amino acids that make up proteins and each
one is coded for by a different gene
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A peptide
bond holds the two amino acids together
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Proteins are made in the ribosomes in the cytoplasm of the cell
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The sequence of amino acids
determines how this is done
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Functions of proteins:
Rubisco: the enzyme with an active site that catalyses the photosynthesis reaction that fixes carbon
dioxide from the atmosphere, providing all the carbon needed by living organisms to make sugars and
other carbon compounds
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Immunoglobulins: antibodies that bind to antigens on pathogens
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Rhodopsin: the pigment that makes the rod cells of the retina light-sensitive
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Collagen: a structural protein
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Spider silk: a structural protein that is used to make webs for catching prey and lifelines on which
spiders suspend themselves
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A proteome is the entire set of proteins expressed by the genome including cells, tissues, and organs
at a certain time
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Enzymes
Enzymes are biological catalysts and have a tertiary structure
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Binding of substrates to active site reduces
energy needed for them to react
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This is because collisions
between substrate and active site happen more frequently at
higher temperatures due to faster molecular motion
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This is because heat causes vibrations inside
enzymes which break bonds needed to maintain the structure
of the enzyme
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Below a certain pH the acidity denatures the
enzyme and it does not catalyse the reaction at all
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Above a certain pH the alkalinity denatures
the enzyme and it does not catalyse the reaction
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More
random collisions occur due to high substrate concentration
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Low concentration increases activity
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Ionic and
hydrogen bonds are broken (disulphide bridges)
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The substrate can no longer bind to form a
compound
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Milk is passed over the
beads and the lactase breaks down lactose into glucose and galactose
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These
combine to form a nucleic acid
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The four organic bases are
adenine, thymine, guanine, and cytosine
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Eventually a long chain of
nucleotides is formed called a polynucleotide
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The strong sugar phosphate backbone makes
the DNA molecule more stable
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Adenine and guanine
are the large bases and cytosine and thymine are the smaller bases
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During cell division, cytokinesis occurs to form new cells with their own nucleus
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Complimentary base pairing is significant because the strands need
to be the same as each other and the parent strand
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coli bacteria are grown on a medium containing 15N, then all their DNA is denser, so it will
move further down the centrifuge tube when centrifuged

During semi-conservative replication DNA helicase breaks the hydrogen bonds linking the base pairs,
the double helix separates into its two strands and unwinds
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DNA polymerase
joins the free nucleotides together and two new strands form
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Each one retains half of the original DNA strand
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The sense strand on DNA has the
same code as mRNA
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This is catalysed by RNA polymerase
This new strand (pre-mRNA) passes out of the nuclear membrane into the cytoplasm
It then goes to the ribosome for translation

Translation is the second step in protein synthesis
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Topic 2 – Molecular Biology
- The first tRNA is released back into the cytoplasm to
pick up another molecule of the same amino acid
- The process continues until a stop codon is reached
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A codon is three bases on
mRNA
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It is also universal, so there is exactly the same code in all organisms
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Aerobic respiration: 6O2 + C6H12O6  6H2O + 6CO2 + Energy
Aerobic respiration has a large yield of ATP – 36 ATPs per glucose molecule
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e
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6CO2 + 6H2O  C6H12O6 + 6O2
Action
Spectrum

Absorption
Spectrum

As chlorophyll absorbs mainly blue and red light it reflects green and therefore appears green
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Topic 2 – Molecular Biology
Factors Affecting Photosynthesis
As light intensity increases, the rate of photosynthesis increases
Further increases in light intensity do not give further increases in
photosynthesis
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g
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An increase in kinetic energy increases the collisions between enzymes and
substrates
As the temperature is increased further, the rate of photosynthesis
decreases due to plant cell enzymes denaturing

The Rf value in chromatography = distance run by pigment / distance run by solvent

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