Lipids Flashcards
1
Q
What are the 4 types of dietary lipids?
A
- Triacylglycerols (TAGs).
- Phospholipids (PLs).
- Cholesterol and cholesteryl esters (CEs).
- Fat-soluble vitamins (FSVs).
2
Q
What are the components of a TAG?
A
Glycerol and 3 Fatty acid tails.
3
Q
What are the 4 FSVs?
A
A, D, E, K.
4
Q
What are the components of a CE?
A
Cholesterol + FA.
*Dietary form of cholesterol.
5
Q
Where are phospholipids found in the diet?
A
Everything that has cells.
6
Q
Where does lipid digestion begin?
A
In the stomach.
7
Q
What enzyme starts lipid digestion in the stomach?
A
Gastric lipase.
8
Q
How does gastric lipase begin lipid digestion?
A
It removes 1 FA from the TAGs on the outside of the “clump” of fat, forming diacylglycerols (DAGs).
*Does not get to all TAGs.
9
Q
What happens when chyme enters the small intestine (SI)?
A
Cholecystokinin (CCK) is released.
10
Q
What does CCK cause to occur?
A
- It causes the pancreas to release pancreatic lipase and pancreatic colipase.
- It causes the gallbladder to release bile*.
*Except for horses, where the liver consistently secretes small amounts of bile directly into the SI, due to lacking a gallbladder.
11
Q
What effect does bile have on lipids?
A
Surrounds the lipids and breaks them into smaller pieces, called emulsified droplets.
12
Q
What are emulsified droplets?
A
Droplets that have a lipid in the center and bile acids/salts around the outside, allowing the emulsified droplets to move through the aqueous environment of the SI.
13
Q
What effect does pancreatic colipase have on lipids?
A
Binds to emulsified droplets and allows pancreatic lipase to access the lipids in the emulsification droplets.
14
Q
What effect does pancreatic lipase have on lipids?
A
Removes 2 FAs from TAGs and 1 FA from DAGs to form monoacylglycerols (MAGs).
15
Q
What are the products of lipid digestion?
A
MAGs and FAs.
16
Q
What are emulsified droplets referred to as during lipid absorption?
A
Mixed bile salt micelles.
17
Q
Where are MAGs and FAs absorbed?
A
At the brush border, where many transporters move them into epithelial cells.
18
Q
What transports MAGs and FAs after absorption?
A
Fatty acid binding proteins (FABP).
19
Q
Where are the MAGs and FAs transported to after being absorbed at the brush border?
A
To the endoplasmic reticulum.
20
Q
What two events happen in the endoplasmic reticulum?
A
- Reesterification of TAGs.
- Packaging into chylomicrons.
21
Q
What are chylomicrons?
A
Lipid transporters that contain all lipid components.
22
Q
What system do chylomicrons enter after leaving the endoplasmic reticulum?
A
The lymphatic system, which returns fluid (and chylomicrons) to the bloodstream at the vena cava.
23
Q
How does lipid digestion occur in ruminants?
A
A TAG is separated into glycerol and 3 fatty acids.
24
Q
What happens to glycerol in the rumen?
A
The glycerol is converted into a VFA, which is absorbed through the rumen wall.
25
What happens to fatty acids in the rumen?
They are turned into polyunsaturated fatty acids (PUFAs) and then undergo biohydrogenation (which removes double bonds) to form saturated fatty acids (SFAs) because PUFAs are toxic to microbes.
26
What are the end products of lipid digestion in the rumen?
VFAs and SFAs.
27
What are the 4 types of lipoproteins?
1. Chylomicrons.
2. Very low density lipids (VLDL).
3. Low density lipids (LDL).
4. High density lipids (HDL).
28
What does the density of the lipid refer to?
The ratio of protein to lipid. The more protein, the higher the density. Vice versa.
29
What are apolipoproteins?
Proteins associated with lipoproteins that have structural, ligand for receptors, or enzyme cofactor function(s).
30
How many functions can a apolipoprotein have?
1-2.
31
What function(s) does the apolipoprotein apo CII have?
Enzyme cofactor.
32
What function(s) does the apolipoprotein apo E have?
1. Enzyme cofactor.
2. Structural.
33
What function(s) does the apolipoprotein apo B100 have?
1. Ligand for receptors.
2. Structural.
34
What is step 1 of chylomicron transport?
Chylomicrons are synthesized in the small intestine.
35
What is step 2 of chylomicron transport?
Chylomicrons enter the lymphatic system and are transported into the bloodstream at the vena cava.
36
What is step 3 of chylomicron transport?
