respiration Flashcards
Cellular respiration
enzymes lower ……… energy
activation
enzymes are often ……….. dependent
pH
enzymes are often inhibited by the end product in the pathway. This is negative/positive feedback
negative feedback
gene expression and protein modification regulate enzymes. Give an example of each
gene expression - if gene is expressed it will be transcribed and translated into the functional protein that makes up the enzyme
protein modification - phosphorylation (can either switch enzymes on or off)
describe a catabolic pathway
the break down of complex molecules into simpler ones. Energy is released. e.g. cellular respiration
describe an anabolic pathway
the building of complex molecules from simpler ones. Energy is required. e.g. the synthesis of starch
what are the 3 steps in aerobic respiration
glycolysis
citric acid cycle
electron transport chain
where does glycolysis occur
in the cytosol
how many ATP are produced in glycolysis
2ATP
how are electrons carried in glycolysis
by NADH
what is the final product of glycolysis
glucose –> pyruvate
where does the citric acid cycle occur
the inner membrane of the mitochondria
What are the main steps in glycolysis
begin with glucose
energy investment of 2ATP - this breaks down into 2ADP and 2Pi
energy payoff phase where 4ATP are formed. NAD+ picks up electrons
pyruvate produced
what are the net gains from glycolysis
glucose –> 2pyruvate +2water
net 2ATP
2NAD+ + 4e- + 4H+ –> 2NADH + 2H+
what are the main steps of glycolysis (lecture notes version)
- glucose –> glucose-6-phosphate (hexokinase uses ATP and phosphorylates glucose)
- Glucose-6-phhosphate –> fructose-6-phosphate (phosphogluco-isomerase)
- fructose-6-phosphate –> fructose-1, 6-bisphosphate (phosphofructo-kinase) molecule starts to look more symmetrical
- fructose-1, 6-bisphosphate –> dihydroxyacetone phosphate + Glyceraldehyde-3-phosphate (adolase)
- Glyceraldehyde-3-phosphate –> 1, 3-bisphosphoglycerate (triose phosphate dehydrogenase)
- 1, 3-bisphosphoglycerate –> 3-phosphoglycerate (phosphoglycerokinase)
- 3-phosphoglycerate –> 2-phosphoglycerate (phosphoglycero-mutase)
- 2-phosphoglycerate –> phosphoenolpyruvate (enolase) 2Water produced
- phosphoenolpyruvate –> pyruvate (pyruvate kinase)
what do kinases do
they phosphorylate
which enzymes is responsible for the conversion between Dihydroxyacetone phosphate and Glyceraldehyde-3-phosphate
isomerase
where does the energy stored in the organic molecule of food ultimately come from
the sun
energy flows into an ecosystem in the form of ………… and out in the form of …………..
light
heat
what does photosynthesis provide
It generates oxygen and organic molecules used by the mitochondria of eukaryotes as a fuel for cellular respiration
what does cellular respiration provide
respiration breaks down organic molecules (fuel) using oxygen - this generates ATP. The waste products of respiration are carbon dioxide and water which are the raw materials for photosynthesis.
what type of metabolic pathway releases energy by breaking down complex molecules into simpler smaller ones
catabolic
organic compounds have potential energy due to the arrangement of what within their structure
the arrangement of electrons in the bonds between their atoms.
