Download Biomolecules 2009 Yingxin

Carbohydrates
Condensation & Hydrolysis Reaction
Condensation Reaction
Condensation is a chemical reaction whereby 2 simple molecules are joined together to form a larger molecule
with the removal of 1 molecule of water
Hydrolysis/ Hydrolytic Reaction
Reaction where a water molecule is added to split complex sugar into simpler component molecules by
- Heating with dilute acids at 100°C (chemical method)
- Treating with suitable enzyme at room temperature/ optimum temperature of the enzyme (enzymatic
method)
Function
General uses of monosaccharides and disaccharides
 Building blocks for larger molecules (e.g. DNA, cellulose, starch, glycogen)
 Source of respiratory energy (glucose)
 Transport compound (sucrose in plant phloem)
 Infant milk (lactose)
 Attraction – flower nectuary, fruit (fructose)
 Honey – Bees food storage
General uses of polysaccharides
 Polysaccharides are many monosaccharides linked by glycosidic bonds
 Examples – starch, glycogen, cellulose
 Energy Storage - starch (plant) and glycogen (animal)
 Structural - Cellulose cell wall (plant) and Chitin (insects/crab/shrimp)
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Contain the elements C, H, O
They are either made from single monosaccharide monomers or from several monosaccharides joined
together
Classified as:
 Monosaccharides eg glucose, fructose, galactose
 Disaccharides eg sucrose, maltose, lactose
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Polysaccharides eg cellulose, glycogen, starch
Other polysaccharides and polysaccharide derivatives eg pectins, chitin and mucopolysaccharides
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Many monosaccharides are joined in a chain to form polysaccharides.
Glycogen and starch are storage carbohydrates in animals and plants respectively.
Monosaccharides
 Trioses – C3H6O3
e.g. glyceraldehyde
 Pentoses – C5H10O5 e.g. deoxyribose
 Hexoses – C6H12O6 e.g. glucose, fructose
 General Formula: (CH2O)n
 Monosaccharides differ ONLY in terms of the details of arrangement of atoms within a molecule, which gives
them their different chemical and biological properties
 Hence, they show isomerism
 Isomers have different structural formulae but same molecular formula
 Types of isomers: aldose and ketose, open-chain and ring forms, alpha and beta
Disaccharides
 Made by combining 2 monosaccharides together
 This is a condensation reaction producing a glycosidic bond (broken by hydrolysis)
 Disaccharides made from hexoses have the formula C12H22O11
 Examples – sucrose (glucose + fructose), maltose (glucose + glucose)
Starch and Glycogen (energy stores)
 Their molecules have many side branches where glucose molecules can be removed from their tips (by
enzymes)
 Their insolubility stops them interfering with osmosis
 Their compactness provides an efficient way to store lots of glucose for future cellular respiration
Cellulose
 Made from long, straight chains of glucose
 Chains cross-linked by H-bonds which holds them tightly together (excludes water)
 Chemically very inert and insoluble – few ‘tips’ on molecule make it difficult to digest
 Many molecules form strong fibrils
 Only some bacteria, fungi and a very small number of animals can secrete cellulase enzymes
Proteins
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Sensitive to pH and heat
Shape determines its function
Special group of proteins are enzymes
Basic unit of proteins
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Amino acids
20 essential amino acids for protein formation
Protein Structures
 Primary
o Order in which amino acids are linked to form a polypeptide chain
o Individual amino acids join to form primary structure
 Secondary
o Way the polypeptide chain is coiled and folded, alpha-helix and beta-pleated
o Helix or sheet
 Tertiary
o Large globular proteins formed by the coiling and folding the already coiled and folded chain eg
enzymes
o 3 dimensional
 Quaternary
o Proteins made from 2 more polypeptides eg haemoglobin
Structural classification
Fibrous proteins
Properties:
Water insoluble
Very touch physically; may be supple or stretchy
Parallel polypeptide chains in long fibres or sheets
Function:
Structural role in cells and organisms (eg collagen found
in connective tissue, cartilage, bones, tendons, blood
vessel walls)
Contractile (eg myosin, actin)
Collagen consists of 3 helical polypeptides wound
around each other to form a ‘rope’. Every 3rd amino acid
in each polypeptide is a glycine molecule where
hydrogen bonding occurs, holding the 3 strands
together
Globular proteins
Properties:
Water soluble
Tertiary structure critical to function
Polypeptide chains folded into a spherical shape
Function:
Catalytic (eg enzymes)
Regulatory (eg hormones, insulin)
Transport (eg haemoglobin)
Protective (eg antibodies)
Bovine insulin is a relatively small protein consisting of 2
polypeptide chains. These 2 chains are held together by
disulfide bridges between neighbouring cysteine
molecules.
