Carbohydrates Flashcards
(190 cards)
1
Q
What is a monosaccharide?
A
The basic unit/building block of a carbohydrate.
ex: Galactose (Milk only), Glucose (Most common), Fructose.
2
Q
What are disaccharides?
A
2 monosaccharides held together by a glycosidic bond.
ex: Lactose (Glucose + Galactose), Sucrose (Glucose + Fructose), and Maltose (Glucose + Glucose).
3
Q
What is an oligosaccharide?
A
3-10 monosaccharides held together by glycosidic bonds. A short chain.
ex: Glycan, dextran.
4
Q
What is a polysaccharide?
A
11+ monosaccharides held together by glycosidic bonds. A long chain.
ex: Starch, chitin, cellulose.
5
Q
What do carbohydrates need to be broken into to be absorbed?
A
Monosaccharides.
6
Q
Where does polysaccharide digestion begin?
A
In the mouth with alpha-amylase* in the saliva.
*Not necessary for polysaccharide digestion, but helps release some of the sweetness of the polysaccharide. Aids palatability.
7
Q
Where does the polysaccharide go after the mouth?
A
Down the esophagus and into the stomach.
*No breakdown occurs in the stomach.
8
Q
Where does the chyme/digesta go after the stomach?
A
Into the small intestine.
9
Q
What happens when chyme/digesta enters the SI?
A
The duodenum releases cholecystokinin (CCK), which acts on the pancreas to cause the release of pancreatic alpha-amylase.
10
Q
What does the pancreatic alpha-amylase do to the polysaccharides in the digesta?
A
It breaks the polysaccharides into oligosaccharides.
11
Q
What 2 enzymes does the brush border secrete as pancreatic alpha-amylase breaks down polysaccharides into oligosaccharides?
A
- Oligosaccharidase: Breaks oligosaccharides into disaccharides.
- Disaccharidase: Breaks disaccharides into monosaccharides.
12
Q
What happens once the polypeptides in the chyme/digesta are broken into monosaccharides?
A
The monosaccharides are absorbed at the brush border.
13
Q
What type of diffusion is required during monosaccharide absorption?
A
Facilitated diffusion, which requires no energy.
14
Q
What is the first step of glucose and galactose absorption?
A
The monosaccharide passes through the Na+-glucose symporter on the brush border to enter the SI epithelium. 2 Na+ move through the symporter with each monosaccharide.
15
Q
What is the second step of glucose and galactose absorption?
A
The monosaccharide passes through the GLUT2 uniporter and into hepatic portal circulation.
16
Q
What is the first step of fructose absorption?
A
Fructose passes through the GLUT5 uniporter into the SI epithelium.
17
Q
What is the second step of fructose absorption?
A
Fructose passes through another GLUT5 uniporter into hepatic portal circulation.
18
Q
What are galactose and fructose turned into when they reach the liver?
A
Glucose.
19
Q
Where in the body can glucose travel freely and why?
A
In the bloodstream due to being water soluble.
20
Q
What are the two types of glucose transport proteins?
A
- Insulin independent.
- Insulin dependent.
21
Q
Which glucose transport proteins are insulin independent?
A
- GLUT1.
- GLUT2.
- GLUT3.
22
Q
Where is GLUT1 found?
A
In small amounts on all body cells.
23
Q
Where is GLUT1 found in high concentrations?
A
Erythrocytes and the cells lining the blood-brain barrier.
24
Q
What does a high concentration of GLUT1 on a cell indicate about that cell?
A
It is highly dependent on glucose.
25
Why do erythrocytes have the concentration of GLUT1 they do?
Glucose is the only form of energy that RBC's can use due to lacking a mitochondria.
26
What is glucose affinity?
How attractive something is to glucose/how easily glucose passes through it.
27
What is the glucose affinity of GLUT1?
High, meaning glucose will always move through it no matter the concentration.
28
Where is GLUT2 found?
1. SI epithelial cells.
2. Hepatic cells.
3. Pancreatic cells.
*All cells above have a high concentration of GLUT2.
29
What is the glucose affinity of GLUT2?
Low, meaning a high concentration of glucose is needed before glucose can move through GLUT2.
30
Where is GLUT3 found?
Neurons.
*High concentration of GLUT3.
31
What is the glucose affinity of GLUT3?
High.
32
What glucose transport proteins are insulin dependent?
1. GLUT4.
33
Where is GLUT4 found?
1. Adipose cells.
2. Muscle cells.
34
When is GLUT4 expressed?
