Medical Molecular Biology Exam Questions and Answers

Classification of Long Non-coding RNA

Long non-coding RNAs (lncRNAs) are classified based on their genomic location and orientation relative to protein-coding genes: 1) Intergenic lncRNAs (lincRNAs) occur between genes, 2) Intronic lncRNAs are within introns, 3) Antisense lncRNAs overlap genes on the opposite strand, 4) Bidirectional lncRNAs are transcribed in opposite direction from nearby genes, and 5) Enhancer RNAs (eRNAs) are transcribed from enhancer regions. They can also be classified by cellular location as nuclear or cytoplasmic.

Why DNA is Genetic Material?

DNA is proven as genetic material through several key experiments, notably the Griffith’s transformation experiment and Hershey-Chase experiment. DNA carries hereditary information via its nucleotide sequence, can self-replicate with high fidelity using complementary base pairing, and can undergo mutations that are inherited by daughter cells. Its double-helix structure provides stability while allowing for variations through base sequences, making it ideal for storing and transmitting genetic information across generations.

Etiology of Alzheimer’s Disease (AD)

Alzheimer’s Disease has a complex etiology involving multiple factors. The primary hallmarks are accumulation of beta-amyloid plaques outside neurons and tau protein tangles inside neurons, leading to neural degeneration. Risk factors include aging, genetics (especially APOE4 gene variant), family history, and lifestyle factors. The amyloid cascade hypothesis suggests that abnormal processing of amyloid precursor protein (APP) initiates the pathological cascade, though the exact triggering mechanisms remain debated.

Role of Small RNA in Epigenetics

Small RNAs play crucial roles in epigenetic regulation through various mechanisms. They guide DNA methylation and histone modifications by recruiting chromatin-modifying complexes to specific genomic locations. Key players include siRNAs (targeting heterochromatin formation), piRNAs (silencing transposons in germline cells), and microRNAs (regulating gene expression post-transcriptionally). Through RNA-directed DNA methylation (RdDM), they establish and maintain DNA methylation patterns, affecting gene expression without altering DNA sequence.

What is the cause of amyloid fibrils formation?

Amyloid fibrils form when proteins misfold and aggregate due to several factors: 1) Mutations in protein sequence that destabilize native structure, 2) Environmental conditions like pH changes, temperature, or oxidative stress that promote protein unfolding, 3) Failure of cellular protein quality control systems (chaperones and degradation), and 4) Age-related decline in protein homeostasis. The misfolded proteins expose hydrophobic regions that drive self-assembly into β-sheet-rich fibrils through nucleation-dependent polymerization. 1. Alignment of the molecules to form β-sheets  fastest stage  involves H-bonds 2. Formation of the cross-β structure  slower than step 1  involves Van-der-Waals forces  interdigitation of residues side chains  “steric zipper” structure 3. Fibril formation  involves non-covalent bonds

Structural characteristics of Transcription Factors

Transcription factors (TFs) possess distinct structural domains: 1) DNA-binding domains (DBDs) that recognize specific DNA sequences through motifs like zinc fingers, helix-turn-helix, or leucine zippers; 2) Trans-activation domains (TADs) that interact with other regulatory proteins and the transcription machinery; 3) Oligomerization domains allowing TFs to form functional dimers or multimers; and 4) Regulatory domains that respond to signals like phosphorylation or ligand binding to modulate TF activity.

Functions of Trans-activation domains

Trans-activation domains (TADs) serve multiple crucial regulatory functions: They recruit and interact with coactivators, chromatin-modifying enzymes, and components of the basal transcription machinery (like RNA Polymerase II and TFIID). TADs often contain regions rich in specific amino acids (like glutamine, proline, or acidic residues) that facilitate protein-protein interactions. Through these interactions, TADs help establish the transcription initiation complex and modify local chromatin structure to enable gene activation.

Intrinsic Factors and External Conditions Affecting Protein Folding

Intrinsic factors affecting protein folding include: amino acid sequence (primary structure), hydrophobic/hydrophilic residue distribution, disulfide bonds, and proline content which influences backbone flexibility. External conditions include: temperature (affects molecular motion), pH (influences charge distribution), ionic strength (affects electrostatic interactions), molecular crowding, presence of chaperone proteins, and oxidative conditions. These factors collectively determine the protein’s folding pathway and final conformation through thermodynamic and kinetic mechanisms.

