chapter 18 - Respiration Flashcards
summarise the process of glycolysis
occurs in the cytoplasm of the cell
anaerobic process
glucose, 6 carbon sugar, is split into two smaller three-carbon pyruvate molecules. ATP and reduced NAD are also produced
what are the main steps in glycolysis
phosphorylation
lysis
phosphorylation
dehydrogenation and formation of ATP
what is a respiratory substrate
an organic substance that can be used/ broken down in respiration to release ATP
why do the organic molecules, e.g. lipids, carbs and protein, release different energy values
because H+ and e- combine with O2 to produce water, the more H atoms in a substrate, the more O2 needed, and more H2O is produced
describe lipids as respiratory substances
- can only be respired anaerobically
- gets hydrolysed into glycerol and fatty acids
- glycerol gets converted into pyruvate
- fatty acids consist of mainly hydrogen atoms
- fatty acids get converted into acetyl groups (2c) through beta oxidation
- acetyl groups combine with CoA and enter Krebs
describe proteins as respiratory substrates
- can only be respired aerobically
- only used during starvation, fasting or prolonged exercise
- get hydrolysed into amino acids
- some amino acids converted into pyruvate
- some converted into acetate
- others enter Krebs cycle directly
what are the typical Respiratory Quotients for
carbs
lipids
proteins
carbs - 1.0
lipids - 0.7
protein - 0.9
what is the Respiratory Quotient
the ratio of the volume of carbon dioxide given out in respiration to that of oxygen used
describe the process of anaerobic respiration
without oxygen: ETC stops (as oxygen is the final electron acceptor)
Krebs cycle stops
link reaction stops
glycolysis can continue if the NAD produced can be re-oxidised
anaerobic pathways provide somewhere for 2H to be donated and reduced NAD to become NAD and reused in glycolysis
what are the two anaerobic respiration pathway
ethanol fermentation - in some fungi and plant tissues
lactate fermentation - in animals
describe the ethanol pathway in anaerobic respiration
two step process
facultative anaerobe
- makes ATP by aerobic respiration
- can switch to alcoholic fermentation if necessary
dies when ethanol builds up to around 15%
slower than aerobic
describe the lactate pathway of anaerobic respiration
occurs in animals
one step process
lactate is toxic and removed by the liver
liver either converts lactate;
- back to pyruvate, can be converted to acetate to be used in Link/Krebs
- to glycogen and stored
liver needs oxygen to do this = oxygen debt
define respiration
the process whereby energy stored in complex organic molecules is used to make ATP
describe the ATP-ADP cycle
ATP is broken down into ADP + P
exergonic (energy released) (releases 30.5kJmol-1)
ADP + P forms ATP
endergonic (energy taken in) (requires 30.5kJmol-1)
how much energy is released in the hydrolysis of
ATP +H2O
ADP +H2O
AMP +H2O
why?
ATP = 30.6 kJmol-1
ADP = 30.6 kJmol-1
AMP = 14.2 kJmol-1
AMP is lower energy as phosphodiester bond is weaker (phosphate and ribose) compared to a phosphate and phosphate bond
what enzyme catalyses the hydrolysis of ATP
ATPase
what enzyme forms ATP
ATPsynthase
what is ATP used for (6)
- metabolic processes - building large molecules
- active transport - change shape of carrier proteins
- movement - for muscle contraction
- nerve transmission - Na+/K+ active transport pump require ATP
- synthesis of materials within cells
- secretion - packaging and transport of secretory products
what are the advantages of using ATP compared to glucose
only one enzyme needed to release energy from ATP (ATPase) (glucose needs more)
- ATP releases energy in smaller amounts and where needed (glycose contains large amounts we don’t need straight away)
- ATP is a common source of energy for multitude of chemical reactions, increasing the efficiency of the cells in the body (international energy currency)
where does oxidative phosphorylation occur?
