Biological Molecules

Question 1

Covalent Bonding?

Answer 1

Atoms share a pair of electrons in the outer shells,

Creates a stable molecule.

Question 2

Polar Molecule?

Answer 2

Electrons aren’t evenly distributed and spend more time in one place of the atom,

Higher charge at one side,

Molecule is polarised.

Question 3

Polymer?

Answer 3

Monomers make up a polymer (long chain/),

Formed by polymerisation,

Monomers of polymers are carbon based.

Question 4

Monomers?

Answer 4

Monomers sub-units link to make long chains,

They are carbon based.

Question 5

Ionic Bonding?

Answer 5

Ions with opposite charges attract,

Electrostatic attraction is an ionic bond.

Question 6

Hydrogen Bonding?

Answer 6

Negative region of a polarised molecule and positive region of another molecule attract,

Weak electrostatic bond is formed,

Can alter physical properties of molecules (especially effective for water).

Question 7

Polysaccharides?

Answer 7

They are polymers formed by combining many monosaccharide molecules,

Basic sub-unit is a monosaccharide (single sugar such as glucose),

They are monosaccharides joined by glycosidic bonds,

Glycosidic bonds are formed by condensation reactions,

Larger molecules,

They are insoluble which makes them useful for storage,

Some polysaccharides (such as cellulose) aren’t used for storage and are used for structural purposes in plants.

Question 8

Polynucleotides?

Answer 8

Made of mono nucleotide sub-units.

Question 9

Polypeptides?

Answer 9

Linked together peptides,

Have amino acids as the basic sub-unit.

Question 10

Examples Of Industrialised Polymers?

Answer 10

Polythene and polyesters.

Question 11

Examples Of Natural Polymers?

Answer 11

Polysaccharides,
Polypeptides,
Polynucleotides,

Made naturally by living organisms.

Question 12

Condensation Reaction?

Answer 12

Formation of polymers in organisms,

Every tune a new sub-unit is attached, a H2O molecule forms.

Question 13

Hydrolysis Reaction?

Answer 13

Polymers can also be broken down from addition of water.

Question 14

Example Of A Condensation Reaction?

Answer 14

Formation of polypeptides from amino acids,

Formation of polysaccharide starch from monosaccharide glucose.

Question 15

Reactions Of Molecules (Condensation/Hydrolosis)?

Answer 15

Nucleotides > Polynucleotides (Nucleic acids),

Monosaccharides > Polysaccharides (Carbohydrates),

Fatty Acids > Lipids,

Glycerol > Lipids,

Amino Acids > Polypeptides (Proteins),

All condensation reactions (>) and all reverse (hydrolysis).

Question 16

Molar Solution?

Answer 16

A solution containing 1 mol of solute in 1 litre of solution.

Question 17

Metabolism?

Answer 17

All chemical processes that take place in living organisms are collectively called metabolism.

Question 18

Carbon Life?

Answer 18

Carbon very readily forms bonds,

This allows many varied carbon atoms in sequences,

Allows for different species to be made.

Question 19

Example Of A Polysaccharide?

Answer 19

Starch,

Found in plants,

Joins from 200 - 100,000 a-glucose by glycosidic bonds.

Question 20

Monosaccharides?

Answer 20

Sweet tasting, soluble substances,

General formula (CH2O)n,

Examples: glucose, galactose and fructose.

Question 21

Number Names?

Answer 21

Mono - one,
Di - two,
Tri - three,
Tetra- four,
Pentra - five,
Hexa - six,
Poly - many.

Question 22

A Glucose?

Answer 22

H at top on both sides,

OH at bottom on both sides.

Question 23

B Glucose?

Answer 23

H at left top and OH at right top,

OH at left bottom and H at right bottom.

Question 24

Test For Reducing Sugars?

Answer 24

All monosaccharides and some disaccharides are reducing sugars,

Reduction is a chemical reaction involving the gain of electrons,

You do the Benedicts test.

Question 25

Benedicts Test?

Answer 25

Test for reducing sugars,

Reagent is an alkaline solution if copper sulfate,

When a reducing sugar is heated with Benedicts solution, it forms an insoluble, red precipitate of copper oxide.

Question 26

Reducing Sugars?

