Friday, November 7, 2008

Chapter 12.2 and Lab Discussion

Discussion of the Lab: Factors Influencing Enzyme Activity

Theme: for all enzymes, there is an optimal environment in which they thrive
*bacteria that can fluctuate between acid and base is called an extremophile
*must always know the biological environment for the enzyme to understand its optimal environment.
(Because each lab group completed Parts A and B, our class discussion today covered Parts C-F in order for students to understand the concepts addressed by other parts of the lab.)

Part C. The Effect of Temperature on Enzyme Activity
* 100' C is a very extreme temperature for the enzyme. Because it is so extreme, the protein most likely denatured and therefore didn't function at all.
* 37' C is very close to optimal temperature for the enzyme. This is slightly warmer than room-temperature and therefore not an extreme environment.
* Temperature can be good for enzymes. (ie: When making tea, the tea diffuses into the water faster when placed in hot water rather than cold or room temperature. The heat speeds up the reaction.) However, there is a point when there is too much heat
* need to be careful with temperature warm is not necessarily bad in all instances.

Part D. The Effect of pH on Enzyme Activity
- Like temperature, enzymes also have an optimal pH, but this value can range from 2-7. If it becmes too acidic, the protein denatures (*remember, in essays you always need to explain vocab words you use)
-from the basic side to acidic side, as we move toward 7, reactions become weaker and weaker

Part E. The Effect of Substrate Concentration on Enzyme Activity
-as it increases, so does the activity.
-As it keeps increasing so does the product, but at the some point the rate of increase will decrease, over-all it is still increasing.
-There is a point where the enzyme has to "wait in line" this causes a plateau in the graph and rate of reaction.
-No denaturation occurs but rather over saturation.

Part F. The Effect of Ion Concentration on Enzyme Activity
-By adding ions to the solution, we introduce a second variable
- the effect that this variable has on the enzyme fluctuates, without a constant rate of increase.
- a 0% concentration has no effect while a 10% concentration dramatically limits the enzymes' ability to function.

Notes on Chapter 12 (continued):

Distribution of Chromosomes During Eukaryotic Cell Division
*In preparation for cell division, DNA is replicated and the chromosomes condense (S phase)
*Each duplicated chromosome has two sister chromatids, which separate during cell
*The chromosome is the narrow "waist" of the duplicated chromosome, where the two
chromatids are most closely attached.
Concept Check: Two sister chromatids are joined prior to mitosis and are joined at the centromere. Which of the following is true? 1)The chromatids make up a diploid chromosome. 2)The two were formed by DNA replication of a single chromatid

*Eukaryotic cell division consists of:
Mitosis the division of the nucleus
Cytokinesis the division of the cytoplasm
*Gametes are produced by a variation of a cell division called meiosis (which we will look at furter in Ch. 13)

*Meiosis yeilds nonidentical daughter cells that have only one set of chromosomes, half as may as the parent cell. (Haploid)

Phases of the Cell Cycle (12.2)

*The cell cycle consists of:
-Mitotic (M) Phase mitosis and cytokinesis (10%)
- Interphase (cell growth and copying of chromosomes in preperation for cell division
*Note: this is not a "resting phase" rather, it is simply not in the process of dividing *the entire cell cycle can take anywhere from a few hours to a few days
* Interphase can be divided into subphases:
- G1 phase (first group) growth 1
- S phase (synthesis) replication (Note: although technically accpetable, Mrs.
Lyon does NOT like the word duplication!)

-G2 phase (second group) growth 2
*The cell grows during all 3 phases, but chromosomes are replicated only during the S phase.
*Mitosis is conventially divided into five phases
- Prometaphase

- Metaphase
- Anaphase
Cytokinesis is well underway by late telophase
*Some ways to remember the order include: PPMAT or Pretty Ponies Magically Appear Today

Prophase Key Points: (before)
*Chromatin condenses
* Nucleolie disappear
* Mitotic spindle begins to form
*Centrosomes moe away from each other
* Each duplicated chromosome appears as two identical sister chromatids

Prometaphase Key Points: (before the middle)
*Nuclear envelope fragments
*Centrosomes are at opposite poes of the cell
* Each of the two chromatids of each chromosome now has a kinetochore
* Nonkinetochores start to interact with the opposite pole.

Metaphase Key Points: (middle)
*Longest stage of mitosis
* Centrosomes are at oppostie poles of the cell
* Chromosomes line up at the metaphase plate (imaginary plane at center of cell)
* For each chromosome, the kinetochors of the sister chromatids are attached to kinetochore microtubules coming from opposite poles.

Anaphase Key Points: (apart)
*Shortest stage of mitosis and the two sister chromatids of each pair part suddenly
* the cell elongates as the chromosomes move toward each pole and the kinetochore microtubules shorten, nonkinetochores lenthen

Telophase Key Points: (end)
*Two daugther nuclei form (nuclei- NOT cells)
* Nuclear envelopes areise from fragments
*Chromosomes become less condensed
*Mitosis is complete (division of one nulceus into two)

Practice Multiple Choice Questions:

1. Which of the following is true of mitosis in a diploid cell?
a. It results in 2 haploid daughter cells.
b. It involves transcription of the cell's DNA.
c. It results in daughter cells who are genetically identical, but physically smaller, than the
original cell.

2. During which stage does DNA replication occur?
a. Prophase
b. Metaphase
c. Anaphase
d. None of These

3. Which answer gives the stages of mitosis in proper chronological order?
a. Anaphase, prophase, metaphase, telophase.
b. Metaphase, anaphase, telophase, prophase
c. Prophase, metaphase, anaphase, telophase.
d. Interphase, prophase, metaphase, anaphase, telophase.

4. In prophase, the nuclear membrane disappears.

Ansewers 1. C 2. D 3. C 4. True

*Don't forget to study for the Quiz on Monday!*

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