Biology 201 Enzymes. What are Enzymes? Enzymes are catalysts. A catalyst is a substance which...
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Transcript of Biology 201 Enzymes. What are Enzymes? Enzymes are catalysts. A catalyst is a substance which...
Biology 201 Enzymes
What are Enzymes?
Enzymes are catalysts.
A catalyst is a substance which increases the rate of chemical reaction
Catalysts themselves are NOT used up Used in living organisms
Reactions must occur at body temp and atmospheric pressure (LOW)
Without catalysts reactions would be too slow
Needed to sustain life
What are Enzymes?
Metabolism is just the cummulation of reactions 1000's of different reactions in an organism Each reaction requires a unique catalyst
These catalysts are called enzymes Enzymes act upon a substance called its substrate (reactant)
Metabolism is a chain of reactions Product of one reaction is substrate for the next A different enzyme for each step in the chain
This is called the metabolic pathway
enzyme1 enzyme2 enzyme3 enzyme4
A ---------> B ---------> C ---------> D ---------> E
How Enzymes Work
Each reaction requires a specific enzyme
Enzymes must be made of something that can take many different shapes
Proteins
There is a small part of the enzyme that contacts the substrate called the active site
Like a small cleft or indent on the surface Substrate fits into active site and interacts with exposed
amino acids by ionic or hydrogen bonding Forms enzyme-substrate complex Reaction then occurs
How Enzymes Work
This is known as the lock and key model
Specific substrate fits specific enzyme
How Enzymes Work
Induced fit model is an alternate mechanism
Enzyme's active site does not fit the substrate until the substrate actually enters the enzyme
The enzyme is not active until this happens
How Enzymes Work
Enzyme-catalysed reactions are reversible
Direction of reaction depends on concentrations
Enzymes don't effect the point of equilibrium
Enzymes only change the time to equilibrium
In cells this in not important because products become substrates for new reactions or used up
Reactions will always go forward
Added Molecules
molecules or ions other than proteins may associate with an enzyme to aid in its function
cofactor coenzyme prosthetic group
Energy Changes During a chemical reaction bonds must be broken and
new bonds are remade to form products Breaking bonds required energy endergonic Making bonds releases endergy exergonic These energies are not equal
Reaction can create a net increase of energy Reaction can require an external source of energy
Anabolic reactions build large complex molecules built up from smaller ones
These reactions are endergonic (requires energy) Protein synthesis Photosynthesis uses light energy
Energy Changes
Catabolic reactions break down large complex molecules into smaller, simpler ones
These reactions are exergonic (releases energy) Respiration releases chemical energy
All reactions begin by breaking bonds which requires an activation energy to start
Enzymes work by lowering the activation energy This is done by the enzyme-substrate complex This complex has lower activation energy Makes the reaction proceed quicker and easier
Without enzyme activation is too high to occur
Energy Changes
Enzyme Activity Factors
The activity of an enzyme is a measure of how well it catalyses its reaction
Temperature Increase temperature --> Increase kinetic energy More collisions between substrate and enzyme More successful conversions Moving higher than optimum temp reduces activity
Enzyme is made of protein High temperatures can denature the enzyme
Tertiary structure is changed 3D structure of enzyme changes too much for substrate to fit
Most enzymes in the human body have an optimum temperature around 40 C
Temperature
Enzyme Activity Factors
pH A change of pH means a change in H+ ions in surrounding Affects the bonding of R-groups Affects the shape of the enzyme Most human enzymes have optimum at 7 (neutral) Stomach enzymes (pepsin) have optimum at 2 Liver enzymes arginase has optimum at 10
pH
Enzyme Activity Factors
Enzyme concentration Enzymes are not used up during reactions Can work effectively at low concentrations Usually substrate molecules are in excess Reaction rate is limited by enzyme concentration Increased concentration --> increased reaction rate
Enzyme Concentration
Enzyme Activity Factors
Substrate concentration If substrate concentration is low some enzyme sites empty Rate of reaction will be lower If substrate conc. is then increased --> rate increases This increase continues until substrate is in excess Reaction rate approaches maximum called Vmax
Enzyme active sites are saturated with substrate
Substrate Concentration
Enzymes- quiz (open book)• 1.What is an enzyme?- identify 4 properties (4 marks)• 2. Name the two different theories that attempt to explain
how enzymes work (2 marks)• 3. Describe how each theory above works (4 marks) • 4. What do enzymes do to help a chemical reactions-
think energy. (2 marks)• 5. Name 4 factors that can effect enzyme effectiveness (4
marks)• 6. Choose two and explain how these factors effect
enzymes. Include a rough graph to support your answer (4 marks)
• 7. What word do you use to describe an enzyme that has changed shape and no longer functions (1 mark).
Co-factors & Co-enzymes
• Enzymes often need “helpers”. • Sometimes ions or metal atoms are used. These
helpers are called cofactors (e.g. iron in haemoglobin, calcium in nerve signalling, nickel in urease etc.)
• Small molecule helpers are called coenzymes.• Coenzymes that we can't build ourselves, that
we need to get from our food in their working form, are called vitamins. (e.g. vitamin B in respiration, vitamin C for turning genes “on”)
Co-factors & Co-enzymes
Inhibitors Inhibitors are chemicals which reduce the rate of enzyme
catalyzed reactions Alter the shape of the active site directly or indirectly
Non-reversible bind permanently disabling enzyme Permanent change of tertiary structure (break disulfide bond) Always non-competitive
Reversible inhibitors bind temporarily to enzyme Competitive inhibitors
Similar shape to substrate and fit into active site Prevents substrate from entering enzyme
Non-competitive inhibitors Bind to other parts of the enzyme altering shape of enzyme Active site no longer fits substrate
Inhibitors
Examples
Heavy metals (such as Pb, Hg, Ag and Cu).
These are non-competitive inhibitors and bid to the enzyme altering the shape. This is non-verseable
Reversible competitive inhibitors:
Antiviral drugs used to treat HIV bind to the enzymes which start DNA replications.
This stops the virus from reproducing