When insulin is present.
35
What is the glucose affinity of GLUT4?
Low.
36
What is the purpose of some cells having a low glucose affinity?
To make sure that glucose enters those cells only when in high amounts, saving the glucose for those cells that need it most.
37
What two hormones regulate blood sugar?
1. Insulin.
2. Glucagon.
38
What gland secretes insulin and glucagon?
The pancreas.
39
What is insulin secreted in response to?
High blood glucose.
40
When would high blood glucose occur?
Right after a meal.
41
What signals for the release of insulin?
GLUT2 receptors transporting glucose.
42
What is the function of insulin?
To reduce blood glucose to normal levels.
43
How does insulin perform its function?
1. Signals for cellular uptake of glucose.
2. Signals for glucose utilization.
3. Signals for glucose storage.
44
What is glucagon secreted in response to?
The absence of insulin.
45
What is the function of glucagon?
To maintain blood glucose at normal levels.
46
How does glucagon perform its function?
1. Signals for the release of stored glucose.
2. Signals for glucose synthesis.
47
What is the fed state?
The period right after an animal has eaten where blood glucose and insulin are high.
48
What is the fasted state?
The period when the animal has not eaten recently and glucagon is being secreted.
*If prolonged, the animal will eventually reach a starved state.
49
What is the two goals of glycolysis?
1. Turning glucose (6-carbon) into 2 pyruvate (3 carbon).
2. Produce ATP.
50
Where does glycolysis happen?
In the cytosol (the liquid portion of the cell).
51
What enzyme is used to convert glucose into glucose-6-phosphate in the liver?
Glucokinase.
52
What animals lack glucokinase?
Ruminants.
53
What enzyme is used to convert glucose into glucose-6-phosphate in the rest of the body?
Hexokinase.
54
What mechanism is required to convert glucose into glucose-6-phosphate?
The dephosphorylation of ATP into ADP.
55
What enzyme is required to convert glucose-6-phosphate into fructose-6-phosphate?
Phosphoglucose isomerase.
56
What enzyme is required to convert fructose-6-phosphate into fructose 1,6-bisphosphate?
Phosphofructokinase-1.
57
What mechanism is required to convert fructose-6-phosphate into fructose 1,6-bisphosphate?
The dephosphorylation of ATP into ADP.
58
What is important about the conversion of fructose-6-phosphate into fructose 1,6-bisphosphate?
It is the first committed step of glycolysis.
59
What enzyme is required to convert fructose 1,6-bisphosphate into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate?
Aldolase.
60
What enzyme is required to convert dihydroxyacetone phosphate into glyceraldehyde 3-phosphate?
Triose phosphate isomerase.
61
What enzyme is required to convert glyceraldehyde 3-phosphate into 1,3-bisphosphoglycerate?
Glyceraldehyde 3-phosphate dehydrogenase.
62
What mechanism is required to convert glyceraldehyde 3-phosphate into 1,3-bisphosphoglycerate?
The reduction of NAD+ to form NADH. 2 Pi are added in and 2 H+ come out.
63
What enzyme is required to convert 1,3-bisphosphoglycerate into 3-phosphoglycerate?
Phosphoglycerate kinase.
64
What mechanism is required to convert 1,3-bisphosphoglycerate into 3-phosphoglycerate?
The phosphorylation of an ADP to create ATP.
65
What enzyme is required to convert 3-phosphoglycerate into 2-phosphoglycerate?
Phosphoglycerate mutase.
66
What enzyme is required to convert 2-phosphoglycerate into phosphoenolpyruvate?
Enolase.
67
What enzyme is required to convert phosphoenolpyruvate into pyruvate?
Pyruvate kinase.
68
What mechanism is required to convert phosphoenolpyruvate into pyruvate?
The phosphorylation of an ADP to form ATP.
69
How many ATP are consumed by glycolysis?
2 ATP.
70
How much gross ATP is generated by glycolysis?
9.
71
How much net ATP is generated by glycolysis?
7.
72
How much ATP is generated from the phosphorylation of ADP?
4.
73
What is the energy equivalency of the reduction of NAD+ into NADH?
2.5 ATP.
74
How much ATP is generated from the reduction of NAD+ to NADH?
5.
75
At what 4 steps is glycolysis regulated?
1. Glucose transport.
2. Glucokinase.
3. Phosphofructokinase-1.
4. Pyruvate kinase.
76
How is glucose transport regulated using GLUT2?
