SCIENCE question - RNA?

Question

what are the steps that occur during transcription of mRNA off the DNA template.

YES, I have researched and read my textbook. But im still soo confused. please please help!

Answer 1

Kinds of RNA

Messenger RNA (mRNA)

Messenger RNA contains genetic information. It is a copy of a portion of the DNA.

It carries genetic information from the gene (DNA) out of the nucleus, into the cytoplasm of the cell where it is translated to produce protein.

Ribosomal RNA (rRNA)

This type of RNA is a structural component of the ribosomes. It does not contain a genetic message.

Transfer RNA (tRNA)

Transfer RNA functions to transport amino acids to the ribosomes during protein synthesis.

Transcription

Transcription is the synthesis of mRNA from a DNA template.

It is like DNA replication in that a DNA strand is used to synthesize a strand of mRNA.

Only one strand of DNA is copied.

A single gene may be transcribed thousands of times.

After transcription, the DNA strands rejoin.

Steps involved in transcription

DNA unwinds.

RNA polymerase recognizes a specific base sequence in the DNA called a promoter and binds to it. The promoter identifies the start of a gene, which strand is to be copied, and the direction that it is to be copied.

Complementary bases are assembled (U instead of T).

A termination code in the DNA indicates where transcription will stop.

The mRNA produced is called a mRNA transcript.

Processing the mRNA Transcript

In eukaryotic cells, the newly-formed mRNA transcript (also called heterogenous nuclear RNA or hnRNA) must be further modified before it can be used.

A cap is added to the 5’ end and a poly-A tail (150 to 200 Adenines) is added to the 3’end of the molecule.

The newly-formed mRNA has regions that do not contain a genetic message. These regions are called introns and must be removed. Their function is unknown.

The remaining portions of mRNA are called exons. They are spliced together to form a mature mRNA transcript.

The Nucleus

DNA is located in an organelle called the nucleus.

Transcription and mRNA processing occur in the nucleus.

The nucleus is surrounded by a double membrane. After the mature mRNA transcript is produced, it moves out of the nucleus and into the cytoplasm through pores in the nuclear membrane.

Translation

Translation is the process where ribosomes synthesize proteins using the mature mRNA transcript produced during transcription. A mature mRNA transcript, a ribosome, several tRNA molecules and amino acids are shown. There is a specific tRNA for each of the 20 different amino acids.A tRNA molecule transports an amino acid to the ribosome. Notice that the 3-letter anticodon on the tRNA molecule matches the 3-letter code (called a codon) in the mRNA. The tRNA with the anticodon "UAC" bonds with methionine. It always transports methionine. Transfer RNA molecules with different anticodons transport other amino acids.An initiation code signals the start of a genetic message. As the ribosome moves along a mRNA transcript, it will not begin synthesizing protein until it reaches an initiation code.

Termination codes signal the end of the genetic message. Synthesis stops when the ribosome reaches a terminator codon.