Transcript Document

HOW CELLS RELEASE
ENERGY (hyperlink on title)
Jill before
teaching inbed
these
hyperlinks
Chapter 8
Define CR:
it is all the biochemical pathways necessary to
extract energy from nutrient molecules in the
presence of oxygen – leaving CO2 as a metabolic
WASTE
 Who does it?
 ALL living organisms!! Even those without a
respiratory system, including plants and fungus
 Anyone who has mitochondria and EVEN if they
DON’T
 Reverse of photosynthesis – moving energy from
carbs into ATP

All cells (prokaryotic & eukaryotic) require
energy to:
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combat entropy
carry out day-to-day functions
repair/replace worn out organelles
reproduce
What form of energy do cells use?
ATP
Link on
picture
How do cells obtain ATP?
All cells must make their own ATP
from nutrients they have either
synthesized (autotrophs) or consumed
(heterotrophs).
Most cells break down nutrients to
make ATP in TWO ways:
• Cellular respiration (aerobic process)
• Fermentation (anaerobic process)
General equation for Aerobic cellular
respiration of glucose:
C6H12O6 + 6O2  6CO2 + 6H2O + 30 ATP
General wquation for Fermentation
(anaerobic cellular respiration)
Not so well defined!
Cellular respiration occurs in 3
stages:
Eukaryotic cells
Cytoplasm
Prokaryotic cells
Glycolysis
Krebs Cycle
Mitochondria
Cytoplasm
Electron
Cell membrane
Transport Chain
Cool Stuff
 When
ATP  ADP, 7.5 kcal/mole of
energy released. How does this
compare to the peanut?
 Extra Credit:
calculate kcal/gram for ATP
Consider peanut: 1.5 to 2.5 Kcal/g
How many ATP’s per peanut?
Formula for ATP C120H16N70O208P93
WHY a biochemical pathway – why not realease energy
in ONE step?
 Glucose
molecule = 686 Kcal/mole
This is 3.81 Kcal/g (more than
twice as much as in an entire
peanut!)
Instant cell death!!!
Efficient?
 Not
very!
 Each step will loose some energy
via heat
 Not all bad – this helps maintain
internal temperature of organism
Glycolysis (“glucose-splitting”) (hyperlink in
pink)

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Glucose (6C) is split into two pyruvate (3C) molecules.
(aka pyruvic acid)
does not require oxygen
energy harvested/glucose:
2 ATP (via substrate-level phosphorylation)
2 NADH (actively transported into mitochondria of
eukaryotic cells for use by the electron transport chain)
1st half: activates glucose – 2 ATP’s used – no ATP gained
2nd half: extracts a little energy
Takes place in cytoplasm (cytosol)
Adding phosphates prevent glucose from migrating out f
the cytoplasm
First half of
glycolysis
activates
glucose by
investing 2
ATP
molecules.
Second half of
glycolysis
extracts
energy by
releasing 4
ATP
molecules.
Where the big stuff happens!
Intermediary step
required before
Kreb can happen:
Pyruvic acid must be
converted to Acetyl
CoA before it can
enter Krebs cycle. PA
moves into
mitochondrial matrix.
PA looses a CO2 (when
NAD reduced to
NADH) and becomes
Acetyl CoA ( 2 Carbon
molecule)
2. Krebs Cycle (aka. citric acid cycle)
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Acetyl Co A enters the Kreb and combines
with oxaloacetate to form citric acid.
cells use carbon skeletons of
intermediates to produce other organic
molecules (amino acids).
Enormous quantities of CO2 produced
energy harvested per acetyl CoA: Per
GLUCOSE molecule (half each cycle)
2 ATP (via substrate-level phosphorylation)
6 NADH
2 FADH2
Thus far, how much useable energy has
been produced from the breakdown of
1 glucose molecule?
4 ATPs
The electron transport chain is needed
to harvest the potential energy in
NADHs & FADH2s.
Electron Transport Chain (ETC)
Series of proteins & electron carriers embedded in
the cristae,inner mitochondrial membrane
(eukaryotes) or cell membrane (prokaryotes).
• O2 is the final electron acceptor
• Uses the energy trapped in NADH and FADH2 in
other steps (become NAD and FAD)
• H2O is the final product (electrons + H ions + O =
water)
• Meantime the H ion released from NADH and
FADH begin to fill the intermembrane
compartment (space between outer mictochondrial
membrane and the cristae)
 Electron Transport, con’t
• Hydrogen ions (protons) slide into a channel of
ATP synthase
• When channel is stimulated, ADP is
phosphoralated to produce ATP.
• Net ATP varies hugely – estimates are around 26
• energy harvested/NADH: 2.5 ATPs (via
chemiosmotic phosphorylation)
• energy harvested/FADH2: 1.5 ATPs (via
chemiosmotic phosphorylation)
How many ATPs can 1 glucose yield?
Can cells use proteins & lipids to
produce energy?
Fermentation
 Biochemical
pathways that try to extract
energy from nutrients, in the absence of
oxygen.
 Glycolysis produces pyruvic acid which is
broken down in fermentation
Alcoholic fermentation
 Pyruvic
acid is broken down to ethanol
and carbon dioxide.
 Ex. yeast (used in production of baked goods
& alcoholic beverages)
NET
ATP???
Lactic acid
fermentation
Pyruvic acid is
broken down to
lactic acid.
Examples:
• certain
bacteria (used
in production of
cheese &
yogurt)
• human muscle
cells in oxygen
debt
Photosynthesis, glycolysis & cellular
respiration are interrelated.
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