Full Answer
How is DNA packed in eukaryotic cells?
Eukaryotes, whose chromosomes each consist of a linear DNA molecule, employ a complex type of packing strategy to fit their DNA inside the nucleus (Figure 4). At the most basic level, DNA is wrapped around proteins known as histones to form structures called nucleosomes.
What is the structure of DNA?
The DNA is not a naked molecule, but it is wrapped around a core of height proteins, called histones (H2A,H2B,H3 and H4). Those protein contribute to package the DNA into the nucleus ( that is few nanometers big, while the uncoiled DNA is around 1 millimeter ! ).
How many pieces of DNA are there in the nucleus?
Humans have 46 pieces of DNA in the nucleus - each strand (plus the protein that keeps the strand organised) is called a chromosome. Each DNA strand is wrapped around proteins so that is it compressed enough to be stored and organised in the nucleus.
What is DNA wrapped around?
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 form an octamer of eight histone proteins attached together.
Why is DNA in the nucleus?
Where does DNA need to be organized?
What is the purpose of DNA primase?
How does DNA primase work?
How does DNA replication work?
What is DNA polymerase 3?
What is the process of making two identical copies of DNA?
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National Center for Biotechnology Information
National Center for Biotechnology Information
What is the region of DNA that contains the genetic material?
The region in the cell containing this genetic material is called a nucleoid (remember that prokaryotes do not have a separate membrane-bound nucleus). Some prokaryotes also have smaller loops of DNA called plasmids that are not essential for normal growth.
How is DNA twisted?
The DNA is twisted by what is known as supercoiling. Supercoiled DNA is coiled more tightly than would be typically be found in a cell (more than 10 nucleotides per twist of the helix). If you visualize twisting a rope until it twists back on itself, you have a pretty good visual of supercoiled DNA.
What are the mated pairs of chromosomes in a diploid organism called?
Matched pairs of chromosomes in a diploid organism are called homologous (“same knowledge”) chrom osomes. Of a pair of homologous chromosomes, one came from the egg and the second came from the sperm.
What are homologous chromosomes?
Homologous chromosomes are the same length and have specific nucleotide segments called genes in exactly the same location, or locus. Genes, the functional units of chromosomes, determine specific characteristics by coding for specific proteins. Traits are the variations of those characteristics.
What is the DNA of a prokaryote?
DNA Organization in Prokaryotes. A cell’s DNA, packaged as a double-stranded DNA molecule, is called its genome. In prokaryotes, the genome is composed of a single, double-stranded DNA molecule in the form of a loop or circle (Figure 1). The region in the cell containing this genetic material is called a nucleoid ...
Why are there variations in a gene?
The variation of individuals within a species is due to the specific combination of the genes inherited from both parents. Even a slightly altered sequence of nucleotides within a gene can result in an alternative trait. For example, there are three possible gene sequences (alleles) on the human chromosome that code for blood type: sequence A, sequence B, and sequence O. Because all diploid human cells have two copies of the chromosome that determines blood type, the blood type (the trait) is determined by which two versions of the marker gene are inherited. It is possible to have two copies of the same allele on both homologous chromosomes, with one on each (for example, AA, BB, or OO), or two different alleles, such as AB.
How many base pairs are in a bacteria genome?
The size of the genome in one of the most well-studied prokaryotes, E.coli, is 4.6 million base pairs (which would be approximately 1.1 mm in length, if cut and stretched out). So how does this fit inside a small bacterial cell? The DNA is twisted by what is known as supercoiling. Supercoiled DNA is coiled more tightly than would be typically be found in a cell (more than 10 nucleotides per twist of the helix). If you visualize twisting a rope until it twists back on itself, you have a pretty good visual of supercoiled DNA. This process allows the DNA to be compacted into the small space inside a bacteria.
Why do we need to hold DNA strands apart?
Holding the strands apart allows the other necessary enzymes to access the DNA for replication.
What are the two types of nitrogen bases on nucleotides?
Both are types of nitrogen bases on nucleotides. Purines are double rings and pyrimidine are single ring structures. Purines include A and G. Pyrimidines are T and C.
How many hydrogen bonds are in a base pair?
A-T base pairs have two hydrogen bonds holding the bases together whereas C-G have three hydrogen bonds holding them together. Two bonds are easier for helicase to break through than three bonds, therefore helicase will start replication at A-T base pairs.
Do all cells in a human body have the same DNA?
All the cells in a person's body have the same DNA and the same genes.
What imaging was used to determine the structure of DNA?
Took x-ray crystallography images of a DNA molecule
Which two nitrogen bases are equal to the nitrogen bases in a human body cell?
Discovered that there were equal amounts of the nitrogen bases A + T and C + G in a human body cell, concluded that A paired with T and C paired with G
How far does one strand move in a replication fork?
One strand moves into the replication fork, from 5' to 3' , and the other strand moves out from 3' to 5'
How does DNA fit into the nucleus?
