Lecture 12-13
Chapter 6
Cellular
Respiration
How do marathon runners and sprinters differ?
• Long-distance runners have many
SLOW FIBERS in their muscles
– Slow fibers break down glucose for ATP
production aerobically (using oxygen)
– These muscle cells can sustain repeated, long
contractions
• Sprinter’s muscles have more FAST FIBERS
- Fast fibers make
ATP without
oxygen—
anaerobically
- They can contract
quickly and supply
energy for short bursts
of intense activity
The dark meat of a cooked turkey is an
example of slow fiber muscle
Leg muscles support sustained activity
The white meat consists of fast fibers
- Wing muscles allow for quick bursts of flight
INTRODUCTION TO
CELLULAR RESPIRATION
• Nearly all the cells in our body break down
sugars for ATP production
• Most cells of most organisms harvest energy
aerobically, like slow muscle fibers
– The aerobic (+O2) harvesting of energy from
sugar is called cellular respiration
– Cellular respiration yields CO2, H2O, and a large
amount of ATP
• Cellular respiration breaks down glucose molecules and
banks their energy in ATP
– The process uses O2 and releases CO2 and H2O
Glucose
Oxygen gas
Carbon
dioxide
Water
Energy
• Breathing supplies oxygen to our cells and removes carbon dioxide
O2
BREATHING
CO2
Lungs
CO2
Bloodstream
O2
Muscle cells carrying out
CELLULAR
RESPIRATION
MITOCHONDRION
Mitochondria use the energy in sugars, fats and proteins
to make ATP
•Cellular respiration oxidizes sugar and produces ATP in three main stages:
–GLYCOLYSIS occurs in the cytoplasm
–The KREBS CYCLE (TCA) and
the ELECTRON TRANSPORT CHAIN
occur in the mitochondria
Fig. 6.16
High-energy electrons
carried by NADH
GLYCOLYSIS
Glucose
Cytoplasmic
fluid
Pyruvic
acid
KREBS
CYCLE
ELECTRON
TRANSPORT CHAIN
AND
CHEMIOSMOSIS
Mitochondrion
Glycolysis harvests chemical energy by
oxidizing glucose to pyruvic acid
Glucose
Pyruvic
acid
• Details of
glycolysis
• Read and think
about each
step so that
you can ‘see’
the big picture
• Memorize and
understand the
NET
REACTIONS
Steps 1 – 3 A fuel
molecule is energized,
using ATP.
Glucose
Step
PREPARATORY
PHASE
(energy investment)
1
Glucose-6-phosphate
2
Fructose-6-phosphate
3
Fructose-1,6-diphosphate
Step 4 A six-carbon
intermediate splits into
two three-carbon
intermediates.
4
Glyceraldehyde-3-phosphate
(G3P)
ENERGY PAYOFF
PHASE
5
Step 5 A redox
reaction generates
NADH.
1,3-Diphosphoglyceric acid
(2 molecules)
6
Steps 6 – 9 ATP
and pyruvic acid
are produced.
