2.5b Mitosis

26/09/2012 § 1 Comment

Though we basically covered the majority of this information in class today, this blogpost will outline what happens during the four different stages of mitosis. As a review, mitosis is nuclear division. An organism’s DNA is duplicated not during mitosis but during the S-stage of the Interphase. Mitosis divides the nucleus and usually follows with cytokinesis, which is the division of the cytoplasm.

The first stage of mitosis is the prophase. In the prophase, chromosomes become short and fat and they do this by supercoiling. The nuclear membrane breaks down near the end of the stage. Vital structures called microtubules grow from opposite poles of the cell via the MTOC (microtubule organizing centre) and reach out to the chromosomes. The microtubules are called the mitotic spindles because they form a spindle-shaped structure.

The next stage of mitosis is the metaphase. In the metaphase, the microtubules attach to the centromeres of the chromosomes. These chromosomes align themselves in the equator of the cell, or the middle of the cell. Microtubules from both poles will attach themselves to one sister chromatid of each chromosome.

The third stage of mitosis is the anaphase. In the anaphase, the microtubule fibers start to pull the sisters chromatids away from each other and towards opposite poles of the cell. Mitosis can create two genetically identical nuclei because of the genetically identical sister chromatids that get pulled to the opposite sides of the cell – the microtubules’ connection on the centromere makes sure of that. The entire time that the chromatids are moving towards the poles of the cell is part of the anaphase stage.

The last stage of mitosis is the telophase. In the telophase, a nuclear membrane starts to form around the new chromosomes (previously the chromatids). A cleavage furrow forms on the cell’s surface and the cell begins to divide.

The cell divides afterward through cytokinesis and the two new daughter cells can restart the cycle and enter interphase.

Touched upon briefly when we discussed tumors last time, cancer is a huge concern when it comes to cell division. Once again, when a cell doesn’t stop dividing, creating an excessive amount of new cells that create a tumor. These tumors are caused by carcinogens, viruses, and overexposure to ultraviolet light. Malignant (uncontrollable) cancers can detach and move to the different parts of the body and start new tumors.


Page 40 centromeres and telomeres

1. Deduce the stage of mitosis that the cell was in, giving reasons for your answer.

The squashed cell in the image was in the metaphase stage of mitosis. This is because we can already see that the chromosomes have coiled to become shorter and fatter. The deciding factor however was that the chromosomes are all starting to fall into place and position themselves in a line along what we can assume is the equator of the cell. 

2. The cell has an even number of chromosomes.

(a) State how many chromosomes there are in this cell.

14 chromosomes.

(b) Explain the reason for body cells in plants and animals having an even number of chromosomes.

This is because in eukaryotes (animals and plants), the resulting cell that comes from sex is given its set of DNA by two parents, which will give the resulting cell 2n chromosomes – an even number.

(c) In the micrograph of a cell in interphase, the centromeres are on one side of the nucleus and the telomeres are on the other side. Suggest reasons for this.

The positioning of the centromeres and telomeres on opposite sides of the nucleus have to do with making sure that later, each sister chromatid of a chromosome will be able to get to each pole of the cell. Also, the centromeres and telomeres have different polarities, which is why the centromeres stick to a chromosome’s middle while the telomeres stick to the ends. This polarity is what repels them from each other.

(d) An enzyme called telomerase lengthens the telomeres, by adding many short repeating base sequences of DNA. This enzyme is only active in the germ cells that are used to produce gametes. When DNA is replicated during the cell cycle in body cells, the end of the telomere cannot be replicated, so the telomere becomes shorter. Predict the consequences for a plant or animal of the shortening of telomeres.

The coiled chromosomes will not be capped and protected at the ends and might risk uncoiling. This might damage the DNA and interrupt the mitotic process. But that’s just my opinion.

My question now is… what is the purpose of a telomere and why have we not studied them along with centromeres?

2.5a Cell Cycle

23/09/2012 § 1 Comment

All organisms, whether prokaryotic or eukaryotic, need to produce new cells to survive. Prokaryotes use binary fission as their form of cell division that replicates the single circular chromosome, moves the two copies to opposite ends of the cell, and through cytokinesis, divides the cytoplasm to form two new cells.

Eukaryotes’ cell division is much more complicated. Eukaryotic cells go through the cell cycle indefinitely and part of the cell cycle includes mitosis, which is the process by which the nucleus divides to form two genetically identical nuclei, the process eukaryotic cells use to divide. Mitosis is required in cells during growth, embryonic development (as the fetus forms), when damages need reparation, and to reproduce asexually.

