2023 USMDO question bank w/ solutions and explanations

What type of glycosidic linkage creates branches in the polysaccharides of glycogen?

A. 1, 4 alpha

B. 1, 6 alpha

C. a, 4 beta

D. 1, 6 beta

B) 1,6 alpha

Explanation: glycogen is the primary storage form of glucose in animals, similar to starch in plants. The glycogen molecule is a highly branched polymer of glucose. The linear chains of glycogen are lined by a (1 -> 4) glycosidic linkages. However, the branches in glycogen are created by a (1->6) glycosidic linkages, which occur approximately every 8-12 glucose residues

Where inside the cell are the ribosomal proteins are rRNA assembled into ribosomal subunits?

A. rough endoplasmic reticulum

B. smooth endoplasmic reticulum

C. nucleolus

D. Golgi apparatus

C) Nucleolus

Explanation: the nucleolus is a specialized region within the nucleus where ribosomal RNA (rRNA) is transcribed, processed, and combined with ribosomal proteins to form ribosomal subunits. Once assembled, these ribosomal subunits are then transported out of the nucleus to the cytoplasm, where they combine to form functional ribosomes that are responsible for protein synthesis

Which of the following is NOT one of the main functions of proteins in the human body?

A. catalysis of chemical reactions

B. transport of substances

C. energy storage

D. Movement

C) energy storage

Explanation: while proteins are involved in many processes in the body, they are not primarily used for energy storage. Carbohydrates (in the form of glycogen) and lipids (in the form of fats) are the body's primary energy storage molecules. While proteins can be broken down and converted into glucose (glycogenesis) when needed, this is not their primary role

Which intercellular junction separates one part of the cell membrane from another and keeps the proteins with different functions in different regions of the cell membrane, such as the apical surface and basolateral surfaces of an epithelial cell?

A. tight junction

B. Desmosome

C. hemidesmosome

D. gap junction

A) tight junction

Explanation: tight junctions, aka zonula occludes, are a type of intercellular junction that seals adjacent epithelial cells together, forming a nearly impermeable barrier. They prevent the free passage of molecules and ions through the space between cells. Importantly, right junctions also maintain the polarity of cells by preventing the lateral diffusion of integral membrane proteins between the apical and basolateral surfaces, ensuring that these surfaces retain distinct identities and functions

Which enzyme in glycolysis serves as the point of negative feedback in the metabolic pathway, stimulated by AMP but inhibited by citrate and ATP?

A. hexokinase

B. phosphoglucose isomerase

C. G3P dehydrogenase

D. phosphofructokinase

D) phosphofructokinase

Explanation: phosphofructokinase-1 (PFK-1) is a key regulatory enzyme in the glycolytic pathway. It catalyzes the phosphorylation of fructose-6-phosphate to fructose-1, 6-biphospate. PFK-1 is allosterically activated by AMP, a sign of low energy levels in the cell, thus promoting glycolysis to produce more ATP. On the other hand, high levels of ATP (indicative of high energy levels) inhibit PFK-1, as does citrate (a key intermediate int he citric acid cycle), ensuring that glycolysis is slowed down when the energy needs of the cells are already being met

Which of the following is not a product of glycolysis?

A. CO2

B. pyruvate

C. ATP

D. NADH

A) CO2

Explanation: glycolysis is the metabolic pathway that breaks down one molecule of glucose (6 carbon sugar) into 2 molecules of pyruvate (a 3 carbon compound). During this process, ATP is produced (from ADP), and NAD+ is reduced to NADH. Importantly, glycolysis does not produce CO2. The generation of CO2 primarily happens during the citric acid cycle (AKA Krebs cycle or TCA cycle) which occurs after glycolysis, especially when pyruvate is further metabolized in the mitochondria

Which of the following enemy pairs illustrates that glycolysis and gluconeogenesis are not identical in reverse, the first of the pair being used in glycolysis and the second being used in glyconeogensis?

