Spectrophotometry and Colorimetry — MCQs
Test for detection of old blood stain is -
Replacing alanine by which amino acid, will increase UV absorbance of protein at 280 nm wavelength?
Which amino acid among the following has significant UV absorption at 280 nm used in protein quantification?
Most accurate method to determine age of bruise between 24-72 hours?
Which of the following techniques is primarily used for RNA analysis?
Which of the following is a primarily RNA based technique?
Which of the following devices does not use the principle of fluorescence in the diagnosis of caries?
Fluorescein dye for ophthalmological diagnosis is injected into:
Which of the following methods is used for demonstrating old washed bloodstains?
Confirmatory test of blood stain:
Spectrophotometry and Colorimetry Indian Medical PG Practice Questions and MCQs
Question 1: Test for detection of old blood stain is -
- A. Precipitin test
- B. Gel diffusion
- C. Absorption elution test
- D. Benzidine test (Correct Answer)
Explanation: ***Benzidine test*** - The **benzidine test** is a highly sensitive **presumptive test** used to detect the presence of blood, either fresh or old, based on the **peroxidase-like activity of hemoglobin**. - It reacts with the heme component of blood, causing a color change (blue), making it suitable for identifying even trace amounts of blood in stains. *Precipitin test* - The **precipitin test** is used for **species identification** (e.g., human vs. animal blood) and not for the detection of blood itself. - It involves the reaction between specific antibodies and antigens to form a **precipitate band**. *Gel diffusion* - **Gel diffusion** methods, such as **Ouchterlony immunodiffusion**, are used to compare antigens and antibodies for **species identification** or to determine specific blood group substances. - They are not designed for the general detection of blood. *Absorption elution test* - The **absorption elution test** is used for **blood group typing** (e.g., ABO) from dried bloodstains. - It relies on the presence of **antigens** on red blood cells and is not a general test for the presence of blood.
Question 2: Replacing alanine by which amino acid, will increase UV absorbance of protein at 280 nm wavelength?
- A. Glycine
- B. Tryptophan (Correct Answer)
- C. Arginine
- D. Lysine
Explanation: ***Tryptophan*** - **Tryptophan** contains an **indole ring**, which is a **chromophore** that strongly absorbs UV light at 280 nm. - Increased tryptophan content in a protein directly correlates with a higher **UV absorbance** at this wavelength. *Glycine* - **Glycine** is the simplest amino acid, with only a **hydrogen atom** as its side chain. - It does not contain any aromatic rings or other groups that absorb UV light at 280 nm, so replacing alanine with glycine would not increase UV absorbance. *Arginine* - **Arginine** is a basic amino acid with a **guanidinium group** in its side chain. - While it has a slightly complex side chain, it does not possess any **aromatic rings** that absorb significantly at 280 nm. *Lysine* - **Lysine** is another basic amino acid with a long **aliphatic chain** and an **amino group** at the end. - Similar to arginine, lysine lacks the necessary **aromatic chromophores** to contribute to UV absorbance at 280 nm.
Question 3: Which amino acid among the following has significant UV absorption at 280 nm used in protein quantification?
- A. Tyrosine (Correct Answer)
- B. Alanine
- C. Histidine
- D. Arginine
Explanation: ***Correct Option: Tyrosine*** - Tyrosine contains a **phenol functional group** (aromatic ring with hydroxyl group), giving it **significant UV absorption at 280 nm** (specifically ~274 nm) - Along with **tryptophan** and **phenylalanine**, tyrosine is one of the three aromatic amino acids used for **protein quantification via UV spectroscopy** - The aromatic side chain with conjugated double bonds enables strong UV light absorption *Incorrect Option: Alanine* - Alanine has a **methyl group** as its side chain (non-polar, aliphatic) - **Lacks aromatic rings** or conjugated systems - Does **not absorb UV light** at 280 nm *Incorrect Option: Histidine* - Histidine has an **imidazole ring** (heterocyclic aromatic) in its side chain - While technically aromatic, it has **minimal UV absorption at 280 nm** (weak absorption around 210-230 nm) - **Not used for protein quantification** at 280 nm due to insignificant absorption at this wavelength *Incorrect Option: Arginine* - Arginine contains a **guanidinium group** (highly basic, polar) - **Non-aromatic structure** without conjugated double bonds - Does **not exhibit UV absorption** at wavelengths used for protein analysis
Question 4: Most accurate method to determine age of bruise between 24-72 hours?
