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What are the three ways atoms may combine
Covalent, Ionic, Hydrogen
What is covalent bonding?
Non-metal atoms sharing a pair of electrons in their outer shells to form a more stable molecule
What is ionic bonding?
When metal and non-metal ions with opposite charges electrostatically attract each other and form ionic bonds, these bonds are weaker than covalent bonds
What is a polar molecule?
A molecules with an uneven distribution of electrons (it has been polarised)
What is hydrogen bonding?
When electrons within a molecule are unevenly distributed but tend to spend more time at one position, this region is negatively charged, and the molecule is a polar molecule. The bonding occurs when the negative region of one polar molecule attracts the positive region of another, forming a weak electrostatic bond
What is the strength of hydrogen bonding?
Each bond is individually weak, however they can collectively form forces that alter the physical properties of molecules e.g. water
How are polymers formed?
From monomers linked in long chains usually created by polymerisation
What element are the monomers in a polymer typically based on?
Carbon
What are 2 examples of industrially produced polymers?
Polythene, polyesters
What are 3 examples of biologically produced polymers?
Polysaccharides, polypeptides, polynucleotides
What is the sub-unit monomer of polysaccharides?
A monosaccharide or single sugar e.g. glucose
What is the sub-unit monomer of polypeptides?
Linking peptides that have amino acids as their basic sub-unit
What is the sub-unit monomer of polynucleotides?
Formed by mononucleotide/nucleic acid sub-units
What is the sub-unit monomer of lipids?
Fatty acids and glycerol
What are condensation reactions?
Formation of polymers by polymerisation in organisms, each time a new sub-unit is attached, as molecule of water is formed e.g. polypeptides from amino acids and polysaccharide starch from monosaccharide glucose
What are hydrolysis reactions?
Polymers are broken down through the addition of water, as water molecules are used when breaking the bonds that link the sub-units of a polymer, splitting the polymer into its parts
What is metabolism?
All the chemical processes that take place in living organisms
What is the mole?
The SI unit for measuring the amount of a substance (mol)
What does one mole contain?
It contains the same number of particles as there are in 12g of carbon-12 atoms (6.022 x10 ^23 carbon atoms)
What is a molar solution (M)?
A molar solution is a solution that contains one mole of solute in each litre of solution, therefore a mole is the molecular mass expressed as grams
How do you make a molar solution of NaCl?
Na (23) + Cl (35.5) = NaCl (58.5), therefore a 1M solution of NaCl contain 58.5g of NaCl in 1 litre of solution
What is atomic number and mass number?
Atomic number - number of protons in an atom Atomic mass - total number or protons and neutrons in an atom
How does carbon form the basis of life?
Carbon atoms readily form bonds with other carbon atoms, forming a carbon "backbone" that other molecules can be attached
What are organic molecules?
Carbon-containing molecules
What is alpha glucose?
-OH on bottom
What is beta glucose?
-OH on top
What elements are most polymers based upon?
Carbon, hydrogen, oxygen and nitrogen
What is the basic monomer unit in carbohydrates?
A sugar called a saccharide
What is a single monomer of a carbohydrate called?
Monosaccharide
What is a disaccharide?
A pair of monosaccharides joined together
What is a polysaccharide?
Monosaccharides combined in long chains
What are monosaccharides?
Sweet=tasting, soluble substances with the general formula (CH2O)n , where n = any number from three to seven
What are 3 examples of monosaccharides?
Glucose, galactose and fructose
What type of sugar are monosaccharides?
All reducing sugars, and some disaccharides e.g. maltose are as well
What is reduction?
A chemical reaction involving the gain of electrons or hydrogen
What is a reducing sugar?
A sugar that can donate electrons/reduce another chemical
What chemical is reduced during the test for reducing sugars?
Benedict's reagent
How does the test for reducing sugars work?
Benedict's reagent is an alkaline solution of copper(II) sulfate. When a reducing sugar is heated with Benedict's reagent if forms an insoluble red precipitate of copper (I) oxide
What are the 3 steps for reducing sugars carried out?
1 - Add 2cm^3 of food sample to test tube 2 - Add equal volume Benedict's reagent 3 - Heat mixture in a gently boiling water bath at 80C for 5 minutes
What type of measurement is Benedict's reagent?
Semi-quantitative
What is the relationship between concentration of reducing sugar and colour of Benedict's reagent?
Blue - none, green - very low, yellow - low, orange - medium, red - high
What are the 3 disaccharides?
