86 Questions
What is the primary function of the sigma () factor in prokaryotic transcription?
To associate with the RNA polymerase core to form a holoenzyme
What is the role of the RNA polymerase holoenzyme in prokaryotic transcription initiation?
To recognize and bind to the promoter sequence
What is the sequence of the -10nt element in the prokaryotic promoter?
TATAAT
How many subunits does the RNA polymerase in prokaryotes consist of?
5
What is the rate of transcription by RNA polymerase in prokaryotes?
50nt / sec
What is the percentage of total cellular RNA composed of tRNA?
10%
Where is the amino acid attached to the tRNA?
3'-end
What is the molecular weight of tRNA?
24,000-31,000
What is the characteristic of the secondary structure of tRNA?
Cloverleaf
What is the function of the anticodon loop in tRNA?
Complementary codon recognition
What is the primary function of DNMT1 during DNA replication?
To restore methylation patterns on newly synthesized DNA
What is the outcome of methyl-binding proteins binding to methylated CpG islands?
Silencing cascade resulting in closed chromatin
During early embryogenesis, what is the characteristic of DNA methylation?
DNA is largely lacking of methylation
What is the role of histone H3K9 in the silencing cascade?
It is deacetylated and then methylated to silence gene expression
What is the primary enzyme responsible for de novo methylation in post-implantation embryos?
DNMT3A and DNMT3B
What is the result of DNMT1's activity on newly synthesized DNA during replication?
Faithful replication of methylation patterns
What is the role of polypeptide chain release factors in eukaryotes?
Triggering hydrolysis of peptidyl-tRNA at the ribosomal peptidyl transferase center
What is the function of the 5S rRNA component?
It forms the large ribosomal subunit
How does the sedimentation coefficient (S) relate to the density of rRNA?
A higher S value indicates a denser particle
What is the difference between the synthesis of rRNA in eukaryotes and prokaryotes?
Eukaryotes have a single precursor RNA, while prokaryotes have multiple precursors
What is the characteristic of prokaryotic transcription and translation?
Transcription is coupled to translation
What percentage of total cellular RNA is composed of rRNA?
80-90%
What is the consequence of nonhomologous end joining on the DNA sequence?
It results in the loss of a few nucleotides
What is the minimum length of single-stranded DNA required for homology-directed repair?
50 nucleotides
What is the accuracy of pairing in the D-loop during homology-directed repair?
90-100%
What is the outcome of homology-directed repair in terms of DNA synthesis?
New DNA synthesis occurs on both strands
What is the difference between homology-directed repair and homologous recombination?
Homology-directed repair results in gene conversion, while homologous recombination results in new genetic combinations
What is the defined feature of meiosis in which homologous recombination plays a role?
Crossover
What is the purpose of histone H1 in the formation of 30-nm chromatin fiber?
Histone H1 stabilizes both nucleosome structure and higher-order chromatin architecture.
What is the significance of the 147 bp DNA wrapping around the core histone octamer?
It forms a nucleosome.
What is the result of the tight coiling of the 250-nm wide-fiber during DNA packaging?
It produces the chromatid of a chromosome.
What is the function of linker DNA in the formation of nucleosomes?
It links the histone cores.
How does the DNA make turns around the nucleosome in the 30-nm chromatin fiber?
It makes approximately 2 complete turns.
What is the significance of chromatin fibers in the cell cycle?
Chromosomes need to be less condensed in the form of chromatin fibers to allow for gene expression.
What is the primary function of TWINKLE in the replication of mtDNA?
To unwind the double-stranded DNA template
What is the significance of the stem-loop structure formed at OL in the replication of mtDNA?
It blocks mtSSB binding, allowing POLRMT to initiate primer synthesis
What is the role of POLRMT in the replication of mtDNA?
To initiate primer synthesis
At what point does POLγ replace POLRMT during the replication of mtDNA?
At the 3′-end of the primer, after about 25 nt
What is the role of mtSSB in the replication of mtDNA?
To bind and protect the exposed parental H-strand
What is the primary difference between the structure of enzymes and transport, defense, and regulatory proteins versus structural and motility proteins?
Enzymes and transport, defense, and regulatory proteins are globular in nature, making them soluble, while structural and motility proteins are fibrous and insoluble.
What is the significance of the initiator tRNA carrying the Met amino acid being bound to the P-site on the ribosome during translation?
It marks the start of polypeptide synthesis and ensures that the translation process begins with a methionine residue.
How does the degeneracy of the genetic code affect the relationship between base substitution and amino acid change?
