What is the elution order in Size-Exclusion (Gel Filtration) Chromatography and why?

LARGE proteins elute FIRST; small proteins elute LAST. The stationary column contains porous polymer beads; large molecules are excluded from pores and travel through the void volume, while small molecules enter pores and follow a tortuous, prolonged path.

What is the difference between Cation-Exchange and Anion-Exchange Chromatography?

Named for the charge of the solutes they BIND: • Cation-Exchange: Stationary phase is negatively charged; binds positively charged (basic) proteins; eluted by increasing salt [Na+] or raising pH. • Anion-Exchange: Stationary phase is positively charged (e.g., DEAE); binds negatively charged (acidic) proteins; eluted by increasing salt [Cl-] or lowering pH.

What information does Mass Spectrometry provide and what is the base peak versus molecular ion peak?

Ionizes molecules and separates ions based on mass-to-charge ratio (m/z). • Base Peak: The tallest peak on the spectrum, assigned 100% relative abundance. • Molecular Ion Peak (M+): The unfragmented radical cation representing the total molecular weight of the analyte.

How do RT-qPCR and standard PCR differ in purpose?

Standard PCR amplifies genomic DNA fragments qualitatively. Reverse Transcription Quantitative PCR (RT-qPCR) uses reverse transcriptase to convert cellular mRNA into complementary DNA (cDNA), and tracks fluorescent reporter accumulation (e.g., SYBR Green or TaqMan) to measure gene expression levels quantitatively.

What are the steps and detection mechanism of a Western Blot?

1. Separate proteins by SDS-PAGE. 2. Transfer proteins electrophoretically to a nitrocellulose or PVDF membrane. 3. Block non-specific binding sites with BSA or nonfat milk. 4. Incubate with primary antibody specific to target protein. 5. Incubate with enzyme-conjugated secondary antibody (e.g., horseradish peroxidase / HRP). 6. Add chemiluminescent substrate to visualize band intensity.

What is the strategic methodology for CARS 'Weaken the Author's Argument' questions?

1. Identify the author's primary conclusion. 2. Pinpoint the unstated necessary assumption bridging evidence to conclusion. 3. Select the answer choice that, if true, introduces an empirical fact that directly refutes the author's necessary assumption.

In MCAT biological passages, what do asterisks and error bars on bar graphs represent?

• Asterisks (*p < 0.05, **p < 0.01): Indicate that the difference between experimental and control groups is statistically significant (null hypothesis rejected). • Error Bars: Typically show Standard Deviation (SD) or Standard Error of the Mean (SEM); overlapping SEM error bars generally mean the difference is not statistically significant.

How do Normal-Phase and Reverse-Phase High-Performance Liquid Chromatography (HPLC) differ?

• Normal-Phase HPLC: Stationary phase is polar (silica); mobile phase is nonpolar; nonpolar solutes elute FIRST. • Reverse-Phase HPLC: Stationary phase is nonpolar (hydrophobic C18 alkyl chains); mobile phase is polar; polar solutes elute FIRST, nonpolar solutes elute LAST.

How does Isoelectric Focusing (IEF) separate proteins?

Proteins are loaded onto a gel with a stable immobilized pH gradient. In an electric field, proteins migrate until they reach the pH equal to their isoelectric point (pH = pI), where their net electric charge becomes zero and electrical force ceases.

What is the mechanistic difference between CRISPR/Cas9 Gene Knockout and siRNA Knockdown?

• CRISPR/Cas9: Targeted sgRNA directs Cas9 endonuclease to introduce double-strand DNA breaks at specific genomic loci, causing frameshift indels via NHEJ that PERMANENTLY eliminate gene function. • siRNA / RNAi: Small interfering RNA guides the cytoplasmic RISC complex to bind and degrade complementary mRNA, TRANSIENTLY knocking down protein translation.

What is the difference between Positive and Negative Experimental Controls in biological assays?

• Positive Control: An experimental condition treated with a known active reagent expected to produce the desired effect, confirming assay sensitivity and system viability. • Negative Control: An untreated or vehicle-treated condition where no effect should occur, confirming assay specificity and ruling out false-positive contamination.

