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IH MCAT Biology > Cell Cycle & Mitosis > Flashcards

Cell Cycle & Mitosis Flashcards

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1
Q

What are some key characteristics that all mammals share?

A
  • Milk producing mammary glands
  • three bones in the middle ear and one in the lower jaw
  • fur or hair
  • heterodont dentition (different kinds of teeth)
  • both SEBACEOUS (oil-producing) and SUDORIFEROUS (sweat) glands
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2
Q

What are the two groups of mammals that birth their young differently?

A
  • PROTOTHERIANS

* METATHERIANS

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3
Q

What are prototherians? How do they give birth?

A
  • Also known as MONOTREMES and include the duck-billed platypus and echidna (spiny anteater)
  • These mammals encase their developing embryos within hard-shelled amniotic eggs and lay them to be hatched, like reptiles
  • This method of development is referred to as OVIPARITY
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4
Q

What are metatherians and how do they give birth?

A
  • Metatherians, also known as MARSUPIALS, include koalas and kangaroos
  • A typical meteatherian fetus undergoes SOME development in its mothers uterus and then climbs its way out of the birth canal and into her marsupium, or POUCH
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5
Q

In animals, what is the difference between autosomal cells and germ cells?

A
  • Autosomal cells are said to be DIPLOID (2n), which means that they contain two copies of each chromosome
  • GERM CELLS are HAPLOID (n), containing only one copy of each chromosome
  • In humans, 2n=46, and n=23, meaning that we inherit 23 chromosomes from each parent
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6
Q

Generally, what is the cell cycle?

A

*EUKARYOTIC cells replicate through the cell cycle, a specific series of phases during which a cell GROWS, synthesizes DNA, and DIVIDES.
For actively dividing cells, the cell cycle consists of FOUR stages: G1, S, G2, and M.
Derangement of the cell cycle can lead to unchecked cell division, and may be responsible for the formation of cancer.

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7
Q

What is interphase in the cell cycle?

A
  • The first three stages (G1, S, and G2) are known as INTERPHASE
  • Interphase is the longest part of the cell cycle, even actively dividing cells spend about 90% of their time in interphase
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8
Q

What is the G0 part of the cell cycle?

A
  • Cells that do NOT divide spend all of their time in an OFFSHOOT of G1 called G0
  • During the G0 stage, the cell is simply living and serving its function, without any preparation for division
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9
Q

What is the difference between the configuration of DNA during interphase vs. during mitosis, and why?

A
  • During INTERPHASE, individual chromosomes are not visible with LIGHT MICROSCOPY because they are in a less condensed form known as CHROMATIN. This is because the DNA must be available to RNA polymerase so that genes can be TRANSCRIBED
  • During MITOSIS, however, it is preferable to condense the DNA into tightly coiled chromosomes to avoid losing any genetic material during cell division
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10
Q

What happens during the G1 phase? What happens at the END of the G1 phase?

A
  • During the G1 phase, also known as the pre-synthetic GAP, cells create organelles for energy and protein production (mitochondria, ribosomes, and endoplasmic reticulum), while also increasing their size
  • Passage into the S (synthesis) stage is governed by a RESTRICTION POINT
  • In order to pass the restriction point, certain criteria, like containing the proper complement of DNA, must be met for the cell to pass the restriction pint and enter the next stage
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11
Q

What happens during the S stage?

A
  • During the S phase, the cell REPLICATES ITS GENETIC MATERIAL so that each daughter cell will have identical copies
  • After replication, each chromosome consists of two identical CHROMATIDS that are bound together at specialized regions known as the CENTROMERE
  • The PLOIDY of the cell does NOT change even though the number of chromatids has doubled. Humans in this stage still only have 46 chromosomes, even though 92 chromatids are present
  • Cells entering G2 have TWICE as much DNA as cells in G1
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12
Q

What does PLOIDY mean?

A
  • Ploidy is the number of sets of chromosomes in a cell
  • Usually a gamete (sperm or egg) carries a full set of chromosomes that include a single copy of each chromosome
  • The gametic or haploid number (n) is the number of chromosomes in a gamete
  • Two gametes form a DIPLOID ZYGOTE with twice this number (2n), meaning there are two copies of autosomal chromosomes
  • For humans, a diploid species, n=23; this means a typical human somatic cell contains 46 chromosomes, composed of 2 complete haploid sets, which makes up 23 HOMOLOGOUS CHROMOSOME PAIRS
  • Cells are described according to the number of chromosome sets present, known as the ploidy level: monoploid (1 set), diploid (2 set), tetraploid (4 set), etc.
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13
Q

What does chromatid mean? What about chromosome?

A
  • Each chromatid is composed of a COMPLETE, double-stranded molecule of DNA
  • Sister chromatids are IDENTICAL COPIES of each other
  • CHROMOSOME may be used to refer to either a SINGLE CHROMATID before S phase or the PAIR of chromatids attached at the centromere after S phase
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14
Q

What happens during G2 phase?

A
  • Also known as the POSTSYNTHETIC GAP
  • During G2 phase, the cell passes through another quality control checkpoint
  • DNA has already been dupliciated, and the cell checks to ensure that there are enough organelles and cytoplasm to divide between the two daughter cells
  • The cell also checks to make sure that DNA replication proceeded CORRECTLY to avoid passing on an ERROR to daughter cells that may further replicate the error in their PROGENY
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15
Q

What happens during M stage (MITOSIS)?