A. hexokinase; glucose dephosphorylase

B. enolase; PEP dehydrogenase

C. phosphofructokinase; fructose 1,6 bisphosphatase

D. pyruvate kinase; pyruvate phosphatase

C) phosphofructokinase; fructose 1,6 bisphosphatase

Explanation: glycolysis and gluconeogenesis are metabolic pathways that process glucose breakdown and synthesis, respectively. Although they largely utilize the same molecules, they aren't simply reverse processes. A notable distinction is the conversion between fructose-6-phosphate and fructose-1,6-biphosphate. In glycolysis, phosphofructokinase (PFK) facilitates the transformation of fructose-6-phosphate into fructose-1,6-bisphosphate. Conversely, in gluconeogeneiss, fructose 1,6 bisphosphatase (FBPase) drives the reverse reaction, turning fructose-1,6-bisphosphate back into fructose-6-phosphate. This enzymatic difference is vital, allowing for independent regulation of the 2 pathways, which is essential for consistent blood glucose levels. This differentiation exemplifies that glycolysis and gluconeogenesis aren't merely inverse pathways

In which of the following cellular organelles does beta-oxidation of fatty acids take place, in addition to mitochondria?

A. smooth e.r

B. peroxisome

C. rough e.r

D. Lysosome

B) peroxisome

Explanation: Beta oxidation is a process by which fatty acids are broken down to produce energy. While mitochondria are the primary sites for beta oxidation, peroxisomes also participate in the initial steps of this metabolic pathway, especially for very long-chain fatty acids. After the initial steps in the peroxisomes, these fatty acids are then shuttled to the mitochondria to complete the oxidation process

In the terminology of genetics, which of the following terms is defined as a single gene or allele having multiple phenotypic effects?

A. Pleiotropy

B. epistasis

C. polygenic inheritance

D. norm of reaction

A) pleiotropy

Explanation: pleiotropy refers to the phenomenon where one gene influences multiple, seemingly unrelated phenotypic traits. An example of this is the Marfan syndrome in humans, which is caused by mutations in a single gene but can affect the skeletal system, cardiovascular system, eyes, and skin

Which of the following may explain why there might be a greater number of different proteins produced in a human than the number of different genes in the human genome?

A. epigenetic inheritance

B. alternative RNA splicing

C. RNA interference

D. transposable element

B) alternative RNA splicing

Explanation: during the process of splicing, introns (non-coding regions) are removed from the pre-mRNA, and exons (coding regions) are joined together. However, in alternative splicing, different combinations of exons can be joined together, leading to different mature mRNA molecules being produced from a single gene. This means that one gene can produce multiple distinct proteins, depending on which exons are included in the final mRNA. For example, the human DSCAM gene can potentially produce thousands of different protein isoforms because of alternative splicing

Which RNA is found in RISC and plays a role in RNA interference?

A. hnRNA

B. snRNA

C. siRNA

D. piRNA

C) siRNA

Explanation: RNA interference (RNAi) is a biological process in which RNA molecules inhibit gene expression, typically by causing the destruction of specific mRNA molecules. In this RNAi pathway, siRNA (short interfering RNA) is incorporated into the RNA-induced silencing complex (RISC). Once incorporated, the RISC uses the siRNA as a template to recognize complementary mRNA molecules, which are then cleaved and subsequently degraded, leading to gene slicing

What is the chemical identity of the endotoxin in the other membrane of gram-negative bacteria?

A. lipopolysaccharude

B. phospholipase

C. glycosyltransferase

D. Ribosyltransferase

A) lipopolysaccharides

Explanation: endotoxin refers to the lipopolysaccharide (LPS) component of the outer membrane of Gram-negative bacteria. LPS plays a crucial role in the structural integrity of the bacteria and triggers strong immune responses in animals when recognized by the hosts immune system. Its presence in the bloodstream can lead to severe inflammatory responses and can be life threatening in high amounts, a condition known as septic shock

Which type of bacterial genetic recombination involves bacteriophages, which transfer bacteria DNA from one bacteria to another?

A. transformation

B. conjugation

C. transduction

D. transversion

C) transduction

Explanation: transduction is the process by which bacterial DNA is transferred from one bacterium to another by a bacteriophage (a virus that infects bacteria). In this process, a phage infects a bacterium and, during its life cycle, mistakenly packages a piece of the bacterial DNA into its viral capsid (protein coat) instead of its own viral DNA. When this phage subsequently infects another bacterium, it introduces the foreign DNA into the new host. The introduced DNA can then recombine with the recipient bacterium's chromosome, resulting in genetic recombination

Which enzyme produced in peroxisomes detoxifies hydrogen peroxide by degrading it to oxygen and water?

