Enzymes Flashcards
What are enzymes?
Enzymes are globular proteins with a specific tertiary structure that catalyses metabolic reactions in living organisms
- They speed up chemical reactions and remain unchanged at the end
- small amount of catalyst can catalyse a large number of substrate molecules
- turn over number (second)
Describe the active site
Large, 100 of amino acids = specific tertiary structure, active site shape (indentation)
- tertiary structure complementary to substrate
- highly specific only catalyses reaction for substrate fits into active site
- shape (so ability) can be altered by changes in temperature, pH as affects bonds in tertiary
Explain intracellular enzymes in a metabolic pathway
Some reactions within cells and organelles are part of a metabolic pathway
- metabolites are reactants, intermediates and products
- catabolic = metabolites broken down to smaller and release energy
- anabolic = metabolites make larger molecules out of smaller (energy used)
- metabolites act as substrates for specific enzymes
Respiration and photosynthesis
Explain extracellular enzymes
Some enzymes secrete out of the cell
- Fungi mucor release hydrolytic enzymes from hyphae, digest carbs, proteins, lipids and the products absorb into hyphae for respiration and growth
- Digestive system: cells lining alimentary canal into gut lumen, digest products of digestion via epithelial cells into blood stream for respiration, growth, tissue repair
- some examples:
- amylase salivary gland digest polysacc starch into disacc maltose, made in pancreas (lumen of small intestine)
- trypsin made in pancreas digest proteins into peptides by hydrolysing peptide bonds 7.5 and 8.5 pH
Explain catalase
Protects cells from damage by reactive O2 by breaking down H2O2 harmful by-product to H2O and O2
- 4 polypeptide chains + haem iron
- fastest acting enzyme
- found in peroxisomes
- WBC to kill microbe
- pH 7 45 C optimum human
What is a cofactor?
A small,non protein molecule that must be present in an enzyme catalysed reaction
What is a prosthetic group and give an example
A cofactor that is permanently bound by covalent bonds to an enzyme
Carbonic anydrase and zinc ion = erthrocytes
CO2 + H2O = H2CO3 = H+ + HCO3-
Enables CO2 to be carried in blood stream from respiring tissues
Describe inorganic ion cofactors
Some enzymes work in the presence of ions that are not attached to them
- they bind to substrate or enzyme, easing the formation of ES, increase rate of enzyme reaction
- cosubstrates form correct shape for AS
- change charge distribution on enzyme or substrate temp bonds easier form
Amylase = starch to maltose Cl-
What are coenzymes?
Small, organic non protein bind temp to AS changed then recycled
Carry chemical groups between enzymes
What vitamins are important for enzyme reaction?
B1 thiamine thiamine pyrophosphate = beriberi B3 nicotinamide NAD NADP = pellagra B6 pantothenate coenzyme A = triglyceride high levels B12 cobalamin = pernious anemia Folic acid tetrahydrofolate = megablastic anemia
Describe and draw the lock and key hypothesis
Kinetic energy
- shape of AS is complementary and specific to substrate
- substrate successfully collides with active site substrate is they key and AS is lock forms an ES complex hold by temp H bonds
- products formed becomes enzyme-product no longer fit so are released
- small no. of enzyme molecules therefore can convert a large no. of substrate = product
Describe the induced fit hypothesis
- substrate molecule collides with complementary and specific AS, enzyme changes shape so AS fits more closely, held by H bonds, ionic bonds, VDW
- ES formed change in enzyme shape destabilises substrate converts to product
- products made EP no longer fit so are released
How do enzymes lower the activation energy?
Ea minimum level of energy required to enable reaction to take place
Enzymes lower the Ea so speed up metabolic reactions
Without the need for high temp (denature and melt)
Bring the substrate and molecules close enough to react
Less energy required
How does temperature effect the collisions between enzyme and substrate?
As temp increases, kinetic energy increases so the molecules move more quickly, this increases the rate of successful collisions, rate of formation of ES increases, so rate of product formation
What effect does heat have on proteins?
Heat makes molecules vibrate, breaks h bonds and ionic bonds, the tertiary structure of AS will change therefore substrate will no longer fit and reaction can’t proceed, the enzyme is denatured
What is the optimum temperature?
The temp at which enzymes works best, it works at maximum rate of reaction
Thermophilic bacteria contain more disulfide bonds that do not break with heat and keep shape stable
What is the temperature coefficient?
The increase in rate of a process when the temperature is increased by 10C
Q10 = rate of reaction (T+ 10)
rate of reaction at T
Draw a graph showing the effect of temperature on enzyme rate
Between A and B increasing temperature increases the rate of reaction due to increased kinetic energy
B is optimum temp gives maximum rate of reaction
Increasing temp beyond B reduces RoR due to breaking of the bonds holding the enzyme’s tertiary structure
C there is no reaction because enzyme is denatured
Describe how an enzyme breaks down a substrate
- substrate is complementary to enzyme’s active site
- substrate fits into the active site of enzyme
- forms ES complex
- destabilises bonds in substrate then forms enzyme-product complex
- products leave active site
What is a buffer?
Something that resists changes in pH, this is to ensure that blood pH remains in narrow limits, they donate or accept hydrogen ions
Used to maintain pH in experiments
How does pH affect molecules?
- H+ holds tertiary structure of active site
- excess H+ ions interfere with H bonds and ionic forces so AS will change shape (RoR decrease if substrate doesn’t fit)
- increasing conc of H+ alters charge on AS protons go to negatively charged R groups interfere with binding of the substrate
How do enzymes work in pH? Draw a graph and label
- work in a narrow pH range
- small changes slow down RoR as shape is disrupted
- permanently changed denatured
How do other enzymes work with examples? Show on a graph
- Amylase starch to maltose pH 6.8
- pepsin (protease) pH 1 and 2
- typsin and enterokinase pH 7.8 salts in bile in liver
Explain the effect of substrate concentration on initial rate of reaction
Substrate conc increases so does RoR
- more ES complexes
- more product molecules form
- limiting factor becuase as it increases so does RoR
- max rate: more substrate won’t increase RoR
- all enzymes AS are occupied with substrate
- if more is added they can’t successfully collide with and fit into AS
