Download E•S - Hobbs High School

Chapter Six
Energy and Metabolism
I. Energy
A. Energy: Kinetic & Potential Energy, Chemical
Energy
B. Two Law of Thermodynamics
Term: Entropy
C. ATP Structure & Function
– Exergonic & Endergonic Reactions
– Coupled Reactions
D.Enzymatic Reactions (E + S ---> E•S ---> E + P)
– Factors that Affect Enzymatic Reactions
I. Energy (pg. 105)
A. Sun = Ultimate source of all energy; (e.g.
radiant energy)
– Living things cannot maintain organization, grow,
repair, or reproduce w/o constant input of
ENERGY
– ENERGY = Capacity to do Work
• Two major categories of energy:
– KINETIC = energy of motion (e.g. mechanical
energy)
– POTENTIAL = stored energy (e.g. chemical energy)
• Potential energy is stored in the chemical bonds
of molecules (e.g. ATP & glucose)
• When chemical bonds are broken, energy is
released
• Provides energy for cellular work
Kinetic
– Movement of muscles (mechanical work)
– Movement of molecules across PM (transport work)
– Synthesis (dehydration) chemical reactions (chemical
work)
• Calorie - a measure of energy
– Amount of heat required to raise the temperature of 1
g of water by 1º C
– 1 Calorie = 1000 calories = 1 kilocalorie
• Oxidation-reduction reactions transfer
electrons while bonds are made or broken.
– OXIDATION = when an atom or molecule losses an
electron
– REDUCTION = when an atom or molecule gains an
electron
• Oxidation and reduction reactions (redox
reactions) always take place together and play
a critical role in the flow of energy through
biological systems.
B. Two laws of thermodynamics: (pg. 105-106)
• Thermodynamics = study of energy
transformations
1. Law of Conservation
– Energy cannot be created nor destroyed but can be
changed from one form to another
– EXAMPLE:
(chemical)
(mechanical)
POTENTIAL
KINETIC
Gas in car
Car moves
Glucose → ATP
Cell work
2. Energy cannot be changed from one form to another
without a loss of usable energy. When energy is
transformed, only some of the energy is converted into
a usable form for cell work. Most of the energy is “lost”
from the system as heat. (NOTE: Heat is not a usable
form of energy for cellular work; however, it can be
used to warm our body.)
– EXAMPLE:
HEAT
POTENTIAL
KINETIC
Gas in car
Car moves
Hood of car gets hot
Glucose → ATP
Cell work
Heat generated helps
maintain body
temperature
HEAT
HEAT
• CONCEPTS:
– Potential energy can be converted into kinetic
energy and vise versa
– Conversion of energy is NOT efficient (cells about
40% efficient; better than machines)
– As energy conversions occur, most energy is
changed into heat
– Living things continually lose heat (energy) to the
environment; therefore, a constant input (solar
energy) is required
• Heat gives disorder to the system
• Amount of disorder in system is measured as amount of
ENTROPY
• Universe as a whole has increasing disorder
C. ATP Structure & Function (pg. 107)
– ALL CELLS use ATP for energy - common currency of energy
– Review Structure of ATP (nucleotide): ribose sugar;
adenine nitrogen base; 3 P groups
+
High energy bond
Adenosine Triphosphate
ATP
Adenosine Diphosphate
ADP
+
Phosphate
P
– Just enough energy is released when ATP → ADP + P so
little energy is wasted
– Consumption and regeneration of ATP of entire pool of ATP
occurs about once each minute.
• Exergonic & Endergonic Reactions (pg. 108)
• Metabolism - Sum of all the chemical reactions occurring in
the cell
• Two types of chemical reactions as they relate to energy
1. Endergonic - Chemical reactions that require an input of
energy
– Building up of molecules - forming bonds
– Synthesis (e.g. dehydration) reactions
– EXAMPLES
A+B→C
INPUT Energy
ADP + P → ATP
PS: CO2 + H2O → (CH2O)n + O2
Solar Energy
• Exergonic - Chemical reactions that release energy
– Breaking down of molecules - breaking bonds
– Degradation (e.g. hydrolysis) reactions
– EXAMPLES
A→B+C
OUTPUT Energy
ATP → ADP + P
CR: (CH2O)n + O2 → CO2 + H2O
36 – 38 ATP Molecules
• Concept:
• Coupled Reactions (pg. 89) - occur in the same place at the same time
• Energy released from exergonic reactions can be used to drive the
endergonic reactions.
A→B+C
OUTPUT
Energy
INPUT
A+B→C
D. Enzymatic Reactions (pg. 109)
– Enzymes speed up chemical (metabolic) reactions.
– Without enzymes, chemical reactions within cells would occur too slowly.
E
Organic catalyst
Speeds up chemical Rx
Protein (can be
denatured)
Lowers E of A
Specific for substrate
Contains active site
where substrate fits
Usually ends in -ase
S
Reactant
E•S complex
Induced Fit
Model
E
Unchanged
P
Formed as a
result of chemical
Rx
• Enzyme - Speeds up chemical reactions by
lowering the energy of activation
• Energy of Activation - Energy needed to start a
chemical reaction
• Active Site - Place on the enzyme where the
substrate(s) fit
• Induced Fit Model - Model that explains how the
active site of the enzyme alters slightly to
accommodate the substrate; Helps achieve an
optimum E•S fit and facilitates the enzyme
reaction
*NOTE: Not all enzymes are proteins. Some
reactions are catalyzed by RNA. Ribozymes are RNA
with enzymatic abilities (Ribosomes)
• Enzymes are specific and can only react with a
certain substrate AND are usually named by
adding (–ase) to the substrate name.
– Substrate: Urea Enzyme: Urease
– Substrate: lactose Enzyme: lactase
• CONCEPT:
– It takes many different kinds of enzymes to catalyze all
the reactions within cells. However, cells do not make
to make large quantities of each because
– enzymes are unchanged (not consumed) during the
chemical reaction
– are used over and over again
• Factors that Affect Rate of Reactions: (*denatures) p. 110-112
– Maximum Rate occurs when there is enough substrate available to
fill the actives sites of all enzyme molecules most of the time
1. Substrate concentration - ↑ sub. Conc = ↑ rate (to a
point)
2. Temperature * - ↑ rate = ↑ rate to a point (Optimal
temp 35-40°C)
3. pH * - optimal pH varies per enzyme; adjust pH = ↑ rate
4. Cofactors / Coenzymes
• As enzymes are needed to be present for reactions to occur,
also cofactors and/or coenzymes may need to be present in
order for enzymes to function properly.
– Cofactors: Inorganic ions
• Examples: Metal ions such as Cu, Zn, Fe
– Coenzymes: Organic non-protein molecules
• Cells make coenzymes from our dietary intake of vitamins
• Examples: NAD+, FAD, CoA
5. Inhibitors (pg. 112)
• Competitive inhibition
– Inhibitor competes with substrate for Active Site
Bad
• Non-Competitive inhibition
– Inhibitor sets in Allosteric Site in vicinity of active site
causing a change in the Active Site of the enzyme
Good •
Feedback inhibition - Method in which cells control
amount of product being made
B-ase
A-ase
C-ase
D-ase
B
C
D
A
E
Binds to
Allosteric Site
NOTE: Inhibitions are usually reversible. But in the cases
of poisons, they can be irreversible.
** OVERVIEW: Factors that affect rate vs. maximizing
the rate of reactions**
Product acts as
Temporary
inhibitor