BIOCHEM Finals (Batch 2026) Flashcards

Question

The inorganic nutrients are: A. Proteins and fats B. Vitamins and minerals C. Minerals and water D. Vitamins and proteins

Answer 1

C. Minerals and water Rationale: Inorganic nutrients, which do not contain carbon, include minerals and water.

Answer 2

A. Palindromic DNA Rationale: Palindromic DNA sequences are the same when read forward or backward, and they are often recognition sites for restriction enzymes.

Answer 3

A. DNA segments Rationale: Electrophoresis is a method used to separate DNA fragments based on their size and charge.

Answer 4

C. Recognition sequence Rationale: Restriction enzymes recognize and cut DNA at specific nucleotide sequences known as recognition sequences.

Answer 5

C. Ligases Rationale: Ligases are enzymes that facilitate the joining of DNA strands together by forming phosphodiester bonds, thus "stitching" together fragments of DNA.

Answer 6

A. Plasmid Rationale: Plasmids are small, circular, double-stranded DNA molecules that exist independently of the chromosomal DNA and can replicate on their own.

Answer 7

C. DNA at specific sites Rationale: Restriction enzymes recognize specific nucleotide sequences in DNA and make cuts at or near these sites.

Answer 8

D. Two DNA segments Rationale: Recombinant DNA technology involves combining DNA from two different sources to create a new genetic combination.

Answer 9

C. Nucleotide excision repair Rationale: Nucleotide excision repair is a complex mechanism involving multiple gene products to recognize and excise damaged DNA, then fill in the gap with new nucleotides.

Answer 10

B. DNA protein kinase Rationale: DNA protein kinase (DNA-PK) plays a critical role in non-homologous end joining (NHEJ), a pathway that repairs double-strand breaks in DNA.

Answer 11

B. Glycosylase Rationale: DNA glycosylase recognizes and removes damaged bases by cleaving the bond between the base and the sugar in the DNA backbone.

Answer 12

A. Mismatch repair Rationale: In bacteria, the mismatch repair system involves the recognition of the GATC sequence and the correction of mismatched nucleotides.

Answer 13

B. Frameshift mutation Rationale: Frameshift mutations result from insertions or deletions of nucleotides that change the reading frame of the genetic code, leading to an altered amino acid sequence.

Answer 14

C. The concentration of deoxyadenosine nucleotides equals that of uracil nucleotides Rationale: Chargaff's Rule states that in DNA, the amount of adenine equals thymine and the amount of guanine equals cytosine. Uracil is found in RNA, not DNA.

Answer 15

B. Nonsense mutation Rationale: A nonsense mutation occurs when a codon is changed to a stop codon (UAA in this case), leading to premature termination of translation.

Answer 16

A. Missense mutation Rationale: A missense mutation results in a change of one amino acid to another. In this case, the codon CCA (proline) changes to UCA (serine), altering the protein sequence.

Answer 17

C. Silent mutation Rationale: Both UCC and UCG code for the same amino acid, serine, so the mutation does not change the amino acid sequence.

Answer 18

B. Nonsense mutation Rationale: A nonsense mutation occurs when a codon is changed to a stop codon, leading to premature termination of translation. UGA = U Go Away. UAA = U Are Away. UAG = U Are Gone.

Answer 19

A. Missense mutation Rationale: A missense mutation results in a codon that codes for a different amino acid, potentially altering the function of the protein.

Answer 20

A. Ribosomal RNA (rRNA) Rationale: rRNA makes up the majority of RNA in the cell and is a key component of ribosomes, which are essential for protein synthesis.

Answer 21

C. Transposons Rationale: Transposons, or "jumping genes," can insert themselves into various locations within the genome, causing mutations and altering the function of genes.

Answer 22

D. DNA primase Rationale: DNA primase is involved in DNA replication, not repair. It synthesizes a short RNA primer to initiate DNA synthesis.

Answer 23

B. Between DNA and protein molecules (e.g., histones) Rationale: Cross-linking can occur between DNA and proteins, such as histones, leading to structural changes and potential mutations.

Answer 24

B. Oxidative free radical formation Rationale: Oxidative free radicals can cause single or double-strand breaks in DNA, leading to mutations.

Answer 25

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

Answer 26

C. 25-30 bp upstream from the transcription start site (TSS) Rationale: The TATA box is a DNA sequence found about 25-30 base pairs upstream of the transcription start site and is crucial for the initiation of transcription.

