Section 1 - Biological molecules: 1. Biological molecules Flashcards
Food test: Reducing Sugars
Benedict’s test:
- Mix equal volumes of food solution and Benedict’s solution
- Heat in water bath for 5 mins
- Results:
Blue = None
Red/brown = Sugars
Food tests: Non-reducing sugars
If no result from reducing sugar test:
- First, mix solution with dilute HCl and heat for 5 mins
- Slowly add sodium hydrocarbonate to neutralise (test with pH paper)
- Re-carry out the test for reducing sugars
Food Tests: Starch
Iodine test:
- Add a few drops of iodine to food solution and shake
- Results:
Orange = None
Blue/Black = Starch present
Food tests: Lipids
Sudan III test:
- Add a few drops of Sudan III solution to food solution and shake.
- Results:
Red stained layer forms on water = Lipids present
Emulsion test:
- Add ethanol to a test tube of crushed food.
- Pour solution into another tube of water (leaving food residue behind)
- Results:
Cloudy liquid / Emulsion = Lipids present
Food tests: Proteins
Biuret test:
- place the solution in a test tube and add an equal volume of sodium hydroxide
- add a few drops of dilute copper (II) sulphate solution and mix gently
- Results:
Blue = None
Purple = Proteins present
What is a covalent bond
Bond between two non-metals where electrons are shared to make each one stable.
What is an ionic bond
Bond between a metal and a non-metal, where the metal loses electron to become a positive ion, the non-metal gains the electrons to become a negative ion. These opposite charges create an electrostatic attraction between the ions, forming an ionic bond.
What is a hydrogen bond
Oppositely charged sides of polar molecules are attracted to each other
What is an isotope
A different form of the same element, with the same number of protons, but a different number of neutrons.
Therefore has the same chemical properties but different mass.
What is a condensation reaction
A reaction that produces water when a bond is formed
What is hydrolysis
The adding of water to break bonds formed by condensation reactions
What is an isomer
A compound with the same molecular formula, but different structure. (eg. ɑ-glucose and ꞵ-glucose)
What are carbohydrates made up of
Basic monomers are units of sugar (saccharides), so carbohydrates are polymers of monosaccharides.
What is a monosaccharide
A single sugar unit that makes up carbohydrates. (eg, glucose)
Basic formula = (CH2O)n
n = 3-7
What is the structure of an alpha glucose monosaccharide
What is the structure of a beta glucose monosaccharide
What is a disaccharide
A pair of monosaccharides bonded together during a condensation reaction, forming glycosidic bonds.
What monosaccharides make up Maltose
Glucose and Glucose
What monosaccharides make up Sucrose
Glucose and Fructose
What monosaccharides make up Lactose
Glucose and Galactose
What is a glycosidic bond (1-4 and 1-6)
A bond formed during a condensation reaction between monosaccharides. 1-4 is between carbon atoms 1 and 4, giving long straight polymers, whereas 1-6 is between carbon atoms 1 and 6 and gives more branches
What is a polysaccharide
A polymer formed by combining together many monosaccharides in condensation reactions
What is the function of starch
Storage of ɑ-glucose in plants, so it can be used in respiration
What is the structure of starch
A polysaccharide of ɑ-glucose made up of 70-90% amylopectin (branched with 1-6 glycosidic bonds) and 10-30% Amylose (unbranched with 1-4 glycosidic bonds)
What is the function of glycogen
Storage of ɑ-glucose in animals and bacteria (stored in muscles and liver)
What is the structure of glycogen
A polysaccharide of ɑ-glucose containing almost exclusively amylopectin (branched chains of 1-6 glycosidic bonds)
What are the structural features of starch and glycogen that make them suited for their role
- Insoluble: Doesn’t dissolve and has no osmotic effect
- Large: Can’t leave the cell by diffusion
- Compact: for efficient storage
- Hydrolysed into ɑ-glucose: can be used to release energy in respiration
- Highly branched: allows for hydrolysis at many points to release ɑ-glucose
What are the main differences between starch and glycogen
Glycogen contains more amylopectin, with a higher proportion of 1-6 glycosidic bonds, meaning it is more highly branched. This means hydrolysis into ɑ-glucose is more efficient, to provide more energy required for movement in animals.
What is the function of Cellulose
Structural support and rigidity in plants as well as being a component in plant cell walls, allowing them to be turgid without bursting
What is the structure of Cellulose
A polysaccharide of ꞵ-glucose, forming long straight chains with no branches
What are the structural features of cellulose that make it suited for it’s role
- Straight unbranched chains: to allow for structural stability
- ꞵ-glucose: The alternating orientation of the monomers means hydrogen bonds can form between them, forming microfibrils with increased strength.
(Supports stems and leaves, giving max SA for photosynthesis). - Insoluble: doesn’t dissolve so can remain for structural support