A. caspase

B. Cyclase

C. carboxylase

D. catalase

D) Catalase

Explanation: catalase is an enzyme found in peroxisomes that play a key role in the detoxifying hydrogen peroxide (H2O2) and oxygen (O2). This is crucial because hydrogen peroxide can be harmful to cells if allowed to accumulate.

Which of the following motor proteins moves from the minus end to the plus end of a microtubule?

A. myosin

B. kinesin

C. dynein

D. Prestin

B) kinesin

Explanation: Kinesis in a motor protein that primarily moves along microtubules from the minus end to the plus end. This direction is typically toward the cell's periphery. Kinesis moves by "walking" along a microtubule in a hand-over-hand fashion using energy derived from ATP hydrolysis. This movement is crucial for a variety of cellular processes, including the transport of vesicles, organelles, and other cellular materials

In what type of genetic inheritance is the same allele expressed only when it is inherited from one parent, either the father or the mother, and not from the other parent?

A. maternal inheritance

B. epigenetic

C. polygenic inheritance

D. sex linked inheritance

B) epigenetic

Explanation: epigenetic inheritance refers to changes in gene function that do not involve changes to the underlying DNA sequence, but instead involve modifications on the DNA or associated proteins. These modification can influence gene expression. Imprinting for of epigenetic inheritance where genes are marked, or "imprinted", in a parent-of-origin specific manner. This means that only the allele from one parent (either the mother or the father) is expressed, while the allele from the other parent is silenced

Which of the following is NOT one of the functions of the smooth endoplasmic reticulum?

A. calcium storage

B. detoxification

C. digestion of fatty acids

D. production of steroids

C) digestion of fatty acids

Explanations: the digestion (or breakdown) of fatty acids primarily takes place in the mitochondria through the process of beta-oxidation. Thus, the statement about the digestion of fatty acids is not a function of the smooth ER

Which of the following is the correct combination of changes to both Vmaz and Km during the non-competitive inhibition of an enzyme?

A. increased Vmax, same Km

B. decreased Vmax, decreased Km

C. same Vmax, increased Km

D. decreased Vmaz, same Km

D) same Vmax, increased Km

Explanation: in non competitive inhibition, the inhibitor binds to the enzyme at a site other than the active site. This means the inhibitor can bind to the enzyme whether or not the substrate is already bound. Binding of the inhibitor alters the conformation of the enzyme such that its catalytic activity is reduced or abolished, leading to a decreased Vmax. However, because the inhibitor does not compete with the substrate for binding at the active site, the affinity of the enzyme for the substrate (Km) remained unchanged

In what type of inhibition does the inhibitor bind to another location on the enzyme other than the active site to prevent the enzyme from binding to the substrate?

A. competitive

B. noncompetitive

C. uncompetitive

D. cooperative

B) noncompetitive

Explanation: in noncompetitive inhibition, the inhibitor binds to a location on the enzyme other than the active site (often referred to as an allosteric site). This binding can induce a conformational change in the enzyme that affects its activity. Because the inhibitor doesn't compete with the substrate for the active site, adding more substrate doesn't overcome the inhibition, which differentiates it from competitive inhibition

Which of the following is not an intermediate of the citric acid cycle?

A. acetate

B. succinate

C. fumarate

D. Oxaloacetate

A) acetate

Explanation: the citric acid cycle, aka Krebs cycle or tricarboxylix acid (TCA) cycle, is a series of enzyme catalyzed chemical reactions that generate energy through the oxidation of acetyl-CoA. The intermediates of the citric acid cycle include citrate, is-citrate, a-ketoglutarate, succinyl-Co

Which of the following products of the citric acid cycle results in the production of the greatest number of ATP's compared to the others?

A. GTP

B. NADH

C. FADH2

D. CO2

B) NADH

Explanation: each NADH moelcyule, when oxidized in the electron transport chain, can produce about 2.5 ATP molcules via oxidative phosphorylation. And combined, its the highest amount

Which second messenger opens calcium channels on smooth endoplasmic reticulum?