Answer 26

Can be found using the Benedicts test,

Is a sugar that can donate electrons to another chemical,

In Benedicts test, the electron is donated to the Benedicts reagent.

Question 27

Step By Step: Benedicts Test?

Answer 27

Add 2cm3 of sample to test tube,

If food sample is not already a liquid, first grind the sample,

Add equal amounts of benedicts solution,

Heat the mixture in a gently boiling water bath for five minutes,

If the reducing sugar is present, the solution turns from blue to orange/brick red.

Question 28

Disaccharides?

Answer 28

When combined in pairs, monosaccharides form a disaccharide,

When they join, a molecule of water is removed (condensation reaction),

This forms a glycosidic bond,

When water is added under suitable conditions, the glycosidic bond break and they turn back to monosaccharides.

Question 29

Examples Of Disaccharides?

Answer 29

Glucose + Glucose > Maltose,

Glucose + Fructose > Sucrose,

Glucose + Galactose > Lactose.

Question 30

Step By Step: Test For Non-Reducing Sugars?

Answer 30

(Test for reducing sugar first),

Grind the substance into water if it is not a liquid,

Add 2cm3 of the sample to 2cm3 of Benedicts reagent,

Filter,

Place test tube into boiling water for 5 minutes. If reagent doesn’t change colour, the reducing sugar is not present,

Add another 2cm3 of sample to 2cm3 of dilute hydraulic acid in test tube,

Place in boiling water for 5 minutes,

Dilute hydronic acid will hydroxide the disaccharide into constituent monosaccharides,

Test the solution with Ph paper to make sure it is an alkaline,

Re-test the solution by heating it with 2cm3 of Benedicts reagent in a water bath for 5 minutes,

If non-reducing sugar is present, the Benedicts will turn to a orange/brown.

Question 31

Step By Step: Test For Starch?

Answer 31

Changes colour of iodine from orange to blue-black,

Place 2cm3 of sample into the test tube,

Add two drops of iodine solution,

Stir,

Look for a blue-black.

Question 32

Starch Properties?

Answer 32

Polysaccharide,

Found in plants in the form of small grains,

Large amounts occur in seeds and storage organs (such as potato tubers),

Major energy source in most diets,

Made of chains of a-glucose monosaccharides linked by glycosidic bonds made of condensation reactions,

Chains may be breached or unbranched,

Unbranched chains is wound into tight coil that makes the molecule compact,

Question 33

Starch Functions?

Answer 33

Main role is energy storage m,

Structure is suited because it is insoluble (water is not drawn into cell cause of osmosis),

Being large and insoluble, it does not diffuse out cells,

Compact so a lot is stored in a small place,

When hydrolysed, it forms a-glucose, which is both easily transported and readily used in respiration,

The beached form has many ends which can be acted in by enzymes simultaneously, meaning that glucose monomers are released rapidly (lots of energy quickly),

Never found in animals cells,

Glycogen is the same as starch in animals.

Question 34

Glycogen Properties?

Answer 34

Found in animals and bacteria,

Never in plants,

Similar structure to starch but shorter chains and more branches,

Major carbohydrate storage,

In animals, stored as small granules in the liver and muscles,

Mass of carbohydrates stored is quite small because fat is the main storage molecule in animals.

Question 35

Glycogen Functions?

Answer 35

It is insoluble and does not tend to draw water from cells via osmosis,

Being insoluble, it does not diffuse out cells,

It is compact, so a lot of it can be stored in a small place,

It is highly branched (more than starch) so enzymes can act on it. It is broken down rapidly to form glucose monomers, which are used in respiration. This is important for animals which have a higher metabolic rate than plants. It allows them to have a higher respiration rate. They are also more active.

Question 36

Cellulose?

Answer 36

Differs from starch and glycogen in one major respect: it is made of monomers of b-glucose,

Also a polysaccharide,

Forms a straight, non-branched structure,

Run parallel to one another, allowing hydrogen bonds to form cross-linkages between adjacent chains,

Each individual hydrogen bond adds little strength to the molecule, the overall number of them makes the polymer strong,

Cellulose acts as a structural material,

Cellulose molecules are grouped together to form microfibrils which arrange in parallel groups called fibres.

Made from long, unbranched chains of beta-glucose, and when beta-glucose join, this forms a straight cellulose chain.

