Metabolism 1 2 Flashcards
(153 cards)
1
Q
What processes are involved in metabolism?
A
catabolism and anabolism
2
Q
What is catabolism
A
breakdown of complex molecules into simpler molecules and release of energy via ATP
3
Q
What is anabolism
A
assembling simple substances to form new complex molecules via energy from ATP
4
Q
Where are the energy stored in ATP?
A
High energy bonds of the three phosphates
5
Q
What happens when ATP is used for energy?
A
It is hydrolyzed to ADP and inorganic phosphate
6
Q
What is oxidation?
A
loss of electron such as when you add oxygen or remove a hydrogen
7
Q
What is reduction?
A
addition of an electron such as when you add hydrogen or remove oxygen
8
Q
Name the following compounds in terms of their oxidation status from least to greates Methane Formic Acid Formaldehyde Methanol Carbon Dioxide
A
CH4 (methane) CH3OH(Methanol) CH2O (Formaldehyde) HOCHO (Formic Acid) CO2 (Carbon Dioxide)
9
Q
What are the most important electron carriers and their reduced forms ?
A
NAD+ =>NADH
NADP+ => NADPH
10
Q
What is the common product that the major products of digestion of carbs, lipids, and proteins in the metabolic pathway lead to?
A
Acetyl CoA
11
Q
What is the primary function of Acetyl-CoA
A
Convey carbon atom within the acetyl group to the TCA Cycle to be oxidized for energy production
12
Q
Where is Acetyl CoA generated?
A
In the mitochondrial matrix
13
Q
Where does the conversion of pyruvate to Acetyl CoA take place?
A
Mitochondrial Matrix
14
Q
What are the 4 fates for Acetyl CoA and which is the primary fate?
A
- Oxidize acetyl groups in CAC for energy generation and produce ATP, CO2, H2O (Primary fate)
- Lipogenesis: Form fatty acids -> esterification -> form triacylglycerol
- Ketogenesis: Form ketone bodies
- Cholesterologenesis: form cholesterol to synthesize steroids
15
Q
Can all components of metabolism (fat, protein, carbs) give rise to the synthesis and storage of fat?
A
Yes, by first converting into acetyl CoA
16
Q
How are fructose and galactose metabolized?
A
Converted to intermediates in the same glycolysis pathway as glucose
17
Q
What happens to excess carbohydrates?
A
stored in glycogen
18
Q
Which organs have the largest stores of glycogen?
A
liver, heart, skeletal muscle
19
Q
What happens to fatty acids?
A
Go through beta oxidation in mitochondria to form Acetyl-CoA
Otherwise, they form Triacylglycerols to be stored in adipose tissue
20
Q
Can cell without a mitochondria have beta oxidation?
A
No because it require mitochondria to beta-oxidize fatty acids to form Acetyl-CoA
21
Q
What happens to amino acids in metabolism?
A
Metabolized to form either Acetyl-CoA or an intermediate in the CAC
22
Q
What is the downside to the metabolism of amino acids
A
Formation of ammonia which is toxic at high levels if not converted to uera
23
Q
How are amino acids stored?
A
As proteins
24
Q
What are the fuel preferences for the liver?
A
fatty acids
glucose
amino acids
25
What are the fuel preferences for adipose tissue?
Fatty acids
26
What are the fuel preferences for skeletal muscle
At rest: fatty acids
| Exertion: glucose
27
What are the fuel preferences for heart muscle?
Fatty acids (still uses everything though just prefers this)
28
What are the fuel preferences for the brain?
Fed state: glucose
| Starvation: ketone bodies/glucose
29
What is the driving force for the coordination of metabolism?
To provide the normal range of glucose levels for hte brain as nerve cells die in a very short period of time
30
What happens in a fasted state (starvation)
low blood insulin -> activate lipolysis in adipose tissue -> raise blood levels of fatty acids -> used in preference to glucose via beta oxidation of fatty acid in liver for ATP used for gluconeogenesis
Brain uses ketone bodies as alternative when ketone body levels iin blood are high enough, BUT brain will never lose its requirement for glucose
31
What are hte kcal/g for carbs, proteins, fats?
