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MCAT Biology > Chapter 4 - Reproduction > Flashcards

Chapter 4 - Reproduction Flashcards

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1
Q

Define: Alleles

A

Genes coding for alternate forms of a given trait

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2
Q

Define: Cell Division

A

Cell division is the process whereby a cell replicates its DNA, doubles its organelles and cytoplasm, and then splits into two daughter cells.

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3
Q

In what two key ways does the cell division process of prokaryotes and eukaryotes differ?

A

Since eukaryotes have multiple chromosomes per cell, eukaryotic organisms must properly segregate these chromosomes during duplication. Moreover, eukaryotes must also make new cytoplasm and organelles.

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4
Q

What are the four phases of the cell cycle, and in what order do they occur?

A

The four phases of the cell cycle, in order, are:

  1. G₁ – Presynthetic Gap
  2. S – Synthesis
  3. G₂ – Postsynthetic Gap
  4. M – Mitosis
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5
Q

What is interphase?

A

Interphase is the phase of the cell cycle in which the cell spends the majority of its time and performs most of its functions, including preparation for cell division. Interphase consists of the G₁, S, and G₂ phases. Terminally differentiated cells spend all of their time in an offshoot of G₁ phase called G₀.

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6
Q

What occurs during the G₁ phase?

A

G₁ (Gap 1) is the phase in which the cell grows and functions normally. During this time, a high amount of protein synthesis occurs and the cell grows (to about double its original size) - more organelles are produced, the volume of cytoplasm increases and mitochondria and chloroplasts divide.

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7
Q

What occurs during the S phase?

A

In the S (Synthesis) phase the cell duplicates its DNA (via semiconservative replication), so that each daughter cell will have identical copies.

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8
Q

During the S phase what occurs to the chromosomes?

A

During S phase the chromosomes duplicate. After replication each chrosome consists of two identical chromatids, which are bound together at a specialized region called the centromere.

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9
Q

What occurs during the G₂ phase?

A

The G₂ (Gap 2) phase is a period of rapid cell growth and protein synthesis during which the cell readies itself for mitosis. It can be thought of as a quality control stage.

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10
Q

Define mitosis

A

Cell division and/or nuclear division in somatic cells that results in the daughter nucleus receiving a full complement of the organism’s genome.

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11
Q

What phases make up the mitotic stage of the cell cycle? Give their order and a brief description of each.

A

The mitotic stage consists of mitosis itself, followed by cytokinesis. Mitosis consists of:

  1. Prophase – chromosomes condense, spindles form.
  2. Metaphase – chromosomes align.
  3. Anaphase – sister chromatids separate.
  4. Telophase – new nuclear membranes form.

Mnemonic: PMAT

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12
Q

Define Chromatin

A

Chromatin is chromosomes in their uncoiled active state. Chromatin is not visible under a light microscope.

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13
Q

What is the centrosome?

A

The centrosome is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell as well as a regulator of cell-cycle progression. It is also the portion of the cell that contains the centrioles.

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14
Q

What organelle accounts for proper chromosome movement? Describe this organelle.

A

The proper movement of chromosomes depends on the centrioles, cylindrical organelles located outside of the nucleus from which the microtubule spindle fibers form and radiate. These attachment points are called asters.

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15
Q

During prophase what occurs to the nuclear structure?

A

During prophase the cell prepares to divide by dissolving the membrane around the nucleus, allowing spindle fibers to enter, and the nucleolus disappears.

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16
Q

During prophase what occurs to the chromatin and centrioles?

A

During prophase the chromatin condenses into chromosomes, the centriole pairs separate and move toward opposite poles of the cell, and the spindle apparatus forms between them. Kinetochores, with attached kinetochore microtubules, appear at the centromere.

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17
Q

What occurs during metaphase?

A

With the centriole pairs now at opposite poles of the cell, the kinetochore fibers interact with the fibers of the spindle apparatus to align the chromosomes at the metaphase plate (equatorial plate), which is equidistant to the two poles of the spindle fibers.

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18
Q

Explain what occurs during anaphase

A

The centromere is cleaved and the sister chromatids are separated by shortening kinetochore microtubules, which pull the sister chromatids to opposite poles of the cell.

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19
Q

What are the first and last parts of the sister chromatids to separate?

A

The centromere is the first and the telomeres are the last parts of the chromatids to separate.

