Lipids

common saturated fatty acids

myristic acid (14:0), Palmitic Acid (16:0), Stearic Acid (18:0)

Precursor to DHA and EPA

alpha linolenic acid (18:3)

precursor to Arachidonic acid

linoleic acid (18:2)

describe triacylglycerol digestion

Lingual lipase allows for minor digestion of triacylglycerol in the mouth, cleaving some fatty acids at the sn-3 position to yield DAG

In the stomach, gastric lipase also cleaves some TAG at the sn-3 position to yield DAG.

In the small intestine, bile emulsifies TAG, DAC, and FFA to form micelles. Then pancreatic lipase cleaves some fatty acids at sn-1 and sn-3 position to create MAG and fatty acids. The micelles allow the lipids to enter the enterocyte while short and medium chain free fatty acids do not require micelles and can be absorbed directly into the enterocytes.

Describe how free fatty acids and MAG get absorbed into the intestinal cell and then into the blood stream

The micelles allow for absorption of FFA, and MAG into the enterocyte. The CD 36 transporter transfers the fatty acids across the membrane into the cell. FABP (fatty acid binding protein) carries these lipids in the cytosol to the ER. In the endoplasmic reticulum, these fatty acids are reformed into TG and packed into chylomicrons. The chylomicrons then exit the enterocyte and enter the lymphatic system, where the lipoproteins can drip into the blood stream

describe how short and medium chain FFAs are absorbed into the intestinal cell and then into the bloodstream

short and medium chain FFAs are able to be absorbed directly into the enterocyte and are transported by albumin directly into the bloodstream.

chylomicron

carries large amount of TG via lymph to the blood stream and eventually to the liver

made in enterocytes, contains mostly TG

VLDL (very-low-density lipoprotein)

made in liver, packages cholesterol and TG for distribution to tissues, about half is TG

LDL (low-density lipoprotein)

major lipoprotein that carries cholesterol in blood

formed from VLDL to IDL and then LDL in the blood

about half is cholesterol

HDL (high density lipoprotein)

brings cholesterol from tissues back to liver

made in liver, about half is protein with other portions of cholesterol and TG

What do chylomicrons transport?

free fatty acids, MAG, exogenous cholesterol, TAG

What transports endogenous cholesterol?

VLDL, LDL, HDL

What does VLDL transport?

endogenous cholesterol and TAG

How much total fat a day for infants?

30-31 g

AI for linoleic acid

17g/day for men, 12g/day for women

AI for alpha linolenic acid

1.6g/day for men, 1.2 g/day for women

AMDR for fat

20-35% of total calories

Reduced saturated fat intake is associated with

decreased total cholesterol, decreased LDL levels, and decreased CVD events

What did Brown and Goldstein discover?

LDL receptors, provided the basis for trials of statin to lower LDL cholesterol

What enzymes do statin inhibit?

HMG-CoA reductase

How can the body produce cholesterol endogenously?

The body can produce cholesterol from acetyl-CoA through a series of reactions

What does HMG-CoA reductase do in the process of synthesizing cholesterol?

it converts HMG-CoA to mevalonate

Which enzyme allows FFA and MAG to enter the adipocyte?

Lipoprotein lipase (LPL) acts on TAG in the chylomicrons and VLDL so that FFA and MAG can enter the cell

What happens to the chylomicron remnant?

CR enters the hepatocyte by endocytosis and is taken up by a lysosome. FFA, MAG, and cholesterol are released and the lipids are reformed to TAG and CE

apoprotein

protein part of a lipoprotein

Explain how LDL is taken up in the cell

1. LDL particle with apoB attached to the LDL receptor

2. Endocytosis of LDL particle and receptors

3. Endocytosis LDL particle fuses with lysosome

4. LDL receptors return to the membrane surface

5. Proteins of LDL particle are hydrolyzed to AAs

6. Free cholesterol released from LDL particle

7. Cholesterol transferred to Golgi, esterified with ACAT, and stored in cell

cholesterol ester

storage form of cholesterol

name the 3 mechanisms used to control LDL cholesterol and how much cholesterol comes into the cell

1. reduce HMF CoA reductase, the enzyme that makes cholesterol

2. increase esterification of cholesterol via ACAT so that it is stored

3. decrease LDL receptors on cell membrane

What can the body use Omega-6 linoleic acid to create?

Arachidonic acid (20:4)

What can the body use Omega-3 alpha linolenic acid to create?

EPA (20:5) and DHA (22:6)

symptoms of fatty acid deficiency

Classic symptoms: retarded growth, scaly dermatitis, male and female infertility

Other problems: increased fragility of RBCs, increased susceptibility to infection, kidney abnormalities

How is essential fatty acid deficiency assessed?

by the tried/tetraene or T/T ration

a ratio of >0.02 or 0.04 is considered an EFA deficiency

Summarize the controversy around coconut oil

Coconut oil is 82% saturated fat, but half is from lauric acid.

When Lauric acid replaces dietary CHOs it does not increase LDL cholesterol as much as some other saturated fats and it increased HDL.

However, it is not advised to use excessively, as it still increases LDL cholesterol

lipoprotein lipase

breaks down TAG in blood to be stored in adipose tissue

hormone sensitive lipase

breaks down stored TAG in adipocytes to be released into the bloodstream for use

Fat sources highest in monounsaturated fats

canola, safflower, avocado, and olive oil

Fat sources highest in omega 3 fatty acids

flaxseed, walnut, and canola oils

Fats highest in Omega 6 fatty acids

sunflower, grapeseed, and corn oil