Carbs:4
Fats:9
Protein:4
32
Carbs/Source/Enzymes:
| Amylopectin
Source; Potatoes, rice, corn, bread
| Enzyme: Isomaltase
33
Carbs/Source/Enzymes::
| Amylose
Source; Potatoes, rice, corn, bread
| Enzyme: Maltase
34
Carbs/Source/Enzymes:
| Starch
Mix of amylose and amylopectin
35
Carbs/Source/Enzymes:
| Sucrose
Source; Table Sugar, desserts
| Enzyme: Sucrase
36
Carbs/Source/Enzymes:
| Lactose
Source: Milk, milk products
Enzyme: Lactase
37
Carbs/Source/Enzymes:
| Fructose
Source: Fruit, honey
Enzyme: none
38
Carbs/Source/Enzymes:
| Glucose
Source: Fruit, hooney, grapes
Enzyme: none
39
Carbs/Source/Enzymes:
| Maltose
Source: Barley
Enzyme: Maltase
40
Carbs/Source/Enzymes:
| Trehalose
Source: Young Mushroom
Enzyme: Trehalase
41
Carbs/Source/Enzymes:
| Cellulose
Source: Fiber in plant foods
Enzyme: none; not digestible by humans, forms bulk of feces
42
What is starch
Polymer of glucose
| Mix of alpha 1-4 and alpha 1-6 linkages
43
What breaks down starch?
Amylase (Salivary and pancreatic)
44
What are the major disaccharides and their components?
Sucrose: glucose and fructose
Lactose: glucose and galactose
45
What breaks down disacchrides?
disaccharidases (Sucrase, Lactase) found in brush border of small intestine
46
What happens to sacchrides that are not hydrolyzed?
Cannot be absorbed, and reach lower tract of intestine at which point past the lower ileum are bacteria
47
What causes lactose intolerance and what problems does it cause?
Deficiency in lactase enzyme production
Dietary lactose not sufficiently hydrolyzed/absorbed -> stays in intestine and causes osmosis of water into the intestine
Intestinal Bacteria can also metabolize lactose to form lactic acid, H+, CO2, CH4 gas, causes bloating, flatulence, and diarrhea
48
What is the treatment for lactose intolerance?
Avoid milk and milk products from diet
49
Whats the difference in lactose intolerance between infants and adults
Infants: congenital lactase deficiency starting at birth causing changes in the secondary structure of the enzyme and truncating it abnormally
Adults: lactose intolerance caused by gradual decrease in activity of hte LCT gene
50
Insulin
Peptide hormone
Secreted by beta cells of pancreas
Function: maintain low blood glucose and promote glycolysis on long term basis and glycogen synthesis
Hyperglycemia => inc insulin
51
Glucagon
Peptide homrone
Secreted by alpha cells of pancreas when blood glucose too low
Causes liver to release glucose into the blood
Hypoglycemia => inc glucagon
52
Glycogenesis
Breakdown of glycogen to G1P and glucose in liver and muscles by enzyme glycogen phosphorylase
53
Glycolysis
Metabolic pathway in cytoplasm in which a single glucose is converted to : 2 pyruvic acid, 2 ATP, 2 NADH and 2 water
54
Gluconeogenesis
Generation of glucose from non-carb carbon substrates like pyruvate, lactate, glycerol, glucogenic amino acids
55
Glycogenesis
Formation of glycogen from glucose
56
Fed State induces what?
Increased glycogen formation
Increased pyruvate and lactate formation via glycolysis
Increased formation of Acetyl-CoA from pyruvate oxidation which feeds into the TCA cycle
Increased insulin release from pancreatic beta cells in response to influx of glucose
No gluconeogenesis by liver
57
Fasted/Starved state induces what?
Increased levels of glucagon by alpha pancreatic cells
Increased levels of epinephrine by adrenal medulla
Increased glycogen degradation to produce G6P
Increased gluconeogenesis
58
How is carbohydrate metabolized in RBCs?
RBCs lack mitchondria so it cannot use amino acid or fatty acid metabolism. Depend entirely on glycolysis
59
How is carbohydrate metabolized in brain tissue cells?
Brain has an absolute requirement for glucose and a very minimal reserve of glycogen. Can carry out TCA cycle
60
How is carbohydrate metabolized in muscle/heart cells?
Have major stores for glycogen. Muscles cannot mobilize glycogen or glucose into circulation. Can carry out TCA and also produce lactic acid from pyruvate
61
How is carbohydrate metabolized in adipose tissue cells?
Convert excess glucose into fat. Can form glycogen but does not carry out TCA
62
How is carbohydrate metabolized in liver cells?
glycolysis, gluconeogenesis, glycogen synthesis, PP Pathway
63
What hexose transporter move down a concentration gradient?
