Download Cellular Respiration

Cellular Respiration
The metabolic processes within cells
that makes ATP using energy from
organic molecules such as glucose.
The need for respiration
Adenosine triphosphate (ATP)
the short-term energy store of all cells
easily transported and is therefore the universal
energy carrier
formed from the nucleotide adenosine
monophosphate by the addition of two further
phosphate molecules
a metabolically active cell may require up to 2
million ATP molecules every second!!!!!!!!
Adenosine triphosphate (ATP)
Adenosine triphosphate (ATP)
Adenosine triphosphate (ATP)
Cellular Respiration
Why can cells obtain energy from oxidising molecules such
as glucose?
 The carbon and hydrogen atoms in cells, for example in
glucose molecules, are not in their most stable form
 The most energetically stable form of carbon is carbon
dioxide and the most energetically stable form of hydrogen
is water.
 A cell can therefore obtain energy from sugar molecules (or
amino acids or fatty acids) by allowing the carbon and
hydrogen atoms in these molecules to combine with oxygen
to form carbon dioxide and water.
 This oxidation occurs through a series of steps called aerobic
respiration
 Overall: C6H12O6 + 6O2  6CO2 + 6H2O
How is this different from burning glucose?
Burning glucose:
C6H12O6
CO2 + H2O
one step oxidation
Respiration:
C6H12O6
CO2 + H2O
multi-step catabolism
Cellular Respiration
This can be divided into 4 main stages:
Glycolysis
Link reaction
Krebs cycle
Electron transport chain
Just to confuse you!!!
The stages of respiration have other names
 Glycolysis - the Embden-Meyerhof pathway
 Krebs cycle - the citric acid cycle
- the tricarboxylic acid (TCA) cycle
 Electron transport chain
- the hydrogen carrier system
- the cytochrome system
Where it all happens:
Glycolysis
Link reaction
Krebs cycle
Glycolysis – in the cytoplasm
Electron transport chain
Link reaction and Krebs cycle
in the matrix of the mitochondria
E.T. chain on the inner membrane
of the mitochondria
Summary of events
Substrates
glucose
Stages
glycolysis
pyruvate
link reaction
Products
ATP
carbon dioxide
acetyl CoA
Krebs
cycle
carbon dioxide
& ATP
H Atoms (H+ & e-)
oxygen
electron transport chain
water &
ATP
Key terms:
ATP
adenosine triphosphate
NAD+ / NADH
oxidised NAD/ reduced NAD
a coenzyme
FAD/ FADH2
oxidised FAD/ reduced FAD
a coenzyme
substrate level
phosphorylation
where a substrate molecule ( X-p ) donates its P to ADP
making ATP
oxidative
phosphorylation
the production of ATP as a result of energy released
during an oxidation reaction
dehydrogenation
the removal of hydrogen in a reaction
decarboxylation
the removal of CO2 in a reaction
coenzyme
a small molecule that is required to bind to an enzyme
to ensure its correct functioning; e.g. NAD & FAD
Oxidation and reduction
 understanding these two terms is central
to understanding respiration
Oxidation is the loss of electrons
Reduction is the gain of electrons
OILRIG
Oxidation and reduction
NAD [and FAD]
act as ‘hydrogen
carriers’
F214
Glycolysis
1
glyco - ‘sugar’ ; lyso - ‘breakdown’
the breakdown of a hexose sugar
into two molecules of the three-carbon
compound pyruvate (pyruvic acid)
occurs in all cells
gives a net gain of 2 ATP molecules
in anaerobic respiration it is the only stage of
respiration
Glycolysis
2
 look at the summary of glycolysis on the worksheet
 do not try to memorise this sequence of reactions
 concentrate on understanding what happens in this stage of respiration
and identifying the important points
 One molecule of glucose(with 6 C atoms) is broken down
into two molecules of pyruvate (with 3 C atoms each)
 Two molecules of ATP are used in the very first steps but
later four molecules are synthesised by substrate level
phosphorylation ( a net gain of two ATP molecules)
 hydrogen atoms are removed from glucose molecules
when two molecules of NAD+ are reduced to NADH
Summary of glycolysis
Substrate-level phosphorylation
Enzyme
P
P
adenosine
ADP
substrate
product
P
P
P
P
ATP
adenosine
Energy changes in glycolysis
 The stages of glycolysis that involve energy changes are shown below:
hexose
1,6-biphosphate
glucose
6-phosphate
glucose
2 x glycerate
3-phosphate
2 x pyruvate
Reaction time
The story so far; 1 …………………….
One molecule of glucose (6c)
Glycolysis
2 molecules of reduced NAD
(NADH)
2 molecules of ATP (net gain)
2 molecules of pyruvate (3C)
cytoplasm
Link reaction
matrix of
mitochondrion
2 molecules of reduced NAD
(NADH)
2 molecules of acetyl CoA (2C)
2 molecules of CO2
The Link Reaction
Link
reaction
Link reaction- formation of Acetyl CoA
 This occurs in the fluid filled centre (matrix) of mitochondria
 The two pyruvate molecules produced by glycolysis enter the
mitochondrial matrix from the cytoplasm
 Here each pyruvate is converted to acetyl coenzyme A (usually
written as acetyl CoA)
 In this reaction carbon dioxide is given off and each pyruvate loses
a pair of hydrogen atoms which results in reduced NAD (NADH)
 Acetyl CoA is a complex molecule incorporating a coenzyme
derived from pantothenic acid (vitamin B5)
Link reaction
pyruvate + coenzyme A  acetyl coenzyme A + CO2
3C
2C
Coenzyme A [CoA]
1C
Link reaction- formation of Acetyl CoA
The story so far; 2 …………………….
One molecule of glucose (6c)
Glycolysis
2 molecules of reduced NAD
(NADH)
2 molecules of ATP (net gain)
2 molecules of pyruvate (3C)
cytoplasm
Link reaction
matrix of
mitochondrion
2 molecules of CO2
2 molecules of reduced NAD
(NADH)
2 molecules of acetyl CoA (2C)
Krebs cycle
1
important for three main reasons:
 enables breakdown of macromolecules with the release of CO2
 provides reducing power for electron
transport system - produces pairs of hydrogen
atoms which are ultimately the source of metabolic
energy for the cell
 acts as an interconversion centre - is a
valuable source of intermediate compounds used
in making e.g. fatty acids, amino acids
Krebs cycle
2
This series of reactions also occurs in the matrix of
mitochondria
Each molecule of acetyl CoA combines with a 4-C
compound (oxalocacetate) to form a 6-C
compound (citrate)
This citrate then undergoes four dehydrogenations the removal of hydrogen
and then two decarboxylations – the removal of
carbon dioxide
Krebs cycle - detail
Krebs cycle
Krebs cycle
as a result of these reactions:
 oxaloacetate is regenerated and can start the cycle off
again
 three molecules of NAD are reduced to NADH
 one molecule of FAD is reduced to FADH2
 two molecules of CO2 are produced
 one molecule of ATP is made by substrate level
phosphorylation
Q How many times will the cycle ‘turn’ during the
catabolism of one molecule of glucose?
2
Krebs cycle
The overall reaction accomplished by two
‘turns’ of the Krebs cycle is:
2 acetyl CoA + 6NAD + 2FAD + 2ADP + 2Pi
4CO2 + 6NADH + 2FADH2 + 2ATP
The story so far; 3…………………….
One molecule of glucose (6c)
Glycolysis
2 molecules ATP (net)
2 molecules of NADH
2 x pyruvate (3C)
cytoplasm
Link reaction
matrix of
mitochondrion
2 molecules of CO2
2 molecules of NADH
2 x acetyl CoA (2C)
Krebs Cycle
4 molecules of CO2
2 molecules of ATP
2 molecules of FADH2
6 molecules of NADH
Electron transport chain
1
the means by which the energy, in the form of
hydrogen atoms, mostly from the Krebs cycle, is
converted to ATP
hydrogen atoms (H+ and e- ), attached to carriers, are
passed along a chain of progressively lower energy
levels (the respiratory chain)
the energy released is harnessed to produce ATP
through the oxidation of the hydrogen atoms (oxidative
phosphorylation)
Electron transport chain
2
Look back at the equations representing the
catabolism of a molecule of glucose so far and you
will notice that a number of reduced coenzyme
molecules (either NADH or FADH2) have been
produced as the glucose molecule has been stripped
of its electrons
Q how many molecules of NADH have been produced?
Q how many molecules of FADH2 have been produced?
10 NADH; 2 FADH2
Electron transport chain
3
In the electron transfer chain these reduced
coenzymes are re-oxidised.
The enzymes which catalyse this re-oxidation
process are located on the folded inner
mitochondrial membrane where they are
arranged in a series.
Q What is the likely advantage of this high degree of
folding of the inner membrane of the mitochondria to
form cristae? increased surface area for the location
of the enzymes of the electron transport
chain
Electron transport chain
4
 The overall reaction of the electron transport chain:
10NADH + 2FADH2 + 6O2

