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Biochem 102 > Lipids > Flashcards

Lipids Flashcards

1
Q

What are lipids?

A

Heterogeneous, hydrophobic organic molecules
- insolubility in water results in compartmentalization

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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
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2
Q

Deficiencies in lipid metabolism lead to…

A

atherosclerosis, diabetes, obesity

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3
Q

Five classes of lipids

A
  1. Free Fatty Acids
  2. Triacylglycerols (TAG)
  3. Phospholipids
  4. Glycolipids
  5. Steroids
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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
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5
Q

What are fatty acids ionized at

A

pH 7

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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
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6
Q

Essential amino acids for diet

A

Linoleate, Linolenate
- body cannot produce large double bonds (omega 3) (don’t have the enzyme)

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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

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7
Q

Saturated

A

contains no double bonds

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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
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9
Q

Essential fats w-3 and w-6

A
  • important precursors to hormones
  • w-3 fats have cardiovascular protective properties
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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
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11
Q

Adipose Tissue

A

TAG are stored in adipose tissue in fat droplets “oil within cell”

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12
Q

Examples of how TAG is stored

A
  • stored in hummingbirds for energy
  • stored in polar bears for warmth
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12
Q

Phospholipids

A

Major class of membrane molecules
- amphipathic

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13
Q

Glycolipids

A
  • sugar containing lipids
  • found in cell membranes
  • role in cell-cell interacions
  • sugar always on extracellular side
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14
Q

Steroids

A

Lipids w/ a steroid nucleus

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15
Q

Functions of Steroids

A
  • hormones, facilitate digestion of lipids (bile salts), fluidity of membrane (dec.)
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15
Q

Dietary Lipids

A
  • dietary lipid intake for an adult is 60-150g/day
  • 90% TAG
  • 10% cholesterol, cholesterol esters, phospholipid, unesterified FFA
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16
Q

Where does lipid digestion begin

A

stomach

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17
Q

What is lipid digestion catalyzed by

A
  1. lingual lipase- released from glands behind the tongue
  2. gastric lipase- released from mucosal cells lining the stomach
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18
Q

What does digestion of lipids degrade?

A

degrade short/med length TAGs to glycerol and FFA

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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
Q

What does mechanical mixing in the stomach begin w/?

A

emulsification of fats (oil in water)

19
Q

What happens in the small intestine?

A
  • dietary lipids undergo further emulsification when mixed w/ bile salt
20
Q

What 2 mechanisms does emulsification help digestive enzymes work effectively w/?

A
  1. Mixture w/ bile salts- inc. SA of lipids available to enzymes
  2. Mechanical mixing by peristalsis
21
Q

Degradation by pancreatic enzymes

A

TAG digestion

21
Q

What is TAG digestion?

A
  • 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
Q

Can FFA freely transport into blood and cytoplasm?

A

No, need chylomicrons to make hydrophobic for transport

22
Q

TAG re-synthesis and transport

A

In intestinal cell lipid digestion products are resynthesized into TAG and packaged for transport

23
Q

What are Lipoproteins?

A

Lipoproteins are complexes of lipids and apolipoproteins found in the blood and plasma

24
Q

Four main classes of lipoproteins

A
  1. Chylomicrons (CM)
  2. Very Low Density Lipoproteins (VLDL)
  3. Low Density Lipoproteins (LDL)
  4. High Density Lipoproteins (HDL)
24
Q

Functions of Lipoproteins

A
  1. Maintain lipids in soluble form in blood
  2. Deliver lipids to tissues
25
Q

Medical relevance of Lipoproteins?

A

Dietary condition or genetic defects in cholesterol metabolism lead to plaque formation and result in atherosclerosis

26
Q

Composition of Lipoproteins?

A
  • A core of TAG and cholesteryl esters
  • a shell of cholesterol, phospholipids, apolipoproteins
27
Q

How are TAG and cholesterol obtained?

A

obtained from diet or de novo synthesis (mix. of fat sources), and packaged into inner core and carried by the particle in blood

28
Q

Size and density of CM?

A
  • largest, lowest density
  • highest lipid, lowest protein content
29
Q

Size and density of VLDL and LDL?

A
  • more dense than CM
  • higher content of protein and lower content of lipid
29
Q

Size and density of HDL?

A
  • smallest and most dense
  • greatest content of protein, lowest content of lipid
30
Q

Composition of CM?

A
  • mostly TAG
  • carry dietary fats to rest of body
31
Q

Composition of VLDL

A
  • mostly TAG
  • carry de novo synthesized fats from liver to rest of body
32
Q

Composition of LDL

A
  • very rich in cholesterol and cholesteryl esters (bad cholesterol)
  • after TAG is delivered to tissues from VLDL, LDL is what remains
32
Q

Composition of HDL

A
  • acceptor of free cholesterol
  • very rich in phospholipids and apolipoproteins
  • carrier of good cholesterol
  • cholesterol scavanger
33
Q

What are Apolipoproteins?

A

Protein component of lipoproteins

34
Q

Functions of Apolipoproteins

A
  1. Structural components of lipoproteins
  2. Recognition site for cell-surface receptors
  3. Activators or coenzymes for lipoprotein metabolic enzymes
35
Q

What do CM and VLDL release?

A

Release TAG to tissues

36
Q

What does Lipoprotein lipase release?

A
  • located on surface of tissues (adipose)
  • releases fatty acids from TAG into tissues
37
Q

Where do CM remnants go?

A

Return to liver

38
Q

What happens to VLDL?

A

Becomes LDL to deliver cholesterol to tissues

39
Q

Metabolism of LDL?

A
  • carry cholesterol to the peripheral tissues
  • contain apo B-100
40
Q

How is LDL removed from blood?

A
  • removed via cellular uptake
  • LDL receptors recognize apo B-100 and LDL is endocytosed
41
Q

What does the degradation of LDL release?

A

Releases cholesterol, a.a, FAs, phospholipids

42
Q

What happens to LDL receptors?

A

Recycled to the cell surface
- to bring more cholesterol in

43
Q

How does cholesterol uptake stop?

A

Once signalled enough cholesterol, will make a feedback loop, reducing number of receptors, reducing # of LDL’s

43
Q

What happens when cholesterol is oversupplied?

A
  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
Q

What is atherosclerosis?

A
  • characterized by elevated levels of LDL in the plasma
  • high cholesterol decreases the receptors for LDL
44
Q

What happens to excess LDL?

A

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
Q
A

Biochem 102 (13 decks)

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