89 Questions
What is the role of thymidylate synthase in pyrimidine synthesis?
Catalyzing the reaction between dUMP and tetrahydrofolate to generate dTMP
What is the primary function of fibronectin in the ECM?
Connecting ECM to integrin receptors on cell surfaces
What is the role of the extracellular matrix in cell-cell communication and gene regulation?
Participating in cell-cell communication and gene regulation
What is the function of proteoglycans in the ECM?
Acting as a water-hydrated gel to resist compression
Which of the following cells are unable to produce purines?
Erythrocytes, polymorphonuclear leukocytes, and brain cells
What is the role of collagen in the ECM?
Acting as a fibrous protein to provide tensile strength and recoil
What is the primary function of phospholipase C (PLC) in the G-protein-coupled receptor signaling pathway?
To cleave phosphatidylinositol 4,5-bisphosphate (PIP2) into inositol 1,4,5-triphosphate (IP3) and diacylglycerol (DAG)
What is the role of folic acid in the synthesis of purine nucleotides?
It is essential for the synthesis of purine nucleotides
What is the effect of increased cytosol calcium concentration on IP3 receptors and ryanodine receptors?
It inhibits them at a delayed time
What is the characteristic of the ECM that allows it to fix the relative positions of different cells?
Framework for fibrous proteins
What is the role of diacylglycerol (DAG) in the G-protein-coupled receptor signaling pathway?
It helps activate protein kinase C (PKC) along with calcium and phosphatidylserine
What is the function of phosphoribosyl pyrophosphate (PRPP) in purine nucleotide synthesis?
It is an early participant in the synthesis of purine nucleotides
What is the result of the binding of IP3 to IP3 receptors on the endoplasmic reticulum surface?
It releases calcium ions from the endoplasmic reticulum into the cytosol
What is the purpose of the 'salvage reactions' in mammalian cells?
To convert ribonucleosides and deoxyribonucleosides into their respective nucleotides
Which enzyme is involved in the conversion of orotic acid into UMP?
Uridine monophosphate synthetase (UMPS)
What is the function of G-protein Gq in the G-protein-coupled receptor signaling pathway?
It activates phospholipase C (PLC)
What is the result of the increased calcium concentration in the cytosol on protein kinase C (PKC) activity?
It translocates PKC from the cytosol to the plasma membrane
What is the difference between cytosolic carbamoyl phosphate synthase II and mitochondrial carbamoyl phosphate synthase I?
The former is involved in pyrimidine synthesis, while the latter is involved in urea synthesis
What is the primary function of kinetochore fibers during mitosis?
To generate fibers that attach sister chromatids to spindle fibers
What is the correct sequence of events during prophase?
Chromatin condenses, mitotic spindle fibers form, and nucleolus disappears
What is the primary function of the mitotic spindle fibers?
To generate fibers that separate chromosomes during mitosis and meiosis
What is the consequence of the disappearance of the nucleus and nucleolus during prophase?
Chromatin condenses and mitotic spindle fibers form
What is the correct term for the phase of the cell cycle that includes stages G1, S, and G2?
Interphase
What is the function of centrioles in animals?
To form asters
What is the primary function of tight junctions in the context of cell-cell adhesion?
Providing selective permeability and maintaining cell surface protein distribution
Which of the following proteins is essential for the formation of tight junctions?
Claudin
What is the primary function of gap junctions in the context of cell-cell communication?
Allowing the passage of small water-soluble molecules and signaling between two cells
Which of the following is a characteristic of the G1 phase of the cell cycle?
Cell growth and preparation for mitosis
What is the term for the combination of DNA and proteins that form the chromosomes in higher organisms?
Chromatin
What is the term for the phase of the cell cycle where the cell exits the cycle and does not reproduce again?
G0 phase
What is the approximate length of DNA that wraps around the histone octamer to form a nucleosome?
147 bp
What is the purpose of the histone protein H1 in the formation of chromatin fibers?
To bind to the nucleosomal core particle around the DNA entry and exit sites
What is the structure formed when multiple nucleosomes are packed together?
30-nm chromatin fiber
During which phase of the cell cycle do the chromosomes condense even further?
Mitosis
What is the process by which the 300-nm fiber is compressed and folded to produce a 250-nm wide-fiber?
Compressing and folding
Why do chromosomes need to be less condensed?
To allow for gene expression
What is the function of the RNA polymerase in prokaryotes during transcription?
To recognize the promoter sequence and unwind the double helix of DNA
What is the role of the sigma (σ) factor in prokaryotic transcription?
To form a complex with RNA polymerase and recognize the promoter sequence
What is the sequence of the core promoter in prokaryotes?
TTGACA
How many subunits does the RNA polymerase in prokaryotes consist of?
5
What is the rate of RNA synthesis by RNA polymerase in prokaryotes?
