Glycolysis. Flashcards
1
Q
What is glycolysis?
A
The process used by the body to break down and obtain energy from glucose.
2
Q
Which cells will glycolysis primarily occur in?
A
In almost every cell in the body.
3
Q
Does glycolysis occur under aerobic or anaerobic conditions?
A
It can occur under either aerobic or anaerobic conditions.
4
Q
What part of the cell does glycolysis occur in?
A
The cytoplasm.
5
Q
Why are blood glucose levels so tightly controlled?
A
Because, too much or too little glucose in the bloodstream can lead to debilitating effects for the individual.
6
Q
What is the condition called, when there is too much glucose in the bloodstream?
A
Hyperglycaemia.
7
Q
What is the condition called, when there is too little glucose in the bloodstream?
A
Hypoglycaemia.
8
Q
What food group is broken down to give glucose?
A
Carbohydrates.
9
Q
What are the 4 pathways that involve the metabolism of glucose?
A
Glycolysis.
Glycogenolysis.
Gluconeogenesis.
Glycogenesis.
10
Q
What are the 2 metabolic pathways that consume glucose?
A
Glycolysis.
Glycogenesis.
11
Q
What are the 2 metabolic pathways that produce glucose?
A
Gluconeogenesis.
Glyogenolysis.
12
Q
What does the glycolysis pathway do?
A
Glycolysis takes glucose and will break it down to create energy in the form of ATP.
13
Q
Does glycolysis take place in the fasting state or the well fed state?
A
Well fed state.
14
Q
What does the glycogenesis pathway do?
A
This pathway takes glucose molecules and stores them as glycogen.
15
Q
Why does glycogenesis convert glucose to glycogen?
A
Glycogen is made when glucose levels are high so that the energy can be store and then used to produce energy when glucose levels are low.
16
Q
Does glycogenesis take place in the fasting state or the well fed state?
A
In the well fed state.
17
Q
What does the gluconeogenesis pathway do?
A
This pathway will synthesise glucose from smaller molecules when glucose levels are low.
18
Q
Why does gluconeogenesis take place in the fasting state or the well fed state?
A
In the fasting state.
19
Q
What does the glycogenolysis pathway do?
A
It releases glucose into the bloodstream by breaking down stored glycogen.
20
Q
Why does glycogenolysis take place in the fasting state or the well fed state?
A
In the fasting state.
21
Q
How is glucose bought into the cell from the bloodstream?
A
By specific transport proteins.
22
Q
Can any transport protein carry any organic molecule?
A
No.
Each class of transport protein can only carry one form of organic molecule.
23
Q
Where are transport proteins found?
A
Embedded into the cell membrane.
24
Q
Where are GLUT-1 transporters found?
A
In all cells except the kidney and small intestinal cells.
25
What is the function of GLUT-1 transporters?
They have a high affinity for glucose and will transport it from the bloodstream into the cell.
26
Is there anything GLUT-1 transporters won't carry?
Galactose or fructose.
27
Where are GLUT-2 transporters found?
These are found in red blood cells, pancreatic beta cells and kidney tubules.
28
What is the function of GLUT-2 transporters?
It can transport glucose in and out of the cell and is said to be bi-directional.
At high blood glucose levels, it will initiate glucose uptake in the liver and serves as a glucose sensor for insulin independent cells.
29
What is the specificity of GLUT-2 transporters?
It will transport glucose but has a higher affinity for galactose and fructose.
30
Where are GLUT-3 transporters found?
In the neurons, placenta and testes.
31
What is the function of GLUT-3 transporters?
It is similar to GLUT-1 as it has a high affinity for glucose and galactose, but not fructose.
32
Where are GLUT-4 transporters found?
In skeletal and cardiac muscle and also in fat tissue.
33
What are the characteristics of GLUT-4 transporters?
It is the only insulin sensitive transporter.
Meaning that insulin can activate the cell surface receptor of GLUT-4 which will increase the amount of receptors.
34
Where are GLUT-5 transporters found?
Small intestine, sperm, brain, kidney, muscle and fat tissue.
35
What is the function of GLUT-5 transporters?