The cellulose chains are linked by hydrogen bonds to form strong fibres called microfibrils. The strong fibres means cellulose provides structural support for cells.

Question 37

Cellulose In Plants?

Answer 37

It is a major component of plant cell walls,

Prevents wall from bursting as water enters it by osmosis,

Does this by exerting an inward pressure that stops any further influx of water,

As a result, living plant cells are turgid and push shading on another, making non-woody parts of the plant semi-rigid,

This is especially important in maintaining stems and leaves in a turgid state so they can provide maximum surface area for photosynthesis.

Question 38

Cellulose Functions?

Answer 38

Cellulose molecules are made of b-glucose and so form long, straight, unbranched chains,

These cellulose molecular chains run parallel to each other and are cross linked by hydrogen bonds which add collective strength (for structural support of the plant),

These molecules are grouped to form microfibrils which in turn are grouped to form fibres which again, gives the plant strength.

Question 39

Lipid Properties?

Answer 39

Varied group of substances that share the following characteristics:

Contain carbon, hydrogen and oxygen,

Proportion of oxygen to carbon and hydrogen is smaller than carbohydrates,

Insoluble in water,

Soluble in organic solvents such as alcohols and acetone,

Main groups of lipids are triglycerides (fats and oils) and phospholipids.

Question 40

Lipid Functions?

Answer 40

Phospholipids contribute to the flexibility of membranes and the transfer of lipid-soluble substances across them,

Source of energy - when oxidised, lipids provide more than twice the energy as the same mass of carbohydrate and release valuable water,

Waterproofing - lipids are insoluble in water and therefore useful as a waterproofing. Both plants and insects have waxy, lipid outsides that conserve water, while mammals produce oily detection from sebaceous glands in the skin,

Insulation - fats are slow conductors of heat and when stored beneath body surface, help to retain body heat, they also act as electrical insulators in the myelin sheath around the nerve cells,

Protection - fat is often stored around delicate organs, such as kidneys,

Fats are solid at room temperature and oils are liquids.

Question 41

Triglycerides?

Answer 41

Three fatty acids combined with a glycerol back bone,

Each fatty acid forms an Easter bind with glycerol in a condensation reaction,

Hydrolosis of a triglyceride therefore produces glycerol and three fatty acids,

Glycerol molecule in all triglycerides is the same so differentiations of the fats and oils come from variations of the fatty acids.

Question 42

Fatty Acids And Bonds?

Answer 42

Over 70 fatty acids and all have carboxyl (COOH) group with a hydrocarbon chain attached,

Carbon can only form 4 bonds,

If this chain has no carbon-carbon double bonds, the fatty acid is then described as saturated, because all the carbon atoms are linked to the maximum possible me number of hydrogen atoms,

If there is a single double bond, the fatty acid is then mono-unsaturated,

Is there is more than one double bond, the fatty acid is then polyunsaturated.

Question 43

Triglycerides Functions?

Answer 43

High ratio of energy-storing carbon-hydrogen bonds to carbon atoms and therefore are an excellent source of energy,

Have low mass to energy ration, making them good storage molecules because much energy can be stored in a small volume. This is especially beneficial to animals as it reduces the mass they have to carry,

Being large, non-polar molecules, they are insoluble in water. Their storage does not affect osmosis in cells or the water potential of them,

High ratio of hydrogen to oxygen atoms so they release water when oxidised and therefore provide an important source of water (especially for organisms in dry deserts).

Question 44

Phospholipids Properties?

Answer 44

Similar to lipids except that one of the fatty acid molecules is replaced by a phosphate molecule,

Fatty acids repel water (are hydrophobic), phosphates attract water (are hydrophilic),

A phospholipid is made of two parts:

• hydrophilic ‘head’ which interacts with water but not with fat,
• hydrophobic ‘tail’ which orients itself away from water but mixes readily with fat,

Molecules that have two ends (poles) that behave differently in this way age said to be polar,

This means when these polar phospholipid molecules are placed in water, they position themselves so that the hydrophobic are as far away from water and possible and the hydrophilic are as close to water as possible.

Question 45

Phospholipids Functions?