Characteristics of G protein-coupled receptors

G protein-coupled receptors (GPCRs) are characterized by: 1) Seven transmembrane α-helical domains spanning the cell membrane; 2) An extracellular N-terminus and intracellular C-terminus; 3) Three extracellular and three intracellular loops; 4) Ability to interact with G proteins on the intracellular side when activated; 5) Diverse ligand-binding sites that can recognize hormones, neurotransmitters, or other signaling molecules; 6) Capacity to undergo conformational changes upon ligand binding that trigger downstream signaling cascades through G protein activation.

Why is it called N terminus and C terminus

The terms N-terminus and C-terminus refer to the ends of a polypeptide chain based on the chemistry of amino acid polymerization:

N-terminus refers to the end with a free amine (NH2) group - this is where protein synthesis begins. During translation, amino acids are added sequentially starting from this nitrogen-containing end, hence “N-terminus.”

C-terminus refers to the end with a free carboxyl (COOH) group - this is where protein synthesis ends. As new amino acids are added, they join to the carbon-containing carboxyl group of the growing chain, hence “C-terminus.”

The naming convention thus reflects the fundamental chemistry and directionality of protein synthesis from N → C.

Characteristics of Single transmembrane receptors

Single transmembrane receptors (also called receptor tyrosine kinases) have these key characteristics: 1) One α-helical domain spanning the membrane; 2) An extracellular ligand-binding domain that recognizes specific molecules like growth factors; 3) An intracellular domain with enzymatic activity (often tyrosine kinase); 4) Ability to dimerize upon ligand binding; 5) Activation through auto-phosphorylation of tyrosine residues; 6) Multiple phosphorylation sites that serve as docking stations for downstream signaling proteins. They typically function in growth, differentiation, and metabolism signaling pathways.

Primary research areas and distinctive characteristics of epigenetics

Primary research areas in epigenetics include:

DNA Methylation - Study of methyl group additions to cytosine bases, typically at CpG sites, affecting gene expression without changing DNA sequence.

Histone Modifications - Investigation of chemical changes to histone proteins (acetylation, methylation, phosphorylation) that alter chromatin structure and gene accessibility.

Non-coding RNAs - Research on how small RNAs and long non-coding RNAs influence gene expression through various epigenetic mechanisms.

Distinctive characteristics of epigenetics include:

1. Heritability - Epigenetic marks can be passed to daughter cells during cell division and sometimes across generations
2. Reversibility - Unlike genetic changes, epigenetic modifications are potentially reversible
3. Environmental sensitivity - Epigenetic marks can be influenced by environmental factors, diet, stress, and lifestyle
4. Tissue specificity - Different cell types maintain distinct epigenetic patterns despite identical DNA sequences
5. Development regulation - Crucial role in cellular differentiation and development

Metabolic dysregulation stemming from epigenetic alterations

Metabolic dysregulation due to epigenetic alterations involves several interconnected pathways and consequences:

DNA methylation changes can affect key metabolic genes, altering glucose homeostasis, lipid metabolism, and energy balance. For example, altered methylation of PPARGC1A affects mitochondrial function and glucose regulation.

Histone modifications influence metabolic gene expression patterns. Disrupted histone acetylation can affect genes involved in insulin signaling and fatty acid metabolism. H3K9 methylation changes are linked to obesity and diabetes development.

These epigenetic changes can be triggered by dietary factors, obesity, physical inactivity, and aging, creating a cycle where metabolic dysfunction further impacts epigenetic regulation. This leads to conditions like type 2 diabetes, obesity, and metabolic syndrome through disrupted energy homeostasis and cellular metabolism.

Early life exposure to metabolic stressors can establish long-lasting epigenetic patterns affecting lifetime metabolic health.

Medical Molecular Biology Exam Q&A

1. DNA as Hereditary Material

Q: Why DNA serves as the hereditary material?

DNA serves as hereditary material due to four key properties: stability, replication fidelity, information storage capacity, and ability to undergo controlled variation. Its double-helix structure with complementary base pairing enables accurate self-replication, while its sugar-phosphate backbone provides chemical stability. DNA’s four nucleotides can encode vast amounts of genetic information, and its sequence can be modified through mutation and recombination, allowing evolution while maintaining essential functions.

2. Non-coding RNAs

Q: What are non-coding RNAs? Please classify them and provide three examples for each category.