- A. Histology
- B. Photography
- C. Visual examination
- D. Spectrophotometry (Correct Answer)
Explanation: ***Spectrophotometry*** - **Spectrophotometry** attempts to objectively measure the concentrations of **hemoglobin degradation products** (oxyhemoglobin, deoxyhemoglobin, methemoglobin, bilirubin) in bruised tissue - Theoretically provides **quantitative assessment** of pigment changes that occur over time - Considered by some textbooks as the **most objective method** for bruise age estimation in the 24-72 hour window - **Note:** Recent research suggests significant limitations exist in accurately dating bruises regardless of method used *Histology* - Shows cellular changes, inflammatory response, and presence of hemosiderin-laden macrophages - More invasive and provides information about **healing stages** rather than precise time estimation - Has significant **inter-individual variability** making narrow timeframe dating (24-72 hours) difficult - Still considered more objective than visual methods but less precise than spectrophotometric analysis *Photography* - Documents bruise appearance but relies on **subjective color interpretation** - Affected by multiple variables: lighting conditions, skin tone, camera settings, and depth of bruise - Lacks **quantitative analytical capability** for objective measurement - Useful for documentation but not for accurate age determination *Visual examination* - **Highly subjective** and least reliable method for bruise age determination - Wide variation in bruise appearance based on skin tone, location, depth, individual healing factors, and trauma severity - Traditional color-change timeline (red→blue→green→yellow) has been shown to be **unreliable** in forensic practice - Cannot provide accurate age estimation within narrow timeframes
Question 5: Which of the following techniques is primarily used for RNA analysis?
- A. Sanger's technique
- B. Western blot
- C. Next generation sequencing (Correct Answer)
- D. PCR
Explanation: ***Next generation sequencing*** - **Next-generation sequencing (NGS)**, particularly RNA-Seq, is widely used for **transcriptome analysis** to quantify and discover RNA molecules. - RNA-Seq allows for the precise measurement of **gene expression levels**, identification of **novel transcripts**, and detection of **splicing variants**. *Sanger's technique* - **Sanger sequencing** is primarily used for **DNA sequencing** to determine the exact order of nucleotides in a DNA molecule. - While it can be applied to cDNA (synthesized from RNA), it is not directly used for **RNA analysis** itself. *Western blot* - **Western blot** is a laboratory technique used to detect specific **proteins** in a sample. - It involves separating proteins by size using gel electrophoresis and then transferring them to a membrane for antibody-based detection, making it unsuitable for direct **RNA analysis**. *PCR* - **Polymerase Chain Reaction (PCR)** is used to amplify specific **DNA sequences**. - While **Reverse Transcription PCR (RT-PCR)** can quantify RNA by first converting it to cDNA, PCR itself does not directly analyze the RNA molecule.
Question 6: Which of the following is a primarily RNA based technique?
- A. Western blotting
- B. Northern blotting (Correct Answer)
- C. Southern blotting
- D. Sanger's technique
Explanation: ***Northern blotting*** - **Northern blotting** is a molecular biology technique used to study **gene expression** by detecting specific **RNA molecules** (mRNA) in a sample. - It involves separating RNA fragments by **gel electrophoresis**, transferring them to a membrane, and then detecting specific sequences using **labeled probes**. *Western blotting* - **Western blotting** is a technique used to detect specific **proteins** in a sample. - It involves separating proteins by **gel electrophoresis**, transferring them to a membrane, and then detecting specific proteins using labeled **antibodies**. *Southern blotting* - **Southern blotting** is a molecular biology method used for the detection of **specific DNA sequences** in DNA samples. - It involves separating **DNA fragments** by **gel electrophoresis**, transferring them to a membrane, and then hybridizing with a labeled probe. *Sanger's technique* - **Sanger sequencing**, or the **dideoxy chain-termination method**, is a widely used method for **DNA sequencing**. - It uses **dideoxynucleotides** to terminate DNA synthesis at specific bases, allowing the determination of the **DNA sequence**.
Question 7: Which of the following devices does not use the principle of fluorescence in the diagnosis of caries?