GLUT2 only allows for the transport of glucose when glucose is in high concentrations. This means that glycolysis can only happen in the liver and pancreas when blood glucose is high.
77
How is glucose transport regulated using GLUT4?
GLUT4 only allows for the transport of glucose in the presence of insulin. This means that glycolysis can only happen in adipose and muscle tissue in the presence of insulin.
78
How is glucokinase regulated?
Glucokinase requires high intracellular glucose in order to be active. So, if intracellular glucose is not high enough, glycolysis cannot happen.
79
What is glucokinase's glucose affinity?
Low.
80
How is phosphofructokinase-1 regulated by ATP?
High ATP concentration inhibits the activation of phosphofructokinase-1 to prevent more ATP from being made. Any of the unused reactants are stored.
81
How is phosphofructokinase-1 regulated by insulin?
1. The presence of insulin activates phosphofructokinase-2.
2. Phosphofructokinase-2 converts fructose 6-phosphate into fructose 2,6-bisphosphate.
3. Fructose 2,6-bisphosphate activates phosphofructokinase-1.
82
How is pyruvate kinase regulated through activation?
Pyruvate kinase is activated by the presence of fructose 1,6-bisphosphate.
83
How is pyruvate kinase regulated through inhibition?
Pyruvate kinase is inhibited by the hormone glucagon, which allows pyruvate to be converted into phosphoenolpyruvate.
84
What is glycogen?
Complex polymer of glucose molecules.
85
What is the name of the protein at the center of a glycogen molecule?
Glycogenin.
86
What does the shape of a glycogen molecule allow for?
Glucose to be released from many different sites.
87
Where is glycogen found?
1. Liver.
2. Muscle.
88
What % of the liver's weight is glycogen?
Up to 6%.
89
Why is glycogen found in the liver?
To restore blood glucose.
90
How much glycogen is stored in the liver?
Enough for an overnight fast.
91
What % of the weight of muscles is glycogen?
Up to 1%.
92
Why is glycogen found in muscles?
For use in muscle contractions.
93
What kinds of chains are found in glycogen?
1. Branched chains/branch points.
2. Straight chains.
94
What kind of bonds connect straight chains?
alpha-1,4 (glycosidic) linkages.
95
What kind of bonds connect branch points?
alpha-1,6 (glycosidic) linkages.
96
What is the synthesis of glycogen called?
Glycogenesis.
97
Where does glycogenesis happen?
Cytosol.
98
What enzyme is required to convert glucose into glucose 6-phosphate in the liver?
Glucokinase.
99
What enzyme is required to convert glucose into glucose 6-phosphate in the muscle?
Hexokinase.
100
What mechanism is required to convert glucose into glucose 6-phosphate?
The dephosphorylation of ATP into ADP.
101
What enzyme is required to turn glucose 6-phosphate into glucose 1-phosphate?
Phosphoglucomutase.
102
What enzyme is required to convert glucose 1-phosphate into uridine diphosphate (UDP) -glucose?
UDP-glucose pyrophosphorylase.
103
What mechanism is required to convert glucose 1-phosphate into uridine diphosphate (UDP) glucose?
The dephosphorylation of uridine triphosphate and glucose 1-phosphate. Led to the release of pyrophosphate (PPi) and the bonding of UDP to glucose.
104
What enzyme is required to convert uridine diphosphate-glucose into (Glucose)_n+1?
Glycogen synthase.
105
What mechanism is required to convert uridine diphosphate-glucose into (Glucose)_n+1?
(Glucose)_n is attached to the glucose (+1) and UDP is removed to allow this to happen.
106
How is the glucose attached to the glycogen during glycogenesis?
Using alpha-1,4 (glycosidic) linkages.
107
What enzyme complex is required to add branch points to (Glucose)_n+1?
Branching enzymes.
108
How do branching enzymes function?
It activates once an 11 glucose chain has formed and removes a 7 glucose chain and adds it to another glucose at an alpha-1,6 linkage that is at least 4 glucoses away from all existing branch points.
*Added to the 4th glucose.
G(B)--G--G--G--G (B)
109
What are the two steps that glycogenesis is regulated at?
1. Glucose transport.
2. Glycogen synthase.
110
How is glucose transport regulated in the liver during glycogenesis?
GLUT2 will only transport glucose when blood glucose is high, due to having a low glucose affinity. Therefore, glycogenesis can only happen in the liver when blood glucose is high and glucose storage is needed.
111
How is glucose transport regulated in the muscle during glycogenesis?