Non-coding RNAs (ncRNAs) are functional RNA molecules that don’t encode proteins but play crucial regulatory and structural roles. They are classified into:

1. Short ncRNAs (< 200 nucleotides):

   • microRNAs (miR-21, let-7, miR-155) - regulate gene expression
   • siRNAs (TAS3, IR71, DCL4) - defend against viruses and transposons
   • piRNAs (piR-1, piR-2, piR-3) - protect germline cells

2. Long ncRNAs (> 200 nucleotides):

   • XIST, HOTAIR, MALAT1 - regulate gene expression and chromatin structure
   • NEAT1, FIRRE, KCNQ1OT1 - organize nuclear architecture
   • TERRA, NORAD, SAMMSON - involved in telomere maintenance and cell survival

Memorable lncRNA Examples:

1. HOTAIR (HOX Transcript Antisense RNA) - Like “hot air” - silences genes in HOX cluster
2. NEAT1 (Nuclear Enriched Abundant Transcript 1) - “Neat and tidy” - organizes nuclear structure
3. MALAT1 (Metastasis Associated Lung Adenocarcinoma Transcript 1) - Think “malady” - linked to cancer spread

3. G Protein-Coupled Receptors and Cyclin-CDK Complexes

Q: Briefly describe G protein-coupled receptors; explain the regulatory role of cyclin-CDK complexes during the G1 phase.

GPCRs are transmembrane proteins with seven membrane-spanning domains that detect external signals (hormones, neurotransmitters, light) and activate internal G proteins. Upon ligand binding, they undergo conformational changes, triggering GDP-GTP exchange in G proteins, which then activate downstream signaling cascades affecting cellular responses.

During G1, cyclin D-CDK4/6 and cyclin E-CDK2 complexes progressively phosphorylate retinoblastoma protein (Rb). This releases E2F transcription factors, promoting expression of S-phase genes. These complexes act as cell cycle checkpoints, ensuring proper conditions before DNA replication commitment at the G1/S transition.

4. Tumor Metabolism

Q: Changes in glucose, lipid, and protein metabolism following tumor onset and progression.

Cancer cells exhibit the Warburg effect - preferentially using glucose through aerobic glycolysis rather than oxidative phosphorylation, even in oxygen-rich conditions. They upregulate glucose transporters and increase glucose uptake dramatically. Lipid metabolism shifts toward fatty acid synthesis to support membrane formation. Protein synthesis increases while protein degradation decreases, supporting rapid growth. Tumors also increase glutamine consumption as an alternative energy source and for biosynthesis of macromolecules.

5. Protein Misfolding

Q: Causes of misfolding and protein aggregation

1. Primary causes:

   • Mutations affecting amino acid sequence
   • Errors in translation or post-translational modifications
   • Oxidative stress causing protein modifications
   • High temperature disrupting protein structure

2. Environmental factors:

   • pH changes affecting protein charge distribution
   • High salt concentrations disrupting ionic interactions
   • Mechanical stress
   • Absence of proper chaperone proteins

3. Age-related factors:

   • Decreased efficiency of protein quality control
   • Accumulation of damaged proteins
   • Reduced chaperone function
   • Impaired protein degradation systems

6. Human Genome Characteristics

Q: Characteristics of the Human Genome

1. Size and Structure:

   • Contains approximately 3 billion base pairs
   • Organized into 23 chromosome pairs
   • Only about 2% consists of protein-coding genes

2. Gene Distribution:

   • Contains roughly 20,000-25,000 genes
   • Genes are unevenly distributed across chromosomes
   • Many genes have multiple splice variants

3. Non-coding Regions:

   • Large portions are repetitive sequences
   • Contains regulatory elements like enhancers and silencers
   • Includes mobile genetic elements (transposons)

4. Unique Features:

   • High GC content in gene-rich regions
   • CpG islands near promoters
   • Complex regulatory networks
   • Extensive alternative splicing
   • High degree of conservation in crucial regions

7. Epigenetics

Q: Definition and characteristics of epigenetics, with two illustrative examples.

Epigenetics refers to heritable changes in gene expression that don’t involve changes to DNA sequence. Key characteristics include:

• Reversibility of modifications
• Inheritance through cell divisions
• Environmental influence
• Tissue-specific patterns
• Dynamic regulation during development

Two illustrative examples:

1. DNA Methylation in Cancer:

   • Hypermethylation of tumor suppressor gene promoters (like BRCA1) silences these protective genes, promoting cancer development.

2. Imprinting in Prader-Willi Syndrome:

   • Parent-specific methylation patterns on chromosome 15 determine gene expression. Disruption leads to developmental disorders.

8. Long Non-coding RNAs

Q: Major classes of lncRNAs and their modes of regulation.

