Biology Exam Questions PDF

Biology exam questions 1)​ Which of the following features of the metaphase chromosome is not a morphological feature of the chromosome? Banding pattern Position of the centromere Number of chromosomes Chromosome length 2)​ What compounds does tRNA transport? Peptides amino a...

Biology exam questions 1)​ Which of the following features of the metaphase chromosome is not a morphological feature of the chromosome? Banding pattern Position of the centromere Number of chromosomes Chromosome length 2)​ What compounds does tRNA transport? Peptides amino acids codons Proteins 3)​ What interactions are not involved in the formation of the tertiary structure of RNA?: Creation of an A-type helix Interactions of arm stems with other arm stems Binding of basic proteins or ions that neutralize the negative charge of RNA Formation of non-canonical pairs or triplets 4)​ What characterizes the pseudouridine loop, or T-loop, of tRNA?: It contains the site where the tRNA binds to the ribosome Contains a D loop containing dihydrouridine mobilizes tRNA during the process of protein synthesis Contains an unpaired CCA sequence at the 3' end 5)​ Which type of receptors are designed for neurotransmitters when a rapid response is necessary?: * ionotropic (ion-channel-coupled) receptors receptors for lipophilic metabotropic hormones catalytic receptors G-proteins coupled receptors  6)​ What process causes the elongation of DNA replication to become an irreversible process?: Release of PPi from the nucleotide Hydrolysis of pyrophosphate (PPi) to inorganic phosphate PP Loss of ATP as an energy source Connection of the new thread to the matrix thread 7)​ What is combinatorial control of gene expression?: * This is a process that involves the use of a single transcriptional regulator for normal gene expression This is a process that involves the use of a group of transcriptional regulators working together to express a gene correctly This is a process for which the use of only a gene activator is sufficient for proper gene regulation This is a process that involves only genes arranged in operons 8)​ What is Mitogen-activated Protein Kinase (MAPK)?: * The final serine-threonine kinase following the activation of Ras protein Binding to the GEF protein and formation of a complex that is involved in the exchange of GDP for GTP in the Ras protein The result of dephosphorylation of serine and threonine residues from other kinases The attachment of the adaptor protein to a tyrosine residue 9)​ What element, apart from protein, can be a component of a glycoprotein?: * Lipids Metal ions Oligosaccharides Phosphoric acid molecules 10)​ How do we define carbohydrates that are made up of more than 10 subunits?: * Disaccharides Polysaccharides Oligosaccharides Monosaccharides 11)​ How are HSCs collected via apheresis?: * Using fluorescent antibodies selective for the CD34 surface protein Bone marrow collection from the plate of the hip bone Enzymatic digestion of the collected material Cell expansion on culture medium  12)​ What kind of bonds form between the codon-anticodon bases?: * Covalent bonds Hydrogen bonds Phosphodiester bonds Electrostatic interactions 13)​ In which segment of the lipid bilayer are its hydrophobic components contained?: * Inside the lipid bilayer All answers are incorrect On the inner surface of the lipid bilayer On the outer surface of the lipid bilayer 14)​ What DNA repair process involves the MGMT protein, which removes the oxygen-bound methyl group O6 of guanine?: * Direct repair (DR) Base Cutting Repair (BER) Mispaired nucleotide (MMR) repair Nucleotide excision repair (NER) 15)​ What histone protein does not form part of the nucleosome core?: * H3 H1 H4 H2A 16)​ In which phase of the cell cycle is the concentration of mitotic cyclin (cyclin B) the highest?: * In phase S In phase M In phase G1 In phase G0 17)​ Under what conditions does programmed cell death (apoptosis) occur?: * It occurs only during embryonic development when the activation of a cell-death intracellular program is initiated During gametogenesis when the body is under stress No energy is needed  18)​ How many basic amino acids are found in human proteins?: * 6 20 32 10 19)​ What kind of secondary structure of a protein is stabilized by the hydrogen bond between the NH and CO of the amino acid residue i and i+3?: * Parallel β-sheets β-turns Anti-parallel β-sheets α-Helix 20)​ Interphase is the phase of the cell cycle that the cell is in for the majority of the time. What phases does it include? * G1, S, and G2 phases altogether mitosis only S phase, G2 phase, and mitosis G1 and S phase only 21)​ What step does not occur during nucleotide excision repair?: * Cutting the DNA strand on both sides of the damage by XPG and XPF endonucleases Removal of the damaged nitrogenous base by specific DNA glycosylase Synthesis of a new DNA strand fragment by β polymerase Unraveling of the double strand around the damaged nucleotide by helicases 22)​ What is a chromosome considered when its arms are equal in length?: * Submetacentric Metacentric Acrocentric Telocentric 23)​ In which phase of mitosis do the sister chromosomes separate?: * In prometaphase In prophase In metaphase In anaphase  24)​ What is the smallest living unit on Earth?: * an Organelle the Cell Protein DNA 25)​ What areas do chromosomes occupy in a cell between divisions?: * They occupy distinct areas in the interphase nucleus They have the same nuclear territory as their homologue They are limited to the nucleolus They are completely entangled with other chromosomes 26)​ In which structure of RNA do apical loops (hairpins) exist? * Tertiary structure of RNA Primary RNA structure Quaternary structure of RNA Secondary RNA structure 27)​ Which type of membrane transport is the sodium-potassium pump classified as?: * Primary active transport Facilitated diffusion Simple diffusion Secondary active transport 28)​ The secondary lysosome is a result of the combination of: * a primary lysosome with a macrophage a primary lysosome with a phagosome a primary phagosome with a peroxisome the endoplasmic reticulum with a vesicle 29)​ What happens when an mRNA attaches to a ribosome? * A conformational change to the large subunit to bind to the ER the sedimentation rate of the subunit changes from 50S to 70S the large subunit and small subunit become conjoined to begin translation the large subunit and small subunit separate to begin translation  30)​ What functions do lysosomes perform in the cell?: * Break down of carbohydrates, proteins, fats and nucleic acids Sorting of transport vesicles Transport of materials to the Golgi apparatus Storage of excess macromolecules 31)​ In interphase, heterochromatin: * is genetically inactive all answers are correct stains dark under a microscope is in a condensed state 32)​ For which ligands are "orphan" receptors intended?: * unknown ligands active vitamin D3 (1,25-dihydroxyvitamin D3) active vitamin A (retinol) lipophilic hormones 33)​ Where does the electron transport chain occur? * the nucleus the inner membrane of the mitochondria the cytoplasm the mitochondria 34)​ What type of membrane transport is associated with the formation of a phagosome?: * secondary active transport receptor-mediated endocytosis pinocytosis phagocytosis 35)​ How many times does interphase DNA shorten into metaphase chromosomes?: * 10,000x 100,000x 100x 1,000x  36)​ What compound is necessary for aerobic respiration in which the cell breaks down macromolecules stepwise for energy in the form of ATP? * Nitrogen Guanine Sulfur Oxygen 37)​ In which DNA condensation process is histone H1 directly involved?: * Chromatin in the "string of beads" formation Interphase chromatin formation formation of the 30nm fiber Creating DNA loops 38)​ What type of ligands are transported through the circulatory system?: * only neurotransmitters, like adrenalin (epinephrine) neurotransmitters and hormones, like adrenalin (epinephrine) only hormones, like adrenalin (epinephrine) none of the answers include ligands transported through the circulatory system 39)​ Which of the following phospholipid movements may be catalyzed by enzymes in the cell membrane?: * Transverse “flip-flop” movement Flexion Lateral diffusion Rotational motion 40)​ What is a codon?: * Three nucleotides of DNA Three nucleotides of RNA Three amino acids Three DNA nucleotides or 3 RNA nucleotides 41)​ How is the START codon