Dna Transfers To Messenger Rna example essay topic

Nucleic Acids and Protein Synthesis 7-1 DNA Cells "know" how to how to produce ATP, how to build cilia and centrioles, how to produce membranes and enzymes. A program, or code, in living cells must be able to duplicate itself quickly and accurately and must also have a means of being decoded and put into effect. The Genetic Code Biologists call the program of the cell the genetic code. The work genetic refers to anything that relates to heredity. The genetic code is the way in which cells store program that they seem to pass from one generation to another. Transformation When a strain of information is passed to another, it is called transformation.

The Transforming Factor DNA is the nucleic acid that stores and transmits the genetic information from one generation of an organism to the next. DNA carries the genetic code. Bacteriophages Some virus us are known as bacteriophages which mean bacteria eaters. Bacteriophages are composed of a DNA core and a protein coat. They attach themselves to the surface of a bacterium and then inject a material into the bacterium.

Once inside the bacterium, the injected material begins to reproduce, making may copies of the bacteriophage. Soon the bacterium bursts, and several hundred bacteriophages are released to infect other cells. Because the material injected into the bacterium produces new bacteriophages, it must contain the genetic code. The Structure of DNA DNA is a polymer formed from units called nucleotides. Each nucleotide is a molecule make up of three basic parts: a 5-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous, or nitrogen-containing, base. DNA contains four nitrogenous bases.

Two of the nitrogenous bases, adenine and guanine belonging to a group of compounds known as purines. The remaining two, cytosine and thymine, are known as pyrimidines. Individual nucleotides are joined together to form a long chain. X-Ray Evidence Fibers that make up DNA are twisted, like the strands of a rope.

Large groups of molecules in the fiber are spaced out at regular intervals along the length of the The Replication of DNA Because each of the two strands of the DNA double he hx has all the information, by the mechanism of base pairing, to reconstruct the other half, the strands are said to be complementary. There are four nitrogenous bases in DNA. Each strand of the double helix of DNA serves as a template, or pattern, against which a new strand is made. Before a cell divides, it must duplicate its DNA.

This ensures that each resulting cell will have a complete set of DNA molecules. This copying process is known as replication. DNA replication, or DNA synthesis, is carried out by a series of enzymes. These enzymes separate, or "unzip", the two strands of the double helix, insert the appropriate bases, and produce covalent sugar-phosphate links to extend the growing DNA chains. The enzymes even "proofread" the bases that have been inserted to ensure that they are paired correctly. The unzipping occurs when the hydrogen bonds between the base pairs are broken and the two strands of the molecule unwind.

Each of the separated strands serves as a template for the attachment of complementary bases. Two DNA molecules identical to each other and to the original molecule are made. 7-2 RNA The double helix structure explains how DNA can be replicated, or copied. However, it does not explain how information is contained in the molecule or how that information is put to good use. DNA contains a set of instructions that are coded in the sequence, or order, of nucleotides. The first step in decoding that message is to copy part of the sequence into RNA (ribonucleic acid).

RNA is the nucleic acid that acts as a messenger between DNA and the ribosomes and carries out the process by which proteins are made from amino acids. The Structure of RNA RNA, like DNA, consists of a long chain of macromolecules made up of nucleotides. Each nucleotide is made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base. The alternating sugars and phosphate groups form the backbone of the RNA chain.

There are three major differences between RNA and DNA. The sugar in RNA is ribose, whereas the sugar in DNA is deoxyribose. Another difference between RNA and DNA is that RNA consists of a single strand of nucleotides, although it can form double-stranded sections by folding back on itself in loops. DNA, as you will recall, is double-stranded. Lastly, the nitrogenous bases found in DNA are adenine, thymine, cytosine, and guanine. RNA also contains adenine, cytosine, and guanine, but uracil (to om-uh-s ihl) is present instead of thymine.

Like DNA, RNA follows the base pairing rules. Adenine bonds to uracil, and cytosine bonds to guanine. Although a cell contains many different forms of RNA, there are three main types that are involved in expressing the genetic code. In its own way, an RNA molecule is a disposable copy of a segment of DNA. The ability to copy a DNA base sequence into RNA makes it possible for a specific place on the DNA molecule to produce hundreds or even thousands of RNA molecules with the same information as DNA. Transcription: RNA Synthesis As you will recall, DNA replication is also known as DNA synthesis because the molecule being synthesized turns out to be the same as the molecule being copied.

