Exam 3 Flashcards
Vitamins and Signal Transduction
What is the role of an enzyme cascade in a signal transduction?
Amplification
Epinephrine binding to its receptors stimulates an increase in blood glucose levels, whereas insulin has the opposite effect. What term applies to a situation in which both hormones are bound to their receptors on the same cells?
Integration (the ability of the system to receive multiple signals and produce a unified response)
An agonist is best defined as:
A) an effector molecule synthesized in a cell in response to an external signal such as a hormone.
B) a compound that interferes with the physiological action of another substance, usually at a hormone or neurotransmitter receptor.
C) a noncatalytic protein that holds together other protein molecules that function in concert.
D) a compound, typically a hormone or neurotransmitter, that elicits a physiological response when it binds at its specific receptor
B. a compound that interferes with the physiological action of another substance, usually at a hormone or neurotransmitter receptor.
Antagonists are molecules that bind a receptor without triggering the normal effect and thereby block the effects of agonists, including the natural ligand.
Which method could help determine what signaling system is likely stimulated through a receptor that binds a newly described nonsteroidal hormone?
A. tandem mass spectrometry
B. two-dimensional gel electrophoresis
C. ramachandran plot
D. hydropathy plot
D. hydropathy plot
Hydropathy analysis would predict seven membrane-spanning regions of the receptor molecule, suggesting the G-protein coupled signaling system.
Which statement describes the active form of the guanosine nucleotide-binding protein?
A. GTP binds the α subunit.
B. GDP binds the α subunit.
C. GTP binds the β subunit.
D. GDP binds the β subunit.
E. GTP binds the γ subunit.
A. GTP binds the α subunit.
The binding site for GDP or GTP is on the α subunit. When GTP is bound, the G protein is in its trimeric, active form.
Which sequence correctly identifies the order of events that take place during desensitization of the β-adrenergic receptor? 1. binding of β-arrestin to the receptor
- recruitment of βARK to the membrane
- dissociation of Gsβγ from Gsα
- phosphorylation of Ser residues on the receptor
A. 2, 1, 4, 3
B. 3, 2, 4, 1
C. 1, 2, 4, 3
D. 4, 2, 1, 3
B. 3, 2, 4, 1
After epinephrine binds to the adrenergic receptor, Gsβγ dissociates from Gsα . Then, ARK associates with the receptor and phosphorylates Ser residues. β-arrestin binds to the phosphorylated receptor, leading to endocytosis of the receptor-arrestin complex.
Which molecule in signaling is NOT considered a second messenger?
A. calcium
B. GTP
C. inositol 1,4,5-triphosphate
D. cyclic AMP
B. GTP
GTP activates G proteins in GPCR signaling systems. However, GTP is not a second messenger. A second messenger is a low molecular weight metabolite or inorganic ion that activates or inhibits one or more downstream targets, often protein kinases.
How does PLC activate PKC?
A. It increases cAMP levels.
B. It converts phosphatidylcholine to phosphatidic acid, which activates PKC.
C. It converts phosphatidylcholine to DAG and phosphocholine to activate PKC.
D. It converts phosphatidylinositol-4,5-bisphosphate to diacylglycerol and IP3 to activate PKC.
D. It converts phosphatidylinositol-4,5-bisphosphate to diacylglycerol and IP3 to activate PKC.
The G protein (Gq ) acts through phospholipase C, which cleaves phosphatidylinositol 4,5-bisphosphate (PIP2 ) to diacylglycerol and IP3 . By opening Ca2+ channels in the endoplasmic reticulum, IP3 raises cytosolic [Ca2+]. Diacylglycerol and Ca2+ act together to activate protein kinase C, which phosphorylates and changes the activity of specific cellular proteins.
Which process is NOT a feature of β-adrenergic receptors?
A. activate protein kinase A
B. interaction with β-arrestin
C. cause binding of Ca2+ to calmodulin
D. phosphorylation
C. cause binding of Ca2+ to calmodulin
Cellular [Ca2+] regulates (often through calmodulin) many enzymes and proteins involved in secretion, cytoskeletal rearrangements, and contraction. Many of the target enzymes are in the family of Ca2+-activated protein kinases (PKCs). This is distinct from signaling through βadrenergic receptors.
How do BOTH major classes of G proteins become activated?