recognized in eukaryotes during translation initiation?: By binding tRNA By recognizing the ATC codon as the origin of translation Through the binding of the small unit of ribosome, mRNA and initiator tRNA By scanning along the mRNA from the 5' end  42)​ Which of the following is a component of a glycolipid?: * insulin sphingosine guanine none are components of a glycolipid 43)​ Which of the following DNA strands can form a DNA duplex by pairing with itself at each position? A)​ 5’-AAGCCGTT-3’ B)​ 5’-AAGCCGAA-3’ C)​ 5’-AAGCGCAA-3’ D)​ 5’-AAGCGCTT-3’ What is the role of EDTA in blood collection and laboratory experiments? A) Stimulates blood clotting​ B) Prevents blood clotting by binding calcium ions​ C) Enhances the formation of blood clots for analysis​ D) Acts as an anticoagulant by increasing platelet aggregation What is a key safety consideration when using Midori Green in molecular biology experiments? A) It is non-toxic and safe to handle without precautions​ B) It is toxic and should be handled with care, using gloves and eye protection​ C) It can cause contamination in PCR reactions​ D) It is only toxic to bacteria, not human cells Answer: B) It is toxic and should be handled with care, using gloves and eye protection What is the primary use of Midori Green in molecular biology? A) Stains the DNA for visualization in gel electrophoresis​ B) Enhances protein synthesis during cell culture​ C) Makes agarose gels solidify​ D) Inhibits DNA replication Answer: A) Stains the DNA for visualization in gel electrophoresis 1. What is the structure of a DNA helix? A) A single strand of nucleotides​ B) A double-stranded, right-handed helix​ C) A triple-stranded helix​ D) A coil of amino acids Answer: B) A double-stranded, right-handed helix​ Explanation: The DNA helix consists of two complementary strands twisted around each other in a right-handed spiral, forming the well-known double helix structure. 2. In PCR, what is the purpose of the denaturation step? A) To cool the DNA template for primer binding​ B) To separate the DNA strands by breaking hydrogen bonds​ C) To add nucleotides to the growing DNA strand​ D) To activate the DNA polymerase enzyme Answer: B) To separate the DNA strands by breaking hydrogen bonds​ Explanation: The denaturation step in PCR involves heating the DNA to separate the strands, making them available for primer binding in the next step. 3. What is the function of mitochondria in human cells? A) To synthesize proteins​ B) To store genetic information​ C) To generate ATP through cellular respiration​ D) To regulate cell division Answer: C) To generate ATP through cellular respiration​ Explanation: Mitochondria are the powerhouses of the cell, responsible for generating ATP via cellular respiration. 4. What is the typical annealing temperature used in PCR? A) 50-65°C​ B) 75-85°C​ C) 90-100°C​ D) 20-30°C Answer: A) 50-65°C​ Explanation: The annealing temperature in PCR is typically between 50°C and 65°C, where the primers bind to the template DNA. 5. What is the main feature of the structure of biological membranes? A) A rigid, protein-based structure​ B) A fluid bilayer of phospholipids with embedded proteins​ C) A single lipid layer​ D) A cellulose wall Answer: B) A fluid bilayer of phospholipids with embedded proteins​ Explanation: Biological membranes are primarily composed of a phospholipid bilayer with proteins that are either embedded in or associated with the membrane, giving it flexibility. 6. What is deoxyribonucleic acid (DNA) made of? A) Amino acids​ B) Nucleotides containing a phosphate group, sugar, and nitrogenous base​ C) Fatty acids​ D) Carbohydrates Answer: B) Nucleotides containing a phosphate group, sugar, and nitrogenous base​ Explanation: DNA is composed of nucleotides, each consisting of a phosphate group, a deoxyribose sugar, and a nitrogenous base (adenine, thymine, cytosine, or guanine). 7. Agarose is made of which of the following? A) Polysaccharide from seaweed​ B) Protein from bacteria​ C) Synthetic polymers​ D) Lipid molecules Answer: A) Polysaccharide from seaweed​ Explanation: Agarose is a polysaccharide derived from seaweed, commonly used in gel electrophoresis. 