Chylomicrons associate with apo CII in the blood, which binds to lipoprotein lipase on capillary walls.
37
What is step 4 of chylomicron transport?
Lipoprotein lipase causes TAGS to be broken into glycerol and FAs.
38
What is step 5 of chylomicron transport?
1. Glycerol goes to the liver.
2. FAs go to nearby tissues for energy and storage.
39
What is step 6 of chylomicron transport?
The chylomicrons continue to circulate until 80% of the TAGs are released.
40
What is step 7 of chylomicron transport?
Apo CII disassociates from the chylomicron and the chylomicron becomes a chylomicron remnant.
41
What is step 8 of chylomicron transport?
The chylomicron remnant is removed from the bloodstream when apo B48 binds to receptors on liver cells.
42
When is chylomicron synthesis occurring?
Fed state.
43
What is step 1 of VLDL transport?
VLDLs enter the bloodstream and associates with apo CII.
44
What is step 2 of VLDL transport?
Apo CII binds to lipoprotein lipase on the capillary walls.
45
What is step 3 of VLDL transport?
TAG is broken into glycerol and FAs by lipoprotein lipase.
46
What is step 4 of VLDL transport?
1. Glycerol goes to the liver.
2. FAs go into nearby tissues for energy and storage.
47
What is step 5 of VLDL transport?
VLDL continues to circulate in the blood until roughly 50% of the TAGs have been released. Apo CII dissociates and VLDL becomes intermediate density liquids (IDL).
48
What is step 6 of VLDL transport?
IDL circulates and releases TAGS through apo E receptors on the capillary walls.
49
What is step 7 of VLDL transport?
Once another roughly 30% of the TAGs are released, apo E dissociates and IDL becomes LDL.
50
When does VLDL transport occur?
When fat is synthesized in the liver and transported to other tissues in the body.
51
What apolipoproteins do VLDLs have?
1. Apo B100.
2. Apo E.
52
What is step 1 of LDL transport?
Travels through the bloodstream for 2-3 days.
53
What is step 2 of LDL transport?
LDL encounters apo B100 receptors and cholesterol diffuses out of LDL into tissue.
54
What is step 3 of LDL transport?
Once most of the cholesterol in the LDL has been removed, the LDL is removed from circulation via apo B100 receptors on the liver.
55
When does LDL transport occur?
When cholesterol needs to be transported from the liver to other tissues.
*Secondary way to form LDL.
56
What apolipoprotein is associated with LDL?
Apo B100.
57
What is step 1 of HDL transport?
HDL is released from the liver and travels through the bloodstream.
58
What is step 2 of HDL transport?
HDL binds Apo AI receptors on the capillary walls, resulting in the desorption of cholesterol from tissues.
59
What is step 3 of HDL transport?
HDL returns to the liver with cholesterol via apo AI receptors.
60
When does HDL transport occur?
Transporting cholesterol from peripheral tissue to the liver.
61
What apolipoprotein does HDL have?
Apo AI.
62
What are the 4 biological roles of lipids?
1. Structural components of membranes (ex: phospholipids).
2. Energy source.
3. Lubricants (ex: sebaceous gland secretions).
4. Signaling molecules (ex: Steroid hormones).
63
What 3 locations in the body does fatty acid synthesis occur in?
1. Adipose tissue (store).
2. Liver (sent out).
3. Lactating mammary glands (milk fat).
64
Where is acetyl-CoA found?
Mitochondria.
65
What enzyme is required to convert pyruvate into acetyl-CoA?
Pyruvate dehydrogenase.
66
What cofactors are required to convert pyruvate into acetyl-CoA?
CoA and NAD+ go in, CO2 and NADH+H^+ come out.
67
What enzyme is required to convert acetyl-CoA and oxaloacetate into citrate?
Citrate synthase.
68
What cofactor is required to convert acetyl-CoA and oxaloacetate into citrate?
H2O goes in, CoA comes out.
69
What enzyme is required to convert citrate into isocitrate?
Aconitase.
70
What enzyme is required to convert isocitrate into alpha-ketoglutarate?
Isocitrate dehydrogenase.
71
What are the cofactors required to convert isocitrate into alpha-ketoglutarate?
NAD+ goes in, NADH + H^+ and CO2 come out.
72
What would prevent isocitrate from being converted into alpha-ketoglutarate?
The ratio of NADH + H^+ : NAD+ being too high.
73
What happens if isocitrate dehydrogenase is inhibited?
Aconitase converts isocitrate back into citrate and citrate leaves the mitochondria.
74
What happens as citrate leaves the mitochondria?
A malate enters the mitochondria and is converted into oxaloacetate.
