Biology - Enzymes

function of enzymes

enzymes lower the activation energy of chemical reactions by providing an alternative pathway for reactions

All enzymes are ______

1. globular proteins (mostly tertiary, some quaternary)

2. they all have precise 3D structure due to interactions between R groups

3. soluble because hydrophobic R groups are inside and, hydrophilic R groups are outside

How do substrates bind to the active site

1. Lock and key mechanism: active site does not change shape, shape of the active site is fully complementary to the shape of substrate.

2. Induced fit mechanism: active site is flexible and moulds around the substrate, shape of active site in partially complementary to the substrate (results in a better fit)

Where do enzymes operate?

Some are intracellular and some are extracellular. Intracellular are synthesized inside the cell and retained for internal use. Extracellular enzymes are synthesized by the cells and secreted for external use.

Mode of actions for enzymes

1. Collisions occur between the enzyme and substrate, but only collisions with the right orientation and enough energy result in a successful reaction

2. only the enzyme with the active site of a specific shape that is complementary to the substrate will be able to bind

3. Formation of enzyme substrate complex

   substrate interactions with R groups of amino acid at active site forming temporary bonds, active site changes shape to mould around substrate. substrate binds strongly to active site and ESC is formed

4. Formation of products, interactions of substrate with active site brings substrates closer together putting strain on the reactants so bonds can break or form more easily. this lowers the activation energy

How to measure rate of reaction

Either by measuring rate of rate at which product is formed or by how quick the substrate disappears

Steps to measure rate of reaction

1. measure the formation of product or substrate disappearance (either by volume or conc)

2. plot a time course graph

3. Find the gradient (conc/time = ROR)

Starch be tested by what test

iodine test

Starch gets broken down into

Amylase and maltose

Describe the iodine test

1. Test samples of iodine at known time intervals

2. colour will change from dark blue to yellow (dark blue indicates that alot of starch is still present, yellow/brown indicates that starch is hydrolyzed)

The course of reaction, why is the rate high at first then decreased and then 0

1. At high [S] the substrate is in excess

2. Over time more substrates get used up, lesser substrates are available (resulting in lower [S])

3. After all the substrates are converted to products, there’s no more substrates available for binding

4. Trend: Product conc. increases over time then levels off and, substrate conc. decreases over time. Enzyme conc is constant. The substrate concentration is the limiting factor

Factors affecting rate of reaction of enzymes

1. Enzyme concentration

2. Substrate concentration

3. pH

4. temperature

5. Inhibitors

At low [S]

1. some active sites are available for binding

2. fewer collision between active site and substrate

3. Less substrate bind with active site

4. fewer ESC formed, substrate conc is the limiting factor

At high [S]

1. all active sites are saturated

2. max no of ESC formed

3. [E] is the limiting factor

4. an increase in [S] will not increase the ROR

For enzymes with higher Km and low affinity

1. higher [S] is needed to reach ½ Vmax

2. enzyme needs higher [S] to reach Vmax

3. Enzyme forms fewer ESC

Low [E], as [E] increases

1. More enzymes are present, hence more active sites for substrate to bind to

2. Increase in frequency of collisions

3. More ESC formed

4. Rate of reaction increases as [E] increases

At low temp, as temp increases

1. increase in kinetic energy

2. increased collision between active site ad substrate

3. substrates bind to the active site more often resulting in more ESC formed

Two types of inhibitors

1. Competitive: inhibitors that are similar in shape to the substrate and bind to the enzymes active site

2. Non-competitive inhibitors: are not similar in shape to the substrate and bind to the the allosteric site altering the shape of active site making the substrate unable to form ESC