Biochemistry: Lipids and Membranes
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Questions and Answers

What is a key consequence of folate deficiency during the early weeks of pregnancy?

  • Reduced absorption of vitamin B12
  • Higher likelihood of neural tube defects (correct)
  • Increased risk of cardiovascular diseases
  • Enhanced DNA synthesis

What does the active form of folate, FH4, require to stimulate nucleotide biosynthesis?

  • Calcium
  • Vitamin D
  • Carbon atoms from certain amino acids (correct)
  • Iron

What condition results from vitamin B12 deficiency due to the destruction of parietal cells?

  • Iron-deficiency anemia
  • Thalassemia
  • Megaloblastic anemia (correct)
  • Sickle cell disease

Which of the following foods is the best source of vitamin B12?

<p>Meat and dairy products (C)</p> Signup and view all the answers

Which is a symptom associated with deficiencies of both folate and vitamin B12?

<p>Angular cheilitis (A)</p> Signup and view all the answers

How does a lack of vitamin B12 affect FH4 metabolism?

<p>It traps FH4 in a methyl form (B)</p> Signup and view all the answers

Which vitamin plays a role in regulating hormones?

<p>Vitamin B6 (C)</p> Signup and view all the answers

What is likely to happen if there is low dietary intake of vitamin B12 over time?

<p>Development of pernicious anemia (C)</p> Signup and view all the answers

What role does apoprotein C-II play in lipid metabolism?

<p>Activates lipoprotein lipase (A)</p> Signup and view all the answers

Which of the following processes is associated with the conversion of IDL to LDL?

<p>Hepatic lipase activity (C)</p> Signup and view all the answers

What impact does high levels of HDL have on heart disease risk?

<p>Helps protect against heart disease (A)</p> Signup and view all the answers

What is the primary mechanism of action of statins in cholesterol biosynthesis?

<p>Inhibition of HMG-CoA reductase (D)</p> Signup and view all the answers

What is the role of LCAT in lipid metabolism?

<p>Catalyzes the transfer of cholesterol to fatty acids (D)</p> Signup and view all the answers

Which enzyme is considered the rate-limiting enzyme in bile acid synthesis?

<p>7a-hydroxylase (B)</p> Signup and view all the answers

What is the primary result of insulin resistance on glucose uptake in muscle and adipose tissues?

<p>Decreased uptake of glucose (A)</p> Signup and view all the answers

What is a consequence of oxidized LDL in blood vessels?

<p>Promotes macrophage recruitment (C)</p> Signup and view all the answers

What differentiates primary bile salts from secondary bile salts?

<p>Secondary bile salts are formed by bacterial action on primary bile salts in the intestine. (B)</p> Signup and view all the answers

Which enzyme is responsible for the rate-limiting step in cholesterol synthesis?

<p>HMG-CoA reductase (D)</p> Signup and view all the answers

Which statement about the enterohepatic circulation of cholesterol is accurate?

<p>Bile salts recycling occurs during fat digestion. (B)</p> Signup and view all the answers

What role do GLUT4 transporters play in glucose metabolism?

<p>They transport glucose into cells (D)</p> Signup and view all the answers

What happens if sphingolipids cannot be degraded?

<p>They accumulate within cells and can lead to toxicity. (D)</p> Signup and view all the answers

What effect does the inhibition of cholesterol synthesis by statins primarily have?

<p>Down-regulates intracellular cholesterol and up-regulates LDL receptors (D)</p> Signup and view all the answers

Which process is stimulated by high levels of insulin?

<p>Protein synthesis (D)</p> Signup and view all the answers

What role does cholestyramine play in cholesterol management?

<p>It binds bile acids and facilitates their excretion. (D)</p> Signup and view all the answers

What happens to ketone body production with prolonged fasting or impaired insulin?

<p>It becomes accelerated (D)</p> Signup and view all the answers

What defines a carbohydrate at the molecular level?

<p>Must contain three or more carbons (A)</p> Signup and view all the answers

What are the starting materials for sphingolipid synthesis?

<p>Sphingosine and fatty acyl-CoA (B)</p> Signup and view all the answers

Which condition is characterized by elevated levels of glucose in the blood?

<p>Hyperglycemia (C)</p> Signup and view all the answers

How does hyperglycemia contribute to tissue damage in diabetes?

<p>It depletes NADPH and increases reactive oxygen species (B)</p> Signup and view all the answers

What is a consequence of conjugating bile acids?

<p>It enhances their emulsifying properties. (A)</p> Signup and view all the answers

What is the impact of advanced glycation end products (AGEs) on proteins?

<p>They impair protein function (D)</p> Signup and view all the answers

Which of the following contributes to increased production of ketone bodies in diabetes?