8. What are lipid rafts? A) Membrane structures containing only cholesterol​ B) Lipid-rich regions in cell membranes involved in signaling and trafficking​ C) Structures found only in plant cells​ D) Regions of the mitochondria membrane Answer: B) Lipid-rich regions in cell membranes involved in signaling and trafficking​ Explanation: Lipid rafts are microdomains within the cell membrane that are rich in cholesterol and sphingolipids, playing a role in cellular signaling and protein trafficking. 9. Which of the following are types of chromosomes? A) Prokaryotic and eukaryotic chromosomes​ B) Metacentric, submetacentric, acrocentric, and telocentric chromosomes​ C) DNA and RNA chromosomes​ D) Mitochondrial and chloroplast chromosomes Answer: B) Metacentric, submetacentric, acrocentric, and telocentric chromosomes​ Explanation: Chromosomes are classified based on the position of their centromere into metacentric, submetacentric, acrocentric, and telocentric types. 10. What is the difference between autosomes and allosomes? A) Autosomes are sex chromosomes, and allosomes are body chromosomes​ B) Autosomes are non-sex chromosomes, and allosomes are sex chromosomes​ C) Autosomes are found only in plants, and allosomes are found in animals​ D) There is no difference between autosomes and allosomes Answer: B) Autosomes are non-sex chromosomes, and allosomes are sex chromosomes​ Explanation: Autosomes are the non-sex chromosomes (chromosomes 1-22 in humans), while allosomes are the sex chromosomes (X and Y in humans). 11. What is the function of the cristae in mitochondria? A) To store genetic material​ B) To synthesize proteins​ C) To increase surface area for ATP production​ D) To maintain cell shape Answer: C) To increase surface area for ATP production​ Explanation: Cristae are the folds in the inner mitochondrial membrane that increase the surface area for the enzymes involved in ATP synthesis. 12. What is the function of centrosomes in the cell? A) To synthesize proteins​ B) To organize microtubules and form the mitotic spindle​ C) To store genetic material​ D) To regulate protein synthesis Answer: B) To organize microtubules and form the mitotic spindle​ Explanation: Centrosomes are involved in organizing microtubules and forming the mitotic spindle, which is essential during cell division. 13. What is the function of the kinetochore? A) To produce energy in the form of ATP​ B) To regulate cell metabolism​ C) To attach chromosomes to the spindle during cell division​ D) To store cellular nutrients Answer: C) To attach chromosomes to the spindle during cell division​ Explanation: The kinetochore is a protein structure on chromosomes where spindle fibers attach during cell division, helping to separate the chromosomes. 14. What percentage of a cell is water? A) 10-20%​ B) 30-40%​ C) 50-70%​ D) 80-90% Answer: C) 50-70%​ Explanation: The majority of a cell’s content is water, which accounts for 50-70% of the total cell mass. 15. What is the purpose of a positive control in PCR? A) To ensure that the PCR process works by using a known DNA sample​ B) To degrade unwanted DNA in the sample​ C) To prevent contamination during PCR​ D) To amplify the target DNA Answer: A) To ensure that the PCR process works by using a known DNA sample​ Explanation: A positive control is a known DNA sample used in PCR to ensure that the reaction is working properly. 16. What are stem cells? A) Cells that only divide in the presence of growth factors​ B) Cells that have the ability to divide and differentiate into various cell types​ C) Cells that do not divide but provide structural support​ D) Cells that perform specific functions without division Answer: B) Cells that have the ability to divide and differentiate into various cell types​ Explanation: Stem cells have the unique ability to divide and differentiate into various types of cells, making them essential for growth and repair. 17. What phase of the cell cycle is interphase? A) The phase when the cell is actively dividing​ B) The phase when the cell is preparing for division​ C) The phase when the cell is not growing​ D) The phase when the cell is completing mitosis Answer: B) The phase when the cell is preparing for division​ Explanation: Interphase is the phase of the cell cycle where the cell grows and prepares for division, consisting of G1, S,and G2 phases. 