A. GTP is hydrolyzed to GDP.
B. GDP is phosphorylated.
C. GDP leaves the G proteins and GTP binds.
D. GDP binds after the α subunit dissociates from the δ and γ subunits.
C. GDP leaves the G proteins and GTP binds.
When an agonist binds to a G protein-coupled receptor, GDP is replaced with GTP on the G protein, activating the protein. In this active form, the G protein can transmit the signal from the activated receptor to its downstream effector protein
Receptor tyrosine kinases:
A. bind two cAMPs when active.
B. do not regulate gene expression.
C. are not prone to dimerization.
D. autophosphorylate.
D. autophosphorylate.
Ligand binding activates tyrosine kinase activity by autophosphorylation. Autophosphorylation opens the active site so that the enzyme can phosphorylate Tyr residues of other target proteins.
What is the connection between signaling through voltagegated ion channels, receptor tyrosine kinases, and microdomains (i.e., rafts)?
A. All are based on a conformational change in membrane proteins.
B. All are highly exergonic events.
C. All require increased concentrations of a second messenger.
D. All are stimulated through phosphorylation.
A. All are based on a conformational change in membrane proteins.
Voltage-gated ion channels, receptor tyrosine kinases, and microdomains all undergo a conformational change as part of their signaling system.
What is unique about steroid receptor signaling?
A. It is the only one of the six signaling systems that has ligand receptors in the nucleus.
B. It is the only system used for hormone signaling.
C. It is the only one of the six signaling systems that stimulates a change in gene expression.
D. It is the only system that does not use second messenger molecules
A. It is the only one of the six signaling systems that has ligand receptors in the nucleus.
In target cells, steroid hormones pass through the plasma membrane and nuclear membrane by simple diffusion and bind to specific receptor proteins in the nucleus. The hormone-receptor complex binds specific regions of DNA at the hormone response elements and interacts with other proteins to regulate the expression of nearby genes.
When a cell exists the quiescent phase, which phase does it immediately enter?
A. S
B. M
C. G1
D. G2
E. G0
C. G1
After passing through mitosis and into G1, a cell either continues through another division or ceases to divide, entering a quiescent phase (G0) that may last hours, days, or the lifetime of the cell. When a cell in G0 begins to divide again, it reenters the division cycle through the G1 phase.
Which statement is false?
A. Oncogenes are genetically dominant.
B. Oncogenes are mutated versions of proto-oncogenes.
C. The proteins pRb, p53, and p21 derive from tumor suppressor genes.
D. Tumor suppressor genes encode defective signaling proteins.
D. Tumor suppressor genes encode defective signaling proteins.
Oncogenes encode defective signaling proteins. Tumor suppressor genes encode regulatory proteins that normally inhibit cell division.
Considering the various types of genes associated with the formation of cancers, mutations in which gene groups would MOST LIKELY have the greatest contribution to the formation of a cancer?
A. genes stimulating cell growth
B. genes involved in DNA damage repair
C. genes inhibiting cell growth
D. genes involved in cell cycle progression
B. genes involved in DNA damage repair
Cancer is generally the result of an accumulation of mutations in oncogenes and tumor suppressor genes. Thus, mutations in genes involved in DNA damage repair would likely allow these mutations in oncogenes and tumor suppressor genes to accumulate and cause cancer.
Vitamin A
- Characteristics: Nonpolar, Hormone precursor
- Chemical Name: Retinol
- Biological Process: Derives Retinoic acid and all-trans retinal, which is essential in the activation of rhodopsin in the vertebrate eye
- Source: Orange vegetables (beta-carotene), Fish liver oils, Eggs, Milk, Butter
- Deficiency: Dry skin, Hindered neuronal development, night blindness
Vitamin D
- Characteristics: Nonpolar, Hormone Precursor
- Chemical Name: Cholecalciferol
- Biological Process: Regulates calcium uptake in the intestines, kidneys, and bones
- Source: Formed in the skin from the photochemical 7-dehydrocholesterol driven by UV radiation
- Deficiency: Rickets, soft bones, osteoporosis, and seasonal depression
- Only vitamins where a slight deficiency can have an effect (usually the only deficiencies seen in a first world country)
Vitamin E
- Characteristics: Nonpolar, Oxidation Reduction Cofactors
- Chemical Name: Tocopherols
- Biological Process: Biological antioxidant. Associates with the cell membrane, lipid deposits, and lipoproteins in the blood.
