Metabolic Pathways and Enzymes
• Cellular reactions are usually part of a
________________, a series of linked reactions
• Illustrated as follows:
E1
E2
E3
E4 E5 E6
A → B → C → D → E →F → G
• Letters A-F are reactants or ____________, B-G
are the _______________ in the various
reactions, and E1-E6 are ___________________.
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter8/animations.html
• Enzymes – ________________ the rate of
chemical reactions
• Substrates – molecules ________________ with
enzymes
• Only one small part of an enzyme, called the
_______________, reacts with the substrate(s).
• Active site may undergo a slight change in
____________ in order to fit with the substrate
• The enzyme is ________________ by the
reaction (active site returns to its original state),
and it is free to act again.
E1
E2
E3
E4 E5 E6
A → B → C → D → E →F → G
Induced Fit Model
•Because the enzyme must undergo a slight change
in shape to fit with the substrate, this is known as
the _________________________.
Activation Energy
• Energy of activation (Ea) - the energy that
must _____________ to cause molecules
to react with one another
• Enzyme ____________the amount of
energy required for reaction to occur
• Enzymes allow reactions to take place at
________________ – otherwise,
reactions would not be able to occur at
_____________ body temperatures
Energy of activation (Ea)
When no enzyme is
present – more
energy required
When an enzyme is
added – less energy
required
Enzymatic Reaction
Substrate is broken down
into smaller products
Substrates are combined into
a larger product
Enzyme Names
• Every reaction in a cell requires a specific
enzyme.
• Enzymes are named for their substrates:
Substrate
Lipid
Enzyme
________
Ureas
_________
Maltose
__________
Ribonucleic acid
____________
http://www.lewport.wnyric.org/JWANAMAKER/animations/Enzyme activity.html
Factors Affecting Enzymatic Speed
• _____________________
• _____________________
• _____________________
• Temperature and pH:
• As the temperature _______, enzyme activity
______________.
• If the temperature is too high, enzyme activity
declines rapidly because the enzyme is ________.
• When enzyme is denatured, its _______________
and it can no longer attach to the substrate.
• Each enzyme has an _____________________ at
which the rate of reaction is highest.
• Change in pH can alter the ______________ of
the enzyme, and can eventually cause enzyme to
________________.
Rate of an enzymatic reaction as a function
of temperature and pH
•Rates and concentration:
•Reaction rate depends
on the number of
enzyme-substrate
______________ that
can be formed.
•When all available
enzymes and active sites
are filled, the rate of
activity _____________
further.
•Substrate concentration
•Enzyme activity increases as
________________________
increases because there are more
collisions between substrate molecules
and the enzyme.
•Enzyme concentration
•Enzyme activity increases as
__________________________
increases because there are more
collisions between substrate molecules
and the enzyme.
Overview of Cellular Respiration
• Makes ATP (potential energy) from glucose
(chemical energy)
• Releases energy in 4 reactions
• Glycolysis, Transition reaction, Citric acid cycle
(Kreb’s cycle), and Electron transport system
• An ________________ process that requires O2
• If oxygen is not available (______________),
glycolysis is followed by _________________
Coupled Reaction
The four phases of complete glucose
breakdown
Where does each step occur?
•Outside the mitochondria
•Step 1 - _____________________
•Inside the mitochondria
•Step 2 - ____________reaction (matrix)
•Step 3 – __________________ (matrix)
•Step 4 – _________________________
(cristae)
Structure of mitochondria:
•Has a ________________________, with
an intermembrane space between the two
layers.
•___________ are folds of inner membrane
•The _______, the innermost compartment,
which is filled with a gel-like fluid.
Reaction that Occurs in Cellular Respiration
•It is an _________________________, or redox reaction
for short.
•Oxidation is the _________ of electrons; hydrogen atoms
are removed from glucose.
•________________________is the gain of electrons;
oxygen atoms gain electrons.
