Flashcards in Chapter 1: Biological Molecules Deck (80):
What is the general formula for monosaccharides?
What is the test for reducing sugar?
1) Add 2cm^3 of food sample in liquid form to a test tube.
2) Add equal volume of Benedict's reagent.
3) Heat the mixture in a gently boiling water bath for five minutes.
4) If reducing sugar present, solution turns orange-brown.
What is Benedict's reagent?
Alkaline solution of copper (II) sulfate.
What is a reducing sugar?
Able to reduce/ donate electrons to another chemical.
Glucose + Fructose =
Glucose + galactose =
What is the reaction and bond formed when monosaccharides join?
A condensation reaction and a molecule of water is removed.
Glycosidic bond is formed.
What happens when water is added to disaccharide under suitable conditions?
Glycosidic bonds break in a hydrolysis reaction.
Example of reducing disaccharide.
Example of non-reducing disaccharide.
How to test for a non-reducing sugar?
1) Add 2cm^3 of sample in liquid form to test tube.
2) Add 2cm^3 of Benedict's reagent and filter.
3) Place test tube in gently boiling water bath for 5 minutes. If no colour change is present, a reducing sugar is not present.
4) Add another 2cm^3 of food sample to 2cm^3 of dilute hydrochloric acid in a test tube. Place in gently boiling water bath for 5 minutes.
5) Slowly add some sodium hydrocarbonate to neutralise the HCl. Test with pH paper, the solution is alkaline.
6) Re-test resulting solution by heating with 2cm^3 of Benedict's reagent in a gently boiling water bath for 5 minutes.
7) If non-reducing sugar was present in original sample, Benedict's reagent will turn orange-brown.
What is the role of dilute HCl in the test for non-reducing sugars?
Will hydrolyse any disaccharide into its constituent monosaccharides.
What is the test for starch?
1) Place 2cm^3 of sample into test tube.
2) Add two drops of iodine solution and shake and stir.
3) Presence of starch is indicated by blue-black coloration.
What is starch chains made up of?
Alpha glucose linked by glycosidic bonds formed by condensation reactions.
Does starch have a branched or unbranched structure?
Why is the unbranched structure of starch useful?
Unbranched is wound into a tight coil which makes it compact.
What are the features of starch?
-Insoluble and so doesn't affect water potential.
-Large and insoluble so does not diffuse out of cells.
-Compact so a lot can be stored in one place.
-Branched form has many ends and so can be acted on simultaneously by enzymes.
Is starch found in animals or plants?
Is glycogen found in animals or plants?
Why the structure of glycogen suit it to storage?
-Insoluble and so does not draw water into cells by osmosis.
-Insoluble so does not diffuse out of cells.
-Compact so a lot can be stored in one place.
-More highly branched than starch so more ends which can be acted on simultaneously by enzymes.
Is glycogen branched or unbranched?
What monosaccharides is glycogen made up of?
How does cellulose differ from glycogen and starch?
Made up of beta glucose.
Does cellulose has branched or unbranched chains?
What is the structure of cellulose?
Unbranched chains run parallel to each other, hydrogen bonds form cross-linkages between adjacent chains. Collectively they add strength.
What are cellulose molecules grouped together called?
What are groups of microfibrils called?
How is cellulose suited to its function of providing support and rigidity?
-Form long straight unbranched chains.
-Chains run parallel to each other and hydrogen bonds add collective strength.
-Molecules are grouped to form microfibrils which in turn are grouped to form fibres.
Give four roles of lipids.
-Source of energy.
How are lipids waterproof?
They are insoluble in water.
How are lipids good for insulation?
Fats are slow conductors of heat and help to retain body heat.
Act as electrical insulators in the myelin sheath around nerve cells.
Why are lipids a good source of energy?
When oxidised, they provide more than twice the energy the same mass of carbohydrate and release valuable water.
What are triglycerides made up of?
Three fatty acids and a glycerol.
What type of bond occurs between a fatty acid and a glycerol?
What reaction joins a glycerol and fatty acid?
One double bond
More than one double bond
No double bonds present
How is the structure of triglycerides related to their properties?
-High ratio of energy storing carbon-hydrogen bonds to carbon atoms and so a good source of energy.
-Low mass to energy ratio so a lot of energy can b stored in one place.
-As they are large and non polar they are insoluble in water. Therefore their storage does not affect water potential of cells.
-High ratio of hydrogen to oxygen atoms, when oxidised they can therefore provide water.