GLUT4 will only transport glucose in the presence of insulin, due to being insulin dependent. Therefore, glycogenesis can only happen in the muscle when insulin is present, which requires blood glucose to be high.
112
How is glycogen synthase regulated through dephosphorylation?
Glycogen synthase is active when it is dephosphorylated by proteinphosphotase-1, which is activated by insulin.
113
How is glycogen synthase regulated through phosphorylation?
Glycogen synthase is deactivated when it is phosphorylated by protein kinase-a, which is activated by glucagon.
114
What is the breakdown of glycogen called?
Glycogenolysis.
115
Where does glycogenolysis occur?
Cytosol.
116
What is the end-product of glycogenolysis in the liver?
Glucose.
117
What is the enzyme required to convert (Glucose)_n into glucose 1-phosphate?
Glucose phosphorylase.
*Only at alpha 1,4-(glycosidic) linkages.
118
What is the mechanism required to convert (Glucose)_n into glucose 1-phosphate?
Pi in and (Glucose)_n-1 out.
119
What is the enzyme required to convert glucose 1-phosphate into glucose 6-phosphate?
Phosphoglucomutase.
120
What happens after glucose 6-phosphate is created in the muscle?
It is used for glycolysis.
121
What happens after glucose 6-phosphate is created in the liver?
Glucose 6-phosphotase converts it into glucose. H2O in and Pi out. The glucose then enters the bloodstream.
122
What is debranching enzyme?
The enzyme that break an alpha 1,6-(glycosidic) linkage to create a free glucose after removing and reattaching a chain of 3 glucoses to another chain via an alpha 1,4-(glycosidic) linkage.
123
When does debranching enzyme activate?
When 4 glucoses are remaining on a chain.
124
At what step is glycogenolysis regulated?
Glycogen phosphorylase.
125
What is glycogen phosphorylase activated by?
Phosphorylation by protein kinase-a, which is activated by glucagon (more powerful in liver) or epinephrine (more powerful in muscle).
126
What is glycogen phosphorylase inactivated by?
Dephosphorylated by proteinphosphotase-1, which is activated by insulin.
127
What is the synthesis of glucose?
Gluconeogenesis.
128
Where does gluconeogenesis occur?
1. Liver (primarily).
2. Kidneys (only during extreme starvation).
129
What is the purpose of gluconeogenesis?
Maintenance of blood glucose.
130
What are the precursors for pyruvate in gluconeogenesis?
1. Glycerol.
2. Amino acids.
3. Lactate.
131
What is glycerol produced as a result of?
Fat (triacylglycerol) breakdown.
132
What is the main precursor for pyruvate used during the fasted state?
Glycerol.
133
What are amino acids produced as a result of?
Protein breakdown.
134
Where are most amino acids in the body derived from?
Muscle.
*Skeletal muscle first.
135
When are amino acids used as a precursor for pyruvate?
When fat stores have been depleted and the animal is in a starvation state.
136
What is lactate produced as a result of?
The use of pyruvate during anaerobic respiration.
137
What is lactate used for once it enters the bloodstream?
Gluconeogenesis in the liver.
138
Where is lactate produced?
1. Muscle.
2. Erythrocytes.
139
Where does gluconeogenesis begin?
The mitochondria.
140
What enzyme is required to convert pyruvate into oxaloacetate?
Pyruvate carboxylase.
141
What mechanism is required to convert pyruvate into oxaloacetate?
The dephosphorylation of ATP to form ADP + Pi.
142
What enzyme is required to convert oxaloacetate into phosphoenolpyruvate?
Phosphoenolpyruvate carboxykinase.
143
What mechanism is required to convert oxaloacetate into phosphoenolpyruvate?
The dephosphorylation of ATP to ADP. A CO_2 is also produced.
144
What enzyme is required to convert phosphoenolpyruvate into 2-phosphoglycerate?
Enolase.
145
What mechanism is required to convert phosphoenolpyruvate into 2-phosphoglycerate?
The addition of a water.
146
What enzyme is required to convert 2-phosphoglycerate into 3-phosphoglycerate?
Phosphoglycerate mutase.
147
What enzyme is required to convert 3-phosphoglycerate into 1,3-bisphosphoglycerate?
Phosphoglycerate kinase.
148
What mechanism is required to convert 3-phosphoglycerate into 1,3-bisphosphoglycerate?
The dephosphorylation of ATP into ADP.
149
What enzyme is required to convert 1,3-bisphosphoglycerate into glyceraldehyde 3-phosphate?