So as to how it fits into the nucleus, it fits because quite a bit is wrapped around histones, which in turn form the DNA into chromosomes, which allow for tight packing of the long strands of DNA.
What is the structure of DNA that is tightly packed up to fit in the nucleus of every cell?
Histone proteins act like molecular spools that coil the strands of DNA into bead-like units called nucleosomes. A nucleosome contains eight histones wrapped by DNA, and serves as the repeated primary unit for organizing the higher levels of chromatin structure. These nucleosomes coil and stack together to form fibers called chromatin. Chromatin, in turn, loops and folds with the help of additional proteins to form chromosomes. Condensing DNA into chromosomes prevents DNA tangling and da
How is DNA stored in a loop?
The DNA is put into a loop shape around the histones, which are protein structures. The loop shape of the DNA in the DNA/histone complex allows a larger amount of DNA to be compacted in the small space of the nucleus. The DNA/histone complex is collectively referred to as chromatin; the monomer of chromatin is a unit called the nucleosome, which has 8 histone units and DNA. Imagine coiling a garden hose so each coil is about a foot long. The hose can now be stored in a smaller space than storing it in terms of finding a place long enough to put the hose in when it is completely unwound and at
How does DNA control the cell?
Think of how DNA “controls” the cell; proteins essentially react with the DNA and the environment by catalyzing the polymerization of an RNA DNA complex that is quickly split apart . Once the RNA polymer has been produced, the RNA is modified by RNA and protein complexes, excising out introns, or “non-coding material”. The remaining RNA can then be put together in different orders for a wide range of functions. This RNA, mRNA, enters the cytoplasm and interacts with a
How is information coded on DNA copied?
The EXPRESSION of the information coded on the DNA is done through the messenger RNA (mRNA), another polymer like DNA but with the difference that it has a uracil (U) instead of a thymine (T) base. The information is copied from the DNA to the mRNA in a process called transcription. The term transcription refers to the same sense as in usual English language. The information on the DNA is written in a SCRIPT of four letters (A, T, G and C) while the same information is written on the RNA in a slightly different SCRIPT, again of four letters (A, U, G and C). So only the script changes, the grammar and the words remain same.
How long is E. coli DNA?
It is indeed a huge problem for the cell to manage the DNA. The total length of an E. coli (the most widely studied bacterium and the most trusted friend of molecular biologists) is about 2 micron and its diameter is around 1 microns with a volume of around 1 cubic microns. Although the exact length of the total DNA contained in the cell is difficult to estimate due to its compact structure even after removal from the cell and also due to the presences of several short fragments, the estimate is that the total length is in several hundred microns (1). The reason I am giving to you the example o
Why is DNA not in its most highly condensed chromosome form most of the time?
It is important to note that the reason the DNA is not in its most highly-condensed chromosome form most of the time (when the cell is not dividing) is so that the DNA may be accessed for gene transcription. Looser DNA = easier access.
Why is DNA in the nucleus?
DNA is usually sprawled out among the entire nucleus. This allows its code to be available for transcription machinery which will lead to the production of proteins. However, when each cell starts to grow and divide, the DNA needs to be organized and packaged within the nucleus for an orderly division during mitosis.
Where does DNA need to be organized?
DNA needs to be organized in the nucleus so it condensed to go through the stages of mitosis. The DNA helix is first wrapped around histone proteins to form nucleosomes. These nucleosomes condense together to make chromatin which is further condensed into a full chromosome.
What is the purpose of DNA primase?
Once the DNA is separated and exposed, DNA Primase comes in to make an RNA primer complementary to a few base pairs. This primer is required to start the synthesis of DNA and is a sort of landing site for the next enzyme in the process ‐ DNA Polymerase III. DNA Polymerase III is ultimately responsible for the replication and creation of the new strands of DNA.
How does DNA primase work?
However, it can't do this starting with an exposed single strand of DNA. DNA Primase resolves this problem by coming in and starting the process of DNA synthesis.
How does DNA replication work?
When DNA replication begins, the DNA is separated and positions called origins of replication are formed which signal the replication machinery to be recruited to this spot. The DNA is then separated from its double-helical structure into single strands by an enzyme called helicase. The helicase acts like a zipper to pull apart the DNA into 2 separate strands, exposing the DNA base pairs. As DNA strands are complementary to each other, the same information will be carried onto each of the new strands of DNA.
What is DNA polymerase 3?
DNA Polymerase III is a key molecule for DNA replication. DNA Polymerase III synthesizes the DNA by adding complementary nucleotides to the existing strand of DNA. This process must happen exactly, as the code of DNA needs to be replicated precisely. When replicating errors happen in this process it leads to mutations in the DNA, which can cause severe illnesses or diseases.
What is the process of making two identical copies of DNA?
DNA replication is the process of making two identical copies of the DNA in a cell. Cells usually never stop growing and dividing and the same number of chromosomes needs to be given to both cells.