compounds that participate in exergonic reactions can act as what
fuels
when enzymes degrade complex molecules that are rich in potential energy into simpler waste products with less energy what happens to the energy released for the reaction
some of the energy can be used for work and the rest is dissipated as heat
what happens in fermentation
the partial degradation of sugars and other organic fuels without the use of oxygen
what is the most efficient catabolic pathway
aerobic respiration
give an overview of aerobic respiration
oxygen is consumed as a reactant along with the organic fuel. The fuel is broken down to release ATP and the waste products - water and carbon dioxide
which cells carry out aerobic respiration
all eukaryotes and some prokaryotes
some prokaryotes do not carry out aerobic respiration and use substances other than oxygen in a reaction with a similar process to aerobic respiration, harvesting chemical energy without oxygen. What is this process called
anaerobic respiration
what does the term cellular respiration include
technically aerobic and anaerobic respiration but is mostly used as a reference to aerobic respiration
name some molecules from food that can be used as fuel in respiration
carbohydrates, fats and protein
in animal diets what is the major source of carbohydrates
starch - a storage polysaccharide that can be broken down into glucose
what is the formula for aerobic respiration using glucose as the fuel
C6H12O6 + 6O2 –> 6H2O + 6CO2 + energy(ATP + heat)
is the breakdown of glucose endergonic or exergonic
exergonic - catabolic - releases energy
catabolic pathways do not directly perform work. How is catabolism linked to work
by ATP - it provides the energy for the reactions that result in work
during the breakdown of glucose how is energy released
relocation of electrons during the chemical reactions releases energy stored in organic molecules and the energy is used to synthesise ATP
what are electron transfer reactions called
oxidation-reduction reactions or redox reactions
what happens in a redox reaction
the loss of electrons from a substance oxidation and the gain of electrons by a substance is called reduction - the combination of these to reaction makes a redox reaction
what is the reducing agent
the electron donor that is itself oxidised
what is the oxidising agent
the electron acceptor that is itself reduced
do all redox reactions involve complete transfer of an electrons from one substance to another
no e.g. in methane combustion the electron transfer is only partial - there is just a change in electronegativity meaning the electrons are pulled more towards one atom than before
is energy required to pull an away from an atom
yes - the more electronegative the atom the more energy required to pull an electron away from it
an electron loses potential energy when it sifts from a less/more electronegative atom to a less/more electronegative atom
less
more
a redox reaction that moves electrons closer to oxygen takes in/releases energy
releases energy that can be put to work
in aerobic respiration the fuel (glucose) is reduced/oxidised and the oxygen is reduced/oxidised
glucose - oxidised
oxygen - reduced
why are organic molecules abundant in hydrogen excellent fuels for respiration
they make good fuels because their bonds are a source of electrons whose energy may be released as the electrons fall down the concentration gradient during their transfer to oxygen
in respiration the oxidation of glucose transfers electrons to a lower energy state what is the result of this
the process releases energy that can be used for ATP synthesis
In general the fuels of respiration have multiple C-H bonds that are oxidised into products with multiple C-? bonds
C-O bonds
what are the main energy yielding foods
carbohydrates and fats - they are reservoirs of electrons associated with hydrogen (C-H bonds)
does cellular respiration oxidise glucose in a single step
no - glucose is broken down in a series of steps, each one of these catalysed by an enzyme
How do the electrons get transferred in respiration
they are transferred from glucose and travel with a proton i.e. they travel as hydrogen atoms
What happens to the hydrogen ions in respiration that transfer the electrons from glucose to oxygen
the Hydrogen atoms are not transferred directly
They are passed to an electron carrier, a coenzyme called NAD
what is NAD derived from
the B vitamin niacin
why does NAD a good electron carrier
because it can easily change from its oxidised form (NAD+) to its reduced form (NADH)
what does NAD+ function as during respiration
an oxidising agent
how does NAD+ trap electrons for glucose and other molecules in food
- enzymes called dehydrogenases remove a pair of H atoms (removing 2 electrons and 2 protons) from the substrate, oxidising it
- The enzyme delivers the 2 electrons along with one proton to its coenzyme NAD+ forming NADH
- the other proton is released as a hydrogen ion into the surrounding solution
explain in terms of protons and electrons hoe the charge on NAD becomes neutral when in the reduced form
Recall: oxidised form (NAD+), reduced form (NADH)
NAD+ gains 2 electrons and one proton from the dehydrogenases that pick these up from food molecules.
