The macro-molecules of life
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Transcript of The macro-molecules of life
The macro-molecules of life
What are the main components of our diet?
The key components life are carbon-based macromolecules
• Carbohydrates• Lipids• Proteins• (Nucleic Acids –
GENETICS)
These large macromolecules may consist of thousands of
covalently bonded atoms
How big is a macromolecule?
How big is a macromolecule?
Where is carbon on the periodic table?
Carbon has 4 valence electrons
Therefore it can have bond with up to 4 other elements.
Monomer units join together via CONDENSATION REACTIONS
• Monomers are connected by reactions in which two molecules are covalently bonded together through the loss of a water molecule
• This reaction is called a condensation (dehydration) reaction
Breaking Down a Polymer: Hydrolysis
Bonds between monomers are broken by the addition of water molecules
Carbohydrates: Sugars, Starches, Fibre
Where do carbohydrates come from?
Mainly from PLANTS: animals store very little
carbohydrate (as glycogen) in the
body
Why do we need carbohydrates?
Why do we need carbohydrates?
• Instant energy: 17 kJ/g of soluble sugar: glucose
• Stored energy: Starch (plants)/ Glycogen(animals)
• Structure: Cellulose (plant cell walls), Chitin (insect exoskeleton)
What are carbohydrates made of?
3 kinds of atoms: carbon, hydrogen, oxygen [CA
(H2OB)
Different kinds of sugars
Simple (reducing) sugars: Monosaccharides
• All have the chemical composition (C6 H12 O6)
• Glucose – respiratory substrate
• Galactose (milk sugar)• Fructose (fruit sugar)• Small• Sweet • soluble
Complex sugars: Disaccharides
• Small• Soluble• sweet
Complex sugars: Disaccharides
Disaccharide Plant/Animal Functions/Uses
Sucrose Plant Stable, unreactive, transports glucose
around phloem
Lactose animal Hydrolysed by lactase in intestinal villae for easy
absorption
Maltose animal Dimer of glucose broken down by digestion
Polysaccharides: LARGE carbohydrates
• Insoluble• Not sweet
• Used for energy storage and plant,
fungal cell wall structure
Energy Storage Polysaccharides: Starch
Energy storage in plants: easily converted into glucose, and vice versa
Energy Storage Polysaccharides: Glycogen
Found in animals, stored in liver and muscle cells. Extensively branched
• In humans, glycogen banks are SMALL, do not last longer than a day
Structural Polysaccharides: Cellulose
• major component of plant cell walls• Cellulose forms straight unbranched chains• Because of the different structure, very few
organisms have the enzymes necessary to break down cellulose
• A very strong and resistant “insoluble fiber”
Solubility of carbohydrates in water
• Small carbohydrates (simple sugars and disaccharides) are soluble in water
• Complex polysaccharides are often insoluble in water – cellulose, fibre
Testing for sugars: Benedict’s solution
All simple sugars (and some complex, including maltose)
will reduce blue copper salts to a red
colour
Testing for starch: Iodine solution
Brown iodine solution turns blue-
black in the presence of starch
Fats
What are the sources of fat in our diet?
Animal FatsAdipose tissueMilk fatFish oils
Plant oilsOils stored in plant seeds as a store of energy for germination
Why do we need fats?
Fats Serve Many Functions• Energy storage: store twice as
many calories/gram as carbohydrates; 36 kJ/g
• Protection of vital organs• Insulation • Cell membrane structure and
function• Lipid hormones (based on
cholesterol) are used as chemical messengers
Fats (triacyglycerols or triglycerides)
Large molecules created by condensation
reactions between glycerol and 3 fatty
mainly composed of carbon and hydrogen (with a small number
of oxygen atoms)
Saturated or Unsaturated Fatty Acids
Stearic acidSolid at room tempSATURATED
Oleic acidLiquid at room tempUNSATURATED
Saturated and Unsaturated Fatty Acids
Saturated fatty acids• have no double bonds
between carbons• tend to be solid at room
temperature• linked to cardiovascular
disease• are commonly produced
by animals• Examples: butter and lard
Unsaturated fatty acids• have some carbon double
bonds resulting in kinks• tend to be liquids at
room temperature• are commonly produced
by plants• examples are olive and
corn oils
15
What differentiates a saturated from an unsaturated fatty acid?
• Saturated/unsaturated
Are fats soluble in water?
• Of course not!
