PA CAT Biochemistry

What is the rate-limiting enzyme of the citric acid cycle?

Isocitrate dehydrogenase.

What is the main function of pyruvate dehydrogenase?

To convert pyruvate to acetyl-CoA.

What is the citric acid cycle also known as?

Kreb cycle or tricarboxylic acid cycle.

What is the major source of energy production from aerobic respiration of carbohydrates?

The citric acid cycle.

What is the end product of glycolysis?

Pyruvate.

What is the key entry point into the citric acid cycle?

Conversion of pyruvate to acetyl-CoA.

What happens in pyruvate dehydrogenase deficiency?

Inability to convert pyruvate to acetyl-CoA.

What are the high sources of energy produced in the citric acid cycle?

NADH, FADH, and GTP.

What is the equivalent energy yield of each NADH molecule in the citric acid cycle?

Three ATP molecules.

What is the equivalent energy yield of each FADH molecule in the citric acid cycle?

Two ATP molecules.

How many acetyl-CoA molecules are produced from each glucose molecule in the citric acid cycle?

Two.

What is the total ATP yield per glucose molecule at the end of the citric acid cycle?

38 ATP molecules.

What does alpha-ketoglutarate dehydrogenase convert?

Alpha-ketoglutarate to succinyl-CoA.

What does citrate synthase do in the citric acid cycle?

Forms citrate from oxaloacetate and acetyl-CoA.

What does lactate dehydrogenase do?

Converts pyruvate to lactic acid.

When does lactate dehydrogenase convert pyruvate to lactic acid?

When pyruvate does not enter the citric acid cycle.

What are the products of the citric acid cycle?

NADH, FADH, and GTP.

What are some causes of liver dysfunction?

Alcohol use, hepatotoxins, hepatitis B or C infections, trauma

What is cirrhosis?

A condition where the liver cannot carry out its normal functions

What are some metabolic functions of the liver?

Breaking down estrogen and progesterone, breaking down toxins like ammonia, albumin production, production of coagulation factors, conjugation of bilirubin, platelet production

What is the consequence of a deficiency in albumin production?

Worsening of ascites

What is the consequence of impaired production of coagulation factors?

Easy bleeding and bruising

What is the consequence of impaired conjugation of bilirubin?

Jaundice

What is the consequence of impaired platelet production?

Decreased platelet count

What is liver failure?

A complex disease with a spectrum of severity, where the liver gradually loses function if the underlying cause is not addressed

What is the effect of increased estrogen levels in cirrhosis?

Findings such as gynecomastia

What is the effect of increased hepatic vascular resistance in cirrhosis?

Findings such as esophageal varices, caput medusae, and hemorrhoids

What is the effect of increased ammonia levels in cirrhosis?

Hepatic encephalopathy, presenting with confusion and asterixis

What is a likely diagnosis in a patient with cirrhosis who is vomiting blood?

Bleeding esophageal varices

What is erythropoiesis?

Process of red blood cell production.

Where does embryonic red blood cell production occur?

Yolk sac, liver, spleen, lymph nodes, and bone marrow.

Which bones produce red blood cells until about age 5?

Nearly all bones in the body.

After age 20, which bones become quiescent in red blood cell production?

Long bones, except for proximal humeri and tibiae.

Which bones continue erythropoiesis throughout adulthood?

Membranous bones such as vertebrae, sternum, ribs, and ilia.

What are the origins of all circulating blood cells?

Multipotential hematopoietic stem cells.

What factors contribute to the differentiation of stem cells into erythrocytes?

Stimulation of growth inducer proteins, differentiation inducer proteins, and hypoxemia.

What is the first differentiating cell in the red blood cell line?

Proerythroblast.

What are the subsequent stages of differentiation in the red blood cell line?

Basophilic erythroblast, polychromatophilic erythroblast, orthochromatic erythroblast, reticulocyte, and erythrocyte.

Which organs produce erythropoietin?

Kidneys (and liver to a smaller extent).

What is the function of erythropoietin?

Stimulates bone marrow to produce erythrocytes in response to decreased tissue oxygenation.

What are some factors that contribute to tissue hypoxia?

Anemia, pulmonary disease, and bleeding disorders.

What happens to erythropoietin production and red blood cell synthesis at high altitudes?

Increases to restore adequate oxygen delivery to tissues.

What is the role of iron in red blood cell production?

Required to make heme, which is required to make hemoglobin.

How does heme synthesis begin?

Tricarboxylic acid cycle forms succinyl-CoA.

What molecules combine to form a pyrrole molecule in heme synthesis?

Two succinyl-CoA molecules and two glycine molecules.

What molecules combine to form protoporphyrin IX in heme synthesis?

Four pyrrole molecules.

