Question

RECALL What are micro RNAs?

Short answer

Micro RNAs (miRNAs) are small non-coding RNAs that regulate gene expression by binding to target mRNAs, leading to their degradation or translation inhibition.

Step-by-step solution

Define Micro RNAs

Micro RNAs, often abbreviated as miRNAs, are small non-coding RNA molecules found in plants, animals, and some viruses. They are typically about 22 nucleotides long.

Function of Micro RNAs

miRNAs play a crucial role in regulating gene expression. They bind to complementary sequences on target mRNA transcripts, usually resulting in their silencing by causing mRNA degradation or inhibiting translation.

Importance in Biological Processes

Micro RNAs are involved in a wide array of biological processes including development, differentiation, cell proliferation, and apoptosis. Their dysregulation can lead to a variety of diseases, including cancer.

Unique Features

One unique feature of miRNAs is their ability to target multiple mRNAs, thereby influencing various pathways simultaneously. They are also known for their evolutionary conservation across different species.

How They Are Produced

miRNAs are transcribed as primary miRNAs (pri-miRNAs) and processed into precursor miRNAs (pre-miRNAs) in the nucleus. These pre-miRNAs are then exported to the cytoplasm, where they are further processed by Dicer enzyme into mature miRNAs.

Key concepts

gene expression regulation

Micro RNAs (miRNAs) are powerful regulators of gene expression. They achieve this by binding to complementary sequences on messenger RNA (mRNA) transcripts. This binding leads to either mRNA degradation or inhibition of translation, effectively silencing the gene.
Gene expression regulation is crucial because it allows cells to respond to changes in their environment. It plays a role in determining the identity and function of a cell. For instance, it helps stem cells differentiate into specialized cell types.
By regulating gene expression, miRNAs ensure that genes are turned off or on when they are needed, maintaining cellular function and health.

biological processes

Micro RNAs are key players in various biological processes.
They are involved in:

• Development: miRNAs guide the development of organisms from a single cell into a complex, multicellular organism.
• Differentiation: They help stem cells transform into specific cell types.
• Cell proliferation: miRNAs regulate the rate at which cells divide and grow.
• Apoptosis: They can trigger or inhibit programmed cell death, which is essential for removing damaged or unnecessary cells.

Dysregulation of miRNAs can disrupt these processes and lead to diseases like cancer.

miRNA biogenesis

The production of miRNAs is a multi-step process called miRNA biogenesis.
It involves:

• Transcription: miRNAs are first transcribed as long primary miRNAs (pri-miRNAs) in the nucleus.
• Processing: Pri-miRNAs are then processed into shorter precursor miRNAs (pre-miRNAs) by the Drosha enzyme.
• Export: Pre-miRNAs are exported from the nucleus to the cytoplasm.
• Dicing: In the cytoplasm, the Dicer enzyme further processes pre-miRNAs into mature miRNAs.

These mature miRNAs are then incorporated into the RNA-induced silencing complex (RISC) to regulate gene expression.

mRNA degradation

One of the primary functions of micro RNAs is to promote the degradation of target mRNA molecules.
This process involves:

• Binding: miRNAs bind to complementary sequences on the target mRNA.
• Recruitment: This binding recruits other cellular machinery to the mRNA.
• Degradation: The recruited machinery degrades the mRNA, preventing it from being translated into protein.

mRNA degradation is crucial because it helps fine-tune the levels of proteins in a cell, ensuring that only the necessary proteins are produced.

evolutionary conservation

Micro RNAs exhibit remarkable evolutionary conservation across different species.
This means that miRNAs have been preserved throughout evolution in plants, animals, and even some viruses.
The conservation of miRNA sequences and their targets suggests that they play fundamental roles in cellular processes.
Such conservation also aids researchers in studying miRNA functions in model organisms and applying this knowledge to understand human biology and disease.