Transcript Cellular Respiration

Cellular Respiration
Harvesting Chemical Energy
Chapter 9
Chemical Energy & Food
 How much energy is in
food?

A lot – 1 gram of sugar
glucose, when burned in
the presence of oxygen,
releases 3811 calories of
heat energy
 A calorie is the amount of
energy required to raise
the temperature of 1 gram
of water 1 degree Celcius
Chemical Pathways - Overview
Overview of Cellular Respiration
 Cellular respiration is the process that
releases energy by breaking down food
molecules in the presence of oxygen

Organisms that respire: animals, fungi, plants
(during night hours)
 Cellular respiration requires a food molecule
(such as glucose), oxygen, and it gives off
carbon dioxide
 Because is occurs in the PRESENCE of
OXYGEN, cellular respiration is known as
AEROBIC respiration
Overview of Cellular Respiration
Glycolysis takes place in cytoplasm of cell. The Krebs Cycle and Electron Transport
chain take place inside the mitochondria.
Chemical Formula - Cellular Respiration

The chemical formula for cellular respiration is:

6O2 + C6H12O6 → 6 CO2 + 6 H2O + Energy

oxygen + glucose → carbon dioxide + water + energy

The reactants of cellular respiration are:

oxygen (O2) & glucose (C6H12O6)

The products of cellular respiration are:

carbon dioxide (CO2) and water (H2O)

The 3 main stages of cellular respiration are:
1.
Glycolysis
2.
Krebs Cycle (Citric Acid Cycle)
3.
Electron Transport

http://www.sumanasinc.com/webcontent/animations/content
/cellularrespiration.html
IT ALL HAPPENS HERE - Mitochondria
Energy Yielding Pathways - Catabolic
 Cellular respiration and fermentation are
energy-yielding pathways (catabolic).
 To understand what happens when a
catabolic pathway decomposes glucose, you
must first understand:

Redox Reactions: a chemical reaction
involving the transfer of one or more electrons
from one reactant to another.


OXIDATION: loss of electrons from a substance
REDUCTION: addition of electrons to a
substance
Redox Reactions
 As electrons from redox reactions are transferred
from one substance to another, energy is transferred
as well.



RECALL THAT ELECTRONS HAVE ENERGY!
Oxidized substances LOSE energy
Reduced substances GAIN energy
Fate of Catabolic Pathways
 The fate of glucose in the body can take one
of two catabolic pathways:
1.
CELLULAR RESPIRATION



2.
a.k.a. aerobic respiration
absolutely requires oxygen
occurs in mitochondria
FERMENTATION


occurs without oxygen
less efficient than cell respiration (makes less
ATP)
Visual Overview of Cellular
Respiration
Visual Overview of Cellular
Respiration
Krebs
Cycle
Substrate Level Phosphorylation
 Some ATP created
during cell
respiration is made
by direct enzymatic
transfer of a
phosphate group
from a substrate to
ADP.
Oxidative Level Phosphorylation
 ATP synthesis can be powered by the flow of H+ back
across mitochondrial membrane (chemiosmosis)
Glycolysis
http://www.sumanasinc.com/webcontent/animations/content/cellularrespiration.html
 The first set of reactions in cellular
respiration is glycolysis




Glycolysis is the process in which 1
molecule of glucose is broken in half,
producing 2 molecules of pyruvic acid.
Glycolysis occurs in the cytoplasm of
the cell.
Glycolysis produces a total of 4 ATP,
but requires 2 ATP in the beginning to
get the pyruvic acid through the
membrane of the mitochondria to
enter the next phase.
Therefore, the NET ATP YIELD of
glycolysis is 2 ATP!
Glycolysis – Visual Overview
Glycolysis is the 1st stage of cellular respiration. During glycolysis,
glucose is broken down into 2 molecules of pyruvic acid.
Glycolysis means “splitting of sugar”. During glycolysis, a six-carbon
sugar is split into 2 three-carbon sugars. These smaller sugars are
then oxidized (lose electrons) and their remaining atoms rearranged to
form 2 molecules of pyruvate. This is a 10-step process, each
catalyzed by a specific enzyme…with an energy input and energy
payoff phase (Figure 9.8 page 161).
10 Steps of Glycolysis
Glycolysis “NEED TO KNOW”
http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_glycolysis_works.html
 The first step is the phosphorylation of glucose
(glucose molecule gains 2 phosphates) – this
ACTIVATES the glucose to split.
 The second step is the splitting of glucose –
breaking it down into (2) 3-carbon molecules
called pyruvic acid.
 2 ATPs are needed to produce four ATPs
(energy investment and energy payoff phases).
 A second product in glycolysis is 2 NADH,
which results from the transfer of H+ to the
hydrogen carrier NAD+.
 Occurs in the cytoplasm
 Net of 2 ATPs produced
 2 pyruvic acids formed
 2 NADH produced
FIRST - Convert Pyruvate into Acetyl CoA
 The conversion of pyruvate
to acetyl CoA is the junction
between glycolysis (step 1)
and the Krebs cycle (step 2).
 If oxygen is present,
Pyruvate (3 C each) from
glycolysis enters the
mitochondrion.
 Using Coenzyme A, each
pyruvate is converted into a
molecule of Acetyl CoA (2 C
each).
 What happened to the
other carbon from each
molecule of pyruvate?
 CO2 released!
 NAD+ is reduced to form
NADH
The Krebs Cycle (Citric Acid Cycle)
 In the presence of oxygen,
the pyruvic acid produced
during glycolysis passes to
the second stage of cellular
respiration: the Krebs Cycle.
 During the Krebs cycle,
pyruvic acid is broken
down into carbon dioxide
in a series of energyextracting reactions.