in the inner membrane (cristae) of mitochondria
where do the link reaction and Krebs cycle occur
in the matrix of the mitochondria
what is the endosymbiotic theory
that some of the organelles in today’s eukaryotic cells were once microbes
what is the primary substrate for respiration
glucose (C6H12O6)
what is oxidation and reduction in respiration?
oxidation - loss of hydrogen (and electrons)
reduction - gain of hydrogen (and electrons)
how do Co-enzymes work
aid enzymes in the reduction or oxidation reactions because they can pick up and lose hydrogen atoms
what are the co-enzymes used in respiration
NAD
CoA - Coenzyme A
FAD
what are reduced coenzymes used for
in the final stage of respiration (oxidative phosphorylation) which produces a lot of ATP
how do co-enzymes work - NAD example
substate - hydrogen lost - oxidised substrate
hydrogen atom accepted by coenzyme (NAD-> NADH)
coenzyme is oxidised (NADH-> NAD)
hydrogen is removed and used to generate ATP
when is NAD reduced?
in the first 3 stages of respiration
when is FAD reduced
in the Krebs cycle
what are the four main stages of aerobic respiration
glycolysis
link reaction
Krebs cycle
Oxidative Phosphorylation
describe the process of glycolysis
glucose broken down into 2 pyruvate molecules
- occurs in the cytoplasm and does not require oxygen
(first step in both aerobic and anaerobic)
glycolysis results in 2 pyruvate molecules, 2 NADH and 2 ATP molecules
describe the process of glycolysis
- ATP is hydrolysed
- energy released is used to attach Pi to the glucose at carbon 6 - phosphorylation
- destabilises glucose and prevents it from leaving the cell as it is an ion
- repeated after isomerisation
- hexose 1,6 biphosphate splits into 2x triose phosphate (3C)
- 2 hydrogens are removed from TP by dehydrogenase enzyme
-NAD accepts hydrogen becoming NADH
(process repeated for each triose phosphate)
final step = formation of ATP via substrate level phosphorylation - intermediate compounds provide Pi at this stage,
in addition to ATP pyruvate (3C) is formed
all of the above happens twice
what is the net production of ATP after glycolysis
2
what are the key points of glycolysis
occurs in cytoplasm
no oxygen required
enzymes are used in each step
4 ATP molecules made
net ATP production = 2
2 NADH produced
2 pyruvate (3C) made
what are the key points of the Link reaction
occurs in matrix of mitochondria
pyruvate and NADH from glycolysis is actively transported into mitochondria
link reaction involves conversion of pyruvate to acetyl CoA
why is everything in the link and Krebs cycle doubled?
as there are 2 pyruvate molecules
what enzyme removes 2 hydrogen atoms from pyruvate in the link reaction
pyruvate dehydrogenase
describe the process of the link reaction
- pyruvate dehydrogenase removes 2 hydrogens from pyruvate
- NAD accepts hydrogens to become NADH
- pyruvate decarboxylase removes carboxyl group and CO2 is formed
after removal of 2H and carboxyl groups, pyruvate (3C) has been converted into acetate (2C)
- CoA accepts acetate to become acetyl CoA
- Acetyl CoA moves into the Krebs cycle
what are the products of the link reaction
- 2NADH
- 2CO2
- 2 Acetyl CoA
(no ATP produced)
what are the products at the stages 1-6 of the Krebs cycle
and what are the reactions that happen to these products
- acetate 2C - joins with oxaloacetate (4C)
- Citrate 6C - oxidised and decarboxylated
- 5C compound - oxidised and decarboxylated
- 4C compound - converted into another 4C and ATP is produced
- 2nd 4C - dehydrogenated into 3rd 4C
- 3rd 4C dehydrogenated into oxaloacetate (4C)
all happens twice!
