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1 - Biological Molecules (1 - Biological Molecules)

INTRODUCTION TO BIOLOGICAL MOLECULES
BONDING AND THE FORMATION OF MOLECULES
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covalent bonding - atoms share a pair of electrons in their outer shell
Ionic bonding - bond formed between ions with opposite charges
Hydrogen bonding - a polar molecule has an uneven distribution of charge
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12g of carbon-12 atoms contain 6
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This number is called the avogadro constant
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A chain of monosaccharides is called a
polysaccharide

MONOSACCHARIDES
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Monosaccharides are sweet tasting, soluble substances
Monosaccharide have the general formula (𝐶𝐻2𝑂)𝑛 , n can be any number
between 3 and 7

TEST FOR REDUCING SUGARS
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All monosaccharides and some disaccharides are reducing sugars
Reduction is a chemical reaction involving the gain of electrons or hydrogen

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The Benedict’s test:

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Add 2𝑐𝑚 of the food sample to a test tube
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Test with pH
paper to check is solution is alkaline

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3

3

3

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3

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Re-test solution by heating with 2𝑐𝑚 of Benedict’s reagent, in a gently
boiling water bath for 5 minutes
If a non-reducing sugar is present the benedict’s reagent will turn orange
-brown

POLYSACCHARIDES
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Polysaccharides are very large molecules and insoluble
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This is important as animals have a
higher metabolic rate than plants and also a higher respiration rate
Insoluble and compact

CELLULOSE
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Made of monomers of β glucose
Cellulose has straight unbranched chains with hydrogen bonds between them
Cellulose molecules group together to form microfibrils, these are then arrange
in groups called fibres
It is a structural material used in plant cell walls
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Lipids are used for:
○ Cell membranes - phospholipids help with flexibility of membranes
○ Source of energy - when oxidised they provide energy and release water
○ Waterproofing - insoluble in water
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A polypeptide is then formed
The sequence of amino acids forms the primary structure
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The O of -C=O has a negative charge
The 2 groups form hydrogen bonds
The polypeptide chain is twisted into a 3d shape called an α helix

THE TERTIARY AND QUATERNARY STRUCTURE OF PROTEINS
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The α helices are twisted and folded into a 3D structure
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If it remain blue then no proteins
are present

ENZYME ACTION

ENZYMES AS CATALYSTS LOWERING ACTIVATION ENERGY
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For reactions to take place naturally:
○ Substrate must collide with sufficient energy to alter arrangement
of atoms
○ Free energy of products just be less than substrates
○ Activation energy level must be overcome for reaction to proceed
Enzymes lower the activation energy which enables metabolic processes
to occur rapidly

ENZYME STRUCTURE
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Enzymes are globular proteins
The active site is made of amino acids
The molecule on which an enzyme acts is called a substrate
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This means more enzyme-substrate
complexes are formed and the rate of reaction increases
○ A temperature rise can cause hydrogen and other bonds to break
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g
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This means enzyme-substrate complexes can’t be
formed
○ It may also cause bonds maintaining enzymes tertiary structures to
break
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This alters the shape of the enzyme so substrates can’t occupy it
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The 2 trends are twisted to form a double helix

THE STABILITY OF DNA
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The phosphodiester backbone makes DNA stable because it protects
chemically reactive bases
Hydrogen bonds link base pairs
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THis is why sweat is effective in cooling the body
Water has large cohesive forces
○ Cohesion is molecules sticking together, these allow it to be pulled up
through the xylem vessel

THE IMPORTANCE OF WATER IN LIVING ORGANISMS
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Water in metabolism
○ Water is used in photosynthesis, hydrolysis and condensation reactions
○ Chemical reactions take place in aqueous solutions
Water as a solvent
○ Water dissolves other substances such as gases, wastes, inorganic ion
and small hydrophilic molecules like amino acids, enzymes
Water isn’t easily compressed and so provides support
It’s transparent so plants can photosynthesis as light can pass through



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