Before mitosis, however, cells go through the interphase, which is the longest portion of the cell cycle. There are three stages of the interphase:

  • G1: in which the cell grows, transcribes DNA and synthesizes proteins, as well as produces an increase in the number of mitochondria and other organelle structures
  • S phase: in which all the DNA in the nucleus is replicated
  • G2: in which the cell prepares for division

Afterwards is mitosis, which consists of the stages prophase, metaphase, anaphase, and telophase. This will be covered in more detail in the next blog but these stages essentially take the cell through the process of providing each daughter nucleus with a copy of the DNA (in the form of chromatids) so that the new daughter cells (that will form when the original cell undergoes cytokinesis to split the cytoplasm) have a copy of the original DNA.

There are these things called tumors and all cells are prone to being raided by a tumor – this includes tissues and any organs. Tumors can grow when a cell loses control of the mitosis that it is experiencing and the cells continually reproduce and divide, creating more and more cells – unnecessary cells – too many cells. Tumors are caused by cancer.

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2.4b Active Transport

23/09/2012 § Leave a comment

Sometimes cells work against the concentration gradient and pump particles out of its interior and out of the cell even if there is already a high concentration of that particle outside of the cell. The same happens vice versa (bringing substances inside the cell even if there’s already a high concentration of that substance inside of the cell) but less frequently. This is active transport, where the movement of substances across a membrane uses energy from ATP (adenosine triphosphate – the currency of energy in a cell) to transport substances from areas of higher concentration to areas of lower concentration. For this, cells use protein pumps (like channel proteins or transporter proteins, I’m assuming) that can only accept certain substances so that the entry and exit of all substances can be maintained.

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Let’s talk superhero action figures. (Chapter 3 Q&A)

20/09/2012 § Leave a comment

#2 List three possible reasons why the supply for automobiles, for example, would increase and explain how this change will result in a new equilibrium.

Three reasons why the supply for automobiles would increase include production efficiency (productivity), a decrease in the price of related goods (like Metal A is suddenly cheaper to use than Metal B), and a decrease in the cost of production (related to efficiency). Say for example Car Company X upgraded their technology and could make twice as many cars as they could in the time it previously took to make a certain amount of cars. This increase their productivity and ability to supply cars. The increase in supply causes a momentary surplus in the car market and to adjust, the suppliers will reduce their price a little. The decrease in the price will encourage consumers to increase their quantity demanded, which, on a supply/demand graph is movement to the right on the demand curve. This lower price but higher quantity demanded is the new equilibrium for automobiles.

#4 Using a diagram, explain the concept of community surplus.

Community surplus is the total of consumer surplus and producer surplus. In a particular market, this is the added benefit both the producers and consumers receive as a result of the price of the good being lower than they are willing to purchase (consumers) or the price being higher than they are willing to supply (suppliers).

Let’s talk, like, I don’t know, relatively exclusive superhero action figures. Some people are willing to pay higher than the set market price for this good, therefore, with consumer surplus, the consumers will pay a price below what they are willing to pay. Maybe Sheldon is willing to pay $10 more than the market price of that action figure because he thinks it’s really valuable. If the market price were, say, $15, and he were willing to pay $25 for the action figure, his consumer surplus would be $10.

It’s similar with producer surplus. A supplier will receive the benefit of a producer surplus when they receive a price above the one for which they were willing to sell their good. Remember, consumers like lower prices but suppliers like higher prices. So, perhaps the factories that are producing Sheldon’s action figures are very efficient and the suppliers were alright with selling their goods at $8. Since the market price is set to $15 (this is where the market equilibrium is), then the supplies will receive the benefit of a producer surplus of $7.

Community surplus is the total of these values. In a graph, you’d have to find the area of the shaded consumer surplus and the area of the shaded producer surplus. Both producer and consumer surplus are shaded as the area between the demand/supply curve, respectively, and the market price equilibrium. You should use the equation for the area of a triangle (because, you know, the shape on the graph is a triangle) to find the producer/consumer surplus at all possible points.

2.4a Cells: Membranes

20/09/2012 § Leave a comment

EDITED: Now with accompanying DBQs!

Alright, we’re off to start a new unit that links perfectly to the previous one: membranes! As we know, membranes run rampant in all cells. Seems as though this is the focus for the next two weeks – really, just two weeks. We have a test in two weeks, so heads up!