This is mainly used to transort fructose for which it has a high affinity.
36
Is there anything GLUT-5 transporters won't carry?
They do not have a high affinity for glucose or galactose.
37
Where are GLUT-7 transporters found?
In the ER membranes of the liver and pancreas cells (hepatocytes).
38
Which type of transporters are not found in the cell membrane?
GLUT-7 transporters.
39
Where are SGLUT-7 transporters found?
In the epithelial cells of the small intestine and kidneys.
40
What is the function of GLUT-7 transporters?
It moves glucose from the lumen of the ER to the cytoplasm so that it can be released from the cell by GLUT-2.
41
What is the function of SGLUT-7 transporters?
It co-transports glucose or galactose with Na+ from the intestinal lumen. This allows it to go against a concentration gradient.
42
Is there anything SGLUT-7 transporters won't carry?
Fructose.
43
Diabetics often have problems with which glucose transporter?
GLUT-4.
44
Why do diabetics often have a problem with the GLUT-4 transporter?
If GLUT-4 transporters are faulty, then the cells cannot sense rises in insulin and glucose will remain in the bloodstream an not enter the cell.
45
How many carbons does glucose have?
6.
46
What is 1 molecule of glucose broken down to at the end of glycolysis?
2, 3 carbon pyruvate molecules.
47
How many steps are there in glycolysis?
9 in aerobic glycolysis.
10 in anaerobic glycolysis.
48
Glycolysis produces energy in what forms?
ATP and NADH.
49
Why is there an extra step in anaerobic glycolysis?
Because, pyruvate is converted to lactate as the electron transport chain cannot occur without oxygen.
50
Does the conversion of pyruvate to lactate require any energy?
Yes.
1 NADH is used to convert a pyruvate molecule to lactate.
51
Does aerobic or anaerobic glycolysis produce more energy?
Aerobic glycolysis as anaerobic glycolysis uses up 2 NADH molecules when the 2 pyruvates are converted to lactate.
52
What are the 2 distinct stages that glycolysis can be broken down to?
The energy investment stage.
The energy pay off stage.
53
How many ATPs are invested in the energy investment phase?
2.
54
How many ATPs are generated in the energy pay off phase?
4 ATPs are generated along with 2 NADH molecules.
55
How many gross ATPs are generated by glycolysis?
4.
56
How many net ATPs are generated by glycolysis?
2 as 2 ATPs are used up to initiate glycolysis.
57
How many NADH molecules are generated by glycolysis?
2.
58
How many pyruvate molecules are generated by glycolysis?
2.
59
What is generated by anaerobic glycolysis?
2 ATPs and 2 lactate molecules.
60
How does the brain oxidise glucose?
It will get all of the energy it can out of glucose and will oxidise it all the way to CO2 via the TCA cycle and the electron transport chain.
61
How does the liver oxidise glucose?
It will oxidise glucose to CO2.
It can form lactate from pyruvate.
It can convert pyruvate to ACoA and then to fat, so that the energy can be stored for later use.
62
What organ is responsible for releasing glucose into the bloodstream?
The liver.
63
How does adipose tissue oxidise glucose?
It will convert pyruvate to ACoA and then to fat.
64
How does muscle oxidise glucose?
It will usually convert pyruvate to CO2.
Except under anaerobic conditions during strenuous exercise, where it will form lactate instead.
65
How do erythrocytes oxidise glucose?
They are only able to oxidise glucose to lactate.
66
Why can erythrocytes only form lactate from glycolysis?
Because they have no mitochondria.
To completely oxidise glucose to CO2, mitochondria must be present.
67
What is the only form of energy for red blood cells?
Glycolysis.
68
When will glucose be converted to glycogen?
If there is sufficient energy levels in the body, glucose will be stored as glycogen and its energy will be saved for later use.
69
How many steps of glycolysis make up the energy investment phase?
The 1st 3 steps of glycolysis are the energy investment phase.
70
In what step of glycolysis are the 2 NADH molecules generated?
In step 5.
71
In what steps of glycolysis are the ATP molecules generated?
In steps 6 and 9.
72
What are the irreversible steps of glycolysis?
