Chapter 15: Lipid Synthesis and Storage Flashcards
How do you designate which C on the FA is C1?
The carboxyl carbon is number 1
What is C2 of the FA also referred to as?
α-carbon
The name palmitic acid can be interchangeably referred to as what?
palmitate
Difference between saturated fatty acids and unsaturated fatty acids.
saturated fatty acids have no double bonds vs unsaturated fatty acids which have ≥ 1 double bonds
What are 2 important essential fatty acids discussed in this chapter?
linolenic acid and linoleic acid
Are linolenic and linoleic acid saturated or unsaturated fatty acids?
polyunsaturated fatty acids
C16:0 stands for what fatty acid and what does this numbering system tell you about the fatty acid?
palmitate: there are 16 C’s and 0 double bonds
What omega family would C18:2 (9,12) be?
omega(ω) 6 family (18-12)
How would you name the FA C18:3 (9,12, 15) using the omega nomenclature?
omega 3 family
Why may the use of omega - 3 FAs be associated with a decreased risk of cardiovascular disease?
These types of fatty acids may replace some of the arachidonic acid (an omega 6 fatty acid) in platelets –> lowering the production of thromboxane and tendency of the platelets to aggregate
Omega-3 is found in what foods?
high in some cold-water fish (salmon, tuna, herring), nuts (walnuts), and seeds (flaxseed)
High omega 3 fatty acids have not only been associated with a decrease in cardiovascular disease risks, but how else are they known to benefit humans?
they are associated with a decrease in serum triglycerides
Trans double bonds are often found in what food sources?
margarine and other foods where partial hydrogenation of vegetable oil is used in their prep
Which types of FAs are solid at room temp?
saturated and trans FA
Do trans fatty acids increase or decrease membrane fluidity?
decrease
What types of foods contain saturated fatty acids?
butter fat
Trans fatty acids and saturated fatty acids are associated with what condition?
atherosclerosis
Fatty acid + CoA + ATP forms what products?
Fatty acyl CoA + AMP + PPi
Upon entry of fats into the intestinal lumen, what is secreted by the liver to emulsify lipid contents?
bile
The pancreas secretes pancreatic lipase, colipase, and cholesterol esterase which degrades the lipids to what products?
2-monoglyceride, fatty acids, and cholesterol
Which enzymes are promoted by insulin in the process of FA synthesis?
- glucokinase (induced)
- PFK-2/PFK-1 (PFK-2 dephosphorylated)
- pyruvate dehydrogenase (dephosphorylated)
Major enzymes of fatty acid synthesis:
acetyl CoA carboxylase (dephosphorylated, activated)
fatty acid synthase (induced)
In the cytoplasm, which enzyme splits citrate back into acetyl CoA and oxaloacetate?
citrate lyase
Create a diagram for the synthesis of palmitate from glucose.
Acetyl CoA is activated in the cytoplasm for incorporation into fatty acids by what enzyme?
acetyl CoA carboxylase
What is the rate-limiting enzyme in the formation of fatty acid biosynthesis?
Acetyl CoA carboxylase
Acetyl CoA carboxylase requires what coenzymes/energy sources/hormones?
biotin, ATP, and CO2
- activation by insulin (dephosphorylated)
- activation by citrate
The CO2 added to form malonyl CoA is never incorporated into the fatty acid because it is removed by what enzyme? Explain.
fatty acid synthase during the addition of the acetyl group to the fatty acid
What is another name for fatty acid synthase?
palmitate synthase
What is the only fatty acid that humans can synthesize de novo?
palmitate
Palmitate contains an acyl carrier protein ACP that requires what vitamin?
pantothenic acid
How many acetyl CoA groups are req’d to produce palmitate?
8 acetyl CoA groups
Fatty acyl CoA may be elongated and desaturated (to a limited extent) in humans using enzymes associated with what organelle?
enzymes associated with the smooth endoplasmic reticulum (SER)
The smooth endoplasmic reticulum enzymes that are able to modify fatty acyl CoA cannot introduce double bonds past what position of the fatty acid?
position 9
What are the 2 sources of glycerol 3-P for triglyceride synthesis?
reduction of dihydroxyacetone phosphate (DHAP) from glycolysis by glycerol 3 P dehydrogenase, an enzyme in both adipose tissue and liver
Phosphorylation of free glycerol by glycerol kinase, an enzyme found in liver but not in adipose tissue
What is the function of glycerol kinase?
allows the liver to recycle the glycerol released during VLDL metabolism (insulin) back into new triglyceride synthesis
During fasting how does glucagon effect FA production in the liver?
glycerol kinase allows the liver to trap glycerol released into the blood from lipolysis in adipose tissue for subsequent conversion to glucose
Is glycerol kinase absent or present in adipose tissue?
absent
Create a diagram for triglyceride synthesis and storage.
What is the function of glycerophospholipids?
for membrane synthesis and for producing a hydrophilic surface layer on lipoproteins such as VLDL
In cell membranes, they also serve as a reservoir of second messengers such as diacylglycerol, inositol 1,4,5 triphosphate, and arachidonic acid
Describe the structure of glycerophospholipids.
similar to that of triglycerides, except that the last fatty acid is replaced by phosphate and a water-soluble group such as choline (phosphatidylcholine, lecithin) or inositol (phophatidylinositol)
How are TGs and cholesterol transported in the blood?
as lipoproteins
How are lipoproteins names?
according to their density, which increases with percentage of protein in the particle
Name the lipoproteins from least to most dense.
chylomicrons < VLDL < IDL (intermediate-density lipoproteins) < LDL (low-density lipoproteins) < HDL (high density lipoproteins)
Create a diagram on lipoprotein metabolism.
Create a diagram on lipoprotein and Apoprotein classes and appropriate lipoprotein function.
What enzyme is responsible for the metabolism of both chylomicrons and VLDL?
lipoprotein lipase
What are chylomicrons composed of?
dietary triglycerides,
cholesterol esters,
4 lipid soluble vitamins
apoproteins on surface
What is the purpose of Apo 48?
is attached to the chylomicron and is required for release from the epithelial cells into the lymphatics
Where do chylomicrons leave the lymph and enter peripheral blood?
leave the lymph and enter the peripheral blood where the thoracic duct joins the left subclavian vein
While in the blood, chylomicrons acquire what apo proteins from HDL particles?
ApoC-II and apo E from HDL
Which apo protein on the chylomicron activates LPL in adipose tissue?
apoC-II
Which apo receptor picks up chylomicrons and brings the into the liver?
apoE receptor
Most of the TG from the chylomicrons is sent to which tissue?
the adipose tissue
Purpose of Apo B-100 on VLDL?
to mediate release into the blood
What is the resulting particle of VLDL remnant?
IDL
How does IDL become LDL?
when cholesterol esters are tranferred from HDL particles they are converted into LDLs
Endocytosis of LDL is mediated by what apo receptor?
apoB-100 receptors (LDL receptors)
What are the pathways by which the liver has for acquiring cholesterol?
- de novo synthesis
- endocytosis of LDL
- transfer of cholesterol from HDL via the SR-B1 receptor
- Endocytosis of chylomicron remnants with residual dietary cholesterol
What is the rate-limiting step of de novo cholesterol synthesis?
HMG-CoA reductase
High or low cholesterol decreases the expression of HMG-CoA reductase?
high cholesterol