<p>Unimpeded lipolysis and elevated fatty acids (A)</p> Signup and view all the answers

How do insulin and glucagon regulate enzyme activity in target cells?

<p>Insulin dephosphorylates key regulators, glucagon phosphorylates them. (C)</p> Signup and view all the answers

What is the primary role of cAMP in relation to glucagon signaling?

<p>It activates protein kinase A (PKA). (D)</p> Signup and view all the answers

Why does glucose transport via insulin not occur in RBCs and the brain?

<p>They require a constant supply of glucose. (B)</p> Signup and view all the answers

Which enzyme is primarily involved in the dephosphorylation process stimulated by insulin?

<p>Protein phosphatase-1 (D)</p> Signup and view all the answers

What distinguishes the glucose transport response in muscle and adipose tissue from that in the liver?

<p>Liver only imports glucose while muscle and adipose tissues can use fat. (C)</p> Signup and view all the answers

What role do reactive oxygen species (ROS) play in macrophages and neutrophils?

<p>They are used for signaling pathways and pathogen destruction. (C)</p> Signup and view all the answers

What is the consequence of phosphorylation of enzymes by glucagon?

<p>Activation of enzymes that facilitate gluconeogenesis and glycogenolysis. (A)</p> Signup and view all the answers

Which of the following statements regarding NADPH oxidases is true?

<p>They generate reactive oxygen species during the transfer of electrons to oxygen. (C)</p> Signup and view all the answers

What does incomplete penetrance refer to in genetics?

<p>The proportion of individuals with a genotype that express the associated phenotype (A)</p> Signup and view all the answers

How are blood types determined in the ABO blood group system?

<p>By the combination of alleles A, B, and O (C)</p> Signup and view all the answers

What is meant by expressivity in genetics?

<p>The degree to which a genotype is expressed in an individual (C)</p> Signup and view all the answers

Which of the following best describes anticipation in genetic disorders?

<p>Earlier onset and more severe symptoms in successive generations (B)</p> Signup and view all the answers

Which blood type contains both A and B antigens and no antibodies?

<p>Type AB (A)</p> Signup and view all the answers

What is a common characteristic of ectodermal dysplasia?

<p>Reduced hair, sweating, and abnormal teeth (B)</p> Signup and view all the answers

Which of the following is an indicator of potential genetic disease?

<p>Multiple primary cancers of different tissues in one individual (B)</p> Signup and view all the answers

What does mosaicism refer to in genetic terms?

<p>The presence of two or more genetically different cell lines in the same individual (B)</p> Signup and view all the answers

Flashcards

HMG-CoA Reductase Regulation

HMG-CoA reductase activity is controlled through transcriptional methods, protein breakdown, and phosphorylation.

Cholesterol Transport

Cholesterol synthesized in the liver is transported to other tissues via VLDL, IDL, and LDL.

Bile Acid Synthesis

7α-hydroxylase is the enzyme that controls the conversion of cholesterol to bile salts.

Cholesterol Removal

Converting cholesterol to bile salts is the main way cholesterol is removed from the body, primarily within the liver.

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Primary Bile Salts

Bile salts directly derived from cholesterol by the liver; conjugated to enhance emulsification.

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Statin Mechanism

Statins block HMG-CoA reductase, the enzyme that produces cholesterol, thus lowering cholesterol levels.

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Enterohepatic System

The recycling system that moves bile from the liver to the intestines, aiding in digestion and removing cholesterol.

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Sphingolipid Synthesis

Sphingosine is a key component, created in ER, for sphingolipid creation.

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LDL Receptor

A protein on the surface of cells that binds to LDL particles, allowing them to be taken into the cell for use or breakdown.

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Lipoprotein Lipase (LPL)

An enzyme that breaks down triglycerides in chylomicrons and VLDL, releasing fatty acids for energy.

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Cholesterol Esters

Form when LCAT attaches a fatty acid to cholesterol, making it less water-soluble and easier to transport.

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HDL: 'Good' Cholesterol

High-density lipoprotein that collects excess cholesterol from cells and delivers it to the liver for breakdown.

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Oxidized LDL

Damaged LDL that can contribute to atherosclerosis by causing inflammation and cell damage.

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Foam Cells

Macrophages that have taken up oxidized LDL, becoming filled with cholesterol and contributing to plaque formation.

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Fatty Streaks

Early stage of atherosclerosis, where foam cells accumulate in the inner lining of blood vessels.

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Statins: HMG-CoA Reductase Inhibitors

Medications that block the enzyme HMG-CoA reductase, which is involved in cholesterol synthesis, thus lowering cholesterol levels.

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Folate's Role

Folate, in its active form FH4, accepts a single carbon atom from serine and glycine, which is then transferred to either nucleotide biosynthesis or vitamin B12 methylation. FH4 acts as a crucial carrier for this single carbon unit.