GLUT1-4
64
What hexose transporters move agasint a concentration gradient and what does it use for energy?
SGLT1, SGLT2, uses electrochemical gradient of sodium to co-transport with hexose
65
Which transporters have a high affinity for glucose?
GLUT 1,3,4
66
Which transporters have a low affinity for glucose and why is this important?
GLUT2; allows it to change transport rate in proportion ot increasing glucose concentrations after a meal
67
Which GLUT transporters are glucose transporters?
Class I: GLUT 1-4
68
Which GLUT transproters are fructose transporters?
Class II : GLUT 5,7,9,11
69
SGLT1
Co-transport 1 glucose or galactose with 2 sodium ions
Does not transport fructose
Insulin independent
70
SGLT2
Co-transports glucose and sodium ions
| Does not transport fructuse of galactose
71
GLUT1
Insulin independent
| Found in RBCS, brain, endothelial cells
72
GLUT2
Insulin independent and low affinity
Found in liver(bring in glucose) , intestines (glucose out), kidney
Serves as glucose sensor in pacreatic beta cells
73
GLUT4
Insulin DEPENDENT High affinity
Found in muscle, heart, adipocytes
Not active during fasting state
74
GLUT 5
Fructose transporter
75
What are the 3 enzymes that catalyze the regulated steps of glycolysis?
Hexokinase/Glucokinase: Glucose to G6P
Phosphofructokinase-1: F6P to F1,6bisphosphate
Pyruvate Kinase: PEP to pyruvate
76
How are the enzymes of glycolysis regulated?
Allosterically
Covalent modifications
Amount/synthesis of enzymes
77
Does glycolysis require a mitochondria?
No. Takes place in cytoplas. Found in all cell types
78
What does Aldolase A do in glycolysis?
It's the most highly regulated part of glycoclysis that carries out the splitting stage to produce dihydroxyacetone phosphate and glyceraldehyde3-phosphate
79
What is allosteric regulation?
molecule or ligand interacts with enzyme active site to either speed it up or slow it down
Reversible and quick/transient
80
What is covalent modification
Example: phosphorylation and dephosphorylation by kinase/phosphatase causing conformational changes that alter the activity of the enzyme
Insulin activates phosphatases to inhibit epinephrine and glucagon activity
81
Where can hexokinase be found in?
All cells
82
What regulates hexokinase?
Allosterically inhibited by its product, glucose-6 phosphate
83
Is Hexokinase a constitutive enzyme?
Yes. Constitutive, non-inducible, constant amount with low Km for glucose (high affinity)
84
Can hexokinase handle high levels of glucose?
No
85
Where can glucokinase be found?
Liver and pancreas
86
What's unique about glucokinase?
Translocate between nucleus (inactive) and cytosol (active)
87
How is glucokinase regulated?
Fructose 6-phosphate, a downstream product, decreases its activity by promoting translocation to nucleus
Glucose increases its activity by promoting translocation to cytosol
88
Is glucokinase constitutive?
No; It is an inducible enzyme and it's synthesis is induced by INSULIN
Has a high Km
89
Can glucokinase handle high levels of glucose?
Yes
90
What reaction does PFK-1 (Phosphofructokinase 1) catalyze?
Frcutose 6 phosphate -> Fructose 1,6 bisphosphate
91
What are the positive regulators for PFK1
Fructose-2,6 bis phosphate, AMP, ADP
92
What are then negative regulators for PFK1
ATP, citrate
93
How is Fructose 2,6 bis phosphate formed and what is its role?
Major activator of hepatic PFK1
| Formed from fructose-6-phosphate by a non-glycolitic step catalyzed by PFK-2
94
What is the reaction forming fructose 2,6 bisphosphate
F6P --PFK2+ATP -->Fructose 2,6 bisphosphate
95
When is fructose 2,6 bisphosphate formed?
When blood glucose and insulin levels are high
| It is NOT formed when blood glucose is low
96
What inhibits the formation of fructose 2,6 bisphosphate in the liver?
Glucagon and epinephrine indirectly by stimulation formation of cAMP and activating PKA to phosphorylate the kinase domain of PFK-2 and inhibiting it.
97
What does PFK2 do?
Forms Fructose 2,6 bisphosphate from Fructose 6 phosphate
98
What inhibits PFK2
Phosphorylation by PKA
99
Is PFK-2 uni or bi directional?
Bidirectional. It can make fructose 2,6 bisphosphate as well as convert it back to fructose 6 phosphate
100
How can PFK-2 carry out both the forward and reverse reactions?
