BIOD15 Midterm Exam Review: Scientific Papers, Gene Expression, and Methodologies

Comprehensive short answer flashcard bank covering critical paper analysis, epigenetic mechanisms of gene expression, and modern molecular methodologies.

What makes a research question significant in a scientific paper, and how can you assess whether the hypothesis aligns with the study's objectives?

The research question should address a gap in the field and have clear relevance. The hypothesis must logically follow from the background provided and align with the study's stated objectives.

What methodological factors should be examined when comparing two scientific papers with conflicting results?

Examine differences in experimental design, sample size, controls, statistical analyses, and study systems (e.g., species or conditions). Also consider the broader context, such as whether one study has corroborative replication studies while the other does not.

How does the methods section of a paper affect its reproducibility and credibility, and what are key indicators of a well-written methods section?

It ensures reproducibility by providing all necessary information for replication. Key indicators include clear descriptions of protocols, appropriate controls, and justification for sample size and statistical tests.

What steps should be taken to critically evaluate whether a paper's conclusions are justified by its results?

Examine if the figures and tables align with textual conclusions, check for alternative interpretations of the data, evaluate whether statistical analyses were appropriate, and look for overgeneralizations or unsupported claims in the discussion.

How can conflicting findings between two papers advance scientific understanding, and what strategies reconcile such contradictions?

Conflicting findings highlight gaps in knowledge or limitations in methodologies, prompting further investigation. Researchers can reconcile contradictions by performing meta-analyses, replicating studies using standardized methods, or exploring complementary approaches.

How does the funnel structure of an introduction frame a research question, and how would you critique an introduction failing this structure?

The funnel structure narrows from a broad context down to a specific research question, logically guiding readers. A critique of a failing introduction might highlight jumping directly to specifics without context or failing to clearly state the knowledge gap and hypothesis.

How do the roles of the Results and Discussion sections differ, and how can you evaluate whether they are effectively separated?

Results objectively present data without speculation, while Discussion interprets findings and contextualizes them within the field. Separation is evaluated by checking if Results contain interpretations or if the Discussion introduces new data.

What criteria should be used to assess whether a scientific figure effectively communicates complex data?

Figures should stand alone, accurately represent data, and be easily understood. Criteria include clear labeling, appropriate scale, color use for accessibility, suitability of figure type (e.g., bar graph vs. scatter plot), and whether figures enhance rather than merely repeat textual information.

What red flags should you look for in the acknowledgments and data availability sections of a scientific paper?

Red flags include vague statements about data access, undisclosed funding sources, or a lack of key collaborator acknowledgments that might indicate incomplete methodology disclosure.

What is the primary role of supplementary data in modern scientific publishing?

Due to space constraints, key control experiments and data that support the main text findings are often included as supplemental data, making it essential to review when critically evaluating a paper.

What are three primary epigenetic mechanisms and their biological roles?

DNA methylation silences genes by adding methyl groups to cytosines in a CpG context; histone modifications alter chromatin structure via chemical modifications on histone tails; and non-coding RNAs regulate gene expression through RNA interference or recruitment of chromatin modifiers.

How does DNA methylation regulate gene expression?

DNA methylation, most commonly occurring at CpG dinucleotides, blocks transcription factor binding or recruits repressive chromatin proteins. This typically reduces transcription by making chromatin less accessible.

Why is CpG methylation particularly important in gene regulation?

CpG sites are hotspots for DNA methylation and often occur in gene promoters. Methylation at these specific sites displays the strongest correlation with transcriptional activity.

How do histone modifications regulate gene expression?

Histone tail modifications (such as acetylation or methylation) alter chromatin compaction. Loosely packed chromatin promotes transcription, whereas tightly packed chromatin represses it.

Why can the effect of a histone modification on gene expression be difficult to predict?

Multiple modifications can occur on histone tails simultaneously, so the effect of one modification may depend on the other modifications present.

How do DNA methylation and histone modifications collaboratively regulate gene expression?

DNA methylation recruits repressors and compacts chromatin, while histone modifications tighten or loosen chromatin structure to regulate transcription.

Why are long non-coding RNAs (lncRNAs) considered key players in chromatin remodeling?

lncRNAs serve as scaffolds for histone-modifying complexes (for example, XIST recruits Polycomb Repressive Complex 2) and guide these complexes to specific genomic loci.