A

*The M stage consists of MITOSIS itself along with CYTOKINESIS
*Mitosis is divided into four phases: prophase, metaphase, anaphase, and telophase
8Mitosis is the process by which TWO IDENTICAL daughter cells are created from a SINGLE CELL
*Mitosis occurs in SOMATIC CELLS, or cells that are NOT involved in sexual reproduction
*Cytokinesis is the SPLITTNG of the cytoplasm and organelles into two daughter cells

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16
Q

What is the difference between division in autosomal cells vs. germ cells?

A
  • In autosomal cells, division results in TWO genetically identical daughter cells
  • In germ cells, the daughter cells are NOT EQUIVALENT
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17
Q

What is the cell checking for at the G1/S checkpoint? What happens if the conditions to pass the checkpoint are not met?

A
  • The cell is looking to see if the DNA is in good enough condition for SYNTHESIS
  • This checkpoint is also known as the restriction point
  • If there has been damage to the DNA, the cell cycle goes into arrest until the DNA has been repaired
  • The main protein in control of this is known as p53
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18
Q

What is the cell checking for at the G2/M checkpoint?

A
  • At this checkpoint, the cell is mainly concerned with ensuring that the cell has achieved adequate SIZE and the organelles have been properly replicated to support two daughter cells.
  • P53 also plays a role here
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19
Q

What are the molecules responsible for the cell cycle?

A
  • The molecules responsible for the cell cycle are known as CYCLINS and CYCLIN-DEPENDENT KINASES (CDK)
  • In order to be activated, CDK’s require the right kind of cyclins to be present
  • During the course of the cell cycle, concentrations of various cyclins increase and decrease during specific stages. These cyclins BIND to CDK’s, creating an activated CDK-cyclin complex
  • The CDK-cyclin complex can then PHOSPHORYLATE transcription factors, and these transcription factors THEN promote transcription of genes required for the next stage of the cell cycle
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20
Q

What happens when the p53 gene, called TP53, is mutated?

A
  • CANCER
  • One of the most COMMON mutations found in cancer is mutation of the gene that produces p53, called TP53
  • When this gene is mutated, the cell cycle is NOT stopped to repair damaged DNA, which allows for mutations to accumulate, eventually resulting in a CANCEROUS CELL that divides CONTINUOUSLY and without regard to the quality or quantity of the new cells produced
  • Cancer cells will often rapidly divide, creating TUMORS
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21
Q

What is metastasis and how can it happen?

A
  • If a cancerous cell (i.e. a cell with a mutated p53 gene) begins to produce the right factors, like proteases that can DIGEST basement membranes or factors that encourage blood vessel formation, the damaged cells are then able to reach other tissues
  • This may include LOCAL invasion as well as DISTANT spread of cancerous cells throughout the bloodstream or lymphatic systems
  • Metastasis is when the cancerous cells spread throughout the body
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22
Q

What are the two main kinds of cancer causing genes?

A
  • ONCOGENES: genes that, when mutated, ACTIVELY promote cell division
  • TUMOR SUPRESSOR GENES: genes that, when mutated, lose their ability to regulate or pause the cell cycle
  • Different cancer types are often associated with specific mutations in either ONCOGENES or TUMOR SUPRESSOR GENES or BOTH
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23
Q

What happens during prophase?

A

o Prophase is the FIRST phase in mitosis
o First step in prophase involves CONDENSATION of the chromatin into CHROMOSOMES
o The centriole pairs separate and move toward opposite poles of the cell; these paired cylindrical organelles are located OUTSIDE the nucleus in a region known as the CENTROSOME and are responsible for the correct division of DNA
o Once the centrioles migrate to opposite poles of the cell, they begin to form SPINDLE FIBERS, which are made of microtubules
o Each of the spindle fibers radiate outward from the centrioles
o Some microtubules form ASTERS that anchor the centrioles to the cell membrane while others extend toward the middle of the cell
o The NUCLEAR MEMBRANE also dissolves during prophase, allowing the spindle fibers to make contact with the chromosomes
o The nucleoli becomes less distinct and may disappear completely
o Kinetochores appear at the centromere

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24
Q

What are kinetochores?

A

*Kinetochores are protein structures located on the centromeres that serve as attachment points for specific fibers of the spindle apparatus appropriately called kinetochore fibers

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25
Q

In general, what happens during each phase of mitosis to the chromosomes?

A
  • Prophase: chromosomes CONDENSE, spindle apparatus forms
  • Metaphase: chromosomes ALIGN
  • Anaphase: sister chromatids separate
  • Telophase: new nuclear membranes form
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26
Q

What happens during METAPHASE?

A
  • During metaphase, the centriole pairs are now at opposite ends 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 between the two poles of the cell
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27
Q

What happens during anaphase?

A
  • During anaphase, the centromeres SPLIT so that each chromatid has its own distinct centromere, thus allowing the sister chromatids to separate
  • The sister chromatids are pulled toward the opposite poles of the cell by the shortening of the kinetochore fibers
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28
Q

What happens during telophase?

A
  • Telophase is the reverse of prophase
  • The spindle apparatus disappears
  • A nuclear membrane reforms around each set of chromosomes, and the nucleoli reappear
  • The chromosomes uncoil, resuming their interphase form
  • Each of the two new nuclei has received a complete copy of the genome identical to the original genome and to each other
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29
Q

What is cytokinesis?

A

*At the end of telophase, cytokinesis is the separation of the cytoplasm and organelles so that each daughter cell has sufficient supplies to survive on its own

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30
Q

Typically how many times do human cells divide?