Key fats in life:Steroids• Steroid hormones are synthesised in the
adrenal glands and the sex organs.• They include sex hormones: testosterone,
oestrogen, progesterone and stress hormones (cortisol)
• They are involved in metabolism, sexual function, inflammation and the immune response
• They are able to diffuse easily through the phospholipid cell membrane into cells
Key fats in life: phospholipids• Phospholipids have only
2 fatty acids. The third space is filled with a phosphate group.
• Phospholipids are ampipathic because they have a negatively charged “head” which is hydrophilic and a non-polar “tail” which is hydrophobic
Cholesterol• Cholesterol is a steroid
which is a common component of animal cell membranes keeping them fluid
• Many hormones including human sex hormones (oestrogen, progesterone, testosterone) are made of steroids: progesterone, testosterone, oestrogen etc
Testing for fat: The emulsion test
This test is used to test for the presence of lipids in a substance.• Lipids are soluble in ethanol but
insoluble in water.• The substance is first dissolved
in ethanol, then mixed with water
• If lipid (fat) is present, then it will precipitate to the top of the solution as an emulsion
Emulsion Test: Procedure1. Add the food sample to
ethanol, shake well.2. Allow to settle in a test tube
rack for 2 minutes for food to dissolve in ethanol.
3. Empty any clear liquid into a test tube containing distilled H2O.
• A milky-white emulsion is a positive result: lipid is present.
• If the mixture remains clear, there are no fats present in the sample
• Lipids are insoluble in water and soluble in ethanol (an alcohol).
• After lipids have been dissolved in ethanol and then added to H2O, they will form tiny dispersed droplets in the water. This is called an emulsion.
• These droplets scatter light as it passes through the water so it appears white and cloudy.
Proteins
Where do proteins come from?PLANTS and
ANIMALS
Why do we need proteins?
Why do we need proteins?• Growth and repair of new cells• Movement – skeletal and heart
muscle• Repair• Communication- hormones• Enzyme function• Cell membrane function (channel
and receptor proteins)• Immune response to infection
(antibodies)
• Energy: 17 kJ/g
• 50% of the dry mass of any cell is protein
• >10,000 different proteins
• The most sophisticated, complex 3-dimensional
structures
What are proteins made of?
• several kinds of atoms: carbon, hydrogen, oxygen, nitrogen, sulphur
• Proteins are polymers of amino acid monomers
• There are many different types of proteins• Key types include STRUCTURAL proteins
and FIBROUS proteins
Structural (fibrous) proteins
• Water insoluble• VERY tough, may also be
supple or stretchySilk: cocoons and webs Keratin: hair, horns, skin, nails, wool, beaksCollagen: tendons and ligamentscontractile proteins in muscle
Globular proteins
• Water soluble• Enzymes• hormones (insulin)• Transport: haemoglobin)• Immune function:
immunoglobulins
Globular proteins:Transport proteins
Haemoglobin, myoglobin: transport of essential substances (oxygen, carbon dioxide)Myoglobin was the first protein to be thoroughly described
Amino Acid (Monomers)Amino acid structure:
NH3 - C - COOH
Amino acids differ due to the R (functional) group
The structure of the R-group determines the chemical properties of the amino acid
20 Amino Acids
Amino Acids link together to form polypeptides
• 2 Amino Acids form a covalent bond, called a PEPTIDE BOND,through a condensation reaction to form a dipeptide
• Multiple amino acids can bond to each other one at a time, forming a long chain called a POLYPEPTIDE
Peptide Bonds – link amino acids
Proteins are folded into unique shapes
• The marvellous shapes of proteins• form the Protein data bank• Beautiful proteins…
Testing for proteins: Biuret’s Test
• Uses potassium hyroxide and copper
sulphate solution mixed together
• The deeper the purple colour, the
more protein present
Testing for protein: Biuret’s Test
Food tests are often used in combination
Carbohydrates Fats (lipids) Proteins
Elements they contain C,H,O C,H,O C,H,O,N, S
Individual units Simple sugars (monosaccharides)
Glycerol and fatty acids
Amino acids
Solubility in water Simple sugars and small sugars are
soluble. Fibre can be insoluble
insoluble Globular proteins are soluble/fibrous
proteins are insoluble
Why organisms need them
Easily available energy (17 kJ/g)
Structural carbohydrates:
cellulose and chitinStorage : starch and
glycogn
Energy storage (39 kJ/g)
Insulation and protection
Cell membranesSteroid hormones
Movement-musclesGrowth and repair
EnzymesImmune function:
antibodiesEnergy
HormonesCel membrane
receptorsFoods that contain
themPlants only: breads, fruits, rice, wheat
Animal and plant sources
Animal and plant sources