What is the biological role of microRNAs (miRNAs) in regulating gene expression?

miRNAs are small non-coding RNAs that post-transcriptionally regulate gene expression by base-pairing with target mRNAs to promote their degradation or inhibit their translation.

What is the biological role of circular RNAs (circRNAs) in regulating gene expression?

circRNAs are covalently closed RNA molecules that regulate gene expression mainly by acting as sponges for microRNAs and RNA-binding proteins, modulating transcription and mRNA stability, and sometimes being translated into functional peptides.

How do riboswitches regulate gene expression?

Riboswitches are RNA elements located in mRNA $5'\text{UTRs}$ that bind metabolites, inducing structural changes that either expose or occlude ribosome-binding sites to control translation.

What distinguishes genomic imprinting from random X-inactivation?

Imprinting involves parent-of-origin-specific methylation (e.g., Igf2 paternal expression) and serves as a potential mechanism for transmitting experience-based epigenetic changes across generations. Random X-inactivation randomly silences one X chromosome in females early in development.

How does XIST lncRNA mediate X-chromosome inactivation in females?

XIST RNA targets one X chromosome, recruiting histone modifiers (such as Polycomb repressors) and DNA methyltransferases to establish heterochromatin and silence genes on that chromosome.

What general effects can post-transcriptional modifications have on RNA transcripts?

RNA modifications can affect RNA splicing, stability, trafficking, and protein interactions.

How does the mRNA modification $m^6\text{A}$ influence mRNA stability and translation?

Some $m^6\text{A}$ readers (such as YTHDF2) target modified mRNAs for decay, while others (such as YTHDF1) enhance ribosome recruitment to increase translation.

What evolutionary advantages might RNA modifications provide over DNA-level epigenetic changes?

RNA modifications enable rapid, reversible responses to environmental stimuli using an existing mRNA pool, optimizing resource allocation under changing conditions.

Why are technical challenges greater in epitranscriptomics compared to epigenetics?

RNA's unstable nature complicates preservation, and many modifications (such as pseudouridine) lack antibodies for enrichment, requiring specialized sequencing methods.

What is gene-environment interplay (GxE)?

Gene-environment interplay refers to how environmental signals (such as stress, nutrition, and social experience) interact with genetic and epigenetic mechanisms to shape gene expression across an individual's lifespan.

What is transcriptional memory?

Transcriptional memory refers to the ability of a gene to respond more strongly upon repeated stimulation.

How can maternal diet induce transgenerational epigenetic effects?

Nutritional factors might alter DNA methylation patterns in germ cells, potentially bypassing reprogramming to affect offspring phenotypes.

How do transgenerational and intergenerational inheritance differ regarding environmental exposure?

Intergenerational effects involve direct fetal exposure (such as maternal stress impacting the $F_1$ generation), whereas transgenerational effects persist in unexposed generations (such as the $F_3$ generation).

Why do endocrine disruptor-induced epigenetic changes often fail to persist beyond one generation?

Germline reprogramming erases DNA methylation patterns, resetting epigenetic marks during gametogenesis.

What biological information does DNA sequencing provide?

DNA sequencing determines the nucleotide order of a genome or genomic region and reveals genetic variation such as mutations, insertions, and deletions.

What is the difference between whole-genome sequencing and whole-exome sequencing?

Whole-genome sequencing fragments and sequences all genomic DNA across coding and non-coding regions. Whole-exome sequencing uses hybrid-capture probes to enrich for exons (and sometimes flanking regions) and sequences only that targeted subset.

Why is bisulfite sequencing considered the gold standard for DNA methylation analysis?

It provides single-base resolution by converting unmethylated cytosines to uracil (read as thymine) while methylated cytosines remain unchanged, allowing high-throughput genome-wide assessment of DNA methylation.

What does RNA sequencing (RNA-seq) measure?

RNA-seq quantifies RNAs genome-wide to provide a snapshot of gene expression. It detects alternative splicing, non-coding RNAs, and expression changes across biological conditions.

How is differential gene expression analysis defined, and what experimental techniques are typically used?

It is the statistical comparison of gene expression levels between biological conditions to identify genes whose expression changes significantly in response to biological variables, typically using high-throughput techniques like RNA-seq (bulk and single-cell) or microarrays.