*Called the citrate shuttle.
75
What enzyme is required to convert citrate into acetyl-CoA and oxaloacetate?
ATP-citrate lyase.
76
What cofactors are required to convert citrate into acetyl-CoA and oxaloacetate?
ATP, CoA, and H2O go in, ADP + Pi comes out.
77
What enzyme is required to convert oxaloacetate into malate?
Malate dehydrogenase.
78
What cofactor is required to convert oxaloacetate into malate?
NAD+ goes in, NADH + H^+ comes out.
79
What enzyme is required to convert acetyl-CoA into malonyl CoA?
Acetyl-CoA carboxylase.
80
What activates acetyl-CoA carboxylase?
1. Insulin.
2. Glucose.
81
What inhibits acetyl-CoA carboxylase?
Glucagon.
82
What cofactors are required to convert acetyl-CoA into malonyl CoA?
HCO3 and ATP go in, ADP + Pi comes out.
83
Why is the conversion of acetyl-CoA into malonyl CoA important?
It is the first committed step of fatty acid synthesis.
84
How much malonyl CoA, acetyl-CoA, and NADPH + H^+ are required to complete fatty acid synthesis?
7 malonyl CoA, 1 acetyl-CoA, and 14 (NADPH + H^+).
85
What is required to convert 7 malonyl CoA, 1 acetyl-CoA, and 14 NADPH + H^+ into the final products of fatty acid synthesis?
Fatty acid synthase.
86
What are the final products of fatty acid synthesis?
Palmitate (16 carbon chain), 8 CoA, 14 NADP+, 7 CO2, and 6 H2O.
87
What are the 2 ways that palmitate is modified?
1. Elongation.
2. Desaturation.
88
Where does elongation occur?
In the ER.
89
How is elongation done?
Malonyl CoA donates 2 carbons that are added to the carboxyl end of the palmitate.
*Body always synthesizes even numbered fatty acids.
90
Where do odd numbered FAs in the body come from?
The diet.
91
What is the goal of desaturation?
To form a monounsaturated fatty acid.
92
Where does desaturation occur?
In the ER.
93
Where are the double bonds added during desaturation?
At the delta-9, 5, and 6 carbons.
*Delta-9 is always first.
94
How are the double bonds added?
Delta-# desaturase.
95
In what direction are the carbons labeled?
Starting at the carboxyl group and moving right.
96
What are the types of fatty acids that are found above delta-9?
w(omega)-3 or 6 fatty acids.
97
What directions are w-carbons counted in?
Starting at the methyl group and moving left.
98
Can w-3 and w-6 fatty acids be synthesized in the body?
No, they are primarily found in plants and fish.
*Important in cell signaling.
99
What happens after FAs are produced in the liver and adipose tissue?
TAG synthesis.
100
Where does TAG synthesis occur?
In the ER.
101
Why does TAG synthesis occur?
For the transport and/or storage of fatty acids.
102
What happens if FAs in the liver are not converted into TAGs?
A fatty liver.
103
What are TAGs packaged into before leaving the liver?
VLDLs.
104
Where are the TAGs absorbed?
In extrahepatic tissues.
105
What enzyme facilitates TAG release and storage?
Lipoprotein lipase.
106
What enzyme is responsible for TAG mobilization?
Hormone sensitive lipase.
107
What hormone inhibits hormone sensitive lipase?
Insulin.
108
Where does glycerol go during TAG mobilization?
To the liver for gluconeogenesis.
109
Where do FAs go during TAG mobilization?
To tissues that need energy.
110
How are FAs transported in the blood?
Attached to albumin.
111
When is fatty acid oxidation high?
During a starvation state.
112
When is fatty acid oxidation low?
During a fed state.
113
What is the rate of FA oxidation proportional to?
The concentration of FA in blood plasma.
114
What is the first step of FA transport to the mitochondria?
FAs enter the cytosol.
115
What is the second step of FA transport to the mitochondria?
A CoA gets attached to form FACoA.
116
What is the third step of FA transport to the mitochondria?
The carnitine cycle allows for transport of FACoA from cytosol into mitochondria.
117
What 3 enzymes are involved in the carnitine cycle?
1. Carnitine palmitoyltransferase-I (CPT-I).
2. Carnitine-palmitoylcarnitine translocase.
3. Carnitine palmitoyltransferase-II (CPT-II).
118
What is carnitine?
An amino acid-like protein that is synthesized from lysine.
119
What is the function of CPT-I?
Converts FACoA into FA carnitine in the cytosol.
120
What is the function of carnitine-palmitoylcarnitine translocase?
Transports FA carnitine into the mitochondria in exchange for a free carnitine.
