Transcript Chemical reaction

The Chemistry of Life
Chemical Basis of Life
Enzymes
Lesson Objectives
• Describe what happens in a chemical reaction,
and identify types of chemical reactions.
• Explain the role of energy in chemical reactions,
and define activation energy.
• State factors that affect the rate of chemical
reactions.
• Explain the importance of enzymes in
organisms, and describe how enzymes work.
Introduction
• Chemical compound usually very different
from substances that make it…
– Example: Sodium chloride
NaCl (table salt)
WHAT ARE CHEMICAL
REACTIONS?
• Chemical reaction: a process that changes some
chemical substances into other chemical substances
– substances that start a chemical reaction are called
reactants
• reactants are used up to create the products
– substances that form as a result of a chemical reaction are
called products
• Example: Methane needs oxygen to burn.
CH4
Methane
+
2O2
Oxygen

CO2
Carbon
dioxide
+
2H2O + heat + light
Water
FIRE
Chemical Equations
• Can be represented by a chemical
equation (see below)
• Arrow in a chemical equation separates
the reactants from the products and shows
the direction in which the reaction occurs
CH4
Methane
+
2O2
Oxygen

CO2
Carbon
dioxide
+
2H2O + heat + light
Water
FIRE
Types of Chemical Reactions
• combustion reaction occurs when a compound or element
burns in oxygen, like methane burning in presents of oxygen
• Substance burns in presence of oxygen
• synthesis reaction occurs when two or more chemical
elements or compounds unite to form a more complex product.
For example, nitrogen and hydrogen unite to form ammonia:
N2 + 3H2 ---> 2NH3
• decomposition reaction occurs when a compound is broken
down into smaller compounds or elements. For example, water
breaks down into hydrogen and oxygen:
2H2O ---> 2H2 + O2
• substitution reaction occurs when one element replaces
another element in a compound. For example, sodium
replaces hydrogen in hydrochloric acid, producing sodium
chloride and hydrogen gas:
2Na+ + 2HCl ---> 2NaCl + H2
CHEMICAL REACTIONS AND
ENERGY
Some chemical reactions consume energy, whereas other
chemical reactions release energy.
Exothermic Reactions
• RELEASE ENERGY
– example is the combustion of methane described at
the beginning of this lesson
• In organisms, exothermic reactions are called
catabolic reactions.
– catabolic reactions break down molecules into smaller
units.
– an example is the breakdown of glucose molecules
for energy.
• Exothermic reactions can be represented by the
general chemical equation:
Reactants → Products + Heat.
Endothermic Reactions
• CONSUME ENERGY
– example is the synthesis of ammonia, described earlier.
N2 + 3H2 ---> 2NH3
• In organisms, endothermic reactions are called anabolic
reactions.
– anabolic reactions construct molecules from smaller units.
– an example is the synthesis of proteins from amino acids.
• Endothermic reactions can be represented by the
general chemical equation:
Reactants + Heat → Products.
Activation Energy
• Whether reactions are exothermic or endothermic, they all need energy to get started.
This energy is called activation energy.
Short Video & Demo
• Let’s explore activation energy.
http://www.youtube.com/watch?v=VbIaK6PL
rRM&feature=related
Rates of Chemical
Reactions
•
Chemical reactions in organisms are involved in processes ranging from the
contraction of muscles to the digestion of food.
– For example, when you wave goodbye, it requires repeated contractions of
muscles in your arm over a period of a couple of seconds. A huge number of
reactions must take place in that time, so each reaction cannot take longer than
a few milliseconds. If the reactions took much longer, you might not finish waving
until sometime next year.
•
Factors that help reactant molecules collide and react speed up chemical
reactions. These factors include the concentration of reactants and the
temperature at which the reactions occur.
–
Reactions are usually faster at higher concentrations of reactants. The more
reactant molecules there are in a given space, the more likely they are to collide
and react.
– Reactions are usually faster at higher temperatures. Reactant molecules at
higher temperatures have more energy to move, collide, and react.
ENZYMES AND BIOCHEMICAL
REACTIONS
• Rate of most biochemical reactions must be increased by a catalyst
(a chemical that speeds up chemical reactions).
– In organisms, catalysts are called enzymes
– enzymes are not reactants
• Special properties of enzymes:
–
–
–
–
Speed up ONLY reactions that normally occur slowly
They help the reactants interact but are not used up in the reactions.
May be used over and over again.
Are usually highly specific for particular chemical reactions. They
generally catalyze only one or a few types of reactions.
– Can catalyze up to several million reactions per second.
• As a result, the difference in rates of biochemical reactions with and without
enzymes may be enormous. A typical biochemical reaction might take hours
