The DNA is twisted by what is known as supercoiling. Supercoiling means that DNA is either under-wound less than one turn of the helix per 10 base pairs or over-wound more than 1 turn per 10 base pairs from its normal relaxed state. Some proteins are known to be involved in the supercoiling; other proteins and enzymes such as DNA gyrase help in maintaining the supercoiled structure.
Eukaryotes, whose chromosomes each consist of a linear DNA molecule, employ a different type of packing strategy to fit their DNA inside the nucleus Figure 6.
At the most basic level, DNA is wrapped around proteins known as histones to form structures called nucleosomes. The histones are evolutionarily conserved proteins that are rich in basic amino acids and form an octamer. The DNA which is negatively charged because of the phosphate groups is wrapped tightly around the histone core. This nucleosome is linked to the next one with the help of a linker DNA.
This is further compacted into a 30 nm fiber, which is the diameter of the structure. At the metaphase stage, the chromosomes are at their most compact, are approximately nm in width, and are found in association with scaffold proteins.
In interphase, eukaryotic chromosomes have two distinct regions that can be distinguished by staining. The tightly packaged region is known as heterochromatin, and the less dense region is known as euchromatin. Heterochromatin usually contains genes that are not expressed, and is found in the regions of the centromere and telomeres.
The euchromatin usually contains genes that are transcribed, with DNA packaged around nucleosomes but not further compacted. Figure 6. These figures illustrate the compaction of the eukaryotic chromosome. Answer the question s below to see how well you understand the topics covered in the previous section. This short quiz does not count toward your grade in the class, and you can retake it an unlimited number of times. Use this quiz to check your understanding and decide whether to 1 study the previous section further or 2 move on to the next section.
Skip to main content. Search for:. Practice Questions The order of nucleotides in a gene in DNA is the key to how information is stored. Show Answer Answer c. The sequence of the bases codes for the instructions for protein synthesis. The shape is DNA is not related to information storage. The sugar-phosphate backbone only acts as a scaffold.
The presence of two strands is important for replication, but their information content is equivalent, as they are complementary to each other. Therefore, ten base pairs are present per turn of the helix.
The diameter of the DNA double helix is 2 nm, and it is uniform throughout. Only the pairing between a purine and pyrimidine can explain the uniform diameter. The twisting of the two strands around each other results in the formation of uniformly spaced major and minor grooves Figure 4. Figure 4. DNA has a a double helix structure and b phosphodiester bonds. The genetic information of an organism is stored in DNA molecules. How can one kind of molecule contain all the instructions for making complicated living beings like ourselves?
What component or feature of DNA can contain this information? It has to come from the nitrogen bases, because, as you already know, the backbone of all DNA molecules is the same. The sequence of these four bases can provide all the instructions needed to build any living organism.
But think about the English language, which can represent a huge amount of information using just 26 letters. Even more profound is the binary code used to write computer programs. This code contains only ones and zeros, and think of all the things your computer can do. The DNA alphabet can encode very complex instructions using just four letters, though the messages end up being really long.
For example, the E. The human genome all the DNA of an organism consists of around three billion nucleotides divided up between 23 paired DNA molecules, or chromosomes. The information stored in the order of bases is organized into genes : each gene contains information for making a functional product.
The genetic information is first copied to another nucleic acid polymer , RNA ribonucleic acid , preserving the order of the nucleotide bases. In order for DNA to function effectively at storing information, two key processes are required.
Every minute in , Google conducted 3. By an estimated 1. The magnetic or optical data-storage systems that currently hold this volume of 0s and 1s typically cannot last for more than a century, if that.
Further, running data centers takes huge amounts of energy. In short, we are about to have a serious data-storage problem that will only become more severe over time. An alternative to hard drives is progressing: DNA-based data storage.
Data can be stored in the sequence of these letters, turning DNA into a new form of information technology. It is already routinely sequenced read , synthesized written to and accurately copied with ease. DNA is also incredibly stable, as has been demonstrated by the complete genome sequencing of a fossil horse that lived more than , years ago.
More on transcription. How are polymerases different in prokaryotes and eukaryotes? How is bacterial transcription unique? How is transcription regulated? Once an mRNA molecule is complete, that molecule can go on to play a key role in the process known as translation.
During translation , the information that is contained within the mRNA is used to direct the creation of a protein molecule. In order for this to occur, however, the mRNA itself must be read by a special, protein-synthesizing structure within the cell known as a ribosome. Watch this video for a summary of eukaryotic transcription.
What are introns and exons? Key Concepts RNA replication transcription. Topic rooms within Genetics Close. No topic rooms are there. Browse Visually. Other Topic Rooms Genetics. Student Voices. Creature Cast. Simply Science. Green Screen. Green Science. Bio 2. The Success Code. Why Science Matters.
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