Download RESPIRATION Metabolic processes that need energy include

RESPIRATION
What is Respiration?
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Process whereby energy stored in complex organic molecules is used to make ATP.
Occurs in living cells.
All living organisms need energy to drive their biological processes. All reactions that take place
within organism are known collectively asmetabolism:
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Anabolic – Building large molecules
Catabolic – Breaking large molecules into smaller ones. Energy from catabolic reactions is
released in the form of heat. This is useful because >>>>
Metabolic reactions are controlled by enzymes. Organisms needed to maintain a suitable
temperature to allow enzyme actions to proceed at the speed that will sustain life.
Metabolic processes that need energy include:
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Active Transport
 Moving ions and molecules against the concentration gradient.
 Cell membranes have sodium-potassium pumps which maintain the resting potential.
Secretion
 Large molecules made in some cells are exported by exocytosis.
Endocytosis
 Bulk movement of large molecules into the cells.
Synthesis of large molecules into smaller ones
 E.g. Proteins to Amino acids, Steroids from Cholesterol, Cellulose from Beta Glucose. (All
Anabolic)
Replication of DNA and Synthesis of Organelles
Movement
 E.g. Movement of bacteria flagella, eukaryotic cilia and undulipodia.
 E.g. Muscle contraction
 E.g. Microtubules motors that move organelles around inside the cell.
Activation of Chemicals
 Glucose is phosphorylated at the beginning of respiration. This is more unstable and can
be broken down to release energy.
Where does Energy come from?
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Phooautotrophs
 Plants, Protoctists (Eukaryotic organism), and some bacteria.
 Use sunlight energy to make large, inorganic moleculesthat contain chemical potential
energy.
 This chemical potential energy is used by consumers and decomposers (e.g. fungi,
animals, and most bacteria).
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Respiration then releases this energy. This energy is used to phosphorylate ADP to make
ATP. This phosphorylation also transfers energy to the ATP molecule.
ATP – Structure and Role
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ATP = Phosphorylated Nucleotide
Structure of ATP
Adenine
P
P
Adenine
P
Ribose
Adenosine
Adenosine Monophosphate
Adenosine diphosphate
Adenosine triphosphate
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ATP =Universal energy currency
 Provides immediate source of energy in biological processes
 Hydrolysed to ADP (adenosine diphosphate) and P (inorganic phosphate).
 This releases 30.6 KJ energy per mol.
 Energy is immediately available in small, manageable amounts that will not damage
the cell and will not be wasted.
 Hydrolysis of ATP is coupled with a synthesis reaction, such as DNA replication or
protein synthesis, in cells. These synthesis reactions require energy from ATP.
Energy can never be created or destroyed, so ENERGY IS NEVER PRODUCED. Respiration
RELEASES ENERGY to PRODUCE ATP.
Energy released for use by cells to do work
HYDROLYSIS
ATP
ATP Synthase
ADP + P
CONDENSATION
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Energy released from organic substrate, during respiration
GLYCOLYSIS
Glycolysis
Anaerobic
Pyruvate
Aerobic
LINK REACTION
Lactate
fermentation(Mammalian)
Ethanol
fermentation(Yeast)
Pyruvate
Acetyl CoA
CO2
tissue)
KREBS CYCLE
Lactate
CO2
Ethanol + Carbon Dioxide
OXIDATIVE
PHOSPHORYLATION
Coenzymes
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During glycolysis, the link reaction and Krebs cycle – HYDROGEN ATOMS ARE REMOVED FROM
SUBSTRATE MOLECULES OXIDATION REACTIONS.
 Enzymes are not very good at catalysing oxidation and reduction reactions.
 Coenzymes are needed to help them carry out the oxidation reactions in respiration.
 Oxidation and reduction reactions are coupled - when one substrate becomes oxidised,
the other becomes reduced. In respiration, the coenzyme becomes reduced so the
substrate becomes oxidised.The reduced coenzyme later becomes reoxidised so it can
be used again.
 Coenzymes carry hydrogen ATOMS which later become protons or electrons. (DO NOT
SAY THEY CARRY HYDROGEN IONS).
NAD – (Nicotinamide Adenine Dinucleotide)
 Organic, non-protein molecule.
 Helps dehydrogenase enzymes to carry out oxidation reactions.
 Accepts two hydrogen atoms with their electrons – REDUCED
 Loses electrons – OXIDISED
 Operates during glycolysis, link reaction, krebs cycle, and during the anaerobic and
lactate pathways.
