2: PCR Variants (MIDTERMS) Flashcards
Identify the PCR variant:
a process that involves a reverse transcriptase (RTase), an enzyme that uses RNA as the template to make complementary DNA (cDNA)
Reverse Transcription
For how long does Reverse Transcription last?
3-4 hours
T or F
Reverse Transcription-PCR is the same with RT-PCR COVID-19 swab test
F (COVID uses Real-Time PCR)
What enzyme does Reverse Transcription-PCR use?
Reverse Transcriptase
T or F
PCR can amplify both complementary DNA and RNA
F (PCR can only amplify DNA because the polymerase being used is DNA polymerase which can only detect a DNA sample)
What is the needed temperature to activate Reverse Transcriptase
37°C
What is the main mechanism of Reverse Transcription?
use RNA Template → complementary DNA
What are the 2 primers used in Reverse Transcriptase-PCR?
- Oligo (dT) primers
- Random Primers
Primers used in RT-PCR:
→ choosy
→ used when the template is messenger RNA
(mRNA)
→ anneal when the template contains a polyadenylated tail (poly-A tail) which is present in most eukaryotic RNA at the 3’
→ 18-base-long single stranded poly dT sequences
Oligo (dT) primers
Primers used in RT-PCR:
→ Can be random hexamers or random decamers
→ Used if RNA is degraded RNA or has no poly- A tail
→ Any RNA template is used
→ For prokaryotic RNA or degraded RNA
→ 6 or 10-base long single-stranded
oligonucleotides of random sequences
Random primers
Which primer for RT-PCR is used when template is messenger RNA (mRNA)
Oligo (dT) primers
Oligo (dT) primers only anneal to the template when there is the presence of?
polyadenylated tail (poly-A tail)
This primer for RT-PCR is 18-base-long single-stranded poly dT sequences
Oligo (dT) primers
Which primer for RT-PCR is used when RNA is degraded RNA or has no poly- A tail?
Random primers
This primer for RT-PCR is 6 or 10-base long single-stranded oligonucleotides of random sequences
Random primers
What are the 2 ways to perform Reverse Transcriptase PCR?
- One-step
- Two-step
A way to perform RT-PCR where the primers, reverse transcriptase, and standard PCR reagents (buffer magnesium, dNTPs) are all combined in an epender tube and placed in PCR machine
One-Step
Identify what way to perform RT-PCR:
Advantage: quicker, less prone to contamination
Disadvantage: If error occurs, process is repeated
One-Step
A way to perform RT-PCR that involves 2 tubes and 2 steps:
1st tube is where RNA is converted to cDNA while 2nd tube if getting aliquot of DNA and adding standard PCR reagents
Two-Step
IDENTIFY WHAT TUBE IS USED in Two-step way of performing RT-PCR:
RNA is converted to cDNA; only the
primer and reverse transcriptase is added
1st tube
IDENTIFY WHAT TUBE IS USED in Two-step way of performing RT-PCR:
Getting an aliquot of the cDNA then adding standard PCR reagents
2nd tube
Two-step way of performing RT-PCR:
T or F
In the 1st tube of two-step, dNTP, buffer, primer, and reverse transcriptase is added
F (only the PRIMER and REVERSE TRANSCRIPTASE is added)
Identify what way to perform RT-PCR:
Advantage: more sensitive, easier to
troubleshoot, you already have a stock of cDNA
Disadvantage: prone to contamination
Two-Step
Identify the PCR variant:
→ Is a technique used to amplify multiple target sequences in a single PCR reaction using multiple primer sets.
→ This method is used to detect deletions, polymorphisms, mutations, etc.
→ This method is also used to detect different viral, bacterial, and other pathogens in a single tube.
→ consumes less time and effort in obtaining the results.
Multiplex PCR
T or F
In a traditional/conventional PCR, the ratio of sample and primer is 1:1
T bading ka
T or F
In a Multiplex PCR, there can be either a:
Multiple samples, 1 primer, 1 reaction tube w/ standard PCR reagents
OR
Multiple primers, 1 sample, 1 reaction tube w/ standard PCR reagents
T
Multiplex PCR:
Uses several sets of primers to amplify specific regions within a template
Single-template PCR reaction
Multiplex PCR:
Uses multiple templates and several primer sets in the same reaction tube.
multiple-template PCR reaction
→ This method is used to detect deletions, polymorphisms, mutations, etc.
Multiplex PCR
→ This method is also used to detect different viral, bacterial, and other pathogens in a single tube.
Multiplex PCR
Identify what PCR variant:
Advantages: Rapid, Save costly polymerase and template in short supply
Disadvantages: Difficult to optimize, Nag-aagawan reagents, Unable to mix organism with same amplicaon size, More complicated to develop, often is less sensitive than single-primer-set PCR
Multiplex PCR
T or F
In Multiplex PCR, if it is positive, 1 solid band forms with the 3 primers added
F (multiple bands form with 3 primers added)
T or F
In Conventional/Traditional PCR, if it is positive, 2 solid bands form
F (1 solid band)
In Multiplex PCR, if the sample if COVID-19, what band/s are present?
Red band only
T or F
Primers used in multiplex reactions must be selected carefully to have similar annealing temperatures and must be complementary
F (must NOT BE complementary to each other)
What temperature should be checked first in Multiplex PCR?
Melting temperature
T or F
Melting temperature should be close to annealing temperature, if not, the primer will not bind to the target sequence
T
Identify the PCR variant:
→ Is a modification of PCR that was designed to improve sensitivity and specificity
→ use of two primer sets (external primers and nested primers) and two successive PCR reactions.
Nested PCR
Nested PCR involves the use of primer sets which are?
- External primer
- Nested primer
What does Nested PCR require?
2 primer sets (external primers/nested primers) and 2 successive PCR reactions
T or F
Nested PCR is repeated 2x to increase sensitivity and specificity
T
Mechanism of Nested PCR?
1ST ROUND:
Outer primer bind to target template → Annealing → Extension → Amplified product
2ND ROUND:
Template for 2nd round is the amplified product of 1st round → Inner/Nester binds to target sequence → Annealing → Extension → Specified nested product
Identify the correct answer: Nested PCR
- Primer in 1st round _______
- Primer in 2nd round _______
a. Inner/Nested primer
b. Outer primer
c. Primase
d. Normal primer
- Primer in 1st round: b. Outer primer
- Primer in 2nd round: a. Inner/Nested primer
Nested PCR:
Increased sensitivity is attributed to what?
increased/high cycle (20 cycles on 1st round plus 20 cycles → It monitors the amplification of a targeted DNA on 2nd round)
Nested PCR:
Increased specificity is attributed to what?
increased/added primer (2 primers are used: outer primer and nested primer)
What are the 2 types of nested PCR?
- Traditional Nested PCR
- Semi-nested Asymmetrical PCR
Identify what type of nested PCR:
The target is amplified. Open the tube and use the first product for the 2nd round. Add the inner primer then amplify.
Traditional Nested PCR
Identify what type of nested PCR:
Almost the same as traditional but less time and less cycle because the inner and outer primers are combined in 1 reaction or tube
Semi-nested Asymmetrical PCR
Use this card to familiarize the application of Nested PCR
- Detection of Rickettsia, Bartonella, and similar organisms in blood (bacteremia) and tissues
- Detection of herpesvirus and enterovirus in the CSF
- Detection of M. tuberculosis in sputum sample
What is the recommended PCR variant when the quality of template is not that great? (Its concentration is low and less pure)
Nested PCR (will improve its sensitivity and specificity)