chapter 2: reproduction Flashcards
differentiate between diploid and haploid cells.
- diploid: contain two copies of each chromosome; example: autosomal cells
- haploid: contain one copy of each chromosome; example: germ cells
describe the daughter cells of autosomal cells and germ cells after division
autosomal: division results in two genetically identical daughter cells
germ: daughter cells are not equivalent
for actively dividing cells, what are the stages of the cell cycle?
G1, S, G2, and M
what stages of the cell cycle make up interphase?
- G1, S, and G2 make up interphase
- interphase is the longest part of the cell cycle; actively dividing cells spend about 90% of their lives in interphase
what stage do non actively dividing cells spend their time in? explain this stage.
- non actively dividing cells spend all their time in the G0 stage
- the G0 stage means the cell is simply living and carrying out its functions, without any prep for division
explain the behavior/image of genetic material during interphase.
- during interphase, individual chromosomes are not visible w light microscopy because they are in a less condensed form known as chromatin
- this is because DNA must be available to RNA polymerase so that genes can be transcribed
explain the behavior/image of DNA/genetic material during mitosis
DNA is more condensed into tightly coiled chromosomes to avoid losing any genetic material/info during cell division
what occurs during G1 stage?
can cells move freely into S phase?
- G1 stage is first stage of interphase
- G1 stage: presynthetic gap
- cells create organelles for energy and protein production (mitochondria, ribosomes, ER)
- cells also increase their size
- passage into S phase is governed by a restriction phase; certain criteria must be met (such as proper complement of DNA) before entering S phase
what occurs during S stage?
- S stage: synthesis of DNA
- second stage of interphase
- the cell replicates its genetic material so that each daughter cell will have identical copies
- after replication, each chromosome consists of two identical dhromatids that are bound together at the centromere
what occurs during G2 stage?
- G2 stage: postsynthetic gap
- third stage of interphase
- during this phase, cell passes another quality control checkpoint
- DNA has already duplicated, and cell checks to** ensure that there are enough organelles and cytoplasm for two daughter cells**
- cell also checks that DNA replication proceeded correctly
What does the M phase consist of?
mitosis (prophase, metaphase, anaphase, and telophase) and cytokinesis (the splitting of the cytoplasm and organelles between the two daughter cells)
how is the cell cycle controlled?
- the cell cycle is controlled by two checkpoints: G1/S checkpoint and G2/M checkpoint
what occurs at the G1/S cycle?
what happens if there has been damage to the DNA?
- the cell determines if the condition of the DNA is good enough for synthesis
- 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 p53
what occurs at the G2/M checkpoint?
- the cell is mainly concerned with ensuring the cell has achieved adequate size and the organelles have been properly replicated to support two daughter cells
- p53 also involved
what molecules are responsible for the cell cycle? explain in detail.
- molecules responsible for the cell cycle are cyclins and cyclin dependent kinases (CDKs)
- in order to be activated, CDKs require the presence of the right cyclins
- during the cell cycle, concentrations of various cyclins increase and decrease during specific stages
- these cyclins bind to CDKs, creating an activated CDK-cyclin complex
- this complex can then phosphrylate transcription factors
- transcription factors then promote transcription of genes required for the next stage of the cell cycle
when does cancer occur? tumors?
- cancer occurs when cell cycle becomes deranged, and damaged cells undergo mitosis
- tumors occurs when cancer cells undergo rapid cell division
- metastasis: spread of tumor cells; occurs when cells product the right factors and the damaged/cancerous cells are able to reach other tissues
give a brief overview of mitosis.
- mitosis is the process by which two identical cells are created from a single cell
- mitosis consists of four phases: prophases, metaphase, anaphase, and telophase
- mitosis occurs in somatic cells (cells not involved in sexual reproduction
explain prophase.
- first step involves condensation of chromatin into chromosomes
- centriole pairs seprarate and move toward opposite poles of cell (these are known as centrosome, and they are responsible for the correct division of DNA)
- once centrioles migrate to opposite poles, they. begin to form spindle fibers (made of microtubules)
- this establishes the centrosome as one (of two) microtubule organizing centers of the cell (the other is the basal body of flagellum or cillium)
- each of the fibers radiate outward (some form asters that anchor the centrioles to cell membrane, some extend toward middle of cell)
- the nuclear membrane disolves, allowing spindle fibers to contact chromosomes
- nucleoli becomes less distinct; may disappear completely
- kinetochores (appear at the centrosome) serve as attachment points for specific fibers of the spindle apparatus
explain metaphase.