7
3-Phosphoglyceric acid
(2 molecules)
8
2-Phosphoglyceric acid
(2 molecules)
2-Phosphoglyceric acid
(2 molecules)
9
See Figure 6.18
Pyruvic acid
(2 molecules
per glucose molecule)
6.7 Using Coupled Reactions to Make ATP
•
Glycolysis is the first stage in cellular respiration
– Takes place in the cytoplasm
– Occurs in the presence or absence of oxygen
– Involves ten enzyme-catalyzed reactions
• These convert the 6-carbon glucose into two 3-carbon molecules of pyruvate
Priming reactions
1
6-carbon glucose
(Starting material)
Cleavage reactions
2
Energy-harvesting reactions
3
2 ATP
P
P
6-carbon sugar diphosphate
P
P
6-carbon sugar diphosphate
P
P
P
P
3-carbon sugar3-carbon sugar 3-carbon sugar 3-carbon sugar
phosphate
phosphate
phosphate
phosphate
NADH
NADH
2 ATP
Fig. 6.17
2 ATP
3-carbon 3-carbon
pyruvate pyruvate
6.8 Harvesting Electrons from Chemical Bonds
• The oxidative stage of
aerobic respiration occurs
in the mitochondria
Fig. 6.20
• It begins with the
conversion of pyruvate
into acetyl coA
Depending
on needs
The Krebs Cycle
•
•
•
Takes place in the mitochondria
It consists of nine enzyme-catalyzed reactions that can be divided into three stages
– 1 Acetyl CoA binds a 4-carbon molecule producing a 6-carbon molecule
– 2 Two carbons are removed as CO2
– 3 The four-carbon starting material is regenerated
Krebs cycle enzymes strip away electrons and H+ from each acetyl group generating
many NADH and FADH2 molecules
1
3
2
CoA–
(Acetyl-CoA)
4-carbon molecule
(Starting material)
6-carbon
molecule
6-carbon molecule
NADH
CO2
4-carbon
molecule
Fig. 6.22
ATP
5-carbon
molecule
NADH
CO2
4-carbon molecule
(Starting material)
NADH
FADH2
4-carbon molecule
6.9 Using the Electrons to Make ATP
Energy Transfer
in the Mitochondria
6.9 Using the Electrons to Make ATP
•
Glucose is entirely consumed in the process of cellular respiration
•
Glucose is converted to six molecules of CO2
– used to buffer the pH of blood
– breathe out as waste
•
The glucose energy is transformed to
–
4 ATP molecules
– 10 NADH electron carriers
–
2 FADH2 electron carriers
• THE REDUCING POWER IN
THESE ELECTRON CARRIERS
IS USED TO MAKE 32 ATP
MOLECULES IN THE
ELECTRON TRANSPORT CHAIN
6.9 Using the Electrons to Make ATP
Intermembrane space
Pyruvate from
cytoplasm
H+
H+
e–
NADH
H+
1. Electrons are harvested
and carried to the transport
system.
Acetyl-CoA
NADH
2. Electrons provide
energy to pump
protons across the
membrane.
e–
H2O
e–
Krebs
cycle
FADH2
3. Oxygen joins with
protons to form water.
1
2
O2
O2
+ 2H+
CO2
32
2
ATP
H+
ATP
Mitochondrial matrix
4. Protons diffuse back
in, driving the synthesis
of ATP.
ATP
synthase
Fig. 6.26 An overview of the electron transport chain and chemiosmosis
• The electrons carried by NADH and FADH2
are donated to the electron transport chain
• Energy released by the electrons is used to
pump H+ into the space between the
mitochondrial membranes
• In chemiosmosis,
the H+ ions diffuse through
ATP synthase complexes,
which capture the energy
to make ATP
Fig. 6.25
• Chemiosmosis in the mitochondrion
Protein
complex
Intermembrane
space
Electron
carrier
Inner
mitochondrial
membrane
Electron
flow
Mitochondrial
matrix
ELECTRON TRANSPORT CHAIN
Figure 6.12
ATP SYNTHASE
Other Sources of Energy
• Food sources, other than sugars,
can be used in cellular respiration
• These complex molecules are first digested into simpler
subunits
– Polysaccharides can be hydrolyzed to
monosaccharides and then converted to glucose for
glycolysis
– Proteins can be digested to amino acids, which are
chemically altered and then used in the Krebs cycle
– Fats are broken up and fed into glycolysis and the
Krebs cycle
Fig. 6.27
How cells
obtain
energy
from foods
Anaerobic Respiration
• The use of inorganic terminal electron acceptors
other than oxygen
Organism
Terminal
electron
Reduced
Product
acceptor
Methanogens
Archaea
Sulfur bacteria
CH4
CO2
Methane
SO4
H2S
Sulfate
Hydrogen
sulfide
Fermentation
•
•
•
The use of organic terminal electron acceptors
The electrons carried by NADH are donated to a derivative of pyruvate
– This allows the regeneration of NAD+ that keeps glycolysis running
Two types of fermentation are common among eukaryotes
– Lactic fermentation and Ethanolic fermentation
Occurs in
animal
muscle cells
Fig. 6.19
Occurs
in yeast
cells
Sunlight energy
BIG PICTURE
Life from the Sun
• Nearly all the chemical
energy that organisms
use comes ultimately
from sunlight
This is a
VERY IMPORTANT
cycle
Chloroplasts,
site of photosynthesis
CO2
+
H2O
Mitochondria
sites of cellular
respiration
Glucose
+
O2
(for cellular work)
Heat energy