Coenzyme A (CoA)
 Accepts acetate to become acetylcoenzyme A to be carried to the Krebs cycle.
FAD
Tightly bound to the dehydrogenase enzyme that is embedded in the intermembrane.
Hydrogen atoms accepted by FAD are passed back into the mitochondrial membrane.
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GLYCOLYSIS
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Occurs in the Cytoplasm of all living things that respire (Prokaryote and Eukaryote).
Four stages: Phosphorylation, Splitting of hexose 1,6-biphosphate, Oxidation of triose phosphate, conversion of
triose phosphate to pyruvate.
Glucose (6C)
One ATP molecule is hydrolysed and the
phosphate group released is attached to
the glucose molecule at carbon 6 to form
glucose 6-phosphate.
Glucose molecules are stable and need to be
activated before they can split into two.
ATP
Glucose 6-phosphate
Glucose 6-phosphate is changed
to fructose 6-phosphate.
ATP is hydrolysed and the phosphate group
released is attached to the 6-phosphate at
Carbon 1.
Energy from the hydrolysed ATP molecules
activates the hexose sugar and prevents it
from being transported out of the cell.
Fructose 6-phosphate
ATP
Activated, phosphorylated sugar = hexose 1,6biphosphate
Two hydrogen atoms
removed from each
triose phosphate
molecule. This
involves
dehydrogenase
enzymes which are
aided by NAD.
(Hydrogen acceptor)
Triose phosphate (3C)
ATP
Reduced
NAD
Intermediate
compound (3C)
ATP
Pyruvate (3C)
Hexose 1,6-biphosphate
Each molecule of
Hexose 1,6biphosphate is split
into two molecules
of triose phosphate
– Each with one
phosphate
attached.
Two molucules of ADP
are phosphorylated to
two molecules of ATP
(by substrate level
phosphorylation).
Triose phosphate (3C)
ATP
Reduced
NAD
NAD combines
with hydrogen
atoms, becoming
reduced NAD.
Two molecules
of ATP formed –
Substrate level
phosphorylation
Intermediate
compound (3C)
ATP
Pyruvate (3C)
Products of Glycolysis:
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Two molecules of ATP. Net Gain of ATP = Two molecules.
Two molecules of Reduced NAD – will carry hydrogen atoms to inner mitochondrial membranes, and used to generate
more ATP during oxidative phosphorylation.
Two molecules of Pyruvate – Actively transported into mitochondrial matrix, or changed to lactate or ethanol in cytoplasm
(in the absence of oxygen)
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The LINK REACTION and KREBS CYCLE
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Pyruvate produced during Glycolysis is transported across the outer and inner mitochondrial
membrane to the matrix.
Link Reaction – Pyruvate to Acetate
Krebs Cycle – Acetate oxidised
Pyruvate Dehydrogenase
removes hydrogen atoms from
pyruvate.
PyruvateHydrogen
Dehydrogenase
NAD accepts
atoms
Pyruvate hydrogenase removes carboxyl group
from pyruvate, which eventually becomes CO2
Pyruvate (3C)
Reduced NAD
removes hydrogen atoms from
pyruvate.
Acetate from acetyl
coenzyme A joins with
oxaloacetate to form 6carbon citric acid.
4-carbon compound
is further
2H
dehydrogenated Reduced
NAD
and regenerates
oxaloacetate.
4C
Another molecule of
Compound
NAD is reduced.
2H
CO2
Decarboxylation and dehydrogenation of pyruvate
to acetate = enzyme-catalysed reactions
CoA accepts Acetate to become Acetyl Coenzyme A.
CoA carries Acetate to the Krebs cycle.
Acetyl CoA (2C)
Oxaloacetate (4C)
Coenzyme A is released and
becomes available to collect
more acetate.
Citrate (6C)
CO2
Reduced FAD
4-carbon compound is
changed into another 4carbon compound. A
pair of hydrogen atoms
is removed and
accepted by the
coenzyme FAD, which is
reduced.
2H
Reduced
NAD
4C
Compound
ATP
The pair of hydrogen
atoms is accepted by a
molecule of NAD,
which becomes
reduced.
5C Compound
4C
Compound
The 4-carbon compound is changed into
another 4-carbon compound. A
molecule of ADP is phosphorylated to
produce a molecule of ATP = Substrate
level phosphorylation.
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Citrate is decarboxylated, and
dehydrogenated to form a 5carbon compound.
