Download Bio05 Enzymes

Enzymes, Coenzymes, And
Energy
Chapter 5
Nutrients
• Nutrients are molecules required by
organisms for growth, reproduction, or repair.
• Nutrients are a source of energy.
• Nutrients are a source of the building blocks
for new molecules in the body.
Biochemical Reactions
• Biochemical reactions involve the formation,
breakdown, and rearrangement of molecules
to provide organisms with the following:
– Energy
– Building blocks
Activation Energy
• Activation Energy is the amount of energy
input required to get the reaction started.
• Random chemical processes would take
millions of years to break down a candy bar
and release its energy.
• We can increase the rate of a chemical
reaction by increasing its temperature.
• Cellular proteins become denatured at high
temperatures.
Catalyst
• A catalyst is a chemical that speeds up the rate of the
chemical reaction.
• Catalysts lower the amount of activation energy required to
start a reaction.
• The catalyst is not used up in the chemical reaction.
• The catalyst is unchanged when the chemical reaction is
complete.
• The cell manufactures specific proteins to act as catalysts.
• An Enzyme is a protein molecule that acts as a catalyst to
speed the rate of a chemical reaction.
• The DNA regulates which enzymes are produced by the
cell.
Formation Of Enzymes
• The DNA guides the production of the
enzyme.
• A specific sequence of amino acids is linked
together at the ribosomes.
• The chain of amino acids folds and twists to
form a particular three-dimensional shape.
Enzyme-Substrate Complex
Formation
• The specific three-dimensional shape, size,
and charge of the enzyme allows it to combine
with a specific reactant.
• This combination lowers the activation energy
required for chemical reaction.
• The enzyme physically fits with the reactant.
Enzyme-Substrate Complex
Formation
• The substrate is the molecule (reactant) to
which the enzyme attaches itself.
• A new, temporary molecule called the
enzyme-substrate complex is formed.
• Enzymes are specific to certain substrate
molecules because their shape can only
combine with specific parts of certain
molecules.
Binding Site
• The binding site or attachment site is the
specific location on the enzyme where the
substrate attaches.
Enzymes
• Enzymes can be used again and again.
• Eventually they break down and new ones
need to be synthesized.
• Enzymes have a particular surface geometry
that matches the geometry of their respective
substrates.
Induced Fit Hypothesis
• The induced fit hypothesis states that
enzymes can fold to fit the substrate.
• The enzyme molds or adjusts itself to fit the
substrate when the two come into contact
with each other.
Active Site
• The active site on the enzyme is the place that
causes a specific part of a substrate to change.
• Chemical bonds are either formed or broken
here.
• Activation energy is lowered at this site.
• Electrons are shifted to change the bonds.
Naming Enzymes
• The 1st part of an enzymes name is usually the
name of the molecule to which it can become
attached.
• The 2nd part of an enzymes name tells us the
type of reaction it facilitates.
• The 3rd part of an enzymes name is “-ase”.
This indicates that the molecule is an enzyme.
Naming Enzymes
• Examples:
– Glycogen synthetase.
– DNA polymerase.
– Amylose hydrolase (amylase)
Cofactors
• Some enzymes need an additional molecule to
help them function.
• Cofactors are either inorganic or organic
molecules that help enzymes.
• Ions such as zinc, iron, and magnesium assist
enzymes.
• A Coenzyme is an organic molecule that acts
as a cofactor.
Vitamins
• Vitamins are organic molecules that are used
to make certain coenzymes.
• Vitamins help to regulate gene action.
• Vitamins are either water soluble or fat
soluble (A,D,E,K)
• We are not able to manufacture vitamins;
therefore, it is necessary to obtain them from
our diet.
Turnover Number
• The turnover number is the number of
molecules of substrate with which a single
enzyme molecule can react in a given time.
Turnover Number
• Some enzymes can perform incredible
numbers of reactions in a single minute.
• Enzymes can facilitate chemical reactions
anywhere from one thousand (103) to ten
thousand trillion (1016) times faster than
uncatalyzed reactions)
Factors That Affect Enzyme
Function
• Temperature
– Increased temperature increases molecular
motion and therefore the number of reactions.
– Temperature that is too high will denature the
protein structure of the enzyme and slow or even
stop the chemical reaction.
• pH
– pH determines how many hydrogen ions are
present and will attach the enzyme side chains.
Factors That Affect Enzyme
Function
– The positively charged hydrogen ions will affect
the reactivity of the enzyme.
– Many enzymes function best at a neutral pH of
around 7; however, some work better in more
acidic or more alkaline environments.
• Pepsin – works well in stomach acid pH 1.5 to 2.2
Factors That Affect Enzyme
Function
• Arginase – works well in basic pH of 9.5 – 9.9
• Enzyme-Substrate concentration
– If all of the enzymes are occupied, the reaction
time will be limited.
Enzymatic Competition
• Enzymatic competition occurs when there are
several kinds of enzymes available to combine
with the same kind of substrate molecule
• Different enzymes have different effects upon
the same substrate.
Gene Regulation
• Gene regulator proteins are chemical
messengers that inform the genes of the cell’s
need for enzymes.
– Gene-repressor proteins decrease protein
production.
– Gene-activator proteins increase protein
production.
Inhibition
• An inhibitor is a molecule that attaches itself
to an enzyme and interferes with that
enzyme’s ability to form an enzyme-substrate
complex.
Competitive Inhibition
• Some inhibitors have a shape that closely
resembles that of the substrate.
• They compete with the substrate for binding
sites.
Negative Feedback Inhibition
• Certain end product molecules with stop the
enzyme from functioning.
• As the concentration of end product increases,
it slows the rate of reaction of the enzyme,
which ultimately decreases the rate of the
reaction.