Carbohydrates Flashcards
(140 cards)
1
Q
What are the functions of carbohydrates?
A
Major energy source
Involved in metabolic processes
Store potential energy
Structural and protective functions
Cell-cell communication
2
Q
What are monosaccharides?
A
Simplest form of sugar and most basic unit of carbohydrates
They cannot be hydrolysed into simpler chemical compounds
3
Q
Name three monosaccharides
A
Glucose
Galactose
Fructose
4
Q
What structure can monosaccharides have?
A
Some are in a ring shape
Others are linear
5
Q
What are disaccharides?
A
Sugar formed when two monosaccharide units join together
6
Q
What bonds join two monosaccharides together?
A
Glycosidic bonds
7
Q
What are glycosidic bonds?
A
Covalent bonds formed when the hydroxyl of one monosaccharide reacts with a H atom of another monosaccharide’s anomeric C.
This leaves and O in the middle of the bond
Reaction is a condensation reaction as we form water
8
Q
What is an anomer of disaccharide?
A
Disaccharides that are mirror images of each other
9
Q
What is the anomeric carbon?
A
Carbon labelled number one on glucose and is the carbon that was part of the carbonyl group before bonding took place
Only carbon that can be oxidised
10
Q
Name three disaccharides
A
Maltose
Lactose
Sucrose
11
Q
What is maltose?
A
Disaccharide
Formed from the breakdown of starch or when two glucose monosaccharides join together
Reducing sugar - anomeric carbon is available for oxidation, which means that it can lose its hydrogen atoms
12
Q
What is lactose?
A
Formed from a glycosidic bond between galactose and glucose
Reducing sugar - anomeric carbon is available for oxidation, which means that it can lose its hydrogen atoms
13
Q
What is sucrose?
A
Non-reducing sugar - no anomeric carbon is available for oxidation, as none of them are available to five up their hydrogen
14
Q
What are polysaccharides?
A
Carbohydrate molecules that are composed of long chains of monosaccharide units bound together by glycosidic bonds
15
Q
What are homopolysaccharides?
A
Polysaccharides where all the monosaccharide units are the same
16
Q
What are heteropolysaccharides?
A
Polysaccharides where the monosaccharide units are different
17
Q
Name five polysaccharides
A
Starch
Glycogen
Glycoproteins
Glycosaminoglycans
Proteoglycans
18
Q
What is starch?
A
Formed from two types of glucose polymers, which is the same type of glucose just different structures
19
Q
What two types of glucose polymers make up starch?
A
Amylose
Amylopectin
20
Q
What is amylose?
A
Formed from two glucose monosaccharides linking together, specifically via alpha 1 to alpha 4 bonds.
This means that it is a linear molecule
21
Q
What are alpha one to alpha four bonds?
A
Bonds between carbon one and carbon four of two molecules
In glucose, these carbons are on either end of the hexagon shape, which means that glucose polymers form one linear chain
22
Q
What is amylopectin?
A
Formed from two glucose monosaccharides linking together, via alpha one to alpha four bonds AND alpha one to alpha six bonds
This means that it is a branched molecule
23
Q
What are alpha one to alpha six bonds?
A
Bonds between carbon one and carbon six of two molecules
In glucose, this results in branches within the molecule
24
Q
How many non-reducing ends and reducing ends are found in in starch?
A
Many non-reducing ends
Few reducing ends
25
What is glycogen?
Multibranched polysaccharide of glucose
Formed of both alpha one to alpha four bonds AND alpha one to alpha six bonds
26
What do the branches in glycogen allow?
More glucose to be packed in
27
Where is glycogen mainly found?
Skeletal muscle
Liver
28
How is glycogen used in skeletal muscle?
Breaks down to form ATP for contraction
29
How is glycogen used in the liver?
To replenish blood glucose
30
Why do we store glucose as polymers?
Allows them to be stored in a compact manner
Increases the number of non-reducing ends, which allows them to be resynthesised and degraded easily
31
What are glycoproteins?
