Chapter 7: Cellular Respiration Flashcards
redox reaction
a pair of oxidation-reduction reactions that transfer an electron from one compound to another
oxidation
removal of an electron from a molecule
reduction
addition of an electron to a molecule
NAD
derivative of vitamin B3 and serves as an electron carrier
vitamin B3
niacin
NAD+
oxidised form of NAD
NADH
reduced form of NAD
What does an “H” indicate about a carrier molecule?
It is generally reduced
FAD
derivative of vitamin B2 and serves as an electron carrier
vitamin B2
riboflavin
FAD+
oxidised form of FAD
FADH2
reduced form of FAD
NADP
variation of NAD
What is adenosine monophosphate composed of?
An adenine, ribose and phosphate group
Why is energy required to bond phosphate groups to AMP and ADP?
Phosphate groups have a negative charge and repel each other, so more energy is needed to bond with each other
dephosphorylation
the release of one or two phosphate groups from ATP
Where does the energy needed to regenerate ATP come from?
The metabolism of glucose, fructose or galactose
phosphorylation
addition of an electron to a compound
substrate-level phosphorylation
the direct transfer of a phosphate group from an intermediate reaction to form ATP from ADP
Which two mechanisms can ATP be produced during the breakdown of glucose?
Substrate-level phosphorylation and oxidative phosphorylation
Which mechanism yields most of the ATP produced during the breakdown of glucose?
Oxidative phosphorylation
glycolysis
process of breaking glucose down to release energy
anaerobic
not requiring oxygen
Where does glycolysis take place?
In the cytoplasm of cells
What are the two ways glucose can enter the cell?
Through secondary transport against its gradient or through facilitated transport by integral proteins
GLUT protein
transport proteins that aide in facilitated transport of glucose
pyruvate
three-carbon sugar that results from glycolysis
What does glycolysis begin and end with?
It starts with a molecule of glucose and ends with two molecules of pyruvate
How many phases of glycolysis are there?
Ten
What happens in the first step of glycolysis?
Glucose is phosphorylated into glucose-6-phosphate
What enzyme converts glucose into glucose-6-phosphate?
Hexokinase
Where does hexokinase obtain the energy to phosphorylate glucose into glucose-6-phosphate?
ATP
What effect does the attached phosphate group have on glucose-6-phosphate?
It cannot interact with GLUT proteins due to its negative charge and cannot leave the cell anymore
What happens in the second step of glycolysis?
Glucose-6-phosphate is converted into fructose-6-phosphate
Which enzyme converts glucose-6-phosphate into fructose-6-phosphate?
Isomerase
isomerase
enzyme that catalyses the conversion of a molecule into one of its isomers
hexokinase
enzyme that catalyses the phosphorylation of six-carbon sugars
What happens in the third step of glycolysis?
Fructose-6-phosphate is phosphorylated into fructose-1,6-biphosphate
Which enzyme phosphorylates fructose-6-phosphate into fructose-1,6-biphosphate?
Phosphofructokinase
What type of enzyme is phosphofructokinase and what does this mean?
It is a rate-limiting enzyme so it is very active during high ADP amounts and not very active during low ADP amounts
What happens in the fourth step of glycolysis?
Fructose-1,6-biphosphate is split into dihydroxyacetone phosphate and glyceraldehyde-3-phosphate
Which enzyme splits fructose-1,6-biphosphate?
Aldolase
What happens in the fifth step of glycolysis?
Dihydroxyacetone-phosphate is transformed into glyceraldehyde-3-phosphate
Which enzyme transforms dihydroxyacetone-phosphate into glyceraldehyde-3-phosphate?
Isomerase
How much ATP is used in the first half of glycolysis?
Two ATP molecules
What happens in step six of glycolysis?
Glyceraldehyde-3-phosphate is oxidised and then phosphorylated into 1,3-bisphosphoglycerate
Where do the oxidised electrons from glyceraldehyde-3-phosphate go?
They are picked up by NAD+
How much NADH is yielded from step six in glycolysis?
