Lipid Metabolism. Flashcards
1
Q
Define amphipathic?
A
They are molecules that have a hydrophobic region and a hydrophilic region.
2
Q
What is cholecystokinin (CCK)?
A
A secreted molecule that leads to the release of pancreatic enzymes.
3
Q
Define emulsification?
A
It is the breakdown of large fat droplets into much smaller droplets.
4
Q
How does emulsification help enzymes function?
A
The emulsification of fat droplets creates a larger surface area for enzymes to work on.
5
Q
What is a glycocalyx?
A
The glycocalyx is made up of sugars and proteins and covers the outside of the plasma membrane.
6
Q
What is a lipase enzyme?
A
A lipase is an enzyme that cleaves triacylglycerols.
7
Q
What is a phospholipase enzyme?
A
An enzyme that can cleave phospholipids.
8
Q
Are fatty acids synthesised when blood glucose levels are high or low?
A
When they are high and glycogen stores are full.
9
Q
Why are fatty acids synthesised when blood glucose levels are high?
A
So that blood glucose levels can be reduced.
10
Q
What condition does fatty acid synthesis prevent?
A
Hyperglycaemia.
11
Q
The synthesis of fatty acids is a way of storing what?
A
Energy.
12
Q
Are lipids hydrophobic or hydrophilic?
A
Hydrophobic.
13
Q
What kind of lipids are non polar?
A
Triacylglycerols (TAGs).
Cholesteryl esters.
14
Q
What kind of lipids are amphipathic?
A
Fatty acids that have a negative charge.
Cholesterol.
Polar lipids that make up biological membranes.
15
Q
What kind of tissue are lipids stored in?
A
In adipose tissue.
16
Q
How does a human consume most of their lipids?
A
In the diet.
17
Q
What are 2 dietary essential fatty acids?
A
Fatty acids of the ω3 and ω6 family.
18
Q
What are the fatty acids of the ω3 and ω6 family required for?
A
Membrane fluidity.
They are used as a precursor to make other molecules.
19
Q
ω3 fatty acids are used used to help protect the body against what?
A
To protect the body against cardiovascular disease and dementia.
20
Q
Are TAGs polar or non polar?
A
Non polar.
21
Q
How much of the diet do TAGs make up?
A
Around 40%.
22
Q
What is the main storage form of fatty acids in adipose tissue?
A
TAGs.
23
Q
What is structure of a TAG?
A
A 3 carbon glycerol backbone which bound to 3 fatty acid chains.
24
Q
Why are fatty acids amphipathic?
A
Because they have a hydrophilic hydrocarbon chain and a polar hydroxyl group.
25
What is the structure of fatty acids?
They have a long carbohydrate chain that contains a carboxyl group.
26
What charge does a fatty acids carboxyl group have at physiological pH?
Negative.
27
Do natural fatty acids contain cis or trans double bonds?
Natural fatty acids contain cis bonds.
28
Are trans fats found in nature?
No.
29
Why can free fatty acids damage cell membranes?
Because they have detergent characteristics.
30
How is the detergent characteristics of free fatty acids reduced?
They are esterified into various molecules such as TAGs and cholesteryl esters.
31
What is the structure of a phospholipid?
They have a phosphoglycerol head that is bound to 2 fatty acid chains.
32
Is the phosphoglycerol head of a phospholipid polar or non polar?
It is polar and hydrophilic.
33
What is the structure of the plasma membrane?
It is made up of 2 layers of phospholipids.
34
How is the phospholipid bilayer of the plasma membrane arranged?
The hydrophilic heads of the phospholipids will face out and the hydrophobic tails from both layers will be on the interior.
35
What is the name of the separation in the phospholipid bilayer?
Lipophilic separation
36
What covers the extracellular side of the plasma membrane?
The glycocalyx.
37
What is the glycocalyx made from?
Glycolipids and glycoproteins.
38
What is the function of the glycocalyx?
To protect the cell.
To help with cell-cell recognition.
39
Does the plasma membrane contain cholesterol?
Both layers of the plasma membrane will also contain free cholesterol.
40
What is the function of cholesterol in the plasma membrane?
It helps with membrane fluidity.
41
What is the main characteristic of phospholipids?
They contain phosphate.
42
What suffix will phospholipids that contain phosphatidic acid have?
Phosphatidyl.
43
What is the major component of cell membranes?
Phospholipids.
44
Do phospholipids contain a charge?
They are uncharged molecules.
45
What is the main characteristic of glycolipids?
They contain sugars.
46
What sugar do most glycolipids contain?
Sphingosine and are named sphingolipids.
47
How many carbons does cholesterol have?
27.
48
What is the only polar part of a cholesterol molecule?
A hydroxyl group.
49
How many ring structures does a cholesterol molecule have?
4.
