Getting Ready for the Test

Be sure to read the questions posted by your classmates and the responses as you get ready for the test. Remember, you are welcome to answer each others questions. It would be a good way to prepare for the test. Also, as you re-read the chapters and chapter summaries, if questions pop up send it as a comment to this post.

Mr. Baker

Morning Cup O' Java - aka TQT Time

Ca asked -
1. What caused the decline of "maturation promoting factor" (M-phase) at the end of the mitosis cycle?
Answer - The M-phase promoting factor, the complexing of B-cyclin and Cdk-1, signals the cell to move to metaphase and initiate the anaphase-promoting complex (APC). Once activated the APC will signal the separation of sister chromatids and the destruction of B-cyclins thus "turning off" the M-phase promoting factor.

2. A protein is released by a certain body to stimulate other cells to divide. At which point would cells stop dividing?
Answer - I don't know much about this but what I know is, a cell is signaled to grow and divide when growth factors are released from other cells. When this signal is turned off cells cease growing a dividing. This is an area of active research.

3. What are the differences between density-dependent inhibition and anchorage dependence?
Answer - Both are related to the growth and division of cells but are different in that density-dependent inhibition is about the restraint of cell division and anchorage dependence is about stimulating cell division. As the number of cells increases and thus the density, a point is reached where the cells no longer divide. This is density-dependent inhibition. In anchorage dependence cells do not divide unless they are on some sort of substrate (surface). This was originally discovered when researchers notice that when cultured cells were suspended in a liquid medium they greatly slowed or stopped their division. But when placed on a solid medium the same cells freely divided (until density-dependent inhibition).

Tahira, your questions make me smile. I am not sure how to answer them but I like 'em.


Hong-An asked -
1. In many online science website, mitosis has a prometaphase. Does that mean that the distinction between prophase and metaphase stage is very broad?
Answer - Really, the entire cell cycle is a continuous process not a series of steps. We teach it as steps to aid understanding and the introduction of intermediate steps such a prometaphase introduces emphasis on what is happening. So regarding prophase, prometaphase, and metaphase; prophase is when the chromosomes are condensing and the nuclear membrane disintegrates, prometaphase is when further condensation happens and microtubules begin to attach to the kinetochore, and metaphase is when the chromosomes have lined-up at the equator of the cell.

2. In pictures they always show four chromosomes. Is this to simplify?
Answer - You bet. The mechanics of mitosis is the same no matter the number of chromosomes. It is just easier and hopefully clearer if we sketch 4 chromosomes rather than 46 (humans), 68 (coastal cutthroat trout), or 114 (lilly).

That took two cups of coffee and I am sufficiently caffinated but it is Saturday and I will have more. BTW - did you know that coffee has its origins in Ethiopia? I learned that when the family visited the Lucy exhibit at the Pacific Science Center over winter break.

More Later Ta-Ta,

Mr. Baker

Su-more TQTQ Answers

Anna asked the following three questions -
One of the chapter quizzes (11) had the following Question:
Lipid soluble signal molecules, such as testosterone, cross the plasma membranes of all cells but affect only their target cells because?
The answer:
Intracellular receptors are present only in target cells.
Could you please explain this?
Typically, lipid signal molecules such as testosterone will bind to a receptor molecule within the cytoplasm. This molecule, now activated will then turn on gene(s).

In chapter 10 there is the talk about photosystems I and II. Can a thylakoid membrane function without one of these? Well, the thylakoid membrane is where the proteins of photosystem I and II are embedded. So the membrane can be seen as scaffolding for the photosystems. They are both part of the photosynthetic structure called a chloroplast.

What exactly is Pyruvate? Recall that cellular respiration is composed of three main steps; glycolysis, Kreb's cycle, and electron transport chain. Glucose, the food molecule, is first processed in series of reactions called glycolysis which occurs in the cytoplasm. During this process glucose is transformed into two, three-carbon molecules called pyruvate. It is pyruvate with the help of a transport protein that enters the mitochondrion for further processing. The goal of glycolysis, Kreb's cycle, and electron transport chain is to harvest the energy and transfer it to form ATP. It is ATP that can be used for work in the cell.