A
  • Each cell undergoes a finite number of divisions before programmed death
  • For human somatic cells, this is usually between 20 and 50
  • After that, the cell can no longer divide continuously
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31
Q

Where does meiosis occur and what generally is it?

A

Meiosis occurs in gametocytes (GERM CELLS) and results in up to four nonidentical sex cells (GAMETES)

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32
Q

What are some similarities between meiosis and mitosis? What are some general differences?

A

SIMILARITIES: In both processes, genetic material must be duplicated, chromatin is condensed to form chromosomes, and microtubules emanating from centrioles are involved in dividing genetic material.

DIFFERENCES: mitosis consists of one round of replication and division while meiosis consists of one round of replication followed by TWO rounds of division

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33
Q

What are the two rounds of division in meiosis?

A

Meiosis I: results in homologous chromosomes being separated, generating haploid daughter cells (REDUCTIONAL DIVISION)

Meiosis II: similar to mitosis, in that it results in the separation of sister chromatids (EQUATIONAL DIVISION)

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34
Q

What is the difference between homologous pairs and sister chromatids?

A

The human genome is composed of 23 HOMOLOGOUS PAIRS of chromosomes (homologues), each of which contains ONE chromosome inherited from each parent.

Homologous pairs are considered SEPARATE CHROMOSOMES (i.e. material chromosome 15 and paternal chromosome 15).

SISTER CHROMATIDS are IDENTICAL STRANDS of DNA connected at the centromere.

After S Phase, there are 92 chromatids organized into 46 chromosomes, which are organized into 23 homologous pairs.

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35
Q

What happens during prophase I of meiosis? Specifically what is the state of the genetic information?

A

The chromatin condenses into CHROMOSOMES, the spindle apparatus forms, and the nucleoli and nuclear membrane disappear.

Homologous chromosomes come together and intertwine in a process called synapsis. Each chromosome consists of TWO SISTER CHROMATIDS, so each synaptic pair contains FOUR chromatids & is referred to as a tetrad.

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36
Q

What first major difference between meiosis and mitosis occurs during prophase I of meiosis?

A

HOMOLOGOUS CHROMOSOMES come together and intertwine in a process called SYNAPSIS.

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37
Q

What is the process of CROSSING OVER that often occurs during prophase I of meiosis?

A

Chromatids of homologous chromosomes may break at the point of synapsis, called the CHIASMA and exchange equivalent pieces of DNA, a process known as crossing over.

Crossing over occurs between HOMOLOGOUS chromosomes and NOT between sister chromatids of the same chromosome (sister chromatids are identical so crossing over wouldn’t produce any change)

Result of crossing over is an altered but structurally COMPLETE set of genes. Genetic recombination like crossing over can unlink linked genes, thereby increasing the variety of genetic combinations that can be produced via gametogenesis.

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38
Q

What does linkage mean in regards to genes?

A

Linkage refers to the tendency for genes to be inherited TOGETHER; genes that are located further from each other physically are less likely to be inherited together, and more likely to undergo crossing over relative to each other.

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39
Q

Why is genetic recombination a benefit in sexual reproduction, and how does this compare to asexual reproduction?

A

ASEXUAL reproduction produces IDENTICAL OFFSPRING.

Sexual reproduction provides the ADVANTAGE of GREAT GENETIC DIVERSITY, which is believed to increase the ability of a species to evolve and adapt to a changing environment.

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40
Q

Chiasma

A

A point at which paired chromosomes remain in contact during the first metaphase of meiosis, and at which crossing over and exchange of genetic material occur between the strands.

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41
Q

How can the distance between two genes on a chromosome be determined?

A

THE RATE of gene unlinking can be used to map differences between two genes on the same chromosome.

The farther apart two genes are, the more likely they are to become UNLINKED during crossing over. These statistics can then be used to determined the distance between genes on the chromosome, measured in units called CENTIMORGANS.

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42
Q

How does crossing over explain Mendel’s second law of independent assortment?

A

Mendel’s second law states that the INHERITANCE of one allele has no effect on the likelihood of inheriting certain alleles for other genes. It states that the alleles of one gene sort into the gametes independently of the alleles of another gene.

Because of crossing over, each daughter cell will have a UNIQUE POOL OF ALLELES (genes coding for alternative forms of a given trait) from a random mixture of maternal and paternal origin. Genes that are on the same chromosome can be inherited together, but crossing over during meiosis may separate them.

The principle or law of independent assortment is applicable to only those factors or genes which occur on different chromosomes. Actually, a chromosome bears hundreds of genes. All the genes or factors present on a chromosome are inherited together except when ‘crossing over’ takes place.

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43
Q

Why is Mendel’s Second Law not always valid for two or more phenotypical traits of an individual?

A

Mendel’s Second Law, or the law of the independent assortment, is valid for genes located in different chromosomes. These genes segregate independently during meiosis.

However, Mendel’s Second Law is not valid for phenotypical features conditioned by genes located in the same chromosome (genes under linkage), since these genes, known as linked genes, do not separate during meiosis (except for the phenomenon of crossing over).

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44
Q

What happens during metaphase I of meiosis?

A

During metaphase I, homologous pairs (TETRADS) align at the metaphase plate, and each pair attaches to a separate spindle fiber by its kinetochore.

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45
Q

How is metaphase I in meiosis distinct from metaphase in mitosis?

A

In mitosis, each CHROMOSOME is lined up on the metaphase plate by two spindle fibers (one from each pole–each spindle fiber connects to one sister chromatid)

In Meiosis, homologous chromosomes are lined up across from each other at the metaphase plate and held by ONE spindle fiber. (each chromosome is attached to one spindle fiber so the homologous chromosomes themselves can be separated)

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46
Q

What happens during anaphase I of meiosis?

