Download 13 cellular respiration

Cellular Respiration
What is cellular respiration?
Why does it occur?
Where does it occur?
What are the steps of the process?
What are the alternatives?
This presentation borrows more heavily than most
from the text illustrations. I hope that is useful here.
Refer to chapters 6 and 8 in text.
http://themedicalbiochemistrypage.org/tca-cyclereactions.jpg
This is the process of cellular respiration.
←glucose
ATP↑
http://erkki.kennesaw.edu/schem229/glycolysis2.jpg
http://www.cellml.org/examples/images/oxidative_phosphorylation_2001/conventional_rendering.gif
ATP: Adenosine TriPhosphate, the energy currency of the cell.
Energy is stored in bonds.
The most common source
of energy for your enzymatic
reactions (anabolism and
catabolism) comes from the
energy stored in this bond …..
From where comes the energy
to recharge this ‘battery’ after
it has been spent?
(When this bond is broken
ATP becomes ADP.)
Energy is captured in chemical bonds (forming carbohydrates)
through photosynthesis (more later!),
and respiration is about getting it back out.
Cell respiration is the controlled release of energy
from organic compounds in cells
to form ATP.
http://www.freewebs.com/rumputrampai98/food.jpg
From the food you eat!
(Or the food you make
if you are an autotroph,
which you aren’t.)
How much energy is there in glucose?
C6H12O6 + 6O2 ->->->-> 6CO2 + 6H2O
A Mole of glucose (180g) with 134 L of O2 (at STP)
yields about 686 kilocalories (C)…
But releasing it all at once, like a bonfire, would be of little use.
(compare to a power plant)
Organisms have a multipart process to harvest this energy
in a useful manner,
starting with glycolysis…
Glycolysis
“breaking glucose”
note:
- starting with glucose
- investment of 2 ATPs
to start process
- splitting of F1,6BP (↓)
into two 3C molecules
↑
where
this
happens
Glycolysis (cont.)
note
- this is shown
happening twice
(once per G3P)
- recovery of ATP
(4 total, 2 net) by
substrate-level
phosphorylation
- generation of NADH↓
nicotinamide adenine
dinucleotide
(2 total)
(redox reactions)
- end product is
2 pyruvates
link reaction, aka bridge reactions
(Mader calls this the preparatory reaction)
getting into the mitochondrion
note:
- 2 per glucose
- first CO2 coming off (decarboxylation) twice
- another NADH made (2 of them per glucose)
- product:(2) acetyl Co(enzyme)A
Krebs Cycle /TCA/ Citric Acid Cycle
note:
- first product is citric acid
(hence the name)
- the balance of carbons:
C2+C4 → C6 → C5+CO2 →
C4+CO2
(two more CO2 off, and
4C oxaloacetate restored.)
- 3 more NADH generated
per round
- 1 FADH2 generated
[flavin adenine dinucleotide:
not a dinucleotide]
- 1 ATP made by substrate
level phosphorylation
- 2 rounds per glucose
molecule
RECAP
Glucose is gone.
4 net ATP made per glucose
2 FADH2
10 NADH…
a little bit of usable energy,
and a bunch of “electron carriers”
note: - electrons from NADH and FADH2 passed from carrier to carrier
in a series of redox reactions.
- H+ pumped into intermembrane space, making an electrochemical gradient.
- oxygen finally receives electrons, and ties up H+ in matrix.
- proton-motive force: protons flood through ATP synthase complex,
generating ATP from ADP + Pi:
This is an aerobic process.
FADH2 dumps
e- here→
electron
transport
chain,
chemiosmosis,
and
ATP synthase
NB
↑
oxidative phosphorylation ↑
Energy ledger: about 38 ATP per glucose
-0 to 2 ATP per link? (NADH can’t cross…) What does this mean↑ “ + about” 34 ATP?