18. What is cell signaling in the context of junxacrina? A) A process where cells communicate through physical contact​ B) A process involving the regulation of protein synthesis by junxacrina​ C) A mechanism by which cells respond to external signals to regulate growth​ D) A signal that inhibits cell division Answer: C) A mechanism by which cells respond to external signals to regulate growth​ Explanation: Cell signaling involves the transmission of signals from the outside of the cell to its interior, regulating various cellular functions like growth and differentiation. The course of the cell cycle is primarily determined by? A) Protein kinases dependent on membrane proteins and lipids​ B) Cyclins dependent on spindle tubulin proteins​ C) Cyclin-dependent protein kinases (cdk), which become enzymatically active due to the attachment of cyclins​ D) None of the above What are mitogens? A) Proteins that regulate mitosis​ B) Genes responsible for the normal course of mitosis and cell division​ C) Extracellular signal molecules that stimulate cell proliferation​ D) Intercellular signals that inhibit cell division How many copies of DNA are produced after 6 PCR cycles? A) 16 copies​ B) 32 copies​ C) 64 copies​ D) 18 copies Which of the following best describes primary active transport? A) Transport of molecules from low to high concentration using energy from ATP​ B) Movement of molecules down their concentration gradient without energy input​ C) Transport of molecules using a carrier protein but without energy input​ D) Movement of molecules against their gradient using energy from light Which type of stem cell has the ability to form all cell types in the body, including the extra-embryonic tissues (such as the placenta)? A) Totipotent stem cells​ B) Pluripotent stem cells​ C) Multipotent stem cells​ D) Unipotent stem cells What is the primary function of protein kinase C (PKC) in cellular signaling? A) To destroy phospholipids and inhibit signal transduction​ B) To add phosphate groups to proteins, regulating cellular processes​ C) To synthesize phospholipids for membrane formation​ D) To degrade RNA and halt protein synthesis What is the structure of DNA? A) A single-stranded molecule composed of nucleotides​ B) A double-stranded molecule composed of amino acids​ C) A polymer of nucleotides with two strands, each containing a nitrogenous base, a five-carbon sugar, and a phosphate group​ D) A double helix of protein subunits What are the key components of the core structure of an amino acid? A) A central carbon atom bonded to a phosphate group, amino group, and carboxyl group​ B) A central carbon atom bonded to a hydroxyl group, amino group, and carboxyl group​ C) A central carbon atom bonded to an amino group, carboxyl group, and hydrogen atom​ D) A central carbon atom bonded to a carboxyl group, peptide bond, and side chain What is the basic structure of the backbone of an amino acid, when ignoring the hydrogen atoms? A) C-C-N​ B) N-C-C​ C) C-N-H​ D) N-C-N How many amino acids are typically found in natural proteins? A) 10​ B) 20​ C) 30​ D) 64 What is the approximate concentration of RNA in a typical cell? A) 1-5%​ B) 10-20%​ C) 30-40%​ D) 50-60% What is the most dominant type of RNA in a cell? A) mRNA (messenger RNA)​ B) tRNA (transfer RNA)​ C) rRNA (ribosomal RNA)​ D) miRNA (microRNA) Where are potassium (K⁺) and sodium (Na⁺) ions most concentrated in a typical cell? A) Potassium: extracellular, Sodium: intracellular​ B) Potassium: intracellular, Sodium: extracellular​ C) Potassium: both extracellular and intracellular, Sodium: intracellular​ D) Potassium: extracellular, Sodium: both intracellular and extracellular What role does cholesterol play in the cell membrane? A) Holds phospholipids together, preventing them from moving​ B) Serves as a rigid barrier to prevent the passage of ions​ C) Modulates membrane fluidity, maintaining flexibility and stability​ D) Acts as a receptor for signaling molecules What is the role of a positive control in a PCR experiment? A) To verify that the analysis process is functioning properly by using a known DNA sample​ B) To