Figure 9. There is a second nucleic acid in all cells called ribonucleic acid, or RNA. Each of the nucleotides in RNA is made up of a nitrogenous base, a five-carbon sugar, and a phosphate group.
In the case of RNA, the five-carbon sugar is ribose, not deoxyribose. RNA nucleotides contain the nitrogenous bases adenine, cytosine, and guanine. Molecular biologists have named several kinds of RNA on the basis of their function.
For this reason, the DNA is protected and packaged in very specific ways. In addition, DNA molecules can be very long. Stretched end-to-end, the DNA molecules in a single human cell would come to a length of about 2 meters.
Thus, the DNA for a cell must be packaged in a very ordered way to fit and function within a structure the cell that is not visible to the naked eye. The chromosomes of prokaryotes are much simpler than those of eukaryotes in many of their features Figure 9. Most prokaryotes contain a single, circular chromosome that is found in an area in the cytoplasm called the nucleoid. The size of the genome in one of the most well-studied prokaryotes, Escherichia coli, is 4. So how does this fit inside a small bacterial cell?
The DNA is twisted beyond the double helix in what is known as supercoiling. Some proteins are known to be involved in the supercoiling; other proteins and enzymes help in maintaining the supercoiled structure. But the pathogens that cause disease are increasingly developing resistance to the ZCCHC4 influences cell Although, other nucleic acid-like polymers are known, yet much remains unknown regarding possible RNA, or ribonucleic acid, is a molecule that plays a central role in the function of The modification is apparently attached to molecules only when cells are under stress, and is rapidly removed Using a novel technique, researchers have been able What Makes Us Human?
The first step in transcription is initiation. During this step, RNA polymerase and its associated transcription factors bind to the DNA strand at a specific area that facilitates transcription Figure 1. Strand elongation. Once RNA polymerase and its related transcription factors are in place, the single-stranded DNA is exposed and ready for transcription. At this point, RNA polymerase begins moving down the DNA template strand in the 3' to 5' direction, and as it does so, it strings together complementary nucleotides.
By virtue of complementary base- pairing, this action creates a new strand of mRNA that is organized in the 5' to 3' direction. This process is called elongation. As the mRNA elongates, it peels away from the template as it grows Figure 5.
This mRNA molecule carries DNA's message from the nucleus to ribosomes in the cytoplasm, where proteins are assembled. However, before it can do this, the mRNA strand must separate itself from the DNA template and, in some cases, it must also undergo an editing process of sort.
In this view, the 5' end of the RNA strand is in the foreground. Note the inclusion of uracil yellow in RNA. Termination and editing. Figure 6: In eukaryotes, noncoding regions called introns are often removed from newly synthesized mRNA. One extends from the upper left corner to the mid-right side. The other strand forms a loop, with the two ends pinched together and nearly touching the first strand. The sugar-phosphate backbone is depicted as a segmented white cylinder.
Nitrogenous bases are represented as blue, green, yellow, or red vertical rectangles extending downward from each segment on the sugar-phosphate backbone. The loop represents a section of mRNA, called an intron, that has been removed from the coding sequence. This process is referred to as termination. In eukaryotes, the process of termination can occur in several different ways, depending on the exact type of polymerase used during transcription.
In some cases, termination occurs as soon as the polymerase reaches a specific series of nucleotides along the DNA template, known as the termination sequence. The four bases that make up this code are adenine A , thymine T , guanine G and cytosine C.
Bases pair off together in a double helix structure, these pairs being A and T, and C and G. RNA molecules, by comparison, are much shorter 3. Eukaryotic cells, including all animal and plant cells, house the great majority of their DNA in the nucleus, where it exists in a tightly compressed form, called a chromosome 4. This squeezed format means the DNA can be easily stored and transferred.
In addition to nuclear DNA, some DNA is present in energy-producing mitochondria, small organelles found free-floating in the cytoplasm, the area of the cell outside the nucleus. The three types of RNA are found in different locations. If it receives the correct signal from the ribosome, it will then hunt down amino acid subunits in the cytoplasm and bring them to the ribosome to be built into proteins 5.
Ribosomes are formed in an area of the nucleus called the nucleolus, before being exported to the cytoplasm, where some ribosomes float freely.
Other cytoplasmic ribosomes are bound to the endoplasmic reticulum, a membranous structure that helps process proteins and export them from the cell 5. Meet The Author.
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