Maltose, sucrose, lactose
How is maltose formed?
Glucose + glucose
How is sucrose formed?
Glucose + Fructose
How is lactose formed?
Glucose + galactose
How is a glycosidic bond formed?
When monosaccharides join and release a molecule of water, this goes to the condensation reaction to form a glycosidic bond
How is the glycosidic bond broken?
When water is added to a disaccharide under correct conditions, it breaks the glycosidic bond releasing the constituent monosaccharides, this is called hydrolysis
What are examples of reducing sugars?
Some disaccharides are reducing sugars e.g. maltose
How do you detect a non-reducing sugar?
Sugar must first be hydrolysed into its monosaccharide components by hydrolysis that takes 7 steps
What are the 7 steps to detecting a non-reducing sugar?
1 - Grind sample up and add water so in solution 2 - Add 2cm^3 of food sample to 2cm^3 of Benedict's reagent in a test tube and filter 3 - Place test tube in water bath (80C) for 5 minutes, if solution doesn't change colour/remains blue, then a reducing sugar is NOT present 4 - Add another 2cm^3 of food sample to 2cm^3 of dilute HCl in a test tube and place in water bath (80C) for 5 minutes, the HCl will hydrolyse any disaccharide into monosaccharide components 5 - Slowly add some sodium hydrogencarbonate to test tube to neutralise the HCl (Benedict's reagent won't work in acidic conditions), test with pH paper to ensure solution is alkaline 6 - Re-test the solution by heating it with 2cm^3 of Benedict's reagent in a water bath (80C) for 5 minutes 7 - If a non-reducing sugar was present in original sample, the Benedict's reagent will turn orange-brown, due to the reducing sugars produced from hydrolysis of non-reducing sugars
What are polysaccharides?
Polymers formed by joining many monosaccharide molecules, through glycosidic bonds that were formed by condensation reactions.
What are 2 features of polysaccharides?
Very large, insoluble - good for storage.
What happens when polysaccharides are hydrolysed?
Break down into mono/disaccharides
What are the 3 steps in the test for starch?
1 - Place 2cm^3 of the sample being tested into a test tube/pipette two drops of sample into a depression on a spotting tile 2 - Add 2 drops of iodine solution and shake/stir 3 - The presence of starch is indicated by a blue-black coloration
What are properties of monosaccharides?
Sweet, soluble in water, crystalline
What are 3 examples of monosaccharides?
Triose - 3C e.g. pyruvate Pentose - 5C e.g. ribose, deoxyribose Hexose - 6C e.g. glucose, fructose
What are isomers?
Same molecular formula different structure
How are disaccharides formed?
Two monosaccharides join together in a condensation reaction forming a disaccharide moleucle
A glycosidic bond forms between the two monosaccharides and water is released
What are cellulose, starch and glycogen polymers of?
Glucose
What happens when glucose is broken into simpler molecules?
Breaking of glucose into smaller molecules (CO2 and H20) releases energy
This energy can be used to produce ATP
The breaking of glucose is carried out in a few small steps , each step requires an enzyme
Animals and plants contain enzymes which can break alpha-glucose but not beta-glucose
What is starch?
A polysaccharide of alpha-glucose found in plants
What is starch made up of?
Made up of chains of alpha-glucose monosaccharides linked by glycosidic bonds that are formed by condensation reaction, the chains may be branched or unbranched
Why is starch compact?
The unbranched chain is wound into a tight coil that makes the sutrcutre of starch very compact
What is starch a mixture of?
Amylose and Amylopectin
What is the percentage and significance of amylose in starch?
30%, made up of unbranched chains, and monomers are joined by 1,4 glycosidic bonds
Molecules contain 300 glucose molecules and adopt a helical shape, this is due to the shape of the glucose molecules and formation of glycosidic bonds
Forms a compact shape and is stored in a small space
Large molecule and insoluble in water (will not diffuse out of cell and doesn't affect water potential/osmosis)
What is the percentage and significance of amylopectin in starch?
70%, made up of glucose molecules linked with 1,4 bonds
Branches occur due to formation of 1,6 glycosidic bonds every 20-30 monomers, creates a branched and coiled into a compact shape
Where is starch stored?
Stored in chloroplasts and membrance bound starch grains, found in plant storage organs e.g. potato tubers
What is starch broken down into?
Easily broken down (hydrolised) into alpha-glucose, which is respired to release energy
Why does starch have branched ends?
Each branched end can be acted upon by enzymes quickly releasing glucose monomers
What type of cell is starch found in?
