CP Biology
2015-2016
Name
______
____________
UNIT 2B: Biochemistry 2 Enzymes Only
CHEMICAL REACTIONS & ENERGY
Everything that happens in an organism is based on a
chemical reaction.
A chemical reaction:
- Changes one set of chemicals into another
- Changes chemical bonds
- Reactants- elements/compounds that enter the
reaction
- Products- are produced by the reaction
Examples of chemical reactions: _cellular respiration,
dehydration synthesis, hydrolysis, digestion,
photosynthesis________________________________
Energy for chemical reactions comes from _living things
(plants & animals)_________.
Plants: _ trap and store energy from sunlight in energyrich compounds, carbs (by performing photosynthesis)
When bonds are made or broken…
- Energy is absorbed (taken in) or
released (given off)
Animals: _consuming plants or other animals_______
- Reactions releasing energy can (but not always)
occur on their own, or spontaneously.
- Reactions absorbing energy will not occur without a
source of energy
Some reactions are reversible, meaning that the reactants &
products can switch places. If the reaction requires
(absorbs) energy in one direction, it would release energy in
the opposite direction.
Paper is made of cellulose which burns in the presence of oxygen,
and releases energy in the form of heat and light. But this packet is
not spontaneously bursting into flames right now. Why not? What
is missing? __the activation energy to begin the reaction_______
Activation Energy: Is the amount of _energy___ that a
reaction needs to _begin (or get started)_________.
Every reaction requires a certain amount of activation
energy to get started, regardless of whether it is an
energy-absorbing or energy-releasing reaction.
*Example of a chemical reaction that releases energy:
ENERGY ABSORBING REACTIONS (Endergonic)
- Products have more energy than the reactants
Endergonic, DH
- Products larger less stable, and more complex than
reactants
- It takes more energy to break bonds in the reactants than is
released by making new bonds in the products
Examples: dehydration synthesis of a dipeptide;
photosynthesis
Exergonic,
Hydrolysis
ENERGY RELEASING REACTIONS (Exergonic)
- Reactants have more energy than the products
- Reactants are larger, less stable, and more complex than
products
- More energy is released when new bonds are formed in the
products than was needed to break the old bonds in the
reactants
Endergonic, DH
Examples: hydrolysis of a dipeptide; cellular respiration
Exergonic,
Hydrolysis
Label the reactions above using the terms :Dehydration
synthesis, Hydrolysis, Endergonic, Exergonic
Personal notes, summary of lesson, questions:
ENZYMES
Some chemical reactions would be too slow or have too
high an activation energy without a little help.
Catalyst- a substance that speeds up a chemical reaction
- works by lowering the activation energy
Cells make special proteins called enzymes to act as
catalysts for chemical reactions.
- There is one type of enzyme for each type of chemical
reaction (its shape (structure) makes it specific for its job)
HOW DO ENZYMES WORK?
- They provide a site for the reactants to be brought together
to react.
- This reduces the energy needed for the reaction.
“Enzyme Catalyzed Reaction”- a reaction sped up by an
enzyme
Substrates- what the reactants are called in an enzyme
catalyzed reaction.
Will the hill be higher or lower than shown if the activation
energy is lowered? _smaller or lower _________
Substrates bind to a place on the enzyme called the active
site which has a specific shape.
Personal notes, summary of lesson, questions: ALL enzymes are proteins, BUT not all proteins are enzymes!
TWO MODELS TO REPRESENT THE ACTION OF
ENZYMES:
1. "”Lock and Key Model": The substrates fit the enzymes
like a key fits into a lock. A very specific interaction!
Substrate / Reactant
Enzyme
2. “Induced-fit Model”: The enzyme binds the substrate(s)
and the enzyme slightly changes its shape to “hug” the
substrate(s) tightly. (like a handshake)
- This places “strain” on existing bonds, allowing bonds
to break and the chemical reaction to go to completion.
WHY aren’t enzymes considered a reactant or a product?
(analyze the reaction to the right for a hint)
____The chemical structure of the enzyme is not
changed in the reaction.
Enzymes are __Reusable (unchanged)_____!