Carbohydrates, such as glucose, that have proteins attached to them
Higher content of carbohydrates than protein
32
Where are glycoproteins found?
Plasma membrane
Blood
Extracellular matrix
33
What are glycosaminoglycans?
Un-branched molecules made up of repeating units of hexuronic acid and an amino acid
34
Describe the structure of glycosaminoglycans and how this relates to their function?
Dynamic as the bonds within the chain aren't strong
Molecules can slip and slide past one another
35
Where are glycosaminoglycans found?
Mucus
Synovial fluid around joints
36
What are proteoglycans?
Formed from glycosaminoglycans which are attached to proteins
Higher content of proteins than carbohydrates
37
Describe the structure of proteoglycans
Rigid
Bonds are stronger due to the presence of proteins
38
Where are proteoglycans found?
On the surface of cells
Extracellular matrix
Forms parts of connective tissue
39
Describe the digestion of carbohydrates
Mouth - amylase in saliva hydrolyses the alpha one to alpha four bonds
Stomach - nothing
Duodenum - pancreatic amylase hydrolyses more alpha one to alpha four bonds
Jejunum - different enzymes form mucous membranes are released
40
What is the duodenum?
First part of the small intestine
41
What is the jejunum?
Middle part of the small intestine
42
What are the main products of carbohydrate digestion?
Glucose
Galactose
Fructose
43
Describe the process of glucose absorption
In epithelial cell membranes, there are sodium glucose symport proteins that allow glucose and sodium to from a high concentration in the intestinal lumen into the low concentration inside the cell
The glucose in the cell is transported out of the cell into the blood through a glucose uniporter
44
What do the sodium glucose symports driven by? Why is this important?
Driven by a high concentration of sodium outside the cell, not reliant on glucose concentration.
Low concentration of sodium outside the cell due to sodium potassium pump, which constantly pumps three sodium atoms out of the cell into the blood.
This system means that even when glucose has a high concentration in the blood it is still transported against its concentration gradient into the cell
45
What happens when glucose has been absorbed into the blood?
Transported to the liver, where its is phosphorylated into G-6-P by hepatocytes, by adding a phosphate onto the sixth carbon of glucose
G-6-P cannot diffuse out of the cell as GLUT transported can't recognise it, trapping it in the cell and allowing it to be used in the cell. This can happen in other tissues too.
46
What two enzymes catalyse the phosphorylation reaction of glucose into G-6-P?
Glucokinase
Hexokinase
47
What is glucokinase?
Specific to the liver
High Km for glucose - low affinity
High Vmax for glucose - very efficient
48
What is hexokinase?
Other tissues, except liver
Low Km for glucose - high affinity
Low Vmax for glucose - not efficient
49
What do the varying properties of hexokinase and glucose allow?
When blood glucose concentration is normal, the liver doesn't grab all of the glucose and that it can be transported to other tissues
Hexokinase in these tissues allow then to grab glucose even at low glucose concentrations as they have a high affinity for it
When blood glucose concentration is high, the liver can grab more glucose and due to its high efficiency, it can phosphorylate glucose quickly and trap it in the liver
50
How is G-6-P used in cells?
Used in a pentose pathway to form pentoses and NADPH
Broken down into pyruvate and 2ATP through glycolysis.
Stored as glycogen in skeletal muscle. This occurs if glucose isn't really needed in the cell. When it is needed, glycogen can convert back into G-6-P
51
How does the liver use glycogen?
If blood glucose concentration falls, glycogen can be converted into G-6-P, which can be dephosphorylated into glucose through the enzyme glucose 6-phosphatase. The glucose is then released into the blood
52
What enzyme dephosphorylates G-6-P into glucose, in the liver?
Glucose 6-phosphatase
53
How does skeletal muscle use glycogen?
