Enzymes

what is metabolism

All the chemical reactions that take place in living cells  

what is an anabolic reaction

The building of large molecules from smaller molecules 

give an example of an anabolic reaction

e.g. synthesis of cellulose or actin/myosin in muscle  

what is a catabolic reaction

The breaking down of large molecules into smaller simpler molecules 

give an example of a catabolic reaction

e.g. digestion, respiration- breakdown of glucose to release energy 

what is the activation energy of a chemical reaction

The minimum amount of energy required for the reaction to take place→ catalysts lower the activation energy

what are the properties of enzymes

• speed up chemical reactions

• not destroyed by the reaction so can be used again

• they are denatured by high temperatures- no longer work

• sensitive to pH- become denatured away from optimum pH

• specific to particular reactions

what is the importance of enzymes in controlling metabolic reactions?

• enzymes control metabolic reactions by ensuring reactions take place in the right order and at the appropriate rate to meet the demands of the cell or organism 

what is the mechanism of enzyme action

• active site of an enzyme is 3→12 amino acid long section of the polypeptide which forms a cleft in the tertiary structure

• precise arrangement means it has strong affinity for the specific substrates

describe the specificity of enzymes

• linked to the shape of the active site

• position of chemicals (R groups) and the bonds within it

• only substrate molecules with a complementary structure will combine with the enzyme

state the order of the lock and key hypothesis 

1. enzyme and substrate

2. enzyme substrate complex

3. enzyme product complex

4. enzyme and products

describe the lock and key hypothesis

• substrate molecule fits exactly into active site (complementary shape) and interacts with amino acids here by temporary bonding, forming a substrate enzyme complex

• substrate is broken down ( or 2 substrates are joined together)→ forms enzyme product complex

• products are released from the enzyme

• the temporary bonds formed put a strain on the substrate, also helping to lower the activation energy of the reaction

describe the induced fit hypothesis

• as the substrate molecule collides with the active site, the active site changes shape slightly to fit more closely around the substrate

• the initial bond between enzyme and substrate are quite weak, but these interactions change the tertiary structure of the enzyme, altering the shape of the active site

• weakens the bond in the substrate and lowers the activation energy

• active site is not fully complementary in shape until the active site has moulded around the complex

what are enzymes? 

• Enzymes are biological catalysts- they allow reactions in cells to take place more quickly without the need for harsh conditions such as high temperature/pressure.  

• Operate within living cells-> biological bit  

• Provides a route with lower activation energy  

• Globular proteins- usually soluble  

• Usually named with the end of the word being: Suffix-ase  

what is the active site

place on the enzymes surface to which substrate molecules become attached

what are intracellular enzymes

• act within the cells where they are produced

• e.g. catalyse breaks down hydrogen peroxide to water and oxygen

what are extracellular enzymes

• functions outside of the cell from where it originates

• e.g. amylase- produced in the salivary glands and pancreas in humans→ acts on the mouth and small intestine

• made in an inactive form→ so that it doesn’t digest anything en route to its final location

what type of nutrition are fungi

• saprotrophic

• enzymes are secreted (extracellular enzymes- act outside the fungus)→ digestion→ soluble products absorbed

what does amylase do

• produced by the salivary glands and the pancreas

• breaks down starch into maltose

what does maltase do

• breaks down maltose to glucose

• produced in the small intestine

what does protease do

• breaks down proteins into smaller peptides and amino acids

• e.g. trypsin- produced in the pancreas and released in the small intestine

describe rate of enzyme reaction at a temperature that is below optimum

• not enough kinetic energy- molecules are moving slowly

• small amount of successful collisions between active site and substrates

• slow rate of reaction

describe rate of enzyme reactions at optimum temperature

• most amount of successful collisions

• fastest rate of reactions

describe enzyme rate of reaction at above optimum temperature

• The active sites become denatured (change shape due to the bonds being broken in the tertiary structure)- substrates can no longer fit into the active site and therefore the reaction cannot take place.  

• Once there is a slight change to the shape of the active site, it can no longer be complementary to the substrate 

• Rate continues to decrease as less successful collisions are occurring 

• Once the temperature reaches a certain point the rate decreases to zero  

describe enzyme temperatures in real life hot environments

• Those adapted to hot environments are more stable due to having an increased number of bonds in their tertiary structure 

• These enzymes are more resistant to changes in temperature 

describe enzymes temperature real life cold environments

• Enzymes that control metabolic activities of organisms in cold environments are adapted to the cold 

• More flexible structures, making them less stable than enzymes that work at high temperatures 

• Smaller temperature changes will denature them 

how does pH effect enzyme activity

• The hydrogen and ionic bonds between R-groups in amino acids hold proteins together in their precise shape.  

• A change in pH leads to change in hydrogen ion concentration 

• The active site will only be in the right shape at certain hydrogen concentrations.  

describe enzyme activity at optimum pH

• When the pH is at its optimum, the active site is at the precise shape to fit the substrates to form a substrate enzyme complex.  

• The rate of reaction is the fastest at the optimum as the most amount of successful collisions can take place.  

describe enzyme activity at too high or low pH

• When the pH is too high or too low there is too high or too little hydrogen concentration. 

• This means that the active site is the wrong shape to fit the substrate.  

• This means that a reduced amount of active sites are the correct shape so that the reactions can take place -> rate of reaction is reduced 

 

how can you calculate the rate of reaction at any time on a graph

• draw a tanget 

• y1-y2 over x1- x2

• rate: …..min-1

what is Vmax

• the point at which rate of reaction stops increasing due to a limiting factor

• used with substrate and enzyme concentrations

describe substrate concentration with rate of reaction

• rate increases with substrate concentration

• reaches the Vmax→ enzymes become a limiting factor

• all active sites become full meaning rate cannot increase any further

describe enzyme concentration and rate of reaction

• rate increases with enzyme concentration

• rate increases until it reaches Vmax

• substrates become a limiting factor

where are many coenzymes derived from

vitamins

where are many coenzymes derived from

cofactors