121
What is the function of CPT-II?
Coverts FA carnitine into FACoA in the mitochondria.
122
What is beta-oxidation?
The breakdown of fatty acid to acetyl-CoA in the mitochondria.
123
What is the function of beta-oxidation?
To supply energy.
124
What are the reactants for beta-oxidation?
Palmitoyl-CoA + 7 CoA + 7 FAD+ + 7 NAD+ + 7 H2O.
125
What are the products for beta-oxidation?
8 acetyl-CoA + 7 FADH2 + 7 (NADH + H^+).
126
How much ATP is produced by the oxidation of palmitoyl-CoA to acetyl-CoA?
28 ATP.
127
What is the ATP equivalency of acetyl-CoA?
10 ATP.
128
How much ATP is produced by the oxidation of acetyl-CoA?
80 ATP.
129
What is the total amount of ATP that is produced during beta-oxidation?
108 per palmitate.
130
What are ketone bodies?
Small byproducts of ketogenesis that are produced as a glucose substitute for the brain and muscle.
131
When are ketone bodies released?
During a starvation or fasted state.
*A small amount is consistently produced.
132
Where are ketone bodies released from?
Liver.
133
What are the 3 ketone bodies released?
1. Acetone (byproduct that is released).
2. Acetoacetate (energy).
3. BHB (energy).
134
What are the levels of ketone bodies in the fed state?
10 micro molar.
135
What are the levels of ketone bodies in the fasted state?
1 Milimolar.
136
What are the levels of ketone bodies after a 2 day fast?
2 Millimolar.
137
Where does ketogenesis occur?
Mitochondria.
138
Where is acetone produced from?
From acetoacetate. Occurs spontaneously.
139
How is acetoacetate created?
Via an enzyme that converts BHB into acetoacetate.
*Reversible.
**Prevents acetone formation.
140
What do ketone bodies become in the mitochondria of muscles and the brain?
Acetyl-CoA, which enters the citric acid cycle to produce ATP.
141
What are the 3 stages of ketosis?
1. Ketonemia.
2. Ketonuria.
3. Ketoacidosis.
*Stage stack and become concurrent.
142
What is ketonemia?
Elevated levels of ketone bodies in the blood.
143
What is ketonuria?
Elevated levels of ketone bodies in the urine, in an attempt to lower the level of ketones bodies in the blood.
144
What is ketoacidosis?
A drop in blood pH due to a build up of ketone bodies, as they cannot be excreted fast enough.
*Is followed by death.
145
What is the treatment for ketosis?
Glucose bolus, glycerol, propylene glycol.
146
How does excess weight prior to lactation contribute to ketosis?
Excess fat is mobilized to form milk fat, instead of having milk fat be synthesized in the mammary glands.
147
Where does cholesterol synthesis occur?
In the cytosol of all nucleated cells.
148
What are the major sites of cholesterol synthesis in the body?
1. Liver (VLDLs, LDLs, and HDLs).
2. Small intestine (chylomicrons).
149
What roles does cholesterol serve in the body?
1. Structural.
2. Cell signaling.
3. Steroid hormone synthesis.
150
What purposes are lipids usually used for in a diet?
1. Increase palatability.
2. Reduce dust.
150
What pathway does the beginning of cholesterol synthesis mimic?
Ketone body synthesis.
151
What state of matter is animal fat in at room temperature?
Solid.
152
What are the three types of animal fat used in diets?
1. Tallow.
2. Lard.
3. Grease.
153
What animals are fed animal fats?
1. Carnivores.
2. Omnivores.
154
What animals is tallow derived from?
Beef and sheep.
155
What animal is lard derived from?
Swine.
156
Where is grease obtained?
From restaurants.
157
What state of matter are oils in at room temperature?
Liquid.
158
What are the oils used in diets?
1. Marine oil.
2. Vegetable oil.
159
Where is marine oil derived from?
1. Krill.
2. Fish.
160
Where is vegetable oil derived from?
A mixture of vegetables.
161
What is a problem that can arise with fats and oils?
Rancidity.
162
What is rancidity?
When O2 reacts with bonds between the fatty acids. This leads to an offensive/rancid odor, decreased palatability, and is toxic to animals (build-up of free radicals).
163
What are fats and oils fed with to try and prevent rancidity?
Anti-oxidants.
164
What % of the diet do fats and oils make up?
3-5%.
*Otherwise, digestive disturbance occurs.
165
What animals can be fed a high lipid (7% lipid) diet?
1. Poultry.
2. Swine.
166
What animals are less tolerant of dietary fat?
Ruminants.