Only found in plant cells, not animal cells
What takes the role of starch in animal cells?
A polysaccharide called glycogen serves the same role
What is the main role of starch?
Energy storage as its structure is suited for it
What is glycogen a polymer of?
Polymer of alpha-glucose monomers with both 1,4 and 1,6 bonds, found in animals
What are the majority of bond types in glycogen?
Mostly 1,6, therefore it breaks down more quickly
What is the structure of glycogen?
It is a highly branched molecule with more 1,6, bonds than amylopectin, more compact than starch
What does glycogen form?
Forms glycogen granules in animal cells, especially liver and muscle cells
What does the more branched ends allow glycogen to do?
More branched ends than starch, so allows hydrolysis by enzymes more quickly than starch, rapidly breaking down into its glucose monomers and used in respiration as animals have higher metabolic rates than plants, therefore respiration rates are higher
What is the role of glycogen?
It is an energy storage molecule in small granules in animals found in the liver and muscle cells, mass of carbohydrate stores is relatively small as fat is main storage molecule in animals
What are 4 adaptation of glycogen that make it more effective for storage?
1 - Compact structure, so lot of it stored in small space 2 - It is insoluble, it does not diffuse out of cells 3 - It is insoluble, it prevents high concentration of glucose in cells = doesn't affect water potential of the cell 4 - Easily hydrolysed into simple glucose monomers, due to branched ends which can be respired and energy released
What is cellulose a polymer of?
It is a polymer of beta-glucose monomers joined by 1,4 bonds forming straight chains called cellulose chains, and is found only in plants
What is the structure of the cellulose?
Each beta-glucose monomer is rotated 180 degrees to the previous one, each chain consists of thousands of beta-glucose monomers with projecting OH groups both above and below the chains. Hydrogen bonding occurs between OH groups on adjacent cellulose chains between C2 and C6.
What is the strength of this cellulose/chains?
Individually the hydrogen bonds are relatively weak, however up to 2000 chain can be held together to form a microfibril, which creates great strength
What are microfibrils?
They are held together by hydrogen bonds, and are arranged in paralled groups, to from macrofibrils, which provides extra strength and rigidity
What are macrofibrils?
They are held in a matric made up of pectins (polysaccharides formed from galactose) and hemiceulloses (similar to cellulose with galactose side chains)
How does cellulose prevent cell lysis (bursting)
As water enter cell by omosis, exerts an inwards pressure that stops further influx of water
What are the main functions of cellulose?
Important structural component of cell walls
Macrofibrils allow water to move through and along cell walls (movement of water - apoplast pathway)
Prevent lysis (bursting) of the cell
Arrangement of macrofibrils in guard cells allows opening and closing of stomata
Cell walls can be reinforced with other substances e.g. lignin
A few organisms possess cellulase e.g. fungi
Ruminant animals depend upon large populations of bacteria to break down cellulose
What are 2 other structural carbohydrates?
Chitin - forms the exoskeleton in insects
Peptidoglycan/murein - forms cell walls in bacterial cells
What are lipids?
A diverse range of chemicals that dissolve in organic solvents, but not in water. They include phospholipids, triglycerides and cholesterol
What do lipids contain?
Carbon, hydrogen, oxygen
What is the proportion of these components?
Proportion of oxygen to carbon and hydrogen is smaller than in carbohydrates
How do lipids behave in water?
They are insoluble in water (hydrophobic), therefore join together to for, gobules
When are lipids soluble?
Soluble in organic solvents such as alcohols and acetone
What are 2 of the main groups of lipids?
Triglycerides (fats and oils) and phospholipids
What % of lipids make up the organic matter of a cell?
5% of organic matter of a cell
How large are lipids?
Relatively small compared to polysaccharides
What are naturally occurring fats and oils called?
Esters
What is the role of lipids in membrane (cell surface and membranes around organelles)?
Phospholipids contribute to the flexibility of membranes and the transfer of lipid-soluble substances across them
What is the role of lipids in energy?
When oxidised they provide more than twice the energy as the same mass of carbohydrates, and release valuable water
What is the role of lipids in waterproofing?
Lipids are insoluble in water, therefore can be used as water-proofing. E.g. plants and insects have waxy, lipid cuticles than conserve water, while mammals produce an oily secretion from sebaceous glands in the skin
What is the role of lipids in insulation?
Fats are slow conductors of heat and when stored beneath the body surface they help to retain body heat, they can also be used as electrical insulators in the myelin sheath around nerve cells
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