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20
Q

Explain what occurs during telophase

A

Telophase is a reversal of prophase events. The spindle apparatus disappears, the nuclear membrane re-forms around each set of chromosomes, and the nucleoli reappear. Chromosomes uncoil and resume their interphase form.

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21
Q

Define cytokinesis

A

Cytokinesis begins at the end of telophase and is the process that completes cell division. During cytokinesis the cytoplasm and organelles separate, yielding two daughter cells.

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22
Q

What are diploid cells?

A

Diploid cells have two copies of each chromosome, usually one from the mother and one from the father. Eukaryotic somatic cells are diploid.

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23
Q

What are haploid cells?

A

Haploid cells have only one copy of each chromosome. Gametes (sperm, eggs) in humans are haploid.

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24
Q

What are three major forms of asexual reproduction?

A

Three major forms of asexual reproduction are binary fission, budding, and parthenogenesis

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25
Q

Define: Budding. What organisms can replicate by this manner?

A

Budding is equal replication followed by unequal cytokinesis. In other words, the daughter cell receives DNA identical to the parent cell, but far less cytoplasm. Yeast, among others, are able to replicate through budding.

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26
Q

Define: Binary Fission

A

Method of asexual reproduction by which prokaryotes divide. The circular DNA molecule replicates and then moves to opposite sides of the cell. The cell then divides into two daughter cells of equal size.

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27
Q

Define parthenogenesis and provide an example

A

Parthenogenesis is the development of an adult organism with haploid cells from an unfertilized egg. Many social insects such as bees and ants produce males via parthenogenesis.

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28
Q

How are haploid cells produced?

A

Haploid cells are produced through meiosis. Whereas mitosis results in two identical diploid (2n) daughter cells, meiosis yields four different haploid (n) gametes.

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29
Q

Which cell type undergoes mitosis? Which undergoes meiosis?

A

Somatic cells undergo mitosis, whereas gametocytes undergo meiosis.

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30
Q

Regarding replication and division, what is the key difference between mitosis and meiosis?

A

Mitosis consists of one round of replication and division each, while meiosis consists of one round of replication followed by two rounds of division (reductional and equational).

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31
Q

What are the two major phases of meiosis, and what are their subphases?

A

Meiosis I (the first division)

  1. prophase I
  2. metaphase I
  3. anaphase I
  4. telophase I

Meiosis II (the second division)

  1. metaphase II
  2. anaphase II
  3. telophase II

Mnemonic: PMATMAT

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32
Q

Regarding chromosome number, how do the two major phases of meiosis compare to mitosis?

A

In meiosis I the chromosome number is halved (reductional division). The daughter cells have the haploid number of chromosomes (23 in humans). Meiosis II is similar to mitosis in that the sister chromatids are separated from one another; therefore, no change in ploidy is observed.

33
Q

Provide a cursory overview of the differences between mitosis and meiosis.

A

Mitosis

  1. 2n→2n
  2. Occurs in all dividing cells
  3. homologous chromosomes don’t pair
  4. No crossing over

Meiosis

  1. 2n→n
  2. occurs in sex cells only (gametocytes)
  3. homologous chromosomes pair up at metaphase plate, forming tetrads
  4. crossing over can occur
34
Q

Which organ is responsible for the production of gametes? What name does this take in males and females.

A

The gonads produce gametes (sperm and ovum). in both males and females the gonads are derived from the same embryological structure. In males the primitive gonads develop into the testes, and in females into the ovaries.

35
Q

What is the pathway of sperm from creation to generation?

A

The pathway of sperm, in order, is

  1. Semineferous tubules
  2. Epididymis
  3. Vas deferens
  4. Ejaculatory duct
  5. (Nothing)
  6. Urethra
  7. Penis

Mnemonic: SEVEN UP

36
Q

What are the two functional components of the testes? What are their functions?

A

The two functional components of the testes are

  1. Semineferous tubules - place of sperm production and nourishment (by Sertoli cells)
  2. interstitial cells (cells of Leydig) - secret testosterone and other male sex hormones (androgens)
37
Q

Where are the testes located? Why is this location important?

A

The testes are located in the scrotum, an external pouch that hangs below the penis. This allows the testes to maintain a temperature 2˚ to 4˚C lower than the body. This is important for proper function of enzymes essential in proper sperm development.

38
Q

Where are the sperm stored until ejaculation? What occurs here in terms of maturation?

A

As sperm mature they are passed to the epididymis where they gain motlity in the form oof flagellum and are stored until ejaculation.

39
Q

During ejaculation, through what anatomical structures does the sperm travel?

