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Biochem 2 - First Exam > 2 - Complex Lipids > Flashcards

2 - Complex Lipids Flashcards

1
Q

Complex lipids overview

A
  1. Glycerolipids
    1. Triacylglycerols
    2. Glycerophospholipids
    3. Ether glycerolipids
  2. Phospholipids
    1. Glycerophospholipids
    2. Ether glycerolipids
    3. Sphingophospholipids
  3. Sphingolipids
    1. Sphingophospholipids
    2. Glycolipid
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2
Q

Representative phospholipids

A

Don’t have to memorize any structure but know that they are located in the membrane

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3
Q

Phospholipids

A
  1. Phospholipids contain a hydrophilic head and a long hydrophobic tail(s). They are the major lipids found in cell membranes
  2. They perform a wide range of functions in the body
    1. Not just structural roles; they have many critical overall role in the organisms
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4
Q

Phosphate + alcohol derivatives

A
  1. The esterification of the phosphate to a second alcohol creates the following derivatives:
    1. PA + serine →phosphatidylserine
    2. PA + ethanolamine →phosphatidylethanolamine
    3. PA + choline →phosphatidylcholine
    4. PA + inositol →phosphatidylinositol
    5. PA + glycerol →phosphatidylglycerol
    6. PA + glycerol-phosphatidic acid →diphosphatidylglycerol
  2. PA = phosphatidic acid
  3. All of these are just variations in the polar head group
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5
Q

Cardiolipin (Diphosphatidylglycerol)

A
  1. Two phosphatidic acid (PA)’s combined with glycerol
  2. Two Phosphate groups; 4 fatty acids groups
  3. Cardiolipin is located in inner mitochondrial membrane, where it functions both in energy production and and also in apoptosis.
    1. Makes sense since mitochondria is in general associated with apoptosis
  4. Cardiolipin also is found in bacterial membranes.
  5. Cardiolipin can serve as an antigen in the Wasserman diagnostic test for syphilis.
    1. An older test to see if you have syphilis; a serological test i.e. using antibodies against the antigen (syphilis bacteria)
    2. Possible since syphilis is bacterial disease and Cardiolipin is found in bacteria
    3. Syphilis is called ‘great immitator’ since it resembles many different diseases
    4. This test is no longer used now days
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6
Q

Cardiolipin (cont.)

A
  1. Antiphospholipid syndrome is characterized by an elevated levels of antibodies against membrane phospholipids such as cardiolipin (and others). Some patients with this syndrome do not have any associated diseases, while others may have lupus (multi-organ affecting; lupus = “wolf”) or other autoimmune diseases.
  2. The clinical manifestations of antiphospholipid syndrome include recurrent arterial or venous thrombosis and/or miscarriage.
    1. Lupus, stroke, miscarriages, many conditions
    2. Not every one who has this are going to show symptoms
    3. Immune disorder that attacks the phospholipids
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7
Q

Phosphatidylcholine

A
  1. “Phosphatidyl-choline” = phosphate + choline
    1. e.g. Acetylcholine = acetyl (2 carbon) + choline
  2. Is major component of lecithin
  3. The most abundant phospholipid in animals and plants
  4. Constituent of outer portion of plasma membrane
  5. Major delivery form of choline, which is a precursor of the neurotransmitter acetylcholine
  6. It has been reported that mucus from patients with ulcerative colitis can have a decreased amount of phosphatidylcholine, and that that the inflammation was alleviated by administration of phosphatidylcholine.
    1. Ulcer = open wounds
    2. Colitis = inflammation of colon
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8
Q

Platelet activating factor

A
  1. Platelet activating factor is an ether glycerophospholipid
  2. PAF is synthesized in different cell types and is a mediator in acute inflammation and hypersensitivity.
    1. Histamine is another inflammation mediator
  3. PAF can function in concentrations as low as 10-12 moles per liter
    1. Very powerful relative to the small amount needed
  4. Don’t have to know the structure in the figure but just know important groups that compose them
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9
Q

Sphingomyelin

A
  1. Sphingomyelin is a critical component of the myelin sheath, a membranous structure that insulates neuronal fibers of the CNS.
  2. It has been reported that disease processes of sphingomyelin might be associated with the development of multiple sclerosis.
    1. Multiple sclerosis = autoimmune disease, affecting women, younger ages
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10
Q

Dipalmitoylphosphatidylcholine (DPPC)

A
  1. Dipalmitoylphosphatidylcholine (DPPC) is main component of pulmonary surfactant
  2. Smaller alveoli have a greater risk of collapse than larger alveoli. The surfactant reduces that risk by interspersion between water molecules and the subsequent reduction of inter-molecular attractive forces; surface tension among water molecules –> fetus can’t breathe
  3. RDS (respiratory distress syndrome) occurs in over half the babies born at less than 28 weeks, as surfactant production begins at week 34
  4. RDS is believed to account for up to 20% of neonatal mortality in the Western world
  5. Acute respiratory distress syndrome (ARDS) can occur in adults, in whom inflammatory processes lead to increased capillary and alveolar permeability
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11
Q