Answer 45

Polar molecules (hydrophobic and hydrophilic properties) so in an aqueous environment, phospholipids form a bilayer within cell-surface membranes and hydrophobic barriers are created inside and outside the cell,

Hydrophilic phosphate heads help to hold the surface of the cell-surface membrane together,

Phospholipid structure allowed them to form glycolipids by combining with carbohydrates within the cell-surface membrane. These glycolipids are important in cell recognition.

They allow for lipid-soluble substances to enter and leave the cell.

They prevent water-soluble substances entering and leaving the cell.

They also make the membrane flexible and self-sealing.

Question 46

Step By Step: Test For Lipids?

Answer 46

Emulsion test,

Take completely dry and grease free test tube,

2cm3 of the sample being tested, add 5cm3 of ethanol,

Shake the tube throughly to dissolved any lipid in the sample,

Add 5cm3 of water and shake gently,

A cloudy-white colour indicated the presence of a lipid,

As a control, repeat the procedures using water instead of the sample; the final solution should remain clear because no lipids are present,

The cloudy water is due to any lipid in the sample being finely dispersed in the water to form an emulsion,

Light passing through this emulsion is refracted as it passed from oil droplets to water droplets making it appear cloudy.

Question 47

Proteins Properties?

Answer 47

Usually very large,

Types of carbohydrates and lipids in all organisms are usually very few and similar,

Shape of all proteins differs,

“Of first importance” - Greek for “proteins”,

Enzymes are proteins.

Question 48

Amino Acid Structure?

Answer 48

Basic monomer units combine to make a polymer called a polypeptide,

Polypeptides combine to make proteins,

About 100 amino acids have been identified and 20 occur naturally in proteins,

Same 20 amino acids occur in all living organisms provides evidence for evolution,

Every amino acid has a central carbon atom which attach to four chemical groups:
- Amino group (NH2 and where the name of amnio acid has come from),

• Carboxyl group (COOH), acidic group which gives part of the amino “acids” name,
• Hydrogen atom (H),
• R (side) group, variety of different chemical groups, there’s 20 naturally occurring amino acids which have these different R’s.

Question 49

Formation Of A Peptide Bond?

Answer 49

Amino acid monomers can combine to form a dipeptide,

Process is essentially the same as monosaccharides monomers combining to form disaccharides,

Condensation reaction occurs - OH from carboxyl group is taken and a H is taken from the amino acid group,

This creates a peptide bond and the two amino acids join,

The peptide bond happens between the carbon of one amino acid and the nitrogen atom of the other amino acid,

Dipeptide can also be broken through addition of water to give two constituent amino acids.

Question 50

Primary Structure Of Proteins?

Answer 50

Through many condensation reactions, amino acid monomers join in a process called polymerisation,

This results in a polypeptide,

The sequence of amino acids in a polypeptide chain forms the primary structure of a protein,

The sequence is determined by DNA,

Countless combinations of sequences do there is many primary structures,

Primary structure determines ultimate shape and function,

Changing a single amino acid could change whole function,

Protein is commonly made of many polypeptide chains but could be one single polypeptide chain.

Question 51

Secondary Structure Of Protiens?

Answer 51

Linked amino acids that make up a polypeptide posses both NH and C=O groups on either side of every peptide bond,

The N of NH has a negative charge and the O of the O=C has a positive charge,

They from hydrogen bonds between them,

This causes a long peptide chain to be twisted into a 3D shape, such as a coil known as an a-helix.

Question 52

Tertiary Structure Of Proteins?

Answer 52

The a-helix of the secondary structure can be twisted and folded even more to give the complex, and often specific, tertiary structure,

3D structure,

Maintained by a number of different bonds,

Where these bonds occur depends on the primary structure of the protein,

Bonds include:

• Disulfide bridges (fairly strong and not easily broken),
• Ionic bonds (between carboxyl and amino groups which are not involved in forming perptide bonds. Weaker than disulfide bonds and easily broken in different ph solutions),
• Hydrogen bonds (numerous but easily broken),

3D shape of a protein that is important when it comes to how it functions,

Makes each protein distinctive and allows it to recognise and be recognised by other molecules,

It can then interact with molecules in a specific way.

Question 53

Quarternary Structure Of Proteins?

Answer 53

Large proteins often form complex molecules containing a number of individual polypeptide chains, linked in various ways,

May also be prosthetic groups associated with the molecule,

Although the 3D shape is important to how the protein functions, it is the sequence of amino acids (primary) that determines the shape in the first place.

