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Dna Replication(Nucleic Acid
Phases of mitosis
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Structure of nucleotides and DNA.
Deoxyribonucleic (DNA) is the molecule that hold the genetic information of living things. In our body every cell contains about 2 meters of DNA. DNA is copied every time a cell divides. Deoxyribonucleic (DNA) is made up of two polynucleotide strands. Polynucleotide strands twist around each other, forming a shape that looks like a ladder called a double helix. The two polynucleotide strands run antiaparallel to each other with nitrogenous bases this means that the stands run in opposite directions, parallel to one another. The DNA molecule consists of two backbones chains of sugars and phosphate groups. The organic bases held together by hydrogen bonds. Although bases bonded together are termed paired and specific way as to which base they join to. An Adenine with only pair with thymine and Cytosine with only pair with guanine.
Deoxyribonucleic (DNA) and ribonucleic acid (RNA) both carry genetic information, although they have a few differences between them. DNA contains a sugar called deoxyribose, whilst RNA contains a sugar called ribose. Also DNA is a double polynucleotide chain while RNA is a single polynucleotide chain as well DNA uses the bases adenine, thymine, cytosine, and guanine; RNA uses adenine, uracil, cytosine, and guanine. Uracil is different from thymine in that it lacks a methyl.
• Replication
DNA replicates by the semi- conservative method. When the cell divides throughout a part of the interphone recognized as the S phase then each DNA molecule replicates. The new molecules contain one stand of the original and one new stand, and this type of replication. DNA must copy when cells divide. This is called replication this process take place during i...
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...and begin to move to chromosomes towards the midline of diving cell.
- Metaphase 2: The chromosome moves to the midline to the dividing cell, facing opposite poles of the dividing cell.
- Anaphase 2: the centromeres divide and the chromatide separate and move towards opposite poles of the cell.
- Telophase 2: Nuclear envelopes reform around the four daughter haploid nuclei. A nuclear membrane forms around the chromosomes in each of the 4 new cells.
• Chromosomal abnormalities
Non disjunction is improper segregation of chromosomes during meiosis cell divisions during meiosis stage 1 or stage 2, both go into the same gamete. This is known as non – disjunction. As an effect of non- disjunction some gametes have two copies of chromosome. No disjunction at the first meiotic division results in both homologs travelling towards the same spindle pole.
DNA is the genetic material found in cells of all living organisms. Human beings contain approximately one trillion cells (Aronson 9). DNA is a long strand in the shape of a double helix made up of small building blocks (Riley). The repeat segments are cut out of the DNA strand by a restrictive enzyme that acts like scissors and the resulting fragments are sorted out by electrophoresis (Saferstein 391).
DNA is made up of nucleotides, and a strand of DNA is known as a polynucleotide. A nucleotide is made up of three parts: A phosphate (phosphoric acid), a sugar (Deoxyribose in the case of DNA), and an organic nitrogenous base2 of which there are four. The four bases are as followed: Adenine (A), Cytosine
In telophase, these separate chromatids uncoil to become chromosomes. This division produces two identical cells.
The process of mitosis can take place in either a haploid (23 chromosomes) or a diploid (46 chromosomes) cell. Before a cell can be ready for a mitotic division it must primarily undergo its interphase stage. Following the interphase stage several other stages come into play. These stages are prophase, prometaphase, metaphase, anaphase, and telophase. During each specific stage certain sequences of events take place that assist to the completion of the division.
Chemistry dictates the structure of DNA. DNA is a polymer of monomers called nucleic acids. These are made of a nitrogenous base, a phosphate group and a sugar. It is the negative charge on the phosphate group that makes DNA an acid. There are 4 different bases: adenine, thymine, guanine and cytosine. In groups of three, these four bases can code for any protein coded for in an organism’s genome. Two strands of nucleic acids stack on top of each other in a double helix. The backbone of the nucleic acids consists of the interaction between phosphate groups and the hydroxide groups of nucleic acids. These are held together by covalent bonds called phosphodiester bonds. The helix itself is held together by hydrogen bonds. Although h...
In the Prophase, chromosome as double threads joined at centromere and then shorten and thicken. Then nucleolus and nuclear membrane disappears. Fibrils of astral rays extend across forming mitotic spindle. After that centriole divides into two.
The cell cycle is the synchronous process by which existing cells give rise to new cells. This process can be broadly divided into two stages: interphase and mitosis. During interphase, cells increase in size, replicate their chromosomes to form sister chromatids, and increase their rates of protein synthesis. During mitosis, sister chromatids are separated and transported to opposite cell poles, followed by cell division (cytokinesis). Recent investigations have revealed much information about the morphological changes that occur in mitotic cells. These morphological changes occur in a precise order and include, in chronological order, condensation of chromosomes, changes in microtubule assembly patterns, nuclear envelope breakdown, chromosome alignment at the center of the cell, chromosome separation to opposite cell poles, and nuclear envelope reassembly prior to cytokinesis. Similar morphological changes have been observed during meiosis, indicating that the processes driving DNA distribution in somatic cells and gametes is similar (Baserga, 1968).