- Source: Eggs and vegetable oils
- Deficiency: Scaly skin, muscle weakness, sterility, fragile erythrocytes
Vitamin K
- Characteristics: Nonpolar, Oxidation Reduction Cofactors
- Chemical Name: Phylloquinone
- Biological Process: Undergoes a cycle of oxidation and reduction during the formation of prothrombin (blood plasma protein). Essential for blood clotting. Converts fibrinogen to fibrin.
- Source: Green plants and bacteria
- Deficiency: Slows the body’s ability to clot. Fatal.
Vitamin C
- Characteristics: Polar, Antioxidant Enzyme cofactor
- Chemical Name: L-Ascorbic Acid
- Biological Process: Cofactor in at least 8 enzymatic reactions. Essential in collagen synthesis
- Source: Fruits and Vegetables
- Deficiency: Scurvy, Dysfunctional collagen, Spongy gums, Bleeding from mucous membranes, and brown spots on skin
Vitamin B1
- Characteristics: Polar, Nitrogen containing
- Chemical Name: Thiamine
- Biological Process: Plays a central role in the generation of energy from carbohydrates. Involved in the conversion of pyruvate to acetyl coenzyme A in metabolism.
- Source: Synthesized in bacteria, fungi, and plants.
- Deficiency: Beriberi, Wernicke’s encephalopathy, Korsakoff’s syndrome
Vitamin B2
- Characteristics: Polar, Nitrogen containing
- Chemical Name: Riboflavin
- Biological Process: Involved in energy production for the electron transport chain, the citric acid cycle, and the catabolism of fatty acids.
- Source: Milk, eggs, cheese, leaf vegetables, liver, kidneys, legumes, mushrooms, almonds.
- Deficiency: Ariboflavinosis, UV sensitivity, Cheilosis, Pseudo-syphilis
Vitamin B3
- Characteristics: Polar, Nitrogen containing
- Chemical Name: Niacin (Nicotinic Acid and Nicotinamide)
- Biological Process: Coenzymes forms NAD and NADP. Plays an important role in energy transfer reactions in the metabolism of glucose, fat, and alcohol
- Source: Synthesized from tryptophan. Liver, chicken, beef, fish, cereal, peanuts, and legumes.
- Deficiency: Pellagra, Nausea, Skin and mouth lesions, Anemia, Headaches, Tiredness
Vitamin B5
- Characteristics: Polar, Nitrogen containing
- Chemical Name: Pantothenic Acid
- Biological Process: Required in the synthesis of Coenzyme A, synthesis, and metabolism of proteins, carbohydrates, and fats.
- Source: Most foods
- Deficiency: Acne and Paresthesia
Vitamin B6
- Characteristics: Polar, Nitrogen Containing
- Chemical Name: Pyridoxine
- Biological Process: Coenzyme in many enzymatic reactions: Amino acid metabolism, hemoglobin synthesis and function, glucose metabolism, gene expression, lipid metabolism.
- Source: Widely distributed in foods. Pork, turkey, beef, bananas, chickpeas, potatoes, and pistachios
- Deficiency: Seborrheic dermatitis-like eruptions, Atrophic glossitis with ulceration, Angular cheilitis, conjunctivitis, Intertrigo, and neurological symptoms
Vitamin B7
- Characteristics: Polar, Nitrogen containing
- Chemical Name: Biotin
- Biological Process: A coenzyme for carboxylase enzymes; involved in the synthesis of fatty acids, isoleucine, and valine; involved in gluconeogenesis
- Source: Intestinal bacteria, peanuts, Swiss chard, leafy green vegetables, raw egg yolk, liver, and Saskatoon berries
- Deficiency: Brittle/thin fingernails, alopecia, conjunctivitis, dermatitis, and neurological symptoms in adults
Vitamin B9
- Characteristics: Polar, Nitrogen Containing
- Chemical Name: Folic Acid
- Biological Process: Required in DNA synthesis, DNA repair, and DNA methylation. Cofactor in certain biological reactions (important in rapid cell division and growth, required for healthy red blood cell production and anemia prevention)
- Source: Dark leafy green vegetables, fruits, nuts, beans, peas, dairy products, poultry and meat, eggs, seafood, grains, and some beers. Most common in avocado, beetroot, spinach, liver, yeast, asparagus, and Brussel sprouts (used as a prenatal supplement)
- Deficiency: Neural tube defects in developing embryos, diarrhea, nerve damage
