The Process of Transcription

Objectives

-Compare DNA and RNA -Describe the process of transcription -Contrast the three forms of RNA

DNA and RNA Differences

-DNA is a long helical ladder of connected nucleotides, while RNA is not double stranded or spiraled and tends to be a long linear strand. tRNA is bent in a number of tight hairpin turns and somewhat resembles the top of the lowercase letter t. rRNA is folded tightly and looks like disorganized cluster, though, in reality, it has a very specific and complex structure. -DNA: contains nitrogenous bases A, C, G, and T. RNA: contains nitrogenous bases A, G, C, and U. -The sugar in RNA is ribose, while the sugar in DNA is deoxyribose. -Differences in sugars makes DNA more stable, meaning it forms longer chains. RNA is less stable and forms shorter chains. -Two DNA molecules easily coil around each other because of the difference in sugar affects shape of the spiral. DNA is a double-stranded molecule. RNA is single-stranded. The single strand of RNA can fold and create structures that contain loops and bulges. -The complex structures of DNA and RNA are made possible by weak bonds between pairs of nitrogenous bases. DNA: A pairs with T, G pairs with C. The bonding between bases in RNA is not as specific as DNA. The U base usually pairs up with A but can also pair up with G, making it easier for RNA folding to occur. -There is one type of DNA; there are three types of RNA: messenger RNA, transfer RNA, and ribosomal RNA. -DNA is found only in the nucleus. Messenger RNA is found in the nucleus, transfer RNA is found in the cytoplasm, and ribosomal RNA is found in ribosomes. -DNA is self-replicating; the amount of DNA remains constant except during cell division. The cell makes RNA; the amount of RNA will vary, as it is made when needed.

Key Words

-Deoxyribose Sugar -Exon -Intron -Messenger RNA -Ribose Sugar -Ribosomal RNA -RNA Polymerase -Transfer RNA

Where does transcription begin?

At a promoter region

Where does transcription end?

At a terminator sequence

Comparing DNA and RNA/Similarities

DNA stands for deoxyribonucleic acid, and RNA stands fr ribonucleic acid. DNA stores genetic information, while RNA transfers genetic information and ensures that proteins are synthesized. The characteristics of each molecule support their roles in the cell. -Both DNA and RNA are made up of units called nucleotides -Each nucleotide has three components: a phosphate group, a sugar, and a nitrogenous base.

What are coding regions of DNA called?

Exons

Prokaryotes vs. Eukaryotes

In prokaryotes, RNA syntehsis and protein synthesis take place in the cytoplasm. In eukaryotes, RNA is produced in the cell's nucleus and then moves to the cytoplasm to play a role in the production of protein.

Transcription

In transciption, 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. RNA polymerase is an enzyme that binds to DNA during transcription and separates the DNA strands. It then uses one strand of DNA as a template from which to assemble nucleotides into a complementary strand of RNA. The ability to copy a single DNA sequence into RNA makes it possible for a single gene to produce hundreds or even thousands of RNA molecules.

Which regions of mRNA are edited out of the premature mRNA molecule to make the mature mRNA molecule??

Intron regions

What are noncoding regions of DNA called?

Introns

What molecules is used to move information from the nucleus to the cytoplasm?

Messenger RNA

Messenger RNA Synthesis and Processing

Messenger RNA molecules are not always ready to be translated into protein. They may have to be edited first. Segments of the protein that are edited out from the molecules are called introns, and the segments that remain are called exons.

Messenger RNA

Most genes contain instruction for assemblind amino acids into proteins. The RNA molecules that carry copies of these instructions are known as messenger RNA. They carry information from DNA to other parts of the cell.

Ribosomal RNA

Proteins are assembled on ribosomes, small organelles composed of two subunits. These subunits are made up of several ribosomal RNA molecules and as many as 80 different proteins.

What are two differences between DNA and RNA?

RNA is single stranded instead of double stranded; uracil replaces thyamine.

The Transcription Process

RNA molecules are created during a process called transcription. This process uses the enzyme RNA polymerase to transcribe segments of DNA into complementary RNA molecules. First the RNA polymerase binds to a promoter region of the DNA to initiate transcription. Then the mRNA is transported from the nucleus to the cytoplasm.

What enzyme carries out the transcription process?

RNA polymerase

Promoters

RNA polymerase only binds to promoters, regions of DNA that have specific base sequences. Promoters are signals in the DNA molecule that show RNA polymerase exactly where to begin making RNA.

What event causes the DNA to begin the process of making a protein?

The cell sends a chemical signal to the DNA that turns on the gene.

Transfer RNA

When a protein is built, a third type of RNA molecule transfers each amino acid to the ribosome as it is specified by the coded messages in mRNA. These molecules are known as transfer RNA.