- A. Diagnodent
- B. QLF
- C. FOTI (Correct Answer)
- D. Soprolife
Explanation: ***FOTI*** - **Fiber optic transillumination (FOTI)** detects caries by illuminating the tooth with a high-intensity light source and observing changes in light transmission, which do not involve fluorescence. - Caries lesions appear as **dark shadows** or translucency changes because demineralized enamel scatters light differently than healthy enamel. *Diagnodent* - The **Diagnodent** device uses a 655 nm laser diode to excite porphyrins produced by cariogenic bacteria within the tooth structure. - These porphyrins emit **fluorescence**, which is then detected by the device to quantify the extent of demineralization. *QLF* - **Quantitative Light-induced Fluorescence (QLF)** uses a specific wavelength of light to excite natural fluorophores in healthy enamel. - Demineralized areas associated with caries show a **loss of autofluorescence** or increased red fluorescence from bacterial byproducts, which is then quantified. *Soprolife* - **Soprolife** is an intraoral camera system that utilizes light-induced fluorescence to detect caries. - It uses specific wavelengths to highlight healthy tissue fluorescence in green and carious lesions with a **red or orange fluorescence**, indicating bacterial presence.
Question 8: Fluorescein dye for ophthalmological diagnosis is injected into:
- A. Antecubital vein (Correct Answer)
- B. Popliteal vein
- C. Femoral vein
- D. Subclavian vein
Explanation: ***Antecubital vein*** - Fluorescein angiography requires rapid delivery of the dye into the **systemic circulation** for quick visualization of retinal and choroidal vasculature. - The **antecubital vein** is a readily accessible, large superficial vein that allows for quick and efficient intravenous dye injection. *Popliteal vein* - The popliteal vein is located behind the **knee** and is not a standard or practical site for routine intravenous injections, especially when rapid delivery to the eye is needed. - Its location makes it less accessible and potentially more uncomfortable for the patient compared to an arm vein. *Femoral vein* - The femoral vein is a large, deep vein in the **groin**, typically reserved for central venous access or specific procedures due to the increased risk of complications like infection or hematoma. - It is not routinely used for peripheral intravenous injections such as fluorescein, where a more superficial and accessible vein is preferred. *Subclavian vein* - The subclavian vein is a **central vein** located under the clavicle, accessed via a more invasive procedure, usually for central venous catheters or hemodialysis access. - It carries higher risks compared to peripheral venipuncture and is not chosen for simple diagnostic dye injections like fluorescein.
Question 9: Which of the following methods is used for demonstrating old washed bloodstains?
- A. Infrared photography
- B. Luminol spray (Correct Answer)
- C. Magnifying lens
- D. Ultraviolet light
Explanation: **Luminol spray** - **Luminol** reacts with the iron in **hemoglobin** to produce a blue-white luminescence, making it highly effective for detecting even heavily diluted or rinsed-away bloodstains. - It is particularly useful for demonstrating **old, washed-up bloodstains** at crime scenes where visual identification might be difficult. *Infrared photography* - While useful for detecting certain hidden details or substances, **infrared photography** is not the primary method for revealing old or washed-up bloodstains. - **Bloodstains** can absorb infrared light to varying degrees, but the chemical reaction of luminol is specifically designed for trace blood detection. *Magnifying lens* - A **magnifying lens** merely enhances the visibility of existing stains or patterns and cannot detect traces of blood invisible to the naked eye, particularly old or diluted ones. - It is a tool for closer inspection, not for chemical detection of hidden substances. *Ultraviolet light* - **Ultraviolet (UV) light** can be used to detect certain biological fluids such as semen or saliva, which **fluoresce** under UV. - However, fresh or old bloodstains typically *absorb* UV light rather than fluoresce, making it less effective for detecting them, especially if they are washed up.
Question 10: Confirmatory test of blood stain:
- A. Kastle-Meyer test
- B. Benzidine test
- C. Spectroscopic test (Correct Answer)
- D. Orthotoluidine test
Explanation: ***Spectroscopic test*** - The **spectroscopic test** is considered a **confirmatory test** for bloodstains due to its ability to identify the characteristic **absorption spectrum of hemoglobin**. - It specifically detects the presence of **hemoglobin derivatives**, unequivocally confirming the presence of blood. *Kastle-Meyer test* - This is a **presumptive test** for blood, relying on the **peroxidase activity** of hemoglobin. - While sensitive, it can yield **false positives** due to other peroxidase-like substances (e.g., plant material, rust). *Benzidine test* - The **benzidine test** is also a **presumptive test** for blood based on peroxidase activity. - It is **highly sensitive** but has been largely replaced by other tests due to the **carcinogenic nature** of benzidine. *Orthotoluidine test* - Similar to the Kastle-Meyer and benzidine tests, the **orthotoluidine test** is a **presumptive test** that detects the peroxidase activity of hemoglobin. - It can also produce **false positive results** from various oxidizing agents or plant peroxidases.
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