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
What is chitin
A structural polysaccharide made up of modified glucose. It is long, fibrous and strong, present in arthropod exoskeletons and fungi cell walls.
How do you make a dilution series to test the amounts of sugar in a solution
To calculate the volume of stock solution that should be added to each beaker in the dilution series:
(Conc. required / Stock conc. ) x Vol. required
Fill up the rest of the volume with distilled water
How do you form a glucose calibration curve
Carry out the benedict’s test for different concentrations of a glucose solution, using a colourimeter to measure the average absorbance of red light after each test.
Plot these concentrations against the absorbance, drawing a curve that will allow you to predict the concentration of a solution based on the absorbance of light.
(Lower absorbance of light suggests a higher conc. as the benedict’s would turn darker)
What are the roles of lipids
- Source of energy: 2x more efficient than carbs
- Waterproofing: insoluble
- Insulator: slow conductor of heat
- Protection: surrounds delicate organs
- Cell membranes: flexible and allow lipid soluble substances to pass through (no large/charged molecules)
What is the structure of a triglyceride
Contains 3 fatty acids bonded to one glycerol in a condensation reaction, forming ester bonds.
Each glycerol is the same, but there are 70 types of fatty acids containing a carboxyl group and an attached hydrocarbon chain.
What is a saturated fatty acid in a triglyceride
A fatty acid with no double bonds between the carbon atoms in it’s hydrocarbon chain
What is a mono-unsaturated fatty acid in a triglyceride
A fatty acid with one double bond between the carbon atoms in it’s hydrocarbon chain
What is a poly-unsaturated fatty acid in a triglyceride
A fatty acid with many double bonds between the carbon atoms in it’s hydrocarbon chain
What is the effect of the double bonds between the carbon atoms in the fatty acids of triglycerides
The double carbon bonds allow the hydrocarbons to bend, so they can’t pack together as closely, so are liquid at room temperature.
(ie. oils are made up of poly-unsaturated fatty acids)
How is the structure of triglycerides related to their properties
- High proportion of energy-storing C-H bonds: good energy store
- Low mass to energy ratio: good energy store and reduces the mass that needs to be carried around by animals
- Insoluble: no osmotic effect
- Release water when oxidised: source of water for the organism.
What is the structure of a phospholipid
Two fatty acids and one phosphate molecule are bonded to one glycerol in a condensation reaction forming ester bonds.
Why are phospholipids polar molecules
They are made up of two parts:
- A hydrophilic phosphate ‘head’ that is attracted to the water
- A hydrophobic fatty acid ‘tail’ that repels the water
What are the 3 structures that phospholipids can form
- Micelle (small groups): balls of phospholipids with the phosphate heads facing out.
- Liposomes (bilayer that forms a ball): sacs made up of two layers of phospholipids with the phosphate head on the inside and out, used to transport medicine in the body
- Bilayer: two layers of phospholipids on top of each other with the phosphate heads on the outside, used as cell membranes
How is the structure of phospholipids related to their properties
- Polar: form bilayer in aqueous environment, to create a hydrophobic barrier (ie. cell membranes)
- Phosphate heads are hydrophilic: keep the structure of the cell membrane
- Can combine with carbs in the cell membrane to form glycolipids: for cell recognition
What are proteins made up of
Amino acids bonded together to form polypeptide chains, in condensation reactions forming peptide bonds
What is the structure of an amino acid
A central Carbon atom with 4 different chemical groups attached:
- Amino group (-NH2)
- Carboxyl group (-COOH)
- Hydrogen atom (-H)
- R group: a range of chemical groups unique to each amino acid
What is the primary structure of a protein
The sequence of the amino acids in the polypeptide chain. This order will determine the interactions between them and dictate how the chains are folded to form the final shape.
What is the secondary structure of a protein
The hydrogen atoms in the amino group of one amino acid and the oxygen atom in the carboxyl group of another form a hydrogen bond, causing the chain to begin to fold.
The chains are folded into ɑ-helix coils or ꞵ-pleated sheets where chains fold back on themselves
What is the tertiary structure of a protein
Complex 3D shape formed when the secondary structures fold and twist as the R groups of the amino acids interact. Forms a specific shape that allows the protein to be suited for it’s function
What are the 4 bonds that can form as the protein folds into it’s tertiary structure
- Disulphide bridges
- Ionic bonds
- Van der Waal’s forces
- Hydrogen bonds
What is a disulphide bridge in the tertiary structure of a protein
Strong covalent bond between two cysteine R groups
What are ionic bonds in the tertiary structure of a protein
Bond between an acidic and a basic R group, and can be broken by changes in pH
What are Van der Waal’s forces in the tertiary structure of a protein
Weak intermolecular forces of attraction between R groups with complementary shapes
What is the quaternary structure of a protein
For some types of protein (eg, antibodies) multiple polypeptide chains are bonded together to form a quaternary structure. Can also contain non-protein prosthetic groups, such as the iron containing haem group in haemoglobin.