Answer 27

C. Molecules with a single, defined amino acid sequence Rationale: Antibodies are glycoproteins that are expressed on the surface of B-lymphocytes and predominate in the primary immune response to antigens. They have variable regions allowing for diversity in antigen binding, not a single defined amino acid sequence.

Answer 28

C. Helper T-cells synthesize and secrete chemokines like interleukin, interferon Rationale: Helper T-cells are crucial in cell-mediated immunity as they release chemokines such as interleukins and interferons to activate other immune cells.

Answer 29

C. T lymphocytes Rationale: T lymphocytes are primarily responsible for cell-mediated immunity, recognizing and responding to infected or abnormal cells.

Answer 30

A. Acquired from the mother Rationale: Natural immunity includes passive immunity acquired from the mother through the placenta or breast milk.

Answer 31

A. Antigen-antibody complex formation on the surface of mature B cell Rationale: The humoral immune response begins when an antigen binds to antibodies on the surface of B cells, leading to their activation and the production of plasma cells that secrete antibodies.

Answer 32

D. IgE Rationale: IgE plays a crucial role in the defense against parasitic helminths and is also involved in allergic reactions.

Answer 33

C. IgA Rationale: IgA is the main immunoglobulin found in mucosal secretions, providing protection against pathogens at mucosal surfaces.

Answer 34

D. All of the above Rationale: IgM is a pentamer and acts as the 'natural antibody', exists as a monomer on the B cell surface, and is involved in the early primary immune response.

Answer 35

B. IgG Rationale: IgG is the only immunoglobulin that can cross the placenta, providing passive immunity to the fetus and newborn.

Answer 36

B. IgG2 Rationale: IgG2 is particularly effective against polysaccharide antigens of encapsulated bacteria.

Answer 37

D. All of the above Rationale: Hemostasis and thrombosis both involve the formation of a platelet aggregate, the creation of a fibrin mesh, and the eventual dissolution of the clot by plasmin.

Answer 38

B. Platelet phase Rationale: The platelet phase is the initial response to vascular injury, involving the adhesion, activation, and aggregation of platelets to form a temporary plug.

Answer 39

A. Very small blood vessels or capillaries Rationale: Disseminated fibrin deposits, as seen in disseminated intravascular coagulation (DIC), are primarily found in small blood vessels and capillaries.

Answer 40

D. None of the above Rationale: A red thrombus, typically rich in erythrocytes, forms under conditions of low flow and is often found in venous thrombosis rather than arterial.

Answer 41

C. NADPH Rationale: NADPH provides the reducing equivalents for cytochrome P450 enzymes involved in oxidative reactions.

Answer 42

C. Smooth endoplasmic reticulum Rationale: Cytochrome P450 enzymes are primarily found in the smooth endoplasmic reticulum of cells, particularly in the liver.

Answer 43

C. Catalyze reactions involving the introduction of two atoms of oxygen into the substrate and one into water Rationale: Cytochrome P450 enzymes typically catalyze the introduction of one atom of oxygen into the substrate and reduce the other atom to water.

Answer 44

D. Liver Rationale: The liver is the primary organ responsible for the metabolism of xenobiotics, using enzymes such as cytochrome P450s.

Answer 45

D. Metabolic activation Rationale: Metabolic activation refers to the conversion of xenobiotics to their active forms, which can sometimes be more toxic than the parent compound.

Answer 46

C. Hydroxylation Rationale: Phase 1 metabolism often involves hydroxylation, which introduces an OH group to the xenobiotic, increasing its solubility and preparing it for further reactions. Phase I metabolism consists of reduction, oxidation, or hydrolysis reactions.

Answer 47

A. Conjugation Rationale: Phase 2 metabolism involves conjugation, where Phase 1 metabolites are linked with endogenous molecules to increase their solubility and facilitate excretion.

Answer 48

A. The heavy chain type Rationale: The class of an immunoglobulin (IgA, IgG, IgM, etc.) is determined by the type of heavy chain it contains.

Answer 49

C. Not specific for each class of antibody Rationale: Light chains (either kappa or lambda) are not class-specific and can be found in all classes of antibodies.

Answer 50

D. 2 DNA molecules, each of which contains one new and one old DNA strand Rationale: DNA replication results in two DNA molecules, each composed of one original strand and one newly synthesized strand (semi-conservative replication).

