Biology: Chapter 2 Flashcards
Cell Cycle
-four stages include G1, S, G2, and M
-The first three stages are known collectively as interphase. Interphase is the longest part of the cell cycle
-During interphase, individual chromosomes are not visible because they are in a less condensed form known as chromatin. During mitosis, it is preferable to condense DNA into tightly coiled chromosomes to avoid losing any genetic material during cell division
G0 Stage
-Cells that don’t divide spend all of their time in an offshoot of G1 called –
-During the – stage, the cell is simply living and carrying out its functions without any preparation for division
G1 Stage: Presynthetic Gap
-Cells create organelles for energy and protein production, while also increasing their size
-Passage into the S (synthesis) stage is governed by a restriction point in which certain criteria (containing the proper complement of DNA) must be met for the cell to pass
S Stage: Synthesis of DNA
-The cell replicates its genetic material so that each daughter will have identical copies
-After replication, each chromosome consists of two identical chromatids that are bound together at a specialized region known as the centromere
-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
G2 Stage: Postsynthetic Gap
-The cell passes through another quality control checkpoint
-DNA has already been duplicated, and the cell checks to ensure that there are enough organelles and cytoplasm for two daughter cells
-The cell also checks to make sure that DNA replication proceeded correctly to avoid passing on an error to daughter cells
M Stage: Mitosis
-Consists of mitosis itself along with cytokinesis
-Mitosis is divided into four phases: prophase, metaphase, anaphase, and telophase
-Cytokinesis is the splitting of the cytoplasm and organelles between the two daughter cells
Prophase (mitosis)
-First step involves condensation of the chromatin into chromosomes
-The centriole pairs also separate and move toward opposite poles of the cell
-Once the centrioles migrate to opposite poles of the cell, they begin to form spindle fibers, which are made of microtubules
-The nuclear membrane dissolves during prophase, allowing spindle fibers to contact the chromosomes
-The nucleoli become less distinct and may disappear
Metaphase (mitosis)
-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
Anaphase (mitosis)
-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
Telophase (mitosis)
-essentially 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 receives a complete copy of the genome identical to the original genome and to each other
Cytokinesis (mitosis)
-occurs at the end of telophase
-separation of the cytoplasm and organelles, giving each daughter cell enough material to survive on its own
Meiosis
-occurs in gametophytes (germ cells) and results in up to four nonidentical sex cells (gametes)
-Consists of one round of replication followed by two rounds of division
-occurs in sex cells only
Meiosis I
results in homologous chromosomes being separated, generating haploid daughter cells
Meiosis II
results in the separation of sister chromatids without a change in ploidy
Prophase I (meiosis)
-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. At this point, each chromosome consists of two sister chromatids, so each synaptic pair contains four chromatids and is referred to as a tetrad
-crossing over
Crossing over (Prophase I)
-Chromatids of homologous chromatids may break at the point of contact, called the chiasma and exchange equivalent pieces of DNA
-Those chromatids involved are left with an altered but structurally complete set of genes. Such genetic recombination can unlink linked genes, thereby increasing the variety of genetic combinations
-each daughter cell will have a unique pool of alleles
Metaphase I (meiosis)
Homologous pairs (tetrads) align at the metaphase plate, and each pair attaches to a separate spindle fiber by its kinetochore
Anaphase I (meiosis)
-Homologous pairs separate and are pulled to opposite poles of the cell, this is called disjunction
-During disjunction, each chromosome of paternal origin separates from its homologous of maternal origin, and either chromosome can end up in either daughter cell. Thus, the distribution of homologous chromosomes to the two daughter cells is random
-The separating of the two homologous chromosomes is referred to as segregation
Telophase I (meiosis)
-A nuclear membrane forms around each new nucleus. At this point, 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 at the end
Prophase II (meiosis II)
The nuclear envelope dissolves, nucleoli disappear, the centrioles migrate to opposite poles, and the spindle apparatus begins to form
Metaphase II (meiosis II)
The chromosomes line up on the metaphase plate
Anaphase II (meiosis II)
-The centromeres divide, separating the chromosomes into sister chromatids
-Chromatids are pulled to opposite poles by spindle fibers
Telophase II (meiosis II)
-A nuclear membrane forms around each new nucleus. Cytokinesis follows, and two daughter cells are formed
-By completion of meiosis II, up to four haploid daughter cells are produced per gametocyte
Spermatogenesis
formation of haploid sperm through meiosis
Spermatogonia
diploid stem cells (spermatogenesis)
Primary spermatocytes (diploid)
after replicating their genetic material (S stage) (spermatogenesis)
Secondary spermatocytes (haploid)
first meiotic division (spermatogenesis)
Spermatids
after meiosis II (spermatogenesis)
Spermatozoa
undergo maturation (spermatogenesis)
Oogenesis
production of female gametes
Primary oocytes (diploid)
by birth, all of the oogonia have already undergone DNA replication and are considered this
Secondary oocyte
after first menstrual cycle, one primary oocyte per month will complete meiosis I, and produce this and a polar body