- centriole pairs are now at opposite ends of cell
- kinetochore fibers interact w the fibers of the spindle apparatus to align the chromosomes at the metaphase plate
explain anaphase.
- centromeres split so that each chromatid has its own distincy centromere, allowing sister chromatids to seperate
- sister chromatids pulled toward opposite poles of the cell by shortneing the kinetochore fibers
explain telophase.
- spindle apparatus disappears
- nuclear membrane reforms around each set of chromosomes
- nucleoli reappears
- chromosomes uncoil, resuming their interphase form
- each of the two nuclei receives a complete copy of the genome identical to the original genome and to each other
explain cytokinesis.
- the separation of the cytoplasm and organelles, giving each daughter cell enough materia to survive on its own
in what type of cells does mitosis occur, and what type of daugter cells are produced?
mitosis occurs in somatic tissue, and it results in two identical daughter cells
what type of cells does meoisis occur in, what type of daghter cells are produced?
meiosis occurs in gametocytes (germ cells), and it results in up to four nonidentical sex cells (gametes)
what are some similarities between mitosis and meiosis?
- genetic material must be duplicated
- chromatin is condensed to form chromosomes
- microtubules emanate from centrioles and are involved in dividing genetic material
compare/contrast rounds of replication and division in mitosis and meiosis.
mitosis:
* one round of replication
* one round of division
meiosis:
* one round of replication
* two rounds of division
What does meiosis 1 result in?
what does meiosis 2 result in?
meiosis 1 results in homologous chromosomes being separated, generating haploid daughter cells; this is known as reductional division
meiosis 2: results in the separation of sister chromatids without a change in ploidy, and is therefore known as equational division
what is the difference between homologous pairs of chromosomes and sister chromatids?
- homologous pair are considered separate chromosomes
- sister chromatids are identical strands of DNA connected at the centromere
- after the S phase, 92 chromatids organized into 46 chromosomes, which are organized into 23 homologous pairs
what occurs during prophase 1 of meiosis?
how does it differ from mitosis?
- chromatin condenses into chromosomes
- spindle apparatus forms
- nucleoli and nuclear membrane disappear
- homologous chromosomes come together and interwine; this is called synapsis
- at this point, each chromosome consists of two sister chromatids, so each synaptic pair contains four chromatids and is refered to as a tetrad
- the homologous chromosomes are held together by the synaptonemal complex
- chromatids of HCs may break at point of contact, which is called the chiasma, and exchnage equivalent pieces of DNA; this is called crossing over; this genetic recombination leads to increased genetic variability (crossing over results in each daughter cell having a unique pool of alleles)
- crossing over is how prophase 1 differs from prophase in mitosis
- crossing over also explains mendel’s second law of independent assortment
HCs = homologous chromosomes
what occurs during metaphase 1 of meiosis? how does it differ from mitosis?
- homologous pairs (tetrads; 2 sister chromatids) align at metaphase plate, and each pair attaches to a seperate fiber by its kinetochore
- difference from mitosis metaphase: in mitosis each chromosome is lined up on the metaphase plate by two spindle fibers (one from each pole); in meiosis, HCs are lined up across from each other at the metaphase plate and are held by one spindle fiber
what occurs during anaphase 1 of meiosis?
- homologous pairs are separate and pulled to opposite poles of the cell; this process is called disjunction, and it accounts for Mendel’s first law of segragation
- during disjunction, each chromosome of paternal origin separates (or disjoins) from its homologue of maternal origin, and either chromosome can end up in either daughter cell
- thus, the distribution of homologous chromosomes to the two intermediate daughter cells is random w respect to parental origin
- the separating of the two HCs is referred to as segregation
what occurs during telophase 1 of meiosis?
- 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 HCs separate, only n chromosomes are found in each daughter cell (23 in humans)
- the cell divides into two daughter cells by cytokinesis
what can occur between cell divisions?
between cell divisions, there may be a short rest period, called interkinesis, during which chromosomes partially uncoil
what occurs during prophase 2 of meiosis?