What is Co-immunoprecipitation (Co-IP), and what is it used to study?

Co-IP uses an antibody against a specific protein of interest to isolate the protein and its interacting molecules (e.g., other proteins, DNA, RNA). It is used to study protein-protein interactions, protein-RNA binding, and DNA target regions of specific proteins.

In gene regulation studies, what key question can ChIP-seq answer that sequence-specific DNA probes (such as FISH) cannot?

ChIP-seq maps genome-wide binding sites of a transcription factor or histone modification, whereas DNA probes typically report only on the presence or position of specific, predefined loci.

How does Ribo-Seq identify ribosome occupancy, and what is its utility in studying epigenetic or epitranscriptomic modifications?

Ribosome-protected fragments are sequenced to map ribosome binding sites, revealing occupancy in regions like $5'\text{UTRs}$. Comparing occupancy between mRNAs with and without modifications (e.g., $m^6\text{A}$) demonstrates changes in translational efficiency.

What is the function of beads in co-immunoprecipitation?

Beads bind to the antibody targeting the protein of interest, providing a mass/weight that enables centrifugation to pellet and isolate targets, effectively separating bound complexes from unbound cellular debris.

Why is scRNA-seq preferable to bulk RNA-seq for studying rare treatment-resistant cell populations, and what is a limitation?

scRNA-seq reveals a rare population's distinct expression profile that bulk averaging masks. A key limitation is lower sensitivity per cell, which can miss lowly expressed genes and make small expression changes harder to detect.

How do RNA-Seq and microarrays compare in terms of transcript detection and cost-effectiveness?

RNA-Seq detects gene expression differences across the entire transcriptome in an unbiased way, whereas microarrays use predefined probes restricted to specific targets. However, microarrays remain more cost-effective than RNA-Seq.

What key advantages does strand-specific RNA-Seq offer over standard RNA-Seq or microarrays?

Strand-specific RNA-Seq identifies antisense transcripts, non-coding RNAs, and precise exon-intron boundaries, which microarrays miss due to probe limitations and standard RNA-Seq cannot distinguish due to lack of directional information.

What justifies the continued use of microarrays despite advancements like RNA-Seq?

Microarrays remain advantageous due to their cost-effectiveness for large cohorts and high-throughput profiling of known genes.

What are the sequential steps of RNA-Seq library preparation?

RNA isolation followed by fragmentation, cDNA synthesis, adapter ligation, and sequencing.

Why are RNA-associated signals detected by CLIP greatly reduced in CLAP, and what limitation must be considered?

Both methods use UV crosslinking, but CLAP covalently anchors tagged proteins to resin, permitting fully denaturing washes that remove non-covalently associated RNA. However, differences in recovery or sensitivity could also explain the signal loss.

What different biological questions do ChIP-seq and Hi-C answer, and how can chromatin folding influence gene expression?

ChIP-seq maps genomic enrichment of a specific protein or histone modification, while Hi-C maps contact frequencies between genomic regions. Chromatin folding can bring distant enhancers close to target promoters to regulate transcription.

Can combining ChIP-seq and RNA-seq following transcription factor depletion prove direct gene regulation?

No. They identify candidate target genes by mapping factor-associated regions and recording expression changes, but this does not prove direct regulation because binding may be nonfunctional and expression changes may be indirect.

Does detecting Protein Y following Co-IP with an antibody against Protein X prove direct interaction, and how can it be tested?

No, because proteins X and Y may associate indirectly via other components within a complex. A binding assay using purified X and purified Y is required to test for direct interaction.

How do CRISPR-Cas9 and Cre-lox differ in DNA modification, and why is Cre-lox useful for conditional gene manipulation?

CRISPR-Cas9 uses a guide RNA to direct DNA cleavage followed by repair editing, whereas Cre recombinase rearranges DNA at pre-existing loxP sites. Cre-lox is useful conditionally because tissue-specific or inducible Cre expression allows DNA manipulation in selected tissues or at specific times.

What is the main advantage of CRISPR-Cas9 over other transgenic techniques?

CRISPR enables precise, targeted genome editing, facilitating the direct testing of gene function by generating knockouts or specific mutations.