Steps 1, 3 and 9.
73
Is step 1 of glycolysis reversible or irreversible?
It is an irreversible, rate limiting step,
74
What happens in step 1 of glycolysis?
Glucose is bought into the cell by a GLUT-1 transporter.
An ATP molecule is used to phosphorylate glucose at carbon 6 to form glucose 6 phosphate.
75
What enzyme is used in step 1 of glycolysis?
Hexokinase or glucokinase.
76
Hexokinase and glucokinase are examples of what kind of family of enzymes?
They are isozymes of each other.
77
How much energy is used in step 1 of glycolysis?
1 ATP.
78
Is step 2 of glycolysis reversible or irreversible?
It is reversible.
79
What happens in step 2 of glycolysis?
An isomerisation reaction takes place and glucose 6 phosphate becomes fructose 6 phosphate.
The carbonyl group is moved from carbon 1 to carbon 2, nothing else changes.
80
In step 2, the sugar is converted from what form to what form?
An aldose sugar to a ketose sugar.
81
What enzyme is used in step 2 of glycolysis?
Phosphoglucose isomerase.
82
Why is glucose phosphorylated in step 1 of glycolysis?
So that it cannot leave the cell.
83
Is step 3 of glycolysis reversible or irreversible?
Irreversible, rate limiting step.
84
What happens in step 3 of glycolysis?
Fructose 6 phosphate is phosphorylated at carbon 1 and the molecule becomes fructose 1, 6 bisphosphate.
85
Which step is often said to be the most important step in glycolysis?
Step 3.
86
How much energy is used up in step 3 of glycolysis?
1 ATP.
87
What enzyme is used is step 3 of glycolysis?
Phosphofructokinase 1.
88
How is phosphofructokinase-1 activated?
Usually by fructose 2,6-bisphosphate and also by low energy molecules.
89
How is phosphofructokinase-1 inhibited?
It is allosterically inhibited by high energy molecules such as ATP and citrate.
90
Why do high energy molecules inhibit glycolysis?
Because, there are already too many high energy molecules and any more energy can be stored as glycogen.
91
Is step 4 of glycolysis reversible or irreversible?
Reversible.
92
What is the 1st thing that happens in step 4 of glycolysis?
Fructose-1,6 BP is broken in half by aldolase and H2O to produce 2 molecules which are dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate.
93
What is the 2nd thing that happens in step 4 of glycolysis?
Next, an enzyme called triose phosphate isomerase converts DHAP to G 3-P.
This gives 2 G 3-P molecules.
94
What enzymes are involved in step 4 of glycolysis?
Aldolase and triose phosphate isomerase.
95
Is step 5 of glycolysis reversible or irreversible?
Reversible.
96
What happens in step 5 of glycolysis?
The 2, 3 carbon glyceraldehyde 3-P molecules are each oxidised by an inorganic phosphate to 1,3 bisphosphoglycerate.
97
What is reduced to form the NADH molecules in step 5 of glycolysis?
2 NAD+ molecules.
98
What happens to the NADH that is formed in step 5 of glycolysis?
It can enter the electron transport chain and be used to form ATP.
99
What enzyme is used in step 5 of glycolysis?
Glyceraldehyde 3-phosphate dehydrogenase.
100
How many NADH molecules are formed in step 5 of glycolysis?
2.
101
1 NADH is the equivalent of how many ATP?
1 NADH = 3 ATP.
102
Is step 6 of glycolysis reversible or irreversible?
Reversible.
103
What happens in step 6 of glycolysis?
The 2, 1,3 BPG molecules are converted to 3-phosphoglycerate molecules. This occurs via the breaking of the phosphate bond on carbon 1.
104
What energy is generated in step 6 of glycolysis?
2 ATP (1 per 1,3 bisphosphoglycerate molecule).
105
What is the name of the process by which ATP is formed in step 6 of glycolysis?
Substrate level phosphorylation.
106
How does step 6 of glycolysis differ in red blood cells from other cells?
The enzyme bisphosphoglycerate mutase is used to convert 1,3 BPG to 2,3 BPG in red blood cells.
