Lipid Synthesis: Storage Lipids, Phospholipids, Cholesterol

Question 1

Have a basic understanding of figure 29.1 (Ex; How are triacyclglycerols formed?

Answer 1

Phosphatidate -precursor for storage lipids and membrane lipids like triacyglycerols and phospholipid synthesis.
Phosphatidate formed from glucose to DHAP to glycerol-3-phosphate
Phosphatidate (Diacylglycerol-3-phosphate) formed from addition of 2 FA’s to 3-phosphoglycerate
Phosphatidate can make phospholipids or triacylglycerols
Triacylglycerol made from Phosphatidate and acyl coa
Phospholipid made from phosphatidate and alcohol (or diacylglycerol with alcohol)
Both triacylglycerol and phospholipids made in Endoplasmic reticulum.

Question 2

What is phosphatidylcholine? What does it do?

Answer 2

Phosphatidlycholine- most common phospholipid in mammals.
it is a phospholipid attached to choline particle.
It is present in human diet like eggs yolk, soybeans and other foods.
when dietary choline insufficienct, liver has enzyme methyltransferase that will make phosphatidylcholine from phosphatidyl ethanoamine.
make ACh

Question 3

what role do sphingolipids play in the cell?

Answer 3

Sphingolipids- have sphingosine backbone in lipid (instead of glycerol). They are present in PM of eukaryotic cell and majority are present in CENTRAL NERVOUS SYSTEM- function in cell growth, differentiation, apoptosis, tissue development, cell adhesion
sphingolipids made from palmitoyl CoA and serine.
they can form Ceramide- sphingosine with acyl attached to amino group
ceramide form sphingomyelin- which is in myelin sheath; phosphorylcholine attach to terminal Oh of ceramide , cerebrosides-galactose attach to terminal Oh group of ceraimide
ganglioside- oligosaccaharide linked to ceramide by glucose

Question 4

*Understand the causes of “respiratory distress syndrome” and “Tay Sachs: disease.

Answer 4

respiratory distress syndrome- failure to synthesize dipalmitoylphophatidlycholine. This phospholipid is seen in alveoli of lung, helps prevent lung from collapsing at end of expiration phase of breathing. NOT ENOUGH of this phospholipid cause this condition in premature infants.
Tay Sachs disease: failure of lipid degradation. occurs after infants born. failure to degrade gangliosides. This occurs due to insufficiency in Beta-hexoaminidase enzyme, leading to build up ganglioside in body, neurons swollen with lymphocytes.
gangliosides mostly seen in gray matter in nervous system.

Question 5

*Understand in a general sense how cholesterol and triacyclglycerols are transported through the body.

Answer 5

through very low density lipoproteins (LDL, HDL).
Triacylglycerols in VLDL are hydrolyzed by lipases on capillary surfaces, and the freed fatty acids are taken into the cells. The cholesterol-rich remnants, called intermediate-density lipoproteins, can be taken up by the liver for processing or converted into low-density lipoprotein by the removal of more triacylglycerols

Question 6

*What are the consequences of aberrant LDL receptors?

Answer 6

elevated cholesterol levels, leading to artherosclerosis (thickennig of arteries), also heart attack
prevent this by LDL receptor mediated endocytosis- get rid of LDL in blood

Question 7

what is the evidence for protective effects of High density Lipoproteins (HDLS)?

Question 8

*Understand the functions of various steroid hormones

Answer 8

answered

Question 9

What are the three classes of lipids and what and their components?

Answer 9

Three classes of lipids:
1. Triacylglycerols- storage form of fatty acids (energy production)
2. Membrane lipids- phospholipids and sphingolipids
3. Cholesterol- Membrane component and precursor to steroid hormones
Cholesterol- lipid, heterocyclic molecule that increases fluidity of membrane.

Question 10

What is Triacylglycerol synthesized from and how is formed? What enzyme is required?

Answer 10

Triacylglycerols are synthesize from Phosphatidate in two steps.
Triacylglycerol synthase (which is bound to ER) will synthesize triacylglycerol from Phosphatidate and Acyl CoA
Steps:
1. Phosphatidate will cleave phosphate to produce DAG (diacylglycerol)
2. DAG then reacts with acyl CoA to from Triacylglycerol (TAG)

Question 11

What is the primary fuel storage in humans?

Answer 11

Triacylglycerols

Question 12

What is the role of Vitamin D? Where does the active form of Vitamin D come from?

Answer 12

Vitamin D plays a key role in Regulation of CALCIUM and Phosphate METABOLSIM
Active form of Vitamin D is CALCITROL which is formed from cholesterol in a pathway that involves Ultraviolet light-induced cleavage of one of the rings of steroid nucleus.
Calcitriol functions in a manner similar to steroid hormones.

