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Questions and Answers
Which type of protein is primarily responsible for transporting oxygen in the blood?
What classification of proteins primarily contains only amino acids?
What is the main outcome of the transamination process?
Which of the following is a conjugated protein?
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Which enzyme is involved in the transamination process?
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Which classification of proteins provide structural support in tissues?
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What is a characteristic feature of fibrous proteins?
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Which of the following statements about biological significance of transamination is correct?
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Which group is NOT part of the one-carbon pool in the body?
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What is the primary contributor for methylene THFA in one-carbon metabolism?
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Which one-carbon group is donated by tryptophan?
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What occurs in the case of B12 deficiency concerning folic acid?
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What compound is synthesized from one-carbon units besides glycine and serine?
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Phenylketonuria (PKU) is caused by a deficiency in which enzyme?
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What is the incidence of phenylketonuria (PKU) in India?
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What is the biochemical outcome of phenylalanine accumulation in PKU?
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What is the recommended dietary allowance (RDA) of Vitamin C for an average adult?
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How does Vitamin C affect iron metabolism?
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What deficiency disease is primarily caused by a lack of Vitamin C?
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What role does ascorbic acid play in collagen formation?
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In what way does Vitamin C act as an antioxidant?
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What effect does Vitamin C have on phagocytosis?
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Which vitamin is necessary for the synthesis of bile acids from cholesterol?
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What is a common symptom of ascorbic acid deficiency that affects blood vessels?
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What is the effect of a frameshift mutation on protein production?
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What are the components involved in the structure of the lac operon?
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What is the role of the Z gene in the lac operon?
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What happens to transcription of structural genes in the absence of lactose?
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How does lactose affect the lac operon?
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What does the term 'derepression' refer to in the context of the lac operon?
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Which best describes the operator in the lac operon?
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Which component of the lac operon is responsible for transporting lactose into the bacterial cell?
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What is one of the primary roles of Vitamin D in bone health?
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What is a consequence of Vitamin D deficiency in children?
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Which condition results from insufficient Vitamin D in adults?
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What is a key effect of calcitriol in the renal tubules?
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Which of the following symptoms is commonly associated with wet beriberi?
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What does infantile beriberi typically manifest as?
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In cases of kidney diseases, why might calcitriol treatment be necessary despite Vitamin D availability?
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Which symptom is NOT associated with dry beriberi?
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Study Notes
Protein Classification
- Proteins can be classified based on their function (catalytic, structural, contractile, transport, regulatory, genetic, protective) or their composition (simple, containing only amino acids; conjugated, containing a non-protein component; derived, degradation products of native proteins).
- Globular proteins are spherical or oval, while fibrous proteins are elongated. The nutritional value of proteins can be divided into nutritionally rich, containing all essential amino acids, and poor proteins, lacking in essential amino acids.
Transamination
- Transamination is the process of transferring an amino group from an amino acid to a keto acid, forming a new amino acid.
- The amino group is often accepted by alpha-ketoglutarate to form glutamate.
- These reactions are catalyzed by aminotransferases, which use pyridoxal phosphate as a prosthetic group.
- Transamination is the first step in amino acid degradation, allowing for the removal of the amino group and its transfer to alpha-ketoglutarate.
One-Carbon Metabolism
- One-carbon metabolism involves the transfer and utilization of one-carbon units in various metabolic reactions.
- These one-carbon units, including formyl, formimino, methenyl, hydroxymethyl, methylene, and methyl groups, are important for the synthesis of various compounds.
- Tetrahydrofolic acid (THFA) is crucial for carrying these one-carbon units, except for the methyl group. THFA is derived from folic acid.
- Different amino acids contribute one-carbon units for various metabolic processes, including serine to glycine for methylene THFA, glycine cleavage for methylene groups, histidine for N5-formimino THFA, tryptophan for formyl-THFA, and choline for hydroxymethyl groups.
Phenylketonuria (PKU)
- PKU is caused by a deficiency of phenylalanine hydroxylase, leading to an inability to convert phenylalanine to tyrosine.
- This results in the accumulation of phenylalanine in the blood, potentially leading to developmental problems.