Enzyme glucose 6-phosphatase is not present. This means that glucose can be converted into G-6-P but cannot be dephosphorylated into glucose
Instead G-6-P is broken down through glycolysis to make lactate
54
How is glycogen synthesised?
Glycogen cannot be from directly from glucose monomers and is synthesised in two steps.
First step involves an enzyme called glycogenin, which covalently binds to glucose from UDP-glucose to form chains of glucose and UDP. Then another enzyme called glycogen synthase, extends the glucose monomers attached to the glycogenin
Second step involves the chains formed from glucose synthase being broken down by glycogen-branching enzyme and re-attached through alpha one to alpha six bonds to give branch points. This increases the number of non-reducing ends, which means more branches can be added This explains why glycogen is a highly branched molecule.
55
What enzymes are involve din glycogen synthesis?
Glycogenic
Glycogen synthase
Glycogen-branching enzyme
56
How is glycogen degraded back into glucose?
Glucose monomers are removed one at time from the non-reducing ends of glycogen. They are removed by the enzyme glycogen phosphorylase, as G-1-P, which is glucoses with a phosphate bonded onto their first carbon
Glycogen phosphorylase can't remove all of the glucose monomers as it can't recognise glucose near the branch. These glucose molecules are removed by a de-branching enzyme.
G-1-P is then converted into G-6-P
57
What are cellulose and hemicellulose (oligosaccharides)?
Fibrous proteins
Cannot be digested by the gut as we don't have the enzyme which breaks then down. Instead they are partially broken down by gut bacteria, which produces methane and hydrogen, which is gas.
58
Why are oligosaccharides an important part of our diet?
They increase faecal bulk and decrease transit time
Therefore if we don't eat enough of them, it can lead to poor health
59
What are disaccharidases?
Enzymes that break down disaccharides into monosaccharides
60
What happens if you are deficient in disaccharides?
Cramps
Abdominal digestion
61
What is lactose intolerance?
Disaccharide deficiency
Occurs because undigested lactose is broken down by gut bacteria, causing gas build up and irritant acids.
It also occurs because lactose is osmotically inactive, thus drawing water from the gut into the lumen, causing diarrhoea
62
How can we avoid the symptoms of lactose intolerance?
Avoiding milk products
Using milk products treated with fungal lactase
Supplementing diet with lactase
63
What is glycolysis?
A series of catabolic reactions, which don't require oxygen, that splits glucose into pyruvic or lactic acid.
ATP is also formed during glycolysis. It is the only way that ATP can be formed from glucose when oxygen is absent in cells
64
Where does glycolysis take place?
Cytosol, which means you don't require mitochondria for glycolysis
65
What is substrate level phosphorylation?
Glycolysis
66
How many steps are in glycolysis?
10
67
What are the two phases of glycolysis?
Preparatory phase
Payoff phase
68
How many ATP are invested during the preparatory phase?
2 ATP per glucose molecule
69
How many ATP are gained during the payoff phase?
4 ATP per glucose molecule
70
What is the net total of ATP formed from glycolysis?
2 ATP per glucose molecule
71
Describe the important steps of glycolysis.
PREPARATORY PHASE.
1. Glycolysis is phosphorylated into G-6-P. This process requires one ATP molecules and is irreversible, G-6-P is now trapped in the cell.
Catalyst - hexokinase
2. G-6-P is converted into F-6-P.
3. F-6-P is phosphorylated to F-1,6-P. There are now two phosphate groups on the structure, which repel one another, which means that the splitting of the molecule in step four is made easier. This process requires one ATP molecule and is irreversible. The first committed step of glycolysis, as F-1,6-P is only used in glycolysis
Catalyst - phosphofructokinase
4. F-1,6-P is split into two different molecules due to the two phosphate molecules repelling one another. The two molecules are formed of 3 carbons, G-3-P and DHAP.
5. Only G-3-P can participate in glycolysis, which means that DHAP is converted into glycolysis. This means that we know have two G-3-P molecules
PAYOFF PHASE.