A

During ejaculation the sperm travel through the ejaculatory duct and urethra, and exit the body through the penis.

40
Q

Regarding the reproductive and urinary systems, what is the major difference between males and females?

A

In males the reproductive and urinary systems share a common pathway, which is not the case in females.

41
Q

What does sperm mix with as it travels through the reproductive tract? Where is this produced, and what is the mixture subsequently called?

A

As sperm passes through the reproductive tract it is mixed with seminal fluid, which is produced through a joint effor by the seminal vesicles, prostate gland, and bulbourethral gland. The combination of sperma and seminal fluid is called semen. The seminal vesicles contribute fructose, while the prostate gland gives the fluid a mildly alkaline property.

42
Q

Define spermatogenesis and where does it occur.

A

Spermatoogenesis is the formation of haploid sperm through meiosis. It occurs in the semineferous tubules through the differentiation of the diploid stem cells known as spermatogonia.

43
Q

Define the order of events in the generation of mature sperm from spermatogonia.

A

Spermatogonia (2n)

(differentiation)

1˚ spermatocytes (2n)

(meiosis I)

2˚ spermatocytes (n)

(meiosis II)

spermatids (n)

​(differentiation)

spermatozoa (n)

44
Q

Know the diagram of the male reproductive system

A
45
Q

What is the structure of a mature sperm cell?

A
46
Q

In spermatogenesis, how many functional sperm are created for each spermatogonium? During oogenesis, how many functional ova are created for each oocyte?

A

spermatogenesis in males creates 4 sperm per spermatogonium, while oogenesis in females creates 1 ovum per oocyte.

47
Q

In females what are the gonads called, where are they located, and what do they consist of?

A

The gonads in females are known as ovaries and are located below the digestive system in teh pelvic cavity. Each ovary consists of thousands of follicles, which are multilayered sacs that contain, nourish, and protect immature ova.

48
Q

What hormones are produced in the ovaries? in the testes?

A

Estrogen and progesterone are produced in the ovaries, while testosterone and otehr male sex hormones (androgens) are produced in the testes.

49
Q

Know how to diagram the female reproductive system

A
50
Q

Describe the path of an egg from generation in the ovaries to excretion during menstruation.

A

One egg per month will be released from the ovaries into the fallopian tube, or oviduct, which is lined with cilia to usher it along to the uterus if fertilized. The primed ovum will remain in the fallopian tubes until fertilization or menstruation. An unfertilized egg will be excreted through the uterus, into the cervix, then into the vaginal canal and out of the vagina.

51
Q

What is the term for the production of female gametes?

A

The production of female gametes is known as oogensis.

52
Q

Define the order of events in the generation of a mature ovum from oocytes.

A

1˚ oocyte (2n)

(meiosis I)

2˚ oocyte (n)

(fertilization)

(meiosis II)

ovum (n)

53
Q

What is an important difference between males and females in the supply of gametes?

A

In females there is no unending supply of stem cells analogous to spermatogonia in males. All the oogonia a woman will ever have are formed during fetal development, and at birth females have a set number of predifferentiated cells known as primary oocytes (2n cells frozen in prophase I).

54
Q

Describe the cell division process that occurs during gametogenesis in females prior to fertilization.

A

Once a woman reaches puberty one primary oocyte (2n) per month will complete meiosis I, producing a secondary oocyte (n) and a polar body (n) through unequal cytokinesis. The polar body does not divide any further and never produces functional gametes. The secondary oocyte remains frozen in metaphase II and does not complete the remainder of meiosis II unless fertilization occurs.

55
Q

What is the zona pellucida?

A

This is is the inner layer of cells surrounding the oocyte. These cells are secreted by follicle cells. Penetration of the zona pellucida by a sperm forces the secondary oocyte to undergo meiosis II.

56
Q

What are the two cell layers that surround the oocyte?

A

The oocyte is surrounded by the zona pellucida and the corona radiata.

57
Q

What is the corona radiata?

A

The corona radiata is the outer layer of cells surrounding the oocyte. These cells are secreted by follicle cells.

58
Q

Upon fertilization, what happens to the secondary oocyte?

A

Upon fertilization the secondary oocyte proceeds through meiosis II and undergoes the seconday division to split into a mature ovum and another polar body, which will eventually die.

59
Q

Hormonally speaking, what occurs after menopause and what is the general result?