What are the molecular principles and separation criteria of SDS-PAGE electrophoresis?

Sodium dodecyl sulfate (SDS) denatures proteins and coats them with a uniform negative charge (~1 SDS molecule per 2 amino acids), masking native charges and rendering the charge-to-mass ratio uniform. Migration through the polyacrylamide gel matrix toward the positive anode separates proteins SOLELY based on molecular weight (smaller proteins migrate faster and further).

In MCAT CARS, how do you distinguish the author's voice from cited scholarly views?

Look for attribution markers ('historians argue', 'critics maintain', 'it has been claimed'). The author's voice appears in subsequent evaluations, qualifications, or pivots ('however, this view overlooks...'). Never attribute a cited opposing scholar's claim to the passage author.

What do Forward Scatter (FSC) and Side Scatter (SSC) measure in Flow Cytometry?

Cells in fluid flow pass single-file through a focused laser beam: • Forward Scatter (FSC): Diffraction angle proportional to cell SIZE. • Side Scatter (SSC): 90-degree refraction/reflection proportional to internal cell COMPLEXITY and GRANULARITY.

Why is an observed genetic correlation or biomarker elevation insufficient to prove causality in MCAT passages?

Co-occurrence can be an epiphenomenon or downstream consequence of an unmeasured common regulator. Establishing causality requires rescue experiments, gene knockouts, or biochemical inhibitor treatments demonstrating that manipulating factor X directly changes outcome Y.

What three elements must an engineered plasmid vector contain for recombinant molecular cloning?

1. Origin of Replication (ori): Ensures autonomous bacterial replication. 2. Selectable Marker: Typically an antibiotic resistance gene (e.g., ampR) to kill non-transformed bacteria. 3. Multiple Cloning Site (MCS) / Polylinker: Unique restriction enzyme cleavage sites for inserting foreign gene inserts.

How does Sanger DNA Sequencing use dideoxynucleotides (ddNTPs) to determine nucleotide sequences?

ddNTPs lack the 3'-OH group required for phosphodiester bond formation with the incoming nucleotide. Incorporating a fluorescently tagged ddNTP terminates chain elongation, generating fragments of every length that are separated by capillary electrophoresis.

How does an Enzyme-Linked Immunosorbent Assay (ELISA) quantify antigens?

Sandwich ELISA coats well plates with capture antibody specific to target antigen -> antigen sample binds -> washed -> enzyme-linked detection antibody binds to different antigen epitope -> chromogenic substrate added -> optical absorbance measured via spectrophotometry is proportional to antigen concentration.

In CARS, why are answer choices with extreme modifiers almost always incorrect?

Modifiers like 'solely', 'exclusively', 'never', 'undeniably', or 'wholly' require absolute proof in the text. CARS passages are characterized by scholarly nuance, making moderate answers with words like 'may', 'partially', or 'tends to' much more defensible.

What is the purpose of a Coomassie Brilliant Blue loading control in Western Blot experiments?

Probing for a housekeeping protein (e.g., beta-actin, GAPDH, alpha-tubulin) confirms that equal total protein amounts were loaded into every gel well, ensuring differences in target band intensity reflect genuine biological regulation rather than pipetting error.

What are the two separation dimensions in Two-Dimensional (2D) Gel Electrophoresis?

1. First Dimension: Isoelectric Focusing (separates proteins horizontally by isoelectric point, pI). 2. Second Dimension: SDS-PAGE (separates proteins vertically by molecular mass).

What is the purpose of Single-Blind and Double-Blind experimental procedures?

• Single-Blind: Research participants are unaware of whether they are receiving the experimental drug or placebo, controlling for Participant Expectancy / Placebo Effects. • Double-Blind: BOTH participants AND experimenters assessing outcomes are unaware of group assignment, controlling for both Placebo Effects and Experimenter/Observer Bias.

In CARS, how do you handle 'Analogous Scenario' questions?