This adds 2 negative charges and one positive charge to NAD+ and since this is already positively charged the result is a neutral molecule of NADH
What is the most versatile electron acceptor in cellular respiration
NAD+
electrons lose most/little of their energy on transfer from glucose to NAD+
little - each NADH molecule formed during respiration represents stored energy - this can be used to make ATP when the electrons complete their fall in a series of steps down an energy gradient from NADH to oxygen
how do electrons that are extracted form glucose and stored as potential energy in NADH finally reach oxygen
respiration uses an electron transport chain to break the fall of electrons to oxygen into a series of energy releasing steps
electron transfer form NADH to oxygen is exergonic. Instead of this energy being released, electrons cascade down a chain from one carrier molecule to the next in a series of redox reactions, losing small amounts of energy with each step until they reach oxygen (terminal electron acceptor)which has a high affinity for electrons each carrier in the chain is more electronegative than the previous one.
the electrons transferred from NADH to oxygen are moving towards a more stable location - oxygen pulls electrons down the electron transport chain
what makes an electron transport chain of respiration
it consists of a number of molecules, most of which are proteins, built into the inner membrane of the mitochondria of eukaryotic cells
electrons removed from glucose by NADH are shuttled to the higher energy end of the chain. At the lower energy end, oxygen captures these electrons along with the hydrogen nuclei (H+) forming water
during respiration what are the steps of travel for electrons
Glucose –> NADH –> electron transport chain –> oxygen
what are the 3 main stages of cellular respiration
- glycolysis
- pyruvate oxidation and the citric acid cycle
- oxidative phosphorylation: electron transport and chemiosmosis
where does glycolysis occur
the cytosol
give an overview of glycolysis
begins the degradation process by breaking glucose down into 2 molecules of pyruvate
what happens to the pyruvate produced in glycolysis
it enters the mitochondrion (in eukaryotes - in prokaryotes this happens in the cytosol) and is oxidized to form acetyl CoA which then enters the citric acid cycle
give an overview of the citric acid cycle
the breakdown of glucose to carbon dioxide is completed
the electron carriers NADH and FADH2 transfer electrons derived from glucose to the ……………………..
electron transport chain
what happens during oxidative phosphorylation
the electron transport chain accepts electrons from NADH or FADH2 generated through the first 2 stages and passes these electrons down the chain
The electrons become bound with oxygen and hydrogen ions forming water
the energy released at each step of the chain is stored in a form the mitochondrion can use to make ATP from ADP.
this mode of ATP synthesis is called oxidative phosphorylation because it is powered by the redox reactions of the electron transport chain
in the earlier steps (glycolysis and citric acid cycle) of cellular respiration, a few molecules of ATP are synthesised - by what process are they synthesised
substrate level phosphorylation
what is the inner membrane of the mitochondrion (eukaryotes - the site in prokaryotes is the plasma membrane) the site for in respiration
electron transport and chemiosmosis - the processes that make up oxidative phosphorylation
which type of phosphorylation accounts for 90% of the ATP generated by respiration
oxidative phosphorylation
when does ATP synthesis by substrate level phosphorylation occur
it occurs when an enzyme transfers a phosphate group from a substrate molecule to ADP, rather than adding an inorganic phosphate to ADP as in oxidative phosphorylation
in respiration what does substrate molecule refer to
an organic molecule generated as an intermediate during the catabolism of glucose
for each molecule of glucose degraded to carbon dioxide and water by respiration, how many molecules of ATP are produced
32
what are the two phases of glycolysis
energy investment and energy payoff
what happens during the energy investment phase of glycolysis
the cell invests 2 ATP
what happens during the energy payoff phase of glycolysis
4 ATP is produced by substrate level phosphorylation and 2 NAD+ is reduced to 2 NADH by electrons released from the oxidation of glucose
what is the net energy yield from glycolysis per glucose molecule
2 ATP and 2 NADH
is any carbon released as CO2 in glycolysis
no - all carbon from glucose is accounted for in the 2 pyruvate molecules (they are 3 carbon chains and glucose is a 6 carbon chain)