A

During anaphase I, homologous pairs SEPARATE and are pulled to opposite poles of the cell–a process called DISJUNCTION and it accounts for Mendel’s FIRST LAW of segregation.

During disjunction, each chromosome of paternal origin separates (disjoins) from its homologue of maternal origin (so homologous pair separates), and either chromosome can end up in either daughter cell depending on how the homologous pair arranged on the metaphase plate. The distribution of homologous chromosomes to the two intermediate daughter cells is random with respect to parental origin. The separating of two homologous chromosomes is referred to as segregation.

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47
Q

How is meisis different from mitosis?

A

The chromosome number is HALVED (reductional division) in meiosis I, and the daughter cells produced have the HAPLOID number of chromosomes (23 chromosomes in humans), and each chromosome in the daughter cells is composed of two chromatids (sister chromatids), which are identical.

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48
Q

How is meiosis II similar to mitosis?

A

Sister chromatids are SEPARATED from one another so no change in ploidy is observed.

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49
Q

What happens during telophase I of meiosis?

A

During telophase I, a nuclear membrane forms around each new nucleus. Each chromosome still consists of TWO SISTER CHROMATIDS joined at the centromere.

The cells are now HAPLOID: once homologous chromosomes separate, only n chromosomes are found in each daughter cell (23 in humans).

The cell divides into two daughter cells by CYTOKINESIS. Between cell divisions, there may be a short REST period (INTERKINESIS) during which the chromosomes partially uncoil.

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50
Q

What happens if during either anaphase I or anaphase II of meiosis the homologous chromosomes (anaphase I) or sister chromatids (anaphase II) fail to separate?

A

One of the resulting gametes will have TWO copies of a particular chromosome and the other gamete will have NONE.

Subsequently during fertilization, the resulting ZYGOTE may have TOO MANY or TOO FEW copies of that chromosome.

Nondisjunction can affect bboth autosomal chromosomes (trisomy 21) and sex chromosomes (Klinefelter’s or Turner syndromes)

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51
Q

What happens during meiosis II?

A

Meiosis II is really similar to mitosis as sister chromatids (not homologues) are separated from each other.

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52
Q

What happens during prophase II?

A

The nuclear envelope dissolves, the nucleoli disappear, the centrioles migrate to opposite poles, and the spindle apparatus forms.

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53
Q

What happens during metaphase II?

A

The chromosomes line up on the metaphase plate

54
Q

What happens during anaphae II?

A

The centromeres divide, separating the chromosomes into sister chromatids. These chromatids are pulled to opposite poles by spindle fibers.

55
Q

What ahppens during telophase II?

A

A nuclear membrane forms around each new nucleus. Cytokinesis follows, and two daughter cells are formed.

By the completion of meiosis II, up to four haploid daughter cells are produced PER GAMETOCYTE. (oogenesis may result in fewer than four cells if an egg remains unfertilied after ovulation)

56
Q

What determines the biological sex in humans?

A

Biological sex is determined by the 23rd pair of chromosomes, with XX being FEMALE and XY being MALE.

57
Q

What kind of chromosome can an ovum carry? what about sperm?

A

An ovum can ONLY carry the X chromosome, while sperm can carry either the X or Y chromosome.

58
Q

What is the size of the X chromosome relative to the Y?

A

The X chromosome is notably larger and has a more active euchromatin region than its Y chromosome counterpart. Further comparison of the X and Y reveal regions of homology between the two. However, the corresponding region in the Y appears far shorter and lacks regions that are conserved in the X throughout primate species, implying a genetic degeneration for Y in that region. Because males have only one X chromosome, they are more likely to have an X chromosome-related disease.

59
Q

What are X-linked disorders? How does this affect males and females differently?

A

Genetic disorders that are due to mutations in genes on the X chromosome are described as X linked.

Males are termed HEMIZYGOUS with respect to many of the genes on the X chromosome because they only have ONE COPY. This means that a male with a disease-causing allele on the unpaired part of the X chromosome will NECESSARILY express that allele.

Females may be homozygous or heterozygous with respect to genes on X chromosome.

60
Q

Why are males more likely to suffer from X-linked disorders (SEX-LINKED)?

A

Because males only get one X chromosome so whatever is there is expressed. SEX-LINKED IS X-LINKED.

Most X-linked disorders are recessively inherited, so females express these disorders FAR less frequently than males.

Females carrying a diseased allele on an X chromosome, but not exhibiting the disease, are said to be CARRIERS.

61
Q

What is the SRY region of the Y chromosome? What does this mean if the Y chromosome is absent?

A

The Y chromosome contains very little genetic information but it does contain a notable gene, SRY, which stands for the SEX-DETERMINING REGION Y.

SRY codes for a transcription factor that initiates testis differentiation and thus, the formation of the male gonads.

In the absence of the Y chromosome, ALL ZYGOTES will be female. In the presence of Y, a zygote will be male.

62
Q

Are there Y-linked diseases, and if so, what do they usually do?

A

There are a handful of Y-linked diseases, most of which result in reduced fertility.
A father would pass a Y-linked disease to all of his sons, assuming fertility hasn’t been lost. These diseases are rare.

63
Q

What are the two functional components of the testes?

A 
In males, the primitive gonads DEVELOP into testes.
#1: The SEMINIFEROUS TUBULES
#2: INTERSTITIAL CELLS (of Leydig)
64
Q

Where are sperm produced in testes?