2H
CO2
Reduced
NAD
The 5-carbon compound is
decarboxylated and
dehydrogenated to form a 4carbon compound and another
molecule of reduced NAD
One turn of the cycle for each molecule of acetate, which was made from one molecule of acetate – to turns of the cycle
Although oxygen is not used in these stages, they won’t occur in the absence of oxygen, so they are aerobic.
Other food substrates besides glucose can be respire…..d.
Fatty acids are broken down to acetates and enter the Krebs cycle through CoA
Amino acids can be deaminated and the rest of the molecule may enter Krebs cycle directly or may be changed to
pyruvate or acetate, depending on the type of amino acid.
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Oxidative Phosphorylation and Chemiosmosis
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Involves electron carriers embedded in the inner mitochondrial membrane, which are folded
into cristae, increasing surface area for electron carriers and ATP synthase enzymes.
Reduced NAD and reduced FAD are reoxidised when they donate hydrogen atoms, which are
split into protons and electrons:
 Protons
 Go to the Matrix
 Flow of protons = chemiosmosis
 Electron
 First electron carrier = NADH dehydrogenase.
 Electrons are passé along a chain of electron carriers and then donated to
molecular oxygen – the final electron acceptor.
CHEMIOSMOSIS:
 Flow of hydrogen ions (PROTONS)
 As electrons flow down the electron transport chain, energy is released and used by
coenzymes associated with some of the electron carriers.
 This energy causes protons to be pumped across the intermembrane space via ion
channels (which are associated with ATP synthase enzyme).
 Protons are always pumped into the intermembrane space because the energy
is from electron flow. (Active transport energy is from ATP)
 This creates a proton gradient = pH gradient, and electrochemical gradient = potential
energy build up in intermembrane space.
OXIDATIVE PHOSPHORYLATION
 Formation of ATP by addition of inorganic phosphate to ADP.
 As protons flow through an ATP synthase enzyme, they drive the rotation of part of the
enzyme and join ADP and Pi to form ATP.
ATP made before oxidative phosphorylation:
 2 molecules during glycolysis by substrate level phosphorylation.
 2 molecules made during krebs cycle by substrate level phosphorylation.
ATP made DURING oxidative phosphorylation:
 ATP is made where the reduced NAD and FAD are reoxidised.
 NAD and FAD provide electrons to electron transport chain, to be used for oxidative
phosphorylation.
 Reduced NAD also provides hydrogen ions that contribute to the build-up of proton
gradient for chemiosmosis.
 Ten molecules of reduced NAD theoretically produces 26 molecules of ATP = One
molecules of NAD produces 2.6 molecules of ATP.
 With ATP made during glycolysis and Krebs cycle, the total yield of ATP molecules, per
molecule of glucose respired = 30.
THEORETICAL YIELD OF ATP IS RARELY ACHIEVED BECAUSE:
 Some protons leak across mitochondrial membranes.
 Some ATP produced is used to actively transport pyruvate to mitochondria.
 Some ATP is used for the shuttle to bring hydrogen (in the cytoplasm) from reduced NAD
made during glycolysis (into mitochondria).
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MITOCHONDRIA
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Found in Eukaryotic cells.
The matrix – LINK REACTION and KREBS CYCLE.
 Contains the enzymes that catalyse these reactions
 Contains oxaloacetate that accepts the acetate from the link reaction.
 Molecules of NAD
 Mitochondrial DNA – Code for mitochondrial enzymes and other proteins.
 Mitochondrial ribosomes – where the proteins are assembled.
The outer membrane
 Proteins – channels and carriers – allow passage of pyruvate.
 Other proteins are enzymes.
The inner membrane
 Different lipid composition to outer membrane and impermeable to most small ions,
including hydrogen ions = protons accumulate in intermembrane space = lower pH than
the matrix.
 Folded into cristae for larger surface area.
 Has electron carriers and ATP synthase enzymes.
 Electron carriers
 Protein complexes
 Arranged in electron transport chain
 Each electron carrier is an enzyme, which are associated with cofactors (nonprotein haem group that contain an iron atom).
 Cofactors accept and donate electrons. Iron atoms become reduced by
accepting an electron, and oxidised by donating an electron.
 Electron carriers = oxidoreductase enzymes – involved in oxidation and
reduction reactions.
 Electron carriers – contain enzymes which pump protons into intermembranal
space, using energy released from passage of electrons.
