Chromosome - Wikipedia
A chromosome is a Deoxyribonucleic acid (DNA) molecule with part or all of the genetic . Instead, their DNA is organized into a structure called the nucleoid. In molecular biology application, this allows for its isolation from plasmid DNA by Mitotic metaphase chromosomes are best described by a linearly organized. Describe the structure of DNA; Describe how eukaryotic and prokaryotic . Molecular biologists have named several kinds of RNA on the basis of their function. The chromosomes of prokaryotes are much simpler than those of eukaryotes in. Read and learn for free about the following article: DNA structure and function. These chromosomes are made up of thousands of shorter segments of DNA, this biological function because of its molecular structure, and because of the . Imagine a basic sort of organism that only makes four proteins, each of which.
A, C, T, G. Each nucleotide monomer is built from three simple molecular parts: The sugar and acid in all four monomers are the same All four nucleotides A, T, G and C are made by sticking a phosphate group and a nucleobase to a sugar.
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The sugar in all four nucleotides is called deoxyribose. The ring contains one oxygen and four carbons. A fifth carbon atom is attached to the fourth carbon of the ring. Deoxyribose also contains a hydroxyl group -OH attached to the third carbon in the ring.
A diagram showing the three main components of a nucleotide: The phosphate group is a phosphorous atom with four oxygen atoms bonded to it. The phosphorous atom in phosphate has a marked tendency to bond to other oxygen atoms for instance, the oxygen atom sticking off the deoxyribose sugar of another nucleotide. The four nucleotide monomers are distinguished by their bases Each type of nucleotide has a different nucleobase stuck to its deoxyribose sugar.
A nucleotide contains adenine G nucleotide contains guanine C nucleotide contains cytosine All four of these nucleobases are relatively complex molecules, with the unifying feature that they all tend to have multiple nitrogen atoms in their structures.
For this reason, nucleobases are often also called nitrogenous bases. Phosphodiester bonds are part of a larger class of electromagnetic attractions between atoms that chemists refer to as covalent bonds.
In order to keep things organized, biochemists have developed a numbering system for talking about the molecular structure of nucleotides. These numbers are applied to the carbon atoms in the sugar, starting at the carbon immediately to the right of the oxygen in the deoxyribose ring, and continuing in a clockwise fashion: A diagram showing the carbons on the ribose ring numbered.
The phosphate group is attached to the 5' carbon. The -OH group is attached to the 3' carbon and the base is attached to the 1' carbon. Many molecules rely on dehydration synthesis to assist with forming polymers.
A diagram showing how dehydration synthesis is used to make a string of DNA. Chromosomes are made of two DNA polymers that stick together via non-covalent hydrogen bonds Chromosomal DNA consists of two DNA polymers that make up a 3-dimensional 3D structure called a double helix.
Diagram showing how the two strands of double stranded DNA runs anti-parallel to each other. One strand runs in a 3' to 5' direction while the other runs in a 5' to 3' direction.
The nucleotides forming each DNA strand are connected by noncovalent bonds, called hydrogen bonds. Considered individually, hydrogen bonds are much weaker than a single covalent bond, such as a phosphodiester bond. But, there are so many of them that the two DNA polymers are very strongly connected to each other. Although the replication and transcription of DNA is highly standardized in eukaryotesthe same cannot be said for their karyotypes, which are often highly variable.
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There may be variation between species in chromosome number and in detailed organization. In some cases, there is significant variation within species. Also, variation in karyotype may occur during development from the fertilized egg.
The technique of determining the karyotype is usually called karyotyping. Cells can be locked part-way through division in metaphase in vitro in a reaction vial with colchicine. Like many sexually reproducing species, humans have special gonosomes sex chromosomes, in contrast to autosomes. These are XX in females and XY in males. How many chromosomes does a normal diploid human cell contain?
Using cells in culture Arresting mitosis in metaphase by a solution of colchicine Pretreating cells in a hypotonic solution 0.
DNA, genes and chromosomes — University of Leicester
It took until before the human diploid number was confirmed as Aberrations[ edit ] In Down syndrome, there are three copies of chromosome 21 Chromosomal aberrations are disruptions in the normal chromosomal content of a cell and are a major cause of genetic conditions in humans, such as Down syndromealthough most aberrations have little to no effect.
Some chromosome abnormalities do not cause disease in carriers, such as translocationsor chromosomal inversionsalthough they may lead to a higher chance of bearing a child with a chromosome disorder.
Abnormal numbers of chromosomes or chromosome sets, called aneuploidymay be lethal or may give rise to genetic disorders. The gain or loss of DNA from chromosomes can lead to a variety of genetic disorders.
Cri du chatwhich is caused by the deletion of part of the short arm of chromosome 5. Affected individuals have wide-set eyes, a small head and jaw, moderate to severe mental health problems, and are very short. Down syndromethe most common trisomy, usually caused by an extra copy of chromosome 21 trisomy DNA But your genes also mean that you probably look a bit like other members of your family.
For example, have you been told that you have 'your mother's eyes' or 'your grandmother's nose'? Genes influence what we look like on the outside and how we work on the inside. They contain the information our bodies need to make chemicals called proteins. Proteins form the structure of our bodies, as well playing an important role in the processes that keep us alive. Genes are made of a chemical called DNA, which is short for 'deoxyribonucleic acid'.
The DNA molecule is a double helix: The DNA double helix showing base pairs The sides are sugar and phosphate molecules. The rungs are pairs of chemicals called 'nitrogenous bases', or 'bases' for short.
There are four types of base: These bases link in a very specific way: A always pairs with T, and C always pairs with G.