Two NADH molecules
Does the phosphorylation in step six in glycolysis require ATP?
No
What is the limiting factor in step six of glycolysis?
The amount of NAD+ available
What happens if there is not enough NAD+ in step six of glycolysis?
Glycolysis will slow down or stop
How can NADH be oxidised when it is short in supply?
It will oxidise readily in the presence of oxygen or fermentation can oxidise NADH without oxygen
What happens in step seven of glycolysis?
1,3-bisphosphoglycerate donates a phosphate group to ADP and 3-phosphoglycerate it formed
How much ATP is yielded in step seven of glycolysis?
Two ATP molecules
What type of phosphorylation happens in step seven of glycolysis?
Substrate-level glycolysis
What happens to the carbonyl group on 1,3-bisphosphoglycerate in step seven?
It is oxidised to a carboxyl group
Which enzyme transforms 1,3-bisphosphoglycerate into 3-phosphoglycerate?
Phosphoglycerate kinase
What happens in step eight of glycolysis?
The phosphate group in 3-phosphoglycerate moves to the second carbon to become 2-phosphoglycerate
Which enzyme transforms 3-phosphoglycerate into 2-phosphoglycerate?
Phosphoglycerate mutase
mutase
a type of isomerase that moves a functional group within the same molecule
kinase
transfers a phosphate group from ATP to another molecule
What enzyme oxidises glyceraldehyde-3-phosphate?
Dehydrogenase
dehydrogenase
removes hydrogen atoms from a molecule
What happens in step nine of glycolysis?
2-phosphoglycerate loses water to become phosphoenolpyruvate
Which enzyme dehydrates 2-phosphoglycerate?
Enolase
What happens in the tenth step of glycolysis?
Phosphoenolpyruvate is dephosphorylated and is transformed into pyruvate
How much ATP is yielded from step ten of glycolysis?
Two ATP molecules
Which enzyme converts phosphoenolpyruvate into pyruvate?
Pyruvate kinase
What is the difference between pyruvate and pyruvic acid?
Pyruvic acid is an acid and pyruvate is in salt form
Why are many enzymes named after their reverse reactions?
Those enzymes can catalyse both forward and reverse reactions
What is produced from glycolysis?
Two pyruvate, four ATP and two NADH
What is the net gain of ATP and NADH?
Two ATP and two NADH
aerobic respiration
when organisms convert energy in the presence of oxygen
What type of enzyme is pyruvate kinase?
It is a rate-limiting enzyme for glycolysis
coenzyme A
derivative of vitamin B5 and is a carrier compound
vitamin B5
pantothenic acid
Where does pyruvate go after glycolysis?
It travels to the mitochondrial matrix
pyruvate dehydrogenase complex
a complex of three enzymes that converts pyruvate into acetyl-CoA
What must happen to pyruvate before it enters the citric acid cycle?
It must be converted into acetyl-CoA
What happens in the first step of the oxidation of pyruvate?
A carboxyl group is removed from pyruvate to produce a hydroxyethyl group
Which enzyme decarboxylates pyruvate?
Pyruvate dehydrogenase
What happens to the carboxyl group removed from pyruvate?
It is released as carbon dioxide
What happens in step two of the oxidation of pyruvate?
The hydroxyethyl group is oxidised
What happens to the oxidised electrons from the hydroxyethyl group?
They are picked up by NAD+ to form NADH
What is coenzyme A bound to?
It is bound to a sulfhydryl group
What happens when a hydroxylethyl group is oxidised?
It becomes an acetyl group
What is the chemical formula for an acetyl group?
CH3CO
What happens in step three of the oxidation of pyruvate?
The acetyl group is transferred to CoA to produce acetyl-CoA
citric acid cycle
series of enzyme-catalysed reactions to extract energy from carbohydrates
What are other names for the citric acid cycle?
The TCA cycle and the Krebs cycle
What is the origin for the name TCA cycle?