Question 54

Prosthetic Groups?

Answer 54

Non-protein groups that link to polypeptides,

This creates the quaternary structure,

Example is the iron-containing haem group in haemoglobin.

Question 55

Step By Step: Test For Proteins?

Answer 55

Biuret test,

This test detects peptide bonds,

First, place sample to be tested in a test tube and add equal volume of sodium hydroxide solution at room temperature,

Add a few drops of very dilute (0.05%) copper sulfate solution and mix gently,

A purple coloration indicates the presence of peptide bonds and hence, a protein,

If no protein is present, the solution will remain blue.

Question 56

Enzymes As Catalysts?

Answer 56

Catalysts work by lowering activation energy.
In order for the reaction to take place, this must happen.

Another thing that must happen is: the energy of the products must be less than the energy of the substrates (the reactants).

Also, the reactants must collide with sufficient energy to alter the arrangement of their atoms to form the products.

If the substrate fits into the enzymes active site, it forms an enzyme substrate complex. This lowers the activation energy.

This is because:

1. if two substrate molecules need to be joined by the enzyme, being attached to the enzyme holds them close together which reduces any repulsion between the molecules so they can bond for easily.
2. If the enzyme is catalysing a breakdown reaction, fitting into the active site put a strain on the bonds in the substrate, so the substrate molecule breaks up now easily.

Question 57

Active Site?

Answer 57

This is a part of an enzyme that is functional.

It is made up of a relatively small number of amino acids.

The active site forms a small depression (dint) within the much larger enzyme molecule.

The molecule on which the active site acts on is called the substrate.

When a substrate and active site combine, it makes an enzyme-substrate complex.

This substrate is held by the active site by bonds that form temporarily between certain amino acids on the active site and groups on the substrate molecule.

Question 58

Induced Fit Model Of Enzyme Action?

Answer 58

When a substrate fits to an enzyme, the enzyme (which is flexible) can mould itself round the substrate.

As it changes its shape, the enzyme puts a strain on the substrate molecule. This strain distorts a particular bond or bonds in the substrate and consequently lowers the activation energy needed to break the bond.

After the substrate has been “broken”, the enzyme will go back to its original shape.

Question 59

For An Enzyme To Work, It Must…?

Answer 59

• Come into physical contact with its substrate.

- Have an active site which fits the substrate.

Question 60

How Do You Measure Enzyme-Catalysed Reactions?

Answer 60

We usually measure the time course of the reaction. The most commonly measured changes are:

• the formation of the products of the reaction, e.g. how much O2 produced from hydrogen peroxide when catalysed.
• the disappearance of the substrate, e.g. reduction in starch when acted on by amylase.

Question 61

Measuring Rate Of Change On A Graph?

Answer 61

“Rate of change” is also the gradient on the graph.

Find the tangent on the curve of the graph, starting from the point you are given (this is the straight line that goes across the curve). The tangent must be a 90 degree angle (should easily form a right-angle triangle). Now form the triangle.

Find the gradient by doing: vertical line up triangle/bottom line on triangle.

Question 62

Effect Of Temperature On Enzyme Action?

Answer 62

A rise in temperature increases the kinetic energy of molecules so molecules move around more rapidly and collide more often.

In an enzyme-catalysed reaction, this means that the enzyme and substrate molecules come together more often in a given time. This means, there are more successful collisions and so the rate of reaction increases.

A rise in a temperature that is too high will cause the hydrogen bonds and other bonds to break. This means the enzyme’s active site will change shape (denature). At first, the substrate will fit less easily into the active site, meaning the rate will slow. For human enzymes, this usually starts at around 45 degrees.

Around 60 degrees, the enzyme is so disrupted that it stops working altogether. It is denatured. This is permanent.

Question 63

What Are Optimum Temperatures For Human Enzymes And Why?

Answer 63

Many enzymes in human body have an optimum of 37 degrees, however, they have evolved to work at 37 degrees.
Why:

Even though our metabolic rate would be fastest at 40 degrees, this is counter-productive because we would need much more energy (food) to maintain the higher temperature of enzymes.

This temperature would denature other enzymes, for example, proteins.

Any temperature higher than this (e.g. in illness when temperatures are really high) might denature the enzymes.