1. cis-acting lncRNAs:

   • Act near their transcription site
   • Example: XIST silences X chromosome through chromatin modification
   • Regulate neighboring gene expression

2. trans-acting lncRNAs:

   • Function away from transcription site
   • Example: HOTAIR regulates HOX genes across chromosomes
   • Often form scaffolds for protein complexes

3. Enhancer RNAs (eRNAs):

   • Transcribed from enhancer regions
   • Facilitate enhancer-promoter interactions
   • Regulate gene activation

4. Natural Antisense Transcripts (NATs):

   • Transcribed from opposite DNA strand
   • Form RNA-RNA duplexes
   • Can block transcription or modify splicing

9. Protein Folding

Q: Describe the protein folding process and its main influencing factors.

Protein Folding Process:

• Primary structure (amino acid sequence) initiates folding
• Secondary structures form through hydrogen bonding (α-helices, β-sheets)
• Hydrophobic collapse drives tertiary structure formation
• Multiple subunits assemble into quaternary structure (if applicable)

Main Influencing Factors:

1. Internal Factors:

   • Amino acid sequence
   • Hydrophobic interactions
   • Disulfide bonds
   • Salt bridges
   • Hydrogen bonding

2. Environmental Factors:

   • Temperature
   • pH
   • Ionic strength
   • Molecular crowding
   • Presence of chaperone proteins

3. Cellular Conditions:

   • Redox state
   • Metal ions
   • Post-translational modifications
   • Cellular compartment conditions

10. Receptors and Cell Cycle

Q: Definition of Receptor, Four Main Types of Single Transmembrane Receptors.

Receptor Definition: A receptor is a protein molecule that receives and responds to specific chemical signals from outside the cell, triggering intracellular signaling pathways and cellular responses.

Four Main Types of Single Transmembrane Receptors:

1. Receptor Tyrosine Kinases (RTKs):

   • Activated by growth factors
   • Dimerize upon ligand binding
   • Auto-phosphorylate tyrosine residues

2. Receptor Serine/Threonine Kinases:

   • Respond to TGF-β family proteins
   • Phosphorylate serine/threonine residues
   • Form heterodimeric complexes

3. Cytokine Receptors:

   • Lack intrinsic enzyme activity
   • Associate with JAK kinases
   • Activate STAT transcription factors

4. Death Receptors:

   • Trigger apoptosis
   • Contain death domains
   • Activate caspase cascades

Q: Definition of Cell Cycle, Role of Cell Cycle Checkpoints

Cell Cycle Definition: The cell cycle is an ordered sequence of events where a cell duplicates its contents and divides into two daughter cells. It consists of four main phases: G1 (growth), S (DNA synthesis), G2 (preparation for division), and M (mitosis/division).

Role of Cell Cycle Checkpoints:

1. G1 Checkpoint:

   • Checks cell size and nutrient availability
   • Ensures DNA integrity
   • Controls commitment to S phase

2. G2 Checkpoint:

   • Verifies complete DNA replication
   • Checks for DNA damage
   • Ensures cell readiness for mitosis

3. Metaphase Checkpoint:

   • Confirms proper chromosome alignment
   • Verifies spindle attachment
   • Controls anaphase entry

Medical Molecular Biology Exam Questions & Answers

1. Apoptosis and Its Changes

Q: Define apoptosis, and describe its morphological and biochemical changes.

Apoptosis is programmed cell death - a controlled, energy-dependent process essential for tissue homeostasis and development. Morphologically, cells undergo chromatin condensation, nuclear fragmentation, cell shrinkage, membrane blebbing, and formation of apoptotic bodies. Biochemically, it involves activation of caspase cascades, DNA fragmentation by endonucleases, phosphatidylserine externalization, and mitochondrial changes including cytochrome c release. These changes ensure cell components are neatly packaged for phagocytosis without triggering inflammation.

2. Cell Differentiation

Q: How do cells differentiate during embryonic development, and what specific functional changes occur?

Cell differentiation during embryonic development occurs through selective gene expression controlled by transcription factors and epigenetic modifications. Cells progressively restrict their developmental potential, transitioning from totipotent to pluripotent to specialized cell types. This involves chromatin remodeling, specific protein synthesis, and morphological changes. Functionally, cells acquire tissue-specific features - for example, muscle cells develop contractile proteins, while neurons form synaptic connections and express neurotransmitter receptors.

3. Oncogene Activation and Tumorigenesis

Q: The molecular mechanisms by which oncogene activation drives tumorigenesis.