A. Ca2+

B. cAMP

C. DAG

D. IP3

D) IP3

Explanation: inositol triphoshate (IP3) is a second messenger that is produced when phosphlipase C (PLC) cleaves phosphatidylinositol 4,5-biphosphate (PIP2) into 2 products: diacylglycerol (DAG) and IP3. Once produced, IP3 binds to its receptor, which is an IP3-gated calcium channel lcoated on the membrane of the smooth endoplasmic reticulum (ER) or sarcoplasmic reticulum (SR). This binding causes the channel to open and release Ca2+ ions from the ER/SR into the cytoplasm, raising the intracellular concentration of calcium

Which checkpoint of the cell cycle allows the repair of DNA damage before DNA duplication?

A. M

B. G1

C. G2

D. S

C) G2

Explanation: the cell cycle consists of multiple phases, including the G1, S, G2, and M phases. The G2 checkpoint, which occurs just before a cell enters mitosis (M phase), ensures that all of the DNA has been accurately replicated in the S phase and checks for DNA damage. If there is unreplicated or damaged DNA, the cell cycle can be halted at the G2 checkpoint to allow for repair before the cell proceeds to mitosis. This ensures that the daughter cells will receive the correct and undamaged genetic information

Which of the following proteins does cyclin bind to in order to form MPF, the maturation-promoting factor, which stimulates the cell to enter mitosis?

A. PKA

B. PKC

C. CDK

D. RTK

C) CDK

Explanation: cyclin binds to cyclin-dependent kinase (CDK) to form the maturation-promoting factor (MPF). MPF is crucial for stimulating the cell to enter mitosis. During the cell cycle, cyclin concentrations rise and bind to CDK's, activating them. This active cyclin-CDK complex (i.e.,MPF) then promotes various processes necessary for mitosis

Which of the following events occurs in both mitosis and meiosis?

A. synapsis

B. formation of tetrad

C. separation of sister chromatids

D. Crossing over

C) separation of sister chromatids

Explanation: Of the options provided, only the separation of sister chromatids occur in both mitosis and meiosis. Specifically, during anaphase of mitosis, sister chromatids of each chromosome separate and move to opposite poles of the cell, ensuring each daughter cell receives an identical set of chromosomes. In meiosis, this separation happens during anaphase ll, after the initial separation of homologous chromosomes in meiosis 1. The other events-synapsis, formation of tetrad, and crossing over-are exclusive to meiosis and facilitate genetic diversity in sexual reproduction

On a pedigree chart, what type of inheritance is most probable when every generation contains at least one individual with the trait in question, and a father can pass on the trait to either sons or daughters?

A. sex-linked dominant

B. sex-linked recessive

C. autosomal dominant

D. autosomal recessive

C) autosomal dominant

Explanation: in autosomal dominant inheritance, an individual with a dominant allele for a particular trait will express that trait. If a trait is autosomal dominant, only one copy of the dominant allele is needed for the trait to be expressed. Therefore, if a person has the train (and is heterozygous), they can pass the dominant allele on to their offspring, and that offspring will also express the trait. Because the trait appears in every generation and can be passed from fathers to sons or daughters, autosomal dominant inheritance is the most likely mode.

During DNA replication, which enzyme releases the strain from the overwinding of DNA upstream of the replication fork?

A. ligase

B. helicase

C. topoisomerase

D. Primase

C) topoisomerase

Explanation: During DNA replication, as the replication fork progresses, the DNA ahead of the fork becomes overwound or supercoiled due to the unwinding of the double helix by helicase. Topoisomerase is the enzyme responsible for relieving this supercoiling or overwinding tension. It does so by introducing temporary breaks in the DNA molecule, allowing it to rotate and thereby release the supercoiling. After relieving the strain, topoisomerase rejoins the broken DNA strands.

Which of the following lipids is amphipathetic?

A. triacylglycerol

B. cholesterol

C. phospholipid

D. Wax

C) phospholipid

Explanation: Amphipathic molecules have both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts. Phospholipids are amphipathic because they have a hydrophilic "head" made up of a phosphate group and a hydrophobic "tail" made of fatty acid chains. In aqueous environments, this property allows phospholipids to spontaneously form bilayers, with the hydrophilic heads facing outward towards the water and the hydrophobic tails tucked away from the water, forming the core of the bilayer. This bilayer structure is the fundamental architecture of cell membranes.

