Biochem Finals (Batch 2027) Flashcards

Question

Which hormone/s will be released upon stimulation of Thyroid Stimulating Hormone (TSH)? A. Thyroxine B. Triiodothyronine C. Thyrotropin-releasing hormone D. Only A and B

Answer 1

D. Only A and B Rationale: Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to produce and release thyroxine (T4) and triiodothyronine (T3).

Answer 2

a. Hydrophobic steroid hormones bound to plasma protein carriers diffuse into the target cell Rationale: Hydrophobic steroid hormones do not diffuse into target cells while bound to plasma protein carriers. They must first dissociate from these carriers to enter the cell.

Answer 3

d. All of the above Rationale: In primary hypersecretion due to an adrenal cortex problem, cortisol levels are high, which leads to feedback inhibition resulting in low levels of CRH (corticotropin-releasing hormone) and ACTH (adrenocorticotropic hormone).

Answer 4

b. Hypoglycemia Rationale: Taking insulin without eating can lead to a significant drop in blood glucose levels, resulting in hypoglycemia.

Answer 5

c. Calcium Rationale: Inositol triphosphate (IP3) stimulates the release of calcium ions from the endoplasmic reticulum, acting as a second messenger in various signaling pathways.

Answer 6

d. Estrogen Rationale: Estrogen primarily acts through intracellular receptors that directly influence gene transcription, rather than using cAMP as a second messenger.

Answer 7

b. Paracrine Rationale: Paracrine signaling involves the release of hormones that act on nearby cells, unlike endocrine signaling which involves hormones traveling through the bloodstream to distant cells.

Answer 8

D. Carboxylations Rationale: Biotin acts as a coenzyme for carboxylase enzymes, which are involved in carboxylation reactions.

Answer 9

B. Copper Rationale: Copper is a key component of many oxidase enzymes, including cytochrome oxidase and ascorbic acid oxidase.

Answer 10

B. Pernicious anemia Rationale: Vitamin B12 deficiency can lead to pernicious anemia, a condition in which the body can't make enough healthy red blood cells.

Answer 11

C. lipoamide Rationale: Lipoamide is not a vitamin that gives rise to a phosphorylated cofactor; it is derived from lipoic acid and acts as a cofactor in its own right.

Answer 12

B. it prevents thrombosis Rationale: Vitamin K is essential for blood clotting and helps in the synthesis of clotting factors; it does not prevent thrombosis but rather supports the clotting process.

Answer 13

A. it is synthesized in skin Rationale: Vitamin A is not synthesized in the skin; this statement is true for vitamin D. Vitamin A is obtained from the diet and is essential for vision, epithelial maintenance, and treatment of severe acne.

Answer 14

A. Amyloid Rationale: Amyloid proteins aggregate to form plaques, which are associated with neurodegenerative diseases such as Parkinson’s and Alzheimer’s.

Answer 15

D. Telomeres shorten after every cell division until senescence sets in Rationale: Telomeres protect chromosome ends but shorten with each cell division, leading to cellular aging and eventual senescence.

Answer 16

C. Selenium Rationale: Selenium is an essential cofactor for the enzyme glutathione peroxidase, which plays a critical role in protecting cells from oxidative damage by neutralizing free radicals. While NADPH is important for the regeneration of glutathione, it is not a cofactor for vitamins C, E, and glutathione peroxidase in the same direct sense as selenium.

Answer 17

D. It helps synthesize steroid hormones Rationale: Cytochrome P450 enzymes are involved in the synthesis of steroid hormones, as well as in the metabolism of xenobiotics. They do not contain selenium and are primarily involved in phase I metabolism.

Answer 18

B. Render the molecule water-soluble Rationale: The main goal of xenobiotic metabolism is to render the molecule more water-soluble, facilitating its excretion from the body, typically via the kidneys.

Answer 19

B. Fat-soluble Rationale: Xenobiotic drugs are often designed to be fat-soluble (lipophilic) to facilitate absorption through cell membranes, which are composed of lipid bilayers.