Oncogene activation promotes tumorigenesis through multiple molecular mechanisms. These include stimulating excessive cell proliferation via constitutively active growth signaling (like RAS mutations), inhibiting apoptosis through upregulation of survival factors (like BCL-2), promoting angiogenesis via VEGF expression, and dysregulating cell cycle checkpoints. Activated oncogenes also often trigger genomic instability and alter cellular metabolism to support rapid growth through the Warburg effect.

4. α1 Gene Insertion

Q: Given an α1 gene insertion, what are the procedures for genetic diagnosis and manipulation?

For genetic diagnosis of an α1 gene insertion, the process involves DNA extraction from patient samples followed by PCR amplification of the target region. Southern blot analysis can confirm insertion size and location. For precise detection, DNA sequencing (Sanger or NGS) determines the exact insertion site and sequence. Genetic manipulation can be achieved through CRISPR-Cas9 gene editing, using specifically designed guide RNAs targeting the insertion site, followed by either removal of the inserted sequence or HDR-mediated repair with a correct template.

5. Gene Function Loss

Q: Describe how gene and genome abnormalities can lead to a loss of gene function.

Gene and genome abnormalities can disrupt gene function through multiple mechanisms. Point mutations can create premature stop codons (nonsense mutations) or alter splice sites, leading to truncated or nonfunctional proteins. Deletions or insertions can cause frameshift mutations, disrupting the reading frame. Chromosomal abnormalities like translocations can disconnect genes from their regulatory elements. Copy number variations can result in dosage imbalances, while epigenetic modifications can silence gene expression without sequence changes.

6. Cyclins in Cell Cycle

Q: Describe the functional roles of cyclins produced during different phases of the cell cycle, within each respective phase.

Cyclins regulate cell cycle progression through phase-specific expression and CDK binding. G1 cyclins (D, E) promote G1/S transition by initiating DNA replication preparation. S-phase cyclins (A) drive DNA synthesis and centrosome duplication. G2/M cyclins (A, B) trigger mitotic entry by activating proteins needed for chromosome condensation, nuclear envelope breakdown, and spindle formation. Each cyclin-CDK complex phosphorylates specific targets essential for their respective phase transitions.

7. Caspase-Dependent Apoptosis

Q: Please describe two pathways of caspase-dependent apoptosis.

The two main caspase-dependent apoptosis pathways are:

1. Extrinsic (Death Receptor) Pathway: Initiated by external death ligands (like FasL, TNF-α) binding to death receptors, triggering DISC formation, which activates caspase-8. This then directly activates executioner caspases-3/7, leading to cell death.

2. Intrinsic (Mitochondrial) Pathway: Triggered by internal stress signals, causing Bax/Bak activation and mitochondrial outer membrane permeabilization. Released cytochrome c forms the apoptosome with Apaf-1, activating caspase-9, which then activates caspases-3/7.

Both pathways converge at executioner caspases, causing cellular degradation.

8. Stem Cells Comparison

Q: Distinguishing characteristics of normal stem cells versus tumor stem cells.

Normal stem cells and tumor stem cells differ in key aspects. Normal stem cells have regulated self-renewal controlled by external signals and maintain genomic stability, differentiating into specific cell types when needed. In contrast, tumor stem cells exhibit uncontrolled self-renewal, genomic instability, and aberrant differentiation. They possess drug resistance mechanisms, can initiate tumor formation, and express altered surface markers. Normal stem cells maintain tissue homeostasis, while tumor stem cells drive tumor growth and metastasis.

9. Epigenetic Regulation

Q: Epigenetic Regulation of Gene Expression

Epigenetic regulation controls gene expression without changing DNA sequence through several mechanisms. DNA methylation at CpG sites typically represses gene expression by preventing transcription factor binding. Histone modifications like acetylation (activating) and methylation (can be activating or repressing) alter chromatin accessibility. Chromatin remodeling complexes change nucleosome positioning, while non-coding RNAs can recruit modifying enzymes. These reversible modifications create heritable expression patterns crucial for development and cell identity.

10. Protein Structure

Q: Briefly describe the quaternary structure of proteins and the forces involved in each level of protein structure.

The quaternary structure represents the assembly of multiple polypeptide chains (subunits) into a functional protein complex. The forces involved across protein structure levels are:

Primary: Peptide bonds between amino acids Secondary: Hydrogen bonds forming α-helices and β-sheets Tertiary: Hydrophobic interactions, hydrogen bonds, ionic bonds, disulfide bridges Quaternary: Same forces as tertiary, plus subunit interfaces stabilized by hydrophobic interactions, salt bridges, and sometimes metal ions or cofactors

For example, hemoglobin’s quaternary structure consists of four subunits held together by these non-covalent interactions.