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Megaloblastic Anemia

A condition caused by folate or vitamin B12 deficiency, resulting in fewer mature red blood cells and an increased number of large, immature blood cell precursors.

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Neural Tube Defects

Birth defects affecting the brain and spinal cord, often caused by insufficient folate during early pregnancy.

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Folate Trap

A situation where folate gets stuck in a specific form (CH3-FH4) in the absence of vitamin B12, preventing its recycling and hindering essential processes.

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Pernicious Anemia

An autoimmune condition leading to B12 deficiency due to impaired absorption, primarily caused by damage to the stomach lining (parietal cells).

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B-Vitamins and Oral Health

Deficiencies in folate and vitamin B12 can cause oral health problems like glossitis (inflamed tongue), angular cheilitis (inflamed corners of the mouth), and recurrent apthous stomatitis (mouth ulcers).

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B12 Deficiency and Other Issues

Apart from anemia, B12 deficiency can lead to heart disease and demyelination (damage to the protective sheaths around nerves).

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B12 Absorption

B12 absorption depends on a complex process involving secretion from the stomach and absorption in the intestines, making it vulnerable to disruptions even with adequate dietary intake.

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Insulin's Action

Insulin, a hormone, primarily dephosphorylates enzymes, leading to a decrease in their activity. This effect is crucial for regulating glucose metabolism.

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Glucagon's Action

Glucagon, a hormone, primarily phosphorylates enzymes, causing an increase in their activity. This helps increase blood glucose levels.

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Insulin and Glucagon: Antagonistic Control

Insulin and glucagon work in opposition to each other. Insulin decreases blood glucose levels, while glucagon increases it. This dynamic balance maintains glucose homeostasis.

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Phosphorylation's Role

Phosphorylation is a key mechanism for regulating enzyme activity. When an enzyme is phosphorylated, it becomes active or inactive depending on the enzyme. This process plays a vital role in metabolic control.

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Source of Reactive Oxygen Species (ROS): NADPH Oxidases

NADPH Oxidases are enzymes that produce ROS by transferring electrons from NADPH to oxygen molecules. These ROS can be used to destroy pathogens or in cell signaling.

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Source of Reactive Oxygen Species (ROS): Electron Transport Chain

The electron transport chain in mitochondria can also produce ROS. When electrons leak from the chain, they can react with oxygen to form superoxide.

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ROS and Immune Cells

Macrophages and neutrophils, key immune cells, utilize ROS as a weapon to fight against microorganisms.

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ROS: A Double-Edged Sword

ROS are essential for several biological processes but can also be damaging to cells. Their production and removal must be tightly regulated.

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Insulin Resistance

Decreased sensitivity of cells to insulin, leading to impaired glucose uptake and utilization.

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Insulin Receptor Downregulation

Reduced number of insulin receptors on cell surfaces, further hindering insulin signaling.

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Hyperglycemia

High blood glucose levels due to impaired insulin function.

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Ketoacidosis

Dangerous buildup of ketone bodies in the blood, a consequence of excessive fat breakdown.

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Glycation

Non-enzymatic attachment of glucose to proteins, causing damage and dysfunction.

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Advanced Glycation End Products (AGEs)

Oxidized and cross-linked glycated proteins that contribute to long-term complications.

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Reactive Oxygen Species (ROS)

Harmful molecules that contribute to AGE formation and cell damage.

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Polyol Pathway

Metabolic pathway that contributes to ROS generation and AGE formation in hyperglycemia.

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Penetrance

The percentage of individuals with a specific genotype who actually express the associated trait.

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Expressivity

The degree to which a gene's influence is seen in an individual, ranging from mild to severe.

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Mosaicism

The presence of different genetic cell lines within a single individual due to mutations during development.

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Anticipation

A phenomenon where genetic disorders become more severe or appear earlier in successive generations.

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ABO Blood Type

A classification system based on the presence or absence of A and B antigens on red blood cells.

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What are the blood types and their genotypes?

Type A: AA or AO, Type B: BB or BO, Type AB: AB, Type O: OO.

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What are red flags for genetic disease?

Multiple affected family members across generations, unusual presentations of common conditions, developmental delays, and multiple primary cancers.

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What is ectodermal dysplasia?

A group of disorders affecting development of skin, hair, nails, and teeth.