It means that base substitution does not necessarily change an amino acid.
How does the quaternary structure of hemoglobin contribute to its function as a conjugated protein?
The quaternary structure of hemoglobin, with its four Fe2+-containing heme groups, allows it to bind oxygen and transport it efficiently.
What is the energy source required for the aminoacyl tRNA synthetase reaction, and how does it facilitate polypeptide synthesis?
The energy source required is ATP, which is used to activate the amino acid and attach it to the tRNA, facilitating the first step in polypeptide synthesis.
What is the role of the A-site on the ribosome during translation?
It is aligned with the next codon, which will be bound with the anticodon of the next tRNA.
What is the significance of the combinatorial nature of protein function in relation to genetic complexity in higher organisms?
The combinatorial nature of protein function allows for a vast range of possible functions without a corresponding increase in gene number, contributing to the genetic complexity of higher organisms.
What is the purpose of the E-site on the ribosome during translation?
It is where the uncharged tRNA is moved to and released from the ribosome.
How do the different levels of protein structure (primary, secondary, tertiary, and quaternary) relate to each other, and what do they describe?
The primary structure is the amino acid sequence, the secondary structure is the local spatial arrangement of the backbone, the tertiary structure is the 3D structure of the entire polypeptide, and the quaternary structure is the arrangement of subunits in a multi-subunit protein.
What is the function of the terminating or release factors (R1, R2, and S) during translation?
They signal the termination of the amino acid chain when the ribosome encounters a termination codon.
What is the role of oligomers in protein function, and how do they relate to monomers?
Oligomers are proteins that work together, composed of individual monomers, which are the component proteins that make up the oligomer.
What is the differentiation between the initiating methionyl tRNAs and those that add methionine internally to the protein?
It is done by initiating factors that participate in the formation of the ribosome complex.
What is the role of the death-inducing signaling complex (DISC) in the extrinsic pathway of apoptosis?
It activates the initiator caspase after binding of Fas ligand to Fas death receptors.
What is the function of cytochrome c in the intrinsic pathway of apoptosis?
It forms an apoptosome with Apaf1, leading to the activation of the initiator caspase.
How do extracellular signal proteins activate the extrinsic pathway of apoptosis?
They bind to cell-surface death receptors, leading to the formation of the DISC and activation of the initiator caspase.
What is the role of the mitochondria in the intrinsic pathway of apoptosis?
They release cytochrome c, which forms an apoptosome with Apaf1, leading to the activation of the initiator caspase.
What is the outcome of the activation of the initiator caspase in the apoptotic pathway?
It leads to the controlled death of the cell through the cleavage of key proteins.
What is the significance of the two pathways of apoptosis in mammalian cells?
They provide two distinct mechanisms for the controlled death of cells in response to different apoptotic signals.
What are the two main classes of nucleic acids that form the chemical basis for the transmission of genetic traits?
Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA)
What are the three components of a nucleotide?
A 5-carbon sugar (pentose), a nitrogenous base, and a phosphate group
What is the difference between a nucleoside and a nucleotide?
A nucleoside is a sugar moiety with a nitrogenous base, while a nucleotide is a nucleoside with a phosphate group attached
What is the sugar moiety in DNA, and how does it differ from that in RNA?
In DNA, the sugar moiety is 2-deoxyribose, while in RNA, it is ribose
What is the process that attaches a phosphate group to a nucleoside, forming a nucleotide?
Phosphorylation
What is the significance of the nitrogenous base in a nucleotide?
It is responsible for encoding genetic information
What is the significance of DNA methylation in the regulation of gene expression, and how does it contribute to compact and silent chromatin?
DNA methylation regulates gene expression by recruiting proteins that bind to methylated DNA, which form complexes with histone deacetylases, resulting in deacetylated histones and compact and silent chromatin.
How does the selective methylation of homologous genes during gametogenesis contribute to the balanced expression of genes in growth and embryonic development?
Selective methylation of homologous genes during gametogenesis ensures balanced gene expression by marking imprinted genes, which are crucial for normal growth and development.
What is the consequence of methylated C residues in the promoter regions of tumor suppressor genes, and how does it contribute to cancer development?
Methylated C residues in the promoter regions of tumor suppressor genes lead to gene inactivation, contributing to cancer development by silencing tumor suppressor genes.
What is the role of epigenetic reprogramming in early embryogenesis, and how does it affect adult patterns of methylation?
Epigenetic reprogramming in early embryogenesis erases adult patterns of methylation, allowing for the establishment of new gene expression patterns necessary for development.