10NAD + 2FAD + 12H2O
 During this oxidative reaction, ATP is produced by oxidative phosphorylation
Electron transport chain
5
 The last cytochrome in the chain is re-oxidised by
donating its electrons to oxygen
 thus producing water - the other waste product of
respiration
 Voila!!!! Respiration is complete. Well, almost …….
How exactly is this ATP made?
The chemiosmosis theory……..
H

H+ + e-
chemiosmosis
chemiosmosis
chemiosmosis
chemiosmosis
oxidative phosphorylation
chemiosmosis
oxidative phosphorylation
chemiosmosis
oxidative phosphorylation
formation of water
chemiosmosis
How much ATP?
10 molecules of reduced NAD ; average 2.5 ATP
molecules from each = 25 ATP
2 molecules of reduced FAD ; average 1.5 ATP
molecules from each = 3 ATP
Added to the 2ATP from glycolysis and 2ATP from
Krebs cycle
Total = 32ATP from one molecule of glucose
How much ATP?
Evidence for chemiosmosis
Evidence for chemiosmosis
Evidence for chemiosmosis
Murder most foul
 A favourite poison for murderers in crime fiction is cyanide




because it works so rapidly. But why is this substance so
poisonous?
The cyanide ion (CN-) binds irreversibly to the enzyme that
catalyses the oxidation of cytochrome a (cytochrome oxidase)
As a result, cyanide stops the flow of electrons essential to
oxidative phosphorylation.
This prevents the re-oxidation of NADH and FADH and thus the
production of the majority of the cell’s ATP
Without ATP muscles go into a permanent state of contraction
leading to the characteristic arching of the back and death by
asphyxiation since the muscles needed for breathing no longer
function.
http://www.indiana.edu/~oso/animations/An7.html
Summary
LINK
REACTION
Phew! I need a lie down