Answer 20

A. amino acids that form antigen binding site Rationale: The hypervariable regions of an antibody, also known as complementarity-determining regions (CDRs), consist of amino acids that form the antigen-binding site.

Answer 21

C. J-chain Rationale: The J-chain (joining chain) links monomers of IgA and pentamers of IgM.

Answer 22

A. fragment crystallization & is the constant region Rationale: The Fc region (fragment crystallizable) is the constant region of an antibody that interacts with cell surface receptors and complement proteins.

Answer 23

B. First antibody type produced against an antigen during the primary antibody response Rationale: IgM is the first antibody produced during the primary immune response, not IgG. IgG is the major antibody in serum and is involved in complement activation and opsonization.

Answer 24

C. IgM Rationale: IgM is the most efficient at fixing complement due to its pentameric structure, which allows for multiple binding sites for the complement system.

Answer 25

D. Fab regions of the antibody Rationale: The antigen-binding sites are located in the Fab (fragment antigen-binding) regions of the antibody, which include the variable regions of both the light and heavy chains.

Answer 26

A. the formation of the membrane attack complex Rationale: The final common pathway in the complement system results in the formation of the membrane attack complex (MAC), which creates pores in the target cell membrane, leading to cell lysis.

Answer 27

D. Factor X Rationale: Factor X is the convergence point of the intrinsic and extrinsic pathways in the coagulation cascade. Activation of Factor X leads to the conversion of prothrombin to thrombin, a key step in the formation of a blood clot.

Answer 28

B. Prostacyclin Rationale: Prostacyclin (PGI2) is a potent vasodilator and inhibitor of platelet aggregation, which works by increasing cyclic AMP (cAMP) levels in platelets.

Answer 29

B. Binds and protects Factor IX Rationale: von Willebrand factor (vWF) glues platelets to damaged endothelium and binds and protects Factor VIII, not Factor IX. It is also secreted by endothelial cells into the plasma.

Answer 30

B. Platelet phase Rationale: The platelet phase, involving the adhesion, activation, and aggregation of platelets to form a platelet plug, is considered the primary mechanism of hemostasis.

Answer 31

B. Consists primarily of platelets and fibrin Rationale: A red thrombus, which typically forms in venous areas, is predominantly composed of erythrocytes trapped in a fibrin mesh. Platelet-rich thrombi (white thrombi) are more common in arterial thrombosis.

Answer 32

b. Patterns of gene expression established during the early developmental stages are not permanent, enabling one cell type to differentiate into a different cell type later in the life cycle Rationale: This statement is incorrect because gene expression patterns established during early development are usually stable and contribute to cell specialization, preventing cells from changing type later in life.

Answer 33

a. is a normal way for organisms to regulate gene expression Rationale: RNA interference (RNAi) is a natural process used by cells to regulate gene expression by degrading specific mRNA molecules or inhibiting their translation.

Answer 34

b. The lac operon messenger RNA is a polycistronic mRNA Rationale: The lac operon produces a single polycistronic mRNA that encodes multiple proteins involved in lactose metabolism.

Answer 35

d. Rapid translation of the leader peptide prevents completion of the mRNA transcript Rationale: In the trp operon, rapid translation of the leader peptide (indicating high tryptophan levels) causes the formation of a terminator structure in the mRNA, preventing completion of the transcript.

Answer 36

d. Neither CAP nor the lac repressor gene are bound to the DNA Rationale: When both glucose and lactose are present, the catabolite activator protein (CAP) is not bound to the DNA due to low cAMP levels, and the lac repressor is not bound because lactose (or its isomer allolactose) inactivates it.

Answer 37

C. Transversions Rationale: A transversion mutation is a type of base pair substitution where a purine (A or G) is replaced by a pyrimidine (C or T), or vice versa.

Answer 38

D. Frameshift mutations Rationale: Frameshift mutations occur when nucleotides are inserted or deleted from the DNA sequence, causing a shift in the reading frame of the mRNA and resulting in altered proteins.