6. Two G-3-P is converted into two 1,3-bisPG molecules. We also produce two NADH molecules
7. Two 1,3-bisPG is converted into two 3-PG molecules to form 2ATP molecules.
10. Phosphate molecule from PEP is transferred to ADP. Due to there being 2 PEP, 2ATP are formed. The end product is pyruvate, which is passed onto the citric acid cycle if oxygen is available. This is an irreversible reaction.
Catalyst - pyruvate kinase
72
What are the three irreversible steps of glycolysis?
Step one
Step three
Step ten
73
What step is hexokinase involved in glycolysis? What is its role?
Step one
Converts glucose into G-6-P
74
What step is phosphofructokinase-1 involved in glycolysis? What is its role?
Step three
Converts F-1-P into F-1,6-P
75
What is the first committed step of glycolysis?
Step three
76
What two steps require ATP?
Step one
Step three
77
What is substrate-level phosphorylation?
Results in formation of ATP or GTP by direct transfer of a phosphate group to ADP or GDP from a phosphorylated compound
78
What is oxidative phosphorylation?
ATP is generated from the oxidation of NADH and FADH2 and the subsequent transfer of electrons and pumping of protons
79
What step is pyruvate kinase involved in glycolysis? What is its role?
Step ten
Converting PEP into pyruvate
80
What is the redox balance in glycolysis?
If there is no NAD+ glycolysis can't occur as it is needed for step six. In this step it binds to H to form NADH.
If oxygen is present, then the pyruvate produced from glycolysis will be converted into lactate. During this conversion, NAD+ will be replenished as the NADH produced from step six will be broken back down into NAD+ and H.
81
What happens to pyruvate in yeast cells?
Form ethanol and CO2.
82
What happens to pyruvate in human cells?
If oxygen is present, undergoes citric acid cycle and electron transport chain to form ATP, CO2 and H2O
If oxygen or mitochondria is absent, undergoes fermentation to form lactate
83
Describe the process of fermentation
Pyruvate is converted into lactate
During this process, NADH is oxidised into NAD+ and h, which can replenish the stores of NAD+ needed for glycolysis
Cori cycle then occurs
84
Describe the cori cycle
Lactate is passed into the blood and travels to the liver, where it can undergo glucogenesis and converted back into pyruvate.
Pyruvate is then converted back into glucose. This glucose molecule is then transported into muscles to take part in glycolysis again.
85
What is glucogenesis?
When non-carbohydrate molecules are converted into glucose.
86
Where does glucogensis take place?
Liver
87
Why is glucogenesis not the reverse of glycolysis? Why is this good?
Not all the steps of glycolysis are reversible.
Require a separate set of enzymes, which means that the processes are controlled separately. Only one process occurs at a time, prevents them from cancelling each other out.
88
Why are steps one, three and ten irreversible?
Large, negative delta G values. This means that thy would require a lot of energy to be supplied to reverse it, making it energetically unfavourable.
89
Are the steps in glucogenesis that replace the irreversible steps of glycolysis, also irreversible? What does this mean?
Yes
Both glucose and glucogenesis as whole processes are irreversible
90
Where are steps A + B (both replace step 10 of glycolysis) taken place?
Mitochondria
91
Where is step C (replace step 3 of glycolysis) taken place?
Cytoplasm
92
What are steps A and B in glucogenesis?
Replace the irreversible step ten of glycolysis.
A - Involves pyruvate entering the mitochondria and being converted into oxoloacetate.
B - oxoloacetate undergoing reactions in the mitochondria to form PEP in the cytoplasm
93
What is step C in glucogenesis? What is the catalyst of this step?
Replaces the irreversible step three of glycolysis
C - control point as it is an irreversible step of glucogenesis. If a direct reverse of glycolysis, it would require ATP to be made again which is energetically unfavourable. Instead phosphate is just removed from F-1,6-P to form F-6-P and isn't added onto ADP.
