Harvesting Chemical Energy
from Sugar, Part 1
Bio 10: Intro to Biology
Instructor: Paul Nagami
Laney College
Sept. 18, 2013
Agenda
• Administrative Stuff
• A Quick Review: Energy, Entropy,
Calories, ATP
• Getting Waste out of the Cell, and
Nutrients in
• Glycolysis
• Breaking Down Sugar
• Enzymes and Activation Energy
• NAD+ and NADH
• Fermentation (and muscle burn)
• Wrap-up
Entropy (or, Not All Energy Is Equally Useful)
ATP: A Cellular “Battery”
ADP can then be
recycled into ATP by
putting the phosphate
back on, starting the
cycle over.
Can this cycle simply be repeated over and over to generate
energy? Explain on your index card.
Getting Waste out and Nutrients in
Exocytosis
Exo = outside/out of
Cyto = cell
Endocytosis
Endo = inside/into
Cyto = cell
Two Challenge Statements:
1) “Cells need mitochondria to make ATP.”
2) “Plants have chloroplasts to perform
photosynthesis, unlike animals, which
have mitochondria to perform
respiration.”
On your card: Do you agree or disagree with
each of these? Why? Talk it over with a
neighbor.
Not Everything Has Mitochondria!
Prokaryotes don’t have any organelles at all.
Mitochondria need free oxygen, and the
earth didn’t always have oxygen!
Breaking Down Sugar: First Steps
Even organisms without mitochondria can
break down sugar!
The process of breaking down sugar is called
glycolysis. This happens before the rest
of respiration
Glycolysis does not require oxygen.
Eukaryotes perform glycolysis and
respiration. Bacteria perform glycolysis.
Understanding Glycolysis
But what’s actually
going on here?
What do these
arrows and circles
really mean?
What Do Those Arrows Mean?
Arrows in the glycolysis diagram represent chemical
reactions that are made possible by enzymes. (Proteins)
What goes in =
reactant/substrate
What comes out = product
Enzymes lower the activation
energy needed for the
reaction to happen!
The Induced Fit Model
On your index card:
Name another enzyme
and its substrate(s).
Glycolysis Needs Many Enzymes!
Hexokinase
Enzymes make metabolism possible.
Reactions in Context
Hexokinase
Breaking down sugar
requires an initial
investment of energy!
ATP is broken down to
stick phosphate on the
sugar. Energy released
as heat.
Not all reactions release
energy; some take it in!
Understanding Glycolysis
Make a Guess
How many enzymes are needed to break
glucose into two molecules of pyruvic acid
in glycolysis? The book lists 3 major steps,
but how many chemical reactions are
needed?
Do NOT Memorize
Understanding Glycolysis
What went in? What came out? On your index cards in two columns, write a
list of the inputs and outputs of glycolysis, based on this diagram. Check with
your neighbor.
Glycolysis: Inputs and Outputs
Input
Output
(molecules) (molecules)
1 Glucose
2 Pyruvic
Acid
2 ATP
2 ADP
4 ADP
4 ATP
?????
2 NAD+
2 NADH
4P
2P
+
NAD :
An Electron Carrier
NAD+ is a molecule that can be used to carry
electrons and store chemical energy.
Not as generally useful as ATP, though.
Two electrons are transferred together with
an H+ to turn NAD+ into NADH.
FYI: The “A” in NADH is adenine,
the “A” DNA base (in GTAC) and
the A in ATP! Evolution re-uses
chemicals a lot!
What Do We Do with All those HighEnergy Electrons?
When oxygen is available, organisms with
mitochondria can use them in respiration.
But what about bacteria? And what about
our own muscles when we’re low on
oxygen?
To get rid of extra NADH and pyruvic acid
without using oxygen, organisms perform
fermentation.
Lactic Acid Fermentation: A Source
of “Muscle Burn”
Fermentation turns pyruvic acid into lactic
acid and recycles NADH.
Other Uses of Fermentation
What other organisms perform fermentation?
Review!