RNA Notes

DNA is the genetic material of cells, with the sequence of nucleotide bases carrying a code.
The cell must be able to understand this code for it to work.
The bases in DNA code for specific information, and the cell has a decoding system.

RNA differs from DNA in three important ways:
- The sugar in RNA is ribose instead of deoxyribose.
- RNA is generally single-stranded, not double-stranded.
- RNA contains uracil (U) in place of thymine (T).
Genes contain coded DNA instructions for building proteins.
The first step in decoding genetic instructions is to copy part of the base sequence from DNA into RNA.
RNA, like DNA, is a nucleic acid consisting of a long chain of nucleotides.
RNA uses the base sequence copied from DNA to direct protein production.

Each nucleotide in DNA and RNA consists of a 5-carbon sugar, a phosphate group, and a nitrogenous base.
Differences between RNA and DNA:
- Sugar: RNA has ribose, while DNA has deoxyribose.
- Strands: RNA is single-stranded, and DNA is double-stranded.
- Bases: RNA has uracil, and DNA has thymine.
These chemical differences allow enzymes in the cell to distinguish between DNA and RNA.
The roles of DNA and RNA are similar to master plans and blueprints used by builders.
DNA is like a master plan containing all the information needed to construct a building.
RNA is like inexpensive, disposable blueprints copied from the master plan.
DNA stays safely in the cell's nucleus, while RNA molecules go to the protein-building sites (ribosomes) in the cytoplasm.

An RNA molecule can be thought of as a disposable copy of a DNA segment, a working copy of a single gene.
Most RNA molecules are involved in protein synthesis.
RNA controls the assembly of amino acids into proteins.
Each type of RNA molecule specializes in a different aspect of this process.
Three main types of RNA:
- Messenger RNA (mRNA)
- Ribosomal RNA (rRNA)
- Transfer RNA (tRNA)

Most genes contain instructions for assembling amino acids into proteins.
Messenger RNA (mRNA) carries copies of these instructions from DNA to other parts of the cell.

Proteins are assembled on ribosomes, which are small organelles composed of two subunits.
Ribosome subunits are made up of ribosomal RNA (rRNA) molecules and as many as 80 different proteins.

When a protein is built, transfer RNA (tRNA) transfers each amino acid to the ribosome as specified by the coded messages in mRNA.

In transcription, segments of DNA serve as templates to produce complementary RNA molecules.

During transcription, segments of DNA serve as templates to produce complementary RNA molecules.
The base sequences of the transcribed RNA complement the base sequences of the template DNA.
In prokaryotes, RNA synthesis and protein synthesis occur in the cytoplasm.
In eukaryotes, RNA is produced in the cell's nucleus and then moves to the cytoplasm to play a role in protein production.
Transcription requires an enzyme called RNA polymerase, which is similar to DNA polymerase.
RNA polymerase binds to DNA during transcription and separates the DNA strands.
RNA polymerase uses one strand of DNA as a template to assemble nucleotides into a complementary strand of RNA.

RNA polymerase binds only to promoters, which are regions of DNA with specific base sequences.
Promoters are signals in the DNA molecule that indicate where to begin making RNA.
Similar signals in DNA cause transcription to stop when a new RNA molecule is completed.

RNA molecules sometimes require bits and pieces to be cut out before they can function.
The portions that are cut out and discarded are called introns.
In eukaryotes, introns are removed from pre-mRNA molecules while they are still in the nucleus.
The remaining pieces, known as exons, are then spliced back together to form the final mRNA.
Some pre-mRNA molecules may be cut and spliced in different ways in different tissues, allowing a single gene to produce several different forms of RNA.
Introns and exons may also play a role in evolution, allowing small changes in DNA sequences to have dramatic effects on how genes affect cellular function.