Strip away the topical details from the passage situation to derive the abstract structural and causal relationship. Scan the answer choices to identify the novel scenario that matches the exact same abstract relational pattern.

How does Affinity Chromatography work and how is a 6xHis-tagged protein purified?

Purifies proteins based on high-affinity biological interactions with immobilized ligands on beads. Recombinant proteins with a 6xHis-tag bind specifically to Ni2+-nitrilotriacetic acid (Ni-NTA) agarose columns and are eluted competitively by adding Imidazole (which mimics the histidine side chain).

What are the structural features of DNA Restriction Endonuclease recognition sites?

Type II restriction endonucleases recognize specific 4-to-8 base pair Palindromic sequences, where the 5'-to-3' sequence on one strand is identical to the 5'-to-3' sequence on the antiparallel complementary strand (e.g., EcoRI: 5'-GAATTC-3'). Cleavage produces either cohesive 'sticky' overhangs or blunt ends.

What target biomolecule does each blotting technique detect (mnemonic: SNOW DROP)?

• Southern Blot: DNA (uses labeled single-stranded DNA/RNA probe). • Northern Blot: RNA / mRNA transcript abundance (uses labeled probe). • O: O • Western Blot: Protein abundance and post-translational modifications (uses specific antibodies).

What is the formula for the Retention Factor (Rf) in Thin-Layer Chromatography (TLC)?

Rf = (Distance traveled by compound) / (Distance traveled by solvent front). On polar silica gel plates with nonpolar organic solvent, nonpolar compounds interact weakly with silica and travel furthest (highest Rf), while polar compounds interact strongly and travel least (lowest Rf).

What parameters determine retention time in Gas Chromatography (GC)?

Separates volatile, vaporized compounds carried by an inert gas (He, N2) through a column coated with liquid stationary phase. Retention time is governed by: (1) Boiling Point (lower boiling point compounds vaporize into gas phase and elute FIRST); (2) Polarity matching the stationary phase.

What are the three thermal steps and necessary reagents in a Polymerase Chain Reaction (PCR) cycle?

• Steps: (1) Denaturation (95°C, separates dsDNA strands); (2) Primer Annealing (50-65°C, forward and reverse primers bind complementary sequences); (3) Primer Extension (72°C, heat-stable Taq polymerase synthesizes complementary strands). • Reagents: Template DNA, sequence-specific DNA primers, dNTPs, Mg2+ buffer, Taq polymerase.

What is the difference between Reducing and Non-Reducing SDS-PAGE?

• Reducing SDS-PAGE: Includes a reducing agent (beta-mercaptoethanol or DTT) that cleaves covalent disulfide bonds (-S-S-), breaking multimeric complexes joined by disulfides into individual monomeric subunits. • Non-Reducing SDS-PAGE: Retains disulfide bonds intact; multimeric disulfide-linked complexes run as single intact bands.

How do you interpret a Lineweaver-Burk plot comparing an uninhibited enzyme to an inhibited enzyme?

• If lines intersect on y-axis: Competitive inhibition (same Vmax, Km increased). • If lines intersect on negative x-axis: Noncompetitive inhibition (same Km, Vmax decreased). • If lines are parallel: Uncompetitive inhibition (both Km and Vmax decreased proportionally).

How do you deduce the molecular weight of a protein complex with subunits from SDS-PAGE data?

Compare non-reducing lane (intact complex) with reducing lane (+ beta-mercaptoethanol). If non-reducing lane shows a single 150 kDa band and reducing lane shows 50 kDa and 25 kDa bands, the complex is a heteromultimer composed of disulfide-linked 50 kDa and 25 kDa subunits (e.g., two 50 kDa and two 25 kDa subunits, like IgG antibodies).

Bioquímica — Avançat (C1/C2) 4: Advanced Passage Reasoning & High-Yield Lab Techniques

[Català] Bioquímica: SDS-PAGE, Western/Southern/Northern blotting, PCR, chromatography (size-exclusion, affinity, ion-exchange, HPLC), mass spectrometry, NMR spectroscopy, and CARS passage inference logic.

