4.7
Complementary DNA
Overzicht
Alleen genen die worden getranscribeerd in messenger RNA (mRNA) zijn actief of komen tot expressie. Wetenschappers kunnen daarom het mRNA ui…
- [Verteller] Bijna elke cel in het lichaam heeft hetzelfde DNA maar verschillende celtypes, zoals neuronen en spiercellen, uiten verschillende genen omdat alleen bepaalde genen overgebracht worden in messenger RNA of mRNA in elke cel. In het laboratorium kunnen mRNA's gebruikt worden als template om complementair DNA, cDNA, te synthetiseren om genexpressie te bestuderen. Een gangbare methode is RNA extraheren van cellen, dan het mRNA isoleren van andere soorten RNA, zoals robisomaal RNA of transfer RNA, door het sample over een kralenkolom te laten lopen waaraan strengen thymine nucleotiden bevestigd zijn.
Deze binden met de poly(A)-staart, een keten van adenine nucleotiden specifiek aanwezig aan de drie uiteindes van eukaryotisch mRNA. De andere soorten RNA binden zich niet en worden weggespoeld. Nadat het mRNA geïsoleerd is, wordt een poly(T)-primer gebonden aan de poly(A)-staart, en vormt een startpunt voor reverse-transcriptase enzymes om een enkelstrengs cDNA te translateren van het mRNA.
Stoffen zoals RNase enzymen worden dan toegevoegd om het RNA te degraderen. DNA polymerase enzymen worden dan gebruikt om een streng te synthetiseren, complementair met het cDNA wat resulteert in dubbelstrengs cDNA, dat ingevoegd kan worden in een bacteriële of virale vector en gebruikt wordt in moleculair biologie-onderzoek.
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Q1: What is complementary DNA and how is it made?
Complementary DNA (cDNA) is synthesized from a messenger RNA (mRNA) template using the enzyme reverse transcriptase. This process converts the genetic information stored in RNA back into DNA form, creating a stable copy that represents only the expressed genes from a specific cell or tissue at a particular time.
Q2: Why is complementary DNA useful in molecular biology research?
Complementary DNA is valuable because it represents only actively expressed genes, eliminating introns and non-coding sequences found in genomic DNA. This makes cDNA ideal for studying gene expression patterns, cloning genes, and creating cDNA libraries that reflect the functional genes present in specific cell types or developmental stages.
Q3: How does complementary DNA differ from genomic DNA?
Complementary DNA contains only exons and represents genes actively transcribed in a cell, while genomic DNA includes all DNA sequences, including introns and regulatory regions. cDNA is synthesized from mRNA and lacks introns, making it smaller and more suitable for expressing eukaryotic genes in prokaryotic systems.
Q4: What role does reverse transcriptase play in cDNA synthesis?
Reverse transcriptase is the key enzyme that catalyzes cDNA synthesis by reading an mRNA template and synthesizing a complementary DNA strand. This enzyme enables researchers to convert the temporary RNA message into stable DNA that can be amplified, cloned, and analyzed using standard molecular biology techniques.
Q5: How can complementary DNA be amplified and analyzed?
Complementary DNA can be amplified using PCR or rapid amplification of cDNA ends (RACE) techniques, then analyzed through methods like agarose gel electrophoresis for separation of DNA fragments or sequencing. These approaches allow researchers to identify specific genes and determine their expression levels in different tissues or conditions.
Q6: What are cDNA libraries and why are they important?
A cDNA library is a collection of cloned cDNA sequences representing all genes expressed in a particular cell type or tissue. These libraries are important for functional genomics research, allowing scientists to study gene expression patterns, identify tissue-specific genes, and isolate genes for further characterization and protein production.
Q7: How is complementary DNA used in gene expression studies?
Complementary DNA serves as the template for measuring gene expression through techniques like real-time RT-PCR, which quantifies mRNA levels. Since cDNA represents only expressed genes, it provides an accurate snapshot of which genes are active in specific cells, tissues, or disease states.