Every time you exhale, you
expel the CO2 produced by
the Krebs cycle.
NOW – Enter the Krebs Cycle
http://www.sumanasinc.com/webcontent/animations/content/cellularrespiration.html
For each turn of the 8-step
cycle, 5 pairs of high energy
electrons are captured by the
carrier molecules NADH and
FADH2.
NADH and FADH2 are energy
carriers! They carry electrons
captured during the Krebs
Cycle to the Electron Transport
Chain – so we can make ATP!!!
Electron Transport
 Following the Krebs cycle, the electrons captured by
NADH and FADH2 are passed to the electron
transport chain:




The electron transport chain uses the high-energy
electrons from the Krebs cycle to convert ADP to ATP
Every time 2 high energy electrons transport down the
ETC, their energy is used to transport H+ across the
inner membrane of the mitochondria…this creates a +
charge on the inside of the membrane and a – charge
in the matrix of the mitochondria
As a result of this charge difference, H+ ions escape
through channel proteins called ATP synthase causing
it to rotate
Each time it rotates, the enzyme ATP synthase grabs a
low energy ADP and attaches a phosphate, forming
high-energy ATP
Electron Transport Chain
http://www.sumanasinc.com/webcontent/animations/content/cellularrespiration.html
The Energy Totals
http://www.science.smith.edu/departments/Biology/Bio231/glycolysis.html
 The complete breakdown of 1 glucose molecule through cellular
respiration results in the production of 36 molecules of ATP
Overview…In the Presence of Oxygen
Respiration in the Absence of Oxygen
 When oxygen is NOT present, glycolysis is
followed by a different pathway called
fermentation.


Fermentation releases energy from food
molecules in the absence of oxygen
Because fermentation does not require
oxygen, it is said to be anaerobic
 The 2 main types of fermentation are:
 alcoholic fermentation
 lactic acid fermentation
No Oxygen
 Fermentation – aside from the original 2
ATP’s made during glycolysis, the only
energy produced is that which is in the bonds
of…
ethyl alcohol -- C2H6O
and lactic acid – C3H5O3
Lactic Acid Fermentation
In the absence of oxygen, a cell will use fermentation to produce ATP
by substrate-level phosphorylation.
Lactic Acid Fermentation converts glucose into lactic acid. This type
of fermentation occurs in human muscle cells during strenuous
exercise when breathing cannot supply the cells with enough oxygen.
Overview of Cellular Respiration
A. Glycolysis –
*takes place in cytosol
*breaks glucose into 2 molecules of pyruvate
*produces a net of 2 ATP’s
B. Krebs cycle -
*takes place in mitochondrial matrix
*makes a derivative of pyruvate into carbon dioxide
*produces a net of 2 ATP’s
C. ETC and Oxidative Phosphorylation –
*takes place in inner membrane of mitochondrion
*accepts e-’s from A and B via NADH
*at end, e-’s are combined with H+ and oxygen to form water
*forms a net of 34 ATP’s
D. Fermentation Pathways
*takes place in cytosol
*2 types: Alcoholic and Lactic Acid Fermentation
*stores most of the energy in chemical bonds
*no production of ATP
Glycolysis (2 ATP)
No oxygen present
Oxygen present
(Anaerobic respiration)
(Aerobic respiration)
Fermentation pathways
2 types:
Krebs Cycle
(2 ATP)
1. Alcoholic fermentation
(Citric Acid Cycle)
2. Lactic Acid fermentation
*found in yeasts and a few
other microorganisms
Electron Transport
Chain (34 ATP)
*found in most heterotrophs
*involves 2 more “shopping
cart” molecules – NADH and
FADH2
Figure 9.18 Pyruvate as a Key Juncture in Catabolism
Glycolysis is common to
fermentation AND respiration.
The end product of glycolysis
is pyruvate…represents a fork
in the catabolic pathways of
glucose oxidation.
In a cell capable of both
respiration and fermentation,
pyruvate is committed to one
of those two pathways, usually
depending on the presence of
oxygen.
Figure 9.6 An overview of cellular respiration (Layer 1)
Figure 9.6 An overview of cellular respiration (Layer 2)
Figure 9.6 An overview of cellular respiration (Layer 3)
Figure 9.12 A summary of the Krebs cycle
Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis
Figure 9.16 Review: how each molecule of glucose yields many ATP molecules
during cellular respiration:
http://www.wadsworthmedia.com/biology/0495119814_starr/big_picture/ch07_bp.html