Lipids Flashcards
1
Q
Define what lipids are
A
Substances that are insoluble in water but soluble in organic solvents
2
Q
What are the 3 main functions of lipids in the human body?
A
Structural component of biological membranes
Main source of energy
Precursors to steroid hormones, bile and signalling molecules
3
Q
Name 2 neutral lipids
A
TAGs
Cholesterol Esters
Cholesterol
4
Q
Name two polar lipids
A
Sphinolipids
Phospholipids
5
Q
What are TAGs
A
Triacylglycerides
These are esters of glycerol and fatty acids
6
Q
What is the basic formula structure for a fatty acid?
A
CH3 (CH2)n COOH
7
Q
What are the classes of fatty acids?
A
Saturated
Monounsaturated
Polyunsaturated
8
Q
How can you classify MUFAs and PUFAs?
A
Omega n- system
This is numbering the first carbon from the methyl carbon end where the first double bond comes in
9
Q
Name 2 saturated fatty acids
A
Butyric
Palmitic
Stearic
Arachidic
10
Q
Name two animal and two plant sources of saturated fatty acids?
A
Animal -> butter, lard
Plant -> palm & coconut oil
11
Q
Name 2 MUFAs
A
Oleic & Palmoleic
12
Q
Name two animal and two plant sources of MUFAs
A
Animal -> butter and lard
Plant -> olive oil for oleic acid & then nuts including cashews and almonds plus avocado
13
Q
Name 3 n-3 PUFAs & a dietary source of each
A
Alpha-linoleic -> linseed oil
EPA, DPA, DHA -> marine oils (e.g. oily fish)
14
Q
Name 3 n-6 PUFAs & 3 dietary sources
A
Linoleic, Gamma-linoleic, arachidonic
Vegetable oils -> sunflower, soybean, safflower, corn (linoleic)
15
Q
How is structure of a fatty acid affecting its water solubility?
A
Longer the chain length, less soluble it is
16
Q
How is structures of fatty acids affecting is melting point?
A
Chain length & saturation affects melting point. (The more saturated a molecule is the more likely it is to be solid at room temperature)
17
Q
What is the difference between cis and trans fats?
A
Both cis and trans fats have double bonds.
Cis isomers bends the fatty aid chain, making the fats morelikely to be a liquid at room temp and is found naturally in plants
Trans isomers keeps the chain more straight allowing fats to be more solid at room temperature and is more common in animal and manufactured/processed products (i.e. partial hydrogenation)
18
Q
What is the general structure of a phospholipid?
A
Glycerol + 2 fatty acids + one phosphate group
19
Q
Why is a phospholipid amphiphatic?
A
The phosphate head carries a negative charge and ionically bound to positive charge radicals (quite often amine groups like choline). This polar head is water soluble.
The fatty acid chain is water insoluble
20
Q
Name 3 types of phospholipids
A
Sphingolipids
Cardiolipids
Glycolipids
21
Q
What is the structure of a sphingolipid?
A
Phospholipid where phosphorylcholine is esterfied with sphingosine
22
Q
Where is sphingolipids found?
A
Myelin
23
Q
What is the structure of a cardiolipid?
A
Two phospholipids linked via a glycerol through their phosphate radicals
24
Q
Where is cardiolipids found?
A
Mitochondrial membranes of heart muscles
25
What is the structure of glycolipids?
Sphingosine bound to hexoses & complex carbohydrates instead of phosphorus
26
Where do you find glycolipids?
Most cell membranes
| Particularly found in cerebrosides and gangliosides
27
What is sterols?
Solid alcohols with a multiple ring strucutre
28
What are the two main types of sterols?
Cholesterol & Phytosterols
29
Name 3 functions of cholesterol in the body?
Structural component of membranes
| Precursors of bile acids, adrenal and gonadal enzymes and vitamin D
30
What is the main source of cholesterol in the diet?
Eggs
31
WHat is the average daily intake of lipids in a day?
500mg/day
32
What is the difference in cholesterol structure between cholesterol free in cells and plasma and cholesterol within atheroma plaques
Cholesterol in atheromatous plaques are esterfied with a hydroxyl group in the c3 position
Whereas cellular cholesterol is free form
33
What two processes occur to cholesterol to form bile acids?
Hydroxylation & oxidation
34
What are the two main bile acids?
Chenodeoxycholic & cholic acids
35
What must occur to the two acids produce by the liver to form finalised detergents in bile?
In the bile the two acids must be conjugated with taurine or glycine
36
What is important to note about plant sterols?
Phytosterols are poorly absorbed but may interfere with animal cholesterol absorption
37
Where is ergosterol located and what is its functional use?