what happens after glycolysis if oxygen is present
the chemical energy stored in pyruvate and NADH is extracted by pyruvate oxidation, the citric acid cycle and oxidative phosphorylation
what are the 9 steps in glycolysis (textbook version - just reactant and product pls)
ENERGY INVESTMENT
1. glucose –> glucose 6-bisphosphate
2. glucose 6-bisphosphate –> fructose 6-phosphate
3. fructose 6-phosphate –> fructose 1,6-bisphosphate
4. fructose 1,6-bisphosphate –> glyceraldehyde 3-phosphate (G3P) + dihydroxyacetone phosphate (DHAP)
ENERGY PAYOFF
5. G3P –> 1,3-bisphosphoglycerate
6. 1,3-bisphosphoglycerate –> 3-phosphoglycerate
7. 3-phosphoglycerate –> 2-phosphoglycerate
8. 2-phosphoglycerate –> phosphoenol-pyruvate (PEP)
9. phosphoenol-pyruvate (PEP) –> pyruvate
what enzymes are involved for each of the steps in glycolysis
- hexokinase
- phosphoglucoisomerase
- phosphofructokinase
- aldolase
- triose phosphate dehydrogenase
- phosphoglycerokinase
- phosphoglyceromutase
- enolase
- pyruvate kinase
which enzyme converts between glyceraldehyde 3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP)
isomerase
what specifically happens in each of the steps of glycolysis
- hexokinase transfers a phosphate group from ATP to glucose - making it more reactive
- glucose 6-phosphate is converted to fructose 6-bisphosphate
- phosphofructokinase transfers a phosphate group from ATP to the opposite end of the sugar, investing a second molecule of ATP - key step for regulation
- aldolase cleaves the sugar molecule into two different 3 carbon sugars
- 2 sequential reactions:
(1) G3P is oxidised by the transfer of electrons to NAD+, forming NADH
(2) using energy from this exergonic redox reaction, a phosphate group is attached to the oxidised substrate, making a high energy product - phosphate group transferred to ADP (substrate level phosphorylation - ATP released) in an exergonic reaction. Carbonyl group of G3P has been oxidised to the carboxyl group of 3-phosphoglycerate
- phosphoglyceromutase relocates the remaining phosphate group
- enolase causes double bond to form in the substrate by extracting a water molecule, yielding phosphoenolpyruvate (PEP) (has high potential energy)
- the phosphate group is transferred from PEP to ADP (substrate level phosphorylation - ATP released) forming pyruvate.
most/little of the energy from glucose remains stored in the pyruvate molecules after glycolysis
most
when oxygen is present the pyruvate in eukaryotic cells enters a mitochondria where what happens
oxidation of glucose is completed - in prokaryotic cells this occurs in the cytosol
upon entering the mitochondria what is pyruvate converted to
acetyl coenzyme A
what step links glycolysis to the citric acid cycle
conversion of pyruvate to acetyl coenzyme A
how is pyruvate converted to acetyl coenzyme A
it is carried out by a multienzyme complex that catalyses 3 reactions:
(1) pyruvates carboxyl group is fully oxidised and given off as a molecule of CO2
(2) the remaining 2 carbon fragment is oxidised and the electrons transferred to NAD+, storing energy in the form of NADH
(3) coenzyme A is attached via its sulfur atom to the 2 carbon intermediate forming acetyl CoA
what is acetyl coA used for in the citric acid cycle and what type of reaction is this
it is used to transfer the acetyl group to another molecule in the citric acid cycle
the reaction is highly exergonic
pyruvate is broken down into how many carbon dioxide molecules
3 - this includes the molecule released during the conversion from pyruvate to acetyl CoA
how much ATP does the citric acid cycle generate and by what means is it produced
1 ATP per turn by substrate level phosphorylation
where is most of the energy generated by the citric acid cycle transferred to
NAD+ and FAD during redox reactions - NADH and FADH2 then shuttle these electrons to the electron transport chain
describe in detail the 8 steps of the citric acid cycle
- acetyl CoA (from oxidation of pyruvate) adds its 2 carbon acetyl group to oxaloacetate, producing citrate
- citrate is converted to its isomer, isocitrate, by removal of one water molecule and addition of another
- isocitrate is oxidised, reducing NAD+ to NADH. then the resulting compound loses a CO2 molecule, producing alpha-ketoglutarate
- another CO2 is lost and alpha-ketoglutarate is oxidised and attached to coenzyme A to produce succinyl CoA, reducing NAD+ to NADH
- coenzyme A is displaced from succinyl Co A by a phosphate group (to form succinate), which is transferred to GDP forming GTP, a molecule with functions similar to AT. GTP can also be used to generate ATP
- 2 hydrogens are transferred to FAD, forming FADH2 and oxidising succinate