act as a template for amplification of unknown samples​ C) To decrease the efficiency of DNA amplification​ D) To replace the need for a DNA sample from the experimental subjec What is the main purpose of cellular respiration? A) To break down glucose and produce ATP​ B) To synthesize glucose from carbon dioxide and water​ C) To store energy in the form of starch​ D) To break down lipids and produce glucose Which of the following correctly represents the sequence of events in cellular respiration? A) Hydrolysis → Krebs cycle → Electron transport chain​ B) Glycolysis → Krebs cycle → Electron transport chain​ C) Glycolysis → Hydrolysis → Electron transport chain​ D) Krebs cycle → Glycolysis → Electron transport chain What does a long carbon chain in a carbohydrate do? A) Makes it more soluble in water​ B) Makes it less soluble in water​ C) Increases its reactivity​ D) Makes it more polar What is a carbohydrate composed of more than 10 molecules called? A) Monosaccharide​ B) Disaccharide​ C) Oligosaccharide​ D) Polysaccharide What is a carbohydrate composed of up to 10 molecules called? -​ A) Monosaccharide​ B) Disaccharide​ C) Oligosaccharide​ D) Polysaccharide What do ribosomes that freely float in the cytoplasm produce? A) Proteins that are secreted outside the cell​ B) Proteins that function in the cytosol​ C) Lipids for membrane production​ D) RNA for protein synthesis What do amyloplasts primarily contain? A) Proteins in the form of enzymes​ B) Carbohydrates in the form of starch grains​ C) Lipids in the form of fat droplets​ D) Nucleic acids in the form of DNA What is the first amino acid in all proteins produced by the mitochondria, chloroplasts, and bacteria? A) Methionine​ B) N-formylmethionine​ C) Alanine​ D) Serine What happens if the annealing temperature is set too high in a PCR reaction? A) The primers will bind to the template more efficiently.​ B) The DNA polymerase will become inactive.​ C) The primers will not bind to the template.​ D) The template DNA will denature. Which of the following best describes the main components of the cytoplasm? A) DNA, RNA, and ribosomes​ B) Water, salts, and organic molecules​ C) Lipids, proteins, and nucleotides​ D) Cell wall components and carbohydrates A protein containing disulfide bridges primarily exhibits which level of protein structure? A) Primary structure​ B) Secondary structure​ C) Tertiary structure​ D) Quaternary structure Which of the following nitrogenous bases has a double-ring (purine) structure? A) Thymine​ B) Cytosine​ C) Adenine​ D) Uracil Which of the following nitrogenous bases has a single-ring (pyrimidine) structure? A) Adenine​ B) Guanine​ C) Cytosine​ D) None of the above Which of the following best explains how degeneracy in the genetic code can occur? A) Different codons for the same amino acid usually vary at the first nucleotide position.​ B) Codons encoding the same amino acid mostly differ at the third nucleotide position (wobble position).​ C) Every amino acid is encoded by only one unique codon.​ D) The presence of introns in mRNA allows codon flexibility. What does "degeneracy of the genetic code" mean? A) A single codon can specify multiple amino acids.​ B) An amino acid can be encoded by more than one codon.​ C) The genetic code varies significantly among different species.​ D) All three nucleotides in a codon must always be unique for each amino acid. Which amino acid contains a thiol (-SH) group in its side chain? A) Serine​ B) Cysteine​ C) Alanine​ D) Lysine Which amino acid contains a hydroxyl (-OH) group in its side chain? A) Cysteine​ B) Threonine​ C) Phenylalanine​ D) Valine Which of the following amino acids has a non-polar, aliphatic side chain? A) Serine​ B) Leucine​ C) Tyrosine​ D) Glutamine Which of the following non-polar amino acids contains a cyclic side chain? A) Methionine​ B) Proline​ C) Asparagine​ D) Threonine Which of the following statements best describes the sub-classification of α‑amino acids (other than glycine) based on the spatial orientation of the amino group at the chiral center? A) They are classified as D‑ or L‑amino acids depending solely on the size of their side chain.