Produced/Found in yeasts and is converted to vitamin D via UV light
38
What is the role of bile ad nd pancreatic juice in digestion & absorption of lipids?
Pancreatic Juice = enzyme digestion
| Bile = emulsification
39
Name 3 enzymes involved in lipid digestion, their targets and substrates.
Pancreatic Lipase acts on TAGs to make mono & di glycerides, glycerol and fatty acids
Phospholipase acts on phospholipids to make FAs and lysophospholipids
Cholesterol Esterase acts on cholesterol esters to form FAs and cholesterol
40
What is the role of bile emulsification in the SI?
Bile acids act as detergents. These are able to break up insoluble lipid droplets into smaller micelles to increase lipid surface area for lipid enzymes to work upon. Bile acids are amphiphatic and present their lipid portion to the centre of the micelle and their hydrophilic portion to the outside to allow for repelling of droplets -> i.e. emulsification
41
How is lipids absorbed?
Micelles cross the mucous layer within the SI which creates a microclimate which is slightly more acidic allowig for micelles to really their contents to the microvilli which can diffuse through into the epithelium
42
How much % of fatty acids and cholesterol is absorbed on average?
95% FAs
| 40% cholesterol
43
What two further processes occur within lumen epithelial cells before release?
Monoglyceride lipase able to hydrolyse monoglycerides to make FAs and glycerol
All the FAs and glycerol is used to form new TAGs through reesterification
44
What happens once newly synthesised TAGs are formed in gut epithelial cells?
Packaged into chylomicrons, transported to lacteals, into lymph system, go into the blood via the thoracic duct and goes to the liver where they are absorbed via B-48 apolipoprotein & LDL-receptors
Called the exogenous pathway
45
WHat is the difference between short, medium and long fatty acid chains in absorption and digestion?
Short chain FAs are not really part of the diet
Medium chain FAs are dirtectly secreted into the blood and transported via albumin
Long chain FAs require chylomicron transport and packaging
46
How are bile acids recycled?
Bile acid conjugates can be recycled and reabsorbed in the ileum and transported back to the liver
The bile acids that enter the colon can be deconjugated by the gut microbiota and this allows the deconjugated acids to be partially reabsorbed to go back to the liver for conjugation
47
What two mechanisms are present in babies in lipid D&A? And why do they require them?
Lingual serous glands secreting lipases
Maternal milk containing lipases
Require these because biliary and pancreatic secretions are not fully developed
48
What are the main way to deliver fatty acids to tissues in the body?
As NEFAs -> non-esterfied fatty acids -> these are bound to albumin
49
What two ways are lipids are transported in the body?
Bound to albumin -> NEFAs
| Or within lipoproteins
50
How many fatty acids can albumin bind to?
7 non-esterfied FAs
51
When does the concentration of NEFAs increase?
Starvation -> i.e. the release of FAs from adipose tissue stores
52
What are the 3 main functions of lipoproteins?
Transport of water immiscible lipids within blood
Delivery of cholesterol to tissues
Reverse transport of cholesterol
53
Describe the general structure of a lipoprotein?
Lipid rich core containing TAGs, cholesterol esters + phospholipids
Coated in a monolayer of phospholipids
Impregnated into the monolayer is free cholesterol & specific apolipoproteins
54
What are 2 main functions of apolipoproteins
Stabilisation of the molecule complex
Activiate / Inhibit enzymes e.g. hepatic / lipoprotein lipases
Responsible in interaction of special receptors for uptake into cells and tissues
55
What is the function of chylomicrons in lipid transport?
To carry TAGs (+ cholesterol esters) to the liver
56
What is the general function of VLDLs, IDLs, LDLs in relation to lipids?
Delivery of cholesterol to tissues
57
What is the general function of HDLs in relation to lipids?
Reverse transport of cholesterol to remove it from the system
58
How to the contents of the chylomicrons; VLDL,IDL, LDL group; and HDL compare?
Chylomicrons are TAGs rich, cholesterol esters low
VLDL, IDL, LDL begin being TAG rich and cholesterol esters low but as lipoprotein and hepatic lipases work on them they lose TAGs and consequently the cholesterol ester concentrations increase
HDLs are relaitively cholesterol rich, TAG deplete
59
What are the more specific functions of apolipoproteins A, B, C?
A = activates LCAT = lecithin-cholesterol acyltransferase = found in HDL molecules which is able to esterfy cholesterol
B (48+100) = structural & LDL-r = allows for the chylomicrons, VLDL, IDL and LDL to be absorbed be tissues and liver that display the LDL-receptor
C = cut = lipoprotein lipase & hepatic lipase = these are found on VLDL and IDL and HDL molecules to allow for the above enzymes to hydrolyse TAGs to release FAs
60
What is special about LDL apolipoprotein structures?