11. TGF-β Pathway

Q: Describe the TGF-β signaling pathway.

The TGF-β signaling pathway begins when TGF-β ligand binds to type II receptors (TβRII), which then recruit and phosphorylate type I receptors (TβRI). Activated TβRI phosphorylates receptor-regulated SMADs (R-SMADs 2/3), which then form complexes with co-SMAD4. These complexes translocate to the nucleus and regulate target gene expression in cooperation with other transcription factors. The pathway is crucial for cell growth, differentiation, and apoptosis regulation.

12. PI3K-AKT Pathway

Q: Describe the mechanistic roles of the PI3K-AKT signaling pathway in glucose and lipid metabolism.

The PI3K-AKT pathway plays a central role in metabolic regulation through multiple mechanisms: Upon insulin stimulation, PI3K generates PIP3, activating AKT, which then:

1. Promotes glucose uptake by triggering GLUT4 translocation to cell membrane
2. Stimulates glycogen synthesis by inhibiting GSK3
3. Enhances glucose metabolism through activation of glycolytic enzymes
4. Regulates lipid metabolism by activating lipogenic enzymes and inhibiting lipolysis through mTOR signaling
5. Suppresses gluconeogenesis by inhibiting FOXO transcription factors

These coordinated actions maintain glucose homeostasis and regulate energy storage.

13. Oncogene Activation

Q: Describe the mechanisms of oncogene activation.

Oncogenes can be activated through several molecular mechanisms:

1. Point mutations that create constitutively active proteins (like RAS mutations)
2. Chromosomal translocations that create fusion proteins or place genes under stronger promoters (like BCR-ABL)
3. Gene amplification leading to increased copy number and overexpression (like HER2/neu)
4. Promoter alterations that increase transcription
5. Loss of negative regulatory elements
6. DNA hypomethylation leading to aberrant expression
7. Insertion of viral enhancers near proto-oncogenes

These changes result in uncontrolled cell growth signaling and cancer development.

Medical Molecular Biology Exam Q&A

Q1: Describe the guanylate cyclase (GC) signaling pathway.

The guanylate cyclase (GC) signaling pathway begins when ligands like natriuretic peptides bind to membrane-bound GC receptors, activating their intracellular catalytic domain. This activation converts GTP to cyclic GMP (cGMP), which acts as a second messenger. Increased cGMP levels activate protein kinase G (PKG), triggering downstream phosphorylation cascades that regulate various cellular processes, including smooth muscle relaxation, ion channel function, and gene expression.

Q2: Briefly outline the implementation strategies of the Human Proteome Project.

The Human Proteome Project employs two complementary strategies: chromosome-centric (C-HPP) and biology/disease-driven (B/D-HPP) approaches. C-HPP systematically maps proteins encoded by each chromosome, while B/D-HPP focuses on protein networks in specific biological processes and diseases. The project utilizes mass spectrometry, antibody-based detection, and bioinformatics to identify and characterize all human proteins, their modifications, and interactions.

Q3: Explain the fundamental principles of RNA interference.

RNA interference (RNAi) is a biological process where small RNA molecules suppress gene expression through sequence-specific targeting. Double-stranded RNA is processed by Dicer into small interfering RNAs (siRNAs), which are then loaded into the RISC complex. The guide strand directs RISC to complementary mRNA sequences, leading to mRNA cleavage or translational repression, effectively silencing the target gene.

Q4: Describe the key characteristics of transcriptional regulation in eukaryotic genes.

Eukaryotic transcriptional regulation involves multiple layers of control through enhancers, silencers, and promoter elements that can be thousands of base pairs from the transcription start site. Chromatin structure plays a crucial role, with histone modifications and DNA methylation affecting accessibility. Transcription factors work combinatorially with co-activators and co-repressors to fine-tune gene expression in response to cellular signals.

Q5: Describe the fundamental process of recombinant DNA technology.

Recombinant DNA technology involves isolating and manipulating DNA from different sources to create novel genetic combinations. The process begins with DNA isolation and restriction enzyme digestion to create compatible ends. These fragments are then joined using DNA ligase to form recombinant molecules, typically within a vector (like plasmids). The vectors are introduced into host cells for replication and expression of the inserted genes.