Overview of Lipid Biochemistry Flashcards
Structure
cholesterol
Characteristics of cholesterol structure
Structure?
phospholipids
Characteristics of phospholipid structure
- hydrophillic head
- fatty acid chains = hydrophobic
Structure?
fatty acid
Characteristics of Fatty Acid Structure
- hydrocarbon chain
- saturated vs. unsaturated
- carboxyl group
Chemical properties of lipids
- less polar than gluocse or amino acids
- not water soluble
Fatty acids: chemical properties & sources
- Chem prop
- Most polar
- Sources
- Acetyl CoA → de novo lipogenesis
- Diet for essential fatty acids
- Sugars, AA’s, fats
Phospholipids: chemical properties & sources
- Chem prop
- 2nd most polar
- Sources
- membranes
Cholesterol: chemical properties & sources
- Chem prop
- 3rd most polar
- Sources
- Diet
- Synthesized from Acetyl CoA in liver
Cholesterol ester: chemical properties & sources
- Chem prop
- not very polar
- Cholesterol ester = precursor to cholesterol
Triglycerides: chemical properties & sources
- Chem prop
- non polar
Fatty acids: General fxns
- Float in blood during exercise
- Major component of cell membranes
- Store calories
- Precursors for eicosanoids like prostaglandins, leukotrienes, thromboxanes
Phospholipids: General fxns
form membranes
Cholesterol: General fxns
- Cell membrane component
- precursor for steroid proteins
- bile acids
De Novo lipogenesis pathway (general)
- glucose is present in the liver or adipose tissue in excess (fed state) undergoes glycolysis to pyruvate
- ==> mitochodria ==>converted to acetyl CoA
- ==> citrate ==> leaves the mitochondria
- ==> fatty acid @ cytoplasm.
De Novo Lipogenesis @ liver & adipose tissue
Liver: Acetyl CoA → Citrate → leaves mitochondria → Acetyl CoA → Malonyl CoA → Fatty Acid
Adipose tissue: Fatty acid + glycerol → Tryglyceride. Or it can be stored as VLDL.
Beta-oxidation pathway
- body is in negative energy balance such as (short-term fasting or during exercise)
- fat = important alternative fuel for muscle and liver in an effort to preserve glucose for the brain.
- oxidation of fat during fasting provides the energy (ATP) which is needed to fuel gluconeogenesis.
- Occurs in mitochondria.
- Triglycerides in adipose tissue → Fatty acids → Acyl carnine → into mitochondria → Acetyl CoA
Ketogenesis pathway general conditions
- insulin is very low or absent and counter-regulatory hormones quite high
- occurs during long-term fasting
- acetyl CoA produced by beta-oxidation in the liver can take an alternate route and become a ketone body
Purpose of ketogenesis pathway
- Ketones (3-hydroxybutyrate and acetoacetate) serve as an alternative fuel for the brain and other tissues in states of prolonged dietary “glucose insufficiency” (fasting or low carbohydrate diets).
- body decides that continuing to break down muscle to provide substrate for gluconeogenesis is counter-productive and the brain begins to use an alternate fuel that comes from fat to preserve lean body mass.
Specific conditions ==> ketogenesis pathway
- starvation, diabetic ketoacidosis and alcoholic ketoacidosis
- commonalities btwn these conditions:
- very low insulin levels
- high counter-regulatory hormones
- An abundant source of substrate: fatty acids in the case of fasting and diabetic ketoacidosis, and EtOH in the case of alcoholic ketoacidosis
* Acetyl CoA produced by both fatty acid and alcohol metabolism
- An abundant source of substrate: fatty acids in the case of fasting and diabetic ketoacidosis, and EtOH in the case of alcoholic ketoacidosis
Characteristics of lipoprotein pathways
- non polar lipids cholesterol, cholesterol esters, triglyceride and phospholipids do not dissolve in water ==>must move through the blood in some other way
- They move in particles called lipoproteins that contain apo-lipoproteins and lipids in varying amounts.
- lipoproteins classified based on differences in composition of varying in size and density
Major lipoprotein pathways
- Dietary fat pathway / Chylomicron pathway: triglyceride rich (majority) + phospholipid (minority) particles deliver dietary fat to skeletal muscle and adipose tissue.
- VLDL pathway: triglyceride derived from the liver is delivered to skeletal muscle and adipose tissue
- HDL pathway: largely functions as a reservoir and transport system for a variety of lipids including cholesterol from the periphery to the liver.
Characteristics of cholesterol synthesis
- Cholesterol = important component of cell membranes & precursor for steroid hormones & bile acids
- also causes atherosclerosis.
- Some cholesterol comes from the diet, but it can also be synthesized from acetyl CoA thru the formation of hydroxymethyl glutaryl CoA.
- Acetyl CoA → leaves mitochondria → HMG CoA (HMG CoA Reductase) → Mevalonate → Cholesterol
Classes of specialized lipids
- phospholipids
- sphingolipids
- glycosphingolipids
- arachidonic acid ==> LTs or PGs/thromboxanes
Characteristics of phospholipids
- Phospholipids that have a glycerol backbone and a PO4 group attached to one of the positions of the glycerol backbone
- fxns = cell membranes and lipoprotein particles especially and come in several classes depending on the side chains that are attached to the PO4 group.
Characteristics of sphingolipids
- Sphingolipids are built on a ceramide backbone.
- The backbone is unique because it is derived in part from an amino acid (serine), thus it contains a nitrogen atom.
Characteristics of glycosphingolipids
- Glycosphingolipids have a ceramide backbone
- also have sugar residues attached to the “head group”.
Characteristics of arachidonic acid derivatives
- Made from arachidonic acid which can form either leukotrienes or prostaglandins/thromboxanes.
- important regulatory molecules in a number of cell types involved in inflammation.
- Cyclo-oxygenase 1 and 2 are the critical enzymes in this synthetic pathway.