Phosphatidylinositol

A
  1. Phosphatidylinositol can serve as a reservoir for arachidonic acid (on carbon 2 of the glycerol).
  2. Important point: Arachidonic acid is a polyunsaturated fatty acid (PUFA), 20 carbons in length. It is a precursor of the eicosanoids (20C). Linoleic acid can be desaturated and elongated to from arachidonic acid. If linoleic acid is deficient, then arachidonic acid must be supplied in the diet
    1. Linoleic acid is Omega six; 18C long
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12
Q

Inositol triphosphate

A
  1. Inositol triphosphate participates in the intracellular signal transmission initiated by a variety of different hormones, neurotransmitters, and growth factors.
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13
Q

Phosphatidylinositol 4,5-bisphosphate (PIP2)

A
  1. Structure of Phosphatidylinositol 4,5-bisphosphate (PIP2). Cleavage by phospholipase C produces IP3and DAG.
  2. Notice diacylglycerol group in the figure
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14
Q

Glycosyl phosphatidyl-inositol (GPI) anchor

A
  1. Anchor linking proteins to outer face of plasma membrane (known as glycosylphosphatidylinositol-anchored proteins)
  2. GPI-anchored proteins include acetylcholinesterase and alkaline phosphatase
    1. Acetylcholinesterase - chops off Ach from postsynaptic site;
    2. Nerve gas and insecticides inactivate acetylcholinesterase
  3. GPI-anchored proteins, unlike peripheral or integral proteins, can be released from cell surface by phospholipase C
  4. Phospholipase A2 , on the other hand, releases arachidonic acid from phosphatidylinositol
  5. Certain parasitic protozoans have cell surface proteins bound to GPI (glucosyl phosphatidylinositol)
    1. e.g. Malaria
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15
Q

Phospholipases

A
  1. The phospholipases are located in lysosomes or in cell membranes.
  2. Phospholipases can be found in pancreatic juice.
    1. Important for digestion of phospholipids in food
  3. Phospholipases can also be found in different venoms and toxins
    1. Arachidonic acid induces extreme inflammatory response; a powerful enough one meant to do you damage leading to anaphylactic shocks
  4. Membrane phospholipids are in a state of constant degradation and subsequent synthesis on account of ongoing oxidative insults and hormonally regulated phospholipolysis
    1. All of these are NOT stable; constantly regulated and exposed to oxidation, hormonal effect, and etc.
  5. Clostridia - botulism, etc. are quite lethal
  6. How might phospholipases in venom acting on phosphatidylinositol possibly function?
    1. Extreme inflammatory reaction that is designed to hurt you
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16
Q

Glycosphingolipids (Glycolipids)

A
  1. Representative glycosphingolipids (glycolipids) can function as:
    1. Cellular receptors for cholera (not the germ but the toxins secreted) and for tetanus toxins
    2. Blood group antigens
    3. Embryonic antigens
    4. Tumor antigens
17
Q

Sphingolipidoses

A
  1. Sphingolipidoses include defects in the degradation of sphingomyelin and also glycolipids (gangliosides, cerebrosides, etc.)
    1. According to Dr. Marvit, we don’t have to try to piece these together, just know the things listed on the very first slide.
  2. Tay-Sachs & Gauchers Disease
    1. Tay Sachs is very destructive because it involves the brain; build-up of materials
    2. Accumulation of gangliosides
    3. Rapid, progressive, and fatal neurodegeneration
    4. Blindness
    5. Cherry-red macula
    6. Muscular weakness
    7. Seizures
    8. Tay-Sachs common among Jews from eastern Europe and Cajun (Canada; archadia); these two ethnic groups are genetically independent
  3. Gaucher Disease
    1. Accumulation of glucocerebrosides
    2. Most common lysosomal storage disease
    3. Hepatosplenomegaly
    4. Osteoporosis of long bones
    5. CNS involvement in rare infantile and juvenile forms
  4. Lysosomal storage disease
  5. Sphingolipidoses are characterized by substrate accumulation. Neurons are often affected because of both undigested material and also because of the extremely slow rate of cell turnover. Mononuclear phagocytic cells likewise tend to be affected because of their enhanced presence of lysosomes.
  6. Subtypes and variants of these diseases can exist
    1. Tay-Sachs can have variations
18
Q

Eicosanoids

A
  1. Eicosanoids are paracrine and/or autocrine agents (or sometimes intracrine agents)
    1. Paracrine agents operate locally, while autocrine agents are restricted to same cell type (intracrine agents operate within the environment of the same cell); NO endocrine
      1. Very unstable agent
      2. Nearby cells utilize all available agent
      3. Agent cannot traverse extracellular-matrix
  2. Four major families of eicosanoids
    1. Leukotrienes (Leuko - white blood cells)
    2. Thromboxanes (Thrombo - clot)
    3. Prostaglandins (Prosta - prostate glands; prostaglandins are also found in females too although there isn’t any prostate gland)
    4. Prostacyclins
19
Q

Eicosanoids (cont.)