What happens when protoporphyrin IX binds with iron in heme synthesis?

Forms a heme molecule.

Where does the final step of heme synthesis occur?

Mitochondrion

What is the process in which RNA polymerase reads DNA to create mRNA?

Transcription

What is the name of the enzyme used to replicate DNA?

DNA polymerase

What is the starting point for DNA polymerase to begin synthesis of a new strand?

Primase

What is the enzyme that extends the ends of DNA?

Telomerase

What is the name of the enzyme that unwinds DNA for replication?

Helicase

What type of molecules can pass through the cell membrane: polar or nonpolar?

Nonpolar.

What is the composition of the cellular membrane?

Primarily lipids, mostly phospholipids and cholesterol.

What is the structure of a phospholipid?

A hydrophilic head and two hydrophobic fatty acid chains.

How do phospholipids arrange in the cellular membrane?

They form a bilayer with the lipid tails meeting at the interface.

What is the function of proteins in the cell membrane?

To allow particular materials to pass into or out of the cell.

Are carbohydrates the primary macromolecule in the cell membrane?

No, they are present but not the primary macromolecule.

Are nucleic acids found in the plasma membrane?

No, they are not found in the plasma membrane.

What are the different classes of G proteins?

Gq, Gs, and Gi.

Which receptors are associated with Gq?

H1, alpha-1, V1, M1, and M3 receptors.

Which receptors are associated with Gs?

Beta-1/2/3, D1, H2, and V2 receptors.

Which receptors are associated with Gi?

M2, alpha-2, and D2 receptors.

How does Gq protein act?

Via phospholipase C, cleaving lipids into phosphatidylinositol 4,5-bisphosphate, diacylglycerol, and inositol triphosphate.

What is the downstream effect of calcium in Gq signaling?

Protein kinase C activation and smooth muscle contraction.

How is Gs protein coupled?

To adenylate cyclase, converting ATP into cAMP.

What is the net effect of cAMP in Gs signaling?

Activation of protein kinase A.

How is Gi protein coupled?

To adenylate cyclase, inhibiting the conversion of ATP to cAMP.

What is the function of G proteins?

To mediate downstream intracellular effects when their receptors are activated.

What is the messenger molecule produced by adenylate cyclase in Gs signaling?

Cyclic adenosine monophosphate (cAMP).

What is the function of protein kinase A?

To activate downstream cellular processes.

What are membrane proteins?

Proteins present in the cell membrane that allow for cellular permeability and serve as receptors.

What is a glycoprotein?

A protein with a carbohydrate group attached that may be present in the cell membrane.

What are hormones?

Molecules that transmit messages between cells through the bloodstream.

What are the three classifications of hormones based on their chemical structure?

Polypeptides, steroids, and amino acid derivatives.

How are steroid hormones synthesized?

From cholesterol in the smooth endoplasmic reticulum.

What is the precursor for estrogen synthesis?

Pregnenolone.

What is the structure of cholesterol?

Consists of three six-membered rings and one five-membered ring, with a hydroxyl group.

What is the structure of cell membranes?

Lipid bilayer with a similar structure to cholesterol.

How do steroid hormones cross the cell membrane?

They can cross directly through the cell membrane.

What is the role of estrogen?

To stimulate the development of secondary sexual characteristics in female adolescents.

What is epinephrine?

An amino acid-derived hormone.

What are the components of an amino acid?

Amino group, carboxyl group, hydrogen, and side chain group.

How do amino acid-derived hormones enter a cell?

Through a protein channel.

What are the roles of epinephrine and norepinephrine?

Important in metabolism and the fight-or-flight response.

What is insulin?

A polypeptide hormone crucial for glucose use.

How does insulin enter a cell?

Through a protein channel.

What type of hormone is thyroxine?

An amino acid-derived hormone crucial for metabolism.

How does thyroxine enter a cell?

Through a protein channel.

What is oxytocin?

A polypeptide hormone involved in stimulating uterine contraction.

What is the first step in cholesterol synthesis?

Conversion of acetyl-coenzyme A.

What is the target of statins?

HMG-CoA reductase inhibitors.

What can cholesterol be converted into?

Steroid hormones, cell membrane, vitamin D, and bile acids.

What is the main regulatory enzyme in bile acid production?

7-alpha-hydroxylase.

What role does atherosclerosis play in vascular diseases?

Implicated in the disease process.

What lipoproteins are associated with disease?

Elevated LDL levels.

What happens when LDL becomes oxidized?

Phagocytosed by macrophages.

What is the downstream cascade in atherosclerosis?

Involves smooth muscle cells, platelets, and chemical mediators.

What is the result of reactive intimal hyperplasia?

Denuded endothelium and platelet adhesion.