Background Information
Role in metabolism
Chemical composition
Specificity on substrates
Effects of the environment on activity
All known enzymes are proteins -> high molecular weight compounds composed of amino acid chains linked together by peptide bonds
Amino acids linked together into long linear chains
Peptide bond -> right side of one strongly attracted to left side of another
Chains have been folded into specific complex three-dimensional shape -> globular protein molecules
Effective functioning dependent on shape
Most enzymes composed of more than one chain of amino acids -> some consist of single chain
Chains mostly have identical structures
Amino acids: organic compounds made of Carbon, Hydrogen, Oxygen, Nitrogen & Sulfur (in some cases) bonded in characteristic formations
May have side chains -> large/small, acidic/basic, hydrophilic/hydrophobic
Can have non-protein group- cofactor -> assists active site formation
Most are globular proteins -> consist of long chains of amino acids
Enzymes specificity essential b/c keeps enzyme pathways functioning during metabolism separate
Substrate is molecule on which enzyme acts
Enzyme & substrate fit perfectly together -> smaller substrate specifically aligning on surface of larger enzyme -> active site (lock & key model)
Slight conformational change in active site -> enzymes fits tightly w/ substrate & forms enzyme-substrate complex (induced fit model)
Substrate must fit into enzyme’s active site before catalysis -> only specific molecules can be substrates for specific enzymes
Not all are highly specific
[e.g.] digestive enzymes (pepsin) can act on any protein
Some are highly specific
[e.g.] thrombin only reacts protein fibrinogen for blood-clotting
Set of amino acids in active site give specific size/shape/chemical behaviour
Enzymes lower activation energy of reaction -> binds to substrate & holds it in way that allows reaction to happen more efficiently
Some speed up chemical reactions by bringing two substrates together
Others create environment inside active site to favour the reaction
Make environment more acidic/basic to enable quicker reaction
Lock & key model
On substrate, there’s a folded group of polypeptide chains -> form a groove
Correct enzyme will have similar group of chains -> allows it to bind to substrate
Enzyme then freed & can be reused to break down another molecule
Induced fit model
Binding of substrate to enzyme must cause change in enzyme’s shape -> results in proper alignment
Conformational change creates tighter fit
Catalytic groups at active site react w/ substrate to form products -> products separate from enzyme surface & enzyme can repeat sequence
Factors affecting enzyme activity
temperature, pH, substrate concentration
Enzymes work best w/ specific temp. & pH ranges
Sub-optimal range denatures enzyme
Temperature
Temp. increase generally speeds up reaction
Temp. decrease slows down reaction
Can cause loss of activity/deactivation
Extreme high temp can cause denaturation -> around 60°C
Excessive heat breaks Hydrogen bonds in enzyme -> alters shape & structure
Enzymes within cells function best at body temp -> up to 40°C
pH
Enzymes function best within specific narrow pH range
Optimum pH is at neutral levels (pH 7)
Changing pH outside of optimum range slows down activity
Extreme values (too acidic/basic) can cause denaturation
EXAMPLES
Pepsin functions best in strong acid -> breaks down proteins in digestive tract
Amylase functions best in weak alkaline -> breaks down starches in mouth
Substrate concentration
Increasing concentration increase reaction rate to certain point -> saturation point
If concentration increases beyond saturation point, reaction rate won’t increase b/c enzymes are working at max. turnover rate
Enzymes are indispensable to life -> responsible for numerous functions in the body: storage & release of energy, course of reproduction, processes of respiration, etc.
**[e.g.] some enzymes break down large molecules (proteins, fats, carbohydrates) into smaller molecules; other enzymes form large molecules from small molecules to produce cellular constituents**
Synthesis of enzymes need to be regulated b/c needs of cells & organisms vary
Cells constantly carrying out thousands of chemical reactions needed to keep cell & body alive/healthy -> reactions often linked together in chains/pathways
Each enzyme can promote one type of chemical reaction
Operate in tightly organise metabolic systems called pathways
Act on compounds called substrates
Metabolism: all chemical reactions in an organism
[enzymes] Substrate specific -> only one particular substrate molecule can work w/ one particular enzyme
Anabolic: reaction where product is built up by reactants joining together- usually requires energy (endergonic)
Catabolic: reaction where reactant is broken down- usually releases energy during process (exergonic)
In metabolic web of cell:
Some chemical reactions release energy & can happen spontaneously (w/o energy)
Others need added energy to take place
Cells need continual energy inflow to power energy-requiring reactions
Catalysts
Can speed up/slow down reactions w/o change in temp. -> vital b/c heat damages living tissue
An activation energy level must be reached for reaction to occur
role of enzyme: reduce activation energy by providing alternate reaction pathway / by bringing specific molecules together
Each reaction step in pathway is facilitated/catalysed by protein (enzyme)
[enzymes] perfect catalyst b/c can change chemicals within cells w/o changing themselves
Bind w/ particular reactants until reaction occurs, then free themselves
Enzyme never chemically altered by reaction so can be reused in subsequent reactions -> enzyme controlled reactions always reversible
Most chemical reactions within cells require catalyst to get started
Metabolic pathway: series of connect chemical reactions that feed each other -> pathway takes in starting molecules & converts them into products
Product of one step in metabolic pathway = substrate of succeeding step in pathway
[e.g.] muscle contraction involves lots of chemical steps in which 1+ substrates convert to substances called products
Enzyme-Substrate combinations
Word equations
Optimum ranges