Only have B100 -> so the only thing that can happen to it is be taken up by tissues or liver
61
How do cells regulate cholesterol content?
Reducing LDL-r expression
Inhibition of synthetic processes of cholesterol
62
What are the sources of cholesterol for discoidal HDL molecules?
The cholesterol released from the conversions of VLDL to IDL to LDL when the molecules get smaller and experience excessive amounts of free cholesterol
From cells and tissues that display putative HDL-r / SR-B1 receptors
63
What is CETP standing for?
Cholesterol ester-transfer protein
64
What is the role of CETP?
Cholesterol ester-transfer protein acts as an alternative method for removing cholesterol from the system.
Post-Prandial, chylomicrons are high in TAGs concentration. The CETP is able to transfer TAGs into HDL2 molecules in return for cholesterol esters to enter the chylomicron. This movement is based on diffusion along the concentration gradients
This increases cholesterol removal because chylomicrons are directly absorbed by the liver so increases cholesterol deposition into the liver that way.
Also increases the level of TAGs in the HDL2 molecules allowing more hydrolysis of these molecules (instead of CEs) and then convert back to HDL3 which are smaller molecules which can pick up even more Cholesterol before going to the liver
65
What is the main storage place for lipids inthe body?
Adipose tissue
66
How does adipose tissue receive lipids for adipose tissue synthesis?
Via chylomicrons, VLDLs and IDLs
67
Other than lipids from lipoproteins how else does adipose tissue get sources for adipose tissue synthesis?
Dietary glucose is able to enter adipose tissues if in excessive amounts and can be converted to TAGs
68
How does insulin stimulate lipogenesis?
Insulin activates lipoprotein lipases to release TAGs and FAs from lipoproteins & stimulates TAG synthesis within the adipose tissue & prevents mobilisation
69
How do catelcholamines and glucagon prevent lipogenesis / promote lipolysis?
Promotes mobilisation of FAs from TAGs within adipose tissues to be released to the liver to be resynthesised into TAGs for energy metabolism
70
What is the main fatty acid released from the adipose tissue?
Oleic
71
How is fatty acids metabolised?
B-oxidation
72
Where does fatty acid metabolism take place?
Mitochondria
73
Explain b-oxidation?
The fatty acids are activated into CoA Thiolester / acyl CoA.
With each cycle a 2 carbon portion of the acyl CoA is removed (acetyl CoA) by a 4 enzyme complex
Acetyl CoA enters the citric acid cycle to be degraded into water and CO2 and produces NADH2 and FADH which is oxidised in the electron transport chain / oxidative phosphorylation stage to produce ATP
74
How much ATP does 1 palmitate molecule produce?
129 ATP
75
What is different about very long chain FA b-oxidation?
First need to be cut into smaller FAs in peroxisomes
76
What is the most essential fatty acid for life?
Arachidonic
77
What fatty acid does arachidonic acid come from?
Linoleic Acid
78
What is the main difference between synthesis of saturate and unsaturated fatty acids in de novo?
Liver and adipose tissues can synthesise all essential saturated fatty acids from precursors such as glucose and amino acids
The biosysnthesis of MUFAs and PUFAs is based on desaturation and elongation of dietary MUFAs and PUFAs i.e. cannot completely synthesis from scratch
79
What is the most important enzyme involved in the synthesis of PUFAs?
Delta-desaturase
80
What is the main enzyme in saturated fatty acid syntehsis
Fatty Acid Synthase
81
What is the main enzyme involved in lipogenesis
Fatty acid synthase
82
Name the essential fatty acids
Alpha-linoleic acid
| Linoleic acid
83
Why is linoleic and alpha linoleic acids essential in the diet?
These are the precursors to the n-3 and n-6 PUFAs which the body is unable to synthesise
84
What is the precursor of n-3 fatty acids?
Alpha-linoleic acid
85
What is the precursor of n-6 fatty acids?
Linoleic acid
86
What are some of the essential acids the body can make out of the two essential fatty acids?
```
Alpha-linoleic = n-3 = EPA and DHA
Linoleic = n-6 = arachidonic acid
```
87
Name two cardioprotective n-3 fatty acids?
EPA, DHA
88
Give 4 mechanisms that make n-3 fatty acids cardioprotective
Lowers TAG levels
Inhibits TxA2 synthesis & reduces platelet aggregation
Less vasoconstriction
Anti-arrhythmia
Stabilises atherosclerotic plaques
Reduces inflammation when in proinflammatory status
89
Why are n-3 and n-6 fatty acids associated with cardioprotective qualities? i.e. underlying mechanism?
Believed to be linked to their ability to form eicosanoids
90
What is the more potent cardioprotective fatty acid - n-3 or n-6?
n-3
