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What is a chromosome?
In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.
To achieve the overall packing ratio, DNA is not packaged directly into final structure of chromatin. Instead, it contains several hierarchies of organization. The first level of packing is achieved by the winding of DNA around a protein core to produce a "bead-like" structure called a nucleosome. This gives a packing ratio of about 6. This structure is invariant in both the euchromatin and heterochromatin of all chromosomes.
The second level of packing is the coiling of beads in a helical structure called the 30 nm fiber that is found in both interphase chromatin and mitotic chromosomes. This structure increases the packing ratio to about 40. The final packaging occurs when the fiber is organized in loops, scaffolds and domains that give a final packing ratio of about 1000 in interphase chromosomes and about 10,000 in mitotic chromosomes.
Eukaryotic chromosomes consist of a DNA-protein complex that is organized in a compact manner which permits the large amount of DNA to be stored in the nucleus of the cell. The subunit designation of the chromosome is chromatin. The fundamental unit of chromatin is the nucleosome.
Chromatin is the unit of analysis of the chromosome; chromatin reflects the general structure of the chromosome but is not unique to any particular chromosome
Nucleosome is simplest packaging structure of DNA that is found in all eukaryotic chromosomes; DNA is wrapped around an octamer of small basic proteins called histones; 146 bp is wrapped around the core and the remaining bases link to the next nucleosome; this structure causes negative supercoiling.
The nucleosome consists of about 200 bp wrapped around a histone octamer that contains two copies of histone proteins H2A, H2B, H3 and H4. These are known as the core histones. Histones are basic proteins that have an affinity for DNA and are the most abundant proteins associated with DNA. The amino acid sequence of these four histones is conserved suggesting a similar function for all.
The length of DNA that is associated with the nucleosome unit varies between species. But regardless of the size, two DNA components are involved. Core DNA is the DNA that is actually associated with the histone octamer. This value is invariant and is 146 base pairs. The core DNA forms two loops around the octamer, and this permits two regions that are 80 bp apart to be brought into close proximity.
Thus, two sequences that are far apart can interact with the same regulatory protein to control gene expression. The DNA that is between each histone octamer is called the linker DNA and can vary in length from 8 to 114 base pairs. This variation is species specific, but variation in linker DNA length has also been associated with the developmental stage of the organism or specific regions of the genome.
The next level of organization of the chromatin is the 30 nm fiber. This appears to be a solenoid structure with about 6 nucleosomes per turn. This gives a packing ratio of 40, which means that every 1 µm along the axis contains 40 µm of DNA. The stability of this structure requires the presence of the last member of the histone gene family, histone H1. Because experiments that strip H1 from chromatin maintain the nucleosome, but not the 30 nm structure, it was concluded that H1 is important for the stabilization of the 30 nm structure.
The final level of packaging is characterized by the 700 nm structure seen in the metaphase chromosome. The condensed piece of chromatin has a characteristic scaffolding structure that can be detected in metaphase chromosomes. This appears to be the result of extensive looping of the DNA in the chromosome.
The last definitions that need to be presented are euchromatin and heterochromatin. When chromosomes are stained with dyes, they appear to have alternating lightly and darkly stained regions. The lightly-stained regions are euchromatin and contain single-copy, genetically-active DNA. The darkly-stained regions are heterochromatin and contain repetitive sequences that are genetically inactive.
What else can I help you with?
What is it called when a DNA copies itself?
DNA replication
During which phase does the DNA make a copy of itself?
DNA is replicated in the Synthesis stage of the cell cycle.
How are the three subphases of interphase alike?
The first sub-phase is the G1 phase. In this phase, the daughter cell formed in mitosis grows in size, while maintaining normal metabolic rates. The second sub-phase is the S phase. In this phase, the DNA in the nucleus replicates itself. The third sub-phase is the G2 phase. In this phase, the cell prepares itself for mitosis by starting to condense the chromatin into chromosomes.
How does six feet of DNA fit into the nucleus?
DNA, or deoxyribonucleic acid, is bunched up and wound together in order to fit into the nucleolus. It is very thin, so it occupies a small space. It is almost as thin, even thinner, than one strand of hair.
What is conservative replication in science?
Conservative replication and semiconservative replication are the ways DNA reproduces itself. The difference being whether the newly formed strands pair with each other or with an old one.
What structure into which DNA arranges itself?
DNA arranges itself into a double helix.
Which DNA code can make a copy of itself?
The universal DNA code can make a copy of itself.
Which DNA code can move itself into the cytoplm?
The DNA code that can move itself into the cytoplasm is ribosomes.
By which process does DNA duplicate itself?
The process in which DNA duplicates itself is called DNA replication. This process is an important factor in biological inheritance.
Why are the RNA viruses not able to package DNA?
RNA viruses lack the necessary machinery to package DNA because their replication process is specific to RNA. These viruses use RNA-dependent RNA polymerase to replicate their genetic material, not DNA. Additionally, their capsid proteins are designed to encapsulate RNA genomes, not DNA.
Why would you use model of DNA rather than the DNA itself to understand its structure?
Because you can not Really see DNA itself and the mode will give you a better insight on the DNA
The process by which DNA copies itself is called?
DNA replication
When DNA copies itself what is this process called?
DNA Replication :)
What is it called when a DNA molecule reproduce itself?
DNA replication
Can DNA live by itself?
No
What small DNA strand makes a copy of itself?
A virus is a small strand of DNA or RNA that copies itself.
What is the name of the family of DNA binding proteins that function to package DNA into chromatin?
histones are the proteins that compact and order DNA into subunits in the first step of the making of chromatin
