Download Cellular Respiration

Cellular Respiration
Topic 3.7 and 3.8
Assessment Statements: Core
3.7.1 Define cell respiration.
3.7.2 State that, in cell respiration, glucose in the
cytoplasm is broken down by glycolysis into pyruvate,
with a small yield of ATP.
3.7.3 Explain that, during anaerobic cell respiration,
pyruvate can be converted in the cytoplasm into lactate,
or ethanol and carbon dioxide, with no further yield of
ATP.
3.7.4 Explain that, during aerobic cell respiration,
pyruvate can be broken down in the mitochondrion into
carbon dioxide and water with a large yield of ATP.
Assessment Statements: Higher Level
Energy metabolism and REDOX
reactions
• Metabolism is the sum of
all of the chemical
reactions in an organism:
catabolic (breakdown)
and anabolic (synthetic)
• Respiration is a catabolic
pathway
• Photosynthesis is an
anabolic pathway
• The two processes are
closely linked in plants
• REDOX (oxidationreduction) reactions play
a key role in energy flow
through organisms
• This is because the
electrons flowing from
one molecule to another
are carrying energy with
them
REDOX reactions
OXIDATION
REDUCTION
Loss of electrons
Gain of electrons
Gain of oxygen
Loss of oxygen
Loss of hydrogen
Gain of hydrogen
Results in C-O bonds
Results in C-H bonds
Results in a compound with lower
potential energy
Results in a compound with higher
potential energy
OIL RIG
LEO says GER
Definition of cellular respiration
Controlled release
of energy from
organic
compounds to
produce ATP
• Cells break down
organic compounds by
SLOW oxidation
• Chemical energy is
stored in covalent
bonds
• By releasing energy in a
controlled way, it can be
trapped in the ‘useful’
form of ATP
REDOX reactions in respiration
Cells tap energy from electrons transferred from
organic fuels to oxygen
Glucose gives up energy as it is oxidized: it transfers
its electrons (and energy) to water
The protons follow the electrons to produce water
Loss of hydrogen atoms
Energy
Gain of hydrogen atoms
Where Does Cellular Respiration
Take Place?
glycolysis occurs in
the cytoplasm
Krebs Cycle & ETC Take place
in the mitochondria
Cellular Respiration: Standard level
How does the process of cellular respiration
yield ATP (chemical energy) from food?
1. What do you already know about cellular
respiration?
2. What organelle in the cell is the
“powerhouse” that makes energy for the
cell?
What is ATP?
• Energy ‘currency’ used by all cells
• Adenosine triphosphate
• Organic molecule containing high-energy
phosphate bonds
Chemical Structure of ATP
Adenine Base
3 Phosphates
Ribose Sugar
How Do We Get Energy From ATP?
By breaking the highenergy bonds
between the last
two phosphates in
ATP
ATP hydrolase
(ATP’ase) catalyses
the breakdown of
ATP into ADP + Pi
Each day, you hydrolyse 1025 ATP molecules
ATP-ase
ATP Synthetase
HYDROLYSIS (Adding H2O)
H 2O
How is ATP re-made?
• Substrate-level phosphorylation
(using enzymes: in the cytoplasm of the cell
and the matrix of the mitochondrion)
• Chemiosmosis (in the mitochondria, using
ATP synthase)
Substrate level phosphorylation and
chemiosmosis
GLYCOLYSIS
Glucose
Pyruvic
acid
Substrate Level Phos.
KREBS
CYCLE
Substrate Level Phos.
ELECTRON
TRANSPORT CHAIN
AND CHEMIOSMOSIS
Oxidative Phos.