- addition of a water molecule rearranges bonds in the substrate - producing malate
- malate is oxidised, reducing NAD+ to NADH and regenerating oxaloacetate
what makes the citric acid cycle a cycle
the fact that oxaloacetate is regenerated
for each acetyl group entering the cycle, how many NAD+ are reduced to NADH
3
for each acetyl group entering the citric acid cycle, how many FAD are reduced to FADH2
1
what does FAD accept
2 electrons and 2 protons - so is neutral when it forms FADH2
where does the only generation of ATP from the citric acid cycle occur
step 5 - the GTP can be converted to one molecules of ATP
each glucose gives rise to how many acetyl Co A molecules entering the citric acid cycle
2
what is produced from the citric acid cycle as a whole - remember that one cycle involves 2 molecules of acetyl Co A
6 NADH
2FADH2
the equivalent of 2ATP - GTP isn’t always converted to ATP
most of the ATP produced in respiration results from what kind of phosphorylation
oxidative phosphorylation when the NADH and FADH2 produced in the citric acid cycle and glycolysis relay electrons to the electron transport chain
in eukaryotic cells all the citric acid cycle enzymes are located in the mitochondrial matrix except from which one
the one that catalyses step 6 and resides in the inner mitochondrial membrane
during oxidative phosphorylation chemiosmosis couples electron transport to what
ATP synthesis
how many ATP molecules are produced in total from glycolysis and the citric acid cycle per glucose molecule
4 ATP: 2 from each process
how are the ATP produced in glycolysis and the citric acid cycle
by substrate level phosphorylation
up until oxidative phosphorylation, which molecules account for most of the energy extracted from glucose
FADH2 and NADH
give an overview of oxidative phosphorylation
it uses energy released by the electron transport chain to power ATP synthesis
what is the electron transport chain
a collection of molecules embedded in the inner membrane of the mitochondrion in eukaryotic cells (plasma membrane in prokaryotes)
what about the inner membrane increases it surface area
it folds into cristae - providing thousands of copies of each component of the electron transport chain in a mitochondria
most components of the electron transport chain are proteins - how are the proteins arranged
multiprotein complexes attached to prosthetic groups
what are prosthetic groups
non protein components such as cofactors or coenzymes essential for the catalytic function of certain enzymes
what happens to the components of the electron transport chain when they accept electrons from their uphill neighbour
they become reduced
when a component of the electron transport chain passes its electrons downhill what happens to it
it becomes oxidised
going down the electron transport chain the components become progressively less/more electronegative
more - oxygen - the most electronegative component is at the end of the chain
free energy is gained/released going down the electron transport chain
released
what are the electrons collected from earlier steps in respiration transferred to in the electron transport chain
they are transferred to the first molecule in the electron transport chain in complex I
what is the first molecule in the electron transport chain in complex I
a flavoprotein
where does the flavoprotein in complex I pass the electrons
to an iron-sulfur protein in complex I
where does the iron sulfur enzyme in complex I pass the electrons to
a compound called ubiquinone
what is ubiquinone (coenzyme Q)
a small hydrophobic, the only member of the electron transport chain which is not a protein. ubiquinone is individually mobile within the membrane rather then residing in a particular complex
what are most of the remaining electron carriers between ubiquinone and oxygen called
they are proteins called cryptochromes
what are cryptochromes
proteins whose prosthetic group is a heme which has an iron atom which accepts and donates electrons
how are all the different cryptochromes in the electron transport chain named
cyt with a letter and number to distinguish it as a different protein with a slightly different electron carrying heme group
what is the last cryptochrome in the chain called and what does it do
cyt a3 passes its electrons to oxygen
as well as picking up electrons what else does oxygen pick up and why
a pair of hydrogen ions from the aqueous solution - neutralising the negative charge due to the added electrons - the result is the formation of water
where does FADH2 add its electrons in the electron transport chain
from within complex II, at a lower energy than NADH does
do NADH and FADH2 donate the same number of electrons
yes - they each donate 2 electrons