It has both a kinase domain and a phosphatase domain
101
What happens when formation of Fructose 2,6 bis phosphate is blocked?
Hepatic glycolysis is blocked since Fructose 2,6 bisphosphate is a positive regulator of PFK-1 reaction to form Fructose 1,6 bisphosphate from F6P in the glycolysis pathway
102
What is citrate and what does it do with regards to PFK-1
CAC intermediate formed in the mitochondria that accumulates when ATP production in mitochondria is high -> isocitrate dehydrogenase (CAC enzyme) inhibited -> leading to buildup
Inhibits PFK-1 enzyme to signal that there is enough ATP generation going on and to halt progression of glycolysis
103
Why does ATP inhibit PFK-1?
It signals that there is enough cytosolic ATP
104
Why are AMP and ADP activators of PFK-1
Associated with low energy and low cytoplasmic ATP and aneed for glycolysis to replenish ATP
105
Under normal conditions, what role does fructose-26 bisphosphate play in PFK-1 activity?
It is essential. If it is not present, PFK-1 is inhibited under normal conditions
106
How does regulation of heart/skeletal muscle differ from hepatic cells?
Epinephrine inhibits hepatic glycolysis but stimulates hear/skeletal muscle glycolysis ( activates PFK-2 in heart and skeletal muscle and thus activates glycolysis by favoring F2,6BP formation)
There are no glucagon receptors in heart and skeletal muscles
107
Why does epinephrine activate PFK-2 in heart/skeletal muscle but opposite in hepatic cells?
PFK-2 is of a different form in heart and skeletal muscle than hepatic cells. Lacks a hydroxyl group in the kinase domain and has a hydroxyl in the phosphatase domain -> allows kinase activity and thus formation of F26BP
108
What reaction does pyruvate kinase catalyze in glycolysis?
PEP -> pyruvate and formation of ATP
109
What activates pyruvate kinase?
Fructose 1,6 bisphosphate (feeds forward reaction)
110
What inhibits pyruvate kinase?
ATP
| alanine: amino acid that increases in fasting mode and serves as precursor for gluconeogenesis
111
What effect do glucagon and epinephrine have on pyruvate kinase?
Act vai cAMP and PKA to phosphorylate and thus inactivate hepatic pyruvate kinase
112
What is needed to activate an inactivated pyruvate kinase?
Phosphoprotein phosphatase (remove phospho group)
113
At low blood glucose what is the state of pyruvate kinase?
phosphorylated (inactive)
114
At high blood glucose, what is the state of pyruvate kinase?
dephosphorylated (active)
115
What genetic condition results from a deficiency of pyruvate kinase?
hemolytic anemia
116
What are the counter-enzymes to the 3 allosterically regulated enzymes in the glycolytic pathway favoring gluconeogenesis?
Hexokinase: Glucose-6phosphatase
Phosphofructokinase-1 : Fructose 1,6 bisphosphatase
Pyruvate Kinase: PEP Carboxylase
117
What effect do glucagon and epinephrine have on hepatic glycolysis?
inhibits it
118
Where are glucagon's effects most prominent at?
Liver. Glucagon receptors are present in the liver but not in skeletal muscle or heart; Released by alpha pancreatic cells at times of low blood glucose
119
Where are epinephrine's effects most promienent at?
Generally everywhere; Not limited to liver like glucagon
Inhibitiion of glycolysis in other cells preserves glucose for use by tissues that highly prefer glucose over other sources
120
How does glucagon/epi regulate hepatic glycolysis?
Covalent modification (phosphorylation) of :
PFK-1: indirectly via inhibition of PFK-2
Pyruvate Kinase : direct
Decreases synthesis of the 3 irreversible enzymes of glycolysis
121
What does increased insulin or decreased cAMP result in?
Increased synthesis of the 3 irreversible enzymes of glycolysis (Glucokinase, PFK-1, Pyruvate Kinase)
122
What must be regenerated in order for glycolysis to continue?
NAD+
NAD/NADH is in limited supply in cytoplasm
NADH is oxidized when pyruvate is converted to lactate
123
How can cytoplasmic NAD+ be regenerated?
