1.4.2 Enzymes Flashcards
Why are enzymes proteins?
Only proteins have such a wide variety of shapes because proteins are made up of 20 amino acids, all with different combinations and tertiary bonds determining their specific 3D shape
What is the structure of enzymes?
- Tertiary proteins
- Globular shape
- has an active site (pocket or cleft area which has a specific 3D shape) where the reaction takes place
What is the function of enzymes?
- biological catalysts - Proteins that speed up metabolic reactions without being used up
- provide an alternative pathway during a reaction
The specific substrate has a ………….. shape to the active site
The specific substrate has a complementary shape to the active site
What is enzymes role in digestion?
They hydrolyse polymers into monomers
E.g polypeptides into amino acids
An individual cell contains over a ….. different enzymes which are involved in ……… reactions such as hydrolysis reactions in digestion and ……………. and respiration
An individual cell contains over a 1000 different enzymes which are involved in metabolic reactions such as hydrolysis reactions in digestion and photosynthesis and respiration
what is the equation linking substrate and product
how can you tell if something is an enzyme from the name?
the name of the enzyme is usually derived from its substate and it has the suffix ‘ase’
Name the reaction and biological importance for the following enzymes:
- lactase
- catalase
- RUBISCO
- ATPsynthase
- Glycogen synthetase
What is activation energy?
The extra energy that is required to enable a reaction to occur
(Often supplied through heat in a laboratory reaction)
How do enzymes speed up the rate of a reaction?
Enzymes are biological catalysts that are able to lower the activation energy of a reaction allowing it to proceed more quickly at lower temperatures in the body so that molecules can be broken down and new ones formed. Enzymes produced and alternative route during a chemical reaction, lowering the activation energy
What is the lock and key model?
Enzymes have a specific shaped active site which is complementary to the shape of the substrate molecules being used in the reaction
What is the induced fit model?
• the substrate, not complementary, collides and binds with the active site
• the active site shape changes slightly to fit more closely and becomes complementary to the substrate molecule and is held in position by oppositely charged R groups - the tertiary structure of the enzymes active site changes
• an enzyme-substrate complex is formed
• a change in the enzymes active site shape places a strain on the ionic/hydrogen bonds in the substrate molecule (so they are more likely to break or form) allowing the reaction to occur more easily
• this strain lowers the activation energy needed for the reaction to occur
• an enzyme-product complex now forms
• the product no longer fits into the active site
• product is released. The enzyme can catalyse another reaction
What is the rate of reaction like at low temperatures?
Rates of reactions are very slow at low temperatures as enzyme and substrate molecules have little kinetic energy and few enzyme substrate collisions take place
What happens to the rate of reaction as temperature increases and why?
- The kinetic energy of substrate and enzyme molecules increases
- more successful collisions between enzyme and substrate
- meaning more enzyme - substrate complexes form
- rate of reaction increases initially
What is the v max (regarding temperature)?
When the rate of reaction reached its maximum - the optimum temperature of the enzyme reaction
How can the rate of reaction be calculated from the gradient of a graph (showing volume of product formed or substrate catalysed against time) ?
- Draw a tangent at the point mentioned in the question
- make a triangle (the bigger the more accurate)
- calculate the gradient using the change in Y / change in x
How do you calculate the initial rate?
Draw a tangent at zero then read off a point
How can the rate be calculated measuring the decrease in substrate over time?
What is the effect of increasing substrate concentration on the rate of an enzyme catalysed reaction?
• If the conc of enzyme remains constant and conc of substrate increases the number of collisions between the enzyme and substrate molecules will increase
• more ESC forming
• rate of reaction increases
• a point will be reached when all the enzymes active sites are occupied at all times, so increasing the substrate concentration will not increase the rate of reaction any further so it remains at a maximum rate (V max)
• the concentration of enzymes is said to be limiting the rate of reaction
Why would a further increase in enzyme concentration when all substrate molecules are occupying active sites not increase the rate of reaction anymore?
The concentration of substrate limits any further increase - V max is achieved
Explain how competitive inhibitors work
• have a similar shape to the substrate molecule and must be complementary to the active site of the enzyme
• they bind with active site forming an enzyme- inhibitor complex and prevent the normal substrate from entering by blocking the active site
• the number of ESC are reduced and rate of reaction falls
For competitive inhibitors: what happens to the level of inhibition If the concentration of substrate is increased?
Decreases since this will increase the chance of normal substrate binding with the active site
Explain how non competitive inhibitors work
• inhibitor (can be a completely different shape to substrate) attaches at the allosteric site
• distorting the tertiary shape of the enzyme leading to a change in the shape of the active site
• substrate no longer fits the active site
• ESCs cannot form
• rate of reaction decreases