Question 13

What kind of pathologies result from a deficiency of Vitamin D?

Answer 13

A deficiency of Vitamin D results in a pathological condition called RICKETS: Inadequate Calcification of cartilage and bone. Rickets commonly seen in Children
In adults, Vitamin D deficiency results in OSTEOMALACIA, a condition characterized by soft and weak bones.

Question 14

How are cholesterol and triacylglycerols transported into the blood? What do lipoprotein particles consist of? What is the role of proteins in lipoprotein particle?

Answer 14

Cholesterol and triacylgylcerol are transported in the blood in the form of lipoprotein particles.
Lipoprotein particles consist of a protein component and various lipids, depending on type of particle.
Protein serves to solubilize lipids and direct the particles to specific targets.

Question 15

How are lipoproteins classified?

Answer 15

Lipoproteins are classified according to DENSITY: the greater the proportion of lipid, the LESS DENSE the particle.

Question 16

What is the major carrier of cholesterol in the blood?

Answer 16

Low-density lipoprotein (LDL) is the major carrier of cholesterol in the blood.

Question 17

What is the role of HDL?

Answer 17

High-Density lipoprotein carries cholesterol that is released into blood black to the, a process called REVERSE cholesterol transport.

Question 18

compare and contrast LDL and HDL

Answer 18

HDL - Healthy, GOOD form of cholesterol as it can be returned to your liver and remove cholesterol before going to blood and building up in arteries. HDL will scavenge cholesterol and FA’s to liver for metabolism.
LDL- BAD form of cholesterol (goes directly to arteries, hence cause build up of cholesterol in arteries)
LDL distribute cholesterol and Free FA’s to heart, leading to build up plaques.

Question 19

What is the role and function of cholesterol in the body?

Answer 19

Cholesterol is VITAL to the body: it maintains proper FLUIDITY of animal cell membranes and is the precursor of steroid hormones such as progesterone, testosterone, estradiol and cortisol.

Question 20

What is the major site of cholesterol biosynthesis?

Answer 20

LIVER is the major site of cholesterol biosynthesis.

Question 21

How is Cholesterol synthesis regulated and what factors is it based on? What is the major enzyme in this process?

Answer 21

Regulation of cholesterol synthesis occurs through controlling the amount and activity of HMG CoA reductase (allosteric enzyme)
HMG CoA reductase catalyzes synthesis of mevalonate
First step: acetyl CoA + acetoacetyl CoA will give mevalonate (committed step)
Regulation of HMG CoA Reductase:
-gene expression- rate of mRNA synthase
-Rate of translation of mRNA
-Degradation of HMG CoA Reductase protein
-Phosphorylation of HMG CoA Reductase decreases activity.
when this enzyme is phosphorylated it is inactive. Dephosphorylate enzyme- activate it.

Question 22

What are functions of steroid hormones that are later produced from precursor of cholesterol?

Answer 22

Cholesterol (27 C) will later lose carbons to form Progestagens (21 c) which will form steroid hormones like Glucocorticoids (21 c), Mineralcorticoids (21 c) and Androgens (19 c) and Estrogens (18c)
Functions of hormones:
1. Glucocorticoids- release cortisol and induce inflammation
2. Mineralcorticoids- control salt and water by kidney (produce aldosterone)
3. Androgens and Estrogens- sex hormones

Question 23

What happens when you have high LDL?
What do the properties of Plasma lipoproteins depend on?
What happens as lipid particles become more dense?

Answer 23

High LDL- lead to more cholesterol build up, which is BAD.
Properties of plasma lipoproteins depend on ratio of lipids to proteins.
As lipid particles become more dense, you lose TAG’s, so 50% of TAG decreases, protein increases.
Liver- center for receiving and distributing, HDL and LDLs.

Question 24

What are Apolipoproteins?

Answer 24

Apolipoproteins are proteins that deliver protein to their specific tissues
ex: apoplipoprotein for Chylomicron is B48, C, E
solubilize hydrophobic lipids and contain cell-targeting signals

Question 25

What kind of process are Low- density Lipoproteins (LDL) an example of?

Answer 25

LDL is an example of RECEPTOR Mediated Endocytosis.
LDL will bind to LDL receptor attached to cell membrane, internalize (form vesicle) and then undergo lysosomal hydrolysis (release of amino acids and cholesterol oleate (cholesterol will bind to ER)
This helps regulate cholesterol metabolism by clearing out LDL receptor from blood and preventing atherlescleoris (hardening of arteries)

Question 26

*Understand the different forms of lipoproteins?

Answer 26

LDL- transport cholesterol to peripheral tissues and regulate de novo cholesterol synthesis.
HDL- picks up cholesterol released into the plasma from dying cells and from membranes undergoing turnover, and transport them to liver. a process termed reverse cholesterol transport.