A

Sperm are produced in the highly coiled SEMINIFEROUS TUBULES, where they are NOURISHED by Sertoli cells.

Seminiferous tubules are located within the testes, and are the specific location of meiosis, and the subsequent creation of male gametes.

65
Q

What is the function of the interstitial cells of Leydig?

A

The cells of Leydig secrete TESTOSTERONE and other male sex hormones (androgens)

66
Q

What are Sertoli Cells?

A

A Sertoli cell (a kind of sustentacular cell) is a “nurse” cell of the testicles that is part of a seminiferous tubule and helps in the process of spermatogenesis; that is, the production of sperm.

Because its main function is to nourish the developing sperm cells through the stages of spermatogenesis, the Sertoli cell has also been called the “mother” or “nurse” cell. Sertoli cells facilitate the progression of germ cells to spermatozoa via direct contact and by controlling the environment milieu within the seminiferous tubules.

67
Q

Where are the testes located, and why is that important?

A

The testes are located in the SCROTUM.
The SCROTUM is an external pouch that hands below the penis and maintains a temperature 2 to 4 degrees celsius lower than that of the body.

68
Q

What role do the vas deferens play in maintaining the correct temperature of the vas deferens?

A

There is a layer of MUSCLE around the vas deferens (ductus derens) that can RAISE and LOWER the testis to maintain the PROPER TEMPERATURE for sperm development

69
Q

Where are sperm stored?

A

As sperm and formed, they are passed to the EPIDIDYMIS where their flagella gain MOTILITY, and they are then STORED until ejaculation.

70
Q

What happens to sperm during ejaculation?

A

Sperm travel through the vas deferens to the EJACULATORY DUCT at the posterior edge of the prostate gland.

The two EJACULATORY DUCTS then FUSE to form the URETHRA which carries sperm THROUGH the penis as they exit the BODY. In males, the reproductive and urinary systems share a COMMON PATHWAY.

71
Q

Whats a clelver mnemonic used to remember the pathway of sperm through the male reproductive system?

A

SEVE(N) UP

#1. Seminiferous tubules
#2. Epididymis
#3. Vas Deferens
#4. Ejaculatory Duct
#5. (NOTHING)
#6. Urethra
#7. PENIS
72
Q

Besides sperm, what other fluid is in ejaculation?

A

SEMINAL FLUID.
As sperm pass through the reproductive tract, they are mixed with seminal fluid, which is produced through the combined effort by the SEMINAL VESICLES, PROSTATE GLAND, and BULBOURETHRAL GLAND.

As the sperm is transferred from the vas deferens through the ejaculatory duct and into the urethra, secretions from the male accessory sex glands are added.

The combination of SPERM and SEMINAL FLUID is known as SEMEN.

73
Q

What do the seminal vesicles contribute to semen? What about the prostate gland?

A

The seminal vesicles contribute FRUCTOSE to nourish sperm.

BOTH the seminal vesicles and the prostate gland give the fluid MILDLY ALKALINE PROPERTIES so that the sperm will be able to survive in the relative acidity of the female reproductive tract.

74
Q

What do the Bulbourethral (Cowper’s) glands contribute to semen?

A

They produce a CLEAR viscous fluid that cleans out any remnants of URINE and lubricates the urethra during sexual arousal.

75
Q

What is benign prostatic hypertrophy?

A

The prostate ENLARGES with AGE and frequently causes problems in older males.

Because the prostate surrounds the urethra, classic symptoms of this condition include URINARY FREQUENCY, URGENCY, and nighttime awakening to use the bathroom.

76
Q

What is the process of SPERMATOGENESIS?

A

Spermatogenesis is the formation of haploid sperm through meiosis, and occurs in the SEMINIFEROUS TUBULES.

In males, the DIPLOID STEM CELLS are known as SPERMATOGONIA.
After replicating their genetic material (S stage), they develop into diploid PRIMARY SPERMATOCYTES.

The first meiotic division will result in haploid secondary spermatocytes, which then undergo meiosis II to generate haploid SPERMATIDS.

The Spermatids then undergo maturation to become SPERMATOZOA.

Spermatogenesis results in four functional sperm for each spermatogonium.

77
Q

What is the general structure of mature sperm cells?

A

Mature sperm cells are very compact.

They consist of a HEAD (containing genetic material), a midpiece (generates ATP form FRUCTOSE) and a flagellum (for MOTILITY).

78
Q

How do sperm have the energy to move?

A

The midpiece area of SPERM is FILLED WITH MITOCHONDRIA, which generate the energy to be used as the sperm swims through the female reproductive tract to reach the ovum in the fallopian tubes.

79
Q

What is the composition of the sperm head, and what is its function?

A

Each sperm head is covered by a CAP known as the ACROSOME.
The acrosome is derived from the GOLGI APPARATUS and is necessary to penetrate the OVUM.

In Eutherian mammals the acrosome contains digestive enzymes. These enzymes break down the outer membrane of the ovum, called the zona pellucida, allowing the haploid nucleus in the sperm cell to join with the haploid nucleus in the ovum.

80
Q

How frequently are sperm produced?

A

Once a male reaches sexual maturity during puberty, approximately 3 million sperm are produced PER DAY through the rest of life.

81
Q

What are eutherian mammals?

A

Eutherians, like their closest relatives the marsupials, give birth to live young. In eutherians, however, the young are nurtured within the body of the mother by the placenta, which allows nutrients to pass from the blood of the mother almost directly into the blood of the young. The placenta also allows oxygen to reach the developing young, thereby making more energy available than in marsupials.