Catalyst - fructose 1,6-biphosphatase
94
What is step D in glucogenesis?
Replaces the irreversible step one of glycolysis
D - If a direct reverse of glycolysis, it would require ATP to be made again which is energetically unfavourable. Instead phosphate is just removed from G-6-P to form glucose and isn't added onto ADP.
95
Where does step D (replaces step one in glycolysis) in glucogenesis take place?
Usually, after G-6-P is formed during glucogeneis, glucogenesis stops. This allows the cell to trap it in the cell.
Step D is carried out in the lumen of the endoplasmic reticulum, which is a structure found in the cytoplasm. Contains proteins which allow G-6-P to be transported in and glucose to be transported back into the cytoplasm
96
How is galactose fed into the glycolysis pathway? What enzyme does this?
Converts into G-6-P and enters the glycolysis pathway at step two.
Galactokinase
97
How is fructose fed into the glycolysis pathway? What two enzymes do this?
Different stages depending on the tissue it is found in.
If it is found in adipose tissue, it can be converted into F-6-P, which enter at step three
If it is found in the liver, it can be converted into DHAP AND G-3-P and enter at stage five. This is known as the fructose 1-phosphate pathway. This pathway uses one or two ATP for each fructose molecule converted.
Aldolase + Triose kinase
98
What is the pentose phosphate pathway?
Produces NADPH and pentoses (5C sugars)
99
Describe the pentose phosphate pathway
Two phases; the oxidative, irreversible phase and the non-oxidative, reversible phase.
Oxidative - generates NADPH by converting G-6-P into a pentose phosphate (catabolic)
Non-oxidative - pentose phosphate to convert back to G-6-P (anabolic)
These two reactions are coupled together by NADPH and NAP+. When coupled, they generate lots of NADPH, as we build stuff up to break it down again which forms NADPH. The pathway that we build stuff again is not the direct reversal of the oxidative phase, which means that we don't break down the NADPH formed and just continue to form more.
100
What is NADP+?
An electron carried. It has a phosphate attached to it and NAD+ doesn't.
It is involves in the pentose pathway not glycolysis like NAD+
The enzymes involves in these reactions have different spceifities for these electron carriers which stops them being used for the wrong reaction
101
What inhibits glucogenesis?What is the effect of reduced glucogenesis?
Ethanol is able to inhibit glucogenesis. This leads to an increased blood concentration of lactate and glucose.
102
Where does the citric acid cycle occur?
Mitochondrial matrix.
103
Does the citric acid cycle produce ATP?
No, it instead removes electrons from molecules and passes these electrons onto electron carriers to form NADH and FADH2.
These electron carriers are then passed onto the electron transport chain, which produces lots of ATP.
104
Why is the citric acid cycle very efficient?
Cyclical
Only a small number of reactant molecules is needed to make lots of NADH and FADH2.
105
Does the citric acid cycle require oxygen? Why?
Yes
To produce CO2
106
How is pyruvate converted into acetyl coA?
Pyruvate dehydrogenase converts pyruvate into acetyl coA. It does this by removing a C from the pyruvate.
This process releases two electrons in the form of two H ions. These are passed onto NAD to form NADH.
The decarboxylated pyruvate is then added to a coA complex.
107
Where is acetyl coA formed?
Mitochondrial matrix
108
Describe the structure of pyruvate dehydrogenase
Contains copies of three enzyme subunit. Each subunit carries out a different part of the reaction.
E1 - decarboxylates pyruvate
E2 - transfers coA to the decarboxylated pyruvate
E3 - produces NADH
109
Describe the citric acid cycle
Acetyl coA combines with oxoloacetta to form citrate. The citrate molecules is broken down.
During its break down,, two carbons are removed and GTP is formed. GTP can be readily converted into ATP, hence ATP is indirectly formed from this process.
Eventually, we form oxoloacetate again which can combine with acetyl coA to form citrate and start the cycle again.
110
How is the start of the citric acid cycle controlled?