- The frequency of PKU is considered to be 1 in 10,000 births, with an incidence of 1 in 25,000 births in India.
- The elevated phenylalanine levels can lead to premature termination of protein synthesis and loss of functional activity.
Frameshift Mutation
- Frameshift mutation is caused by the addition or deletion of bases in the DNA sequence. This shifts the reading frame, altering all subsequent triplet codons.
- Consequently, a non-functional or no protein is produced.
Lac Operon
- The lac operon is a unit of gene expression in bacteria, composed of structural genes, control elements (operator, promoter), and a regulator gene (inhibitor gene).
- The structural genes encode proteins involved in lactose metabolism: Z gene encodes beta-galactosidase, Y gene encodes permease, and A gene encodes thiogalactoside transacetylase.
- The lac operon is controlled by a repressor protein encoded by the "i" gene.
- When lactose is absent, the repressor binds to the operator, blocking RNA polymerase and preventing the transcription of the structural genes.
- When lactose is present, it binds to the repressor, causing a conformational change that makes the repressor unable to bind the operator. This allows RNA polymerase to transcribe the structural genes, leading to the production of the enzymes needed for lactose metabolism.
Vitamin D, Bone, and Renal Tubules
- Vitamin D (calcitriol) plays a role in bone mineralization by increasing osteoblast activity.
- Calcitriol also increases the reabsorption of calcium and phosphorus by renal tubules.
- The production of calcitriol is regulated by feedback mechanisms, responding to changes in serum calcium, phosphorus, PTH, and calcitriol itself.
Deficiency of Vitamin D
- Deficiency of vitamin D leads to rickets in children and osteomalacia in adults.
- Rickets is characterized by soft bones, bone bending due to insufficient mineralization, and clinical manifestations like bow legs, knock-knee, and pigeon chest.
- Osteomalacia leads to soft bones and increased susceptibility to fractures.
- Renal rickets occurs in kidney diseases where calcitriol synthesis is impaired, even with adequate vitamin D levels.
Deficiency of Thiamine (Beriberi)
- Thiamine deficiency leads to beriberi, characterized by weakness, anorexia, dyspepsia, and easy exhaustion.
- Wet beriberi affects the cardiovascular system, causing edema, palpitations, breathlessness, and potentially, heart failure.
- Dry beriberi affects the CNS, leading to difficulty walking, peripheral neuritis, and potentially paralysis.
- Infantile beriberi affects infants born to thiamine-deficient mothers, causing restlessness and sleeplessness.
- Wernicke-Korsakoff syndrome, also known as cerebral beriberi, is a neuropsychiatric disorder resulting from thiamine deficiency.
Vitamin C (Ascorbic Acid)
- The RDA for vitamin C is 75 mg/day, increasing to 100 mg/day during pregnancy and lactation.
- Vitamin C is readily absorbed from the gastrointestinal tract and excreted in urine.
Biochemical Functions of Vitamin C
- Vitamin C acts as an antioxidant, helping to protect cells from damage.
- It is essential for the hydroxylation of proline and lysine, which are required for the formation of collagen cross-links.
- Vitamin C plays a role in tryptophan and tyrosine metabolism.
- It facilitates iron absorption by converting ferric iron to ferrous iron.
- Vitamin C is involved in hemoglobin metabolism, helping to convert methemoglobin back to hemoglobin.
- It assists in the conversion of folic acid to tetrahydrofolic acid.
- Vitamin C participates in steroid synthesis and bile acid production.
- It stimulates phagocytosis and antibody formation.
- It may help reduce the risk of cancer formation and cataract development.
Deficiency of Vitamin C (Scurvy)
- Vitamin C deficiency leads to scurvy, characterized by hemorrhagic tendencies and internal hemorrhaging.
- The deficiency causes abnormal collagen and brittle intercellular cement substance, making capillaries fragile and leading to bleeding.
- Scurvy can cause internal bleeding, including epistaxis, hematuria, and melena.
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Description
Explore the classification of proteins based on their function and composition, from globular to fibrous forms. This quiz also covers the crucial process of transamination, detailing how amino groups are transferred and the roles of aminotransferases. Test your knowledge of these essential biochemical concepts.