Personal notes, summary of lesson, questions:
Example of an enzyme-catalyzed reaction: _carbonic
acid_ is formed by combining _CO2 & H2O___ and water
in the presence of the enzyme “_induced-fit model___”.
Some enzymes help to synthesize larger molecules, other
help to break them down (hydrolysis)
Examples of some types of biologically-important
hydrolytic enzymes
The suffix "–ase" commonly indicates that a protein is an
enzyme.
1. protease- any enzyme that speeds hydrolysis or
breakdown of proteins
2. sucrase (a disaccharidase) - an enzyme which speeds the
breakdown of __sucrose____________
3. lipase - any enzyme which speeds the breakdown of
_____lipids____________________
4. nuclease - any enzyme which speeds the breakdown of
______nucleotides_________________
5. amylase - an enzyme which speeds the breakdown of
amylose (=starch!)
FACTORS AFFECTING ENZYME ACTIVITY
Temperature, pH, and regulatory molecules affect enzyme
activity
- An increase in temperature will increase the rate
of a reaction to a certain point
- After that point, the enzyme will no longer work
Think! Why are temperature and pH important factors in
Denaturation - when a protein unfolds and loses its overall maintaining homeostasis?
shape (and thus function) due to increased temp or changes ________________________________________________
________________________________________________
in pH.
- A denatured enzyme loses the shape of its active site and ________________________________________________
________________________________________________
will no longer function.
pH
Order the following substances in order
Water is one of the most important inorganic substances of increasing acidity: human blood,
in living organisms.
acid rain, bleach, seawater, stomach
acid.
Sometime water molecules will break apart to form ions.
Ion- a positively or negatively charged atom (set of atoms)
due to loss or gain of electrons
1. _bleach____(least acidic / most basic)
2. _seawater____
3. __human blood_
4. _acid rain_____
5. _stomach acid____(most acidic)
About 1 water molecule in 550 million splits in this way.
Because the number of positive H+ ions is equal to the
number of negative OH- ions, pure water is neutral.
The pH scale- measures the concentration of hydrogen ions
[H+] in a particular solution.
•
•
•
•
•
Measured 0-14
Each step represents a factor of ten (10).
7 is neutral (like water)
Lower than 7 becomes more acidic
Higher than 7 becomes more basic
Acid, Base, or Neutral? Strong or weak?
pH 7:__N____ pH 13.5:___SB____ pH 8:___WB__ pH 2:___SA__
Which one is more acidic?(circle one)
pH of 2
-or-
How many times more?___100________
Which one is more basic? (circle one) Tomato juice
-or-
Soap
How many times more?___1,000,000_____
Personal notes, summary of lesson, questions:
ACID- compound that forms H+ ions in solution
pH of 4
9
ACIDS
BASES
BASE- compounds that forms OH- ions in solution
• Study the reaction below. Is this substance an ACID or BASE?
(circle)
Dissociation In Water
HCl
Hydrogen Chloride

H+
+
Hydrogen ion
(Proton)
Cl-
Solutions have a pH
_less than (<)__7
Solutions have a pH
greater than (>) 7
Taste sour
Taste bitter
Can corrode metals
Can denature proteins
Can denature proteins
feel " slippery"
In solution: [H+] __>____ In solution: [H+] __<_____
[OH-]
[OH-]
Chloride ion
ACIDIC
NEUTRAL
BASIC
• Study the reaction below. Is this substance an ACID or BASE?
(Circle)
Dissociation In Water
NaOH
Sodium Hydroxide

Na+
Sodium ion
+
OHhydroxide ion
Range of pH
less than 7
Range of pH
equal to 7
[H+] _>__[OH-] in [H+] __=__[OH-]
this type of solution. in this type of
solution.
Personal notes, summary of lesson, questions:
Range of pH
greater than 7
[H+] __<__ [OH-]
in this type of
solution.
10
BUFFERS
Controlling pH is important for maintaining homeostasis in
cells. The pH of most cells in the human body must be kept
between ___6.5_____ and ___7.5____.
Buffers- Weak acids or bases that react with strong acids or
bases to prevent sharp, sudden changes of pH.
Example: Sudden pH changes in blood are prevented by
buffers such as bicarbonate and phosphate ions.
Personal notes, summary of lesson, questions:
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