1. The advantage of substrate-level phosphorylation is

1.    Explain how substrate-level phosphorylation and oxidativephosphorylation produce ATP.

             ATP synthesisconsists of two mechanisms known as substrate-level phosphorylation andoxidative phosphorylation. Substrate-level phosphorylation involves the directtransfer of a phosphate group to change ADP into ATP. This process occurs in theanaerobic process known as glycolysis and the aerobic process known as the KrebsCycle. In glycolysis, this process occurs in the return phase and allows forthe production of 4 ATP. In the Krebs Cycle, this process produces 1 ATP percycle. The advantage of substrate-level phosphorylation is that is able toproduce ATP quickly as opposed to oxidative phosphorylation.

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Even though oxidativephosphorylation is a slower process, it is capable of producing more ATP thansubstrate-level phosphorylation. This occurs in the electron transport chainand is a chemiosmotic process that turns potential energy into chemical energy.In the electron transport chain, NADH and FADH give off their electrons,causing H+ to be pumped into the membrane. This results in a gradient where theH+ wants to go back into the matrix of the mitochondria. When the H+ goes downthe ATP synthase, the gradient energy helps attach the ADP and phosphate groups(Marieb 924).  2.    Explain how short-term and long-term controls ofeffect the hypothalamic command of appetite and food intake.                                                                                             3.

    Describe the regulation of the ovarian anduterine cycles. As a child, a female’s ovaries prevent theGonadotropin-releasing hormone (GnHR) from being released by constantly creatinga little bit of estrogen. When GnHR is finally released around the time ofpuberty, the follicle stimulating hormone (FSH) and luteinizing hormone (LH)are produced as a response. The FSH causes the granulosa cells to releaseestrogen and the LH causes the cells to release androgens that are turned intoestrogens.

When estrogen levels get too high, the hypothalamus and anteriorpituitary experience negative feedback and FSH and LH are not able to beproduced. FSH also experiences negative feedback from inhibin. Only onefollicle remains alive after this and it creates raised estrogen levels.Positive feedback happens when the estrogen reaches a certain blood level,resulting in the release of gonadotropin. When there is a lot of estrogen, LH isreleased which causes the oocytle of the follicle to experience meioticdivision resulting in another oocyte.

Ovulation takes place after about 14 days.This is associated with vascular permeability and the release ofmetalloproteinase enzymes. A portion of the follicle wall breaks and leaves ahole for the oocyte to go through. The follicle that burst turns into a corpusluteum, which makes progesterone and estrogen. Negative feedback on thehypothalamus and pituitary takes place when the progesterone and estrogenlevels get too high. If the egg is not fertilized, the blood levels go backdown, the estrogen and progesterone levels go back down and the corpus luteumgets destroyed (Marieb 1058). The uterine cycle involves the changes that the endometriumexperiences in response to ovarian hormones.

The changes experienced relate towhat is going on in the ovarian cycle. The first step of the uterine cycle iscalled the menstrual phase and it occurs over a span of 1-5 days. In this phasethere is bleeding due to the shedding of the endometrium. On the last day, thefollicles make more estrogen.

The next phase is the proliferative phase and itsspan is 6-14 days. It involves the reformation of the endometrium that happensunder increased estrogen levels. At the end of this phase, ovulation occurs. Thesecretory phase happens over a span of 15-24 days. This phase involves gettingready for the embryo to implant. Progesterone levels increase to form thecervical plug that keeps all unwanted things out, such as pathogens. Thisincrease also stops LH from being released. If fertilization does not occur, progesteronelevels decrease back to the normal range, LH blood levels go back down and the corpusluteum deteriorates.

Menstrual blood flow indicates the starting of this cycleagain (1059).  4.    Define meiosis.

Compare and contrast meiosis tomitosis.             Meiosis is atype of nuclear division that typically takes place in the gonads. Meiosisresults in the production of four daughter cells that contain half as manychromosomes as the normal chromosome number. This diploid chromosome number is46. The cells are not identical and contain genetic components from eachparent. Meiosis goes through two separate divisions known as Meiosis I and MeiosisII (Marieb 1036).

Meiosis I consists of prophase I, metaphase I, anaphase I andtelophase I. In prophase I, the homologous pairs form tetrads. In metaphase I,the tetrads line up on the spindle equator.

In anaphase I, the sisterchromatids stay together and go to opposite sides of the cell. In telophase I, thetwo haploid daughter cells go through interkinesis before going through thesteps of Meiosis II. Mitosis contains the steps of prophase, metaphase,anaphase and telophase, but contains differences from Meiosis I. In prophasethe centrioles move to different ends of the cell and the nuclear membrane and nucleolusdisappear. In metaphase, the chromosomes line up in the center on the spindleequate. In anaphase, the centrioles split and go to opposite ends of the cell.This is different in the anaphase I stage of meiosis because the sisterchromatids stay together rather than splitting apart. In telophase, the chromosomesuncoil to create chromatin (Marieb 98).

Meiosis plays the role creating cellsinvolved in reproduction while mitosis creates cells involved with growth andrepair of tissues. Meiosis results in four non-identical haploid cells whilemitosis results in the production of two identical diploid cells. Meiosis andmitosis both experience DNA replication and they both go through the same stepsof prophase, metaphase, anaphase and telophase. They also both contain the sameamount of DNA as one another (Marieb 1037).


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