REDOX reactions in respiration
Cells tap energy from electrons transferred from
organic fuels to oxygen
Glucose gives up energy as it is oxidized: it transfers
its electrons (and energy) to water
The protons follow the electrons to produce water
Loss of hydrogen atoms
Energy
Gain of hydrogen atoms
+
NAD
Hydrogen carriers such as
shuttle
electrons in redox reactions
Enzymes remove electrons from glucose molecules
and transfer them to a coenzyme
OXIDATION
Dehydrogenase
and NAD+
REDUCTION
Redox reactions release energy when electrons
“fall” from a hydrogen carrier to oxygen
• NADH delivers electrons to a series of electron
carriers in an electron transport chain
• As electrons move from carrier to carrier, their
energy is released in small quantities
Electron flow
Two mechanisms generate ATP
• ATP can be made by
transferring phosphate
groups from organic
molecules to ADP
• This process
is called
substrate-level
phosphorylation
• Occurs in cytoplasm
and in matrix of the
mitochondrion
Two mechanisms generate ATP
1. Cells use the energy
released by “falling”
electrons to pump H+
ions across a membrane
• The energy of the
gradient is harnessed to
make ATP by the process
of chemiosmosis
• also known as oxidative
phosphorylation
High H+
concentration
ATP synthase
uses gradient
energy to
make ATP
Membrane
Electron
transport
chain
ATP
synthase
Energy from
Low H+
concentration
Figure 6.7A
Definition of cellular respiration
Controlled release
of energy from
organic
compounds to
produce ATP
• Cells break down
organic compounds by
SLOW oxidation
• Chemical energy is
stored in covalent
bonds
• By releasing energy in a
controlled way, it can be
trapped in the ‘useful’
form of ATP
Cellular Respiration
Breakdown of one
glucose results in 36
to 38 ATP molecules
• Metabolic Pathway
that breaks down
carbohydrates
• Process is exergonic as
high-energy glucose is
broken into CO2 and
H2O
• Process is also catabolic
because glucose breaks
into smaller molecules
Equations for aerobic respiration
All of these are fine!....
Equation for Cellular Respiration
C6H12O6
+ 6O2
YIELDS
6CO2 + 6H20 + e- + 36-38ATP
+ heat
Stages of Cellular Respiration
1.
Glycolysis ALWAYS
OCCURS
2.
Anaerobic pathways if no
oxygen available (Lactic
acid and Ethanol
fermentation)
3.
Aerobic pathways if
oxygen available (Link
reaction, Krebs cycle,
electron transport chain)
Where Does Cellular Respiration
Take Place?
glycolysis occurs in
the cytoplasm
Krebs Cycle & ETC Take place
in the mitochondria
Glycolysis: Always the initial
stage of respiration
•
•
•
•
Location: cytoplasm
Substrate: glucose
Requires input of 2 ATP
Products: pyruvate,
(NADH), 4 ATP
Glycolysis is an
anaerobic process: no
oxygen required
the movie...
Glycolysis
Summary of glycolysis
1. Occurs in the cytoplasm of the cell
2. Two ATP molecules are used to start the process (‘energy
investment phase’)
3. A total of 4 ATP’s are produced (net gain of 2 ATP)
4. 2 molecules of NADH are produced
5. Involves substrate level phosphorylation, lysis, oxidation
and ATP formation
6. Controlled by enzymes: when ATP levels in the cell are
high, feedback inhibition will block the first enzyme in the
pathway
7. Produces 2 pyruvate molecules at the end
If no oxygen is
available, glycolysis
(anaerobic) is
followed by
fermentation
(anaerobic)
Why fermentation?
