Lipids Flashcards
What is a lipid?(2)
An organic compound
That is readily soluble in non polar solvent but not in polar solvent
What are the forms of fatty acids in the body?(5)
FFAs TAGs Cholesterol esters Phospholipids Glycolipids
What is a fatty acid?
A long hydrocarbon chain with a terminal carboxyl group
What is energy from dietary lipids mainly dependant on?
Chain length
How many double bonds does saturated fatty acid have?
0
How many double bonds does monounsaturated fatty acid have?
1
Short chain fatty acids (4)
Less than 8 carbons
Water soluble
Mainly found in products containing ruminant milk
Don’t become part of body lipid pool
Medium chain fatty acids (4)
8-14 carbons
Arise during synthesis of LCFA
Found in coconut milk and milk fat
Rarely incorporated into body lipid pool
Long chain fatty acids (2)
Greater than 14 carbons
Main constituent of dietary fat
Where does fatty acid synthesis occur?
Cytosol
Which compound does fatty acid synthesis require?
Acetyl CoA
Explain C18:2 cis 9, 12 (3)
18 carbons
2 double bonds at carbon 9 and 12 from the carboxyl end
Explain C18:2 n-6 (3)
18 carbons
2 double bonds at carbon 6 counting from the methyl end
Which pathway does 6-desaturase prefer and why?
N-3
To ensure essential fatty acids are produced
Explain lipid re-esterification during absorption process (4)
2-MAGs and FFAs enter enterocytes
It is the converted to DAG by adding a fatty acid and removing CoA
DAG is then converted toTAG
The common saturated fat (2)
Palmatic acid C16:0
Stearic acid C18:0
Common monounsaturated fat
Oleic acid C18:1
Common polyunsaturated fats (2)
Linoleic acid C18:2
DHA C22:6
What form is most body fat stored as?
TAG
Fatty acid synthesis in the cytosol (5)
Acetyl CoA C2:0 Malonyl CoA C3:0 Palmitic acid C16:0 Stearic acid C18:0 Oleic acid C18:1
Enzymes of fatty acid synthesis in the cytosol (4)
Acetyl CoA carboxylase
Fatty acid synthase
Elongase
9-desaturase
What is the importance of the enzymes 6-desaturase?(2)
All fatty acid pathways use this enzyme
It’s the key enzyme that determines which PUFAs are produced
What is the average fat intake in the western diet?(2)
50-100g per day
35-40% total energy
Why are dietary lipids important?(8)
Provide energy Cell signalling Food texture Food flavour Hormone precursors Supply fat soluble vitamins Supply essential fatty acids Insulation
Explain the gastric stage of TAG digestion (5)
Lingual lipase secreted from glands under tongues Travels with food to stomach Penetrates milk fat globules Hydrolyses fatty acids Chyme is released into the duodenum
Duodenal phase of digestion (6)
TAG (in chyme) is released into the duodenum
Chyme stimulates the release of CCK
Bile acids are secreted from the gall bladder
Pancreatic lipase are released
Lipid droplets are then coated in bile salts
Which forms micelles
What does pancreatic lipase do?(3)
Binds to micelles
Hydrolyses TAG in the presence of Ca2+
Produces two fatty acids and 2-MAG
How are fats solubilised?(2)
By associating with bile salts and forming micelles
Why must fats be emulsified?(3)
To increase accessibility of fats to digestive enzymes
This is because fats are hydrophobic
And digestive enzymes are hydrophilic
What happens after TAG esterification during absorption process? (4)
They are packed into chylomicrons
So they are able to be transported
Chylomicrons are then released into the lymphatic system
The chylomicron then passes into the blood stream
Chylomicron metabolism (4)
Interacts with lipoprotein lipase
TAG in chylomicrons is hydrolysed to release FFAs
FFAs are either oxidised for energy in muscle
Or re-esterified to form TAG for storage in adipose tissue
What happens after most of the TAG in the chylomicron is hydrolysed?(2)
It becomes a chylomicron remnant
It is then removed from the blood by the liver
What is the function of plasma lipoproteins (2)
Transport lipids from the site of production or absorption to the site of utilisation and storage
Role of LDL
Transport cholesterol from liver to body tissues
Role of VLDL
Transport newly synthesised TAG from liver to peripheral tissues
Role of HDL
Transport cholesterol from tissues to liver
What are the essential fatty acids obtained by and their formula (2)
Linoleic acid C18:2, n-6
a-linolenic acid C18:3, n-3
Potential consequences of essential fatty acid deficiency (2)
Increase permeability to water and small molecules
Reduced efficiency of oxidative phosphorylation in mitochondria
Ketone can be used by tissue that can’t use ____
FAs
Name some organs that can’t use fatty acids (3)
Brain
Kidney medulla
Eye
Classes of lipids (4)
Simple
Complex
Derived
Miscellaneous
Examples of simple lipids (3)
FAs esterified with glycerol
TAG
Waxes
Example of complex lipids (3)
Phospholipids
Glycolipids
Lipoproteins
Examples of derived lipids (3)
Saturated fats
Monounsaturated fats
Polyunsaturated fats
Major biological roles of FAs (4)
Energy storage
Protection
Essential components of biological membranes
Precursors of bio active molecules
Sources of palmitic acid (3)
Meat
Dairy products
Palm oil
Sources of oleic acid (3)
Meat
Dairy products
Olive oil
Stearic acid sources (3)
Animal fats
Vegetable fats
Cocoa butter
Linoleic acid sources (2)
Sunflower oil
Corn oil
DHA sources
Oily fish
What are bile salts?(3)
Hydroxylated steroids derived from cholesterol
Conjugated to an AA side chain
Amphipathic
What is FA transport across the membrane dependent on?