In which level of protein structure do the backbone constituents form hydrogen bonds with each other to form the alpha helix and the beta-pleated sheet?

A. primary

B. secondary

C. tertiary

D. quaternary

B) secondary

Explanation: Secondary structure refers to the local spatial arrangement of the polypeptide backbone. At this level, hydrogen bonds form between the backbone constituents (namely the carbonyl oxygen and the amide hydrogen) of the amino acid residues. These hydrogen bonds lead to the formation of stable arrangements like the alpha helix and the beta-pleated sheet.

In which level of protein structure do the side chains interact chemically to form the 3-dimensional shape of the protein?

A. primary

B. secondary

C. tertiary

D. Quaternary

C) tertiary

Explanation: The tertiary structure level describes the overall 3D shape of the entire polypeptide chain. It results from interactions between the side chains (R-groups) of the amino acids. These interactions can include hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions.

Which of the following amino acids is polar?

A. methionine

B. tyrosine

C. alanine

D. Asparagine

D) asparagine

Explanation: Tyrosine has a phenolic side chain. It is polar due to the hydroxyl (-OH) group, but it's also sometimes classified with aromatic amino acids because of its phenyl ring. At the same time, asparagine has a carboxamide side chain which is polar due to the presence of the amide group. Hence, both tyrosine and asparagine are polar, but asparagine is the most straightforward representative of polar amino acids from the given list.

Which of the following is NOT one of the possible destinations of protein transported by vesicles from the Golgi Apparatus?

A. cell membrane

B. peroxisome

C. outside the cell

D. Lysosome

C) outside the cell

In the electron transport chain on the inner mitochondrial membrane, which protein complex is associated with ubiquinone and is not an hydrogen ion transporter?

A. complex I

B. complex II

C. complex III

D. complex IV

B) complex ||

Explanation: The electron transport chain (ETC) consists of several protein complexes embedded in the inner mitochondrial membrane. These complexes work together to transfer electrons from electron donors to electron acceptors and, in the process, create a proton gradient across the membrane. Complex II (Succinate dehydrogenase) accepts electrons from succinate and transfers them to ubiquinone. It does NOT transport hydrogen ions across the membrane, which is why it is the correct answer to your question.

Which of the following is NOT an amino acid phosphorylated by kinases in humans?

A. serine

B. threonine

C. histidine

D. Tyrosine

C) histidine

Explanation: In eukaryotic cells like humans, the primary amino acids that are phosphorylated by kinases are serine, threonine, and tyrosine. These represent the most common sites for phosphorylation in proteins. Histidine can indeed be phosphorylated, but this is more characteristic of prokaryotic cells in a process known as two-component signaling. However, histidine phosphorylation is less common in eukaryotic cells and is not typically targeted by the majority of kinases found in humans.

Which of the following enzymes is involved in apoptosis?

A. caspase

B. cyclase

C. carboxylase

D. Catalase

A) caspase

Explanation: Apoptosis is a form of programmed cell death that is essential for the development and maintenance of healthy tissues. Caspases are a family of cysteine-aspartic proteases that play essential roles in initiating and executing apoptosis. They are produced in the cell as inactive pro-caspases and become activated in response to various apoptotic signals, leading to a cascade of events that culminate in cell death.

Which protein holding the two sister chromatids together is cleaved during the metaphase of mitosis?

A. cohesin

B. condensin

C. coagulin

D. Connectin

A) cohesin

Explanation: During mitosis, sister chromatids are held together by the cohesin protein complex. During the transition from metaphase to anaphase, the protein separase cleaves cohesin, allowing the sister chromatids to separate and move to opposite poles of the cell.

What is the arrangement of microtubules in the cross-section of a centriole?

A. 9 + 0

B. 9 + 1

C. 9 + 2

D. 9 + 3

A) 9 + 0

Explanation: In the cross-section of a centriole, there are nine sets (triplets) of microtubules arranged in a circular pattern. Each set consists of three microtubules (A, B, and C tubules). There are no central microtubules in this structure, which is why it is referred to as a "9 + 0" arrangement.

Which DNA repair mechanism is used to repair thymine dimers?