How does DNA methylation contribute to the dysregulation of gene expression in disease states, and what are the consequences of this dysregulation?
DNA methylation dysregulation in disease states can lead to aberrant gene expression, contributing to the development and progression of diseases, including cancer.
What is the significance of DNA methylation in maintaining genomic stability, and how does it relate to chromatin structure and gene expression?
DNA methylation maintains genomic stability by regulating gene expression and chromatin structure, ensuring proper gene expression patterns and preventing aberrant gene expression.
What is the role of TWINKLE in mtDNA replication, and how does it interact with POLγ during this process?
TWINKLE is a DNA helicase that travels in front of POLγ to unwind the double-stranded DNA template during mtDNA replication.
Describe the mechanism of L-strand DNA synthesis in mtDNA replication, including the key enzymes involved and the timing of their action.
L-strand DNA synthesis occurs after about 25 nt, when POLγ replaces POLRMT at the 3′-end of the primer, and POLγ synthesizes the new DNA strand.
What is the significance of the stem-loop structure formed at OL during mtDNA replication, and how does it affect mtSSB binding?
The stem-loop structure formed at OL blocks mtSSB binding, allowing POLRMT to initiate primer synthesis and L-strand DNA synthesis to occur.
Compare and contrast the roles of POLRMT and POLγ in mtDNA replication, including their specific functions and the timing of their action.
POLRMT initiates primer synthesis, while POLγ synthesizes the new DNA strand. POLRMT acts first, followed by POLγ, which replaces it at the 3′-end of the primer after about 25 nt.
What is the significance of the exposed, parental H-strand being protected by mtSSB during mtDNA replication, and how does this protection contribute to the replication process?
mtSSB protects the exposed, parental H-strand from degradation, allowing it to serve as a template for DNA synthesis and ensuring the integrity of the genetic material.
What is the primary mechanism by which DNA polymerase corrects base pairing errors during DNA replication?
Proofreading and 3' to 5' exonuclease activity
What is the function of primase in DNA replication, and how does it differ between leading and lagging strands?
Primase intersperses RNA primers in the lagging strand; leading strand requires only one priming event
What is the role of DNA polymerase I in prokaryotes and eukaryotes during DNA replication?
In prokaryotes, it removes RNA primers; in eukaryotes, enzymes such as FEN1 and RNase H perform this function
What are Okazaki fragments, and how are they formed during DNA replication?
Okazaki fragments are short, discontinuous DNA fragments formed on the lagging strand during DNA replication
What is the direction of DNA synthesis in the leading strand, and how does it differ from the lagging strand?
Leading strand synthesis occurs in the 5' to 3' direction, while lagging strand synthesis occurs in short, discontinuous fragments
What is the role of exonuclease activity in DNA replication, and how does it ensure the accuracy of DNA synthesis?
Exonuclease activity removes incorrect nucleotides, ensuring the accuracy of DNA synthesis
What is the primary function of the checkpoints in the cell cycle, specifically the G1 and G2 checkpoints?
The primary function of the checkpoints in the cell cycle, specifically the G1 and G2 checkpoints, is to ensure that the cell is ready to proceed to the next stage of the cell cycle, and if the cell is not ready, it may be signaled to undergo apoptosis.
What is the outcome of a cell failing to pass the G1 checkpoint?
If a cell fails to pass the G1 checkpoint, it may be signaled to undergo apoptosis.
What is the significance of apoptosis in the development of digits, as seen in the interdigital cell death?
Apoptosis plays a crucial role in the development of digits, as seen in the interdigital cell death, by eliminating excess tissue between the developing digits, allowing for proper formation and separation of the digits.
What is the outcome of a cell failing to pass the G2 checkpoint?
If a cell fails to pass the G2 checkpoint, it may be signaled to undergo apoptosis.
What is the role of apoptosis in the regulation of cell growth and development?
Apoptosis plays a crucial role in the regulation of cell growth and development by eliminating damaged or defective cells, allowing for proper tissue formation and development.
What are the key morphological features of a cell during the events of apoptosis?
The key morphological features of a cell during the events of apoptosis include cell shrinkage and condensation, flipping of the plasma membrane, collapse of the cytoskeleton, disintegration of organelles, disassembly of the nuclear envelope, condensation and break-up of chromatin, and formation of apoptotic bodies.
Learn about the differences in transcription initiation between prokaryotes and eukaryotes, including the role of RNA polymerase and additional factors. Compare the simpler process in bacteria with the more complex process in eukaryotes. Understand the DNA sequences involved in transcription.
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