Inward diffusion gradient
What happens to bile acids during absorption (4)
Pass through to ileum
Absorbed and recirculated in the portal vein
To the liver
Re-enter the duodenum
Where do LCFAs originate from?(3)
Diet
Synthesis of acetyl CoA
Elongation of SCFA
Stages of TAG digestion (3)
Gastric
Duodenal
Ilial
Production of PUFAs (3)
Derived from MUFA
Double bond inserted into LCFAs
Uses desaturase enzyme
What is co-lipase?(3)
Co-enzyme secreted by pancreas
And absorbed on to surface of oil droplet
Acts as an anchor for pancreatic lipase at the oil/water interphase
Where does the majority of fat absorption occur?
Jejunum
When does fat absorption occur?
When the micelles come into contact with the microvillus membrane of the enterocytes
Fat absorption process (3)
Lipids absorbed but not bile salts
Lipids transferred from micelles to enterocyte
Facilitated by FA binding proteins
Why are some fatty acids essential?(2)
Mammals lack the enzymes to insert double bonds beyond C9 in a chain
Between existing bond and carboxyl group
N-9 pathway (6) C18:1 - C24:4
Oleic acid C18:1 C18:2 C20:2 C20:3 C22:3 C24:4
N-6 pathway (6) C18:2 - C22:5
Linoleic acid C18:2 a-linolenic acid C18:3 C20:3 Arachidonic acid C20:4 C22:4 Docosapentanoic acid C22:5
N-3 pathway (6) C18:3 - C22:6
a-linolenic acid C18:3 C18:4 C20:4 EPA C20:5 C22:5 DHA C22:6
Which essential fatty acid is a component of the retina?
DHA
Roles of eicosanoids (3)
Mediate variety of cellular functions
Local hormones
Modulate inflammatory response
Which cellular functions do eicosanoids mediate?(2)
Smooth muscle contraction Platelet aggregation (Blood clotting)
Role of eicosanoids as local hormones (2)
Paracrines
Autocrines
How do eicosanoids modulate inflammatory responses?(3)
Regulate constriction and dilation of blood vessels
Prostacyclins inhibit platelet aggregation
Thromboxanes stimulate platelet aggregation
What are eicosanoids?
Derivatives of omega 3 and omega 6
Which type of fatty acid produces more potent eicosanoids?
Omega 6
Mechanisms by which omega 3 reduces CVD risk?(5)
Reduced susceptibility of heart and ventricular arrhythmia Reduces adhesion molecule expression Anti-inflammatory effect Promotes endothelial relaxation Mildly hypotensive
What are conjugated linoleic acids?
Linoleic acids which have double bonds next to each other
How are CLAs produced?(3)
Rumen bacteria tend to saturate double bonds in fatty acids
CLAs are produced as intermediates of this process
Some of the intermediates escape and enter tissues
Potential health benefits of CLAs (5)
Anti-carcinogenic Modulation of body composition Anti-diabetic Immunity enhancement Improved bone mineralisation
How much energy does a gram of fat produce?
39.1kJ
What are the two predominant CLAs?
Cis-9, trans 11
Trans 10, cis 11
What are micelles?(3)
Spherical aggregates of amphipathic molecules
Consists of a hydrophobic core
And hydrophilic surface
