Lipids Flashcards
1
Q
What are lipids?
A
Heterogeneous, hydrophobic organic molecules
- insolubility in water results in compartmentalization
2
Q
Functions of lipids
A
- major source of energy
- structural component of cell membranes
- may serve as fat-soluble vitamins
- structural component of prostaglandins and steroid hormones
2
Q
Deficiencies in lipid metabolism lead to…
A
atherosclerosis, diabetes, obesity
3
Q
Five classes of lipids
A
- Free Fatty Acids
- Triacylglycerols (TAG)
- Phospholipids
- Glycolipids
- Steroids
4
Q
Fatty Acids
A
- chains of hydrocarbons that terminate in COOH
- simplest lipids
- most common fuel source
- also building blocks for membranes
- can contain double bonds and vary in length
5
Q
What are fatty acids ionized at
A
pH 7
6
Q
Naming Fatty Acids
A
- C of COOH is C 1
- final methyl group is w
- double bond is represented by a delta superscript w/ numbers rep. the position of the bond from the end
6
Q
Essential amino acids for diet
A
Linoleate, Linolenate
- body cannot produce large double bonds (omega 3) (don’t have the enzyme)
7
Q
Unsaturated
A
contains double bonds
- can be cis or trans double bonds
- trans bad and unnatural
- decreases the M.P
- longer HC, greater M.P
7
Q
Saturated
A
contains no double bonds
8
Q
Too much saturated and trans unsaturated fats are bad
A
- elevated cholesterol and cardiovascular disease
- biochemical basis unknown but trans-unsaturated fats trigger immune response
9
Q
Essential fats w-3 and w-6
A
- important precursors to hormones
- w-3 fats have cardiovascular protective properties
10
Q
Triacylglycreols (TAGs)
A
- Glycerol backbone w/ three fatty acid chains
- primary storage molecule
- FFA are strong acids, low pH
- 1 gram of TAG = 6x the energy of 1 gram of glycogen
11
Q
Adipose Tissue
A
TAG are stored in adipose tissue in fat droplets “oil within cell”
12
Q
Examples of how TAG is stored
A
- stored in hummingbirds for energy
- stored in polar bears for warmth
12
Q
Phospholipids
A
Major class of membrane molecules
- amphipathic
13
Q
Glycolipids
A
- sugar containing lipids
- found in cell membranes
- role in cell-cell interacions
- sugar always on extracellular side
14
Q
Steroids
A
Lipids w/ a steroid nucleus
15
Q
Functions of Steroids
A
- hormones, facilitate digestion of lipids (bile salts), fluidity of membrane (dec.)
15
Q
Dietary Lipids
A
- dietary lipid intake for an adult is 60-150g/day
- 90% TAG
- 10% cholesterol, cholesterol esters, phospholipid, unesterified FFA
16
Q
Where does lipid digestion begin
A
stomach
17
Q
What is lipid digestion catalyzed by
A
- lingual lipase- released from glands behind the tongue
- gastric lipase- released from mucosal cells lining the stomach
18
Q
What does digestion of lipids degrade?
A
degrade short/med length TAGs to glycerol and FFA
18
Q
Importance of lipid digestion
A
- important for lipid digestion in infants where milk (high in TAGs) is primary source of energy
- important in CF patients who have pancreatic insufficiency
19
What does mechanical mixing in the stomach begin w/?
emulsification of fats (oil in water)
19
What happens in the small intestine?
- dietary lipids undergo further emulsification when mixed w/ bile salt
20
What 2 mechanisms does emulsification help digestive enzymes work effectively w/?
1. Mixture w/ bile salts- inc. SA of lipids available to enzymes
2. Mechanical mixing by peristalsis
21
Degradation by pancreatic enzymes
TAG digestion
21
What is TAG digestion?
- TAG molecules too large for mucosal cellular uptake
- pancreatic lipase preferentially removes fatty acids from C 1 and 3
- primary products are two FFA and 2-monoacylglycerol
22
Can FFA freely transport into blood and cytoplasm?
No, need chylomicrons to make hydrophobic for transport
22
TAG re-synthesis and transport
In intestinal cell lipid digestion products are resynthesized into TAG and packaged for transport
23
What are Lipoproteins?
Lipoproteins are complexes of lipids and apolipoproteins found in the blood and plasma
24
Four main classes of lipoproteins
1. Chylomicrons (CM)
2. Very Low Density Lipoproteins (VLDL)
3. Low Density Lipoproteins (LDL)
4. High Density Lipoproteins (HDL)
24
Functions of Lipoproteins
1. Maintain lipids in soluble form in blood
2. Deliver lipids to tissues
25
Medical relevance of Lipoproteins?
Dietary condition or genetic defects in cholesterol metabolism lead to plaque formation and result in atherosclerosis
26
Composition of Lipoproteins?
- A core of TAG and cholesteryl esters
- a shell of cholesterol, phospholipids, apolipoproteins
27
How are TAG and cholesterol obtained?
obtained from diet or de novo synthesis (mix. of fat sources), and packaged into inner core and carried by the particle in blood
28
Size and density of CM?
- largest, lowest density
- highest lipid, lowest protein content
29
Size and density of VLDL and LDL?
- more dense than CM
- higher content of protein and lower content of lipid
29
Size and density of HDL?
- smallest and most dense
- greatest content of protein, lowest content of lipid
30
Composition of CM?
- mostly TAG
- carry dietary fats to rest of body
31
Composition of VLDL
- mostly TAG
- carry de novo synthesized fats from liver to rest of body
32
Composition of LDL
- very rich in cholesterol and cholesteryl esters (bad cholesterol)
- after TAG is delivered to tissues from VLDL, LDL is what remains
32
Composition of HDL
- acceptor of free cholesterol
- very rich in phospholipids and apolipoproteins
- carrier of good cholesterol
- cholesterol scavanger
33
What are Apolipoproteins?
Protein component of lipoproteins
34
Functions of Apolipoproteins
1. Structural components of lipoproteins
2. Recognition site for cell-surface receptors
3. Activators or coenzymes for lipoprotein metabolic enzymes
35
What do CM and VLDL release?
Release TAG to tissues
36
What does Lipoprotein lipase release?
- located on surface of tissues (adipose)
- releases fatty acids from TAG into tissues
37
Where do CM remnants go?
Return to liver
38
What happens to VLDL?
Becomes LDL to deliver cholesterol to tissues
39
Metabolism of LDL?
- carry cholesterol to the peripheral tissues
- contain apo B-100
40
How is LDL removed from blood?
- removed via cellular uptake
- LDL receptors recognize apo B-100 and LDL is endocytosed
41
What does the degradation of LDL release?
Releases cholesterol, a.a, FAs, phospholipids
42
What happens to LDL receptors?
Recycled to the cell surface
- to bring more cholesterol in
43
How does cholesterol uptake stop?
Once signalled enough cholesterol, will make a feedback loop, reducing number of receptors, reducing # of LDL's
43
What happens when cholesterol is oversupplied?
1. High cholesterol inhibit HMG CoA reductase (sterol dependent degradation), resulting in decreased cholesterol synthesis
2. High cholesterol reduces the number of LDL receptors = less uptake
3. Storage of cholesterol as cholesteryl esters
44
What is atherosclerosis?
- characterized by elevated levels of LDL in the plasma
- high cholesterol decreases the receptors for LDL
44
What happens to excess LDL?
Becomes oxidized
- instigates immune response
- macrophages take up oxLDL and become engorged forming foam cells
- foam cells get trapped in the blood vessel walls contributing to plaque formation
45