82
Q

What are the female gonads?

A

The gonads, known as the OVARIES, produce estrogen and progesterone.

The ovaries are located in the PELVIC CAVITY; each ovary consists of thousands of follicles, which are multilayered sacs that CONTAIN, NOURISH, and PROTECT immature OVA (eggs).

83
Q

What is an ovarian follicle?

A

An ovarian follicle is a roughly spheroid cellular aggregation set found in the ovaries. It secretes hormones that influence stages of the menstrual cycle.
Women begin puberty with about 400,000 follicles, each with the potential to release an egg cell (ovum) at ovulation for fertilization.
These eggs are developed only once every menstrual cycle.
Ovarian follicles are the basic units of female reproductive biology. Each of them contains a single oocyte (immature ovum or egg cell). These structures are periodically initiated to grow and develop, culminating in ovulation of usually a single competent oocyte in humans.

84
Q

What is an oocyte?

A

An oocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis.

85
Q

What happens during ovulation?

A

Ovulation is when a mature egg is released from the ovary, pushed down the fallopian tube, and is made available to be fertilized. Approximately every month an egg will mature within one of your ovaries.

During ovulation, an ovarian follicle ruptures, causing the oocyte to be released from the ovary via the oviduct. The secondary oocyte leaves the ruptured follicle and moves out into the peritoneal cavity/peritoneal sac, which lines the abdominal cavity. It is then drawn into the fallopian tube or OVIDUCT, which is lined with cilia to propel the egg forward. The fallopian tubes are connected to the muscular UTERUS, which is the site of fetal development.

86
Q

What is the follicular stage?

A

The follicular phase is the phase of the menstrual cycle during which the ovarian follicles mature. The follicular phase lasts from the beginning of menstruation to the start of ovulation

87
Q

What is the lower end of the uterus connected to?

A

The lower end of the uterus, known as the CERVIX, connects to the vaginal canal, where sperm are deposited during intercourse. The VAGINA is also the passageway through which childbirth occurs.

88
Q

Vulva

A

The vulva consists of the external genital organs of a woman.

89
Q

What is oogenesis?

A

The production of female gametes is known as OOGENESIS.

90
Q

What is a significant difference in regards to the production of female gametes in comparison to the production of MALE gametes?

A

There is NO unending supply of stem cells analogous to spermatogonia in females; all of the oogonia a woman will ever have formed during fetal development. By birth, all of the oogonia have already undergone DNA replication and are considered PRIMARY OOCYTES.

91
Q

What is the beginning process of OOGENESIS?

A

Oogenesis starts with the process of developing oogonia, which occurs via the transformation of primordial follicles into primary oocytes. By birth, all of the oogonia have already undergone DNA replication and are considered primary oocytes. These cells are 2n and are arrested in prophase I.

92
Q

What happens once a woman reaches her menarche? (the later half of oogenesis)

A

Menarche is a woman’s first menstrual cycle. Once this happens, one primary oocyte PER MONTH will complete MEIOSIS I, producing a secondary oocyte and a POLAR BODY.

The division is characterized by UNEQUAL CYTOKINESIS, which doles ample cytoplasm to ONE daughter cell (secondary oocyte), and nearly NONE to the other (the polar body).

93
Q

What happens to the secondary oocyte? what about the polar body?

A

The SECONDARY OOCYTE remains arrested in metaphase II and does not complete the remainder of meiosis II unless fertilization occurs.

The POLAR BODY generally does NOT divide any further and will NEVER produce functional gametes.

94
Q

What are the two layers that surround OOCYTES?

A 
#1. ZONA PELLUCIDA
#2. CORONA RADIATA
95
Q

What is the zona pellucida?

A

The zona pellucida surrounds the oocyte itself and is an acellular mixture of glycoproteins that PROTECT the oocyte and contain compounds necessary for sperm cell binding.

96
Q

What is the corona radiata?

A

The corona radiata lies OUTSIDE the zona pellucida and is a layer of cells that ADHERED to the oocyte during ovulation.

97
Q

How is Meiosis II triggered?

A

Meiosis II is triggered when a sperm cell penetrates these layers (zona pellucida and corona radiata) with the help of acrosomal enzymes.

98
Q

What happens when the secondary oocyte undergoes meiosis II?

A

The secondary oocyte undergoes the second meiotic division to SPLIT into a mature ovum and another polar body, which will eventually be broken down.

99
Q

What is the structure/composition of a mature ovum? What does the ovum contribute to the zygote compared to the sperm?

A

A mature ovum is a VERY LARGE CELL consisting of large quantities of CYTOPLASM and ORGANELLES.
The OVUM contributes nearly EVERYTHING to the zygote (half of the DNA, the cytoplasm, organelles including mitochondria, RNA for early cellular processes, and physical space), where as sperm only contribute half of the DNA.

Upon completion of meiosis II, the haploid pronuclei of the sperm and ovum join, creating a diploid zygote.

100
Q

What is a pronucleus?

A

A pronucleus (plural: pronuclei) is the nucleus of a sperm or an egg cell during the process of fertilization, after the sperm enters the ovum, but before they fuse. Sperm and egg cells are haploid, meaning they carry half the number of chromosomes.

101
Q

What happens prior to puberty in terms of hormonal control?

A

Prior to puberty, the hypothalamus restricts production of gonadotropin-releasing hormone (GnRH).

102
Q

What is GnRH?