- nuclear envelope dissolves
- nucleoli disappears
- centrioles migrate to opposite poles
- spindle apparatus begins to form
what occurs during metaphase 2 of meiosis?
chromosomes line up on the metaphase plate
what occurs during anaphase 2 of meiosis?
- centromeres divide, separating the chromosomes into sister chromatids
- chromatids are pulled to opposite poles by spindle fibers
what occurs during telophase 2 of meiosis?
- nuclear membrane forms around each new nucleus
- cytokinesis follows, and two daughter cells are formed
- by the completion of meiosis 2, up to four haploid daughter cells are produced per gametocyte
what is the pathway of sprem through the male reproductive system?
- Seminiferous tubules
- Epididymis
- Vas deferens (ductus deferens)
- Ejaculatory duct
- Urethra
- Penis
the primitive gonads develop into…
testes
what functional components make up the testees? further explain these components.
where are the testes located?
- the testes have two functional components: the seminiferous tubules and the interstitial cells of Leydig
- sperm is produced in the highly coiled seminiferous tubules, where they are nourished by Sertoili cells
- testes located in the scrotum, which hands below the penis, allowing it to maintain a temperature 2 to 4 degrees celsium lower than the body
explain what happens to sperm after they are formed in the testes.
what happens during ejaculation?
- after sperm are formed, they are passed to the epididymis, where their flagella gain motility, and they are stored until ejaculation
- during ejaculation, sperm travel through the vas defererns and enter the ejaculatory duct at the posterior edge of the prostate gland
- the two ejaculatory ducts then fuse to form the urethra, which carries the serm through the penis as they exit the body
in males, what two systems carry a common pathway?
the reproductive and the urinary systems
what happens as sperm passes through the reproductive tract?
explain the three glands.
- as sperm passes through the reproductive tract, sperm is mixed with seminal fluid (sperm + seminal fluid = semen)
- seminal fluid is produced by the seminal vesicles, prostate gland, and bulbourehtral gland
- the seminal vesicles contribute fructose to nourish sperm
- the semincal vesicles and prostate gland give semen a mildly alkaline property so that the sperm can survive in the relative acidity of the female reproductive tract
- the bulbourethral (Cowper’s) glands produce a clear viscous fluid that cleans out any remnants of urine and lubricates the urehtra during sexual arousal
explain spermatogenesis.
- spermatogenesis: the formation of haploid sperm through meiosis; occurs in seminiferous tubules; results in four functional sperm for each spermatogonium
- in males, diploid stem cells are known as spermatogonia
- after replicating their genetic info in the S phase, they develop into diploid primary spermatocytes
- the firt meiotic division will result in halpoid secondary spermatocytes, which then undergo meiosis 2 to generate haploid spermatids
- finally, the spermatids undergo maturation to become mature spermatozoa
explain mature sperm.
- very compact
- consist of a head (contain genetic material), a midpeice (which generates ATP from fructose), and a flagellum (for motility)
- the midpiece is filled with mitochondria, which generate the energy for swimming through the female reproductive tract to reach the ovum in the fallopian tubes
- each sperm head is covered by a cap known as an acrososme; this structure is derived from the Golgi and is necessary to penetrate the ovum
explain the female reproductive anatomy.
- the gonads are known as ovaries, which 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)
- between puberty and menopause, one egg per month is ovulated into the peritoneal sac, which lies in the abdominal cavity
- the egg is then drawn into the fallopian tube, or oviduct, which is lined with cilia to properl the egg forward
- the fallopian tubes are connected to the muscular uterus, which is the site of fetal development
- the lower end of the uterus, the cervix, connects to the vaginal canal, where sperm are deposited during intercourse
- the external parts of the femal genitalia organs are the vulva
explain oogenesis.
- by birth, all the oogonia a female will ever have are formed during fetal development (no unending supply like in males); all oognia have undergone DNA replication and are considered primary oocytes
- primary oocytes are 2n (like primary spermatocytes), and are arested in prophase 1
- after menarche (first menstrual cycle), one primary oocyte per month will complete meiosis 1, producing a secondary oocyte and a polar body. the division is characterized by unequal cytokinesis, which distrubutes ample cytoplasm to secondary oocyte and nearly none to polar body
- the secondary oocyte remains arrested in metaphas 2 and does not complete remainded of meiosis unti fertilized
- meiosis 2 is triggered when a sperm penetrates zona pellucida and corona radiata
- the secondary oocye finishes meiosis 2 to split into a mature ovum and another polar body, which eventually will be broken down
what are the two layers that surround oocytes?