The first two intermediates of the cycle are tricarboxylic acids
tricarboxylic acid
acid with three carboxyl groups
Where does the citric acid cycle happen?
In the mitochondrial matrix
oxaloacetate
four-carbon molecule
citrate
six-carbon molecule that has three carboxyl groups
What happens in step one of the citric acid cycle?
An acetyl group and oxaloacetate combine to create citrate
Why is step one of the citric acid cycle irreversible?
It is highly exergonic
What happens to CoA after the acetyl group bonds with oxaloacetate?
It diffuses away to bond with another acetyl group
condensation
chemical reaction when two small molecules form a larger one but with the removal of a functional group or molecule
What type of reaction is citrate synthesis?
Condensation reaction
How is the rate of citrate synthesis controlled?
By negative feedback and the amount of ATP available
How does the amount of ATP affect citrate synthesis?
The more ATP available, the slower the reaction
negative feedback
when a process feeds back into itself and slows the process down
What happens in step two of the citric acid cycle?
Citrate is converted into isocitrate
How is citrate converted into isocitrate?
It loses a molecule of water, then gains another
isocitrate
isomer of citrate
What happens in step three of the citric acid cycle?
Isocitrate is oxidised into alpha-ketoglutarate
What is produced in step three of the citric acid cycle?
Carbon dioxide
What happens to the oxidised electrons from isocitrate?
NAD+ is reduced to NADH
How is alpha-ketoglutarate production regulated?
By the negative feedback from ATP
What happens in step four of the citric acid cycle?
Alpha-ketoglutarate is oxidised into a succinyl group that to CoA to form succinyl-CoA
How is succinyl-CoA production regulated?
Feedback inhibition of ATP, succinyl-CoA and NADH
What enzyme catalyses citrate production?
Citrate synthase
What enzyme catalyses isocitrate production?
Aconitase
What enzyme catalyses alpha-ketoglutarate production?
Isocitrate dehydrogenase
What enzyme catalyses succinyl-CoA production?
Alpha-ketoglutarate dehydrogenase
What is produced in step four of the citric acid cycle?
Carbon dioxide
What type of reactions occur in steps three and four of the citric acid cycle?
Oxidation and decarboxylation reactions
What happens to the oxidised electrons from alpha-ketoglutarate?
NAD+ is reduced to NADH
What happens in step five of the citric acid cycle?
Succinyl-CoA is converted to succinate
How is succinyl-CoA converted to succinate?
A phosphate group substitutes CoA in succinyl-CoA which is then phosphorylated to succinate
What type of phosphorylation occurs in step five of the citric acid cycle?
Substrate-level phosphorylation
Where does the phosphorylated phosphate group from succinyl-CoA go?
It joins to create either ATP or GTP
Guanosine triphosphate
Energy equivalent to ATP but it has the base guanine instead of adenine
What enzyme catalyses succinate production?
Succinyl-CoA synthetase
synthetase
enzyme that catalyses a synthesis reaction by using energy from ATP or GTP
What is the difference between synthetase and synthase?
Synthetase uses energy from ATP or GTP and synthase does not
How many forms of succinyl-CoA synthetase are there and how do they differ?
There are two forms, one which specialises in ATP production and another in GTP
isozyme
different forms of enzymes with the same formula but different structures
What happens in step six of the citric acid cycle?
Succinate is converted to fumarate
How is succinate converted to fumarate?
Two hydrogen atoms are stripped from succinate
Where do the stripped hydrogen atoms from succinate go?
They are picked up by FAD to reduce it to FADH2
Why is FAD used in step six of the citric acid cycle instead of NAD+?
The electrons in the hydrogen atom are not energetic enough so they can only reduce FAD
How do FAD and NAD+ differ when transferring electrons?
FAD transports electrons directly to the electron transport chain
Which enzyme catalyses fumarate production?
Succinate dehydrogenase
What happens in step seven of the citric acid cycle?
Fumarate is converted to malate
How is fumarate converted to malate?
Water is added to fumarate
Which enzyme catalyses malate production?