A. proofreading by DNA polymerase

B. mismatch repair

C. base excision repair

D. Nucleotide excision repair

D) nucleotide excision repair

Explanation: Thymine dimers are covalent bonds that form between adjacent thymine bases in DNA due to exposure to ultraviolet (UV) radiation. They distort the DNA helix and can interfere with normal DNA replication and transcription. Nucleotide excision repair (NER) is a mechanism that detects and repairs bulky DNA lesions, such as those caused by UV-induced thymine dimers. In NER, a stretch of the DNA strand containing the lesion is recognized and removed, and then the gap is filled in using the complementary strand as a template, with the aid of DNA polymerase.

Which of the following enzymes can prevent the shortening of chromosomes during every replication of DNA?

A. ligase

B. telomerase

C. DNA polymerase

D. Primase

B) telomerase

Explanation: Telomerase is an enzyme that adds repetitive DNA sequences (TTAGGG in vertebrates) to the 3' end of DNA strands in the telomere regions, which are located at the ends of eukaryotic chromosomes. This elongation counteracts the shortening that occurs during DNA replication because the standard DNA replication machinery cannot completely replicate the very ends of linear chromosomes, leading to a progressive shortening with each cell division. Telomerase prevents this shortening and, thereby, can confer a prolonged lifespan to certain cells, such as stem cells and cancer cells.

Which of the following processes tends to turn heterochromatin into euchromatin?

A. acetylation of histone tails

B. methylation of histone tails

C. dephosphorylation of DNA nucleotides D. methylation of DNA

A) acetylation of histone tails

Explanation: Heterochromatin and euchromatin are two types of chromatin states in the cell. Heterochromatin is generally transcriptionally silent and more compact, while euchromatin is more open and transcriptionally active. Histone acetylation is associated with transcriptional activation and chromatin relaxation. When histone tails are acetylated, they tend to neutralize the positive charge of histones, reducing their affinity for the negatively charged DNA backbone. This results in a more open chromatin structure, which is more accessible to transcriptional machinery, favoring the formation of euchromatin.

During transcription, which general transcription factor binds to the TATA box within the promoter first?

A.TFIIA

B. TFIIB

C. TFIID

D. TFIIH

C) TFIID

Explanation: TFIID is a multi-subunit complex and one of its components, called TBP (TATA-binding protein), binds specifically to the TATA box within the promoter region of genes. This binding serves as the initial step in the formation of the pre-initiation complex, which includes several other transcription factors and RNA polymerase II. Once TFIID (with TBP) binds to the TATA box, other transcription factors like TFIIA, TFIIB, and TFIIH can sequentially associate to form a competent transcription initiation complex.

In eukaryotes, which part of the mRNA does the small ribosomal subunit use to recognize it as an mRNA and bind to it? A.Start codon

B. Stop codon

C. 5’ cap

D. 3’ poly-A tail

C) 5’ cap

Explanation: In eukaryotes, the 5' cap of the mRNA is essential for several functions during the process of translation. This cap is a modified form of a guanine nucleotide added to the 5' end of the mRNA. The small ribosomal subunit, in association with several initiation factors, recognizes and binds to the 5' cap of the mRNA, and this facilitates the ribosome's scanning downstream to locate the start codon (AUG), where translation begins.

What type of substitution mutation occurs when the resulting codon codes for a different amino acid?

A. nonsense mutation

B. silent mutation

C. antisense mutation

D. missense mutation

D) missense mutation

Explanation: A missense mutation is a type of point mutation in which a single nucleotide change results in a codon that codes for a different amino acid. This can result in the production of a protein with an altered or non-functional amino acid sequence. A missense mutation is when a substitution changes the codon so that it now codes for a different amino acid.

Which of the following molecules is a marker for protein destruction by proteosome?

A. phosphotidylserine

B. ubiquitin

C. acetylglucosamine

D. palmitate

B) ubiquitin

Explanation: When proteins are destined for degradation by the proteasome, they are tagged with multiple molecules of ubiquitin, a small protein. This process is called ubiquitination. The polyubiquitin chain serves as a signal for the 26S proteasome to recognize, unfold, and then degrade the tagged protein into small peptides. The ubiquitin-proteasome system plays a critical role in regulating numerous cellular processes, including the cell cycle, gene expression, and responses to oxidative stress and DNA damage.

Which of the following is not a defense mechanism against viruses by bacteria?