The most important part of a membrane is what it’s made of: phospholipids. Phospholipids have two specific parts to them – the first being the two tails made of hydrogen and carbon. These tails are hydrophobic, meaning they are not attracted to water. The second part is called the phosphate head, smaller so than the two hydrocarbon tails, and hydrophilic, which means it is negatively charged and attracted to water.

These relationships to water mean that, when mixed with water, phospholipids will arrange themselves automatically to become layers where the hydrophobic tails stick together while the hydrophilic phosphate heads face the water that is attracted to them. This arrangement creates the phospholipid bilayers, which is the basic structure of a cell membrane. They’re very stable because of the bonds that form between the surrounding water and the phosphate heads but are a collectively strong unit because there are so many tails that interact with each other. Because membranes are adjoined and continuous (very long), it’s hard to break them as you would have to break an entire length and many, many tail interactions for the membrane to give.

Besides the phospholipid bilayer, a membrane is also made up of different proteins. The integral proteins are embedded into the phospholipid and have a solid hold in the system. Peripheral proteins, less so, as they are only loosely attached to the surface of the membrane. On the outside surface of phospholipid bilayers (the surface that faces the extracellular fluids and away from the cytoplasm) are glycoproteins that have short chains of sugar molecules. For what exactly, I’m not quite sure but that’s what we have Mr. Ferguson for!

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making old people stretch their limits – rude!

17/09/2012 § Leave a comment


1. Explain which non-price determinant of demand is affecting the market.

Demographic change among Japan is what is affecting the market in this story. A non-price determinant of demand is a factor that affects the demand of a market of goods that does not involve changing the price of the good. If this story were represented by a demand graph, for example, the demand for health foods in Japan, then the overall demand would shift to the right because with an increase in the number of older individuals in Japan’s society comes an increase in the demand for health foods (which are popular with the elderly). The demographics of Japan are what affects the market and would cause a shift (to the right) in the demand for health foods (and other goods).

2. Evaluate the economic possibilities of Japan’s industries/firms as the population ages.

As Japan’s population ages, it’s likely that Japan’s industries and firms will start to target most of its products towards the elderly. This means that instead of producing goods that will satisfy a younger generation or the working generation, industries will adjust to making goods that older people would be willing to buy. On one hand, this could risk a drop in total spending – if the majority of goods available on the market are only there for old people, then everyone under that age won’t be able to and won’t spend as much. On the other hand, if senior citizens in Japan really are starting to show an increase in their spending and the baby boom generation from the ’40s are reaching senior citizenship, then the total spending may just help to strengthen Japan’s economy as the money is cycling – industries are providing the right goods for the spenders, the spenders (old people) are constantly feeding the industries with money, and money is moving all throughout Japan’s economy, giving it the boost it needs to slowly climb its way back to the top of all economies.

an intro to economics, and an attempt at understanding it (Chapter 1 Q&A)

16/09/2012 § Leave a comment

Answers to the practice questions of #1 on page 20 of the textbook.

(a) Economics is the study of the allocation of scarce resources. Scarcity is the most basic economic problem in which the wants and needs of people meets limited resources. Allocation is the distribution of such resources within an economy.

A production possibility curve demonstrates the opportunity cost, growth, and potential development of a country. The axes depict the product or resource which the country is allocating. When point A (or B) is on the line of a PPC curve, resources are being used efficiently, and when a point resides within the curve, a country’s resources are NOT being used efficiently. Sometimes the curve itself will shift on the graph, growing or shrinking in area. This shift represents the country’s production potential and shows how much a country can produce out of its available resources. Economics focuses on how to use, allocate and distribute the different products and resources, as shown on this graph, that are available to a country.

(b) The government is not more effective in the allocation of scare resources than the free market. Typically, a government spends and controls its economy inefficiently because it has no motivation or self-interest to produce more and make a profit. Though a slightly extreme example, Fidel Castro tried to use a socialist command economy to control (via the government) Cuba’s economy. Such command economies with authoritative powers like the government dictating production proved to be ineffective for all people.

Free markets, however, contain individuals who share a mutual interest in giving and getting. They aim to produce a lot and profit a lot while exchanging goods and services in the market. Independent and motivated individuals that constantly cycle money through the economy efficiently is what has proved to be beneficial for societies and we can see proof in this in the countries that are all beginning to shift towards (or are already) market economies, such as China or Serbia, who is trying to adapt a market economy through its current financial crisis.

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