From Keely, this is interesting -
Since genetic disorders come from mutation in chromosomes in gametes why doesn't the body find a way to destroy mutated gametes? Like how the body destroys mutated cells during mitosis. Answer - It does seem that just as defective cells are destroyed but the immune system the same should hold true for gametes. So why not? Until release, gametes are protected by cells that in effect guard them. The cells keep away the macrophages that may destroy them.

That's all for now. I see a couple of interesting questions from Ca. I will get to those tomorrow.

Mr. Baker

And More TQTQ 1-8-09 Responses

Zena asked - What is meristem? Meristem is a type of cell in plants that has not differentiated. This means that the cells have not become a specific type of cell. Because of this they can become many types of cell. So when you see that we are looking at apical meristem in the onion root tip this tells us that the tissue is likely rapidly dividing and can become vascular tissue, epidermis, root hairs, root cap, and others.

Zena also asked - Does an ameoba have cell division? Yes, they do what is called binary fission. During this process the nucleus does replicate its DNA and divides it equally. This is how you get more ameobas.

Wendy asked - Is it a conicidence that the cell cycle and one day are 24 hours in duration? The answer for the cells we were looking at, yes. Remember, there is a great range of cell cycle times. For example a nerve cell never divides, whereas a bacterial cell can divide in as few as 15 minutes. So the time for cell cycle completion depends on the type of cell you are looking at.

Going to the lab now, more later.

Mr. Baker

Some More Responses to TQTQ 1-8-09

I have a few minutes here and with my cup of coffee in hand here goes -

Inwoo asked - Without centrioles, how do plant cells split? It is interesting that though animal cells have centrioles, plant cells do not. So clearly the organization of the spindle does not require centrioles. But I read Inwoo's question as asking about chromatid splitting during anaphase. The movement of chromatids is due to the action of kinetochore motor proteins "walkimg" along a kinetochore microtubule, dragging its chromatid along.

Gotta go,

Jon

Some Responses to TQTQ for 1-8-09

Hey thanks for the great questions. I have only enough time for a few answers now but tune in later for more.

Cintia asked why cancer cells lose their density dependent inhibition and anchorage dependence. Briefly, this is due to multiple gene mutations in the original tumor cell. Cancer likely is the result of more than one mutation and if those mutations involve genes that regulate the cell cycle, density dependent inhibition, and anchorage dependence; you have a tumor that can metastasize.

Which leads us to a question by Inwoo, what is metastasis? This is the spreading of cancer cells throughout the body. Rather than being encapsulated and a benign tumor, a metastatic tumor is malignant and spreads, this is one of the reasons they are so deadly.

Inwoo also asked why human chromosomes are purple. The answer is they are not. The chromosomes you saw in class were stained (probably with aceto orcin stain) which causes them to be purpleish-pink and easily visible.

More later,

Mr. Baker

Three Question Thursday Time

Write your TQTQ for 1-8-09 here. Just click on comments and submit your questions. I will respond to some of them and each week post a new TQTQ request.

Peace,
Mr. Baker

Snow is Pretty - Particularly in the Mountains

As you know by now, we are two hours late today. This means a short class period and no lab. Instead, we will review mitosis and meiosis and familiarize everyone with the blog.

See you in class,
Mr. Baker

Prepare for the Lab Monday

Monday through Thursday we will conduct the mitosis and meiosis lab. It would be best if you would review mitosis and look ahead to meiosis. Mitosis is covered in chapter 12 while meiosis is found in chapter 13.



Though chapter 13 is not included in the next exam, pairing the learning of mitosis and meiosis allows you to compare and contrast each. Meiosis is the type of cell division that reduces the chromosome complement by 1/2 and is done by gametes (sex cells / sperm and eggs).

Test is Looming

The chapter 7-12 exam will be this Friday. It will be all multiple choice with 40 to 50 questions. If you have questions about the chapters reply with a comment to this posting and I will answer as soon as I can.

Mr. Baker