In the absence of oxygen, glycolysis soon
stops unless there is an alternative
acceptor for the electrons produced from
the glycolytic pathway
Fermentation
1. Alcoholic
fermentation
Pyruvate is
converted into
ethanol plus
carbon dioxide
and NAD+
2. Lactate
fermentation
Pyruvate is
converted into
lactate and NAD+
Alcoholic fermentation in yeast
Alcoholic fermentation in yeast
• Pyruvate is produced from glycolysis
• 3-carbon pyruvate is converted to 2-carbon ethanol and
carbon dioxide
• Generation of carbon dioxide helps bread products to rise
• Yeast is used to produce ethanol
Lactate fermentation in mammals
• Lactate is a 3carbon molecule
• NAD+ is
regenerated to
allow glycolysis to
continue
Aerobic respiration: Higher level
8.1.4: Explain aerobic respiration: the Link reaction,
the Krebs cycle, the role of NADH and H+, the
electron transport chain and the role of oxygen
8.1.5: Explain oxidative phosphorylation in terms of
chemiosmosis
Aerobic respiration
• Takes place in the
mitochondria of eukaryotic
cells
• Substrate: pyruvate
• Produces LOTS of ATP (28 –
38 ATP): 90% of total ATP
from respiration
• Also produces carbon
dioxide, water and heat
• Oxygen is the final electron
acceptor
Aerobic respiration
• 2 pyruvate molecules
enter the mitochondrion
• Pyruvate loses a CO2
molecule and becomes
acetyl CoA
• Krebs cycle produces 2
ATP, 4 CO2, 6 NADH and 3
FADH2
• Electron transport chain
produces 34 ATP and
water
• Aerobic respiration
completely oxidises
glucose
• Anaerobic respiration
does not completely
oxidise glucose – ethanol,
lactate and carbon
dioxide are by-products
Get to know your mitochondrial
structure!
Stages of aerobic respiration
1. The ‘link’ reaction
2. The Krebs cycle
3. The electron transport chain
4. Chemiosmosis and oxidative phosphorylation
The Link Reaction
Steps 2 in aerobic respiration (step 1 is glycolysis in
the cytoplasm)
After glycolysis, when there is ample oxygen…
2 pyruvate molecules from glycolysis move into the
matrix of the mitochondrion for the Link reaction and
the Krebs cycle
Matrix – Link Reaction
2
Krebs Cycle
2
The Link reaction
The link reaction converts pyruvate (3C) into acetyl
Coenzyme A (2C), producing carbon dioxide and
NADH in the process
The Krebs Cycle (Citric Acid/TCA cycle)
•
•
•
•
•
Krebs: The walk-through...
Krebs: the movie…
The 2C acetyl Coenzyme A enters the Krebs cycle
It joins oxaloacetate (4C) to form citrate (6C).
Two carbon atoms are then lost as carbon dioxide
and the cycle repeats.
• Hydrogen is released during this cycle to reduce the
coenzymes NAD+ and FAD to 3 NADH and 1 FADH2
for each cycle
• ATP is also released
Krebs cycle turns TWICE for each
molecule of glucose
Each molecule of glucose
produces
• 2 pyruvates in
glycolysis
• Leading to 2 acetyl CoA
molecules in the link
reaction
Fill in your table!
Substance Oxidised/Reduced/Neither Reason
NAD+
NADH
FADH2
FAD
How did you do?
Substance Oxidised/Reduced
Reason
/Neither
NAD+
oxidised
+ve due to lost
electron
gained H from
NADH
reduced
organic molecule
gained H from
FADH2
reduced
organic molecule
no loss/gain of
FAD
neither
H/electrons
Production PER glucose molecule
Glycolysis: 2 ATP, 2 NADH, 2 pyruvate
Link:
Krebs :
2 NADH, CO2
2 ATP, 6 NADH, 2 FADH2, 2 CO2
Overall: 4 ATP, 10 NADH, 2 FADH2
and finally….
The electron transport chain,
chemiosmosis and oxidative
phosphorylation
• The movie…
Chemiosmosis in the mitochondrion
Protein
complex
Intermembrane
space
Electron
carrier
Inner
mitochondrial
membrane
Electron
flow
Mitochondrial
matrix
ELECTRON TRANSPORT CHAIN
ATP SYNTHASE
Poisons interrupt critical events in cellular
respiration
Rotenone
Cyanide,
carbon monoxide
ELECTRON TRANSPORT CHAIN
Oligomycin
ATP SYNTHASE
Chemiosmosis powers most ATP production
• The electrons from NADH and FADH2 travel
down the electron transport chain to oxygen
• Energy released by the electrons is used to
pump H+ (protons) into the space between the
mitochondrial membranes
• In chemiosmosis, the H+ ions diffuse back
through the inner membrane through ATP
synthase, which capture the energy to make
ATP
Questions…
• What is the role and the position of oxygen in
the electron transport chain?
