Enzymes 2.1.4 Flashcards
1
Q
what are enzymes?
A
Enzymes are biological catalysts. They are globular proteins that interact with substrate molecules causing them to react at much faster rates without the need for harsh environmental conditions.
2
Q
Properties of enzymes
A
- Enzymes are globular proteins , their function is dependent on their exact structure.
- The enzyme catalases a change in the substrate to convert it into a product
- Active site = 3D crevice in the enzyme structure formed by the folding of the protein chain, it is the region of the enzyme where the substrate molecule binds and undergoes a chemical reaction to form a product.
- Enzymes are extremely specific
- Enzymes have a very high turn over number
- Enzymes may be intra or extracellular
3
Q
The role of enzymes in reactions
A
- The synthesis of large polymer based components require anabolic reactions which are catalased by enzymes.
- Energy is released from many large molecules, like glucose, in metabolic pathways consisting of many catabolic reactions, these are catalysed by enzymes.
- Digestion is catalased by a range of enzymes.
4
Q
What is metabolism?
A
Metablolismis the sum of all the different reactions and reaction pathways in an organism.
5
Q
What is activation energy?
A
The minimum ammount of energy needed for a reaction to happen
6
Q
Lock and key hypothesis
A
- Shape of active site is exactly complementary to the shape of the substrate.
- When the substrate is bound to the active site an enzyme substrate complex is formed
- The substrate is held so the right atom groups are close enough to react. The R groups within the active site of the enzyme will also interact with the substrate, forming temporary bonds which put a strain on the substrate which helps the reaction along.
7
Q
Induced fit hypothesis
A
- A change in shape of the active site in response to substrate binding.
- The weak interactions between between the enzyme and substrate induce changes in the enzyme’s tertiary structure that strengthen the binding, putting a strain on the substrate molecule.
8
Q
Intracellular enzymes
A
- Act within cells
- Have an essential role in both the structure and the function of cells and whole organisms.
- The synthesis of polymers from monomers, e.g. making polysaccharides from glucose requires intracellular enzymes.
- The enzyme catalase ensures hydrogen peroxide is broken down into oxygen. Catalase is found in ornganelles called peroxisomes in all eukaryotic cells.
9
Q
Extra cellular enzymes
A
- Made inside cells (on ribosomes) and work outside of cells and secreted out of cells using secretory vessicles made by the golgi by the process of exocytosis.
- Mostly digestive enzymes
- Both single and multi celluylar organisms rely on extracellular enzymes to make use of polymers for nutrition.
10
Q
Digestion of starch
A
- The digestion of strach begins in the mouth and continues in the small intestine. Starch is digested in 2 steps involving different types of enzymes, different enzymes are needed because each enzyme only catalyses one specific reaction:
- Starch polymers are partially broken down into maltose (a disaccharide) by the enzyme amylase. Amylase is produced by the salivary glands and the pancreas.
- Maltose is then broken down into glucose ( a monosaccharide) by the enzyme maltase, maltase is present in the small intestine.
11
Q
Digestion of proteins
A
- Trypsin is a protease, a type of enzyme that catalyses the digestion of proteins into smaller peptides which can be broken down further into amino acids by other proteases.
- Trypsin is produced in the pancreas and released with the pancreatic juice into the small intestine, where it acts on proteins
12
Q
Mechanism of enzyme action
A
- Substrate binds to enzyme at the active site to make a temporary enzyme substrate complex
- substrate is changed to product at the active site
- an enzyme product complex is formed, producs are released by the enzyme.
13
Q
What are the 2 categories of metabolism?
A
- Anabolism = synthetic reactions (monomers to polymers), condensation reactions, requires a overall input of energy (endothermic)
- Catabolism = breakdown reactions (polymers to monomers), hydrolysis, digestion, releases energy
14
Q
What are the factors that affect enzyme activity?
A
pH, temperature, enzyme concentration and substrate concentration
15
Q
Effect of temperature on enzyme concentration
A
- Increasing the temp of the reaction environment increases the ammount of kinetic energy the particles have, as temp increases the particles move faster and there are more frequent collisions.
- The temperature coefficient of a reaction (Q10) is a measure of how much the ror increases with a 10 degree rise in temperature. For enzyme controlled reactions this is usually taken as 2 meaning the ror doubles with a 10 degree increase in temperature.
- As enzymes are proteins their structure is affected by temperature. As temp increases the bonds holding the proteins together vibrate and eventually break which results in a chnage in the tertiary structure, this causes the enzyme to change shape and denature.
- The optimum temp of enzymes can vary significantly, many enzymes in the body have optimum temps of 40 degrees.
16
Q
Effect of pH on enzyme activity
A
- Hydrogen and ionic bonds between the amino acid R groups hold proteins in their precise 3 dimensional shape.
- A change in pH refers to a change in hydrogen ion concentration. More hydrogen ions are present in low pH environments.
- When the pH changes from optimum the enzyme active site is altered, however if it returns back to optimum then the original shape will be restored (renaturation).