Answer 39

A. Somatic mutations Rationale: Somatic mutations occur in non-reproductive cells and are not passed on to offspring, affecting only the individual in which the mutation occurs.

Answer 40

A. Silent mutations Rationale: Silent mutations do not alter the amino acid sequence of a protein due to the redundancy (degeneracy) of the genetic code, where multiple codons can encode the same amino acid.

Answer 41

C. Nonsense mutations Rationale: Nonsense mutations introduce a premature stop codon, leading to the early termination of translation and resulting in a truncated, often nonfunctional protein.

Answer 42

B. binds to incoming to aminoacyl-tRNA which has the anti-codon for the corresponding codon in the mRNA Rationale: The A (aminoacyl) site of the ribosome binds to the incoming aminoacyl-tRNA, which carries the anticodon that matches the codon on the mRNA.

Answer 43

B. codon and anticodon Rationale: The wobble hypothesis explains that the third base of the codon and the first base of the anticodon can form non-standard base pairs, allowing for flexibility in the genetic code.

Answer 44

C. inhibition or activation of translation in bacteria Rationale: The Shine-Dalgarno sequence is important for the initiation of translation in bacteria. A mutation in this sequence can inhibit or alter the efficiency of translation initiation.

Answer 45

A. Many ribosomes can translate the same mRNA molecule simultaneously. Rationale: In eukaryotic cells, multiple ribosomes can attach to a single mRNA molecule, forming a polysome, and translate it simultaneously, allowing for efficient protein synthesis. The other statements are incorrect because: B: In eukaryotes, transcription and translation are separated processes; translation does not begin before transcription is completed. C: The 18S rRNA is part of the small ribosomal subunit (40S) in eukaryotes, not the 50S subunit (which is found in prokaryotes). The peptidyltransferase activity is associated with the 28S rRNA in the 60S large ribosomal subunit in eukaryotes. D: Diphtheria toxin inhibits eukaryotic protein synthesis by inactivating elongation factor-2 (EF-2), not prokaryotic protein synthesis.

Answer 46

B. UAC Rationale: The first codon of the mRNA during translation is usually the start codon AUG, which is recognized by the anticodon UAC on the initiator tRNA carrying methionine.

Answer 47

A. It stimulates recruitment of the 40s ribosomal subunit to mRNA Rationale: The poly-A tail enhances the stability of the mRNA and aids in the recruitment of the ribosomal subunits during translation initiation. It interacts with the poly-A binding proteins and other factors to facilitate the assembly of the translation initiation complex.

Answer 48

B. 2’, 3’ dideoxyadenosine triphosphate Rationale: 2', 3' dideoxyadenosine triphosphate (ddATP) lacks the 3'-OH group necessary for forming a phosphodiester bond with the next nucleotide, thus halting DNA chain elongation.

Answer 49

C. making short strands of RNA at the site of replication initiation Rationale: Primase synthesizes short RNA primers that are necessary for DNA polymerase to begin DNA synthesis.

Answer 50

B. DNA ligase Rationale: DNA ligase is responsible for sealing the nicks between Okazaki fragments on the lagging strand, forming a continuous DNA strand.

Answer 51

B. a Y-shaped structure where both DNA strands are replicated simultaneously Rationale: The replication fork is the Y-shaped region where the DNA double helix is unwound and both strands are replicated.

Answer 52

B. DNA helicase Rationale: DNA helicase unwinds the DNA double helix ahead of the replication fork, allowing the strands to be replicated.

Answer 53

B. A DNA molecule consists of one parental strand and one new strand Rationale: In semiconservative replication, each new DNA molecule consists of one old (parental) strand and one newly synthesized strand.

Answer 54

C. 7-methylguanosine cap Rationale: The 5' end of eukaryotic mRNA molecules is capped with a 7-methylguanosine cap, which is important for mRNA stability, splicing, and translation initiation.

Answer 55

A. Exons Rationale: Exons are the coding sequences that remain in mature mRNA after introns have been spliced out.

Answer 56

C. 25-30 bp upstream from TSS Rationale: The TATA box is a DNA sequence found about 25-30 base pairs upstream of the transcription start site and is important for the initiation of transcription by RNA polymerase II.