Zona pellucida
surrounds the oocyte itself and is a mixture of glycoproteins that protect oocyte and compounds needed for sperm cell binding
Corona radiata
lies outside zona pellucida and is a layer of cells that adhered to oocyte during ovulation
Mature ovum
contributes half of DNA, all of the cytoplasm, organelles (including mitochondria), and RNA to offspring
Mature sperm
contribute half of DNA to offspring
Diploid zygote
joining haploid pronuclei of sperm and ovum upon completion of meiosis II
Sexual Development
-Prior to puberty, hypothalamus restricts production of gonadotropin-releasing hormone (GnRH)
-At the start of puberty, restriction is lifted and GnRH is released, which trigger anterior pituitary gland to synthesize and release follicle-stimulating hormone (FSH) and luteinizing hormone (LH). These hormones trigger production of other sex hormones that develop and maintain reproductive system
Male sexual development
-Testosterone is produced by testes, and production increases dramatically after puberty, and sperm production begins
-FSH stimulates Sertoli cells and triggers sperm maturation
-LH causes interstitial cells to produce testosterone
-Testosterone develops and maintains male reproductive system but also develops secondary sexual characteristics
-Testosterone declines as men age
Female sexual development
-Estrogens are secreted in response to FSH and result in development and maintenance of female reproductive system and secondary sexual characteristics
-In embryo, estrogens stimulates the development of the reproductive tract
-In adults, estrogens lead to thickening of the lining of the uterus each month in preparation for implantation of a zygote
-Progesterone is secreted by corpus luteum in response to LH. Involved in development and maintenance of the endometrium but not in initial thickening
Follicular phase (menstrual cycle)
-Begins when menstrual flow begins
-GnRH secretion increases in response to decreased concentrations of estrogen and progesterone, which fall off toward the end of each cycle
-Higher concentrations of GnRH cause increased secretions of FSH and LH which develop several ovarian follicles
-Follicles begin to produce estrogen, which has negative feedback effects and decreases concentrations of GnRH, LH, and FSH
-Estrogen stimulates regrowth of the endometrial lining
Ovulation (menstrual cycle)
-Late in the follicular phase, the developing follicles secrete higher and higher concentrations of estrogen
-Eventually, estrogen concentrations reach a threshold that results in positive feedback and GnRH, LH, and FSH levels spike
-Surge in LH induces ovulation, the release of the ovum from the ovary into the abdominal cavity
Luteal phase (menstrual cycle)
-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 lead to negative feedback of GnRH, FSH, and LH, preventing ovulation of multiple eggs
Menstruation (menstrual cycle)
-If implantation doesn’t occur, the corpus luteum loses its stimulation from LH, progesterone levels decline, and the uterine lining is sloughed off
-Loss of high levels of estrogen and progesterone removes the block on GnRH so next cycle can begin
Pregnancy
-If fertilization does occur, the zygote will develop into a blastocyst that will implant in the uterine lining and secrete human chorionic gonadotropin (hCG)
-This maintains corpus luteum
-hCG is critical during first trimester because estrogen and progesterone secreted by corpus luteum keep the uterine lining in place
-By the 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 estrogen and progesterone continue to serve as negative feedback on GnRH
Menopause
-As a woman ages, her ovaries becomes less sensitive to FSH and LH, resulting in ovarian atrophy
-As estrogen and progesterone levels drop, the endometrium also atrophies and menstruation stops
Gonad
-produces gametes
-develop into testes
Testes
-produces spermatozoa
-seminiferous tubules and interstitial cells of Leydig
Seminiferous tubules
where sperm is produced
Sertoli cells
support, protect, and provide nutrition to sperm
Cells of Leydig
secrete testosterone and other male sex hormones
Scrotum
-where testes are located
-hangs below penis
-maintains a temperature 2-4 degrees lower than the rest of the body
Epididymis
where sperm is stored until ejaculation
Vas deferens
–transports mature sperm to the urethra in preparation for ejaculation
-joins with seminal vesicle ducts to form ejaculatory ducts
Ejaculatory duct
moves through prostate and picks up prostatic fluid to add to semen
Urethra
-two ejaculatory ducts fuse to form this
-carries sperm through the penis as it exits the body
Seminal fluid
-mixed with sperm
-combined from seminal vesicles, prostate gland, and bulbourethral gland
Seminal vesicles
contribute fructose to nourish sperm
Bulbourethral (Cowper’s) gland
produce clear, viscous fluid that cleans out any remnants of urine and lubricants
Semen
combination of sperm and seminal fluid
Mature sperm
-Midpiece: filled with mitochondria, which generate energy for swimming through female reproductive system
-Head: covered by cap known as acrosome. Derived from golgi apparatus and is necessary to penetrate the ovum
Ovaries
female gonads, produce estrogen and progesterone; located in the pelvic cavity
Follicles (female reproductive system)
in ovaries, contain, nourish, and protect immature ova (eggs)
Peritoneal sac
-one egg per month is ovulated into here
-lines the abdominal cavity
Fallopian tubes
-where egg is drawn into from the peritoneal sac
-lined with cilia to propel egg forward
Muscular uterus
-connected to fallopian tubes
-site of fetal development
Cervix
-lower end of the uterus
-connected to the vaginal canal
Vaginal canal
where sperm is deposited during intercourse
Vulva
external female anatomy