LDH (cytosolic)
Malate-Aspartate Shuttle (Cytosolic + Mitochondria)
Glycerol-Phosphate Shuttle (Cytosolic + Mitochondria)
124
Lactate Dehydrogenase
Catalyze conversion of Pyruvate +NADH to form Lactate and NAD+ (Overall: Get 2 lactate, 2 ATP, 2 H2O in this path)
Is present in all cells
Lactate is acidic and can lead to acidosis if accumulates
125
What are the LDH Isozymes
LDH-5: M4: found in skeletal muscle and prefers catalyzing the conversion of pyruvate to lactate for high bursts of energy
LDH-4: kidneys, placenta, pancreas
LDH-3: lungs
LDH-2: ciruclatory system
LDH-1: H4: Heart muscle; Prefers conversion lactate to pyruvate to allow more sustained energy production via Acetyl-CoA and TCA
126
What is the normal ratio in serum of lactate/pyruvate?
10/1
127
What is Pyruvate Dehydrogenase (PDH)?
Multienzyme that catalyzes conversion of Pyruvate to Acetyl-CoA
128
What are the isozymes of PDH
E1: pyruvate dehydrogenase activity
E2: dihydrolipoyl transacetylase
E3: dihydrolipoyl dehydrogenase
129
What happens to pyruvate by PDH?
Decarboxylated to a 2C compound and added to thiamine pyrophosphate, which donates the acetyl group to the E2 -> eventually transfers to become Acetyl-CoA
Lipoic acid is then alternated between ox and red forms by E3
130
What does PDH deficiency lead to?
Inability to make Acetyl CoA -> impairs tissue function and survival. Brain and heart mainly affected
131
What does arsenic poinson cause?
Prevents the shuttling of the lipoic acid between ox and red forms and thus mimics PDH deficiency, leading to pyruvate and lactate accumulations in the blood
132
Does glucagon and epi inhibit PDH?
No
133
What inhibits PDH?
End products via allosteric regulation (NADH, Acetyl COA)
Phosphorylation of PDH inhibits its activity
134
What does LDH-1>LDH-2 indicate?
Potential MI
135
Which enzyme complex of PDH requires which vitamin cofactor to be active?
E1 (PDH): Thiamine (B1)
E2(DHL Transacetylase): Pantothenate (B5)
E3 (DHL dehydrogenase): Riboflavin (B2) + Niacin (B3)
136
What happens if have deficiency of Vitamins B1, B2, B3, B5?
Less active PDH
137
What happens in LDH deficiency?
Pts cant exercise due to inability to use glycolysis for ATP under anaerobic conditions
NAD+ levels are insufficient due to inability to carry out glycolysis.
138
What are the inputs and outputs of glycolysis?
Inputs: glucose, 2NAD+, 2 ATP, 4ADP
Output: 2 pyruvate, 2 NADH, 4 ATP, 2 ADP
139
Does lactate formation require oxygen?
No. Glycolysis does not require O2 as well
140
Does PDH and TCA require oxygen?
YEs. Aerobic
141
What processes require O2?
REoxidation of mitochondrial NADH from PDH enzyme
Reoxidation of cytosolic NADH by the shuttles
142
What does low levels of cellular NADH lead to?
decreased lactate formation
143
How can we metabolize galactose and fructose?
Enzymes to convert them to a glycolytic intermediate
144
What enzymes are needed for galactose metabolism
Galactokinase + Gal-1-P Uridyltransferase
Galactose ->Galactose1P -> Glucose 1P -> G6P
145
What is galactosemia?
genetic disorder caused by deficiency of either galactokinase or Gal-1-P-uridyltransferase
146
What forms in galactosemia?
Galactitol (toxic)
147
What sx are found in galactosemia?
Cataracts, increased blood galactose, galactosuria
148
Whats the main difference between galactokinase deficiency and Gal-1P-uridyl Transferase deficiency (classical galactosemia)
Autosomal Recessive
See Galactose 1 Phosphate accumulation in addition to the typical sx of galactosemia
Leads to hepatic and brain dysfunctions
149
How do you treat galactosemia?
rapid detection and removal of galactose (lactose) from diet
150
What enzymems are needed for fructose metabolism?
Fructokinase: produce F1P
| Aldolase B: cleaves F1P to glyceraldehyde3 phosphate or DHAP(a glycolytic intermediate)
151
What happens in Aldolase B deficiency?
Accumulation of fructose 1 phosphate (toxic) and depletion of ATP (P tied up in F6P)
Low glucose levels
152
What are sx seen with fructose intolerance? Treatment?
hypoglycemia, vomiting, jaundice, liver failure
| Tx: avoid foods with fructose
153
What is essential fructosuria?
defect in fructokinase; fructose found in blood and urine but benign and asymptomatic