A
  1. Phospholipase A2 activity leads to lysophospholipid & arachidonic acid; if inhibited, no eicosanoids will be made downstream
    1. Cortisol (corticosteroids) inhibit phospholipase A2
  2. Thromboxanes, prostaglandins, and prostacyclins are produced via the (fatty acid) cyclooxenase pathway
    1. The microsomal (i.e. [smooth] ER) cyclooxygenase complex consists of cyclooxygenase and peroxidase
    2. Cyclooxygenase creates a ring structure, while utilizing 2 molecules of oxygen
    3. Leukotriene, on the other hand, goes through entirely different pathway i.e. Lipooxygenase pathway but also is derived from arachnoic acid
  3. There are 2 isozymes of cyclo-oxygenase:
    1. COX-1
      1. Expressed in a constitutive (continuous) manner
      2. NOT found in erythrocytes and few other cells/tissues
      3. Associated with tissue homeostasis, cytoprotection, and intercellular communication
      4. Protects your stomach and any issue with it causes potential problems
    2. COX-2
      1. Enzyme is induced by a wide range of inflammatory mediators
      2. Enzyme is associated with angiogenesis, mitogenesis (i.e. causing cell division), and inflammation
      3. Enzyme is expressed primarily in white blood cells, but also in smooth muscle and epithelium
  4. Eicosanoid pathways lead to conflicting effect between pro-inflammatory and anti-inflammatory e.g. TXA2 and GPI2 on the figure
    1. Proper inflmmation have both aspects mixed in to keep balance between hyper- or hypo-inflammatory reaction
20
Q

Activation of eicosanoids

A
  1. Initiated by insult such as trauma, infection, cancer, etc.
  2. Release of cytokines and other mediators of inflammation
  3. Inflammatory mediators bind to receptor on target cell membrane
  4. Activation of membrane bound phospholipase A2(and phospholipase C)
21
Q

Arachidonic acid

A
  1. Arachidonic acid is a polyunsaturated fatty acid (PUFA) found in cell membranes
  2. It is involved in:
    1. Second messenger cellular signaling
    2. Intermediate of inflammation
  3. Release of arachidonic acid into cytosol
    1. Production of prostaglandins, prostacyclins, thromboxanes by cyclooxygenase
      1. Self-catalyzed destruction of cyclooxygenase regulates amount of product
    2. Production of leukotrienes by lipooxygenase
    3. Production of epoxides by cytochrome P450 monooxygenases
22
Q

Inhibition of eicosanoid synthesis

A
  1. Glucocorticoids
    1. Include cortisol, cortisone, and synthetic analogs
      1. Inhibit action of phospholipase A2
      2. Inhibit synthesis of COX-2
  2. Nonsteroidalanti-inflammatory drugs (NSAIDs)
    1. Aspirin (acetylsalicylic acid)
      1. Irreversibly inhibits both cyclooxygenase isoforms by acetylation of enzyme
    2. Ibuprophen
      1. Reversibly inhibits both cyclooxygenase isoforms
  3. COX-2 inhibitors
    1. Inhibit synthesis of prostaglandins in white blood cells, but not in stomach
23
Q

Irreversible acetylation of COX-1 and COX-2 by aspirin

A
  1. Salicylic = willow tree
  2. Addition of acetyl group is irreversible
24
Q

Clinical Correlations

A
  1. Linoleic acid (omega-6) is metabolized in the body to DGLA, and DGLA is metabolized to arachidonic acid
    1. Omega-6 to Omega-3 ratio is very important so that we don’t have over-inflammation
  2. Alpha linolenic acid is metabolized in the body into EPA (eicosapentaenoic acid [25 Carbon]). Fish oil contains EPA and also DHA (docosahexanoic acid).
    1. Not very well understood
  3. The EPA appears to offset the inflammatory and clotting effects of the eicosanoids derived from the arachidonic acid
  4. EPA, an omega-3 fatty acid, is thought to compete with arachidonic acid, an omega-6 fatty acid, for the synthesis of different eicosanoids at the level of cyclooxygenases and 5-lipooxygenase.
    1. 5-lipooxygenase lead to 5-HPETE (5-Hydroperoxyeicosatetraenoic acid, which leads to leukotrienes synthesis)
  5. The typical American diet tends to be higher in omega-6 fatty acids than in omega-3 fatty acids. The health implications are under investigation.
    1. Omega-6 = pro-inflammatory
    2. Omega-3 = anti-inflammatory
    3. Mediterrenean diet is good for bringing down inflammation reaction e.g. fish is good due to omega-3 content
    4. Omega-3 helps but there is a lot of contradiction that goes on
    5. Good cholesterol = HDL (high-density lipid)
    6. gamma-Linoleic acid (GLA) - a kind of Omega-6
    7. ELA = omega-3??

Biochem 2 - First Exam (4 decks)

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