- When pH changes significantly the structure of enzyme is irreversibly altered.
17
Q
Effect of enzyme and substrate concentration on enzyme activity
A
- When the conc of substrate is increased the number of molecules increases so more collisions which increases the ror
- When the conc increases ror also increases as it increases the number of available active sites.
- The ror reaches its maximum (vmax) at the point where all active sites are occupied by substrate molecules and no more es complexes can be formed.
18
Q
What is an enzyme inhibitor?
A
molecule which reduces the rate of reaction of an enzyme
19
Q
Competitive inhibitators
A
- Very similiar structure to the substrate so can fit into the active site but no reactions occur as enzyme is specific to the substrate.
- Most types of competitivie inhibition are reversible
20
Q
Non competitive inhibitators
A
- They bind tightly elsewhere on the protein enzyme molecule and change the overall shape of the molecule so the active site is no longer complementray to the substrate.
21
Q
Effects of inhibitators on rate of reaction
A
- Increasing the conc of enzyme or substrate will not overcome the effect of a non competitive inhibitor. However increasing the conc of the inhibitor will decrease the rate of reaction as more active sites will become occupied.
22
Q
Ireversible non competitive inhibitators
A
- Often very toxic
- Organophosphates used as insecticides and herbicides ireversibly inhibit the enzyme acetyl cholinesterase which is an enzyme neccessary for nerve impulse transmission.
- Protein pump inhibitors (PPIs) are used to treat long term indigestion. They ireversibly block an enzyme system responsible for secreting hydrogen ions into the stomach. This makes it very effective in reducing the production of excess acid.
23
Q
End product inhibition
A
- Occurs when the product of a reaction acts as an inhibitor to the enzyme that produces it. This serves as negative feedback control mechanism for the reaction.
- Excess products are not made and resorces are not wasted, it is an example of non competitive reversible inhibition.
- ATP inhibits ATP so it regulates its own production. When levels of ATP are high more ATP binds to the allosteric site on PFK, preventing the addition of the second phosphate group to glucose. Glucose is not broken down and ATP is not produced at the same rate.
- As ATP is used up, less binds to PFK and the enzyme is able to catalyse the addition of a second phosphate group to glucose. Respiration resumes leading to the production of more ATP.
24
Q
The difference between cofactors and coenzymes
A
- Some enzymes need a non protein helper component in order to carry out their function. These are called cofactors.
- If the cofactor is an organic molecules then it is called a co enzyme.
- Inorganic cofactors are obtained via the diet as minerals. For example, amylase which catalyses the breakdown of starch contains a chloride ion which is neccesary for the formation of a correctly shaped active site.
- Many coenzymes are derived from vitamins. For example B3 is used to synthesise NAD which is a coenzyme responsible for the transfer of hydrogen atoms between molecules involved in respiration. Another example is B5 which is used to make coenzyme A which is essential in the breakdown of fatty acids and carbohydrates in respiration.
25
Prosthetic groups
- Prosthetic groups are cofactors.
- Prosthetic groups are tightly bound to form a permanent feature on the protein
26
At the beginning of an enzyme catalysed reaction, if other conditions remained constant, which of the following would explain a reduced rate of reaction?
Increase in concentration of end product
27
What is the correct definition of the term coenzyme?
A non-protein organic molecule that is not permanently attached to the enzyme molecule, but needed for the enzyme to function
28
What molecule causes blue/black colour in starch to dissapear?
maltose
29
When an active site binds a substrate molecule(s), the reaction proceeds at as faster rate because
A strain is put on the bonds in the substrate
30
What term describes an inactive precursor enzyme that can be activated by the addition of a cofactor or coenzyme?
apoenzyme
31
Which enzyme breaks down hydrogen peroxide into oxygen and water?
catalase
32
What phrase describes a way in which cells regulate the production of a molecule by using that molecule to inhibit one of the enzymes in the metabolic pathway that makes the molecule?
End-product inhibition
33
Which factor affects the rate of reaction of an enzyme-controlled reaction by increasing the rate as the value gets higher up until Vmax is reached and then this factor is no longer the limiting factor for the rate of reaction?
substrate concentration
34
What term describes an atom, ion or non-protein molecule that binds strongly, and so permanently, to an enzyme in order to make it functional?
Atoms, ions or non-protein molecules that bind to enzymes to make them function are either cofactors (if they bind loosely and so temporarily) or prosthetic groups (if they bind strongly and so permanently).
A good example of a prosthetic group is the Haem group in Haemoglobin.
Non-organic cofactors are just called cofactors but organic cofactors are called coenzymes.
Coenzymes often bind atoms, or molecular groups from other reactions to take part in the reaction. Examples include NAD, FAD, and Coenzyme A in respiration and NADP in photosynthesis.
35
What term is given to the rate of reaction at 10°C higher than the original temperature divided by the rate of reaction at the original temperature?
Q10
36
Which enzyme hydrolyses starch into maltose?
Amylase
