Biochemistry Chapter on Lipids

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Questions and Answers

What is the role of glucagon and epinephrine in glycolysis?

They stimulate glycolysis by elevating insulin levels.

They decrease the levels of F-2,6-BP. (correct)

They promote the production of F-2,6-BP.

They enhance the activity of hexokinase.

Which enzyme is NOT unique to glycolysis?

PFK-1

Pyruvate carboxylase (correct)

Hexokinase

Pyruvate kinase

In the fed state, what primarily promotes glycolysis in the liver?

Decreased insulin

Decreased blood glucose levels

Increased glucagon

Increased levels of F-2,6-BP (correct)

Which enzyme of the Pentose Phosphate Pathway requires thiamine as a cofactor?

Transketolase Signup and view all the answers

What is a consequence of increased insulin relative to glucagon?

Increased glucose utilization through glycolysis. Signup and view all the answers

Which of the following states is associated with decreased protein degradation?

Starved state Signup and view all the answers

Which enzyme is involved in converting pyruvate to PEP in gluconeogenesis?

PEPCK Signup and view all the answers

What is a primary function of NADPH in the cell?

To prevent oxidative damage to cells. Signup and view all the answers

What is the primary mechanism through which insulin affects its target cells?

Activating protein phosphatase 1 and phosphodiesterase Signup and view all the answers

Which component acts as the second messenger in the signaling pathway of glucagon?

cAMP Signup and view all the answers

What is the main effect of glucagon in terms of protein regulation?

Phosphorylation of enzymes Signup and view all the answers

In which tissues does insulin stimulate glucose transport?

Muscle and adipose tissues only Signup and view all the answers

What is the role of NADPH oxidases in relation to reactive oxygen species (ROS)?

Generating superoxide from oxygen Signup and view all the answers

How do insulin and glucagon function in opposing ways within fuel metabolism?

Insulin initiates energy storage, while glucagon initiates energy mobilization. Signup and view all the answers

Which statement about the electron transport chain (ETC) and ROS formation is true?

Complex II can form superoxide if electrons are not flowing down the chain. Signup and view all the answers

Which fuel sources can muscle and adipose tissues utilize during fasting?

Fats and stored glycogen Signup and view all the answers

What is the primary mechanism of action for statins?

Competitive inhibition of HMG-CoA reductase Signup and view all the answers

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

7a-hydroxylase Signup and view all the answers

What occurs to primary bile salts in the intestine?

They are dehydroxylated and deconjugated Signup and view all the answers

Where does LCAT primarily function?

In the bloodstream Signup and view all the answers

How does cholestyramine function in cholesterol management?

It binds bile acids to form insoluble complexes Signup and view all the answers

What characterizes secondary bile salts compared to primary bile salts?

They are less polar and more prone to excretion Signup and view all the answers

What happens if sphingolipids cannot be degraded properly?

They accumulate and cause cellular dysfunction Signup and view all the answers

What is considered the only practical means of removing cholesterol from the body?

Conversion of cholesterol to bile salts in the liver Signup and view all the answers

What is a common characteristic of reactive oxygen species (ROS)?

They contain oxygen and have reactive properties. Signup and view all the answers

Which of the following is formed when oxygen accepts one electron?

Superoxide anion (O2•‒) Signup and view all the answers

Which enzyme converts superoxide to hydrogen peroxide?

Superoxide dismutase Signup and view all the answers

Which vitamins are considered important non-enzymatic antioxidants?

Vitamin C, Vitamin E, and Niacin Signup and view all the answers

How does glutathione function in protecting cells from ROS?

As a reducing agent donating electrons Signup and view all the answers

What damage can ROS cause to genetic material?

It can induce base damage or strand breaks in DNA and RNA. Signup and view all the answers

What is the role of catalase in a cell?

It breaks down hydrogen peroxide into water. Signup and view all the answers

What factors are necessary for superoxide dismutases to function effectively?

Sufficient amounts of metal ions like Zn+, Cu+, or Mn2+. Signup and view all the answers

Which amino acid is the precursor for serotonin and melatonin?

Tryptophan Signup and view all the answers

What role does S-adenosyl methionine (SAM) play in neurotransmitter synthesis?

It donates methyl groups for neurotransmitter synthesis. Signup and view all the answers

Which of the following neurotransmitters is derived from histidine?

Histamine Signup and view all the answers

What effect do SSRIs have on serotonin levels in the synapse?

They decrease the reuptake of serotonin, increasing its presence. Signup and view all the answers

Which amino acids are primarily involved in the biosynthesis of creatine?

Arginine, glycine, and methionine Signup and view all the answers

Which neurotransmitter functions as an excitatory neurotransmitter?

Glutamate Signup and view all the answers

What is the main function of nitric oxide synthesized from arginine?

Vasodilation and lowering blood pressure Signup and view all the answers

Which branched-chain amino acids are primarily metabolized in muscle and brain for ATP production?

Leucine, isoleucine, and valine Signup and view all the answers

What is a primary characteristic feature of amelogenesis imperfecta?

Abnormal enamel thickness Signup and view all the answers

What type of inheritance is commonly associated with hereditary hemorrhagic telangiectasia?

Autosomal dominant Signup and view all the answers

Which condition is characterized by the presence of café-au-lait spots?

Neurofibromatosis type 1 Signup and view all the answers

What is the primary management focus for osteogenesis imperfecta?

Fracture prevention Signup and view all the answers

What is a noted feature of basal cell nevus syndrome?

Multiple basal cell carcinomas Signup and view all the answers

What type of tumors are primarily associated with neurofibromatosis?

Benign neurofibromas Signup and view all the answers

Which genetic disorder is most likely to lead to internal bleeding due to abnormal blood vessels?

