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Advanced Biology Magazine Cassidy Martin January 23rd, 2013


DNA Replication “DNA- the process by which DNA is copied during the Cell Cycle.” DNA replication takes place before Mitosis, which is the process of cell division. During DNA replication, 46 chromosomes go through a process to copy them and result in double the amount (92 chromosomes). These 92 chromosomes will eventually divide into 46 once again after Mitosis. In the process of DNA replication, the first step is the unzipping of the double helix. Helicase enzymes unzip the double helix along the chromosome at the origins of replication. In this process, hydrogen bonds connecting base pairs are broken, separating the original molecule, and exposing the bases of each strand. Once, exposed, nucleotides floating free in the nucleus start to pair up with the DNA’s existing nucleotides. Once paired up, polymerase enzymes bond the two nucleotides together, forming two new strands of DNA.

Transcription “Transcription- the process of copying a sequence of DNA to produce a complimentary strand of RNA” In transcription, a gene (not a whole chromosome), is transferred into an RNA message. Like DNA polymerases catalyze replication, RNA polymerases’ jobs are to catalyze transcription. RNA polymerases are enzymes that bond nucleotides together to create a new RNA molecule. They are large enzymes that are made of proteins that have a many roles in the process of transcription. At the start of transcription, a large transcription complex composed of RNA polymerase and proteins begins to unwind the segment of DNA once realizing the start of a gene. Then, the RNA polymerase uses one strand of the DNA as a template, which the RNA nucleotides will form base pairs with the DNA template. G bonds with C but A now bonds with U, unlike before when it bonded with T. Translation produces three main types of RNA molecules; messenger RNA (mRNA), ribosomal RNA


(rRNA), and transfer RNA (tRNA). Messenger RNA is a message translated to form a protein, ribosomal forms part of ribosomes, and transfer RNA caries amino acids to a ribosome to help the growing protein. While the RNA strand is being transcribed, it hangs freely and once finished, the DNA strand reseals. After finishing, the RNA strand detaches itself from the DNA strand, which is when the RNA polymerase knows that the transcription is over.

Translation “Translation- the process that converts, or translates, and mRNA message into polypeptide.� Codons are sequences made up of three nucleotides. Codons are codes for amino acids. Start codons are signals that a translation is beginning and stop codons signal the end of a translation. There are many different code variations using U, C, G, and A. Translation takes place in the cytoplasm of eukaryotic and prokaryotic cells. The start of translation takes place when a tRNA carrying a methionine attaches to a start codon. Then, the exposed codon

attracts a complimentary tRNA bearing an amino acid. The anticodon or the tRNA and the codon of the mRNA then pair together. A polypeptide bond forms between both amino acids and the bond between the first tRNA and its amino acid breaks. The mRNA strand is then pulled the length of one codon by the ribosome. Then, the tRNA shifts to the exit site, leaving the ribosome and returning to the cytoplasm to recharge. This leaves the first spot empty, which exposes the next mRNA codon to go through translation.


The Cell Cycle Interphase

The cell cycle begins with Interphase. During interphase, the cell is being prepared for division. A cell with two full sets of DNA that is developed enough to survive is the product at the end of interphase.

Mitosis

In mitosis, the nucleus of the cell is divided into two identical nuclei, each with a full set of DNA There are four main parts of mitosis; prophase, metaphase, anaphase, and telophase.

Metaphase

Alignment upon the cell equator of each chromosome begins as spindle fibers attach themselves upon the protein structure of a centromere, belonging to each chromosome.

Anaphase The sister chromatids begin to separate, as spindle fibers shorten, pulling them away from each other towards opposite sides of the cell. Cytokinesis could begin later in this stage.

Telophase

Identical chromosomes begin to position themselves at each pole of the cell. Spindle fibers fall apart as a nuclear membrane starts to for and chromosome begin to uncoil. Cytokinesis usually starts later in this stage.

Prophase

During prophase, proteins and DNA are condensed into tight chromosomes. Spindle fibers start to form as they move to the center of the cell. The nucleolus disappears as the nuclear envelope breaks down and the centrioles and centrosomes being to move to opposite poles.

Cytokinesis

The cytoplasm is divided into two cells and completion of the cell cycle occurs. Two genetically identical daughter cells enter interphase and begin the cell cycle again.


References Nowicki, Stephen. "Unit 2, Unit 3." Holt McDougal Biology. [Austin, Texas]: Holt McDougal, 2010. N. pag. Print.

Advanced Biology Magazine  

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