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Study Notes

General Study Notes

  • Study guides for exams are available.
  • Subjects covered include fatty acids, triacylglycerols, cholesterol, sphingolipids, and glycerophospholipids.
  • Several types of fatty acids exist (saturated, monounsaturated, and polyunsaturated).
  • Linoleic acid, α-linolenic acid, and arachidonic acid are essential fatty acids.
  • Arachidonic acid is a precursor for eicosanoids (prostaglandins, thromboxanes, and leukotrienes).
  • Eicosanoids regulate inflammatory response, muscle contraction, blood pressure, and other bodily functions.
  • Phosphoglycerols (phosphatidic acid, phosphatidylcholine, and lecithin), sphingolipids (sphingomyelin and sphingoglycolipids), and cholesterol are key cell membrane lipids.
  • Phosphoglycerols are important for signal transduction and metabolic pathways, and contribute to cell membrane fluidity.
  • Sphingolipids are involved in cell death/survival processes, toxin binding, and cell-cell recognition.
  • Cholesterol is a nonpolar tetracyclic ring structure; humans cannot degrade it.
  • Phosphoglycerols and sphingolipids form lipid bilayers.
  • Cholesterol can insert into lipid bilayers.
  • Membrane proteins include integral and peripheral proteins.
  • Carbohydrate moieties are found on the extracellular side of membrane proteins.
  • Triacylglycerols are not found in cell membranes; they are stored in the cytoplasm for fatty acid storage
  • Essential fatty acids are vital for biological function, and trans fatty acids have adverse effects.
  • Digestion of dietary triacylglycerols in the small intestine involves bile salts, pancreatic lipase, co-lipase, and bicarbonate.
  • Bile salts exhibit detergent properties, aiding in digestion
  • Bile acids are synthesized from cholesterol in the liver.
  • Emulsion particles and mixed micelles store non-polar lipid particles inside an interior region.
  • Co-lipase attracts and anchors pancreatic lipase to the surface of the emulsion particles.
  • Dietary triglycerides are hydrolyzed into 2-monoacylglycerol and fatty acids in the small intestine.
  • Mixed micelles are formed by fatty acids, 2-monoacylglycerol, bile salts, and other soluble lipids.
  • Micelles are taken up by intestinal epithelial cells to resynthesize triglycerides, combining with other lipids and apoproteins to form chylomicrons.
  • Pancreatic lipase catalyzes the conversion of triglycerides to 2-monoacylglycerol and fatty acids.
  • Lipid malabsorption can occur due to deficiencies in pancreatic lipase or bile acid.
  • This leads to lipid accumulation in feces (steatorrhea).
  • There is loss of important energy fuels, severe weight loss, and deficiencies in vitamins and essential fatty acids and caloric deficiencies.
  • Fatty acid synthesis takes place from dietary carbohydrates and proteins, primarily in the liver.
  • Acetyl CoA carboxylase is a rate-limiting enzyme that catalyzes the carboxylation of acetyl CoA to form malonyl CoA.
  • Biotin is the carrier of activated CO2.
  • Malonyl CoA provides two-carbon units for each elongation cycle during fatty acid synthesis.
  • NADPH serves as a reducing agent in the synthesis process.
  • NADPH is required for both fatty acid synthesis and the regeneration of glutathione, primarily generated via the pentose phosphate pathway.
  • Cholesterol biosynthesis is regulated by HMG-CoA reductase.
  • This enzyme activity is controlled via transcriptional control, proteolysis, and phosphorylation.
  • Cholesterol synthesis takes place in the liver and is transported to other tissues via VLDL, IDL, and LDL.
  • Bile salt synthesis that converts cholesterol into bile salts is the primary means for cholesterol removal from the body.
  • Bile acids (including conjugated bile salts) made in the liver are called primary bile salts.
  • Conjugation lowers the pKa of bile salts, making them better emulsifying agents.

Additional Information

  • Statins are inhibitors of HMG-CoA reductase.
  • Cholestyramine is a bile salt sequestrant.
  • Everyday, the body processes cholesterol from liver to bile salts in the gall bladder and back to the liver/fat digestion.
  • LCAT and ACAT function is to convert cholesterol to cholesterol esters (LCAT in blood, ACAT in cells).
  • Lipid metabolism pathways are present for digestion and metabolism of triglycerides, cholesterol, and other lipids.
  • A variety of enzymes and transporters play significant roles in these processes.
  • Many key processes occur for biosynthesis and metabolism of fatty acids, triglycerides, cholesterol and hormones.
  • There are different types of lipoproteins: chylomicrons, VLDL, IDL, and LDL.
  • Their roles in transporting lipids in the blood are essential.
  • The role of apolipoproteins in lipoprotein function is included.
  • Insulin and glucagon control glucose homeostasis, with opposing effects on glucose utilization and production.
  • Insulin promotes glucose uptake and storage, while glucagon promotes glucose release.
  • Pathways for glycogen synthesis and breakdown are regulated to maintain glucose levels during fasting and feeding.

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This quiz covers essential topics related to lipids, including fatty acids, triacylglycerols, and various key cell membrane lipids such as cholesterol and sphingolipids. You will explore the roles of these molecules in metabolism, signal transduction, and cellular functions. Test your understanding of lipid types and their biological significance.

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