or even days to occur under normal cellular conditions without an enzyme
but less than a second with the enzyme.
Enzymes: Characteristics
• Activation energy – enzymes reduce the
amount of activation energy needed to start a
reaction. For chemical reactions to take place,
the reactants must collide with enough energy
so that existing bonds will be broken and new
bonds will be formed.
• Rate of reaction – sped up with an enzyme
present because less activation energy is
needed; without them some reactions would
take days to happen not a split second as they
do with enzymes.
Characteristics continued…
• Works on – substrate (reactants of enzymecatalyzed reactions)
• Connects at – active site on the enzyme (which
is complementary to a site on the substrate)
• Sometimes named – catalysts; enzymesubstrate complex; lock-n-key model
• Are made of – proteins by cells that act as
biological catalysts
• Are NOT – consumed by the reaction and can
work over and over again
How Enzymes Work
Lock-and-Key Model
• Enzyme reacts only with a substrate
• Term used to describe enzyme-assisted
reaction  lock-and-key model
– Substrate: a specific molecule that the
enzyme chemically recognizes
• Enzymes bind to the substrates at
something called the active site
Animation of how enzymes work
• http://www.youtube.com/watch?v=CZD5xs
OKres&feature=related
• NOW, Look at the diagram on page 3 of
packet and explain how enzymes and
substrates work together
Enzymatic Activity Criteria
• Activities of enzymes depend on the temperature, ionic
conditions, and the pH of the surroundings.
– Some work best at acidic pHs, while others work best in neutral
environments.
– Digestive enzymes secreted in the acidic environment (low pH) of the
stomach help break down proteins into smaller molecules.
• The main digestive enzyme in the stomach is pepsin (breaks proteins into
smaller chains of amino acids), which works best at a pH of about 1.5.
• Trypsin is another enzyme in the small intestine (breaks amino acid chains
into amino acids), which is not an acidic environment. Trypsin’s optimum pH
is about 8.
• Biochemical reactions are optimal at physiological
temperatures.
– For example, most biochemical reactions work best at the normal body
temperature of 98.6˚F (37 ˚C). Many enzymes lose function at lower and
higher temperatures.
– At higher temperatures, an enzyme’s shape deteriorates and only when
the temperature comes back to normal does the enzyme regain its shape
and normal activity.
Importance of Enzymes
• Enzymes are involved in most of the chemical reactions
that take place in organisms.
• Needed for reactions that regulate cells, enzymes allow
movement, transport materials around the body, and
move substances in and out of cells.
• In animals, another important function of enzymes is to
help digest food.
– Digestive enzymes speed up reactions that break down large
molecules of carbohydrates, proteins, and fats into smaller
molecules the body can use.
– Without digestive enzymes, animals would not be able to break
down food molecules quickly enough to provide the energy and
nutrients they need to survive.
Dehydration Synthesis
and Hydrolysis
• https://www.youtube.com/watch?v=QltPTqEhSaQ
• http://resource.rockyview.ab.ca/t4t/bio20/mm/m7/hydroly
sis/Bio20_Hydrolysis_Final.swf
Lesson Summary
• A chemical reaction is a process that changes some chemical
substances into others. It involves breaking and forming
chemical bonds. Types of chemical reactions include synthesis
reactions and decomposition reactions.
• Some chemical reactions are exothermic, which means they
release energy. Other chemical reactions are endothermic,
which means they consume energy. All chemical reactions
require activation energy, which is the energy needed to get a
reaction started.
• Rates of chemical reactions depend on factors such as the
concentration of reactants, pH, and the temperature at which
reactions occur. Both factors affect the ability of reactant
molecules to react.
• Enzymes are needed to speed up chemical reactions in
organisms. They work by lowering the activation energy of
reactions.
POP QUIZ
Write the word(s) that are the
correct answer only.
1. Enzymes are (carbohydrates///proteins).
2. Enzymes (speed up///slow down) the chemical
reactions in your body.
3. Enzymes are (used up///not used up) during
their reactions.
4. The specific molecules that enzymes react
with are called (substrates///reactants).
5. The lock-and-key model is used to describe
(chemical bonding///enzyme-substrate
complex).
Was energy released or
absorbed during this reaction?
POP QUIZ
ANSWERS>>>>
1. Enzymes are (proteins).
2. Enzymes (speed up) the chemical
reactions in your body.
3. Enzymes are (not used up) during their
reactions.
4. The specific molecules that enzymes
react with are called (substrates).
5. The lock-and-key model is used to
describe (enzyme-substrate complex).
Was energy released or
absorbed during this reaction?
• Released….product below reactants