What is a fibrous protein
Long unbranched polypeptide chains coiled together for structural integrity. 3 chains run parallel in the quaternary structure, with bonds between them, to allow them to be suited for structural functions
(eg, collagen in tendons)
What is a globular protein
A polypeptide chain that folds to form a spherical shape, with hydrophilic amino acids on the outside and hydrophobic amino acids on the inside. They are used for metabolic functions.
(eg. Enzymes and haemoglobin)
What is an enzyme
Globular proteins that act as biological catalysts to increase the rate of a reaction without being used up
What is the function of an enzyme
They provide an alternate reaction pathway with a lower activation energy, to allow collisions with less energy to be sufficient in causing a reaction.
What is the structure of an enzyme
They are made up of a long polypeptide chain, folded into a specific 3D Tertiary structure.
The active site is a region with a shape complementary to the substrate, which binds temporarily to several of the amino acids in this area, to form an enzyme-substrate complex
What is the induced fit model of an enzyme
This is a model that suggests that each enzyme has a general shape, and the active site will mould slightly to fit with the substrate. This change of shape puts strain on the bonds within the substrate, so lowers the energy required to break them.
How do you measure the progress of an enzyme-controlled reaction
- Measure the volume of product formed over time
- Measure the loss of reactants over time
Plot on a graph and work out the gradient of the curve at a given time to calculate the rate.
What is the effect of temperature on enzyme action
Increase in temp. causes increase in kinetic energy, so more collisions and more enzyme-substrate complexes forming.
Too high will cause enzyme to denature (~ 60°)
What is the effect of pH on enzyme action
Each enzyme has an optimal pH what the rate is the highest
Changes in pH can alter amino acid bonds and change the tertiary shape of the protein, denaturing it.
What is the effect of enzyme concentration on the rate of reaction
If there is excess substrate, increasing the enzyme conc. will increase the rate.
If the substrate conc. is limiting (not enough to supply all enzyme active sites at once), increasing the enzyme conc. will have no effect on the rate.
What is the effect of substrate concentration on the rate of reaction
If the enzyme concentration is fixed and is greater than the substrate conc. adding substrates will increase the rate are the spare enzymes can bond to the new substrates.
Once all of the enzymes have bound to substrates, increasing the substrate conc. won’t increase the rate, as no more complexes can be formed at the same time.
What is an enzyme inhibitor
A substance that directly or indirectly interferes with the functioning of the active site of an enzyme, so reduces it’s activity.
What is a competitive enzyme inhibitor
Molecules with a similar shape to the substrate, so bind to the active site meaning an enzyme-substrate complex can’t form (not permanently bound)
What happens to the rate of an enzyme catalysed reaction when a competitive inhibitor is added
The rate decreases, as less substrates bind to the enzymes active sites.
What happens to the rate of an enzyme catalysed reaction when a competitive inhibitor is present, and the substrate conc. is increased
As the substrate conc. increases, the probability of the enzyme binding to the substrate rather than the inhibitor increase, so the rate increases (but is still less than with no inhibitor)
What is a non-competitive enzyme inhibitor
Molecules that bind to an allosteric site of an enzyme (not the active site), changing the shape of the enzyme so that the substrate no longer fits.
What happens to the rate of an enzyme catalysed reaction when a non-competitive inhibitor is added
The rate decreases as less active sites are now available, so less enzyme-substrate complexes form
What happens to the rate of an enzyme catalysed reaction when a non-competitive inhibitor is present, and the substrate conc. is increased
The rate doesn’t change, as there is still a limited number of active sites, so increasing the substrates won’t allow for more complexes to form.
What does V-max mean
The maximum velocity of the enzymes at a particular concentration and temperature (linking to the rate)
What is K-m
The substrate concentration required to give a reaction rate of V-max/2
How do V-max and K-m link to the affinity of an enzyme to a substrate
A higher K-m suggests a lower affinity, as a higher concentration of substrate is required to give a reaction rate of V-max/2
What is the effect of a competitive inhibitor on V-max and K-m
V-max remains the same, but K-m increase, as a higher substrate concentration is required to increase the probability of an enzyme-substrate complex forming enough for the maximum rate to be reached.
What is the effect of a non-competitive inhibitor on V-max and K-m
V-max is reduced and K-m remains similar, as reduction in available active sites means that the maximum rate is lower, but the substrate conc. required to reach half of the maximum rate is about the same
How can enzyme inhibitors be used to control metabolic pathways (end-product inhibition)
So that the concentration of a particular chemical remains constant within a cell, the same chemical often acts as an inhibitor of the enzymes that catalyse the reactions that forms it (usually non-competitive inhibitors).
This means that if the conc. is too high, the reaction forming it is inhibited, so production is stopped, but if the conc. is too low, there are less inhibitors and the rate of production increases.