50
What are the names of the rings in the cholesterol structure?
A,B,C and D.
51
What cholesterol ring has a double bond?
Ring B.
52
What are the 2 organs that will mainly synthesise cholesterol?
The liver.
The brain.
53
What will happen to people who cannot synthesise the double bond in ring B of cholesterol?
They will die.
54
How will free cholesterol arrange itself in the plasma membrane?
The hydroxyl group will be found as close as possible to the polar heads of the phospholipids.
The ring structures separate the fatty acid tails inside the bilayer.
55
What aspect of a cell membrane will cholesterol enhance?
Membrane fluidity.
56
How does cholesterol increase membrane fluidity?
The ring structures decrease the fluidity of membranes at the polar heads and increase fluidity at the tails.
57
Where does lipid metabolism begin?
In the mouth.
58
How does lipid metabolism begin in the mouth?
The enzyme lingual lipase is produced.
59
Will lingual lipase be active in the mouth?
It is not active in the mouth.
It becomes active in the stomach after it is swallowed.
60
What 2 enzymes are produced by lipid metabolism in the stomach?
Lingual lipase.
Gastric lipase.
61
What kind of lipids will be degraded in the stomach?
TAGs and medium chain fatty acids.
62
Where does the majority of lipid metabolism take place?
In the small intestine.
63
What enzymes will degrade lipids in the small intestine?
Pancreatic enzymes.
64
What additional factor do pancreatic enzymes require for lipid degradation?
Bile salts.
65
What kind of lipids are taken up by the intestinal mucosal cells from the large intestine?
Free fatty acids.
MAGs.
Free cholesterol.
66
What is required for lipids to be taken up by the intestinal mucosal cells?
Micelles.
67
What happens after lipids have been taken up into the intestinal mucosal cells?
They are converted into TAGs and cholesteryl esters.
68
What happens to the newly synthesised TAGs and cholesteryl esters in the intestinal mucosal cells?
They are then stored in chylomicrons.
69
What happens to the chylomicrons in the intestinal mucosal cells?
They are released into the lymph and then the blood.
70
What molecule is responsible for increasing proton concentration in the stomach?
Gastrin.
71
What molecule is responsible for the release of gastric lipase in the stomach?
Gastrin.
72
Where will lipids start to be broken down?
In the stomach.
73
What enzymes will break down lipids in the stomach?
Lingual lipase.
Gastric lipase.
74
What lipids lingual lipase and gastric lipase break down?
TAGs and medium chain fatty acids.
75
Why are lingual lipase and gastric lipase important in infants?
Because they cleave the lipids found in milk.
76
Where are the partly digested contents of the stomach released to?
Into the duodenum of the small intestine.
77
What is the partially digested substance that is released from the stomach into the duodenum called?
Acidic chyme.
78
The arrival of acidic chyme into the duodenum will trigger the release of what 2 chemicals?
Secretin.
CCK (cholecystokinin).
79
Where is secretin and CCK released from?
The endocrine cells of the duodenum
80
What happens to the pH of the acidic chyme in the duodenum?
It is changed to a neutral pH so that the small intestine is not damaged.
81
The secretion of CCK leads to the activation of what enzyme?
Enteropeptidase.
82
Where is the enzyme enteropeptidase that is activated by CCK found?
It is a membrane bound protein found in the border of the duodenum.
83
What is the function of enteropeptidase?
To cleave trypsinogen to trypsin.
84
What is trypsin used for?
Trypsin is used to activate proteases.
85
Why do proteases need to be activated?
They must only be active when dietary proteins are present or they will degrade the proteins that make up the stomach.
86
The release of CCK in the duodenum triggers the release of what molecule?
Bile.
Pancreatic proteins and enzymes.
87
Where is bile released from?
The gall bladder.
88
Why does CCK inhibit gastric motility?
To stop the stomach from releasing more chyme into the duodenum.
89
Is bile acidic or alkaline?
Alkaline.
90
What is bile formed from?
Primary bile acids.
91
Where is bile made?
In the liver.
92
Where is bile stored?
In the gall bladder.
93
What 4 things is bile made up of?
Bile salts.
Phosphatidylcholine.
Some free cholesterol.
Conjugated bilirubin.
94
What will the liver use to synthesise primary bile acids?
Free cholesterol.
95
What joins conjugated bile acids together?
Glycine or taurine
96
The joining of bile acids together changes what aspects of the bile acids?
It changes the pKa of the bile acids to make them more negatively charged.
97
What are conjugated bile acids released with?
A small amount of bile salts.
98
What is the pKa of bile acids?
6.
99
What is the pH of bile acids in the body?
7.
100
Will bile acids be charged or uncharged in the body?
They will form a mixture of charged and uncharged molecules.
101
The bile acids with what charge will emulsify best?
