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Biological Molecules 3
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1
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The negative region forms a weak electrostatic bond between the positively
charged region of another molecule
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g
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g
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of monomers joined together

Condensation reactions - joins two molecules, forming a chemical bond and involves the elimination of a water molecule
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Metabolism - sum of chemical processes taking place in a living organism
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A condensation between two monosaccharides form a glycosidic bond:


- Glucose + glucose = maltose

- Glucose + fructose = sucrose

{e
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of disaccharides}


- Glucose + galactose = lactose

Glucose is a hexose sugar (6 carbons)
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A reducing sugar
donates an electron to another chemical
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Should turn orange if a
reducing sugar is present
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Then heat, if it doesn’t change
colour then a REDUCING sugar is not present
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Slowly add sodium hydrogen carbonate to neutralise HCl (Benedict’s reagent does not work in acidic conditions)
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This is due
to the reducing sugars that were produced from the hydrolysis of a non-reducing sugar
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Forms bonds at c1,c4 and c1,c6

• Chains maybe branched or unbranched - branched form a helix shape that makes it compact (so a lot can be held in a
small space)- held by hydrogen bonds
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• TEST FOR STARCH: 2cm3 of food sample, 2 drops of iodine solution, shake, blue-black colour in starch is present


Glycogen: stored in muscle/liver cells

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Large/Insoluble so does not draw water into cells by osmosis


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Compact - a lot can be stored in a small space


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Highly branched, more so than starch, so it has more enzymes acting on it simultaneously
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Forms bonds at c1,c4 and c1,c6


Cellulose: for plants

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Made up of b-glucose
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Straight, unbranched chains, which run parallel to one another, allowing hydrogen bonds to form cross links between
adjacent chains
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Other roles include
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Each fatty acid form an ester bond with the
glycerol in a condensation reaction
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Fatty acids all have a carboxyl group (—COOH) attached to a hydrocarbon;

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fatty acid with no carbon-carbon double bond = saturated (all carbons linked to max possible no
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The fatty acid ‘tail’ is hydrophobic

The phosphate ‘head’ is hydrophilic

Therefore, as the molecule has 2 poles behaving differently, it is polar
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Structure related to its properties:
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As it is polar, in water, it forms a bilayer within cell- surface membranes - so a hydrophobic barrier is formed between
inside and outside the cell


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Allows glycolipids to form by combining with carbohydrates within the cell-surface membrane - important for cell
recognition


3

Test for lipids:
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dry, grease-free test tube


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Add 2cm3 of food sample and 5cm3 of ethanol


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Shake to dissolve any lipids


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Add 5cm3 of water


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A cloudy white colour = lipids present


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As a control, repeat using water


The cloudy white colour is the lipid being finely dispersed in
the water to form emulsion
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4 Proteins

3
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4
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The general structure of an amino
acid:

Every amino acid has a carbon atom which is attached to 4 different chemical groups:


-Amine group (-NH2)

-Carboxyl group (-COOH)]

-A hydrogen atom (-H)

-R group - the 20 amino acids that are common In all organism differ only in their R group

Peptide bond formation: Amino acids react in a condensation reaction to
form a dipeptide; and more than 2 amino acids males a polypeptide
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The structure of proteins:
Primary: the sequence of amino acids

Secondary: The amino acids form weak hydrogen bonds because the
hydrogen on the —NH group has an overall positive charge but the oxygen in
the —C=O group has an overall negative charge
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Tertiary structure: Forms; disulphide bridges, ionic bonds (forms between amine/carboxyl groups), and further hydrogen
bonds
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For example Haemoglobin is formed by a non-protein
group such as iron containing haem group
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2 Enzymes:

An enzyme lowers the activation energy of the reaction it catalyses by offering alternative route

Active site - specific sequence of amino acids with a particular R groups allowing to form temporary bonds with the
complementary substrate
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They have an active site made up of a small no
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A substrate binds to the active site, forming an enzyme substrate complete, and forms temporary bonds
with the amino acids
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Substrate forms temporary
bonds with amino acids due to the properties of the specific R groups
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Factors affecting enzyme action:
Before considering pH, temp and concentration - the enzyme must - come into physical contact with the substrate and
have an active site which fits the substrate
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Then we can identify the height and width and
then we can divide height by the width to find the gradient
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Then, they move around more quickly
and collide more often , increases rate of reaction, and forming enzyme substrates more quickly
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This leads to the active site changing, soothe substrate is no
longer complementary
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Effect of pH: (ph of a solution is a measure of its hydrogen ion concentration)
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pH of a
solution is given by = -log10[H+]
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The pH affects
the rate of enzyme action in the following ways;


