Lipids Flashcards
Chylomicrons
Transport exogenous lipids from intestines to tissues.
VLDL/IDL/LDL
Transport endogenous lipids from liver to tissues.
HDL
Transports excess lipids from tissues back to liver.
ApoB100
Helps with endocytosis of LDL
ApoCII
Activates LPL to free fatty acids from the triglycerides
ApoE
Helps the lipoprotein bind to the cell.
Pathway of chylomicrons
Intestines –> Lymph –> Blood –> ApoCII frees fatty acids –> Back to liver for disassembly
What tissues have the greatest need for fatty acids?
Adipose tissue, muscle tissue, adrenal glands, gonads, lactating mammary glands
Pathway of Lipoproteins
VLDL + ApoB100 leave liver –> blood –> ApoCII and ApoE picked up from HDL –> ApoCII activates LPL, FFAS freed –> IDL –> Returns ApoCII and ApoE –> LDL Gives up cholesterol
What happens to LDL particles?
They are returned to the liver or scavenged by macrophages
What apolipoprotein is associated with foam cells?
LDL (foam cells formed when macrophages take up LDL)
Pathway of HDL
HDL + ApoE + ApoCII leave liver –> Gives ApoE and ApoCII to VLDL –> Takes them back from IDL –> Picks up excess cholesterol for delivery to the liver
Where does ketogenesis occur?
Liver - mitochondria
Where does cholesterol synthesis occur?
Liver - cytosol
What tissues synthesize cholesterol?
Brain, ovaries, testes, intestines, liver (BOTIL)
What process is mevalonate associated with?
Cholesterol synthesis
How do statins work?
They compete with HMG CoA for access to HMG-CoA reductase (short half-life)
What regulates cholesterol synthesis? Where is it located?
SREBP in ER
What phenotypes does SREBP impact?
HMG-CoA reductase, LDL receptor expression
What hormones can be made from cholesterol?
Progesterone, aldosterone, cortisol, estradiol, testosterone (PACET)
In what process does succinyl CoA serve as a source of CoA?
Oxidation of ketone bodies
Where do animals get fatty acids from?
- Diet
- Storage (adipocytes)
- Converting carbohydrates to fats
- Autophagy
Where are triglycerides stored?
-Adipose tissue
- Between muscle fibers and within muscle cells
What tissues respond to signals from glucagon?
Liver & skeletal muscle
What are the three lipases used in triglyceride breakdown?
- Hormone-sensitive lipase (HSL)
- Adipose Triglyceride Lipase (ATGL)
- Monoacylglycerol lipase (MGL)
What does albumin bind to?
Fatty acid transporters on myocytes
What is the product of fatty acid “activation?”
Fatty acyl CoA
Where does carnitine come into play?
Involved in moving fatty acyl CoA from cytosol to matrix for oxidation
What are the products of one round of beta oxidation?
1 FADH2, 1 NADH, 1 acetyl CoA
What does isomerase do?
It converts cis alkenes to trans and can move the alkene into the AB position.
What does reductase do?
It can reduce two adjacent alkenes into one (in the position between the two original alkenes)
What do trans fatty acids do in the body?
They activate SREBP, leading to increased cholesterol synthesis.
Which fatty acids need isomerase and reductase enzymes?
Unsaturated fatty acids
Which fatty acids need to be oxidized in the peroxisome?
Branched and very long chain fatty acids
What is different when FAs are oxidized in the peroxisome?
The FADH2 is used to make H2O2, which is broken into H2O and O2 by catalase.
CPT-I and CPT-II aren’t necessary
Where does beta oxidation occur?
Mitochondrial matrix (liver, brain, adipose tissue, muscle tissue)
What process is propionyl CoA associated with?
Oxidation of odd-chain fatty acids
What differs about how plants carry out beta oxidation?
They oxidize almost entirely within peroxisomes
Which process needs bicarb, biotin/B7, ATP, and B12?
Oxidation of odd-chain fatty acids
Which process involves creating succinyl CoA?
Oxidation of odd chain fatty acids.
What are the conditions for fatty acid synthesis?
Excess acetyl CoA and plentiful ATP
In plants, where does fatty acid synthesis occur?
Stroma
Where does fatty acid synthesis occur?
In the cytosol
What are the two sources of citrate used in fatty acid biosynthesis?
- Excess acetyl CoA combining with OAA
- Reversal of aconitase reaction caused by ATP inhibiting isocitrate dehydrogenase
What does the tricarboxylate transport system do?
It creates and moves citrate across the IMM and into the cytosol for FA synthesis.
What happens to the OAA (from citrate) in the cytosol?
Malate –> Pyruvate –> MPC
*Malate to pyruvate generates NADPH
What are the 2 sources of NADPH in fatty acid biosynthesis?
- Conversion of malate to pyruvate
- Pentose phosphate pathway (PPP)
Where is the NADPH concentration highest in the cell
In the cytosol (where fatty acid synthesis occurs)
Where is the NADH concentration highest in the cell?
In the mitochondria (beta oxidation generates NADH)
What is the “activation” product needed for fatty acid synthesis?
Malonyl CoA
What process is malonyl CoA associated with?
Fatty acid synthesis
What molecule inhibits CPT-I?
Malonyl CoA
What is the regulatory step of fatty acid synthesis?
Creation of malonyl CoA via ACC
What are the 2 components of ACC?
Biotin carboxylase (takes CO2 off of bicarb)
Transcarboxylase (gives CO2 to ACoA)
Where is the thiol on the ACP located?
Phosphatidic acid prosthetic group
What enzymes are used to elongate fatty acids?
Elongase and desaturase
Where does FA desaturation/elongation occur?
ER or mitochondria
What process involves electrons being transported from NADPH to Cyt B reductase and Cyt B?
Desaturation of fatty acids
What is linoleate needed for?
To make arachidonic acid
What is linolenate needed for?
To make omega 3s like DHA and EPA
Pathway of arachidonic acid
Cleaved off membrane by phospholipase A2
Lipoxygenase converts to leukotrienes
COX converts to PGH2
PGH2 can be converted to thromboxane, prostaglandins, and prostacyclin
What pathways are associated with phosphatidic acid?
Synthesis of triglycerides and phospholipids
What is the “activation” product for synthesis of triglycerides and phospholipids?
Phosphatidic acid
What molecules are used to elongate fatty acids in the mitochondria?
Acetyl CoA (reversal of beta oxidation)
What molecules are used to elongate fatty acids in the ER?
Palmitate condensed with malonyl CoA