50 nt/sec
During DNA replication, what is the direction of DNA extension in the leading strand?
5’ to 3’
What is the enzyme responsible for removing RNA primers in prokaryotes?
DNA polymerase I
What is the primary function of the 5' capping process during post-transcriptional modification of mRNA?
To prevent degradation by exonucleases
What is the name of the short, discontinuous fragments formed during lagging strand synthesis?
Okazaki fragments
What is the primary function of exonucleolytic proofreading in DNA replication?
To correct base pairing errors
What is the approximate percentage of total cellular RNA that comprises messenger RNA (mRNA)?
1-5%
During post-transcriptional modification of mRNA, which process is responsible for removing introns?
Splicing
During DNA replication, what is the role of primase?
To synthesize RNA primers
What is the direction of the exonuclease activity of DNA polymerase during proofreading?
3’ to 5’
What is the term for the preliminary RNA molecule that undergoes post-transcriptional modification to form mature mRNA?
Heteronuclear RNA (hnRNA)
Where is messenger RNA (mRNA) typically found in the cell?
Both nucleus and cytoplasm
What is the sequence of the DNA strand that messenger RNA (mRNA) is complementary to?
Non-coding strand
What is the characteristic of the caspase cascade during apoptosis?
Irreversible and destructive
What is the role of the adaptor proteins in the activation of initiator caspases?
They facilitate the dimerization of initiator caspases
What is the result of the cleavage of the executioner caspases by the initiator caspases?
The executioner caspases dimer undergoes an activating conformational change
What is the characteristic of the initiator caspases in their inactive form?
They are inactive monomers
What is the region of the initiator caspase that contains the protease domain?
C-terminal region
What is the result of the binding of the initiator caspase to the adaptor protein?
The initiator caspase is activated
What is the purpose of the 𝜎 subunit of RNAP in prokaryotes during transcription initiation?
The 𝜎 subunit of RNAP increases specificity for promoters, allowing transcription to initiate at correct sites, while reducing affinity for nonspecific DNA.
Describe the process by which the RNAP holoenzyme creates an open complex at the Pribnow box during transcription initiation.
The RNAP holoenzyme detects the -35 sequence, forms a closed complex, and then moves down to the DNA strand, recognizes and binds to the Pribnow box, and unwinds the dsDNA helix to create an open complex (transcription bubble) by performing helicase activity.
What is the significance of the RNA polymerase retaining all its phosphate groups during the synthesis of the first ribonucleoside triphosphate?
The RNA polymerase retains all its phosphate groups during the synthesis of the first ribonucleoside triphosphate, indicating that the RNA synthesis does not require priming.
Describe the fate of the alpha phosphate group during the synthesis of subsequent ribonucleoside triphosphates.
The alpha phosphate group, the one closest to the ribose sugar, is retained during the synthesis of subsequent ribonucleoside triphosphates, while the other two phosphate groups are released as orthophosphate.
What is the role of the RNAP holoenzyme in breaking the hydrogen bonds between the T:A base pairs during transcription initiation?
The RNAP holoenzyme performs helicase activity to unwind the DNA and break the hydrogen bonds between the T:A base pairs, requiring less energy to melt down this region.
What is the significance of the -35 sequence in the recognition of promoters by the RNAP holoenzyme?
The -35 sequence is recognized by the RNAP holoenzyme, allowing it to bind to the promoter and initiate transcription.
What is the significance of alternative splicing in generating phenotypic diversity from a single gene?
Alternative splicing leads to different mRNA transcripts, which can be translated to different proteins with distinct structures and functions, resulting in increased phenotypic diversity.
How do epigenetic mechanisms regulate gene expression without altering the underlying DNA sequence?
Epigenetic mechanisms, such as histone modification and DNA methylation, regulate gene expression by altering chromatin structure and accessibility to transcription factors, without changing the underlying DNA sequence.
What is the importance of the primary, secondary, tertiary, and quaternary structure of protein organization in determining protein function?
The different levels of protein structure are crucial for determining protein function, as they influence the protein's overall shape, binding properties, and enzymatic activity.
How does the translation process involve the polymerization of amino acids into a polypeptide using RNA as a guide?
During translation, amino acids are polymerized into a polypeptide chain through the interaction of ribosomes, messenger RNA, and transfer RNA, with the RNA sequence serving as a template for the growing polypeptide chain.
What is the significance of genomic imprinting in regulating gene expression, and how does it differ from other epigenetic mechanisms?
Genomic imprinting is a mechanism that regulates gene expression by selectively silencing one of the two parental alleles in a diploid cell, resulting in parental-origin-specific gene expression.
How does the regulation of gene expression by epigenetic mechanisms differ from regulation by cis-elements and transcription factors?