​ B) They are classified as D‑ or L‑amino acids depending on the orientation of the amino group in the Fischer projection relative to the asymmetric carbon.​ C) They are classified as R‑ or S‑amino acids exclusively, with no relation to the amino group’s position.​ D) They are not classified because all α‑amino acids (except glycine) have the same spatial arrangement. In the Fischer projection of an α‑amino acid (excluding glycine), the molecule is classified as an L‑amino acid if the amino group is located on which side of the chiral carbon? A) On the right side​ B) On the left side​ C) Above the chiral carbon​ D) Below the chiral carbon Which free amino acids function primarily as excitatory neurotransmitters in the central nervous system?​ A) Glycine and GABA​ B) Glutamic acid and aspartic acid​ C) Tyrosine and phenylalanine​ D) Serine and threonine What role do serine and glycine play in lipid metabolism?​ A) They directly form cholesterol molecules.​ B) They serve as precursors in the synthesis of phospholipids.​ C) They act as hormones regulating lipid storage.​ D) They are involved in the degradation of lipids. Which free amino acids are notably involved in the synthesis of lipids and their derivatives?​ A) Glutamic acid and aspartic acid​ B) Tyrosine and tryptophan​ C) Serine and glycine​ D) Alanine and valine ​ What is a key characteristic of glutamic acid in the context of neuronal signaling?​ A) It functions as an inhibitory neurotransmitter.​ B) It is a primary excitatory neurotransmitter that promotes neuronal firing.​ C) It is only involved in peripheral nervous system signaling.​ D) It is converted directly into energy in neurons. Which free amino acid is a precursor for the synthesis of key hormones such as thyroid hormones and catecholamines?​ A) Glycine​ B) Tyrosine​ C) Glutamic acid​ D) Aspartic acid How does tyrosine contribute to the transmission of hormonal signals in the body?​ A) It acts directly as a hormone receptor on cell membranes.​ B) It is converted into precursors for hormones, such as catecholamines and thyroid hormones.​ C) It degrades circulating hormones to terminate their signals.​ D) It is exclusively used for energy production in endocrine tissues. Ornithine and citrulline are non-protein amino acids that are important because they serve as intermediate metabolites in which metabolic cycle? A) Citric acid cycle​ B) Glycolytic pathway​ C) Urea cycle​ D) Pentose phosphate pathway Answer: C) Urea cycle Which non-protein amino acid serves as the main inhibitory neurotransmitter in the nervous system? A) Ornithine​ B) Citrulline​ C) γ-Aminobutyric acid (GABA)​ D) β-Alanine What is the by-product of the condensation reaction that forms a peptide bond between amino acids? A) Ammonia​ B) Carbon dioxide​ C) Water​ D) Hydrogen peroxide How are the oligosaccharide chains in glycoproteins attached to the protein portion? A) By non-covalent interactions such as hydrogen bonds and van der Waals forces.​ B) Covalently, through glycosidic bonds that link the oligosaccharides to specific amino acid residues.​ C) Through ionic bonds that allow reversible attachment.​ D) By forming disulfide bonds with cysteine residues. Which amino acid residues are most commonly phosphorylated in proteins to form phosphoproteins? A) Lysine and Arginine​ B) Aspartic acid and Glutamic acid​ C) Serine and Threonine​ D) Cysteine and Methionine Why are vitamins considered essential for the functions of the body? A) They act as a direct source of cellular energy.​ B) They serve as organic coenzymes or prosthetic groups that facilitate key biochemical reactions.​ C) They form the primary structure of DNA and RNA.​ D) They are the main constituents of cell membranes. Which checkpoint is responsible for ensuring that all chromosomes are properly attached to spindle fibers before they are separated during mitosis? A) G₁ checkpoint​ B) G₂ checkpoint​ C) M checkpoint​ D) S checkpoint Which type of tRNA is responsible for initiating translation in Eukaryotes? A) Met-tRNA​ B) fMet-tRNAᶠMet​ C) Met-tRNAᵢMet​ D) Fmet- tRNA Why does DNA polymerase require a primer to begin synthesis? A) It can only add nucleotides to an existing strand​ B) It needs ATP to function​ C) It synthesizes RNA instead of DNA​ D) It can start synthesis independently