A. 1. CRISPR-Cas

B. 2. restriction enzymes

C. 3. premature lysis

D. 4. toll-like receptors for viral RNA

C) 3. Premature lysis

Explanation: Premature lysis is not a defense mechanism against viruses by bacteria. In fact, it can be considered detrimental to bacterial survival during viral infections. Lysis refers to the bursting or disintegration of a bacterial cell, releasing its contents into the surrounding environment. While some viruses can induce lysis as part of their life cycle, it is not a mechanism employed by bacteria to defend against viral infections.

Which of the following cells are produced using differentiated cells such as fibroblasts, which are injected with a virus expressing 4 transcription factors that make the cells appear and behave just like embryonic stem cells?

A. monoclonal cells

B. HeLa cells

C. iPS cells

D. totipotent cells

C) iPS cells

Explanation: Induced pluripotent stem (iPS) cells are produced using differentiated cells, such as fibroblasts, which are injected with a virus expressing four transcription factors (Oct4, Sox2, Klf4, and c-Myc) that reprogram the cells to have the ability to differentiate into any cell type in the body, similar to embryonic stem cells.

In CRSPR-Cas9, what type of RNA leads Cas9 to the DNA sequence of the viral genome that is identical to a segment of CRSPR?

A. interfering RNA

B. restriction RNA

C. targeting RNA

D. guide RNA

D) guide RNA (gRNA)

Explanation: In the CRISPR-Cas9 system, the guide RNA (often abbreviated as gRNA) is responsible for directing the Cas9 protein to the specific location in the DNA that matches its sequence. The guide RNA is designed to be complementary to a target DNA sequence. When the gRNA binds to the Cas9 protein, it forms a complex that can search the DNA for a sequence that matches the gRNA. Once this matching sequence is found, the Cas9 protein induces a cut in the DNA, which can result in the disruption or editing of that gene.

Which of the following is mainly involved in anabolism rather than catabolism?

A. glycolysis

B. fermentation

C. citric acid cycle

D. phosphate pentose pathway

D) phosphate pentose pathway

Explanation: The phosphate pentose pathway (pentose phosphate pathway) is mainly an anabolic pathway. It produces ribose-5-phosphate, which is used for the synthesis of nucleotides and nucleic acids. Additionally, the pathway generates NADPH, a crucial reducing equivalent used in various biosynthetic reactions such as fatty acid synthesis.

In the respiratory burst carried out by phagocytes, which of the following is used to generate free radicals and reactive oxygen species to kill the phagocytized bacteria?

A. NADH

B. NADPH

C. ATP

D. GPT

B) NADPH

Explanation: During the respiratory burst in phagocytes, the NADPH oxidase enzyme complex becomes active and transfers electrons from NADPH in the cytosol across the membrane to molecular oxygen, producing superoxide anion (O₂⁻), a reactive oxygen species (ROS). This superoxide can be further converted into other reactive agents, like hydrogen peroxide (H₂O₂) and hydroxyl radicals, which can damage and kill ingested pathogens.

Which of the following amino acids have a poor propensity to form an α helix?

A. leucine

B. lysine

C. glycine

D. Alanine

C) glycine

Explanation: Glycine has a high degree of flexibility due to its small side chain (just a hydrogen atom). This flexibility can interfere with the formation of stable α-helices. Therefore, glycine is often found in turns and loops of proteins.

Which of the following is a protein segment that can fold independently into a compact, stable structure?

A. protein section

B. protein moiety

C. protein conformation

D. protein domain

D) protein domain

Explanation: A protein domain is a segment of a protein sequence that can fold independently into a compact, stable structure. In many cases, these domains can function independently of the rest of the protein chain. Domains are considered the modular units of proteins, and they can appear in various combinations in different proteins, suggesting a modular assembly of proteins from a set of conserved domains. This concept is supported by the observation that many domains have been identified in a wide variety of proteins and are known to be conserved across species. The identification and study of protein domains are essential for understanding the function, evolution, and interactions of proteins.

Which of the following proteins is a triple helix with 3 polypeptides wrapped around each other, with each polypeptide having the amino acid glycine at every third position?

