Enzymes Flashcards
What is a simple protein?
A simple protein is a protein without a prosthetic group
What are conjugated proteins?
Conjugated proteins are proteins with a prosthetic group of a metal ion, molecule or biological molecule
What are enzymes?
Biological catalysts, globular proteins
How do enzymes react?
Interaction of a substrate with an active site
What is anabolism?
Building up of molecules, e.g. metabolism in steroid hormones
What is catabolism?
Breaking down of molecules, e.g. breaking down of ATP to use energy
What are the roles of enzymes?
Anabolism, catabolism, digestion
What are the mechanisms of enzyme reaction?
Lock and key, induced-fit
How does the lock and key theory work?
- enzyme has an active site with a specific shape
- substrate is complementary to the active site
- substrate binds to form a enzyme-substrate complex
- this reacts to form a enzyme-product complex
- the interaction of the R-groups form weak bonds while reacting
How does the induced-fit theory work?
- active site changes shape to strengthen R-group interactions
- this is called the induced-fit hypothesis
- therefore the tertiary structure of the enzyme changes
- this weakens bond/s in the substrate which lowers the activation energy
What is the aim of enzymes?
Lower activation energy of reaction, reaching Vmax
What effects the rate of reaction for enzymes?
Temperature, substrate concentration and pH
What are intracellular enzymes with examples?
Enzymes that catalyse reactions inside of the cell, e.g. Catalase for hydrogen peroxide, synthesis of polymers and polysaccharides
What are extracellular enzymes with examples?
Enzymes that catalyse reactions outside of the cell, e.g. Trypsin and amylase for digestion, breaking down of larger molecules into monomers and monosaccharides
How is starch digested?
- Starch is broken down into maltose by amylase in the saliva
- Maltose is broken down into glucose by maltase in the small intestine
- glucose is small enough to be absorbed into the lining of the digestive tract and then the blood stream
How are proteins digested?
Trypsin catalyses the digestion of proteins into smaller peptides, which can then be broken down into amino acids by other proteases
Where is trypsin made?
The pancreas
How does increasing the temperature effect enzyme activity?
- as thermal energy increases, kinetic energy also increases
- this increases the number of successful substrate-active site collisions
- however the bonds in the enzyme also vibrate
- the more the bonds vibrate, the more they strain and eventually will break
- this is denaturation
What happens when an enzyme denatures?
The active site changes shape permanently and is no longer complementary to the substrate
What is the optimum temperature?
The temperature where an enzyme is at its highest rate of activity, 40 oC for animals
What is optimum pH?
The pH where an enzyme is at its highest rate of activity
What happens if the pH changes too significantly?
The tertiary shape of the protein is irreversibly altered and the active site will no longer be complementary to the shape of the substrate
What are the enzymes present in salvia and what are their function?
Amylase, breaking down starch into maltose
What are the enzymes present in gastric juice and what are their function?
Pepsin, breaking down proteins into polypeptides
What are the enzymes present in pancreatic juice and what are their function?
Trypsin, breaking down proteins into polypeptides
What happens when the concentration of substrate is increased?
The rate of successful collision between the active site and substrate of a protein increases, therefore the rate of reaction increases
What is the difference between an increase of the concentration of substrate and the increase of the concentration of an enzyme?
None, rate of reaction will increase with both
What is the Vmax?
The maximum point of the rate of reaction, after Vmax it’ll either decrease or plateau. The only way to increase is to add another limiting factor
Why can’t enzyme related reactions happen too fast?
There will be an excess of products
What are enzyme inhibitors?
Molecules that prevent/slow down enzymes from carrying out their regular function, there are 2 types- competitive and non-competitive
What is competitive inhibition?
Molecules with a similar shape to the active site and can block the substrate from catalysing the reaction, therefore slowing down the rate of reaction
What is non-competitive inhibition?
A molecule that binds to an enzyme at an area different to the active site called the ‘allosteric site’. This causes the tertiary structure of the enzyme to change, which means the active site changes and the substrate cannot bind to the enzyme, therefore the rate of reaction decreases
Can Vmax be achieved by changing the concentration of enzyme/substrate for inhibition?
Competitive - eventually, yes
Non-competitive - no
What are the positive effects of inhibition?
Controls enzyme activity, may kill foreign bodies, may be reversible
What are the negative effects of inhibition?
Enzyme shape may be permanently changed, may be a foreign body itself, could kill organism
What is an example of competitive inhibition?
Statins competitively inhibit the enzyme that produces cholesterol, and are prescribed to prevent heart disease
What is an example of non-competitive inhibition?
HIV Protease inhibitor, binds to allosteric site on HIV protease to prevent longer strands of HIV RNA being replicated
What is end-product inhibition?
When a product produced by an enzyme reaction inhibits the enzyme that produced it. This acts as a control mechanism
What are cofactors?
An inorganic non-protein component that helps an enzyme carry out its function
Name an example of a cofactor
Chloride ions in amylase that are essential in active site formation
What are coenzymes?
Organic cofactors
What are coenzymes made of?
Vitamins
Name an example of a coenzyme
Vitamin B5 which is used to make coenzyme A, which breaks down fatty acids and carbohydrates in respiration
What is another term used for cofactors?
Prosthetic groups
What is the difference between cofactors and prosthetic groups?
Cofactors are loosely bound and prosthetic groups are tightly bound
Name an example of a prosthetic group
Zinc ions that form carbonic anhydrase, which is used in the metabolism of carbon dioxide
What are inactive precursor enzymes?
Enzymes in their inactive form that only need to be activated under certain conditions because they may be damaging to cells/tissues in their surroundings
How are precursor enzymes activated?
Addition of a cofactor that changes the tertiary structure, and therefore the active site so the substrate can bind
What is a precursor enzyme called before and after a cofactor is added?
Before - apoenzyme
After - holoenzyme
What are other factors that could activate precursor enzymes?
pH changes, other enzymes, temperature:
before - zymogens
after - proenzymes
Name an example of a precursor enzyme
Pepsinogen that gets activated by the acidic pH of the stomach acid
What are biological catalysts?
Enzymes used in metabolism that alter rate of reaction and lower activation energy
How are hydrogen bonds formed in tertiary structure?
Between nitrogen, oxygen and phosphorous; between electronegative and electropositive
Why does rate of reaction increase with the increase of substrate concentration?
Because more active sites are being occupied to achieve Vmax
Why does rate of reaction increase with the increase of substrate concentration?
Because more active sites are being occupied to achieve Vmax