Answer 51

D. Located upstream of the gene. Rationale: Promoters in prokaryotes are sequences located upstream (5' direction) of the gene they regulate.

Answer 52

A. Spliceosome Rationale: Spliceosomes are complexes responsible for removing introns (intervening sequences) and splicing exons together in pre-mRNA.

Answer 53

C. The act of making many identical copies of a DNA molecule Rationale: DNA cloning involves making multiple identical copies of a DNA segment.

Answer 54

A. H1 Rationale: Histone H1 is known as the linker histone because it binds to the linker DNA between nucleosomes, helping to compact the chromatin.

Answer 55

A. Ribonucleic acid (RNA) is a polymer of purine and pyrimidine ribonucleotides linked together by 3-5'-phosphodiester bonds analogous to those in DNA Rationale: RNA consists of ribonucleotides linked by 3'-5' phosphodiester bonds, similar to DNA, but with ribose as the sugar.

Answer 56

B. Rho factor Rationale: The Rho factor is a protein involved in terminating transcription in prokaryotes. Rho = Termination Sigma = Initiation

Answer 57

B. Non-template strand Rationale: The coding strand (or non-template strand) is the DNA strand whose base sequence corresponds to the base sequence of the RNA transcript produced (though with thymine replaced by uracil).

Answer 58

A. Adenine to Uracil Rationale: In RNA synthesis, adenine pairs with uracil instead of thymine.

Answer 59

C. Cells clustered in a single enclosed mass Rationale: Benign tumors are typically characterized by cells that remain clustered in a single mass and do not invade surrounding tissues or metastasize.

Answer 60

B. Glycolysis Rationale: Cancer cells often have increased glycolysis rates to meet their high energy demands, even in the presence of oxygen (known as the Warburg effect).

Answer 61

A. Neuron Rationale: Neurons generally do not regenerate once they are lost, unlike other cells such as hepatocytes and enterocytes.

Answer 62

C. Oncogenic viruses Rationale: Oncogenic viruses can introduce new genes into host cells, leading to uncontrolled cell growth and cancer.

Answer 63

C. Increases with increased melanin content of skin Rationale: Increased melanin content actually provides some protection against UV radiation and lowers the risk of skin cancer.

Answer 64

A. Have a fast rate of formation Rationale: White thrombi typically form slowly under high shear stress conditions found in arterial circulation. They are characterized by a firm consistency, are associated with the arterial system of circulation, and have a hard consistency, but they do not have a fast rate of formation.

Answer 65

A. Formation of a loose and Permanent platelet aggregate at the site of injury Rationale: The formation of a loose and temporary platelet aggregate is part of the initial response, not a permanent solution.

Answer 66

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

Answer 67

E. All of the above Rationale: Entropy increases when a molecule is broken into smaller molecules, when a reaction increases the number of gas moles, when a solid changes to a liquid, and when a liquid changes to a gas.

Answer 68

E. Work Rationale: Work is not a state function because it depends on the path taken, whereas Gibbs free energy, enthalpy, entropy, and internal energy are state functions.

Answer 69

C. Tumor suppressor genes Rationale: Tumor suppressor genes encode proteins that regulate cell growth and division, preventing tumor formation. When these genes are mutated, they lose this regulatory ability.

Answer 70

B. Energy needed to maintain basic physiologic functions under standard conditions Rationale: Basal metabolic rate (BMR) is the amount of energy expended while at rest in a neutrally temperate environment, in the post-absorptive state.

Answer 71

D. All of the above Rationale: Wernicke-Korsakoff Syndrome is associated with a defective transketolase enzyme, is seen primarily in alcoholics, and is caused by chronic thiamine deficiency.

Answer 72

A. A specific codon always codes for the same amino acid Rationale: The genetic code is unambiguous because each codon specifies only one amino acid.

Answer 73

A. Partial thromboplastin time (aPTT or PTT) Rationale: aPTT is used to measure the intrinsic pathway of coagulation.

Answer 74

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

Answer 75

A. Endonuclease Rationale: Endonucleases are enzymes that cut RNA at specific internal sites, which is a crucial step in the process of removing introns from primary RNA transcripts. Spliceosomes, which include ribonucleoproteins with endonuclease activity, carry out this process.

Answer 76

A. Coumarin Anticoagulants - Rationale: Coumarin anticoagulants, such as warfarin, inhibit the carboxylation of vitamin K-dependent clotting factors, thereby preventing blood clot formation.