Fumarase
What happens in step eight of the citric acid cycle?
Malate is converted to oxaloacetate
How is malate converted to oxaloacetate?
Malate is oxidised to oxaloacetate
What happens to the oxidised hydrogen atom from malate?
It reduces NAD+ to NADH
amphibolic
both catabolic and anabolic
What are the overall products of the citric acid cycle?
Two CO2, three NADH, one FADH2 and one ATP or GTP molecule
electron transport chain
series of four protein complexes along with electron carriers that pumps protons across the inner mitochondrial membrane
prosthetic group
tightly-bound nonprotein molecule that is required for protein activity
What is the difference between a prosthetic group and a cofactor?
A cofactor is any nonprotein substance required for protein activity, whereas a prosthetic group has the same role but is tightly bound to the protein
What are the main components of complex I?
An iron-sulphur containing protein, FMN and NADH dehydrogenase
What is the prosthetic group in complex I?
Flavin mononucleotide
flavin mononucleotide
prosthetic group in complex I that is derived from vitamin B2
How many amino acid chains is NADH dehydrogenase made up of?
Forty-five
How many H+ can complex I pump?
Four H+
Where does complex I receive its electrons from?
NADH
What is another name for complex II?
Succinate dehydrogenase
What are the main components of complex II?
Four succinate dehydrogenase subunits and ubiquinone B
ubiquinone
lipid soluble coenzyme that is part of the electron transport chain
How is ubiquinone represented?
Q
What is ubiquinone’s reduced form?
QH2
What does ubiquinone do?
It receives electrons from complexes I and II and delivers them to complex III
Where does complex II receive its electrons from?
FADH2
Why is less ATP produced from NADH2?
Electrons carried by NADH2 bypass the first complex and do not energise the first pump, so less protons are pumped
What factor determines the amount of ATP produced in the electron transport chain?
The number of protons pumped
What is complex III composed of?
A Rieske protein, and cytochrome b and c proteins
What makes up the centre of a Rieske protein?
A 2Fe-2S centre
What is another name for complex III?
Cytochrome oxidoreductase
heme group
molecule with an iron ion at its core
What prosthetic group does cytochrome have?
A prosthetic group of heme
What role does heme play in cytochrome in complex III?
It carries electrons from complex III to complex IV
What are the oxidation states of Fe in cytochrome?
Fe++ and Fe+++
What is complex IV composed of?
Cytochrome c, a and a3
How many heme groups does complex IV have?
Two heme groups, one in cytochrome a and one in cytochrome a3
How many copper centres does complex IV have?
It has a binuclear CuA centre and a CuB centre
Where are electrons in complex IV transported to?
They are used to reduce oxygen
What happens to the reduced oxygen in complex IV?
It picks up two hydrogen ions from its surroundings to create water
chemiosmosis
the movement of ions across the membrane with their electrochemical gradient
What happens to all the pumped H+ from the electron transport chain?
It travels through ATP synthase by chemiosmosis to form ATP from ADP
ATP synthase
enzyme that facilitates the addition of a phosphate group to ADP
What percentage of ATP is produced due to chemiosmosis?
Ninety percent
oxidative phosphorylation
production of ATP through chemiosmosis in the presence of oxygen
fermentation
regenerates NAD+ from NADH when there is no oxygen to serve as the final electron acceptor
anaerobic respiration
when organisms convert energy in the absence of oxygen
methanogen
archaeans that reduce carbon dioxide to methane to oxidise NADH
sulphate-reducing bacteria
bacteria that reduce sulphate to hydrogen sulphide to oxidise NADH
What are the two main types of fermentation?
Lactic acid and alcohol fermentation
Which fermentation method is used by animals?
Lactic acid fermentation
Which types of cells in the body use lactic acid fermentation often?
Red blood cells and skeletal muscle cells
Why must red blood cells use lactic acid fermentation?
They do not have mitochondria and cannot carry out aerobic respiration
What happens to lactic acid that has built up in the muscles?