when FADH2 is the electron donor what fraction of the energy produced from the electron transport chain for ATP synthesis is produced compared to when NADH is the electron donor
2/3
where is the protein ATP synthase found
inner membrane of the mitochondria - eukaryotes
plasma membrane - prokaryotes
what does ATP synthase do
it makes ATP from ADP and an inorganic phosphate
ATP synthase uses the energy of an existing …………… to power ATP synthesis
ion gradient
what is the power source of ATP synthase
the difference in the concentration of hydrogen ions on opposite side of the inner mitochondrial membrane
what is chemiosmosis
an energy coupling mechanism in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work such as the synthesis of ATP
explain the steps of ATP synthesis
- hydrogen ions flowing down their gradient enter a channel in a stator, which is anchored in the membrane
- hydrogen ions enter binding sites within the rotor, changing the shape of each subunit so that the rotor spins within the membrane
- each hydrogen ion makes one complete turn before leaving the rotor and passing through a second channel in the stator into the mitochondrial matrix
- spinning of the rotor causes an internal rod to spin as well. this rod extends like a stalk into the knob below it, which is held stationary by part of the stator
- turning of the rod activates catalytic sites in the knob that produce ATP from ADP and Pi
what is ATP synthase
a multisubunit complex with 4 main parts which are each made up of multiple polypeptides
how does the inner mitochondrial membrane generate and maintain the hydrogen gradient that drives ATP synthesis by ATP synthase
establishing the hydrogen ion gradient is a major function of the electron transport chain. the chain is an energy converter that uses the exergonic flow of electrons from FADH2 and NADH to pump hydrogen ions across the membrane, from the mitochondrial matrix to the intermembrane space
the hydrogen ions have a tendency to flow back across the membrane diffusing down their gradient
to do this they have to flow through ATP synthase which drives phosphorylation of ADP
thus energy stored in the hydrogen gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis
what do the mobile electron carriers do in the electron transport chain
they ferry electrons between large complexes
as the complexes shuttle electrons, they pump protons from the mitochondrial matrix into the …………………..
intermembrane space
electron carriers are spatially arranged in the inner mitochondrial membrane in such a way that hydrogen is accepted from the …………………….. and deposited in …….……………
mitochondrial matrix
intermembrane space
what is the hydrogen gradient in the electron transport chain referred to as
a proton-motive force - the force drives hydrogen back across the membrane through the hydrogen channels provided by ATP synthases
over which membrane do prokaryotes generate their proton gradient
over the plasma membrane - their proton-motive force allows them to make ATP, rotate their flagella and pump nutrients and waste products across the membrane
describe the energy flow during respiration
glucose –> NADH –> electron transport chain –> proton-motive force –> ATP
why can we not state an exact number of ATP molecules generated by the breakdown of one molecule of glucose
- phosphorylation and redox reactions are not directly coupled to each other, so the ratio of NADH:ATP is not a whole number. 1 NADH results in 10H+ being pumped across the inner mitochondrial membrane and 4H+ are needed to generate 1ATP (not known for sure) so 1NADH generates 2.5 ATP
- ATP yield varies slightly depending on the type of shuttle used to transport electrons from the cytosol to the mitochondrion. the electrons captured by NADH in glycolysis are passed to either NAD+ or FAD - more ATP is produced using NAD+ compared to FAD
- the proton motive force can be used to drive other types of work e.g. mitochondria’s uptake of pyruvate from the cytosol
what percentage of the chemical energy in glucose is transferred to ATP
approximately 34%
fermentation and anaerobic respiration enable cells to produce ATP in the absence of what
oxygen
why does ATP yield from aerobic respiration depend on adequate supply of oxygen
because most of the ATP generated is due to the work of oxidative phosphorylation - without the electronegative oxygen to pull electrons down the transport chain, oxidative phosphorylation eventually ceases
what is the difference between fermentation and anaerobic respiration
an electron transport chain is used in anaerobic respiration but not in fermentation
what organisms use anaerobic respiration
some prokaryotic organisms that live in environments without oxygen
