Metabolism — Flashcards

Flashcard 821: What are the followings in relation to phosphorylation of mannose residues on glycoproteins? -Extracellular space -Lysosome -Mitochondria -Nucleus -Plasma membrane

Answer: Extracellular space: doesn't need phosphorylation of mannose residues on proteins. They will just packed in a vesicles which fuse with plasma membrane to release extracellular proteins. -Lysosome: does require phosphorylation of mannose residues on glycoproteins in order for them to enter the lysosome. Will help with degradation. -Mitochondria: They don't need protein phosphorylation. Most mitochondrial proteins will synthesize in the cytosol. -Nucleus: Protein will present with a nuclear signals (nuclear localization signals) to import or enter the nucleus. -Plasma membrane: Protein will covalently bind to an hydrophobic lipid anchor that will facilitate protein interaction with cell membrane.

Flashcard 822: 3 day old boy comes with poor feeding, vomiting, and progressive lethargy. -Parents stated: "Diaper have burnt sugar smell" -Physical Exam: Lethargic infant with dry mucous membranes and generalized hypertonia. -Which of the following should be restricted from this infant's diet?

Answer: Leucine or VAL: Valine, Leucine, Isoleucine Due to Maple syrup urine disease, caused by a deficiency of branched chain a-ketoacid dehydrogenase thus can't metabolize VAL.

Flashcard 823: A 17 y/o boy with type 1 diabetes mellitus is found unresponsive at home. - Glucose fingerstick: 32 mg/dL - Paramedics administer an injection. - The injected substance binds to a transmembrane receptor in hepatocytes, which promotes binding of intracellular GTP to a specific receptor-associated protein. - This leads to the rapid release of glucose into the blood. Which of the following is the most likely mediator responsible for these effects? a.) cGMP dependent protein kinase b.) Janus tyrosine kinase c.) phosphodiesterase d.) Protein kinase A e.) Tyrosine specific protein kinase

Answer: d.) Protein kinase A Glucagon binds to Gs-protein coupled receptors on hepatocytes, activating adenylyl cyclase to increase cAMP levels. cAMP then activates **Protein Kinase A (PKA)**, which triggers glycogenolysis.

Flashcard 824: A researcher is investigating the relationship between insulin concentration and the number of glucose transporters on the cell surface. - **Circles**: Surface transporter count increases as insulin concentration rises. - **Triangles**: Surface transporter count remains constant regardless of insulin concentration. Which cell types are most likely represented by the circles and triangles?

Answer: **Circles**: Skeletal muscle or Adipocytes (Insulin-dependent; uses **GLUT4**) **Triangles**: Most other cells (Insulin-independent; e.g., Liver, Brain, RBCs, Kidney)

Extra: Insulin-dependent glucose uptake occurs in skeletal muscle and adipose tissue via **GLUT4**. In the absence of insulin, GLUT4 is sequestered in intracellular vesicles. Insulin signaling triggers the translocation of these vesicles to the plasma membrane. Most other tissues (Liver, RBCs, Brain, Kidney) use insulin-independent transporters (GLUT1, 2, 3, or 5) which are constitutively present on the cell surface.

Flashcard 825: A researcher develops an agent that specifically blocks the interaction of inositol triphosphate (IP3) with its intracellular receptor. Compared to control cells, decreased activity of which enzyme is most likely to be observed in the experimental cells?

Answer: Protein Kinase C (PKC) IP3 binds to receptors on the smooth endoplasmic reticulum to release intracellular calcium (Ca2+). Both Ca2+ and DAG are required to activate Protein Kinase C.

Flashcard 826: A newborn presents with lethargy, vomiting, and hypotonia during the first few days of life. - Lab: metabolic acidosis with large anion gap, ketosis, & hypoglycemia. - Concentration of propionic acid is increased in the plasma and urine. - Metabolism of which amino acids contributes to this patient's condition?

Answer: Valine, Isoleucine, Methionine, and Threonine (Mnemonic: VOMIT — Valine, Odd-chain fatty acids, Methionine, Isoleucine, Threonine) This patient has Propionic Acidemia, caused by a deficiency of propionyl-CoA carboxylase (requires Biotin/B7 as a cofactor). This enzyme normally converts propionyl-CoA to methylmalonyl-CoA. Accumulation of propionic acid leads to metabolic acidosis, ketosis, and hypoglycemia.

Flashcard 827: In what disease should the followings be restricted? -Galactose -Leucine -Methionine -Phenylalanine -Tyrosine

Answer: Galactose: galactosemia (due to deficiency of Galactose-1-phosphate uridyl transferase) (GALT def.) -Leucine: Maple syrup disease, due to deficiency of branched chain a-ketacid dehydrogenase. -Methionine: should be restricted in homocysteinuria,because methionine converts to homocystein. Instead you will want to give B12 (cobalamine) to convert to methionine & B6 (pyridoxine) to convert to cysteine to relieve the high level of homocysteine. -Phenylalanine: Phenylketonuria (def. of phenyl hydroxylase), musty odor, neurological symptoms. -Tyrosine: restricted in hypertyrosinemia (progressive liver & renal disease) or in alkaptonuria (homogentisate oxidase def.) (black urine on air, black cartillage).

Flashcard 828: 31 y/o patient presents with myalgias, anorexia, & skin rash. -He doesn't do drugs or alcohol. -He has been consuming large amounts of raw egg whites for the past several months. -Physical exam: macular dermatitis of the extremities. -A water-soluble vitamin deficiency is suspected as the cause of his condition. -Which biochemical conversion(s) most likely use the deficient vitamin as a cofactor?

Answer: Pyruvate to oxaloacetate (and other carboxylation reactions) The patient has Biotin (Vitamin B7) deficiency due to excessive consumption of raw egg whites (avidin binds biotin, preventing absorption). Biotin is a cofactor for carboxylase enzymes: 1. Pyruvate carboxylase (Pyruvate → oxaloacetate) 2. Acetyl-CoA carboxylase (Acetyl-CoA → malonyl-CoA) 3. Propionyl-CoA carboxylase (Propionyl-CoA → methylmalonyl-CoA) Deficiency leads to dermatitis, alopecia, myalgias, and lactic acidosis (due to pyruvate being shunted to lactate).

Flashcard 829: What are the following substances associated with in relation to cofactors or chemical reactions? - Biotin - Folic acid - Niacin - Pyridoxine - Riboflavin - Thiamine

Answer: - Biotin (B7): Cofactor for carboxylase enzymes (e.g., Pyruvate carboxylase). - Folic Acid (B9): Cofactor for nucleic acid synthesis (1-carbon transfer). Deficiency leads to megaloblastic anemia. - Niacin (B3): Cofactor for redox reactions (NAD+/NADP+). Deficiency leads to Pellagra (Dermatitis, Diarrhea, Dementia). - Pyridoxine (B6): Cofactor for transamination (e.g., ALT, AST) and decarboxylation. - Riboflavin (B2): Cofactor for redox reactions (FAD, FMN). - Thiamine (B1): Cofactor for α-ketoacid dehydrogenases (Pyruvate DH, α-ketoglutarate DH, Branched-chain α-ketoacid DH) and Transketolase.

Flashcard 830: A study is being performed that includes certain men -Further analysis shows that these men have an X-linked mutation affecting the phosphoribosyl pyrophosphate (PRPP) synthetase gene. -This lead to increased substrate conversion. -What organ is most likely to develop pathology secondary to this mutation?

Answer: Joints due to Gout, PRPP leads to high purines and uric acid that leads to gout.