 ATP synthase enzyme
 Large and protruding from inner membrane into the matrix
 Stalked particles
 Allows protons to pass through them – from intermembrane space into matrix
(chemiosmosis).
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Anaerobic respiration:
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Electron transport chain cannot function – Krebs cycle and Link reaction stop.
Glycolysis becomes the only source of ATP.
Glycolysis needs to keep operating – Reduced NAD has to be reoxidised.
LACTATE FERMENTATION
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Occurs in mammalian tissue during vigorous activity.
Reduced NAD must be oxidised to NAD.
Pyruvate accepts hydrogen from reduced NAD.
NAD is now reoxidised and available to accept more hydrogen atoms from glucose.
ENZYME LACTATE DEHYDROGENASE catalyses the oxidation of reduced NAD, and the reduction
of pyruvate to lactate.
Lactate is carried away in the blood from the muscles to the liver.
When more oxygen is available lactate may convert back to pyruvate to be used for Link reaction
and Krebs cycle. Or recycled to glucose or glycogen.
It is NOT the build-up of lactate that causes fatigue, but the reduction in the pH that will reduce
enzyme activity.
ALCOHOLIC (ETHANOL) FERMENTATION
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Yeast cells
Each pyruvate molecule is decarboxylated (loses carbon dioxide molecule) and becomes ethanal.
Enzyme – Pyruvate decarboxylase – has coenzyme thiamine diphosphate attached to it.
Ethanal accepts hydrogen atoms from NAD which will become oxidised. The ethanal is reduced
to ethanol.
Reoxidised NAD will accept more hydrogen atoms from glucose in glycolysis.
Yeast = Facultative anaerobe. Can survive without oxygen, and killed when ethanol builds up to
15%.
Yeast = Grows faster in AEROBIC conditions.
Enzyme names describe its role. E.g. Pyruvate decarboxylase – Removes carboxyl groups from its
substrate pyruvate.
Respiratory Substrates
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Is an organic substance that can be used for respiration.
More protons = More ATP produced.
More hydrogen atoms in a respiratory substrate = More ATP generated when the substrate is
respired.
More hydrogen atoms per mole of respiratory substance = More oxygen needed to respire that
substance.
CARBOHYDRATE [Cn(H2O)n]
 Some mammalian cells e.g. brain cells and red blood cells, only use glucose for
respiration.
 Glycogen in animals and starch in plants hydrolyse to release glucose for respiration.
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Other monosaccharides, such as Fructose and Galactose, can be changed to glucose for
respiration.
 Theoretical maximum energy yield for glucose = 2870kJ (permole)
 30.6kJ produce 1 mol ATP
 Theoretically 1 mol of glucose should produce nearly 94 mol ATP.
 Actual yield is 30 mol ATP = 32% efficiency
 Remaining energy is released as heat – maintains suitable body temperature for
enzyme-controlled reactions.
PROTEIN
 Excess amino acids can be deaminated by the removal of amine group and conversion to
urea. The rest of the molecule is changed to fat or glycogen which is later respired to
release energy.
 When an organism is fasting, starvation or prolonged exercise – the protein from the
muscle can be hydrolysed to amino acids, which can be respired.
 Some amino acids can be converted to pyruvate.
 Some amino acids can enter directly into the krebs cycle.
 Protein releases more energy than equivalent masses of carbohydrates.
LIPIDS
 Triglycerides are hydrolysed by lipase to fatty acids and glycerol. Glycerol can be
converted to glucose, and respired.
 Fatty acids cannot be respired.
 Fatty acids = long-chain hydrocarbons with a carboxylic acid group. In each molecule
there is carbons and hydrogen atoms – source of many protons for oxidative
phosphorylation so they produce a lot of ATP:
 Each fatty acid is combined with CoA using energy from the hydrolysis of a
molecule of ATP to AMP and two inorganic phosphate.
 The fatty acid-CoA complex is transported o the mitochondrial matrix where it is
broken down into 2-carbon acetyl groups that are attached to CoA.
 During this breakdown (by the beta-oxidation pathway) reduced NAD ad
reduced FAD are formed.
 The acetyl groups are released from CoA and enter Krebs cycle – forms 3
reduced NAD, 1 reduced FAD, and 1 ATP.
 The NAD is reoxidised in oxidative phosphorylation producing large amounts of
ATP by chemiosmosis.
Fats and proteins an only be respired aerobically. They cannot undergo Glycolysis.
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