Hereditary hemorrhagic telangiectasia Signup and view all the answers

What is a potential complication of neurofibromatosis that affects the nervous system?

Hearing loss due to vestibular schwannomas Signup and view all the answers

Study Notes

Biochemistry Study Notes

Fatty Acids: Saturated (single bond), monounsaturated (one double bond), and polyunsaturated (multiple double bonds) are the types. Linoleic acid, α-linolenic acid, and arachidonic acid are essential fatty acids. Nearly all naturally occurring polyunsaturated fatty acids have cis configuration.
Triacylglycerols (TGs): Not found in cell membranes; store fatty acids in cytoplasm.
Cholesterol: A non-polar, tetracyclic ring structure. Humans lack enzymes to degrade it.
Sphingolipids: Derived from ceramide; sphingomyelin and sphingoglycolipids are subtypes. Important components of cell membranes; regulates cell death/survival, toxin binding, and cell-cell recognition.
Glycerophospholipids: Glycerol is the backbone. Examples include phosphatidic acid and phosphatidylcholine (lecithin). Important for cell membranes and involved in signal transduction and metabolic pathways. Contribute to membrane fluidity.
Eicosanoids: Arachidonic acid is a precursor. Includes prostaglandins, thromboxanes, and leukotrienes. Regulate inflammatory response, muscle contraction, blood pressure, and other bodily functions.
Lipid Bilayers: Formed by phosphoglycerols and sphingolipids; cholesterol inserts into the bilayers.
Membrane Proteins: Integral proteins and peripheral proteins; carbohydrate moieties reside on the extracellular side.
Essential Fatty Acids: Important for various bodily functions; humans cannot synthesize them.
Trans Fatty Acids: Formed during hydrogenation of unsaturated fatty acids. They increase LDL cholesterol and decrease HDL cholesterol. Adverse effects on health.

Digestion and Absorption of Dietary Triglycerides

Small Intestine: Bile salts, pancreatic lipase, co-lipase, and bicarbonate are crucial for the digestion of dietary triglycerides.
Hydrolysis: Triglycerides are hydrolyzed into 2-monoacylglycerol and fatty acids in the small intestine.
Mixed Micelles: FA, 2-MG, bile salts, and other lipid-soluble materials, form mixed micelles that facilitate absorption by intestinal epithelial cells.
Chylomicrons: Resynthesized triglycerides are combined with other lipid-soluble materials and apoproteins to form chylomicrons.
Pancreatic Lipase: Catalyzes the hydrolysis of triglycerides to 2-monoacylglycerol and fatty acids.

Fatty Acid Synthesis

Location: Primarily occurs in the liver.
Rate-Limiting Step: Carboxylation of acetyl CoA to malonyl CoA by acetyl-CoA carboxylase (using biotin as a CO2 carrier).
Roles of Coenzymes: Malonyl CoA provides two-carbon units and NADPH acts as a reducing agent during the elongation cycle.

Relationship Between Fatty Acid Synthesis and Pentose Phosphate Pathway

NADPH Source: The pentose phosphate pathway is a primary source of NADPH required for fatty acid synthesis.

Regulation of Fatty Acid Synthesis

Metabolic Stages and Biochemicals: Chain elongation on fatty acid synthase complex produces homodimer.
Thioesterase: Cleaves bond, forming a 16 carbon chain.
ER Membrane: Longer than 16 carbon chains are synthesized by proteins embedded in the ER membrane.

Cholesterol and Bile Acid Synthesis

Rate Limiting Step: Conversion of HMG-CoA to mevalonate by HMG-CoA reductase.
Regulation: Transcriptional control, regulation by proteolysis, and phosphorylation.
Bile Salt Synthesis: 7α-hydroxylase is the rate-limiting enzyme in the biosynthesis pathway converting cholesterol to bile salts.

Inhibition of Cholesterol Synthesis by Statins

Competitive Inhibitors: Statins are competitive inhibitors of HMG-CoA reductase.
Cholestyramine: Is a bile salt sequestrant that binds to bile acids, forming an insoluble complex, excreted in feces. Reducing cholesterol also increases LDL receptors thus getting excess cholesterol out of the blood.

Enterohepatic System

Everyday process is to get rid of cholesterol.
Cholesterol in liver, converted to bile salts.
Bile salts to gall bladder, then to fat digestion
Excretion via feces, reabsorbed by liver.

Lipids

Fats soluble materials are absorbed
Fats form droplets, emulsified by bile salts to micelles
Dietary triglycerides are hydrolyzed by pancreatic lipase
Absorption happens in small intestine, and re-synthesized into chylomicrons in the epithelial cells
Chylomicrons are transported via the lymphatic system to the bloodstream

Pentose Phosphate Pathway (PPP)

Oxidative Phase: Generates NADPH, ribose-5-phosphate.
Non-oxidative phase: Interconverts sugars, important for nucleotide production.
Ribose-5-phosphate: A critical component of nucleotides in cells.
NADPH: Acts as a reducing agent in anabolic processes.

Other

Biological Importance of Essential Fatty Acids: Crucial for various bodily functions; humans cannot synthesize them.
Adverse Effects of Trans Fatty Acids: Increase in LDL cholesterol and decrease in HDL cholesterol.
Enterohepatic System: Continuous cycling of bile salts between the liver and intestine.
Clinical Implications: Conditions associated with defects in lipid metabolism.
Essential Amino Acids: Those that cannot be synthesized by the body. Must be obtained through diet.
Non-essential Amino Acids: Those that can be manufactured by the body.
Protein synthesis
Amino acid metabolism
Nitrogen Metabolism

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Description

Explore the essential concepts of lipids in biochemistry, including types of fatty acids, triacylglycerols, cholesterol, sphingolipids, and glycerophospholipids. This quiz covers their structures, functions, and significance in cell membranes and metabolic pathways.