- Alters charge on the amino acids that make up the active site
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- Depending on how significant the change in pH is, it may cause the bonds maintaining the enzyme’s tertiary structure
to break, therefore active site changes shape
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Change in H+ ions affects this bonding
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Effect of concentration: Once active site on an
enzyme has cited on its substrate, it s free to
repeat the procedure on another molecule
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As long as
there is an an excess of substrates, an increase
in the amount of enzymes leads to the
proportionate increase in the rate of reaction
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This is because there is
more substrate than enzyme’s active sites can
cope with
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If, however, the substrate
is limiting, then any increase in enzymes will not effect rate of reaction
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This is because the available substrate is already being used rapidly as it can be by the existing enzymes
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Meaning substrates and inhibitors compete
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If the substrate concentration is
increased, the effect of the inhibitor is reduced
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Eventually all the substrates will occupy an active
site , but greater the no
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Non competitive inhibitors: Binds to substrate away from the active site, this causes a change in the tertiary structure
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As they
are not competing for the same site, an increase in substrate concentration does not decrease the effect of the inhibition
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A
low value of Vmax means that the enzymes does not convert much
substrate to its products per unit time when the enzyme is saturated
with the substrate
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Enzymes have varying affinities to bind to their substrates
(Km)
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A low value of Km means only a small amount of substrate is
needed to saturate the enzyme, indicating a high affinity for the
substrate
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Therefore, the Km value and the concentration the enzyme is
exposed to, affects the enzymes rate of reaction
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1 Structure of RNA and DNA

Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are important information-carrying molecules
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Nucleotide structure:

Made up of three components;

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A pentose sugar (has five carbon atoms)


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A phosphate group


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A nitrogen containing organic base - Cytosine, Thymine, Uracil, Adenine and Guanine


These components are joined by a series of condensation reactions, to form a single nucleotide (mono)
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RNA structure: A polymer made up of nucleotides
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One type of RNA transfers genetic information from
DNA to the ribosomes
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The third type of
RNA is involved in protein synthesis
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DNA is made up two strands of
nucleotides, which are extremely long and are joined together by hydrogen bonds (between certain bases)
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The quantities of A and T are the same
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-The stability of DNA: due to the - phosphodiester backbone which protects the more chemically reactive organic bases
inside the double helix - and the hydrogen bonds that link the organic base pairs forming bridges between the
phosphodiester uprights
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Function of DNA: is hereditary material responsible for passing genetic information
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g
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g
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2 DNA replication:

DNA held in a nucleus to prevent mutation

Ensures genetic continuity between generations cells
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Semi-conservative replication:

4 requirements

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Four types of nucleotide, each with their bases on A,G,C,T must be present
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The bonds between the phosphate groups are very unstable and have a low
activation energy, which means are easily broken
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ATP + H20 ———> ADP (adenosine diphosphate) + P (phosphate) + E (energy)


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As water is used to convert ATP to ADP, this is a hydrolysis reaction - catalysed by the enzyme ATP hydrolase
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This reaction occurs in three ways - in chlorophyll containing plant seeks during photosynthesis; in plant/animals
cells during respiration
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ATP is for
immediate energy source of a cell
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Better immediate source of energy than glucose;


- each ATP molecule releases less energy than each glucose molecule
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- The hydrolysis of ATP to ADP in a single reaction releases energy
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ATP cannot be stored so has to be continuously made within mitochondria cell
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Energy requiring processes include;


- metabolic processes - provides energy for the build up f macromolecules from their basic units

- Movement

- Secretion


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7 Water

A water molecule is made up of two hydrogen atoms and an oxygen negative (o2) poles and positive (H) poles makes it a dipolar
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The attractive forces between poles is a hydrogen bond
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Latent heat of vaporisation: Hydrogen bonding means that it requires lots of energy to evaporate 1 gram of water
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With its hydrogen
bonding, water has large cohesive forces and these allow it to be pulled up the xylem vessel
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Water in metabolism: water is used to break down molecules by hydrolysis and is needed in photosynthesis
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Each type of ion has a specific role, depending on its properties
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g iron in haemoglobin where they help transport
oxygen by binding to it

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