The histones also have long tails these play an important role in regulation but also contribute to stability of the nucleosomes. Why do histones bind tightly to DNA?
Aug 3, Explanation: Histones are proteins that pack the DNA into manageable packages. Related questions How do I determine the molecular shape of a molecule? By selecting desirable traits and breeding Capsicum plants, people have been able to develop different varieties of peppers, including different colored peppers.
Happy reading — and best of luck to you! The early general belief that proteins were more likely to be the carrier of genetic information than DNA was because. Hello again Nana, What fueled the early belief that proteins — and not DNA — were most likely the carrier of genetic information?
Nucleotides are the monomer units that make up DNA. There are four different DNA nucleotides — adenine A , guanine G , cytosine C , and thymine T — each of which contains a phosphate, a deoxyribose sugar, and a nitrogenous base. Nucleotides are covalently linked to one another via the formation of a phosphodiester bond between the sugar group of one nucleotide and the phosphate group of a second nucleotide. Amino acids are the monomer units that make up proteins, and there are twenty different types of amino acids.
Each amino acid comprises a central carbon atom linked to a carboxylic acid group, a nitrogen-containing group called an amine, a hydrogen atom, and one of twenty different side chain groups that defines the amino acid.
Amino acids are covalently linked to each other via the formation of a peptide bond between the carboxylic acid group of one amino acid and the amino group of a second amino acid. The quick answer to your question is that early molecular biologists predicted that proteins, rather than DNA, were the carriers of genetic information because the number of protein building blocks i.
How can four different nucleotides encode the information required to produce proteins built of twenty different amino acids? The resulting mRNA molecules are made up of codons, which are three nucleotide units used by the translation machinery to produce proteins.
Each spot in a codon can be occupied by one of four nucleotides: A, U, G, and C. All 64 codons are observed in cells, but all do not encode amino acids. The remaining 61 codons represent amino acids. The strange thing is that there are only twenty different amino acids.
Why have 61 codons for only 20 amino acids? Why have three different stop codons? Nucleosomes can move to open the chromosome structure to expose a segment of DNA, but do so in a very controlled manner.
Figure 2. Nucleosomes can slide along DNA. When nucleosomes are spaced closely together top , transcription factors cannot bind and gene expression is turned off. When the nucleosomes are spaced far apart bottom , the DNA is exposed. Transcription factors can bind, allowing gene expression to occur. Modifications to the histones and DNA affect nucleosome spacing. In females, one of the two X chromosomes is inactivated during embryonic development because of epigenetic changes to the chromatin.
What impact do you think these changes would have on nucleosome packing? How closely the histone proteins associate with the DNA is regulated by signals found on both the histone proteins and on the DNA. These signals are functional groups added to histone proteins or to DNA and determine whether a chromosomal region should be open or closed Figure 3 depicts modifications to histone proteins and DNA.
These tags are not permanent, but may be added or removed as needed. These groups do not alter the DNA base sequence, but they do alter how tightly wound the DNA is around the histone proteins. DNA is a negatively charged molecule and unmodified histones are positively charged; therefore, changes in the charge of the histone will change how tightly wound the DNA molecule will be. By adding chemical modifications like acetyl groups, the charge becomes less positive, and the binding of DNA to the histones is relaxed.
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