Glyceraldehyde 3-phosphate dehydrogenase.
150
What mechanism is required to convert 1,3-bisphosphoglycerate into glyceraldehyde 3-phosphosphate?
The oxidation of NADH into NAD+. A Pi is also released.
151
What enzyme is required to convert glyceraldehyde 3-phosphate into dihydroxyacetone phosphate?
Triose phosphate isomerase.
152
What enzyme is required to convert glyceraldehyde 3-phosphate into fructose 1,6-bisphosphate?
Aldolase.
153
What enzyme is required to convert fructose 1,6-bisphosphate into fructose 6-phosphate?
Fructose 1,6-bisphosphotase.
154
What mechanism is required to convert fructose 1,6-bisphosphate into fructose 6-phosphate?
H2O goes in and Pi comes out.
155
What enzyme is required to convert fructose 6-phosphate into glucose 6-phosphate?
Phosphoglucose isomerase.
156
What enzyme is required to convert glucose 6-phosphate into glucose?
Glucose 6-phosphotase.
157
What is the mechanism required to convert glucose 6-phosphate into glucose?
H2O in and Pi out.
158
Where do amino acids and lactate enter gluconeogenesis?
At the conversion of pyruvate to oxaloacetate by pyruvate carboxylase.
159
Where does glycerol enter gluconeogenesis?
When glyceraldehyde 3-phosphate is formed.
160
At what 4 steps is gluconeogenesis regulated?
1. Pyruvate carboxylase.
2. Phosphoenolpyruvate carboxykinase.
3. Fructose 1,6-bisphosphate.
4. Glucose 6-phosphate.
161
How is pyruvate carboxylase activated?
The breakdown of fat (triacylglycerol).
162
How is phosphoenolpyruvate carboxykinase activated?
Glucagon and cortisol.
163
How is phosphoenolpyruvate carboxykinase inhibited?
Insulin.
164
How is fructose 1,6-bisphosphate inhibited?
Fructose 2,6-bisphosphate.
165
How is glucose 6-phosphate inhibited?
Insulin.
166
What is a normal blood glucose level?
4.5-5.5 mmol/L.
167
What is the blood glucose level after a meal?
6.5-7.2 mmol/L.
168
What is the blood glucose level during starvation?
3.3-3.9 mmol/L.
*Amino acids for gluconeogenesis.
169
What is the normal blood glucose level in ruminants?
2.2-3.5 mmol/L.
*Get glucose from gluconeogenesis.
170
What is the normal blood glucose level in poultry?
14 mmol/L.
171
What are the 3 sources of blood glucose?
1. Liver glycogen.
2. Dietary carbohydrates.
3. Gluconeogenesis.
172
How is blood glucose obtained from liver glycogen?
Released during glycogenolysis.
173
How is blood glucose obtained from dietary carbohydrates?
Ingestion and breakdown of carbohydrates.
174
How is blood glucose regulated?
1. Transport (GLUT2 and 4).
2. Glucokinase.
175
How is glucokinase regulated?
It requires a high intracellular glucose concentration to be active.
176
What does the way glucokinase is regulated allow for?
Glucose from glycogenolysis and gluconeogenesis to be released from the cell to maintain blood glucose.
177
What cell releases insulin?
Pancreatic beta-cells.
178
What are pancreatic beta-cells signaled by?
The transport of glucose through GLUT2 receptors.
179
What receptor does insulin signal to in order to lower blood glucose?
GLUT4, which is only expressed in the presence of insulin.
180
What two processes are activated by insulin?
1. Glycolysis.
2. Glycogenesis.
181
What two processes are inhibited by insulin?
1. Glycogenolysis.
2. Gluconeogenesis.
182
What cell releases glucagon?
Pancreatic alpha-cells.
183
What two processes does glucagon activate?
1. Glycogenolysis.
2. Gluconeogenesis.
184
What two processes does glucagon inhibit?
1. Glycogenesis.
2. Glycolysis.
185
How does growth hormone influence blood glucose?
Growth hormone causes increased fat mobilization, resulting in glycogen release and an increase in fatty acid oxidation (activating gluconeogenesis).
186
How does ACTH influence blood glucose?
Stimulates the release of glucocorticoids from the adrenal cortex, which affect blood glucose.
187
What is an example of a glucocorticoid?
Cortisol.
188
What process do glucocorticoids stimulate?
Gluconeogenesis.
189
Where is epinephrine secreted from?
The adrenal medulla.
190
What process does epinephrine stimulate?
Glycogenolysis.