instead of oxygen what tends to be at the end of the electron transport chain
sulfate ion SO4-
in anaerobic respiration when a sulfate ion replaces oxygen in the electron transport chain what is the by-product instead of water
hydrogen sulphide
what is fermentation
a way of harvesting chemical energy without using oxygen or an electron transport chain i.e. without cellular respiration
what is the oxidising agent of glycolysis
NAD+
glycolysis doesn’t generate ATP in the absence of oxygen TRUE/FALSE
FALSE - oxygen has no effect on glycolysis, glycolysis yield 2 ATP whether oxygen is present or not
fermentation is an extension of glycolysis that allows continuous generation of ATP by ……………………. phosphorylation of glycolysis
substrate-level
for fermentation to occur there must be a sufficient supply of ……….. to accept electrons during the oxidation step of glycolysis
NAD+ - although this is always regenerated as under anaerobic conditions the electrons are transferred to pyruvate
name two types of fermentation
alcohol fermentation
lactic acid fermentation
describe alcohol fermentation
pyruvate is converted into ethanol in two steps
- carbon dioxide is released from the pyruvate which is converted to the two carbon compound acetaldehyde
- acetaldehyde is reduced to ethanol by NADH - this regenerates the supply of NAD+ needed for continuation of glycolysis
what organisms often carry out alcohol fermentation under anaerobic conditions
many bacteria
yeast (fungus) carries out alcohol fermentation in addition to aerobic respiration
describe lactic acid fermentation
- pyruvate is reduced directly by NADH to form lactate as an end product, regenerating NAD+ with no release of CO2
where is lactic acid fermentation used in industry
in the dairy industry to make cheese and yoghurt
where is alcohol fermentation used in industry
baking and brewing
which body cells use lactic acid fermentation
human muscle cells make ATP by lactic acid fermentation when oxygen is scarce - during strenuous exercise when sugar catabolism for ATP production outpaces the muscles supply of oxygen from the blood
what happens to the lactic acid produced in the body
blood carries the excess lactate from the muscles to the liver where it is converted back to pyruvate by the liver cells
the pyruvate can then enter the mitochondria in liver cells and complete cellular respiration
what are obligate anaerobes
organisms that carry out only fermentation or anaerobic respiration and cannot survive in the presence of oxygen
what are facultative anaerobes
organisms that can make enough ATP to survive by using either fermentation or respiration
which cells can behave as facultative anaerobes
muscle cells
explain the use of proteins as a fuel for respiration
they can be broken down into their constituent amino acids and made into new proteins
any excess amino acids are converted by enzymes to intermediates of glycolysis and the citric acid cycle
before the amino acids can be used their amino groups must be removed (deamination)
the nitrogenous waste from the amines is excreted
explain the use of fats as a fuel for respiration
fats can be broken down into fatty acids and glycerol
glycerol is converted to glyceraldehyde-3-phosphate - an intermediate of glycolysis
beta oxidation breaks fatty acids down to 2-carbon fragments which enter the citric acid cycle as acetyl coA
………….. are better fuels for respiration compared to carbohydrates
fats
compounds formed as intermediates of glycolysis and the citric acid cycle can be diverted into anabolic pathways as precursors for which cells can synthesise the molecules they require TRUE/FALSE
TRUE
which intermediate of glycolysis can be converted to one of the major precursors of fats
dihydroxyacetone phosphate (DHAP)
how does feedback inhibition provide control
the end product of the anabolic pathway inhibits the enzyme that catalyses an early step of the pathway
what happens to respiration rate when there is a plentiful supply of ATP
it slows down
how can respiration rate be slowed down
step 3 of glycolysis, catalysed by phosphofructokinase is the first step that irreversibly commits the substrate to the glycolytic pathway. by controlling this step we can control the speed of the entire process
which enzyme is considered a pacemaker for respiration
phosphofructokinase
what stimulates phosphofructokinase
AMP - derived from ADP
what inhibits phosphofructokinase
ATP and citrate
what type of enzyme is phosphofructokinase
an allosteric enzyme
where do the different steps of respiration occur
glycolysis - cytosol
pyruvate oxidation - mitochondrial matrix
citric acid cycle - mitochondrial matrix
oxidative phosphorylation - mitochondrial cristae