Denaturation of Proteins
 Loss of 3D structure and biological function
 Often permanent
 Results from alteration of bonds that maintain secondary and tertiary structure of protein
 Amino acid sequence remains unchanged
 Agents that cause denaturation:
o Strong acids and alkalis: disrupt ionic bonds, result in coagulation of protein
o Heavy metals: disrupt ionic bonds, reduce protein charge, causes precipitation of protein
o Heat and radiation: cause disruption of bonds in protein through increased energy
o Detergents and solvents: form bonds with non-polar groups in protein, disrupting hydrogen bonding
Fats
Function
Mammals
 Water repellent properties – waterproof fur and skin.
 Structural – Cell membranes, phospholipids and polar nature
 Electrical insulation – myelin, insulates neurones, impulse transmission more rapid.
 Hormones – steroids e.g. testosterone and oestrogen
 Physical protection – shock absorb, found round delicate organs e.g. kidneys
 Thermal insulation – conducts heat poorly, so insulates. Blubber in diving animals.
 Energy storage – yield twice as much energy compared with carbohydrates
Plants
 Attraction – plant scents contain fatty acids
 Waterproofing – wax for the cuticle (not glycerol, different alcohol used)
 Energy storage – Oil droplets in plant cells
Other
 Honey comb – Bees wax
Properties
 Forms: oil, wax, fat
 Insoluble
 Water- repelling
 Are usually insoluble in water, but soluble in organic solvents.
 Contain C, H and O. (CH3(CH2)nCOOH)
 Less oxygen than carbohydrates
 Identified using the emulsion test.
Triglycerides (fats & oils)
 These are NOT made from monomers
 Each contains 1 glycerol and 3 fatty acid molecules (elements: C, H, O)
 They are linked by ester bonds
 These form during condensation reactions
 Fats (solid) contain saturated fatty acid chains, oils (liquid) have unsaturated chains
 Triglycerides (fats) are formed using ester bonds
Saturated and Unsaturated
 Saturated fatty acid e.g. Stearic acid
 More hydrogen atoms
 No double bonds
 No kinks
 Unsaturated fatty acid e.g. Oleic acid
 Less hydrogen atoms
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Have double bonds
Have kinks
Phospholipids
 Consist of organic group, phosphate group, glycerol and fatty acid
 Bonds between the glycerol and fatty acid are broken by hydrolysis
 Major component of the plasma membrane, because they have a hydrophilic head and hydrophobic tail (polar
molecules), which form a bilayer
 Heads outside, tails inside
 One fatty acid in triglyceride swapped for phosphate base
Water
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Inorganic molecules
Polar molecules
Environment in which metabolic reactions can occur
Water takes part in, and is a common product of many reactions
Dipole nature
Small positive charge on each of the two hydrogens and a small negative charge on the oxygen
Attracted to each other, creating hydrogen bonds
 Strong bonds determine almost every physical property of water and many of its chemical properties
Thermal properties
 Absorbs or releases more heat than many substances for each degree of temperature increase or decrease
 Widely used for cooling/transferring heat in thermal and chemical processes
 Evaporation of water in sweat or in transpiration causes marked cooling
 Much heat is lost by the evaporation of a small quantity of water
 Contents of cells and aquatic environments are slow to freeze in cold water
Colourless
 Plants can photosynthesize at depth in water
 Light can penetrate deeply into living tissues
Surface tension
 Measure of strength of water’s surface film
 Attraction between water molecules creates strong film
 Permits water to hold up substances heavier and denser than itself
 High surface tension
 Sticky and elastic
 Hydrogen atoms are “attached” to one side of the oxygen atom, so it has a positive charge on the side
(hydrogen) and a negative charge on the other side (oxygen)
 Since opposite electrical charges attract, water molecules tend to attract each other
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Small animals can land on and move over surface of water
Water forms droplets on surfaces and runs off
Molecules in motion
 Surface tension is responsible for capillary action
 Allows water (and dissolved substances) to move through roots of plants and through blood vessels in our
bodies
 Water molecules also bind to other substances – adhesion
 For example, in a thin glass tube, when the molecules at the edge adhere to the molecules of glass just above
them, they also tow other water molecules along with them. The water surface pulls the entire body of water
to a new level until the downward force of gravity is too great to be overcome.
