Unit 1.4 - Enzymes and Biological Reactions Flashcards Preview

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All the organism's chemical processes, comprising anabolic and catabolic pathways.


Metabolic pathway

Sequence of enzyme controlled reactions in which a product of one reaction is a reactant in the next.


1) State an example of a anabolic reaction.
2) State an example of a catabolic reaction.

1) Building up molecules - protein synthesis
2) Breaking down molecules - digestion.



Biological catalyst; globular protein made by cells that speeds up rate of a chemical reaction without being used up.



Atom or molecules that alters rate of chemical reaction without taking part or being changed by the reaction


State 4 properties of enzymes.

Speed up reactions, not used up, not changed, high turn-over number.


1) What structure do enzymes have?
2) What makes enzymes soluble?
3) What does the R-group determine?

1) Tertiary structure
2) Chain folds into globular shape with hydrophilic R-groups on the outside of the molecule.
3) Determines bonds the amino acids make with each other.


Which bonds help to maintain an enzymes structure?

Hydrogen bonds, disulphide bridges and ionic bonds.


Active site

Specific 3 dimensional site on an enzyme molecule to which the substrate binds by weak chemical bonds.


1) What happens to enzymes on extracellular sites?
2) State an example.

1) Enzymes are secreted from cells by exocytosis.
2) Amylase moves down the salivary ducts to the mouth.


1) What happens to enzymes on intracellular sites in a solution?
2) State an example.

1) Act in solution inside cells.
2) Enzymes catalyse glucose breakdown in glycolysis (respiration).


1) What happens to enzymes on intracellular sites where it is membrane bound?
2) State an example.

1) Attached to membranes.
2) Cristae of mitochondria.


Enzyme-substrate complex

Intermediate structure formed during an enzyme-catalysed reaction in which the substrate and enzyme bind temporarily.


What is the lock and key model?

Active site and substrate are complementary to each other.


Induced fit

Change in shape of the active site of an enzyme, induced by the entry of a substrate, so that the enzyme and substrate bind closely.


1) What is the induced fit model?
2) State an enzyme that undergoes this formation.

1) Enzyme shape alters slightly to accommodate the substrate (flexible).
2) Lysozyme - anti-bacterial enzyme found in saliva.


Activation energy

Minimum energy that must be put into a chemical system for a reaction to occur.


1) At what temperature do most enzymes begin to denature?
2) How will lowering the activation energy effect the temperature?

1) Above 40°C.
2) Allow enzymes to take place at lower temperatures found in cells.


State 4 factors that affect enzyme action.

Temperature, pH, substrate concentration and enzyme concentration.



Permanent damage to the structure and shape of a protein molecule.



Reversible reduction of enzyme activity at low temperature as molecules have insufficient kinetic energy to form enzyme-substrate complexes.


State the relationship between the rate of reaction and temperature rise.

Rate of reaction doubles for each 10°C rise in temperature.


Describe how an enzyme becomes denatured above 40°C.

Increase kinetic energy, increase vibrations break hydrogen bonds, changes shape of active site, enzyme and substrate are no longer complementary to each other and so no products are formed.


1) What happens at low and high pH?
2) Which bonds are disrupted?

1) Low pH - excess H+ ions attracted to negative charges and neutralise them.
High pH - excess OH- ions neutralise positive charges.
2) Ionic and hydrogen bonds.


Limiting factor

Factor that, when in short supply, limits the rate of a reaction.


1) What happens to the rate of reaction when the enzyme concentration is constant?
2) When is an enzyme saturated?

1) Rate of reaction increases as the substrate concentration increases.
2) All the active sites are full.


1) Why can a low enzyme concentration be used to catalyse a large number of reactions?
2) What is the relationship between enzyme concentration and the rate of a reaction?

1) Enzyme molecule can be reused.
2) Enzyme concentration increases, more active sites available therefor the rate of reaction increases.



Molecule or ion that binds to an enzyme and reduces the rate of the reaction the enzyme catalyses.


Competitive inhibition

Reduction of rate of an enzyme-controlled reaction by a molecule or ion that has a complementary shape to the active site, similar to substrate, and binds to the active site blocking the substrate from binding.


State an example of competitive inhibition.

Malonic acid has a similar shape to succinct acid and so compete for the active site of succinc dehydrogenase.


Competitive inhibition
1) How will increasing the concentration of the substrate affect the inhibitor?
2) What happens when the inhibitor concentration increases?

1) Reduces effect of inhibitor because more substrate molecules present, the greater their chance of binding to active sites, leaving fewer available for inhibitor.
2) Binds and blocks to more active sites and so rate of reaction is slower.


Non-competitive inhibitor

Atom, molecule or ion that reduces rate of enzyme controlled reaction by binding to enzyme at a position other than active site, altering shape and preventing substrate from successfully binding to it.


1) State 2 examples of non-competitive inhibitors.
2) What do they do?

1) Cyaninde and heavy metal ions (lead) bind to allosteric site.
2) Alter shape, substrate can't bind to active site and no enzyme-substrate complexes form.


Non-competitive inhibition
1) What happens when the inhibitor concentration increases?
2) What happens when you increase the substrate concentration?

1) Rate of reaction and final mass of product decrease.
2) No effect.


Immobilised enzyme

Enzyme molecules bound to an inert material, over which the substrate molecules move.


When are enzymes immobilised?

Bound to an inert matrix such as sodium alginate beads or cellulose microfibrils.


Describe how an enzyme is immobilised in a column.

Substrate added to top of column, molecules bind to enzyme molecules' active site both on beads surface and inside beads as molecules diffuse in.
Smaller beads, higher rate of reaction.


State 5 advantages of immobilised enzymes.

1) Increased stability over wider range of temperatures and pH than enzymes free in a solution.
2) Products aren't contaminated with the enzyme.
3) Easily recovered for reuse.
4) Sequence of columns can be used so several enzymes with differing pH/optimum temp can be used in one process.
5) Easily added or removed, giving greater control over reaction.


1) Why does immobilising enzymes with a polymer matrix make them more stable?
2) What effect does trapping an enzyme molecule have?

1) Creates microenvironment allowing reactions to occur at higher temperatures or more extreme pH than normal.
2) Prevents the shape change that would denture its active site, so enzyme can be used in wider range of physical conditions than if it were in free solution.


State 3 differences between immobilised and free enzymes.

Rate of reaction is greater at every temperature with immobilised enzymes, denatures at a higher temperature and has a greater range of optimum temperatures.


State how lactose-free milk is made.

Milk passed down column containing immobilised lactase. Lactose binds to active site on lactase and is hydrolysed into glucose and galactose.


1) What signal do biosensors use?
2) What are they used for?

1) Turn chemical signals into electrical signals.
2) Accurately detect, identify and measure low concentrations of important molecules.


Describe how biosensors are used to detect blood glucose.

Glucose oxidase immobilised on a selectively permeable membrane placed in a blood sample, glucose binds to glucose oxidase. Produces a small electric current detected by electrode and read on the screen.


Describe how high-fructose corn syrup is manufactured from starch.

Starch (a amalyse, 90°C) > Oligosaccharides (glucoamylase, 60°C) > glucose (glucose isomerase) > fructose.