A

Gonadotropin-releasing hormone (GnRH).is a releasing hormone responsible for the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary. GnRH is a tropic peptide hormone synthesized and released from GnRH neurons within the hypothalamus.

103
Q

What happens at the start of puberty in terms of hormonal control?

A

At the start of puberty, the hypothalamus releases PULSES of GnRH, which then triggers the anterior pituitary gland to synthesize and release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These hormones trigger the production of OTHER sex hormones that develop and maintain the reproductive system.

104
Q

What happens in terms of hormones for MALE SEXUAL DEVELOPMENT?

A

During the FETAL PERIOD (from 9 weeks after fertilization until birth), presence of the Y chromosome allows for production of ANDROGENS, resulting in male sexual differentiation. For the duration of infancy and childhood, androgen production is low.

105
Q

Androgens

A

They are also required for masculinization of the developing male fetus (including penis and scrotum formation). Androgen (from Greek andro meaning male human being), also called androgenic hormone or testoid, is any natural or synthetic compound, usually a steroid hormone, that stimulates or controls the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. The primary and most well-known androgen is testosterone.

106
Q

What happens to testosterone during puberty and what effects does this have on male sexual development?

A

Testosterone, produced by the TESTES, increases dramatically during puberty, and sperm production begins.

107
Q

What is happening in terms of hormones during puberty for MALES that allows the development of secondary sex characteristics? What are these secondary sex characteristics?

A

There is a delicate interplay of FSH and LH stimulation on two cell types in the testes.

FSH stimulates the SERTOLI CELLS and triggers SPERM MATURATION, whereas LH causes the INTERSTITIAL CELLS to produce testosterone.

Testosterone not only DEVELOPS and MAINTAINS the male reproductive system, but also results in the development of secondary sexual characteristics, such as facial and axillary hair, deepening of the voice, and changes in growth patterns.

108
Q

How do testosterone levels change over a man’s life and how is this regulated?

A

Testosterone production remains HIGH through adulthood and DECLINES as men age.

This hormone exerts a NEGATIVE FEEDBACK on the hypothalamus and anterior pituitary, so the production is limited to appropriate levels.

109
Q

What is ANDROGEN insensitivity syndrome (AIS)?

A

If the receptors for TESTOSTERONE are ABSENT or DEFECTIVE, it cannot exert its effects. The result is AIS, in which a genetic male (XY) has female secondary sexual characteristics.

In complete androgen insensitivity, a genetic male will appear female at birth; often these individuals are not discovered until puberty when they are examined for AMENORRHEA (failure to menstruate)

110
Q

Where are FSH and LH produced?

A

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are called gonadotropins because stimulate the gonads - in males, the testes, and in females, the ovaries. They are not necessary for life, but are essential for reproduction. These two hormones are secreted from cells in the anterior pituitary called gonadotrophs.

111
Q

How is there Control of Gonadotropin Secretion?

A

The principle regulator of LH and FSH secretion is gonadotropin-releasing hormone (GnRH). GnRH is a ten amino acid peptide that is synthesized and secreted from hypothalamic neurons and binds to receptors on gonadotrophs.

As depicted in the figure to the right, GnRH stimulates secretion of LH, which in turn stimulates gonadal secretion of the sex steroids testosterone, estrogen and progesterone. In a classical negative feedback loop, sex steroids inhibit secretion of GnRH and also appear to have direct negative effects on gonadotrophs.

This regulatory loop leads to pulsatile secretion of LH and, to a much lesser extent, FSH.

112
Q

What happens during female sexual development in terms of hormones? How does this lead to the development of secondary sex characteristics??

A

The ovaries are also under the control of FSH and LH secreted by the anterior pituitary. The ovaries produce ESTROGENS and PROGESTERONE..

Estrogens are secreted in RESPONSE to FSH and they result in the DEVELOPMENT and MAINTENANCE of the FEMALE REPRODUCTIVE SYSTEM and FEMALE SECONDARY SEXUAL CHARACTERISTICS (breast growth, widening of the hips, changes in fat distribution).

113
Q

What does estrogen do for females? As an embryo? As an adult?

A

In the EMBRYO, estrogens stimulate development of the REPRODUCTIVE TRACT.

In adults, estrogens lead to THICKENING of the LINING OF THE UTERUS (endometrium) each month in preparation for the implantation of a ZYGOTE.

114
Q

What does progesterone do for females?

A

Progesterone is secreted by the CORPUS LUTEUM–the remnant follicle that remains after ovulation–in response to LH.

Progesterone is involved in the DEVELOPMENT and maintenance of the ENDOMETRIUM, but not in the initial thickening of the endometrium (that is the role of estrogen).

115
Q

What maintains the endometrium?

A

Both estrogen and progesterone are required for the generation, development, and maintenance of an endometrium capable of supporting a zygote.

ESTROGEN ESTABLISHES and PROGESTERONE PROTECTS the endometrium.

116
Q

By the end of the first semester, how does progesterone get to the fetus?

A

By the end of the first trimester of pregnancy, progesterone is supplied by the PLACENTA, and the corpus luteum atrophies and ceases to function.

117
Q

What is the menstrual cycle?

A

During a woman’s reproductive years (from menarche to menopause), estrogen and progesterone levels rise and fall in a cyclic pattern. In response to these hormonal changes, the endometrial lining of the uterus will grow and be shed. This is known as the Menstrual cycle. This cycle prepares your body for pregnancy each month.

About once a month, the uterus grows a new lining (endometrium) to get ready for a fertilized egg. When there is no fertilized egg to start a pregnancy, the uterus sheds its lining. This is the monthly menstrual bleeding (also called menstrual period).
A cycle is counted from the first day of 1 period to the first day of the next period. The average menstrual cycle is 28 days long.