Level: advanced
Languages: ca → ca
Cards: 32
Markdown: Bioquímica — Avançat (C1/C2) 4: Advanced Passage Reasoning & High-Yield Lab Techniques (.md)

Flashcards (32)

#	Front (Term / Question)	Back (Definition / Answer)
1	What is the elution order in Size-Exclusion (Gel Filtration) Chromatography and why?	LARGE proteins elute FIRST; small proteins elute LAST. The stationary column contains porous polymer beads; large molecules are excluded from pores and travel through the void volume, while small molecules enter pores and follow a tortuous, prolonged path.
2	What is the difference between Cation-Exchange and Anion-Exchange Chromatography?	Named for the charge of the solutes they BIND: • Cation-Exchange: Stationary phase is negatively charged; binds positively charged (basic) proteins; eluted by increasing salt [Na+] or raising pH. • Anion-Exchange: Stationary phase is positively charged (e.g., DEAE); binds negatively charged (acidic) proteins; eluted by increasing salt [Cl-] or lowering pH.
3	What information does Mass Spectrometry provide and what is the base peak versus molecular ion peak?	Ionizes molecules and separates ions based on mass-to-charge ratio (m/z). • Base Peak: The tallest peak on the spectrum, assigned 100% relative abundance. • Molecular Ion Peak (M+): The unfragmented radical cation representing the total molecular weight of the analyte.
4	How do RT-qPCR and standard PCR differ in purpose?	Standard PCR amplifies genomic DNA fragments qualitatively. Reverse Transcription Quantitative PCR (RT-qPCR) uses reverse transcriptase to convert cellular mRNA into complementary DNA (cDNA), and tracks fluorescent reporter accumulation (e.g., SYBR Green or TaqMan) to measure gene expression levels quantitatively.
5	What are the steps and detection mechanism of a Western Blot?	1. Separate proteins by SDS-PAGE. 2. Transfer proteins electrophoretically to a nitrocellulose or PVDF membrane. 3. Block non-specific binding sites with BSA or nonfat milk. 4. Incubate with primary antibody specific to target protein. 5. Incubate with enzyme-conjugated secondary antibody (e.g., horseradish peroxidase / HRP). 6. Add chemiluminescent substrate to visualize band intensity.
6	What is the strategic methodology for CARS 'Weaken the Author's Argument' questions?	1. Identify the author's primary conclusion. 2. Pinpoint the unstated necessary assumption bridging evidence to conclusion. 3. Select the answer choice that, if true, introduces an empirical fact that directly refutes the author's necessary assumption.
7	In MCAT biological passages, what do asterisks and error bars on bar graphs represent?	• Asterisks (p < 0.05, *p < 0.01): Indicate that the difference between experimental and control groups is statistically significant (null hypothesis rejected). • Error Bars: Typically show Standard Deviation (SD) or Standard Error of the Mean (SEM); overlapping SEM error bars generally mean the difference is not statistically significant.
8	How do Normal-Phase and Reverse-Phase High-Performance Liquid Chromatography (HPLC) differ?	• Normal-Phase HPLC: Stationary phase is polar (silica); mobile phase is nonpolar; nonpolar solutes elute FIRST. • Reverse-Phase HPLC: Stationary phase is nonpolar (hydrophobic C18 alkyl chains); mobile phase is polar; polar solutes elute FIRST, nonpolar solutes elute LAST.
9	How does Isoelectric Focusing (IEF) separate proteins?	Proteins are loaded onto a gel with a stable immobilized pH gradient. In an electric field, proteins migrate until they reach the pH equal to their isoelectric point (pH = pI), where their net electric charge becomes zero and electrical force ceases.
10	What is the mechanistic difference between CRISPR/Cas9 Gene Knockout and siRNA Knockdown?	• CRISPR/Cas9: Targeted sgRNA directs Cas9 endonuclease to introduce double-strand DNA breaks at specific genomic loci, causing frameshift indels via NHEJ that PERMANENTLY eliminate gene function. • siRNA / RNAi: Small interfering RNA guides the cytoplasmic RISC complex to bind and degrade complementary mRNA, TRANSIENTLY knocking down protein translation.