- zona pellucida and corona radiata
the ability to reproduce is under hormonal control. explain what happens prior to and at the start of puberty.
- prior to puberty: hypothalamus restricts production of gonadotropin-releasing hormone (GnRH)
- start of puberty: the restriction of GnRH is lifted as the hypothalamus releases pulses of GnRH, which then triggers the antierior 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
explain testosterone and FSH/LH during male sexual development.
- testosterone is produced by the testes, and it increases dramatically during puberty, and sperm production begins
- FSH stimulates sertoli cells and triggers sperm maturation
- LH causes intersitial cells to produce testosterone
- testosterone develops and maintains male reproductive system, but it also results in the development of secondary sexual characteristics (like facial hair, increased bone and muscle mass, deepening of vocie)
- testosterone exerts negative feeback of hypothalamus and anterior pituitary so that production is kept within an appropriate range
what does the anterior pituitary gland synthesize?
- follicle-stimulating hormane (FSH)
- luteinizing hormone (LH)
- testes and ovaries under control of these
ovaries produce…
progesterone and estrogen
when is estrogen secreted, and what does that secretion result in?
- estrogens are secreted in response to FSH
- results in development and maintenance of female reproductive system and female secondary sexual characteristics (breast growth, widening of the hips, changes in fat distribution)
- in embryo, estrogens stimulatre development of reproductive tract
- in adults, estrogens lead to thickening of the endometrium (uterus lining) each month in prep for the implantation of a zygote
when is progesterone secreted, and what does that secretion result in?
- secreted by the corpus luteum (the remains of the ovarian follicle following 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)
*
what are the four phases of the menstrual cycle?
- follicular phase
- ovulation
- luteal phase
- mestruation
explain the follicular phase.
- begins when the mestrual flow (which sheds the uerine lining of the previous cycle) begins
- GnRH secretion from the hypothalamus increases in respose to the decreased concentrations of estrogen and progesterone, which fall off toward the end of each cycle
- higher concentrations of GnRH causes increased secretions of FSH and LH
- FSH and LH work together to develop ovarian follicles
- follicles beging to produce estrogen, which has negative feedback effects and causes the GnRH, LH, and FSH concentrations to level off
- estroen stimilates refrowth of endometrial lining, simulation vascularization of glandularization of decidue.
what occurs during ovulation?
- late in follicular phase, the developing follicles secrete higher and higher concentrations of estrogen
- estrogen concentrations reach a treshold that results in a positive feedback, and GnRH, FSH, and LH levels spike
- surge in LH induces ovulation (the release of the ovum from the ovary into the abdominal cavity
what occyrs dyrung the luteal phase?
- after ovulation, LH causes the ruptured follicle to form the corpus luteum, which secretes progesterone
- progesterone levels begin to rise, while estrogen levels remain high
- high levels of progesterone cause negative feedback of GnRH, LH, and FSH, preventing the ovulation of multiple eggs
what occurs during menstruation?
- assuming implantation doesn’t 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
what occurs during pregnancy?
- fertilization has occured
- zygote will develop into a blastocyst that will implant into the unterine lining and secrete human chorionic gonadotropin (hCG) (an analog of LH); this maintains corpus luteum
- hCG is critical during first trimester development because the estrogen and progesterone secreted by corpus luteum keeps in uterine lining in place
- by second trimester, hCG levels decline because the placenta has grown to a sufficient size to secrete enough progesterone and estrogen by itself
- high levels of E and P continue to serve as a negative feedback on GnRH secretion
what occurs during menopause?
- as E and P levels drop, the endtromedtrium atrophoes, and menstruation stops
bc the negative feedback on FSH and LH is removed, the blood levels of two hormones rise
what are the main steps of the menstrual cycle?
- follices mature during the follicular phase due to FSH and LH
- LH surge at midcycle triggers ovulation
- ruptured follicle becomes corpus luteum, which secretes estrogen and progesterone to build up uterine lining in prep from implantation; LH and FSH are inhibited
- if fertilizatio does not occur, corpus luteum atrophies, P and E levels decrease, menses occurs, and LH and FSH levels beging to rise again