Epigenetic mechanisms, such as histone modification and DNA methylation, regulate gene expression by altering chromatin structure and accessibility, whereas cis-elements and transcription factors regulate gene expression by binding directly to specific DNA sequences.
Describe the process of post-translational modification of proteins, highlighting the types of modifications and their significance.
Post-translational modification of proteins involves the addition of specific functional/chemical groups to amino acid side chains, altering protein conformation and properties. Types of modifications include phosphorylation, acetylation, lipid modification, and glycosylation. These modifications are generally reversible, affecting protein stability, localization, interacting partners, and activity. They play essential roles in regulating the functions of many important eukaryotic proteins.
Explain how a single base substitutional change in a codon can result in a change in amino acid.
A single base substitutional change from A to T can result in the substitution of Val for Glu. This occurs because the change in the codon sequence alters the amino acid specified during translation.
Discuss the differences between silent, missense, and nonsense variants in terms of their effects on protein function.
Silent variants do not change the amino acid sequence, missense variants change the amino acid, and nonsense variants result in a premature stop codon. These variants can have different effects on protein function, ranging from no effect to complete loss of function.
Describe the role of ubiquitination in protein degradation, highlighting the significance of this process.
Ubiquitination is a post-translational modification that marks proteins for degradation by attaching ubiquitin molecules. This process is essential for regulating protein turnover and maintaining protein homeostasis.
Explain the reversibility of post-translational modifications, providing examples of enzymes involved in the process.
Post-translational modifications are generally reversible, with one enzyme adding the modifying group and another enzyme removing it. For example, phosphorylation by protein kinases can be reversed by phosphatases.
Discuss the significance of post-translational modifications in regulating protein function, highlighting their importance in cellular processes.
Post-translational modifications play a crucial role in regulating protein function, influencing protein stability, localization, and activity. They are essential for various cellular processes, including cellular signaling, protein-protein interactions, and protein degradation.
What is the difference between the absorbance of dsDNA and ssDNA at 260nm, and how does it relate to the hypochromic effect?
dsDNA has less absorbance at 260nm than ssDNA due to the stacking interactions between the bases, known as the hypochromic effect. When dsDNA denatures, the absorbance increases.
Describe the structure and function of the nucleoid in prokaryotes, including the components that make it up.
The nucleoid is a region in the cytoplasm of prokaryotes that houses the genetic material, consisting of mostly DNA, together with RNAs and proteins, including mRNAs, transcription factor proteins, and ribosomes. Nucleoid-associated proteins (NAPs) maintain the nucleoid structure.
What is the effect of a nick on a supercoiled plasmid, and how does it relate to the release of torsional energy?
A nick in a supercoiled plasmid allows it to gradually unwind, releasing the torsional energy until it reaches its final, circular, relaxed state.
What is the role of topoisomerases in DNA packaging in prokaryotes, and how do they relate to the interconversion between relaxed and supercoiled forms of DNA?
Topoisomerases catalyze the interconversion between relaxed and supercoiled forms of DNA, allowing for the release of torsional energy and the maintenance of DNA structure.
What is the difference between the bacterial chromosome and eukaryotic nucleus, and how do they relate to the organization of genetic material?
The bacterial chromosome is a single or multiple, circular or linear chromosome found in the nucleoid region of the cytoplasm, whereas the eukaryotic nucleus is a membrane-bound organelle that houses the genetic material. The bacterial chromosome is not surrounded by a nuclear membrane, unlike eukaryotic cells.
What is the relationship between the hyperchromic effect and the denaturation of dsDNA, and how does it relate to the measurement of dsDNA denaturation?
The hyperchromic effect is the increasing ability of DNA to absorb light as it denatures, which is used to measure the denaturation of dsDNA.
What is the primary function of the major noncoding region in mitochondrial DNA?
To harbor promoters for transcription and the origin for H-strand DNA replication
What is the consequence of premature termination of nascent H-strand DNA synthesis at the termination-associated sequence?
The formation of a triple-stranded displacement-loop structure and the production of a short H-strand replication product called 7S DNA
What is the function of the mitochondrial DNA-directed RNA polymerase during mitochondrial DNA replication?
To initiate primer synthesis
What is the difference between the origin of replication for the H-strand and the origin of replication for the L-strand in mitochondrial DNA?
The origin of replication for the H-strand is located within the noncoding region, while the origin of replication for the L-strand is located outside the noncoding region, within a tRNA cluster
What is the characteristic of the short stretches of DNA synthesized on the lagging strand during mitochondrial DNA replication?
Each stretch must start with its own RNA primer
What is the number of mRNA molecules encoded by the mitochondrial genome?
13
Test your understanding of the signal transduction pathway that involves G-protein coupled receptors, phospholipase C, and second messengers such as IP3 and DAG. Learn how these molecules interact to activate protein kinase C and regulate various cellular processes.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
