Difference Between Probe and Primer

Key Difference – Probe vs Primer

The molecular probe is a small DNA or RNA fragment that recognizes the complementary sequences in DNA or RNA and allows identification of the target sequence. Primer is a small stretch ofDNA or RNAwhich serves as a starting point for DNA synthesis. Primers and probes hybridize with the complementarynucleotidesof the template DNA or the target DNA. However, the key difference between probe and primer is thatprimers are necessary forDNA replicationwhile probes are necessary for detection of specific sequences in the sample DNA.

CONTENTS
1.Overview and Key Difference
2.What is Probe
3.What is Primer
4.Side by Side Comparison – Probe vs Primer
5.Summary

What is a Probe?

Probe is a small fragment of DNA or RNA used to detect the target DNA or RNA in the sample by molecularhybridization. They are also known asmolecular markers. The length of the probe can vary (100 to 1000 bases), and probe nucleotides are complementary to the part of the target sequence. For the ease of detection, probes are labeled with radioactive isotopes or with fluorescent dyes orantibodies. Probes bind with the complementary bases of the target sequence and reveal the presence of the target DNA or RNA in the sample. There are two main methods of labelling probes:end labeling and nick translation. Probes are categorized into different types including DNA probes, RNA probes, cDNa probes and synthetic oligonucleotides probes, and they are prepared using different techniques.

Probes are important tools in many microbial and molecular areas such as virology, forensic pathology, paternity testing, DNA fingerprinting, detection of genetic diseases, RFLP, molecular cytogenetics,in situhybridization, etc.

What is a Primer?

Primer is a short DNA or RNA fragment which serves as an initiator for DNA synthesis.DNA polymeraseenzyme adds nucleotides to the 3’ OH group of primer sequence and synthesizes the new strand complementary to the template DNA. Primers are very short fragments with the length of 18 to 20 nucleotides. They are chemically synthesized in the laboratory forin vitroDNA amplification (PCR). Primers can have any sequence of nucleotides since they are designed by the user. They are synthesized to match with the complementary bases of the template DNA. Therefore, it can have any sequence of nucleotides. Primers are of utmost importance forDNA replicationsince DNA polymerase can’t synthesize new DNA without a preexisting piece of DNA. When designing the primers for PCR, following things need to be considered:

• Primers should contain the complementary nucleotides to the flanking end of the DNA that wants to amplify.
• Primers should have melting temperature between 55 – 65⁰C
• G and C content should be between 50 to 60%.

Two primers are used in PCR as forward and reverse to replicate both strands of the sample DNA. Primers are commonly used to performPCR and DNA sequencing.

What is the difference between Probe and Primer?

Probe vs Primer
Probe is a small fragment of DNA/RNA used to detect the presence of the target sequence in a sample by molecular hybridization.	Primer is a small stretch of DNA or RNA that serves as a starting point for DNA replication.
Function
This detects the presence of a specific sequence in the sample of DNA or RNA.	This acts as a starting point for DNA synthesis.
Length
Length can be in the range of 100 – 1000 bases	Length is generally about 18 – 20 bases
Binding with Complementary Sequence
Probe hybridizes with the complementary bases of the target sequence	Primer anneals with the complementary bases of the DNA strands.
Labeling
Probes are labeled for ease of detection	Primers are generally not labeled
Use in PCR
Probes are not used in PCR	Primers are used in PCR

Summary – Probe vs Primer

调查是一个小片段DNA或RNA序列的that can be hybridized with complementary nucleotides to detect a target sequence in the sample. Probes are labeled radioactively, immunologically or fluorescently to see the presence of target sequence. Primer is a very small DNA or RNA fragment that act as the starting point forin vitroDNA amplification. DNA polymerase identifies 3’ OH group primer and initiates the building of new strand complementary to the template. Probes and primers work similarly by hybridizing with complementary nucleotides. Thus, the key difference between probe and primer is their prime function.

Reference:
1.”Primer (molecular biology).” Wikipedia. Wikimedia Foundation, 02 Feb. 2017. Web. 01 Mar. 2017.
2.”Hybridization probe.” Wikipedia. Wikimedia Foundation, 30 Dec. 2016. Web. 01 Mar. 2017
3.”Primer (molecular biology).” Primer (molecular biology) – ScienceDirect Topics. N.p., n.d. Web. 01 Mar. 2017

Image Courtesy:
1. “FISH for Bacterial Pathogen Identification” By Pepetps Togopic Ivan Akira Magnus ManskeTimothy W. Ford –(CC BY-SA 3.0)viaCommons Wikimedia
2. “Primers RevComp Melted2” By Richard Wheeler (Zephyris) – Own work(CC BY-SA 3.0)viaCommons Wikimedia