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BioChem Exam 3 Practice Questions with verified answers
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BioChem Exam 3 Practice Questions with verified answers
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BioChem Exam 3 Practice Questionswith verified answers
Structure and biophysical properties of complex lipids (glycerophospholipids vs. sphingolipids) - correct
answer ✔✔Biophysical property of sphingolipid (detergent resistant) compared to glycerophospholipid
(detergent soluble)
Three components of glycerophospholipids - correct answer ✔✔(1) glycerol backbone; (2) fatty acid
chains at sn-1 and sn-2 position; (3) phospho-head group (choline, ethanolamine, serine, glycerol).
Cardiolipin is a special glycerophospholipid which has shared glycerol as head group
Glycerophospholipids synthesis: de novo pathway or remodeling pathway. - correct answer ✔✔In
remodeling pathway, the head groups of phosphatidylcholines (PC), phosphatidylserine (PS), and
phosphatidylethanolamine (PE) can be interconverted into each other; the fatty acid chains can be
switched between different glycerophospholipids by acyltransferase
Role of phospholipase? - correct answer ✔✔Glycerophospholipids are metabolized by phospholipases
PLA1/2 and release fatty acid, for example, PLA2 releases AA for COX pathway. Phosphors head group
can be released by PLC. For example: PLC hydrolyzes PIP2 to release IP3 that triggers calcium and also
produces DAG that activates PKC pathway. PLC can also release GPI-anchored protein from GPI-anchor.
Three components of sphingolipid - correct answer ✔✔ (1) sphingosine backbone
(2) fatty acid chain
(3) head group (H for ceramide; phosphocholine for sphingomyelin; sugars for glycosphingolipids)
Which sphingolipid plays a central role in sphingolipid metabolism? - correct answer ✔✔Ceramide can
be de novo synthesized and it is the precursor for all other sphingolipids. Ceramide is mainly from de
novo synthesis or metabolized from either sphingomyelin or glycosphingolipids
What are gangliosides and their function? - correct answer ✔✔Gangliosides are glycosphingolipids with
a polysaccharide chain, which contains sialic acid. The polysaccharide chain of gangliosides can serve as
receptor for bacterial proteins: for example, cholera toxin binds to ganglioside GM1
, Sphingolipid metabolism - correct answer ✔✔Sphingolipids are primarily degraded in lysosomes by
lysosomal hydrolases. Deficiency in a certain lysosomal hydrolase activity results in accumulation of
precursor for this hydrolase in lysosomes causing lysosome storage diseases.
Describe Gaucher disease, an example of lysosome storage disease. - correct answer ✔✔Deficiency in
glucosidase, a lysosomal hydrolase hydrolyzes glucosylceramide in ceramide, causes accumulation of
glucosylceramide in lysosomes leading to Gaucher disease
The primary source of each lipoprotein particles? - correct answer ✔✔The source of each lipoproteins:
chylomicron in the intestine, VLDL and HDL in the liver. IDL and LDL are derived from VLDL by lipase.
The relative content of triglycerides and cholesterol in lipoprotein particles - correct answer
✔✔Chylomicron: highest in triglycerides
LDL: highest in CE.
The structural role of apolipoproteins? - correct answer ✔✔Apolipoproteins: structural role, required for
de novo synthesis (ApoB48 for chylomicron; ApoB100 for VLDL, IDL, LDL; ApoA for HDL). Chylomicron,
VLDL, HDL are de novo synthesized. IDL and LDL are derived from VLDL.
Relative lifetime of each lipoprotein particle. - correct answer ✔✔HDL>LDL>VLDL>Chylomicron
- Both ApoB100 and ApoE are ligands for LDLR. However, ApoB100 has lower affinity to LDLR compared
to ApoE. Chylomicron and VLDL have both ApoB and ApoE. The triglycerides in chylomicron and VLDL are
rapidly hydrolyzed by LPL and the chylomicron remnants and VLDL remnants are cleared by liver through
LDLR and LRP. LDL has only ApoB100 but not ApoE. HDL has ApoA but not ApoB100 or ApoE. HDL does
not bind to LDLR
Lipoprotein receptors and their function? - correct answer ✔✔LDLR is regulated by intracellular
cholesterol. Scavenger receptor is not regulated by intracellular cholesterol. Foam cell formation is due
to continuously uptaking of oxidized LDL via scavenger receptor.
Function of lipase? - correct answer ✔✔(1) Lipoprotein lipase (LPL) converts chylomicron to chylomicron
remnant and also converts VLDL to VLDL remnant (IDL)
(2) HTGL converts VLDL remnants (IDL) to LDL
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