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Biology questions
1. Demonstrate your knowledge of the entire process of how a protein is made from the information in DNA. Using your own words, begin with an overview, and then describe the details of how DNA is transcribed to RNA, and how RNA is translated to protein, including where each takes place. Be sure to include all necessary players (factors, enzymes, etc.). Be as concise as possible while being thorough. (400 words or more)
There is information for the creation of proteins and for the control of their use in DNA (just as a cookbook carries information about components and how to use them). One is not meaningful without another, why would we need proteins without application instructions, and on the contrary?
Here is a very simple example to illustrate what happens. Brown eyes are caused by the presence of a certain pigment in the iris of an eye. The iris makes this pigment because a person's DNA tells it to. How does the DNA tell the iris what to do? The DNA does it by making the iris cells produce a particular enzyme. Then the enzyme causes the pigment to be made. Enzymes are proteins, so the DNA really tells the cells what proteins to make. In another way, DNA controls protein synthesis.
Proteins consist of long chains of amino acids. Each type of protein is made of a certain number of specific amino acids linked together in a particular order.
Due to DNA, a cell unites its amino acids together to form a particular protein. DNA consists of a chain of base pairs, and protein is composed of a chain of amino acids. The order of base pairs in the DNA decides the order of amino acids in the protein.
Scientists have shown that three consecutive bases (that is three bases in a row) stand for one amino acid. The genetic code is therefore known as a triplet code. When a cell makes a protein, amino acids bind in an order which is decided by the order of the base triplets in the DNA.
According to its chemical compound, RNA is a twin, though not a full twin, of DNA. It is the basic keeper of the genetic information in a living cell. The main difference is that RNA contains the sugar ribose instead of deoxyribose.
DNA is in the cell nucleus, but proteins are made in the cytoplasm. Somehow the DNA has to tell cytoplasm which proteins to make.
The DNA does this by sending a messenger to the cytoplasm. The messenger is similar to DNA and carries the same code as the relevant part of the DNA. It is called messenger RNA. When it reaches the cytoplasm, it associates with the group of ribosomes and causes the amino acids to come together in the right order to make the required protein. Another type of RNA, called transfer RNA, pulls the amino acids into the correct positions.
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2. Summarize what is happening during each of the stages of mitosis. Be sure to mention the important features (chromosomes, nuclear envelope, spindle, etc.) of the cell as it progresses through each step. (300 words or more)
Prophase, metaphase, anaphase, and telophase are the most principal stages of mitosis. At each of these stages, certain crucial events take place, particularly regarding the chromosomes.
Interphase can be considered as preparation of the cell for division, prophase can be described as mobilization for action. Chromatin threads condense to form distinct chromosomes. Long and thin at first, they gradually become shorter and fatter. Condensing of the chromosomes is one of the most important events in the prophase. If it failed to happen, it would be impossible for the chromosomes to move around the cell without getting tangled up. The cytoplasmic microtubules, which are part of the cell's cytoskeleton, disassemble and reassemble to form a structure that is known as the spindle and composed of spindle fibers.
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There are centrioles in cells. One pair is found at one end of the spindle and the other pair at the other end. It is achieved by one pair skirting the nuclear envelope so that it comes to rest at the opposite side of the nucleus. Two pairs of the centrioles are said to be at the poles, and the spindle fibers can be seen going from one pole to the other.
Metaphase begins with the breakdown of the nuclear envelope. The chromosomes migrate to the central plane of a cell and arrange themselves around the middle of the spindle, known as its equator. Finally, the chromosomes become attached to the spindle fibers at the centromeres.
At the anaphase stage, the chromatids, belonging to each chromosome part, move towards opposite poles of the spindle. Centromeres split the middle. It ends once the separated daughter chromatid arrives at the two poles.
At the last stage of telophase, cytokinesis takes place. In this process daughter cells, produced by mitosis, split up, and the cell is pinched in two. Daughter cells end up with the same quality and the same number of chromosomes.
3. Unlike asexual reproduction, which results in identical offspring, sexual reproduction results in genetic recombination. Explain how special events during Meiosis Prophase I and Metaphase I lead to genetic diversity (variability). (200 words or more)
Gametes (eggs and sperm) are normally produced by meiosis. The gametes, produced by an individual the sperm produced by a man, for example, contain different sets of alleles. In fact, two gametes never contain the same set of alleles.
Two features of meiosis ensure that. They depend on the fact that two chromosomes of a matching (homologous) pair may carry different alleles. For example, one may carry an allele for brown eyes, whereas the other carries an allele for blue eyes.
Matching chromosomes line up in the middle of a cell, and then separate. They do it independently of all the other pairs of matching chromosomes. Chromosomes of each matching pair finish up together in the daughter cells by sheer chance, so all sorts of combinations are possible in the gametes. It is called independent assortment.
When the matching chromosomes line up, they intimately wrap around each other. At certain points, where the chromosomes touch each other, they may break and change places, taking their alleles with them. It is called crossing over and leads to new combinations of alleles in gametes.
Independent assortment and crossing over are entirely random. The way they take place in one process of meiosis differs from the way they occur in another one. As a result, every gamete receives its own unique set of alleles.
When fertilization takes place and gametes unite, a completely new combination of genes is established in the fertilized egg (zygote). It is one of the main reasons why human beings, even close relatives, differ from each other. The principle of being different from each other is called variation.