How do phospholipids differ to glycerides?
One fatty acid is replaced by phosphate molecules.
Hydrophilic head of phospholipids.
Attracts to water.
Hydrophobic tail of phospholipids.
Orients itself away from water.
How is the structure of phospholipids related to their structure?
-Hydrophilic phosphate heads help hold the surface of the cell surface membrane.
-Structure allows them to form glycolipids by combining with carbohydrates within the cell surface membrane.
-They are polar, so they form a bilayer in aqueous environment.
What is the test for lipids?
(1) Add 2cm^3 of sample to 5cm^3 of ethanol in a grease free and dry test tube.
(2) Shake tube.
(3) Add 5cm^3 of water and shake.
(4) Cloudy-white precipitate indicates the presence of a lipid.
What is a control as a test for lipids?
Repeat test using water, the final solution should remain clear.
What is the structure of an amino acid?
What do all amino acids differ in?
Their R group.
What is the primary structure of proteins?
Joining of amino acids in condensation reactions in a process called polymerisation.
What is the secondary sequence of proteins?
Shape due to hydrogen bonding.
Polypeptide chain is twisted into an alpha helix coil or beta pleated sheets.
What are monomers?
Smaller units from which larger molecules are made.
Gives examples are monomers.
What are polymers?
Molecules made from a larger number of monomers joined together.
Structure of alpha glucose
OH on same side.
Structure of beta glucose
OH on opposite sides
What is the tertiary structure of proteins?
Due to twisting and folding of helix into a compact 3D structure. It is maintained by hydrogen bonds, ionic bonds and disulphide bridges.
What are disulphide bridges?
Fairly strong and not easily broken.
What are ionic bonds?
Formed between carboxyl group and amino groups.
Weaker than disulphide bonds and easily broken by changes in pH.
What are hydrogen bonds?
What is the quaternary structure of proteins?
Non-protein groups are associated with the tertiary structure.
Outline the test for proteins.
(1) Place sample into test tube and add equal volume of sodium hydroxide solution at room temperature.
(2) Add a few drops of very dilute (0.05%) copper (II) sulphate solution and gently mix.
(3) Purple coloration indicates the presence of peptide bonds. If no protein present, remains blue.
What is the name of the test for proteins?
What are enzymes?
Globular proteins that act as catalyst.
What conditions must be met for reactions to take place naturally?
-Reactants must collide with sufficient energy to alter arrangement of their atoms.
-Free energy of the products must be less than that of the substrates.
-Activation energy must be met.
What is the induced fit model of enzymes?
Proposes that the active site forms as the enzyme and substrate interact. The active site is flexible and can mould itself around the substrate. As it changes shape, the enzymes puts strain on the substrate molecule. The strain distorts the bonds in the substrate and lowers the activation energy needed to break the bond.
What is the lock and key model?
The enzyme is complementary to the substrate and an enzyme-substrate complex is formed.
Effect of temperature on action of enzymes.
-A rise in temperature leads to an increase in kinetic energy.
-Molecules move faster.
-So more effective collisions.
-More enzyme-substrate complexes formed.
Effect of pH on action of enzymes.
-Change alters the charges on the amino acids that make up the active sites.
-So enzyme-substrate complex is not formed.
-Change may cause tertiary structure to be altered and the active site changes shape.
Effect of enzyme concentration on the reaction rate.
-As long as there is excess substrate, an increase in enzyme will lead to increase in reaction rate.
Effect of a low enzyme concentration.
There are too few enzymes to allow all substrates to find an active site.
Effect of intermediate enzyme concentration.
All substrate molecules can find an active site. Reaction rate is at its maximum.
Effect of a high enzyme substrate concentration.
Addition of more enzymes won't effect the reaction rate as now there are already enough active sites to accommodate all the available substrates.
What is the pH of a solution?
Measure of hydrogen ion concentration.
Effect of low substrate concentration.
Too few substrate molecules to occupy all active sites.
Effect of intermediate substrate concentration.
All active sites are occupied and reaction rate is a maximum.
Effect of high substrate concentration.
Addition of substrate won't effect reaction rate as all active sites are filled.
How do non-competitive inhibitors work?
Attach to site on enzyme other than the binding site. Upon attaching, the inhibitor alters the shape of the active site so that substrates no longer fit it.
An increase in substrate will ... the non-competitive inhibitor.
How do competitive inhibitors work?
Have a molecular shape similar to that of the substrate. Inhibitors do not permanently bind to active sites.