Pyruvate dehydrogenase is regulated by its products (acetyl coA and NADH) and ATP through negative feedback.
When ATP, NADH and acetyl CoA concentrations are high, more of these reactants bind to PDH and inhibit its activity. This decreases the rate of the citric acid cycle as less acetyl coA is produced.
When ATP, NADH and acetyl coA concentrations are low, less of these reactants bind to PDH and inhibit its activity. This increases the rate of the citric acid cycle as more acetyl CoA is produced.
PDH is also regulated by private and ADP through positive feedback.
When pyruvate and ADP concentrations are high, they can bind to PDH and active it. This increases the rate of the citric acid cycle as more acetyl coA is produced.
111
How is the first control point of the citric acid cycle controlled?
Isocitrate dehydrogenase is controlled by ATP and NADH through negative feedback.
When ATP and NADH concentrations are high, they will bind to the enzyme and inhibit its activity, decreasing the rate of the citric acid cycle.
When ATP and NADH concentrations are low, they will inhibit less of the enzyme and increase the citric acid cycle rate.
Isocitrate dehydrogenase is also controlled by ADP through positive feedback
When concentrations of ADP are high, it binds to the enzyme and activates it, increasing the rate of the citric acid cycle.
112
How is the second control point of the citric acid cycle controlled?
Alpha-ketoglutarate is controlled by NADH, ATP and succinyl coA through negative feedback.
When ATP, NADH and succinyl coA concentrations are high, they will bind to the enzyme and inhibit its activity, decreasing the rate of the citric acid cycle.
When their concentrations are low, they will inhibit less and increase the citric acid cycle rate.
113
What is the amphilobic pathway?
The pathway that converts the intermediates of the citric acid cycle into nucleotide bases, heme groups and proteins - when the cellular energy needs have been meet
114
What happens if the citric acid cycle stops due to low concentrations of citric acid cycle intermediates? What is this reaction called?
We top up the concentration of oxoloacetate through glucogenesis, as pyruvate can be converted into oxoloacetate in this pathway. This conversion is carried out by pyruvate carboxylase.
Anaplerotic
115
What is pyruvate carboxylase? How is it activated?
Converts pyruvate into oxloacetate in glucogenesis.
Acetyl coA, which means that when there are higher concentrations of acetyl coA more pyruvate is converted into oxoloacetate.
116
Where is the electron transport carried out?
Inner mitochondrial membrane
117
What is the outer membrane of the mitochondria?
Transports molecules from the cytoplasm into the inter membrane space.
118
What is the inner membrane of the mitochondria?
Transports molecules from the inter membrane into the matrix
119
Describe the structure of the inner membrane of mitochondria.
Folded
Forms cristae, which increases the surface area of the membrane and allows more proteins to be packed into it
120
How is NADH and FADH formed in glycolysis transported from the cytoplasm into the inter membrane space of the mitochondria?
NADH - cannot cross outer membrane, so uses the glycerol phosphate shuttle
FADH - passes through the outer membrane
121
Describe the glycerol phosphate shuttle. What is the disadvantage of this process?
NADH passes its electrons to G-3-P, which passes through the outer membrane. G-3-P then passes the electrons to FADH2.
Oxidation of FADH2 in the electron transport chain generates less ATP than oxidation of NADH.
122
What is the role of complex one in the electron transport chain?
Oxidises NADH to remove two electrons from the molecule and allow them to pass through it.
Electrons are passed through FMN (prosthetic group) in the protein. FMN consists of Fe-S centres, which are where the electrons specifically through through
These electrons combine with ubiquinone (Q) to form ubiquinol (QH2).
QH2 is then passed onto complex three
The movement of electrons through the protein, pumps hydrogens across the inner membrane into the intermemrbane space
123
What three molecules can inhibit complex one?
Amytal
Piercidin A
Rotenone
124
What is the role of complex two in the electron transport chain?