Answer 57

B. Pol II Rationale: RNA polymerase II (Pol II) is responsible for transcribing mRNA in eukaryotic cells.

Answer 58

A. Transcription unit Rationale: A transcription unit consists of the promoter, the RNA-coding region, and the terminator, encompassing the entire region transcribed into RNA.

Answer 59

C. rRNA Rationale: Ribosomal RNA (rRNA) is the most abundant type of RNA, making up about 80% of the total RNA in cells.

Answer 60

D. Z form Rationale: Z-DNA is a left-handed helix with about 12 base pairs per turn.

Answer 61

A. H1 Rationale: Histone H1 is not part of the nucleosome core; it binds to the linker DNA between nucleosomes, stabilizing the chromatin structure.

Answer 62

D. There are three hydrogen bonds between Adenine and Thymine but only two between Guanine and Cytosine Rationale: The statement is incorrect because there are two hydrogen bonds between Adenine (A) and Thymine (T), and three hydrogen bonds between Guanine (G) and Cytosine (C).

Answer 63

C. the concentration of deoxyadenosine nucleotides equals that of Uracil nucleotides Rationale: Chargaff's Rule states that in any sample of double-stranded DNA, the concentration of adenine (A) equals thymine (T), and the concentration of guanine (G) equals cytosine (C). Uracil is found in RNA, not DNA.

Answer 64

A. DNA Rationale: Thymine is one of the four nucleotides in DNA but is not present in RNA, where it is replaced by uracil.

Answer 65

D. Transcription Rationale: Transcription is the first stage in the expression of genetic information, where DNA is transcribed into RNA.

Answer 66

C. 1,2 DAG Rationale: Diacylglycerol (1,2-DAG) is a second messenger involved in the regulation of cytidyl transferase, an enzyme in the synthesis of phospholipids.

Answer 67

A. sphingosine + fatty acid Rationale: Ceramides are composed of a sphingosine backbone linked to a fatty acid via an amide bond.

Answer 68

B. fetal lung maturity Rationale: The lecithin-to-sphingomyelin (L) ratio in amniotic fluid is used to assess fetal lung maturity, with a higher ratio indicating greater maturity and a reduced risk of respiratory distress syndrome.

Answer 69

A. dipalmitoyl lecithin Rationale: Dipalmitoyl lecithin, also known as dipalmitoylphosphatidylcholine (DPPC), is the major component of lung surfactant, which reduces surface tension in the alveoli.

Answer 70

C. sphingomyelinase Rationale: Niemann-Pick disease is caused by a deficiency of the enzyme sphingomyelinase, leading to the accumulation of sphingomyelin in cells.

Answer 71

A. diacylglycerol Rationale: Diacylglycerol is an intermediate in the synthesis of both phospholipids and triacylglycerols.

Answer 72

d. unesterified cholesterol Rationale: Unesterified cholesterol (free cholesterol) is indeed a part of lipoproteins. The correct answer should be different, but given the options, none are completely accurate.

Answer 73

d. The receptors can be recycled whereas the lipoprotein remnants in the vesicles are degraded by lysosomal enzymes releasing cholesterol, fatty acids, amino acids, and phospholipids. Rationale: LDL receptors are indeed recycled, and the lipoprotein remnants are degraded by lysosomal enzymes, releasing their components.

Answer 74

b. VLDL Rationale: Very low-density lipoproteins (VLDL) are composed predominantly of triacylglycerol and transport lipids from the liver to peripheral tissues.

Answer 75

b. chylomicron > VLDL > LDL > HDL Rationale: Lipoproteins decrease in size and increase in density in the order of chylomicrons, VLDL, LDL, and HDL as the lipid-to-protein ratio decreases.

Answer 76

b. apoB48 - Rationale: ApoB48 is the apoprotein found in nascent chylomicrons, which are released by intestinal mucosal cells.