2,3 BPG is then to form 2,3 bisphosphoglycerate which can bind to haemoglobin.
107
What enzymes are used in step 6 of glycolysis?
Phosphoglycerate kinase and bisphosphoglycerate mutase.
108
Is step 7 of glycolysis reversible or irreversible?
Reversible.
109
What happens in step 7 of glycolysis?
The 2, 3-phosphoglycerates undergo an isomerisation to form 2-phosphoglycerate.
The phosphate group is moved from the 3 position to the 2 position.
110
What enzyme is used in step 7 of glycolysis?
Phosphoglycerate mutase.
111
Is step 8 of glycolysis reversible or irreversible?
Reversible.
112
What happens in step 8 of glycolysis?
The 2 molecules of 2 phosphoglycerate undergo a dehydration reaction and a double bond is formed between carbons 2 and 3.
The new molecules are called phosphoenolpyruvate (PEP).
113
What enzyme is used in step 8 of glycolysis?
Enolase with H2O.
114
Is step 9 of glycolysis reversible or irreversible?
Irreversible, rate limiting step.
115
What enzyme is used in step 9 of glycolysis?
The 2 phosphoenol pyruvate molecules are each de-phosphorylated to pyruvate.
116
What enzyme is used in step 9 of glycolysis?
Pyruvate kinase.
117
How many ATPs are formed in step 9 of glycolysis?
2.
118
How can pyruvate kinase be inhibited?
Glucagon will add a phosphate group to the pyruvate kinase via the CAMP pathway in order to inactivate PK.
119
What is covalent modification?
When an enzyme changes the bond structure within a molecule.
120
When does step 10 of glycolysis occur?
Under anaerobic conditions.
121
Is step 10 of glycolysis reversible or irreversible?
Reversible.
122
What happens in step 10 of glycolysis?
The 2 pyruvates undergo a reduction reaction where the carbonyl group is converted to a hydroxyl group and L lactate is formed.
123
What is formed in step 10 of glycolysis?
2 molecules of L-lactate.
124
In what cells does step 10 of glycolysis always occur?
In red blood cells.
125
What is always the final product of glycolysis in red blood cells?
L-lactate.
126
What enzyme is involved in step 10 of glycolysis?
Lactate dehydrogenase.
127
Step 10 of glycolysis occurs in what cells?
Red blood cells.
The lens.
The cornea.
Kidneys.
Testes.
Leukocytes.
128
What energy is used in step 10 of glycolysis?
2 NADH molecules.
129
Will muscles ever undergo anaerobic glycolysis?
Yes.
When they are performing strenuous exercise.
130
If there is a surplus of NADH in the body, what will be formed?
Lactate.
131
When alcohol is metabolised, what is produced?
Lactate.
132
Will alcoholics have a high amount of lactate in their blood?
Yes.
133
What is lactic acidosis?
When there are high levels of lactate in the bloodstream.
134
Hexokinase is found in what cells throughout the body?
Hexokinase is a widely distributed enzyme that is found in almost every cell in the body.
135
Glucokinase is found in what cells throughout the body?
Only in liver cells and in pancreatic cells.
136
What is the Y axis on the Michaelis Menten graph?
The reaction velocity.
137
What is the X axis on the Michaelis Menten graph?
The substrate concentration.
138
What is Km on a Michaelis Menten graph?
The substrate concentration when the enzyme is at 1/2 Vmax.
139
What is Vmax on a Michaelis Menten graph?
The maximum speed that the enzyme can work at.
140
Is the Km for hexokinase high or low?
The Km for hexokinase is low.
141
Does hexokinase have a low or high affinity for glucose?
A very high affinity.
142
Will hexokinase metabolise glucose at low concentrations?
Yes, due to its high affinity for glucose, hexokinase can metabolise glucose at low concentrations.
143
Does hexokinase have a low or high Vmax?
A low Vmax.
144
Will hexokinase become saturated at high or low glucose concentrations?
At low glucose concentrations due to its low Vmax.
145
What will inhibit hexokinase?
By glucose 6-phosphate which is the end product.
146
The activity of glucokinase will increase with what?
Glucose concentration.