11	What is the difference between Positive and Negative Experimental Controls in biological assays?	• Positive Control: An experimental condition treated with a known active reagent expected to produce the desired effect, confirming assay sensitivity and system viability. • Negative Control: An untreated or vehicle-treated condition where no effect should occur, confirming assay specificity and ruling out false-positive contamination.
12	What are the molecular principles and separation criteria of SDS-PAGE electrophoresis?	Sodium dodecyl sulfate (SDS) denatures proteins and coats them with a uniform negative charge (~1 SDS molecule per 2 amino acids), masking native charges and rendering the charge-to-mass ratio uniform. Migration through the polyacrylamide gel matrix toward the positive anode separates proteins SOLELY based on molecular weight (smaller proteins migrate faster and further).
13	In MCAT CARS, how do you distinguish the author's voice from cited scholarly views?	Look for attribution markers ('historians argue', 'critics maintain', 'it has been claimed'). The author's voice appears in subsequent evaluations, qualifications, or pivots ('however, this view overlooks...'). Never attribute a cited opposing scholar's claim to the passage author.
14	What do Forward Scatter (FSC) and Side Scatter (SSC) measure in Flow Cytometry?	Cells in fluid flow pass single-file through a focused laser beam: • Forward Scatter (FSC): Diffraction angle proportional to cell SIZE. • Side Scatter (SSC): 90-degree refraction/reflection proportional to internal cell COMPLEXITY and GRANULARITY.
15	Why is an observed genetic correlation or biomarker elevation insufficient to prove causality in MCAT passages?	Co-occurrence can be an epiphenomenon or downstream consequence of an unmeasured common regulator. Establishing causality requires rescue experiments, gene knockouts, or biochemical inhibitor treatments demonstrating that manipulating factor X directly changes outcome Y.
16	What three elements must an engineered plasmid vector contain for recombinant molecular cloning?	1. Origin of Replication (ori): Ensures autonomous bacterial replication. 2. Selectable Marker: Typically an antibiotic resistance gene (e.g., ampR) to kill non-transformed bacteria. 3. Multiple Cloning Site (MCS) / Polylinker: Unique restriction enzyme cleavage sites for inserting foreign gene inserts.
17	How does Sanger DNA Sequencing use dideoxynucleotides (ddNTPs) to determine nucleotide sequences?	ddNTPs lack the 3'-OH group required for phosphodiester bond formation with the incoming nucleotide. Incorporating a fluorescently tagged ddNTP terminates chain elongation, generating fragments of every length that are separated by capillary electrophoresis.
18	How does an Enzyme-Linked Immunosorbent Assay (ELISA) quantify antigens?	Sandwich ELISA coats well plates with capture antibody specific to target antigen -> antigen sample binds -> washed -> enzyme-linked detection antibody binds to different antigen epitope -> chromogenic substrate added -> optical absorbance measured via spectrophotometry is proportional to antigen concentration.
19	In CARS, why are answer choices with extreme modifiers almost always incorrect?	Modifiers like 'solely', 'exclusively', 'never', 'undeniably', or 'wholly' require absolute proof in the text. CARS passages are characterized by scholarly nuance, making moderate answers with words like 'may', 'partially', or 'tends to' much more defensible.
20	What is the purpose of a Coomassie Brilliant Blue loading control in Western Blot experiments?	Probing for a housekeeping protein (e.g., beta-actin, GAPDH, alpha-tubulin) confirms that equal total protein amounts were loaded into every gel well, ensuring differences in target band intensity reflect genuine biological regulation rather than pipetting error.
21	What are the two separation dimensions in Two-Dimensional (2D) Gel Electrophoresis?	1. First Dimension: Isoelectric Focusing (separates proteins horizontally by isoelectric point, pI). 2. Second Dimension: SDS-PAGE (separates proteins vertically by molecular mass).