The bile acids with a negative charge will emulsify much better than those wit a positive charge.
102
What is the major reason why bile acids are conjugated with glycine and taurine?
To improve their emulsification properties as they will have a negative charge.
103
A conjugated bile acid with glycine has what pKa?
4.
104
A conjugated bile acid with taurine has what pKa?
2.
105
Why do conjugated bile acids usually take up the salt form in the duodenum?
Because of their negative charge.
106
What are conjugated bile acids known as?
Bile salts.
107
What is the function of bile salts?
To increase the solubility of lipids.
108
How do bile salts emulsify lipids?
They surround lipids and emulsify them into smaller lipid droplets by covering the exterior of the lipid so it has no contact with water.
109
Can the body break down free cholesterol?
No.
110
What will help the body get rid of free cholesterol?
Bile salts.
111
What are the 3 functions of bile salts?
To transport free cholesterol and bilirubin from the liver to the duodenum.
To emulsify lipids for digestion.
To help form mixed micelles.
112
What percentage of bile salts are excreted?
5%.
113
How does the liver replace the bile salts that are excreted?
It can use free cholesterol to make more bile salts.
114
How are bile salts re-synthesised?
Bacteria in the ileum will de-conjugate the bile salts to use the glycine and taurine and will modify the primary bile acids to secondary bile acids.
The secondary bile acids are taken up into the liver and are re-conjugated to bile salts.
115
How is phosphatidylcholine obtained?
From the diet or as a component of bile.
116
How is phosphatidylcholine cleaved?
Pancreatic phospholipase A2 which will cleave 1 fatty acid from phosphatidylcholine to form lysophosphatidylcholine and a free fatty acid.
117
What enzyme activates pancreatic phospholipase A2?
Trypsin.
118
What happens to the free fatty acids and lysophospholipids that are generated by the cleavage of phosphatidylcholine?
They will help to emulsify lipids through the use of their detergent characteristics of the fatty acids.
119
Why will the free fatty acids generated by the cleavage of phosphatidylcholine not damage the body?
Because they are not in a cell.
120
What enzymes are secreted by the pancreas into the duodenum?
Pancreatic lipase and procolipase.
121
What happens when procolipase reaches the duodenum?
It is cleaved by trypsin to form colipase.
122
What lipids will colipase and pancreatic lipase cleave?
TAGs.
123
What do colipase and pancreatic lipase need to help them cleave TAGS?
Bile salts.
124
How are TAGs emulsified?
They are surrounded by bile acids and emulsified to form smaller droplets.
125
How does pancreatic lipase work with colipase?
Colipase will separate the bile acids that surround the TAG and will then anchor pancreatic lipase to the TAG so it can break it down.
126
How will pancreatic lipase break down TAGs?
By cleaving 2 fatty acids from the TAG.
This forms a monoacylglycerol (MAG) and 2 free fatty acids.
127
Can TAGs or DAGs cross the intestinal mucosal cells?
No.
Only MAGs can.
128
Is pancreatic lipase synthesised as a zymogen?
No.
It is active when it is synthesised.
129
What is the MAG pathway?
The way that lipids are absorbed into the intestinal mucosal cells and transported to fat cells to be stored.
130
What is step 1 of the MAG pathway?
Pancreatic lipase cleaves TAGs to MAGs and 2 free fatty acids.
131
What is step 2 of the MAG pathway?
MAGs, free fatty acids and cholesterol enter the intestinal mucosal cells.
132
MAGS, FFAs and cholesterol need to form what so they can be taken up into the intestinal mucosal cells?
Mixed micelles.
133
What additional material do MAGS, FFAs and cholesterol need to form mixed micelles?
Bile salts.
134
What is step 3 of the MAG pathway?
The fatty acids in the intestinal mucosal cells are activated to fatty acyl CoA and this is used to form TAGs and cholesteryl esters.
135
What is step 4 of the MAG pathway?
The intestinal mucosal cells will form a chylomicron which transports the TAGs, fat soluble vitamins and cholesteryl esters into the lymph and then the blood.
136
Why is it that TAGs and cholesteryl esters cannot be transported in the blood stream?
They are non polar.
137
What is a chylomicron?
A transport complex for lipids.
138
What is step 5 of the MAG pathway?
Dietary TAGs are cleaved in the capillaries of the heart and in fat cells.
Once the TAGs have been cleaved, it leaves the chylomicron remnants which are transported to the liver.
139
What enzyme will cleave dietary TAGs?
Lipoprotein lipase.
140
What is step 6 of the MAG pathway?
The chylomicron remnants are transported to the liver where they will enter the liver cells by endocytosis.
141
What do chylomicron remnants contain?
A few TAGs.
Lipid soluble vitamins.
Cholesteryl esters.
142
What does the liver use chylomicron remnants for?
To synthesise TAGs.