Oxidises FADH2, which removes electrons and allows them to passed through it
The electrons are passed through Fe-S centres.
Once they reach ubiquionone (Q) they combine with it form ubiquinol (QH2).
QH2 is then passed onto complex three.
The movement of electrons through the protein, DOES NOT pumps hydrogens across the inner membrane into the intermemrbane space
125
Why is there a heme group attached to complex two and three?
Blocks stray electrons
Which is important as if they leak from the complex, they can form free radicals and form cancer
126
What is the role of complex three in the electron transport chain?
Removes the electrons from QH2 and passes them onto cytochrome C.
Cytochrome C is a shuttling protein that shuttles electrons between complex three and four
1QH2 produces two reduced cytochrome C molecules.
The movement of electrons through the protein, pumps hydrogens across the inner membrane into the intermemrbane space
127
What is the role of complex four in the electron transport chain?
Removes electrons from cytochrome C and passes them through Fe-Cu centres.
Electrons then combine with oxygen.
The movement of electrons through the protein, pumps hydrogens across the inner membrane into the intermemrbane space
128
Why does NADH produce more ATP than FADH2?
Complex one pumps protons across the inner membrane but complex three doesn't
129
What is chemiosmosis?
The movement of protons from the matrix to the intermembrane space
130
What is the proton motive force?
The process where protons flow back down their concentration gradient and release energy to do work
131
What drives the proton motive force?
Chemical potential
Electrical potential
132
Why are chemiosmosis and the proton motive force considered as energy transformations?
Potential energy in protons is converted into potential energy in ATP
133
What protein do protons flow from the intermembrane space back into the matrix through?
ATP synthase
134
What is the role of ATP synthase?
Converts ADP + Pi into ATP
135
What are the two components of ATP synthase?
F0 - membrane bound proton conducting unit. Formed from 10 subunits which all connect to F1. It lets one protein leave as another one enters. Each time this occurs, the whole unit moves one 'notch' int he membrane. It also collects energy from the proton motive force.
F1 - protrudes into the mitochondria matrix, place of ATP synthesis. It produces ATP from the energy collected by F0 (proton motive force energy). It consists of three alpha and three beta subunits
136
What are the three stages of ATP synthesis?
1. ADP + Pi enter one of the beta subunits. These substrates interact with one another but don’t bind yet. This makes sense because we have to put energy in to form ATP.
2. The first step causes the F0 subunit to rotate. This rotational results in a conformation change in the beta subunit that contains the substrates.
3. This conformational change causes ADP + Pi to bind together and form ATP, which is then released from the protein.
137
What is the binding change mechanism?
Describes the rotational movement of the F0 subunit during ATP synthase.
When the F0 rotates...
a beta subunit that contains ADP + Pi forms ATP
a beta subunit that contains ATP releases it
a beta subunit that is empty binds to ADP + Pi
138
What does the coupling of the electron transport chain and ATP synthesis mean?
If the inner mitochondrial membrane becomes permeable to protons, the proton gradient cannot be generated.
If this happened, the electron transport chain can still occur, with oxygen being reduced to water and carbon dioxide but no ATP production can occur.
This therefore results in the two processes being uncoupled.
The energy released from electrons passing along the electron transport chain does not make ATP and is released as heat instead.
139
What can increase uncoupling of the electron transport chain and ATP synthesis?
Malignant hyperthermia is a disease caused by leaky mitochondrial membranes that uncouple electrons transport chain and ATP synthase.
Individuals that are exposed to halothane are more susceptible to this disease, as halothane is believed to make the inner mitochondrial membranes in muscle leaky.
140
When does intentional uncoupling of the electron transport chain and ATP synthesis occur? How does it occur?
Occurs in new-born infants.
If a baby becomes cold, nor-epinephrine triggers the opening of a channel in a protein called thermogenin.
Thermogenin is a proton transporter and sits on the inner mitochondrial membrane of brown fat cells, which contain a lot of mitochondria.
