Chapter 1: Biological Molecules Flashcards
Define “Monomer”
The smaller repeating units that make up a polymer.
Describe what occurs during a condensation reaction
A condensation reaction joins two monomers together, and results in the release of a small molecule, typically water
Describe what occurs during a hydrolysis reaction
A hydrolysis reaction breaks the bond between two monomers, using a molecule of water in the process
Describe how you would test for reducing and non-reducing sugars
Reducing:
-Add 2cm^3 of the liquefied food sample to a test tube
-Add an equal volume of Benedict’s reagent
-Heat the mixture in a gently boiling water bath for 5 mins
-if reducing sugars are present a blue->green->yellow->orange->red colour change is observed depending on the amount of reducing sugar in the sample
Non-Reducing:
-After a negative result in the reducing sugar test, add 2cm^3 of the food sample to an equal volume of dilute HCL in a test tube and heat gently in a boiling water bath for 5 mins
-Then add Sodium Hydrogencarbonate to neutralise the HCL
-After the solution is tested to be neutral, add an equal volume of Benedict’s reagent and repeat the test for reducing sugars
-If a non-reducing sugar was present in the original sample, the test will be positive
Define a Polysaccharide
Polysaccharides are polymers, made up of many monosaccharide monomers joined together by glycosidic bonds
Describe the test for Starch
-Place 2cm^3 of prepared food sample into a test tube
-Add two drops of iodine solution and stir
-If starch is present the iodine solution will turn from yellow-brown to blue-black
Describe the features of starch that make it a good storage molecule
-It is insoluble and therefore doesn’t affect the water potential of the cell it is stored within.
-Because it is large and insoluble, it cannot diffuse out of the cell
-It is compact and a lot of starch can be stored in a small space
-When hydrolysed it forms a-glucose which is both easily transported and easily used as a respiratory substrate
-It’s branched structure has many ends to be acted on by exoamylase/enzymes and can be broken down into a-glucose rapidly
Describe the features of glycogen and what makes it a good storage molecule
-It is insoluble and therefore doesn’t affect the water potential of the cell it is stored within.
-Because it is large and insoluble, it cannot diffuse out of the cell
-It is compact and a lot of starch can be stored in a small space
-When hydrolysed it forms a-glucose which is both easily transported and easily used as a respiratory substrate
-It’s branched structure has many ends, more than starch, to be acted on by exoglycogenase/enzymes and can be broken down into a-glucose rapidly as animals have a higher metabolic rate than plants
Describe the structure and function of cellulose
-cellulose is a polymer of beta-glucose
-the individual chains of beta glucose can form hydrogen bonds between each other to form microfibrils which join together to firm fibres which in-turn provide rigidity to the cell walls in plants
Describe the structure of a triglyceride
A triglyceride molecule is made up of one molecule of glycerol bonded to three fatty acids via ester bonds
Describe how the structure of triglycerides relate to their properties.
-Triglycerides have a high ratio of energy storing C-H bonds to Carbon atoms and are therefore an excellent source of energy
-Triglycerides also have a low mass to energy ratio making them ideal storage molecules as it reduces the mass that animals have to carry with them
-as they are large non-polar molecules they are insoluble and therefore do not affect the osmotic potential of cells and cannot diffuse out of them
-as they have a ratio of hydrogen atoms to oxygen atoms, they release water when oxidised and therefore provide an important source of water.
Describe the roles of lipids in the body
-when oxidised, lipids provide more than 2x the energy than the same mass of carbohydrates and release water
-Lipids are insoluble in water as they are hydrophobic, and are therefore used in waterproofing, in animals via sebaceous secretion and in plants via the waxy-cuticle
-Fats are slow conductors of heat and are therefore used to retain body heat and also act as insulators in the myelin sheath around nerve cells
-Fat is also often stored around delicate organs like the kidney to protect it from impacts
fats and oils are both lipids, but while fats are solid at room temperature, oils are liquid
Describe the structure of a phospholipid
Phospholipids are polar molecules are made up of a molecule of glycerol bonded to 2 fatty acid chains and an inorganic phosphate group, making that side of molecule hydrophilic and the side with the fatty acid chains hydrophobic.
Describe the test for Lipids
-Take a completely dry and grease free test tube and add 2cm^3 of the sample being tested
-Then add 5cm^3 of ethanol and shake gently
-If a milky white emulsion forms, then lipids are present in the sample
Describe the structure of an amino acid
an amino acid contains
-an amino group (-NH2)
-a carboxyl group(-COOH)
-a hydrogen atom bonded to the central carbon
-an R group or functional group that changes depending on the amino acid
Describe the formation of a Peptide bond
A peptide bond is formed when a condensation reaction occurs between two amino acids, resulting in one amino acid losing a hydrogen from its amino group, and the other amino acid losing an OH from its carboxyl group which form a molecule of water and result in the formation of a peptide bond, with the resulting molecule being known as a dipeptide.