• What is the benefit of having cristae in the
mitochondria?
Chemiosmosis/ ETC occurs on the inner
membrane of the mitochondria
Protein
complex
Intermembrane
space
Electron
carrier
Inner
mitochondrial
membrane
Electron
flow
Mitochondrial
matrix
ELECTRON TRANSPORT CHAIN
Figure 6.12
ATP SYNTHASE
Final checks and balances
Process
Glycolysis
Krebs cycle
Electron Transport
Chain/
Chemiosmosis
Total
ATP used
ATP produced
Net ATP gain
Final checks and balances
Process
ATP used
ATP produced
Net ATP gain
Glycolysis
2
4
2
Krebs cycle
0
2
2
Electron Transport
Chain/
Chemiosmosis
0
32
32
Total
2
38
36
Review of mitochondrial structure and
function
Outer mitochondrial membrane
Matrix
Cristae
Inner mitochondrial membrane
Space between inner and outer
membranes
Review of mitochondrial structure and
function
Outer mitochondrial membrane
Separates contents of mitochondrion
from rest of cell
Matrix
Like cytoplasm: enzymes for the Link
reaction and the Krebs cycle
Cristae
Increases surface area for oxidative
photophosphorylation
Inner mitochondrial membrane
Carriers for electron transport chain and
ATP synthase and
Space between inner and outer
membranes
Reservoir for protons (H+ ions) to create
concentration gradient
For each glucose molecule that enters cellular
respiration, respiration produces up to 38 ATP
molecules
Cytoplasmic
fluid
Mitochondrion
Electron shuttle
across
membranes
GLYCOLYSIS
2
Glucose
Pyruvic
acid
by substrate-level
phosphorylation
2
Acetyl
CoA
used for shuttling electrons
from NADH made in glycolysis
Maximum per glucose:
KREBS
CYCLE
by substrate-level
phosphorylation
KREBS
CYCLE
ELECTRON
TRANSPORT CHAIN
AND CHEMIOSMOSIS
by chemiosmotic
phosphorylation
Some practice questions on
respiration…
1. How do cells capture the energy released by
cell respiration?
A. They store it in molecules of carbon dioxide.
B. They produce glucose.
C. The energy is released as pyruvate.
D. They produce ATP.
(Total 1 mark)
Some practice questions on
respiration…
2. Which process produces the most ATP per
molecule of glucose?
A. Anaerobic respiration in a yeast cell
B. Aerobic respiration in a bacterial cell
C. Glycolysis in a human liver cell
D. The formation of lactic acid in a human
muscle cell
(Total 1 mark)
Some practice questions on
respiration…
3. Which of the following is the best definition of cell respiration?
A. A process needed to use energy, in the form of ATP, to produce
organic compounds
B. A process used to provide oxygen to the atmosphere
C. A controlled release of energy, in the form of ATP, from organic
compounds in cells
D. A controlled release of energy in the production of food from organic
compounds
(Total 1 mark)
Some practice questions on
respiration…
4. Which of the following processes produces CO2?
I. Glycolysis
II. Alcohol (ethanol) fermentation
III.Lactic acid production
A. I only
B. II only
C. I and II only
D. I, II and III
(Total 1 mark)
Some practice questions on
respiration…
4. Which of the following processes produces CO2?
I. Glycolysis
II. Alcohol (ethanol) fermentation
III.Lactic acid production
A. I only
B. II only
C. I and II only
D. I, II and III
(Total 1 mark)
Some practice questions on
respiration…
4. State a word equation for anaerobic cell
respiration in humans.
(1 mark)