Question 64

Birds Body Temperature?

Answer 64

40 degrees because they have a high metabolic rate for the high energy requirement of flight.

Question 65

What Is pH?

Answer 65

The ph of a solution is a measure of its hydrogen iron concentration.

The pH of a solution is calculated using the formula pH = -log10(H+).

Question 66

Effect Of Ph On Enzymes?

Answer 66

A change in pH away from the optimum affect the rate of enzyme action.

If the change in pH is more extreme, beyond a certain pH, the enzyme becomes denatured.

This works in following ways:
- A change in ph alters the charge on the amino acids that make up the active site of the enzyme so the substrate cannot become attached to the active site and so the enzyme-substrate complex cannot be formed.

• Depending on how significant the change in pH is, it may cause the bonds maintaining the enzymes tertiary structure to break. The active site therefore changes shape, again.

If the pH fluctuations inside orgasms are small, they are far more likely to reduce activity of enzymes then to denature it.

Question 67

What Main Bonds Make Up Enzyme Active Site?

Answer 67

The arrangement of the active site is partly determined by the hydrogen and ionic bonds between —NH2 and —COOH groups of the polypeptides that make up the enzyme.

A change in H+ ions (such as in a different pH) affects this bonding, causing the active site to change shape.

Question 68

Effect Of Enzyme and Substrate Concentration On Rate Of Reaction?

Answer 68

Once an active site of an enzyme has acted on its substrate, it is free to repeat the procedure on another substrate.

As long as there is an excess of substrate, and increase in the amount of enzyme leads to a proportionate increase in the rate of reaction.

Simply, if you increase the substrate, the rate of reaction of the enzymes will also increase.

When all active site are full, the rate of reaction stops increasing.

If however, the substrate is limiting, then any increase in enzyme concentration will not increase the rate of reaction because the active site will remain empty.

Question 69

What Are Enzyme Inhibitors?

Answer 69

Enzyme inhibitors are substances that directly or indirectly interfere with the functioning of the active site. This reduces the activity of the enzyme.

Two ways an enzyme inhibitor does this:

• Competitive inhibitors, which bind to the active site of the enzyme.
• Non-competitive inhibitors, which bind to the enzyme at a position other than the active site.

Question 70

Competitive Inhibitors

Answer 70

Competitive inhibitors have a molecular shape Similar to that of the substrate. They, therefore, can compete with the substrate for the available active site.

The concentration of the substrate determines the effect a competitive inhibitor will have on the enzyme. If the substrate concentration is increased, the effect of the inhibitor is reduced.

The inhibitor will leave the enzyme eventually and either an inhibitor or substrate will take its place. Which depends on how much of each is present.

Sooner or later, all substrate molecules will occupy an active site, but the greater the concentration of inhibitor, the longer this will take.

Question 71

Example Of A Competitive Inhibitor?

Answer 71

Two examples:

• An important respiratory enzyme acts on succinate. Another compound, called malonate, can inhibit the enzyme because it has a very similar shape.
• Another example is the inhibition of the enzyme transpeptidade by penicillin.

Question 72

Non-Competitive Inhibitors?

Answer 72

Noncompetitive inhibitors attach themselves to the enzyme at a binding site which is not the active site.

The inhibitor alters the shape of the enzyme when it attaches which changes the shape of the active site. This stops substrates from binding to the active site.

As the substrate and the inhibitor are not competing for the same site, an increase in substrate concentration does not decrease the effect of the inhibitor (like a competitive inhibitor does).

Question 73

Variety of proteins?

Answer 73

NOT FINISHED

Enzymes - usually spherical in shape and due to tight folding of peptide chains, they’re soluble and often have roles in metabolism. Some enzymes break down large molecules and some help synthesise (make) large molecules.

Antibodies - involved in the immune response. Made up of two light (short) peptide chains and two heavy (long) peptide chains bonded together. They have variable regions - the amino acid sequences in these regions vary greatly.

Transport proteins - For example, channel proteins are present in cell membranes. Channel proteins contain hydrophobic (water hating) and hydrophilic (water loving) amino acids. This causes the protein to fold up and form a channel. These proteins transport molecules and irons across membranes.