The first sub phase of this is prophase 1 and this is split up into 5 stages. The first one is leptotene and this is where the chromosomes supercoil. The second one is zygotene and this is where the homologous chromosomes form pairs and these are called bivalents. Pachytene is where crossing over occurs between the homologous chromosomes and chiasmata form. Diplotene is where they start to separate but remain attached to each other by the chiasmata. Diakinesis is the last stage and this is where they keep separating and the chiasmata moves to the ends of the chromosome (GENIE, 2010). The second phase is prometaphase and this is where the spindle fibres assemble and the chromosomes become anchored to them by their kinetochores. Metaphase 1 is where the bivalents assort randomly on the metaphase plate. This helps to create genetic diversity. Anaphase 1 is where the bivalents separate and the homologous chromosomes move to opposite poles of the cell. Telophase 1 is where the nuclear envelope reforms after disintegrating in prophase 1. Then cytokinesis is where the cell divides to create two new cells which are haploid (GENIE, 2010). The next main stage is meiosis 2 and this is where each chromosome is split into 2 sister chromatids. Prophase 2 is the first stage and this is where the chromosomes supercoil, the mitotic spindle forms and the nuclear envelope disintegrates. Metaphase 2 is where the chromosomes become attached to the
Meiosis, also called reduction division, is a distinct type of cell division that is essential for sexual reproduction to occur. It is one in which two successive divisions of diploid cell occur thereby producing four genetically different haploid daughter cells, also called gametes, each with half the number of chromosomes and thus, half the total amount of genetic material as compared to the amount before meiosis began. Interphase precedes meiosis and thus, paves the way for meiosis to eventuate as the cell’s DNA replicates in the S phase yielding corresponding, identical chromosomes. Interphase sparks the marvelous process of meiosis that allows variation to transpire within the organisms it occurs, hence, giving rise to millions of organisms with unique aspects unlike any other on Earth. Because meiosis is a form of sexual reproduction itself, it is the means through which gametes are produced, each with a reduced number of chromosomes, so that when two gametes fuse during fertilization, not only do they form a diploid zygote with 46 chromosomes, but also have manifested differing features due to the rearrangement (crossing-over) of chromosomes.
A Karyotype is when you cut out individual chromosomes from a picture and rearrange them. There are matching pairs of chromosomes these are called homologous pairs. Each pair is given a number. One of each pair came from the mother and one of each pair came from the father. The pairs can be distinguished as each pair has a distinctive banding pattern when stained. There are two sex chromosomes and the rest are called autosomes. In most karyotype the sex cells are kept to one side so that the sex can be seen easily. In females they have two X chromosomes and in the males they have an X and a Y chromosome. The Y chromosome has a portion missing and is therefore smaller then the X chromosome.
The differences between the two phases of meiosis are that in meiosis I, while the cell undergoes the phases, prophase I, metaphase I, anaphase I, and telophase I, it causes the cell to divide into two with each of the cells having a double stranded chromosome. But in meiosis II, it is just the division of the the cells from meiosis I. The ending result being that four haploid daughter
Meiosis is a specialized form of nuclear division in which there two successive nuclear divisions (meiosis I and II) without any chromosome replication between them. Each division can be divided into 4 phases similar to those of mitosis (pro-, meta-, ana- and telophase). Meiosis occurs during the formation of gametes in animals.
DNA (deoxyribonucleic acid) is a self-replicating molecule or material present in nearly all living organisms as the main constituent in chromosomes. It encodes the genetic instructions used in the development and functioning of all known living organisms and many viruses. Simply put, DNA contains the instructions needed for an organism to develop, survive and reproduce. The discovery and use of DNA has seen many changes and made great progress over many years. James Watson was a pioneer molecular biologist who is credited, along with Francis Crick and Maurice Wilkins, with discovering the double helix structure of the DNA molecule. The three won the Nobel Prize in Medicine in 1962 for their work (Bagley, 2013). Scientist use the term “double helix” to describe DNA’s winding, two-stranded chemical structure. This shape looks much like a twisted ladder and gives the DNA the power to pass along biological instructions with great precision.
Once the sperm fuses with the ovum both chromosomes will pair up and begin the first stages of cell division.
There are certain things that must happen first before the cell can actually split. There is a six step process required during Mitosis. The first five steps of mitosis are called prophase, prometaphase, metaphase, anaphase, and telophase. This is where all the training and preparation is done for cell division. The sixth step is Cytokinesis, and that is when the cell literally splits into two. Like I said, there are certain things in order to happen before it can enter the M phase. first, it must meet the requirements of the certain size and environment. Since in the S phase the cell duplicated it’s amount of chromosomes it be represented as 2N, where N equals the number of chromosomes in the cell. Cells about to enter M phase, which have passed through S phase and replicated their DNA, have 4N chromosomes. Because of this they are now allowed to enter within the M phase to prophase. Here is where the cell thickens up its chromosomes and begin to sprout microtubules from clone centrosomes. Microtubules tub-like are protein filaments and where the chromosomes migrate but are still within the nuclear envelope in the nucleus. There are centromeres, that are inside the chromosomes and during the later process of this phase, specialized microtubules called kinetochores, assemble on the centromere then later attach to these sites. They act like magnets and go