What is the difference between a nucleoid and nucleus? When did (geological time

Question

What is the difference between a nucleoid and nucleus?

When did (geological time) vascular plants come on the scene on earth?

Name four differences between prokaryotic and eukaryotic cells

How do bacteria exchange their genetic material?

Cell differentiation is a distinct phenomenon in eukaryotic animals. Name any four kinds of differentiated cells in your body.

How large is a DNA molecule?

What is the difference between hematopoietic cells and embryonic stem cells?

What are pluripotent stem cells?

What is the difference between a virion and a provirus

What is endosymbiont theory?

Explanation / Answer

1,

The nucleus houses the cell's DNA. The nucleus is only found in eukaryotic cells.

The nucleolus is an organelle inside the nucleus that houses proteins and RNA. Also found in eukaryotic cells.

The nucleoid is an irregularly shaped region that houses genetic material. This is only found in prokaryotes.

2,

The evolution of plants has resulted in widely varying levels of complexity, from the earliest algal mats, through bryophytes,lycopods, ferns to the complex gymnosperms and angiosperms of today. While many of the groups which appeared earlier continue to thrive, as exemplified by algal dominance in marine environments, more recently derived groups have also dislocated previously ecologically dominant ones, e.g. the ascendance of flowering plants over gymnosperms in terrestrial environments.

In the Ordovician, around 450 million years ago, the first land plants appeared.These began to diversify in the Late Silurian, around 420 million years ago, and the results of their diversification are displayed in remarkable detail in an earlyDevonian fossil assemblage from the Rhynie chert. This chert preserved early plants in cellular detail, petrified in volcanic springs.

By the middle of the Devonian, most of the features recognised in plants today are present, including roots, leaves andsecondary wood. Late Devonian free-sporing plants such as Archaeopteris had reached a degree of sophistication that allowed them to form forests of tall trees. By Late Devonian times, seeds had evolved. Evolutionary innovation continued into the Carboniferous and is still ongoing today. Most plant groups were relatively unscathed by the Permo-Triassic extinction event, although the structures of communities changed. This may have set the scene for the appearance of the flowering plants in the Triassic (~200 million years ago), and their later diversification in the Cretaceous and Paleogene. The latest major group of plants to evolve were the grasses, which became important in the mid-Paleogene, from around40 million years ago. The grasses, as well as many other groups, evolved new mechanisms of metabolism to survive the lowCO
2 and warm, dry conditions of the tropics over the last 10 million years.

3,

prokaryotic cells do not have a nucleus and eukaryotic cells do.
- prokaryotic cells lack some organelles and eukaryotic cells do not.
- prokaryotic cells are not found in humans and eukaryotic cells are.
- prokaryotic cells are always unicellular and eukaryotic cells are often multicellular.
- prokaryotic cells reproduce/divide by binary fission and eukaryotic cells reproduce/divide by mitosis/meiosis

4,

Bacterial conjugation is the transfer of genetic material (plasmid) between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells. Discovered in 1946 by Joshua Lederberg and Edward Tatum, conjugation is a mechanism of horizontal gene transfer as are transformation andtransduction although these two other mechanisms do not involve cell-to-cell contact.

Bacterial conjugation is often regarded as the bacterial equivalent of sexual reproduction or mating since it involves the exchange of genetic material. During conjugation the donor cell provides a conjugative or mobilizable genetic element that is most often a plasmid or transposon. Most conjugative plasmids have systems ensuring that the recipient cell does not already contain a similar element.

The genetic information transferred is often beneficial to the recipient. Benefits may include antibiotic resistance, xenobiotic tolerance or the ability to use newmetabolites. Such beneficial plasmids may be considered bacterial endosymbionts. Other elements, however, may be viewed as bacterial parasites and conjugation as a mechanism evolved by them to allow for their spread.

5,

Although it is generally the case that biological cells are too small to be seen at all without a microscope, there are exceptions as well as considerable range in the sizes of various cell types. Eukaryotic cells are typically 10 times the size of prokaryotic cells (these cell types are discussed in the next Chapter). Plant cells are on average some of the largest cells, probably because in many plant cells the inside is mostly a water filled vacuole.:

6,

The human genome is the complete set of genetic information for humans (Homo sapiens sapiens). This information is encoded as DNA sequences within the 23 chromosome pairs in cell nuclei and in a small DNA molecule found within individual mitochondria. Human genomes include both protein-coding DNA genes and noncoding DNA. Haploid human genomes (contained in egg and sperm cells) consist of three billion DNA base pairs, while diploid genomes (found insomatic cells) have twice the DNA content. While there are significant differences among the genomes of human individuals (on the order of 0.1%), these are considerably smaller than the differences between humans and their closest living relatives, the chimpanzees (approximately 4% and bonobos.

The Human Genome Project produced the first complete sequences of individual human genomes. As of 2012, thousands of human genomes have been completely sequenced, and many more have been mapped at lower levels of resolution. The resulting data are used worldwide in biomedical science, anthropology, forensics and other branches of science. There is a widely held expectation that genomic studies will lead to advances in the diagnosis and treatment of diseases, and to new insights in many fields of biology, including human evolution.

