biological molecules Flashcards
3 common disaccarides
maltose- from 2 glucose molecules
sucrose- fructose and glucose
lactose- glucose and galactose
test for reducing sugars
-these include monosaccharides and some disaccharides. eg maltose and lactose
- a reducing sugar is one that can reduce (donate electrons) to another chemical. In this case the chemical is Benedict’s reagent
-benedicts is an alkaline solution of copper (11) sulfate.
- heat solution in hot water bath for 5 mins with benedicts.
If positive should form green to yellow to orange to brick red precipitate. Higher the concentration the further along the colour change
test for non reducing sugars
carbohydrates and some disaccharides eg sucrose are non reducing sugars.
- add benedicts and heat
- if no colour change then reducing sugar is NOT present
- then add HCl and heat again. The HCl will hydrolyse any disaccharide present
- then add sodium hydrogencarbonate solution the neutralise the HCl. Test with pH paper to ensure solution is alkaline
- then retest by adding Benedict’s and heating again
- if non reducing sugar then colour change will be same as benedict’s test for reducing sugar
starch test
add iodine
if starch is present solution will turn blue-black
test for proteins
-biuret test
- add sodium hydroxide and copper (11) sulfate to form biuret solution
- solutions turns from blue to lilac/ purple
water
-electrons not shared equally so water is a polar molecule, allowing water molecules to form hydrogen bonds between each other. This is because the oxygen is more electronegative than hydrogen so has a partial negative charge and the hydrogen has a partial positive charge
- metabolite- used in many reactions eg hydrolysis and condensation, many reactions also take place in aqueous mediums, reactant in photosynthesis
-important solvent- because water is polar can form hydrogen bonds with solute, can surround ions and can bond with other polar molecules. This means living organisms can take up useful substances dissolved in water and transport them around the organisms body
-high specific heat capacity- due to hydrogen bonds. When water heated alot of energy used to break hydrogen bonds so less available energy to raise the temperature. This means water doesnt experience rapid temperature changes so is a good body habitat and can help maintain body temp
-high latent heat of vaporisation. This produces a cooling effect with little loss of water through evaporation. When water vaporises hydrogen bonds between water molecules are broken. It takes alot of heat energy to break hydrogen bonds between the water molecules, so alot of energy is used when water is evaporated. This is useful for living organisms as they can use water loss through evaporation to cool down without loosing too much water
-strong cohesion between water molecules. Supports collumns of water in the tube-like transport cells of plants and provides surface tension where water meets air. Strong cohesion helps water to flow, allowing it to travel up the xylem. High surface tension with air so often pulled back into the body rather than escaping from it
-transparent for light rays for aquatic plants - not easily compressed
role of lipid
- energy store- when oxidised lipids produce more than twice the energy of that as the same amount of carbohydrates
-waterproofing- insoluble so good for waterproofing
-insulation- slow conductors of heat so maintain warmth
-protection. Surrounds many vital organs eg kidneys
structures of lipids related to their properties
- triglycerides have high ratio of energy- storing carbon-hydrogen bonds to carbon atoms so are an excellent source of energy
-low mass to energy ratio, so good storage molecules
-large, non-polar so insoluble and doesnt affect osmosis and water potential - high ratio of hydrogen to oxygen atoms, triglycerides release water when oxidised so provide important source of water, especially for organisms in desert conditions
structure of phospholipids relating to properties
-phospholipids are polar molecules. This means in aqueous environment, form a bilayer within cell surface membrane. As a result a hydrophobic barrier is formed between the inside and the outside of the cell
-hydrophilic heads help to hold at the surface of the cell surface membrane
- the phospholipid structure allows them to form glycolipids by combining with carbohydrates within the cell surface membrane. These glycolipids are important in cell- recognition
lipid test
- add ethanol to grease-free tube containing sample
-shake tube thoroughly - add water
-if lipid present then milky white emulsion will form - control test with just water
effect of pH on enzyme action
The pH can be calculated using -log[H+]
pH alters how an enzyme works by:
- altering the charges on the amino acids in the enzymes active site. This means the substrate can no longer become attached to the active site so the enzyme substrate complex cannot be formed. The arrangement of the active site is partly determined by the hydrogen and ionic bonds between -NH2 and -COOH groups, a change in the H+ ions affects this bonding, causing the active site to change shape
- depending on how significant pH change is, may cause the bonds maintaining enzymes tertiary structure to break. The active site therefore changes shape
nucleotide structure
- made up of:
- pentose sugar (as has 5 carbon atoms)
- phosphate group
- nitrogen containing organic base: U, A, C, T or G
The pentose sugar, phosphate group and organic base are are joined as a result of condensation reactions, to form a single nucleotide. 2 mononucleotides may be joined as a result of a condensation reaction between deoxyribose sugar and phosphate group of 2 different nucleotides
- the bond formed between the two is a phosphodiester bond. New structure is a dinucleotide. The continuous chain is a polynucleotide
RNA structure
- pentose sugar is always ribose, and thymine is swapped for uracil
DNA is stable because
- phosphodiester backbone protects more chemically reactive organic bases in double helix
- hydrogen bonds link organic base pairs forming bridges between phosphodiester uprights. There are 3 hydrogen bonds between cytosine and guanine, so the higher the proportion of C-G pairings, the more stable the molecule
function of DNA
- hereditary material responsible for passing genetic info from cell to cell. The variety of sequences provides genetic diversity within living organisms