In RNA synthesis, the molecule being copied is just one of the two strands of a DNA molecule. Thus the molecule being synthesized is different from the molecule being copied. The term transcription is used to describe this process. Transcription is the process by which a molecule of DNA is copied into a complementary strand of RNA. DNA is found in the nucleus and ribosomes are located in the cytoplasm.

Because DNA does not leave the nucleus, a messenger, or carrier, must bring the genetic information from the DNA in the nucleus out to the ribosomes in the cytoplasm. The molecule that performs this function is messenger RNA (mRNA), one of the three main types of RNA. During transcription, RNA polymerase attaches to special places on the DNA molecule, separates the two strands of the double helix, and synthesizes a messenger RNA strand. The messenger RNA strand is complementary to one of the DNA strands. The base-pairing: mechanism ensures that the messenger RNA will be a complementary copy of the DNA strand that serves as its template. 7-3 Protein Synthesis The information that DNA transfers to messenger RNA is in the form of a code.

This code is determined by the way in which the four nitrogenous bases are arranged in DNA. The nitrogenous bases in DNA contain information that directs protein synthesis. Because most enzymes are proteins, proteins control biochemical pathways within the cell. Not only do proteins direct the synthesis of lipids, carbohydrates, and nucleotides, but they are also responsible for cell structure and cell movement. Together, DNA and its assistant, RNA, are directly responsible for making proteins.

The Nature of the Genetic Code DNA and RNA each contain different nitrogenous bases (DNA contains A, T, C, G; RNA contains A, U, C, G); hence, different nucleotides. In order to code for the 20 different amino acids, more than one nucleotide must make up the code word for each amino acid. The code word of the DNA nucleotides are copied onto a strand of messenger RNA. Each combination of three nucieo- tides on the messenger RNA is called a codon, or three- letter code word. Each codon specifies a particular amino acid that is to be placed in the polypeptide chain.

There is more than one codon for each amino acid. Translation The decoding of a messenger RNA message into a polypeptide chain (protein) is known as translation. There is an elaborate mechanism that involves the two other main types of RNA - transfer RNA (tRNA) and ribosomal RNA (rRNA) - and the cytoplasmic organelle known as the ribosome. Transfer RNA carries amino acids to the ribosomes, where the amino acids are joined together to form polypeptides. Transfer RNA is a single strand of RNA that loops back on it self. Ribosomal RNA makes up the major part of the ribosomes.

THE ROLE OF TRANSFER RNA You will notice that there are three exposed bases on each transfer RNA molecule. These nucleotides will base pair with a codon on messenger RNA. Because the three nucleotides on transfer RNA are complementary to the three nucleotides on messenger RNA, the three transfer RNA nucleotides are called the anticodon. Attached to each transfer RNA molecule is the amino acid speci hed by the codon to which it base pairs. By matching the transfer RNA anticodon to the messenger RNA codon, the correct amino acid is put into place.

Each transfer RNA acts like a tiny beacon for its specific amino acid. THE ROLE OF THE RIBOSOME Messenger RNA molecules do not automatically line up transfer RNA molecules and link their amino acids together. Instead, this process of protein synthesis takes place in organelles known as ribosomes. Ribosomes are made up of two subunits, a large one and a smaller one. Each subunit consists of ribosomal RNA and proteins (about 70 different types). The first part of protein synthesis occurs when the two subunits of the ribosome bind to a molecule of messenger RNA.

Then the initiator codon: AUG binds to the first anticodon of transfer RNA, signaling the beginning of a polypeptide chain. Soon the anticodon of another transfer RNA binds to the next messenger RNA codon. T: his second transfer RNA carries the second amino acid that will be placed into the chain of the polypeptide. The polypeptide chain continues to grow until the ribosome reaches a stop codon on the messenger RNA. A stop codon is a codon for which no transfer RNA molecules exist. When the stop codon reaches the ribosome, the ribosome releases the newly formed polypeptide and messenger RNA, completing the process of translation.

As you can now see, the ribosome, in its own way, is at the center of the whole business of making the genetic code work. In the nucleus, DNA directs the formation of three different kinds of RNA: transfer RNA, ribosomal RNA, and messenger RNA. They all leave the nucleus and then seem to go their separate ways.