A. microtubule

B. actin

C. collagen

D. elastin

C) collagen

Explanation: collagen is the most abundant protein in the extra cellular matrix of connective tissues. It has unique triple helical structure where 3 polypeptide chains, wrap around each other to form the triple helix. A distinctive feature of collagens amino acid sequence is the regular occurrence of the sequence Gly-X-Y, where gly is glycine, and X and Y can be any other amino acid. Glycine, being the smallest amino acid, allows for the close packing of the 3 helices. Proline and hydroxyproline frequently occupy the X and Y positions, which contribute to the stability of the triple helix

Which of the following enzymes removes acety; groups from histone tails to turn euchromatin to heterochromatic and thereby decrease gene expression?

A. HMT

B. HMAC

C. HAT

D. HDAC

D) HDAC

Explanation: histone deacetylases (HDACs) are enzymes that remove acetyl groups from the lysine residues of histone tails. The removal of acetyl groups from histones condenses the chromatin structure, converting euchromatin (which is a more open and transcriptionally active form of chromatin) into heterochromatin (which is a more condensed and transcriptionally repressive form of chromatin). This change leads to a decrease in gene expression because the DNA is less accessible to transcriptional machinery in the condensed heterochromatin state

Which of the following leads to a frame-shift mutation?

A. deamination

B. depurination

C. deoxygenation

D. decarboxylation

B) depurination

Explanation: depurination is the loss of a purine base (adenine or guanine) from the DNA molecule. If this missing base is not repaired by the cellular machinery before the DNA is replicated, it can result in the mispairing of bases during DNA synthesis. If a base insertion or deletion follows the site of depurination during DNA replication, it can lead to a frame-shift mutation. Frame-shift mutations occur when the reading frame of the DNA sequence is altered, which can change the amino acid sequence of the resulting protein, potentially leading to malfunctioning or nonfunctional proteins

Which of the following RNA is involved in the splicing of RNA?

A. siRNA

B. piRNA

C. miRNA

D. snRNA

D) snRNA

Explanation: slicing is the process by which introns (non coding regions) are removed from the pre-mRNA and exons (coding regions) are joined together to form a mature mRNA. This process is essential for gene expression is eukaryotic cells.

Small nuclear RNA's are involved in splicing. They combine with proteins to form small nuclear ribonucleoproteins (snRNPs), which are components of the spliceosome. The spliceosome is the complex machinery that carries out the splicing of pre-mRNA. Specifically, U1, U2, U4, U5, and U6 snRNAs are the major snRNAs that participate in the formation of the spliceosome and the splicing process

What is the first enzyme in the glycolytic pathway?

A. phosphofructokinase

B. phosphoglucose isomerase

C. hexokinase

D. PEP carboxykinase

C) hexokinase

Explanation: glycolysis is the metabolic pathway that converts glucose into pyruvate with the simultaneous production of a small amound of ATP and NADH. The first step in glycolysis involves the phoshorylation of glucose to form glucose-6-phosphate. This reaction is catalyEd by the enzyme hexokinase. Therefore, hexokinase is the first enzyme in the glycolytic pathway

Which of the following amino acids is exclusively ketogenic and can never enter gluconeogenesis?

A. isoleucine

B. lysine

C. valine

D. serine

B) lysine

Explanation: amino acids can be categoried based on their catabolic fate into either glucogenic or ketogenic pathways. Thus, lysine is the only amino acid in the options provided that is exclusively ketogenic and can never enter gluconeogenesis

Which of the following is the uncoupling protein in the mitochondria of brown fat?

A. dinitrophenol

B. salicylic acid

C. linoleic acid

D. thermogenin

D) thermogenin

Explanation: thermogenin, aka uncoupling protein 1 (UCP1), is found in the mitochondria of brown adipose tissue. It functions to uncouple oxidative phosphorylation, meaning that instead of the energy from eelctron transport being used to form ATP, its dissipated as heat. This process is essential for non-shivering thermogenesis in mammals, especially in newborns and hibernating animals. Brown fat's primary role is to generate heat, and thermogenin facilitates this by allowing protons to leak back into the mitochondrial matrix without generating ATP, which leads to heat production.

Dinitrophenol can also cause a similar uncoupling effect in mitochondria but is a synthetic compound and not a protein. Salicylic acid and linoleic acid are not specifically associated with the uncoupling process in brown fat mitochondria