biological molecules
- Created by: mariealevel
- Created on: 11-01-19 10:06
Carbohydrates
2 monosaccharides make a disaccharide:
- Sucrose = α-glucose + fructose
- Maltose = α-glucose + α-glucose
- Lactose = α-glucose + galactose
Polymer: polysaccharide
Pentose sugar = 5 carbon atoms
Hexose sugar = 6 carbon atoms
Amylose and amylopectin: both polysaccharides
glycosidic bond holds two monosaccharides together
α-glucose is used in starch and glycogen, whereas β-glucose is used for cellulose
Starch
Made up of amylose and amylopectin:
- Amylose is a continuous chain of a-glucose, and the hydrogen bonds causes it to coil. Linked by 1,4 glycosidic bonds
- Amylopectin consists of branches, due to 1,6 glycosidic bonds. It contains 1,4 glycosidic bonds too. This enables starch to fold up compactly - therefore storing a large amount of energy
- 1,4 and 1,6 glycosidic bonds means which carbon the bond is on
Used as fuel for humans, used as storage for plants so that bulbs and tubers can survive through the winter.
Especially suited for storage as it is insoluble and does not diffuse out of cells easily, and does not have any affects on water potential and thus osmosis
Starch + amylase = maltose. Maltose is a disaccharide and therefore can be hydrolysed into glucose
Glycogen
More branched than starch, contains more 1,6 glycosidic bonds, hence more compact
Stored in the muscles (so close to the site of respiration)
Liver has larger reserves of glycogen and continually breaks it down to maintain a stable blood glucose concentration
Cellulose
Monomer in cellulose: β-glucose
Cellulose chains: every other molecule of β-glucose is upside-down so the CH₂OH side-chains stick out alternatively on opposite sides. This makes it very straight. Very long, and line up together and become linked by hydrogen bonds.
Small bundles of cellulose molecules make very thin fibres, called microfibrils. They are able to withstand stretching like steel fibres of the same diameter. Groups of microfibrils are joined to make thicker, stronger fibres (just like string)
In cell walls, these fibres are criss-crossed, making the walls resistant to stretching in any direction
So well suited to its function that it is found throughout the plant kingdom. It's (probably) the most abundant carbohydrate.
Neither humans nor mammals can make an enzyme which breaks down cellulose, but cattle and rabbits carry bacteria in their guts which hydrolyse cellulose so they can make use of the energy
Triglycerides
Saturated fatty acids: No double bonds between any carbon atoms. Higher melting point than unsaturated. E.g. butter or lard (solid at room temperature)
Unsaturated fatty acids: Have a double bond between carbon atoms (causes a kink or a bend)
Polyunsaturated fatty acids: Has many double bonds between carbon atoms. E.g. sunflower or olive oil liquid at room temperature)
Glycerol is a type of alcohol. Contains three -OH groups, which allow the molecule to join with three fatty acids to make a triglyceride
In animal cells there are usually 14-16 carbon atoms in the fatty acid chain
Ester bond is formed between glycerol and the fatty acid
Phospholipids
Very similar to triglyceride, but only has two fatty acids and instead has a phosphate attached to the glycerol head
Hydrophilic head: the glycerol and phosphate
Hydrophobic tails: the fatty acids
When mixed in water, they arrange themselves in a double layer with their hydrophobic tails pointing inwards and their hydrophilic heads pointing outwards. This double layer is called the phospholipid bilayer and is used in cell membranes
Proteins
Monomers: amino acids
Polymer: polypeptide
Two amino acids joined together is a dipeptide
There are 20 amino acids found in almost all living organisms. Can be arranged in a large range of different sequences
Human blood is red because it is made of haemoglobin, an iron-containing protein which is vital for transporting oxygen from the lungs to respiring cells
Enzymes are proteins, and antibodies are also proteins.
Bond between the amino acids is a peptide bond
Protein Structure
Primary structure:
- The sequence of amino acids in a polypeptide chain
Secondary Structure:
- The shape the polypeptide chain folds into, e.g. an alpha-helix or a beta-pleated sheet. The bonds between the amino acids can affect this, because they could be ionic bonds (forms between an amino acid with a positive charge and one with a negative charge. Not very strong), hydrogen bonds (which form between the R-groups of amino acids. Not very strong), and disulphide bridges (which form between amino acids that contain sulfur in their R-groups. Quite strong, less breakable than ionic or hydrogen bonding)
Tertiary Structure:
- Further folding of the proteins
Quaternary Structure:
- Multiple polypeptide chains joined together
Food Tests: Benedict’s Test (Reducing)
Tests for: reducing sugars
Steps:
1) Place sample in Benedict's solution
2) Heat test sample
Why does it change colour?: Cu(II) ions in Benedict's solution get reduced to orange Cu(I) ions.
Colour change indicates: Red = Very high number of reducing sugars, Orange = High number of reducing sugars, Yellow = Moderate number of reducing sugars, Green = low amount of reducing sugars, Blue = no reducing sugars
Food Tests: Benedict's Test (Non-Reducing)
Tests for: non-reducing sugars
Steps:
1) Check there is no reducing sugar present by heating part of the sample with Benedict's solution
2) Hydrolyse the rest of the sample by heating with dilute hydrochloric acid
3) Neutralise by adding sodium hydrogencarbonate
4) Follow the test steps for reducing sugars
Food Tests: The Iodine Test
Tests for: starch (amylopectin)
Steps:
1) Add iodine solution to the sample
Colour change: orange to blue-black
Food Tests: The Emulsion Test
Tests for: lipids
Steps:
1) Dissolve the test sample by shaking with ethanol
2) Pour the resulting sample into water in a test tube
You can see lipids present if there is a milky white emulsion on the water
Food Tests: Biuret's Test
Testing for: Proteins
Steps:
1) Add sodum hydroxide to the test sample
2) Add a few drops of dilute copper sulfate solution
Colour Change: blue to mauve/purple
Bonds and Reactions
Condensation Reaction: When one monomer joins to another and a water molecule is removed
Hydrolysis Reaction: When water molecules are added in the process of breaking bonds between molecules, for example when breaking a polymer into monomers
Hydrogen bond: covalent bond between two molecules, also called an ester bond (in fats), phosphodiester bond (in DNA and RNA), glycosidic bond (in sugars) or peptide bond (in proteins)
Organic molecules always have a carbon atom (therefore water is inorganic)
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