•Remember _______ (oxidation is loss, reduction is gain)
Enzymes involved:
• NAD+
• Nicotinamide adenine dinucleotide
• Accepts ______ to become NADH
• FAD
• Flavin adenine dinucleotide (sometimes
used instead of NAD+)
• Accepts ________ to become FADH2
•
•
•
•
•
Step 1. Glycolysis
Occurs in the cytoplasm (outside the
mitochondria)
Glucose  _______________ molecules.
Universally found in all organisms
Does _______ require oxygen
(anaerobic).
Main energy source for prokaryotes
Glycolysis Summary
• Inputs:
•
•
•
•
_______
_______
_______
_______
• Outputs:
•
•
•
•
__________
__________
__________
___ATP (net gain)
•When oxygen is available, ___________ enters
the mitochondria, where it is further broken down
•If oxygen is not available, _____________ occurs
Step 2 - Transition Reaction
• Occurs in the __________ of the mitochondria
• Is the transition between _________and the citric
acid cycle.
• _______________ (made during glycolysis) is
converted to acetyl CoA, and CO2 is released
• NAD+ is converted to NADH + H+
• The transition reaction occurs ________ per glucose
molecule.
Transition reaction inputs and outputs
per glucose molecule
• Inputs:
• ____________
• ____________
• Outputs:
• ______________
• ______________
• ______________
http://www.science.smith.edu/departments/Biology/Bio231/krebs.ht
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Step 3 - Citric Acid Cycle (aka Kreb’s Cycle)
•
•
•
•
•
•
Occurs in the ____________ of the mitochondria.
C2 acetyl group is converted to a C6 citrate.
Each acetyl group gives off __________ molecules.
NAD+ accepts electrons ____________
FAD accepts __________________.
Results in a gain of ____________ per every turn
of the cycle; there are two cycles per glucose, so a
net of 2 ATP are produced.
• The citric acid cycle produces ______________ per
molecule of glucose.
Citric acid cycle
Citric acid cycle inputs and outputs per
glucose molecule
• Inputs:
• _____________
• _____________
• _____________
• _____________
• Outputs:
• __________
• __________
• __________
• __________
•
•
•
•
Step 4 - Electron Transport System (ETS)
______________ oxygen (aerobic)
Located in the ______________of mitochondria
_________________________ carry electrons
picked up during glycolysis, transition reaction, &
citric acid cycle and enter the ETS.
The ETS consists of:
– ________________________________ that pump H+
– _________________________ that transport electrons
– __________________ - H+ flow through it, making ATP
• H+ flow through from _________________________
• For every 3 H+ that flow through, one ______ is made
Overview of the electron transport
system
http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm
http://www.sp.uconn.edu/%7Eterry/images/movs/synthase.mov
http://www.science.smith.edu/departments/Biology/Bio231/etc.html
http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter9/animations.ht
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Energy Yield from Glucose Metabolism
• Per glucose molecule:
– _____________ take electrons to the ETS 
__________ATP from each
– 2 FADH2 take electrons to the ETS 
______ATP from each
• Electrons carried by NADH produced during
glycolysis are shuttled to the electron transport
chain by an organic molecule
Accounting of energy yield per glucose
molecule breakdown
Fermentation
• Occurs when oxygen is _________ available.
• During fermentation, the ______________
formed by ___________ is reduced to lactic acid
.
• Fermentation uses _________ and regenerates
_____________________
• Occurs in _______________ bacteria, fungus, &
human muscle cells.
http://instruct1.cit.cornell.edu/Courses/biomi290/MOVIES/GLYCO
LYSIS.HTML
Advantages and Disadvantages of
Fermentation
• Fermentation can provide a __________________
in muscle cells, even when oxygen is in limited
supply.
• Lactate, however, is _____________ to cells.
• Initially, blood carries away lactate as it forms;
eventually lactate builds up, lowering cell pH, and
causing ____________________________.
• Oxygen debt occurs, and the liver must reconvert
______________________________.
Fermentation inputs and outputs per
glucose molecule
• Inputs:
• ______________
• ______________
• ______________
• Outputs:
• ___ lactate or
• ___alcohol & 2
CO2
• ____ADP
• ____ ATP (net
gain)