what are the products of the Krebs Cycle
- 4 CO2
- 6 NADH
- 2 FADH
- 2 ATP
net ATP production in Krebs = 2
net ATP production so far = 4
what is stage 1 of the Krebs cycle
Acetate (2C) leaves CoA and joins with oxaloacetate (4C) forming citrate (6C)
stage 2 of the Krebs Cycle
- citrate (6C) is oxidised/ dehydrogenated and decarboxylated to form 5C compound
- Enzymes involved - dehydrogenase and decarboxylase
- NAD accepts the hydrogen becoming NADH and CO2 is released
stage 3 of the Krebs Cycle
- 5C compound is oxidised/ dehydrogenated and decarboxylated to form 4C compound
- NAD accepts hydrogen becoming NADH and CO2 is released
stage 4 of the Krebs Cycle
4C compound is then converted into another 4C compound and ATP is produced through substrate level phosphorylation
stage 5 of the Krebs Cycle
2nd 4C compound is then converted into a 3rd 4C compound through dehydrogenation and FAD accepts the 2H atoms becoming FADH
stage 6 of the Krebs Cycle
3rd 4C is then converted into oxaloacetate (4C) through dehydrogenation and NAD accepts the 2H atoms becoming NADH
in oxidative phosphorylation, what are protein carriers referred to as
complexes I-IV
stages 1-3 of oxidative phosphorylation
- NADH is oxidised and donates 2H
- the 2H are split (by enzyme) into 2 electrons and 2 protons
- complex I receives electrons which are passed along the electron transport chain (ETC)
protein carriers contain iron ions (Fe3+)
Fe3+ become Fe2+ until electron is passed to next protein
stage 4 of oxidative phosphorylation
the 2 protons are pumped from the matrix across the inner membrane into the intermembrane space
the energy released from the ETC provides the energy used for active transport
stage 5 of oxidative phosphorylation
FADH is also oxidised and the 2H are split into 2e- and 2p+
the 2 electrons are received by complex II and passed along ETC
2 protons are pumped into intermembrane space
stage 6 of oxidative phosphorylation
hydrogen ions/ protons accumulate in the intermembrane space and are at a higher concentration than in the matrix
- electrochemical gradient - protons move back into the matrix via chemiosmosis (proton motive force)
stages 7 and 8 of oxidative phosphorylation
- the protons travel through a protein channel in ATP synthase
- the movement of protons through the channel changes the shape of ATP synthase allowing it to create ATP from ADP and Pi
stage 9 of oxidative phosphorylation
the protons have re-entered the matrix join with the electrons released at the end of the ETC at complex IV forming hydrogen
hydrogen reacts with O2 to form water (4H+ +4E- + O2 = 2H2O)
oxygen is the driving force - without it then the electrochemical gradient wouldn’t be as steep as protons accumulate in the matrix
how much ATP is produced in oxidative phosphorylation
10 NADH used so 25 ATP produced
2 FADH used so 3 ATP produced
28 in total
how many ATP are made from one molecule of:
NAD
FAD
1 NAD = 2.5 ATP
1 FAD = 1.5 ATP
how much ATP would we expect to be produced in aerobic respiration
(incl. different stages)
glycolysis = 2 net
link = 0
Krebs = 2
oxidative phosphorylation = 28
total = 32 ATP produced
why might less ATP be produced than we expect?
- some protons leak across the membrane in the mitochondria - reducing electrochemical gradient
- some ATP used in transporting pyruvate and reduced NAD from glycolysis into mitochondria
what process converts fatty acids in lipids into acetyl groups (2C)
beta oxidation
What is the:
type of respiration,
Location of enzyme
And inhibitor
Of citrate synthase
Aerobic
Mitochondria
Citric acid
What are the net products of the Krebs cycle for ONE pyruvate molecule
3NADH
1 FADH
2CO2
1ATP
What is a similarity in the way ATP is made in respiration and photosynthesis
Both involve proton gradients
Explain the relative yield of ATP in aerobic and anaerobic respiration
Anaerobic produces less ATP per glucose molecule because NAD is not regenerated in oxidative phosphorylation