147
Does glucokinase have a low or high Vmax?
A high Vmax.
148
Will glucokinase become saturated at high or low glucose concentrations?
At high glucose concentrations due to its high Vmax.
149
Is the Km for glucokinase high or low?
It is high.
150
Does hexokinase or glucokinase have a higher affinity for glucose?
Hexokinase has a higher affinity for glucose.
151
Will glucokinase be inhibited by glucose-6-phosphate?
No.
152
What is the usual blood glucose concentration?
Between 3 and 5 mili molar.
153
Will hexokinase or glucokinase be saturated at normal blood glucose levels?
Hexokinase is usually saturated at normal blood glucose levels.
154
Will hexokinase or glucokinase respond to an increase in blood glucose levels?
Glucokinase, as it has a higher Vmax.
155
Will hexokinase or glucokinase be more likely to be used after a heavy meal?
Glucokinase, as a meal will increase blood glucose levels.
156
Step 3 of glycolysis depends on the concentration of what molecule?
Fructose-2,6 bisphosphate.
157
Is fructose-2,6 bisphosphate a product of glycolysis?
No.
It is made by a separate pathway.
158
Why is fructose-2,6 bisphosphate so important in step 3 of glycolysis?
It is an allosteric activator of PFK-1 which is the enzyme used in step 3 of glycolysis.
159
Will high or low concentrations of fructose-2,6 bisphosphate enhance or inhibit glycolysis?
High levels of F-2,6-BP will enhance glycolysis.
Low levels of F-2,6-BP will inhibit glycolysis.
160
How is F-2,6-BP made?
F-2,6-BP is made from using fructose-6 phosphate as a substrate, but uses a different enzyme.
161
What enzyme is used to make F-2,6-BP?
Phosphofructokinase-2 (PFK-2).
162
What activates PFK-2?
Insulin.
163
F-2,6-BP is an allosteric activator of what enzyme and will enhance what pathway?
It allosterically activates PFK-1 which allows glycolysis to continue.
164
When is insulin produced by the body?
After a meal or snack.
165
Will PFK-2 be activated when blood glucose levels are high or low?
When they are high.
166
What happens once PFK-2 is activated?
The cellular levels of F-2,6-BP will increase.
167
Will glycolysis occur when blood glucose levels are high or low?
When they are high.
168
Is PFK-2 part of a dual enzyme?
Yes.
169
What is the other half of the dual enzyme that PFK-2 is part of?
Fructose-bisphosphatase-2 (FBP-2).
170
What will FBP-2 do and what will FBPase-2 do in step 3 of glycolysis?
The job of PFK-2 is to make fructose-2,6-bisphosphate.
The job of FBPase-2 is to break F-2,6-BP.
171
Can PFK-2 and FBP-2 work at the same time?
No.
172
How is each part of the dual enzyme activated or inhibited?
Insulin will result in the de-phosphorylation of the enzyme complex to activate PFK-2 and inhibit FBP-2.
Glucagon will phosphorylate the complex to inhibit PFK-2 and activate FBP-2.
173
Phosphorylation is an example of what kind of enzymatic reaction?
Covalent modification.
174
When the body is in the well fed state, what will happen to the dual enzyme in step 3 of glycolysis?
Insulin dephosphorylates the PFK-2, FBP-2 complex.
This activates PFK-2 and F-2,6-BP will be produced.
F-2,6-BP will allosterically activate PFK-1 allowing step 3 of glycolysis to occur.
175
When the body is in the fasting, what will happen to the dual enzyme in step 3 of glycolysis?
Glucagon will phosphorylate the PFK-2, FBP-2 complex via the cAMP pathway.
This activates FBP-2 allowing it to convert F-2,6-BP to fructose-6 phosphate.
This means that FBP-2 have removed F-2,6 BP from the cytoplasm which means that F-2,6 BP is not available to activate PFK-1, resulting in the inhibition of glycolysis and the activation of gluconeogenesis.
176
What hormone does the body produce in the fasting state?
Glucagon.
177
What happens once FBP-2 converts F-2,6 BP to fructose-6-phosphate?