Structural proteins - They are physically strong. They consist of long polypeptide chains lying parallel to each other with cross links between them. They include keratin (found in hair and nails) and collagen (founded connective tissue).

Question 74

The lock and key model and why it’s wrong?

Answer 74

The lock and key model suggests that the substrate fits into the enzyme in the same way that I could fit into a lock.

However scientists soon realised that the lock and key model isn’t true.

The enzyme and substrate do you have to fit together in the first place, but new evidence shows that the enzyme substrate complex changes shape slightly to complete the fit.

The induced fit model was then theorised.

Question 75

The induced fit model?

Answer 75

The induced fit model explains why enzymes are so specific and only bond to one particular substrate.

The substrate has to be the same shape to fit the active site, and also has to be specific enough to make the active site changes shape in the right way as well.

Question 76

How are enzyme properties related to their tertiary structure?

Answer 76

1. The active site shape is determined by the enzymes tertiary structure (which is determined by the enzymes primary structure).
2. Each different enzyme has a different active site shape and so a different shaped active site. If the substrate shape doesn’t match the active site, an enzyme substrate complex will not form and the reaction will be catalysed.
3. If the tertiary structure of an enzyme is altered in any way, the shape of the active site will change. This means the substrate won’t fit.
4. Tertiary structure can be altered by PH or temperature changes. The primary structure (amino acid sequence) is determined by genes. If a mutation occurs in that gene, the tertiary structure of the enzyme will change.

Question 77

Practical: measuring rate of an enzyme controlled reaction?

Answer 77

Catalyse catalyses the breakdown of hydrogen peroxide into water and oxygen.

The apparatus consists of a trough (bowl) or water, with an upside down measuring cylinder in the water. A delivery tube is in the cylinder (upside own) with a boiling tube attached to the delivery tube (bung in). The hydrogen peroxide and catalase solution is in the boiling tube.

1. Set up apparatus. Each boiling tube should contain the same volume and concentration of hydrogen peroxide. To keep the pH content, add equal volumes of buffer solution to each tube. Also make a control tube.
2. Put each boiling tube in a water bath set to a different temperature along with another tube containing catalase. Wait 5 mins for catalase to become the temperature.
3. Use a pipette to add the same volume and concentration of catalase to each boiling tube. Then quickly attach the bone and delivery tube.
4. Record how much oxygen is produced in the first minute of the reaction. The recording of oxygen should be taken from the cylinder.
5. Use a stopwatch to measure time. Repeat the experiment at each temperature three times, and use the results to find an average volume of oxygen produced.
6. Calculate the average rate of reaction at it each temperature by dividing the volume of oxygen produced by the time taken.

Question 78

Practical: measuring how fast a substrate is broken down?

Answer 78

Apparatus is a spotting tile, a test tube containing amylase enzyme and starch solution, and a pipette. Also have a stopwatch.

The enzyme amylase catalyses the breakdown of starch to maltose.

1. A drop of iodine in potassium iodide is put into each well on a spotting tile.
2. A known concentration of amylase and starch are then mixed in a test tube.
3. A dropping pipette is used to put a drop of this mixture into one of the worlds containing the iodide solution on the spotting tile at regular intervals (e.g. every minute) and the colour is observed.
4. The iodide solution goes dark blue-black when starch is present but remains in its normal brown-orange colour when there is no starch around.
5. You can see how fast amylase is working by recording how long it takes for the iodide solution to no longer turn blue-black when the starch amylase mixture is added.
6. Repeat the experiment using different concentrations of amylase. Make sure you repeat the experiment 3 times in each amylase concentration.

This experiment can be altered to investigate pH (adding a buffer solution of different pH to the test tubes) or substrate concentration (adding serial solutions to make the substrate higher or lower in concentration). Remember to only change one variable at a time.

Question 79

Using a tangent to calculate initial rate of reaction?

Answer 79

The initial rate of reaction is the rate of reaction right at the start of the reaction - time equals zero on the graph.

1. Draw a tangent to the curve at T = 0. Do this by positioning the ruler so it’s an equal distance from the curve at both sides of where it’s touching it.
2. Make the tangent into a square (just draw lines on the x axis of the line and y axis). Look at page 15).
3. Calculate the gradient of the tangent. Gradient = change is y axis / change in x axis.
4. This is the initial rate of reaction.