Download Enzymes

Enzymes
All enzymes are proteins.
Not all proteins are enzymes.
•Enzymes are catalysts.
•A catalyst is a substance which increases the
rate of chemical reaction
– Catalysts themselves are NOT used up
What are Enzymes used for?
1)Used in industrial processes to reduce heat or
pressure requirements
2)Used in living organisms
– Reactions must occur at body temp and atmospheric
pressure (LOW)
Why are enzymes important?
•Without catalysts reactions would be too slow
•Needed to sustain life
• Enzymes
– Are a type of protein that acts as a catalyst,
speeding up chemical reactions
1
Active site is available for
a molecule of substrate, the
reactant on which the enzyme acts.
Substrate
(sucrose)
2 Substrate binds to
enzyme.
Glucose
OH
Enzyme
(sucrase)
H2 O
Fructose
H O
4 Products are released.
Figure 5.16
3 Substrate is converted
to products.
3
How enzymes work
• Enzymes act upon a substance called its substrate
• Each reaction requires a specific enzyme
• Enzymes must be made of something that can take
many different shapes
• Proteins and their 4 levels of structure work well
• 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
• Proteins and their 4 levels of structure work well
• 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
• 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
Factors that affect How Enzymes Work
1)Temperature
– Increase temperature --> Increase kinetic energy or
movement of molecules
– More collisions between substrate and enzyme
– 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
Enzyme Activity Factors
2) pH
– A change of pH means a change in H+ ions in the
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
Enzyme Activity Factors
3) 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 Activity Factors
4) 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
Energy Changes
Temperature
pH
Enzyme Concentration
Substrate Concentration