I was wondering if you could answer the following question:
How do the cell organelles (apart from the nucleus and mitochondria) found in a human form? Does the nuclear DNA encode for the formation of these organelles (eg Golgi apparatus, Microtubules, cilia etc) in an individual?
Thanking you in advance for your time and help!
How do the cell organelles (apart from the nucleus and mitochondria) found in a human form?
hope these help
Does the nuclear DNA encode for the formation of these organelles (eg Golgi apparatus, Microtubules, cilia etc) in an individual?DNA code for the organelles. Basic organelles are replicate in the cell cycle. as u know that the G1 and S phase where organelles are also doubles so that they can be distributed in the daughter cell.
2. Different cell in case of eukaryotes according to their function have more organelles e.g if the cell is very active than the mitochondria in that is more in number than other cell. or the cells who take part in the production of proteins have more amount of Ribosomes for the synthesis of protein.
Also mitochondria and Chloroplast have their own DNA and replicate own their own and produce their own protein requires for the proper functioning of the organelle.
Although the vast majority of DNA in most eukaryotes is found in the nucleus, some DNA is present within the mitochondria of animals, plants, and fungi and within the chloroplasts of plants. These organelles are the main cellular sites for ATP formation, during oxidative phosphorylation in mitochondria and photosynthesis in chloroplasts (Chapter 16). Many lines of evidence indicate that mitochondria and chloroplasts evolved from bacteria that were endocytosed into ancestral cells containing a eukaryotic nucleus, forming endosymbionts. Over evolutionary time, most of the bacte-rial genes encoding components of the present-day organelles were transferred to the nucleus. However, mitochondria and chloroplasts in today's eukaryotes retain circular DNAs encoding proteins essential for organellar function as well as the ribosomal and transfer RNAs required for their translation. Thus eukaryotic cells have multiple genetic systems: a predominant nuclear system and secondary systems with their own DNA in the mitochondria and chloroplasts.
Mitochondria Contain Multiple mtDNA Molecules
Individual mitochondria are large enough to be seen under the light microscope and even the mitochondrial DNA (mtDNA) can be detected by fluorescence microscopy. The mtDNA is located in the interior of the mitochondrion, the region known as the matrix. As judged by the number of yellow fluorescent “dots” of mtDNA, a Euglena gracilis cell contains at least thirty mtDNA molecules
Since the dyes used to visualize nuclear and mitochondrial DNA do not affect cell growth or division, replication of mtDNA and division of the mitochondrial network can be followed in living cells using time-lapse microscopy. Such studies show that mtDNA replicates throughout interphase. At mitosis each daughter cell receives approximately the same number of mitochondria, but since there is no mechanism for apportioning exactly equal numbers of mitochondria to the daughter cells, some cells contain more mtDNA than others. All the mitochondria in eukaryotic cells contain multiple mtDNA molecules. Thus the total amount of mtDNA in a cell depends on the number of mitochondria, the size of the mtDNA, and the number of mtDNA molecules per mitochondrion.top link
Genes in mtDNA Exhibit Cytoplasmic Inheritance and Encode rRNAs, tRNAs, and Some Mitochondrial Proteins
Studies of mutants in yeasts and other single-celled organisms first indicated that mitochondria exhibit cytoplasmic inheritance and thus must contain their own genetic system (Figure 9-43). For instance, petite yeast mutants exhibit structurally abnormal mitochondria and are incapable of oxidative phosphorylation. As a result, petite cells grow more slowly than wild-type yeasts and form smaller colonies (hence the name “petite”). Genetic crosses between different (haploid) yeast strains showed that the petite mutation does not segregate with any known nuclear gene or chromosome. In later studies, most petite mutants were found to contain deletions of mtDNA.
Mitochondrial inheritance in yeasts is biparental: during the fusion of haploid cells, both parents contribute equally to the cytoplasm of the diploid. In mammals and most other animals, however, the sperm contributes little (if any) cytoplasm to the zygote, and virtually all of the mitochondria in the embryo are derived from those in the egg, not the sperm. Studies in mice have shown that 99.99 percent of mtDNA is maternally inherited, but a small part (0.01 percent) is inherited from the male parent. In higher plants, mtDNA is inherited exclusively in a uniparental fashion through the female parent (egg), not the male (pollen).
The entire mitochondrial genome from a number of different organisms has now been cloned and sequenced, and mtDNAs from all these sources have been found to encode rRNAs, tRNAs, and essential mitochondrial proteins. All proteins encoded by mtDNA are synthesized on mitochondrial ribosomes. All mitochondrially synthesized polypeptides identified thus far (with one possible exception) are not complete enzymes but subunits of multimeric complexes used in electron transport or ATP synthesis. Most proteins localized in mitochondria, such as the mitochondrial RNA and DNA polymerases, are synthesized on cytoplasmic ribosomes and are imported into the organelle by processes discussed in Chapter 17.top link
The Size and Coding Capacity of mtDNA Vary Considerably in Different Organisms
Surprisingly, the size of the mtDNA, the number and nature of the proteins it encodes, and even the mitochondrial genetic code itself, vary greatly among different organisms. Human mtDNA, a circular molecule that has been completely sequenced, is among the smallest known mtDNAs, containing 16,569 base pairs (Figure 9-44). It encodes the two rRNAs found in mitochondrial ribosomes and the 22 tRNAs used to translate mitochondrial mRNAs. Human mtDNA has 13 sequences that begin with an ATG (methionine) codon, end with a stop co