All the F-2,6 BP will be removed from the cytoplasm meaning that F-2,6 BP is not available to activate PFK-1.
This results in the inhibition of glycolysis and the activation of gluconeogenesis.
178
What molecule in step 3 will determine whether glycolysis or gluconeogenesis will occur?
The concentration of fructose-2,6-bisposphate within the cell.
179
If F-2,6-BP levels are high, what will happen?
Glycolysis will occur?
180
If F-2,6-BP levels are low, what will happen?
Gluconeogenesis will occur.
181
What molecule will allosterically stimulate pyruvate kinase in step 9 of glycolysis?
Fructose 1,6 bisphosphate.
182
What molecule will allosterically inhibit pyruvate kinase in step 9 of glycolysis?
ATP.
Alanine.
Via phosphorylation by PKA.
183
How will glucagon de-activate PKA?
Glucagon will activate the cAMP pathway.
The cAMP pathway will activate PKA which will de-activate pyruvate kinase by phosphorylation.
184
When pyruvate kinase is phosphorylated is it active inactive?
Inactive.
185
When pyruvate kinase is not phosphorylated is it active inactive?
Active.
186
How can a deficiency in pyruvate kinase lead to chronic haemolytic anaemia?
Because, red blood cells completely rely on glycolysis for energy and if there is a deficiency in pyruvate kinase, then they are missing out on the 2 ATPs that are produced in step 9 of glycolysis.
187
Chronic haemolytic anaemia affects what factor of red blood cells?
They are killed earlier on as there is a lack of energy.
188
Hexokinase is found where?
In most tissues.
189
Hexokinase is inhibited by what?
By glucose 6-phosphate. (Product).
190
Does hexokinase have a high Km?
Yes.
It works when glucose concentrations are low.
191
Hexokinase has a high affinity for what?
Glucose.
192
Does hexokinase have a high or low Vmax?
Low V max meaning that it does not work well when glucose concentrations are high.
193
What is the main function of hexokinase?
To maintain the levels of glucose 6-P for energy production.
194
Glucokinase is found where?
In the liver and the pancreas.
195
Glucokinase is inhibited by what?
Nothing.
196
Glucokinase is activated by what?
By insulin.
197
Does glucokinase have a high or low Vmax?
High V max meaning that it works well when glucose concentrations are high.
198
What is the main function of glucokinase?
To prevent hyperglycaemia.
199
Phosphofructokinase 1 is inhibited by what?
By high energy molecules such as ATP and citrate. (Allosteric).
200
Phosphofructokinase 1 is activated by what?
By fructose 2-6 BP, ADP, AMP. (Fructose 2,6 BP is always needed).
201
Pyruvate kinase 1 is inhibited by what?
High levels of ATP. Alanine. ACoA. (Allosteric).
Glucagon. (Hormonal).
Phosphorylation by PKA (covalent).
202
Pyruvate kinase 1 is activated by what?
Fructose 2,6 bispohosphate which is produced in step 1 of glycolysis. (Allosteric).
203
What will up-regulate the 3 rate limiting enzymes in glycolysis?
Insulin.
204
What will repress the 3 rate limiting enzymes in glycolysis?
Glucagon.
205
What are the 4 fates of pyruvate?
Pyruvate to lactate.
Pyruvate to alanine.
Pyruvate to acetyl CoA.
Pyruvate to oxaloacetate.
206
How does pyruvate form lactate?
Under anaerobic conditions it can be converted by a reversible reaction to lactate.
For each pyruvate molecule to be converted to lactate, it requires 1 NADH molecule.
207
How much energy is required for a pyruvate molecule to be converted to lactate?
1 NADH per pyruvate molecule.
208
How is pyruvate converted to alanine?
By a reversible reaction.
209
How is pyruvate converted to ACoA?
It can be oxidised further to acetyl CoA.
This is an irreversible reaction where the goal is to try and get more energy out of pyruvate as ACoA can enter fatty acid synthesis or the electron transport chain.
210
How is pyruvate converted to oxaloacetate?
By an irreversible reaction where it is carboxylated by pyruvate carboxylase to form oxaloacetate which is used in gluconeogensis.