 Capillary action: movement of water within spaces of a porous material, due to the forces of adhesion,
cohesion and surface tension
 Can move through extremely narrow spaces (eg between soil particles, and in cell walls)
 Water column does not break or pull apart under tension
 Plants and trees need capillary action to transport water from roots to leaves
Universal solvent
 Ability to dissolve other substances
 Transfers nutrients vital to life in animals and plants
 Medium for chemical reactions of life
Boiling and freezing point
 Freezes at 0 oC and boils at 100 oC
 Solid form (ice) is less dense than liquid form, which is why ice floats
 Ice forms on surface of water, insulating water below
 When surface water does freeze, aquatic life can survive below the ice
 Liquid at room temperature: liquid medium for living things
Neutral pH of 7
 Not acidic nor basic
 Pure water
Specific heat index
 High specific heat index: Can absorb a lot of heat before it begins to get hot
 Valuable to industries as a coolant
 Regulate rate at which air changes temperature, which is why temperature change between seasons is gradual
rather than sudden (especially near oceans)
 Bulky organisms have a stable temperature in the face of fluctuating external temperatures
Viscosity
 Resistance to internal friction between molecules
 Water has low viscosity (vs honey, shampoo)
 Affected by temperature
 At higher temp, viscosity decreases as the molecules take on more kinetic energy, allowing them to move past
each other faster
 Flows readily through narrow capillaries
Vital Minerals
Mineral
Calcium
Phosphorus
Iron
Function
Formation of bones and teeth
Blood clotting
Normal muscle and nerve activity
Formation of bones and teeth
Regulation of blood pH, muscle contraction and nerve activity
Component of enzymes, DNA, RNA, ATP
Component of haemoglobin (carries oxygen to body cells) and
cytochromes (ATP formation)
Iodine
Part of thyroid hormone, required by thyroid gland
Sodium
Regulation of body fluid pH
Transmission of nerve impulses
Transmission of nerve impulses
Muscle contraction
Involved in controlling plant water balance
Muscle and nerve function
Bone formation
Enzyme function
Component of chlorophyll
Tooth structure
Enzyme activator for carbohydrate, protein and fat
metabolism
Important in growth of cartilage and bone tissue
Ingredient in several respiratory enzymes
Needed for development of red blood cells
Component of insulin
Builds hair, nails, skin
Potassium
Magnesium
Fluorine
Manganese
Copper
Sulphur
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Inorganic ions
Important for structure and metabolism of all living organisms
Ion = atom that has gained or lost one or more electrons
Usually soluble in water
Source
Milk, cheese, nuts, whole grains
Milk, whole-grain cereals, meat,
vegetables
Liver, egg yolk, pease, enriched
cereals, whole grains, meat,
raisins, leafy vegetables
Seafood, eggs, milk, iodized
table salt
Bacon, butter, table salt,
vegetables
Vegetables, bananas, ketchup
Potatoes, fruits, whole-grain
cereals, vegetables
Fluoridated water
Wheat germ, nuts, bran, leafy
green vegetables
Kidney, liver, beans, wholemeal
flour, lentils
Nuts, dried fruits, barley,
oatmeal, eggs, beans, cheese