Studying DNA and RNA

Recombinant DNA and gene cloning are tools used to combine DNA from different sources. Scientists use them to isolate a gene, join it to a carrier DNA molecule, and make copies of that DNA.

A plasmid is one common carrier used in this process. A plasmid is a small ring of DNA found in bacteria, and it can carry the inserted gene into a host cell. Once inside the cell, the recombinant DNA can be copied as the cell grows.

This approach is important in biotechnology and genetic research. It...

Genomic DNA extraction methods separate DNA from proteins, RNA, and other cell material. The process usually follows four main steps. First, the cell structure is disrupted with mechanical or chemical methods to make a cell lysate. Then the DNA is protected from damage during processing. After that, the soluble DNA is separated from cell debris. Finally, the purified DNA is eluted, or washed out, for later use.

DNA isolation can follow two main approaches: solution-based methods or solid-phase...

Agarose gel electrophoresis can be used to purify DNA bands after separation by size. In gel extraction, the DNA fragment of interest is cut from the gel and cleaned before later use. This is especially useful in cloning, where pure DNA is needed before ligation, the joining step that links DNA pieces together.

In cloning experiments, both the insert and vector DNA fragments are first cut with restriction endonucleases. These fragments often contain enzymes, salts, and other contaminants. Such...

DNA probes are short DNA fragments with a reporter tag attached so they can be detected or purified. They bind to matching nucleic acid sequences by complementary base-pairing. That binding helps researchers recover or identify specific regions of DNA.

Several reporter tags are commonly used to label DNA probes. These include radioisotopes, fluorophores, and small molecule binding partners such as biotin or digoxigenin. The label choice depends on the probe’s intended use and on the source of...

Southern blotting is a DNA detection method used after agarose gel electrophoresis separates DNA fragments by size. A DNA ladder with fragments of known length is run beside the sample so the fragment size can be estimated. The blot adds another step when scientists need to confirm the sequence identity of the DNA.

First, the target DNA is cut into smaller pieces with a restriction endonuclease and run on an agarose gel. The DNA is then denatured, which means the double strands are separated...

DNA microarrays are gene chips used to compare gene activity in different conditions. They are high-throughput assays, which means they can analyze large amounts of data at once. They are also relatively inexpensive and can be automated, making them useful for genome-wide studies.

These chips are built on glass or silica slides. Probe molecules are covalently attached to the surface through surface functionalization. In many cases, the slides are prepared by chemisorption of silanes to silica...

Complementary DNA, or cDNA, is made from an RNA template. It is a DNA copy of RNA, so it can help students study gene expression in a lab setting.

cDNA is useful when scientists want to work with genes after they have been turned on in a cell. Because it is copied from RNA, it reflects which genes were active at the time the RNA was collected.

This process links RNA and DNA in a simple way. It also gives students a clear view of how genetic information can be copied for analysis.

FISH is a DNA and RNA detection method used in cytogenetics and medical testing. FISH stands for fluorescence in situ hybridization. It uses labeled probes that bind to complementary DNA or RNA sequences on a chromosome or inside a cell.

The method was developed in the early 1980s and became widely used because it can show specific genetic targets with high detail. In the past, probes were made by cloning or by reverse transcription of a DNA template. Today, probe oligonucleotides can also be...

PCR is a DNA amplification method used in genetics labs. PCR stands for polymerase chain reaction. It copies a specific DNA segment so scientists can study small amounts of genetic material.

The process uses repeated heating and cooling steps. These steps let the DNA strands separate, primers bind to the target region, and a DNA polymerase build new strands. With each cycle, the target DNA can increase in amount.

PCR is a core technique in molecular biology and many school-level biology...

Real-time RT-PCR tracks gene expression by measuring how much target DNA is made during PCR. It starts with mRNA, which is converted into complementary DNA, or cDNA, by an enzyme called reverse transcriptase. The cDNA is then amplified by PCR so the target sequence can be measured.

This method can be done in one tube as a single-step reaction or in two separate steps. During amplification, the amount of product is followed in real time with fluorescent dyes or sequence-specific probes linked...

Rapid Amplification of cDNA Ends, or RACE, helps scientists capture the full-length cDNA from an mRNA sequence. It works by linking a known internal region to the unknown sequence at either the 5' end or the 3' end. The method is widely used when the missing end of a gene needs to be identified.

RACE uses a gene-specific primer that binds to the known cDNA region. A hybrid primer then adds a set anchor sequence to the unknown end of the cDNA. After that, PCR amplifies the DNA segment between...

Sanger sequencing reads DNA fragments by separating pieces of different lengths and decoding the order of bases. It is a key method in biology and is often used to study a cloned DNA fragment, a gene mutation, or even much larger genomes.

Fredrick Sanger and his collaborators developed the chain-termination method in 1977. The method works by producing a mixture of DNA fragments with variable sizes. These fragments are then separated by capillary gel electrophoresis, which sorts them by length.

DNA sequencing methods can read millions of DNA fragments at the same time. Next-generation sequencing made this process much faster and much less expensive than older methods. The first human genome project cost $2.7 billion and took 15 years. It was completed in 2003 after major international cooperation among research teams and funding agencies.

To prepare DNA for next-generation sequencing, pure genomic DNA is first broken into smaller pieces. These pieces are used to build a sequencing...

RNA sequencing, or RNA-Seq, is a high-throughput method for studying the transcriptome of a cell. The transcriptome is the full set of RNA molecules in a sample. Transcriptomics helps scientists understand how genomes work, how organisms develop, and how some diseases occur.

Before RNA-Seq, researchers often used microarray methods and Sanger sequencing to study RNA. Microarrays had limited coverage and depended on already knowing the genome sequence. Sanger sequencing was low-throughput,...

Genome assembly and genome annotation are key steps in genome analysis. Genome assembly puts DNA sequencing data back in the correct order to make a close copy of the original genome. Genome annotation then identifies functional parts on that assembled genome.

Assembling a genome is not simple. In human populations, gene copy number can vary, and repeated DNA sequences can make the process harder. Even so, the physical location of human genes stays constant. Bacterial genomes can be more...

Restriction enzymes are bacterial proteins that cut DNA at specific sequence sites. They recognize palindromic DNA sequences, also called inverted repeats, and cut the DNA in a sequence-specific way. These sites are often found in regions with important functions, such as the origin of replication, gene operator sites, and transcription termination signals.

Bacteria protect their own DNA by methylating these same sites. Methylation means adding chemical marks that keep the restriction enzyme...

Chemical cleavage DNA sequencing uses specific chemicals to cut DNA at known sites. Allan Maxam and Walter Gilbert described this method in the same year that the Sanger sequencing method was discovered. It reads the DNA sequence by breaking purified DNA into fragments and then studying the fragment pattern.

The method depends on chemicals that cleave DNA at specific bases. The resulting fragments are separated by electrophoresis, which is a way to sort DNA pieces by size using an electric...