Enzymes
Enzymes a Fun Introduction
http://www.youtube.com/watch?v=XTUm-75-PL4&safe=active
Enzymes: what they are
http://www.youtube.com/watch?v=hoBhOdQV7vw&safe=active
Enzyme Function
http://www.youtube.com/watch?v=E_r3omrnxw&feature=rellist&playnext=1&list=PLC7ZMTERKSOJO
48-GKSQYXM6Z0YH-ZBLG&safe=active
Enzymes and Chemical Reactions
– To function properly, cells must carry out
thousands of chemical reactions
– All chemical reactions require energy
Activation Energy: the initial push of energy to
get a chemical reaction started
– Enzymes lower the
activation energy needed
to begin a reaction
Enzymes
• Large complex protein molecules
• Organic Catalysts: speed up the rate of
chemical reaction in living things
– Rate of Reaction: how quickly product is
produced over time
• Enzymes are not chemically changed by
a reaction, so they can be reused over and
over by the cell.
• You only need a small amount of enzyme
to catalyze thousands of reactions each
second.
• Enzymes often work with co-enzymes
(non-proteins like vitamins).
Making Enzymes:
– Protein molecules
synthesized at ribosomes
– Most used within cells
– Some passed out of cell
(secreted) to catalyze
reactions outside cell
• Ex: Digestive Enzymes
Enzymes are Specific:
– Can only work with one
specific substrate
– Specificity is due to shape
– If shape is altered for
some reason, enzyme will
not function properly
Active Site:
location on enzyme where
substrate binds and reacts
Lock and Key Model
Enzyme binds with
a specific substrate at
active site. (like key in lock)
– Enzyme substrate complex forms
– Reaction takes place
– Substrate gets altered.
– Products get released
– Enzyme can go on to react with more
substrate.
Induced Fit Model: (flexible enzyme)
– Substrate and enzyme may not fit exactly.
– When substrate joins, the enzyme changes
shape slightly making the fit more exact.
(flexible lock)
Note:
– Certain metabolic genetic disorders involve a
single amino acid in an enzyme being changed.
– The enzyme shape is altered and it cannot
function properly
• Ex:
– Sickle Cell Anemia
Names of Enzymes:
– Start with beginning of substrates name
– End in “-ase”
– Ex:
• Protease – enzyme reacts with proteins
• Lipase – enzyme reacts with lipids
• Sucrase – enzyme reacts with sucrose
(disaccharide)
Factors Influencing Enzyme Action
– Temperature
– pH levels
– Concentration of Available Substrate
Changing Temperature
• For most enzymes in humans, the optimum
temp. to function properly is about 98.6°F
(37°C)
– If too cold – reaction slow
– As it heats up - reaction speeds up
– If too high - reaction stops, enzyme denatures
• Denaturation
– At temp. above or below the optimum, the
enzyme starts to lose its shape and stops
functioning.
– Active site no longer fits substrate
Enzyme has
Denatured
Biologist Pick Up Line
Different organisms
have different optimum
temp. for enzyme
activity
Changing pH Levels
• Each enzyme has an optimum pH at which
it functions best.
Ex: Digestive Enzymes
Pepsin: works in stomach (acidic pH)
Trypsin: works in small intestine (slightly basic pH)
Salivary Amalase: works in mouth (neutral pH)
What is the optimum
pH for each of these
enzymes to function?
Changing Concentration of Substrate
• As concentration of available substrate
increases, more is available to react with
enzyme so rate of reaction increases.
• Eventually rate of reaction will level off as
available enzymes are all being used.
(point of enzyme saturation)