Download Cellular Respiration - BIOLOGY

Cellular
Respiration
So we’ve discussed
photosynthesis:
CO2 + H2O  C6H12O6 + O2
>But where does the
C6H12O6 [glucose] and O2
[oxygen] go?
>Animals need them to enact the process of
RESPIRATION!
Cellular Respiration is the process that releases
energy by breaking down food molecules in the
presence of oxygen [aerobic]:
O2 + C6H12O6  CO2 + H2O + Energy
>Notice anything familiar about this equation?
> Cellular respiration has 3 main stages:
1. Glycolysis
2. Krebs cycle
3. Electron Transport Chain
Each of the 3 stages captures energy from
food and uses it to produce ATP
>So photosynthesis produces glucose which the plant
uses as energy. Animals need food in order to get the
energy they need to reproduce and survive.
> How much energy is actually in food?
[[1 gram of glucose when burned releases 3811
calories of heat energy!]]
--A calorie==is the amount of energy needed to raise
the temperature of 1 gram of water 1°C-++Cells don’t ‘burn’ glucose but instead gradually
release the energy from glucose.++
This process begins with a pathway called GLYCOLYSIS
1. Glycolysis
-releases only a SMALL amount of energy!
-1 molecule of glucose [C6H12O6] is broken in
halfproducing 2 molecules of pyruvic acid [3
carbon compound]
-must put IN some energy (ATP) to get the process
going
-NADH= a carrier molecule that can accept high
energy electrons and transfer that energy to another
molecule
-takes place in the CYTOPLASM of the cell.
2 ATP in
4 ATP out 2 net ATP
Glucose ------------[broken in half]-----------> 2 Pyruvic acid
[will be used in
the Krebs cycle]
-at the end of glycolysis90% of energy in glucose is still
unused
--What happens when NO OXYGEN is present?—
>When there is no oxygen present [anaerobic],
glycolysis is followed by a different pathway. The
combined process of this pathway and glycolysis is
called FERMENTATION.
Fermentation
-Fermentation releases energy from food molecules in
the absence of oxygen [anaerobic]
-During fermentation, cells convert NADHNAD+ by
passing high-energy electrons back to pyruvic
acidthis action allows glycolysis to continue
producing a steady supply of ATP.
-There are 2 main types of fermentation:
1. alcoholic fermentation
2. lactic acid fermentation
1. alcoholic fermentation
pyruvic acid + NADH  alcohol + CO2 + NAD+
-Yeasts and a few other microorganisms use alcoholic
fermentation forming ethyl alcohol and CO2 as
wastes.
-yeast requires SUGARproduces CO2
- Alcoholic fermentation causes bread dough to rise.
When yeast in the dough runs out of oxygen, it begins
to ferment RELEASING BUBBLES OF CO2 [air spaces in
bread].
-The small amount of alcohol produced in the bread
evaporates when the bread is baked.
2. lactic acid fermentation
pyruvic acid + NADH  lactic acid + NAD+
-in many cells, the pyruvic acid that accumulates as a
result of glycolysis can be converted to lactic acid.
-this process REGENERATES NAD+ so that glycolysis can
continue.
-lactic acid is produced in your muscles during rapid
exercise when the body cannot supply enough oxygen
to the tissues.
-without enough oxygen, the body is not able to
produce all of the ATP that is required.
-when you exercise vigorously, your muscle cells
rapidly begin to produce ATP by lactic acid
fermentation.
-this is why muscles may feel sore after only a few
seconds of intense activity.
When oxygen is present, glycolysis is followed by the
Krebs cycle and electron transport chain.
2. Krebs cycle
-during the Krebs cyclethe pyruvic acid from
glycolysis is broken down into CO2.
-takes place in the mitochondriaMATRIX OF
MITOCHONDRIA.
-CO2 produced released into the airsource of all CO2
in our breath!
Krebs cycle
1 ATP produced per 1 pyruvate.
But…2 NET ATP produced per 1 glucose [=2 pyruvates]
So our grand ATP totals so far…
Glycolysis--------------------------------------2 ATP
Krebs cycle------------------------------------2 ATP
-What does the cell do with all those high-energy
electrons in carriers like NADH and FADH2???
-used to generate huge amounts of ATP in the:
Electron Transport Chain [ETC]
3. Electron Transport Chain
-occurs in the inner mitochondrial membrane [space
between inner membrane and outer membrane]
-the Krebs cycle generates high-energy electrons that
are passed to NADH and FADH2.
-So… the electron transport chain uses theses highenergy electrons from the Krebs cycle to convert
ADPATP.
-Looking at the figure on the previous page…
-high-energy electrons from NADH and FADH2 are
passed into and along the ETCthe ETC is
composed of series of carrier proteins in the inner
membrane [[[SEE FIGURE]]].
-the high-energy electrons are PASSED FROM ONE
CARRIER PROTEIN TO THE NEXT
-at the end of the ETC, there is an enzyme that
COMBINES ELECTRONS from the ETC with hydrogen
ions and oxygen to form WATER!!
-every time 2 high-energy electrons transport down
the ETC, their energy is used to transport hydrogen
[H+] across the membrane [[[SEE FIGURE]]]…this
process causes the intermembrane space to be
POSITIVE [[because of the build up of H+ ions]].
-therefore, the matrix [where the H+ came
from] is NEGATIVELY charged.
-How does the cell use the charge differences that
build up as a result of electron transport?
-Inside the membranes of the mitochondria have
protein spheresATP SYNTHASES
-H+ ions travel through channels into these proteins
which causes the ATP synthases to spin!
-each time it rotates, ADPATP !!!
[[each pair of high-energy electrons that
moves down the ETC provides enough energy
to convert 3 ADP3 ATP!]]
TOTALS [from 1 molecule of glucose]
So…
-NADH and FADH2 go on to make ATP
through the Electron Transport Chain
-the 36 ATP molecules the cell makes per
glucose represent 38% of the total energy of
glucose.
-the cell more efficient at using food
than an engine of a car is at burning
gasoline.
-what happens to the other 62%?
-released as heat---why body feels
warmer after vigorous exercise!
Comparing Photosynthesis and Cellular
Respiration
Photosynthesis
Cellular
Respiration
Function
Energy
Energy
storage
release
Location
Chloroplasts
Mitochondria
Reactants
CO2, H2O
C6H12O6, O2
Products
C6H12O6, O2
CO2, H2O
CO2 + H2O
C6H12O6 + O2
Equation
C6H12O6 + O2
CO2 + H2O