(In actuality, total is closer to 30…)
The text says your mitochondria produce about your body’s weight worth of ATP daily (p.143)No wonder cyanide (which blocks cytochromes) kills so fast!
Draw and annotate a diagram showing the structure of a mitochondrion
as seen in electron micrographs.
note:
- importance of extensive inner membranes (cristae)
- role of narrow space between inner and outer membranes
- Krebs cycle enzymes in matrix
- electron tomography of mitochondrion
https://www.youtube.com/watch?v=y6AvmNpHkJ0
Note that the reactions of aerobic respiration
also occur in the membranes of prokaryotes!
So, what if there is no oxygen to accept that electron at the end of
the electron transport chain?
No O2 receptor →(“means”)
no electron transport chain →
no oxidation of electron carriers (NADH, FADH2)→
no free receptors for e- in Krebs cycle →
backup through link reactions →
no energy from glucose breakdown.
No O2 means no energy from glucose.
Or does it?
Fermentation
Many organisms are able to get some energy/ATP
from glucose with little or no oxygen.
These allow a bit of ATP to be recharged
in the absence of oxygen
alcohol fermentation
note:
- Oxidizes NADH from
glycolysis in making
a waste product (ethanol).
- Also generates CO2
(makes bread rise).
-Occurs in yeast and
some bacteria, when
little oxygen is present.
- Net gain 2 ATP per glucose.
→
http://fig.cox.miami.edu/~cmallery/150/makeatp/c8.9x18a.alcohol.jpg
Alcohol distillation:
Alcohol is toxic to the yeast at about 10%.
Alcohol’s boiling point is lower than that of water.
Are you surprised? (Alcohol is non-polar….)
Fermented mash is filtered and boiled.
The alcohol vapor, coming off first, is condensed and collected.
The process is stopped as the temperature again rises,
before water vapor hits the condenser.
Commercial uses for distilled alcohol:
1. fuel alternative to fossil fuels
2. industrial solvent
3. old disinfectant/sedative
(isopropanol is made from
petroleum gases)
4. beverages
5. preservative
http://www.goafeni.com/images/distilation.jpg
Fermentation (cont.)
lactic acid fermentation
note:
- in several ways rather the
same as alcohol fermentation:
~ NAD+ regenerated
~ unused product formed
- in several ways this path
unlike alcohol fermentation:
~ no CO2 formed (3C waste)
~ in bacteria, fungi and animals
(such as yourself)
~ used to make yogurt
~ causes muscle pain in you
~ can’t solely sustain your
life, merely supplements,
during high exertion.
Fermentation (cont.)
- sometimes called anaerobic respiration
(though techically some prokaryotes have full
cellular respiration with an electron receptor
other than oxygen…)
- uses the same glycolysis, in cytosol, as aerobic respiration.
- yields far less ATP per glucose:
about 2 ATP net vs. up to 38 ATP
because it doesn’t cash in e- via Krebs and ETC.
- several points suggest glycolysis is oldest energy path:
~ not in mitochondrion
~ life predates atmospheric O2 by 0.8 billion years
~ most widespread metabolic pathway
Glucose isn’t the only food that yields energy through aerobic respiration:
simple sugars are
enzymatically
altered to enter in
glycolysis
protein parts can
enter as pyruvate,
acetic acid, or at
various steps of the
Krebs cycle.
Nitrogen waste is
disposed of as urea.
lipids: the 3C
glycerol backbone
enters as G3P;
fatty acids are
hydrolyzed into
2 carbon acetates.
Provide the differences between the fermentations we covered.
cellular respiration
redox reaction
ATP
proton-motive force
ADP
aerobic
glycolysis
chemiosmosis
substrate-level phosphorylation
electron transport chain
NADH
ATP synthase
pyruvate
oxidative phosphorylation
link reaction
cristae
bridge reactions
matrix
decarboxylation
fermentation
Krebs cycle
alcohol fermentation
citric acid cycle
lactic acid fermentation
preparatory reaction