A

Under normal function the ovaries contribute to a negative feedback loop for FSH and LH through the generation of estrogen and progesterone. After menopause the ovaries become less sensitive to their stimulating hormones (follicle-stimulating hormone [FSH] and luteinizing hormone [LH]), cease to produce estrogen and progesterone, and eventually atrophy. This leads to a dramatic drop in estrogen and progesterone leves, and an accompanying spike in FSH and LH. This prompts profound physical and physiological changes to occur.

60
Q

What are the major hormones that contribute to spermatogenesis in males, and what are their targets and effects?

A

Follicle Stimulating Hormone (FSH) stimulates the Sertoli cells and is necessary for sperm maturation, whereas Luteinizing Hormone (LH) causes the interstitial cells to produce testosterone, the major androgen in males. Testosterone is necessary for male embryonic differentiation, male sexual maturation at puberty, and maintenance of secondary sex characteristics, such as axillary and pubic hair. Testosterone provides negative feedback to FSH, LH, and GnRH.

61
Q

Define polar body

A

The polar body is a small, short-lived haploid cell created during oogenesis that receives little cytoplasm, organelles, and nutrients. It eventually dies.

62
Q

Define Follice

A

The follicle is a multilayered sac of cells that protects and nourishes the developing ovum.

63
Q

What is interkinesis?

A

Interkinesis is a short rest period between meiosis I and meiosis II during which DNA is not replicated. An ovum remains in interkinesis until it is fertilized.

64
Q

What is a zygote?

A

The fusion of the two haploid sperm and egg cells results in the restoration of the diploid chromosome number. This diploid cell is known as a zygote.

65
Q

What are dizygotic twins and what process leads to this result?

A

Dizygotic twins result when two ova are fertilized by two different sperm. Since the two resulting embryos develop from distinct zygotes, they do not have identical alleles.

66
Q

What are monozygotic twins? Describe the embryonic process that leads to this result.

A

Monozygotic twins result when a single zygote splits into two embryos. Since the two resulting embryos develop from the same zygotes, they contain identical alleles and are often called identical twins.

67
Q

What are homologous chromosomes?

A

Homologous chromosomes are chromosomes in a diploid cell that contain different alleles for the same trait at corresponding loci.

68
Q

What are sister chromatids

A

After replication, each chromosome consists of two identical chromatids held together at a central region called a centromere. After the mitotic spindle pulls the sister chromatids apart, each chromatid is referred to as a chromosome.

69
Q

What are somatic cells?

A

Somatic cells are all cells excluding the germ (reproductive) cells.

70
Q

What is meiosis?

A

Meiosis is a two-phase cell division in germ cells taht results in the formation of four haploid cells from one diploid cell.

71
Q

Define crossing over

A

Crossing over is the exchange of genetic material between chromosomes (usually homologous chromosomes) that occurs during prophase I of meiosis. crossing over aids in evolution and genetic diversity by unlinking genes.

72
Q

What does the term disjunction refer to?

A

Disjunction is the separation of homologous chromosomes during anaphase I of meiosis.

73
Q

What are the interstitial cells?

A

The interstitial cells, or cells of Leydig, are located in the testes and secrete testosterone and otehr androgens in response to Luteinizing Hormone (LH).

74
Q

Define spermatozoa

A

Spermatozoa are mature sperm specialized for transportng the genetic information from the male to the ovum.

75
Q

What are primary spermatocytes?

A

Primary spermatocytes are diploid cells that undergo meiosis I to form two haploid secondary spermatocytes.

76
Q

What are the semineferous tubules?

A

The semineferous tubules are located in the testes are are the site of sperm production.

77
Q

Define semen

A

Semen is the fluid discharged during ejaculation. It consists of sperm and seminal fluid (fluid from the prostate and bulbourethral glands).

78
Q

What are the four phases of the menstrual cycle, and what happens both physiologically and hormonally in each?

A

The menstrual cycle consists of

  1. follicular (preovulatory) phase - follicles mature (driven by rise FSH and LH)
  2. ovulation - release of the ovum from the ovary into the abdominal cavity (driven by abrupt spike in FSH, LH, and GnRH)
  3. luteal (postovulatory) phase - ruptured follicle becomes corpus luteum and secretes estrogen and progesterone to build up uterine lining in preparation for implantation (LH and FSH are inhibited and levels drop)
  4. menstruation - if fertilization doesn’t occur, corpus luteum atrophies, progesterone and estrogen levels decrease, and menses occurs (LH and FSH begin to rise again)

MCAT Biology (15 decks)

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