Enzymes
Enzyme Action
Digestion, anabolic (creating reactions) and catabolic (breaking down reactions) reactions are catalysed by enzymes.
Metabolism is the sum of all reactions inside the cell or organism.
Molecules in a solution move and collide randomly, temperatures and pressures increase the molecules move faster as they have more kinetic energy. So higher number of collisions and rate of reaction.
The specificity of enzymes means each enzyme can only catalyse one biochemical reaction.
Lock and Key hypothesis
The active site of the enzyme is complementary to the substrate and it's shape is determined by the enzymes tertiary structure as enzymes are made of proteins.
Only a specific substrate will fit into a specific active site of an enzyme.
Enzyme-Substrate complex is formed when substrate binds onto active site. Substrate then reacts and products are formed in an enzyme-product complex and are released.
The enzyme is left unchanged after releasing products
Induced-fit Hyopthesis
More recent evidence supports this theory
The enzyme changes shape slightly as the substrate binds
Active sites tertiary structure strengthens binding between enzyme + substrate, which is initially weak This puts strain on substrates tertiary structure and can weaken bonds. So it lowers activation energy
Intracellular Enzymes are enzymes that work withing cells e.g. Catalase
Extracellular Enzymes are enzymes that work outside cells. Single-celled organism release onto immediate environment to break down larger molecules to then absorb. Multicellular organisms break down large molecules in digestive system e.g. amylase, trypsin, to absorb into bloodstream. Both organisms use to make use of polymers for nutrition.
Digestion of Protein happens in the small intestine.
Protein --> peptides by trypsin (a type of protease, produced in pancreas).
Peptides --> amino acids by other proteases + are absorbed into bloodstream.
Activation energy is the amount of energy required for a reaction to start.
Digestion of Starch begins in mouth, goes to small intestine. Digested in 2 different ways.
- Starch polymers --> maltose (disaccharide).
Broken down by Amylase which is produced
in the salivary glands (into mouth as saliva) +
pancreas (into small intestine in pancreatic
juice) - Maltose --> glucose (monosaccharide) by
maltase (in small intestine)
glucose is small enough to absorb into bloodstream
Factors Affecting Enzyme Activity
pH
Temp
Substrate + Enzyme conc.
↑ temp, ↑ kinetic energy so particles move faster, so ↑ collisions so ↑ enzyme-substrate complexes formed so ↑ rate of reaction
Hydrogen + ionic bonds are affected. which affects tertiary and primary structure
↑ substrate / enzyme conc. leads to ↑ rate of reaction as ↑ collisions so ↑ ESC formed. but can both be limiting factors if all enzymes are occupied or all substrates are bonded
Denaturation happens when temp is too ↑ and affects bonds in the enzymes tertiary structure so changes shape of enzyme so changes shape of active site. Enzyme active site is no longer complementary to substrate.
Optimum Temperature is the temp at which there is the highest rate of activity, it is specific to each reaction.
Temperature Extremes. Few enzymes are evolved
to function in them.
- Cold ~ more flexible structure, less stable.
- Hot ~ "Thermophiles", more stable, ↑ num of bonds
Change in pH refers to change in hydrogen ion conc.
- more ions in low pH, less R-groups able to interact with each other, leads to bonds breaking
- less ions in high pH
Renaturation - Change in pH changes enzymes tertiary structure but if pH is changed back to optimum so it the enzymes structure. More significant changes in pH mean the structures alterations are irreversible. (enzyme is denatured)
Inhibitors
Inhibitors are molecules that prevent enzymes from functioning as catalysts
Competitive inhibitors ↓ rate of reaction but not Vmax of enzyme. Examples: Statins (inhibits enzymes in production of cholesterol), Asprin (Inhibits COX enzymes used in production of chem. responsible for pain)
- different molecule which is also complementary to active site + has a similar structure to substrate fits into active site and blocks substrate from fitting there.
- enzyme is inhibited as it cannot bind with substrate
- compete with substrates, most bind temp so effects are reversible but some exceptions (asprin)
Non-competitive inhibitors ↓ rate of reaction, ↑ enzyme / substrate conc. will not overcome effects.
- bind to an allosteric site (site other than active site)
- binding causes change in tertiary structure so change in active site shape so no longer complementary to substrate
can be irreversible, e.g. Organophosphates (insecticides/herbicides), Proton Pump Inhibitors (PPI) (block enzyme used to secrete hydrogen ions into stomach)
Cofactors, coenzymes, prosthetic groups
End-product inhibition occurs when product inhibits enzyme that made it. serves as negative-feedback so excess products aren't created + no resources are wasted. Is non-competitive + reversible.
- ATP regulates its own production through this. When ATP levels ↑, more ATP acts as inhibitor. When ATP levels ↓, less ATP acts as inhibitors so more ATP can be produced.
Cofactor ~ A non-protein "helper" component used by enzymes to carry out function.
Coenzyme ~ An organic cofactor
Prosthetic group ~ Cofactors required by certain enzymes, tightly bound + permenant.
Inorganic cofactors gained through diet as minerals / vitamins
e.g. amylase contains chloride ion (cofactor) necessary for formation of correct active site shape.
Precursor activation
- Many enzymes are produced as inactive precursor enzymes (mostly damage causing within cells / actions need to be controlled)
- Often need to change tertiary structure for active site to be active. Achieved by adding cofactor
- Before cofactor added, called an apoenzyme
- Cofactor is added, then called a holoenzyme