Chapter 4 - Enzymes

Roles of enzymes in reactions

• Anabolic reactions - The synthesis of large polymer-based components.

• Catabolic reactions - Reactions to break down large organic molecules along metabolic pathways to release energy for processes.

• Digestion - We get these large organic molecules from digesting food.

Define metabolism

The sum of all the different reactions and reaction pathways happening in a cell/organism because reactions are usually part of multi-step pathways.

What is Vmax

The maximum initial velocity (the highest point an enzyme can increase its ROR to).

Mechanism of enzyme action

-For a reaction to happen molecules need to collide in right orientation.

-Increasing temp and pressure increases speed and therefore successful collisions and ROR.

-Each enzyme catalyses a biochemical reaction which is its specificity

-Reactions need activation energy, enzymes reduce activation energy needed.

Lock and key hypothesis

- An area within the tertiary structure of the enzyme has a shape complementary to the shape of a specific substrate molecule, known as active site.

- Only the specific substrate will fit into enzyme active site.

- When the two are joined they form an enzyme-substrate complex then forming products in an enzyme-product complex. Enzyme can then take part in subsequent reactions.

- Substrate held in enzyme so that right atom-groups are close to react.

- R-groups in enzyme interact with substrate, forming temporary bonds.

Induced-fit hypothesis

- This suggests active site of enzyme changes shape slightly to fit substrate.

- Weak interactions between enzyme and substrate rapidly induce changes in enzyme's tertiary structure which strengthen binding putting strain on substrate.

- This strain can weaken particular bonds in substrate therefore lowering activation energy for reaction.

What are intracellular enzymes

Enzymes acting within the cells catalysing metabolic reactions like respiration. The synthesis of polymers from monomers requires enzymes.

What are extracellular enzymes

Enzymes which work outside the cell that made them, breaking down large molecules into smaller components.

What do single-celled organisms do

They release enzymes into the environment so these enzymes can be used to break down larger molecules.

What do multi-celled organisms do

They eat food to gain nutrients, the nutrients are broken down by enzymes then absorbed into the bloodstream and transported around the body.

Describe the digestion of starch

1. Starch partially broken down into maltose. The enzymes that does this is called amylase which is produced in the salivary glands and pancreas and released in saliva into the mouth, and in pancreatic juice into small intestine.

2. Maltose broken down into glucose. This enzyme is maltase present in small intestine. Glucose is then small enough to be digested into the bloodstream.

Describe the digestion of proteins

The enzymes trypsin (protease) catalyses the digestion of proteins into peptides then amino acids. Produced in the pancreas, released into small intestine. Amino acids produced are then small enough to be absorbed into bloodstream.

Name 4 similarities between Lock and Key model and Induced fit model

• Both models which describe mechanism of enzyme action.

• Both depend on degree of precise binding of substrate to enzyme.

• Both important in describing how enzymes increase rate of reaction.

• Both reduce activation energy

Name a differences between Lock and Key model and Induced fit model

• Induced fit refers to a model for enzyme-substrate interaction in which the active site of the enzyme doesn’t completely fit substrate. Lock and key refers to a second model for enzyme substrate interaction in which active site of enzyme completely fits with substrate.

Define temperature coefficient

A measure of how much the rate of a reaction increases with a 10 degrees celsius rise in temperature.

How does temperature affect enzyme activity

Increasing the temperature of a reaction increases kinetic energy of particles meaning more frequent successful collisions between substrate and enzyme meaning an increased rate of reaction.

Define denature

When the temperature gets too high above an enzyme’s optimum temperature, the bonds holding the protein together vibrate more so they are put under strain and eventually break. The breaking of these bonds results in change in tertiary structure which is why the enzyme denatures at high temperature.

How does pH affect enzyme activity

H bonds and ionic bonds between amino acid R-groups hold proteins in their specific 3D shape. These bonds occur due to interactions between polar R-groups present on amino acids forming primary structure. When pH increases the more the R-groups interact meaning the enzyme will denature. If pH is only slightly changed from the optimum the enzyme and active site is altered but can return to normal shape (renaturation), but if the pH changes significantly the enzyme is irreversibly altered.