It is removed by the bloodstream, loses a hydrogen to become lactate and is metabolised in the liver
What is the chemical equation for lactic acid fermentation?
Pyruvic acid + NADH lactic acid + NAD+
Which enzyme catalyses lactic acid fermentation?
Lactate dehydrogenase
What happens to lactate in the liver?
It can be reconverted to pyruvic acid for further catabolisation
What is the chemical equation for alcohol fermentation?
Pyruvic acid + H+ -> CO2 + acetaldehyde + NADH + H+ -> ethanol + NAD+
What happens in the first chemical reaction of alcohol fermentation?
Pyruvic acid is decarboxylated to produce acetaldehyde
Which enzyme and coenzyme are involved in the first chemical reaction of alcohol fermentation?
Pyruvate decarboxylase and thiamine pyrophosphate
thiamine pyrophosphate
derived from vitamin B1
vitamin B1
thiamine
What happens in the second chemical reaction of alcohol fermentation?
Acetaldehyde is reduced to ethanol and NADH is oxidised to NAD+
Where does the ethanol in alcoholic beverages come from?
Yeast in beverages ferments pyruvic acid into ethanol
obligate anaerobes
organisms that live and grow in the absence of oxygen
glycogen
stores energy in animals
What happens to glucose when there is adequate ATP available?
It is stored as glycogen
Where is glycogen stored in the body?
In the liver and muscle cells
How does glucose stored in glycogen enter the glycolytic pathway?
Glycogen is broken down into glucose-1-phosphate and converted to glucose-6-phosphate to enter the glycolytic pathway
Can fructose and galactose be catabolised the same way glucose can?
Yes
How effective is fructose and galactose catabolism compared to glucose catabolism?
Fructose and galactose produce the same amount of ATP as glucose does
How do proteins find their way into glucose metabolism?
Excess amino acids from hydrolysed proteins can replace intermediates and reactants in glucose metabolism
What must happen to an amino acid before it enters the glycolytic pathway?
It must have its amino group removed
What happens to an amino acid’s removed amino group when it enters the glycolytic pathway?
It is converted to ammonia
What happens to ammonia produced in the body?
The liver synthesises urea from ammonia and carbon dioxide which leaves the body in urine
How do triglycerides enter the glycolytic pathway?
Glycerol can be converted to glycerol-3-phosphate to enter glycolysis, and fatty acids can be oxidised into acetyl groups
How are fatty acids catabolised into acetyl groups?
Through beta oxidation
beta oxidation
oxidation process where fatty acids are catabolised
How can glucose entry to the cell be regulated?
With GLUT proteins
How does GLUT4 control glucose entry to the cell?
When insulin binds to a receptor, it causes a GLUT4 containing vesicle to merge with the plasma membrane to allow glucose to enter
What amino acid can pyruvate be converted to?
Alanine
What is the main enzyme controlled in glycolysis?
Phosphofructokinase
What factors affect phosphofructokinase’s activity?
High levels of ATP or citrate and more acidic pH all slow it down
What does a high concentration of citrate indicate?
There is a possible blockage in the citric acid cycle
What does increased acidity in aerobic respiration indicate?
Acids from fermentation are accumulating
What factors affect pyruvate kinase’s activity?
- High levels of energy and alanine slow it down
- High levels of fructose-1,6-bisphosphate increase activity
- When the enzyme is phosphorylated, it becomes less active
phosphatase
removes a phosphate group from a molecule
What factors regulate pyruvate dehydrogenase?
High levels of acetyl groups or NADH lowers activity, and phosphorylating it slows it down
Which enzymes are regulated in the citric acid cycle?
Isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase
What factors regulate isocitrate dehydrogenase?
High levels of ATP and NADH slow the enzyme down
What factors regulate alpha-ketoglutarate dehydrogenase?
High levels of ATP, NADH and succinyl CoA slow this enzyme down
What can excess alpha-ketoglutarate in the citric acid cycle be used for?
It can be converted to glutamate