Although the sequence of the human genome has been (almost) completely determined by DNA sequencing, it is not yet fully understood. Most (though probably not all) genes have been identified by a combination of high throughput experimental and bioinformatics approaches, yet much work still needs to be done to further elucidate the biological functions of their protein and RNA products. Recent results suggest that most of the vast quantities of noncoding DNA within the genome have associated biochemical activities, including regulation of gene expression, organization ofchromosome architecture, and signals controlling epigenetic inheritance.

There are an estimated 20,000-25,000 human protein-coding genes. The estimate of the number of human genes has been repeatedly revised down from initial predictions of 100,000 or more as genome sequence quality and gene finding methods have improved, and could continue to drop further, Protein-coding sequences account for only a very small fraction of the genome (approximately 1.5%), and the rest is associated with non-coding RNA molecules,regulatory DNA sequences, LINEs, SINEs, introns, and sequences for which as yet no function has been elucidated.

7,

Stem cells can be classified by their ability to differentiated into different, more specific cell types. Embryonic stem cells are pluripotent; they can become muscle cells, neural cells, cardiac cells, ect, ect depending on the developmental signals they encounter. This is obviously a necessity to a developing embryo, who must go from being one cell to an entire functioning infant. For most types of cells, once it had become differentiated, that is a permanent change; a white blood cell, for example, will only ever divide to form more identical white blood cells.

There are some types of cells, however, that remain multipotent into adulthood, which means they can divide into several different cell types. These cells are usually what people refer to as adult stem cells. Hematopoietic cells are one example. They are found in the bone marrow and can divide into several different types of white blood cells as well as red blood cells. These progenitor cells function in the body to retain and repair our organ systems. These cells can only differentiate into a limited number of cell types, however. A hematopoietic can only divide into various blood cells. It will never form skin or liver cells.

The pluripotency of embryonic stem cells is what makes most people believe that they are more promising. Because they can potentially become any cell type in the body, they can potentially be used in many different ways to treat a whole range of diseases and disorders. Adult stem cells are more limited. It's worth noting though that all of the currently approved medical treatments involving stem cells have come from adult stem cells. Most people would argue that that has resulted more from limitations put on embryonic stem cell research rather than a limitation of embryonic stem cell themselves, and that's almost certainly true, but we are still a long way away from being able to fully understand and control embryonic stem cells.

They are doing very interesting work in induced pluripotency that might interest you. They are essentially taking adult cells and reprogramming them back to an embryonic/pluripotent state. If that were possible, it would be a big step towards removing a lot of the ethical dilemmas people see with using embryonic stem cells.

8,

In cell biology, pluripotency (from the Latin plurimus, meaning very many, and potens, meaning having power)refers to a stem cell that has the potential to differentiate into any of the three germ layers: endoderm (interior stomach lining, gastrointestinal tract, the lungs), mesoderm (muscle, bone, blood, urogenital), or ectoderm (epidermal tissues and nervous system). However, cell pluripotency is a continuum, ranging from the completely pluripotent cell that can form every cell of the embryo proper, e.g., embyronic stem cells and iPSCs (see below), to the incompletely or partially pluripotent cell that can form cells of all three germ layers but that may not exhibit all the characteristics of completely pluripotent cells.

Induced pluripotency

Main article: Induced pluripotent stem cells

Induced pluripotent stem cells, commonly abbreviated as iPS cells or iPSCs are a type of pluripotent stem cell artificially derived from a non-pluripotent cell, typically an adult somatic cell, by inducing a "forced" expression of certain genes andtranscription factors These transcription factors play a key role in determining the state of these cells and also highlights the fact that these somatic cells do preserve the same genetic information as early embryonic cells. The ability to induce cells into a pluripotent state was initially pioneered in 2006 using mouse fibroblasts and four transcription factors, Oct4, Sox2, Klf4 and c-Myc; this technique called reprogramming earned Shinya Yamanaka andJohn Gurdon the Nobel Prize in Physiology or Medicine 2012. This was then followed in 2007 by the successful induction of human iPSCs derived from human dermal fibroblasts using methods similar to those used for the induction of mouse cells. These induced cells exhibit similar traits to those of embryonic stem cells (ESCs) but do not require the use of embryos. Some of the similarities between ESCs and iPSCs include pluripotency, morphology, self-renewal ability, a trait that implies that they can divide and replicate indefinitely, and gene expression.

Epigenetic factors are also thought to be involved in the actual reprogramming of somatic cells in order to induce pluripotency. It has been theorized that certain epigenetic factors might actually work to clear the original somatic epigenetic marks in order to acquire the new epigenetic marks that are part of achieving a pluripotent state. Chromatin is also reorganized in iPSCs and becomes like that found in ESCs in that it is less condensed and therefore more accessible. Euchromatin modifications are also common which is also consistent with the state of euchromatin found in ESCs.