22	What is the purpose of Single-Blind and Double-Blind experimental procedures?	• Single-Blind: Research participants are unaware of whether they are receiving the experimental drug or placebo, controlling for Participant Expectancy / Placebo Effects. • Double-Blind: BOTH participants AND experimenters assessing outcomes are unaware of group assignment, controlling for both Placebo Effects and Experimenter/Observer Bias.
23	In CARS, how do you handle 'Analogous Scenario' questions?	Strip away the topical details from the passage situation to derive the abstract structural and causal relationship. Scan the answer choices to identify the novel scenario that matches the exact same abstract relational pattern.
24	How does Affinity Chromatography work and how is a 6xHis-tagged protein purified?	Purifies proteins based on high-affinity biological interactions with immobilized ligands on beads. Recombinant proteins with a 6xHis-tag bind specifically to Ni2+-nitrilotriacetic acid (Ni-NTA) agarose columns and are eluted competitively by adding Imidazole (which mimics the histidine side chain).
25	What are the structural features of DNA Restriction Endonuclease recognition sites?	Type II restriction endonucleases recognize specific 4-to-8 base pair Palindromic sequences, where the 5'-to-3' sequence on one strand is identical to the 5'-to-3' sequence on the antiparallel complementary strand (e.g., EcoRI: 5'-GAATTC-3'). Cleavage produces either cohesive 'sticky' overhangs or blunt ends.
26	What target biomolecule does each blotting technique detect (mnemonic: SNOW DROP)?	• Southern Blot: DNA (uses labeled single-stranded DNA/RNA probe). • Northern Blot: RNA / mRNA transcript abundance (uses labeled probe). • O: O • Western Blot: Protein abundance and post-translational modifications (uses specific antibodies).
27	What is the formula for the Retention Factor (Rf) in Thin-Layer Chromatography (TLC)?	Rf = (Distance traveled by compound) / (Distance traveled by solvent front). On polar silica gel plates with nonpolar organic solvent, nonpolar compounds interact weakly with silica and travel furthest (highest Rf), while polar compounds interact strongly and travel least (lowest Rf).
28	What parameters determine retention time in Gas Chromatography (GC)?	Separates volatile, vaporized compounds carried by an inert gas (He, N2) through a column coated with liquid stationary phase. Retention time is governed by: (1) Boiling Point (lower boiling point compounds vaporize into gas phase and elute FIRST); (2) Polarity matching the stationary phase.
29	What are the three thermal steps and necessary reagents in a Polymerase Chain Reaction (PCR) cycle?	• Steps: (1) Denaturation (95°C, separates dsDNA strands); (2) Primer Annealing (50-65°C, forward and reverse primers bind complementary sequences); (3) Primer Extension (72°C, heat-stable Taq polymerase synthesizes complementary strands). • Reagents: Template DNA, sequence-specific DNA primers, dNTPs, Mg2+ buffer, Taq polymerase.
30	What is the difference between Reducing and Non-Reducing SDS-PAGE?	• Reducing SDS-PAGE: Includes a reducing agent (beta-mercaptoethanol or DTT) that cleaves covalent disulfide bonds (-S-S-), breaking multimeric complexes joined by disulfides into individual monomeric subunits. • Non-Reducing SDS-PAGE: Retains disulfide bonds intact; multimeric disulfide-linked complexes run as single intact bands.
31	How do you interpret a Lineweaver-Burk plot comparing an uninhibited enzyme to an inhibited enzyme?	• If lines intersect on y-axis: Competitive inhibition (same Vmax, Km increased). • If lines intersect on negative x-axis: Noncompetitive inhibition (same Km, Vmax decreased). • If lines are parallel: Uncompetitive inhibition (both Km and Vmax decreased proportionally).
32	How do you deduce the molecular weight of a protein complex with subunits from SDS-PAGE data?	Compare non-reducing lane (intact complex) with reducing lane (+ beta-mercaptoethanol). If non-reducing lane shows a single 150 kDa band and reducing lane shows 50 kDa and 25 kDa bands, the complex is a heteromultimer composed of disulfide-linked 50 kDa and 25 kDa subunits (e.g., two 50 kDa and two 25 kDa subunits, like IgG antibodies).