In eukaryotes such as plants and animals, the great majority of DNA is found in the nucleus and is called nuclear DNA. Mitochondria, organelles that harvest energy for the cell, contain their own mitochondrial DNA , and chloroplasts, organelles that carry out photosynthesis in plant cells, also have chloroplast DNA.
The amounts of DNA found in mitochondria and chloroplasts are much smaller than the amount found in the nucleus. In bacteria and other prokaryotes, most of the DNA is found in a central region of the cell called the nucleoid , which functions similarly to a nucleus but is not surrounded by a membrane. Since all of the cells in an organism with a few exceptions contain the same DNA, you can also say that an organism has its own genome, and since the members of a species typically have similar genomes, you can also describe the genome of a species.
In general, when people refer to the human genome, or any other eukaryotic genome, they mean the set of DNA found in the nucleus that is, the nuclear genome. Mitochondria and chloroplasts are considered to have their own separate genomes. Each species has its own characteristic number of chromosomes. Humans, for instance, have 46 chromosomes in a typical body cell, while dogs have Like many species of animals and plants, humans are diploid 2 n , meaning that most of their chromosomes come in matched sets known as homologous pairs.
Thus, the 46 chromosomes of a human cell are organized into 23 pairs, and the two members of each pair are said to be homologues of one another with the slight exception of the X and Y chromosomes; see below. Human sperm and eggs, which have only one homologous chromosome from each pair, are said to be haploid 1 n. When a sperm and egg fuse, their genetic material combines to form one complete, diploid set of chromosomes.
So, for each homologous pair of chromosomes in your genome, one of the homologues comes from your mom and the other from your dad. The two chromosomes in a homologous pair are generally very similar to one another. Bands appear when the chromosomes are stained with a dye, and the dark bands mark more compacted DNA usually, with fewer genes , while the light bands mark less compacted DNA usually, with more genes.
Most importantly, the two homologues in a pair carry the same type of genetic information. For instance, there is a gene found near the bottom of chromosome 15 that affects eye color [1]. A person might have the blue version, or allele , of this gene on one homologue, but the brown version on the other. Both homologues have the same type of gene in the same place, but they can and often do! They differ in size and shape, with the X being much larger than the Y, and contain different mostly different genes although they do have small regions of similarity.
The X and Y chromosomes are known as sex chromosomes , while the other 44 human chromosomes are called autosomes. The continuity of life from one cell to another has its foundation in the reproduction of cells by way of the cell cycle. Duration: 1 minutes, 30 seconds. ID: Source: www. Related Content. DNA is packaged in a chromosome. Zooming in on the x chromosome. Concept DNA is packaged in a chromosome. Each chromosome is a package for one very long, continuous strand of DNA.
All cells arise from pre-existing cells. Pathways, Making the protein In this section learn that in the cytoplasm, the messenger RNA is released from its carrier proteins and binds to a protein assembly complex called a ribosome. ID: Source: IC. Sickle cell anemia, 3D animation with narration Sickle cell anemia is a genetic disease that affects hemoglobin, the oxygen transport molecule in the blood.
Each chromosome consists of one continuous thread-like molecule of DNA coiled tightly around proteins, and contains a portion of the 6,,, basepairs DNA building blocks that make up your DNA. In this animation we'll see the remarkable way our DNA is tightly packed up to fit into the nucleus of every cell. The process starts with assembly of a nucleosome, which is formed when eight separate histone protein subunits attach to the DNA molecule.
The combined tight loop of DNA and protein is the nucleosome. Six nucleosomes are coiled together and these then stack on top of each other. The end result is a fiber of packed nucleosomes known as chromatin. This structure, is then looped and further packaged using other proteins which are not shown here to give the final "chromosomal" shapes.
It is this remarkable multiple folding which allows six feet of DNA to fit into the nucleus of each cell in our body.
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