Bio: Chapters 12 EC, 13 SI, 16.2 #1-4, 16 EC

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12 EC The result of mitosis is that the daughter cells end up with the same number of chromosomes as the parent cell had. Another way to maintain the number of chromosomes would be to carry out cell division first and then duplicate the chromosomes in each daughter cell. What would be the problems with this alternative? Or do you think it would be an equally good way to organizing the cell cycle?

The duplication would need to come first and not the cell division because if the cell divides before duplication the

The process of carrying out cell division first and then duplicating the chromosomes in each daughter cell will cause many problems. This is because, the whole cell cycle has a purpose and that the purpose of the cell cycle is to follow a variety of steps. You will end up with an identical/normal cell if the steps are followed through. The main goal of mitosis is to have a duplicate # of chromosomes in the cell, then duplicating so it maintains the same set of chromosome #’s. As the chromosomes replicate, it confirms that each cell has the same copy of DNA when they are split apart. The purpose will be broken which means there are possible errors that could have resulted in the process of cell division and then duplicated the chromosomes in each daughter cell. This will lead to a high or low amount of chromosomes and a non-identical cell.

13 SI – You prepare a karyotype of an animal you are studying and discover that its somatic cells each have three homologous sets of chromosomes, a condition called triploidy. What might have happened?

(Human # of chromosomes are used in my answer for example)

Triploidy is a chromosomal abnormality that is caused by an extra set of chromosomes. There are three ways in which triploidy could have occurred in this animal. The first incident is called dispermy, which is when two sperm fertilize one twenty-three-chromosome egg. Triploidy may also occur when nondisjunction happens in the male sperm causing a forty-six –chromosome sperm. The forty-six-chromosome sperm then fertilizes a normal egg causing a sixty-nine-chromosome zygote. This process is called diandry and accounts for twenty-four percent of all triploidy cases. Lastly triploidy can be caused by digyny. Digyny accounts for ten percent of triploidy cases and is caused by complete nondisjunction in an egg; this egg is fertilized by a normal sperm causing a triploidy zygote

16.2 #1-4

  1. What role does complementary base pairing play in the replication of DNA?

Base pair complementary ensures DNA replication. It gives the mechanism for passing on genetic material because a base normally has only one other base it will pair with. You only need one strand to know what goes on the other one. In both replication and transcription, the two strands are separated and various proteins and RNA complexes help construct the complementary strands.

2. Identify two major functions of DNA pol III in DNA replication

One function of DNA pol III is that it could add free nucleotides to only the 3’ end of the newly-forming strand. This will lead to the growth of a new strand in the 5’-3’ direction. DNA pol III has the ability to correct mistakes in newly synthesized DNA. When an incorrect base pair is recognized, DNA polymerase reveres its direction by one base pair of DNA.

3. Why is DNA pol I necessary to complete synthesis of a leading strand? Point out in the overview box in figure 16.16 where DNA pol 1 would function on the top leading strand.

A molecule of a DNA polymerase binds to one strand of the DNA and begins moving along it in the 3′ to 5′ direction, using it as a template for assembling a leading strand of nucleotides and reforming a double helix The leading strand is activated by an RNA primer which is removed and replaced; this takes place in the DNA pol I. In figure 16.16

DNA pol I is necessary to complete synthesis of a leading strand because in this polymerase the leading strand is activated by an RNA primer which is later removed and replaced. DNA pol I remove the primer from 5’ end of the second fragment, replacing it with DNA nucleotides that it adds one by one to the 3’ end of the third fragment. The replacement of the last RNA nucleotide with DNA leaves the sugar phosphate backbone with a free 3’ end.

4. How are telomeres important for preserving eukaryotic genes?

With each round of DNA replication the ends of eukaryotic chromosomes becomes shorter. Telomeres at the ends of the DNA molecules make certain that genes are not lost after the multiple rounds of replication.

Chap 16 EC Many bacteria may be able to respond to environmental stress by increasing the rate at which mutations occur during cell division. How might this be accomplished, and what might be an evolutionary advantage of this ability?

Depending on the environment, the condition could affect the organism deeply. Bacteria may evolve from natural selection. The weaker resistance will die first if the bacteria is constantly hit with antibiotics. Strong bacteria that could with stand the antibiotics could keep dividing and mutating. This leaves the bacteria to become stronger and more resistant to the antibiotics and will enhance their survival. This is the advantage toward mutation.


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