118
Q

Menstruation

A

Menstruation is a woman’s monthly bleeding. When you menstruate, your body sheds the lining of the uterus (womb). Menstrual blood flows from the uterus through the small opening in the cervix and passes out of the body through the vagina

119
Q

What are the four events of the menstrual cycle?

A

The follicular phase, ovulation, the luteal phase, and menstruation.

120
Q

What happens during the follicular phase of the menstrual cycle?

A

The follicular phase begins when the menstrual flow, which sheds the uterine lining of the previous cycle, BEGINS.

GnRH secretion from the hypothalamus increases in response to the decreased concentrations of estrogen and progesterone, which fall off toward the end of each cycle.
The HIGHER concentrations of GnRH cause increased secretions of both FSH and LH. These two hormones work in concert to develop SEVERAL OVARIAN FOLLICLES.

The follicles begin to produce estrogen, which has NEGATIVE FEEDBACK EFFECTS and causes the GnRH, LH, and FSH concentrations to level off.

Estrogen works to REGROW the endometrial lining, stimulating vascularization and glandularization of the decidua.

121
Q

Decidua

A

Decidua is the part of the endometrium that in higher placental mammals undergoes special modifications in preparation for and during pregnancy and is cast off during birth.

The Decidua is the part of the endometrium cast off in the process of menstruation.

122
Q

What happens during the ovulation phase of the menstrual cycle?

A

Estrogen is interesting in that it can have BOTH NEGATIVE and POSITIVE feedback effects.

Late in the follicular phase, the developing follicles secrete HIGHER and higher concentrations of estrogen.

Eventually, estrogen concentrations reach a threshold that paradoxically results in positive feedback, and GnRH, LH, and FSH levels spike.

The surge in LH is important; it induces ovulation, the release of the ovum from the ovary into the abdominal (peritoneal) cavity.

123
Q

What happens during the luteal phase of the menstrual cycle?

A

After ovulation, LH causes the ruptured follicle to form the corpus luteum, which secretes progesterone.

It is PROGESTERONE that maintains the endometrium for implantation. Progesterone levels begin to rise, while estrogen levels remain HIGH.

The HIGH levels of progesterone again cause negative feedback on GNRH, FSH, and LH, preventing the ovulation of multiple eggs.

124
Q

How do oral contraceptive pills (OCPs) work?

A

Oral contraceptive pills are simply estrogen/progesterone (or progesterone-only) preparations.

These block conception by INHIBITING LH and FSH release through negative feedback, thereby inhibiting OVULATION.

When a woman takes the placebo pills at the end of the month, withdrawal menstruation still occurs because estrogen and progesterone levels drop, but there is no egg that passes with the menstrual flow.

125
Q

What happens during menstruation?

A

Assuming the implantation does not occur, the corpus luteum loses its stimulation from LH, progesterone levels decline, and the uterine lining is sloughed off.

The loss of high levels of estrogen and progesterone removes the block on GnRH so that the next cycle can begin.

126
Q

When does the blood concentration of FSH and LH peak? What about estrogen and progesterone

A

LH peaks around day 14, marking OVULATION. (FSH peaks here as well).
Progesterone peaks after ovulation around day 21 of the Luteal postovulatory phase. Estrogen peaks just before FSH and LH do, around day 13 in the follicular/ovulation phases.

127
Q

What happens if fertilization HAS occurred?

A

If fertilization HAS OCCURRED, the resulting zygote will develop into a blastocyst that will implant in the uterine lining and secrete human chorionic gonadotropin (hCG).

128
Q

What is a blastocyst?

A

The blastocyst is a structure formed in the early development of mammals. It possesses an inner cell mass (ICM) which subsequently forms the embryo.

129
Q

What is HUMAN CHORIONIC GONADOTROPIN (hCG)?

A

Blastocysts in the uterine lining secrete hCG. hCG hormone is an analog of LH, meaning it looks very similar CHEMICALLY and can stimulate LH receptors, which maintains the corpus luteum. hCG is critical during first-trimester development because it is the estrogen and progesterone secreted by the corpus luteum that keeps the uterine lining in place.

130
Q

What happens to hCG levels during the second trimester?

A

By the second trimester, hCG levels decline because the placenta has grown to a sufficient size to secrete progesterone and estrogen by itself. The high levels of estrogen and progesterone continue to serve as negative feedback mechanisms, preventing further GnRH secretion.

131
Q

What are key concepts of the menstrual cycle?

A
  • Follicles mature during the follicular phase (FSH, LH)
  • LH SURGE at midcycle triggers ovulation
  • Ruptured follicle becomes corpus luteum, which secretes estrogen and progesterone to build up uterine lining in preparation for implantation; LH and FSH are inhibited
  • If fertilization does NOT occur, corpus luteum atrophies, progesterone and estrogen levels decrease, menses occurs, and LH and FSH levels begin to rise again.
132
Q

What happens during MENOPAUSE?

A

As a woman ages, her ovaries become LESS sensitive to FSH and LH, resulting in ovarian atrophy.

As estrogen and progesterone levels DROP, the endometrium also atrophies, and menstruation STOPS. Because the negative feedback on FSH and LH is removed, the blood levels of these two hormones rise. This is called MENOPAUSE. Profound physical and physiological changes usually accompany this process, including flushing, hot flashes, bloating, headaches, and irritability. Occurs between 45-55.

IH MCAT Biology (4 decks)

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