Due to their great similarity to ESCs, iPSCs have been of great interest to the medical and research community. iPSCs could potentially have the same therapeutic implications and applications as ESCs but without the controversial use of embryos in the process, a topic of great bioethical debate. In fact, the induced pluripotencyof somatic cells into undifferentiated iPS cells was originally hailed as the end of the controversial use of embryonic stem cells. However, iPSCs were found to be potentially tumorigenic, and, despite advances, were never approved for clinical stage research in the United States. Setbacks such as low replication rates and early senescence have also been encountered when making iPSCs, hindering their use as ESCs replacements.

Additionally, it has been determined that the somatic expression of combined transcription factors can directly induce other defined somatic cell fates (transdifferentiation); researchers identified three neural-lineage-specific transcription factors that could directly convert mouse fibroblasts (skin cells) into fully functional neurons. This result challenges the terminal nature of cellular differentiation and the integrity of lineage commitment; and implies that with the proper tools, all cells are totipotent and may form all kinds of tissue.

Some of the possible medical and therapeutic uses for iPSCs derived from patients include their use in cell and tissue transplants without the risk of rejection that is commonly encountered. iPSCs can potentially replace animal models unsuitable as well as in-vitro models used for disease research.

9,A provirus is the virus' genetic material integrated with the genetic material of the host cell. Some viruses stay in this form inside a cell until a specific stimulus causes the provirus to start to reproduce and lyse, or burst, the cell. For instance, some prophages (a provirus from a bacteriophage) the process doesn't continue until UV radiation hits the bacterium.

A virion is the name of the actual virus particle. The virion is comprised of the capsid and the DNA (or RNA) of the virus. The term virion is used in a similar way that bacterium is when referring to a single bacterial cell. Some virions, such as HIV also have a phospholipid bilayer that they gain by 'budding' from the host cell. When a cell is lysed the provirus gives way to viral progeny, the virions.

10,

endosymbiotic theory, is an evolutionary theory which explains the origin of eukaryotic cells from prokaryotes. It states that several key organelles of eukaryotes originated as symbiosis between separate single-celled organisms. According to this theory, mitochondria and plastids (e.g. chloroplasts), and possibly other organelles, represent formerly free-livingbacteria that were taken inside another cell as an endosymbiont, around 1.5 billion years ago. Molecular and biochemical evidence suggest that the mitochondrion developed from proteobacteria (in particular, Rickettsiales, the SAR11 clade, or close relatives) and the chloroplast from cyanobacteria (in particular, N2-fixing filamentous cyanobacteria

Endosymbiotic theory

The endosymbiotic (Greek: ????? endon "within", ??? syn "together" and ?????? biosis "living") theories were first articulated by the Russian botanist Konstantin Mereschkowski in 1910, although the fundamental elements of the theory were described in a paper five years earlier. Mereschkowski was familiar with work by botanistAndreas Schimper, who had observed in 1883 that the division of chloroplasts in green plants closely resembled that of free-living cyanobacteria, and who had himself tentatively proposed (in a footnote) that green plants had arisen from a symbiotic union of two organisms. Ivan Wallin extended the idea of an endosymbiotic origin tomitochondria in the 1920s. A Russian botanist Boris Kozo-Polyansky was the first to explain the theory in terms of Darwinian evolution. In his 1924 book Symbiogenesis: A New Principle of Evolution he wrote, "The theory of symbiogenesis is a theory of selection relying on the phenomenon of symbiosis. These theories were initially dismissed or ignored. More detailed electron microscopic comparisons between cyanobacteria and chloroplasts (for example studies by Hans Ris published in 1961), combined with the discovery that plastids and mitochondria contain their own DNA (which by that stage was recognized to be the hereditary material of organisms) led to a resurrection of the idea in the 1960s.

The endosymbiotic theory was advanced and substantiated with microbiological evidence by Lynn Margulis in a 1967 paper, On the origin of mitosing cells. In her 1981 work Symbiosis in Cell Evolution she argued that eukaryotic cells originated as communities of interacting entities, including endosymbiotic spirochaetes that developed into eukaryotic flagella and cilia. This last idea has not received much acceptance, because flagella lack DNA and do not show ultrastructural similarities to bacteria or archaea (see also: Evolution of flagella andProkaryotic cytoskeleton). According to Margulis and Dorion Sagan,"Life did not take over the globe by combat, but by networking" (i.e., by cooperation). The possibility that peroxisomes may have an endosymbiotic origin has also been considered, although they lack DNA. Christian de Duve proposed that they may have been the first endosymbionts, allowing cells to withstand growing amounts of free molecular oxygen in the Earth's atmosphere. However, it now appears that they may be formed de novo, contradicting the idea that they have a symbiotic origin.

It is thought that over millennia these endosymbionts transferred some of their own DNA to the host cell's nucleus (called "endosymbiotic gene transfer") during the evolutionary transition from a symbiotic community to an instituted eukaryotic cell. The endosymbiotic theory is considered to be a type of saltational evolution.

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