Chapter 22Remember: cell-cell signals and regulatory proteins allow developing of cells to divide, move, interact, and differentiate.1. Game Structure and Functiona. sequence of mitotic and meiotic divisions-process is called gametogenesisb. Fertilization includes subsequent step of development-cleavage, gastrulation, and organogenesisc. sperm and egg each contribute-a haploid genome containing one allele of each gened. Egg cells hundreds or thousands times larger than sperm cells2. Sperm Structure and Function Drawa. mature mammalian sperm has 4 main compartments-the head, neck, mid-piece, and tail b. Sperm Compartments1. Head contains nucleus and enzyme-filled structure called the acrosome-these enzymes allow sperm to penetrate barriers surrounding the egg2. Neck has a centriole that combines w. centriole of egg to form centrosome-centrosome req. for spindle formation during mitosis3. Mid-piece packed w. mitochondria-produces ATP req. to power movement4. Tail consists of flagellum-composed of microtubules and is surrounded by plasma membrane-whips back and forth to swim3. Egg Structure and Functiona. Eggs are large bec. they have nutrients req. for early development of embryo-after about a week mamallian embryos get nutrients from placentab. In species where females lay the eggs-they must be large bec. they are only source of nutrients -until organism is fully developed-nutrients provided by yolk (fat and protein rich cytoplasm loaded into egg cells as they mature)c. eggs of many species have delopmental regulatory molecules-called cytoplasmic determinants that control early events of development-Bicoid mRNA is a cytoplasmic determinant and a master regulatord. many eggs contain organelles called cortical granules (synthesized in golgi apparatus)-small, enzyme filled vesicles activated during fertilizatione. Vitelline Envelope located outside plasma membrane of eggs-is a mat-like sheet of glycoproteins that surrounds the egg-in eggs of mammals this structure is thick and called the zona pellucida4. Fertilizationa. Zygote-a fertilized eggb. fusion limited to single sperm so egg wont have extra chromosomesc. Sea urchins shed gametes into water and fertilize externallyc. sea urchin eggs have external jelly layer that sperm must digest through to fuse w. egg-digests through vitelline envelope using enzymes from acrosomed. sperm nucleus, mitochondria, and centriole enter the egg-sperm and egg nuclei fuse to form zygote nucleus5. How Gametes from the Same Species Recognize Each Othera. Protein on head of sperm called protein bindin-distinct among different species even those closely relatedb. egg-cell membranes have a receptor for bindinc. researchers added a protease to surface of urchin egg-isolated the protein fragments released from cell surface-and found one that bound to sperm and to isolated bindin moleculesd. species-specific bindin molecules on sperm-interact w. species-specific receptors on surface of the egg6. Why Only One Sperm Enters the Egg Draw figure 22.5a. Multiple fertilization-polyspermyb. fertilization results in physical barrier to sperm entry-barrier built when sperm causes calcium ions to exit from storage areas inside the eggc. cortical granules in plasma membrane respond to Calcium signal-by fusing w. membrane and releasing its contents to the exterior-which digest exterior fragment of receptor for spermd. increased concentration of contents bet. egg plasma membrane and vitelline envelope-causes influx of water which lifts envelope matrix-forming a fertilization envelope to prevent entry of additional sperm7. Cleavage-rapid cell divisions of zygote right after fertilizationa. embryogenesis-process by which a single-celled zygote -becomes a multi-cellular embryob. zygote divides continuouslyc. cytoplasm in egg divides into larger number of smaller daughter cellsd. cells created by cell divisions are called blastomeres-mass of blastomere cells called a blastula8. Partitioning Cytoplasmic Determinantsa. cytoplasmic determinants are found in specific locations-within the egg cytoplasm so they end up in specific populations of blastomeresb. by dividing egg cytoplasm to distribute cytoplasmic determinants to certain cells-cleavage initiates process that results in cell differentiation9. Cleavage in Mammalsa. In mammals cleavage occurs in the fallopian tube or oviduct-structure that connects reproductive organs called the ovary and uterusb. Ovary is organ in which egg matures-Uterus-where embryo developsc. cleavage occurs as the embryo travels down the fallopian tube twd. the uterus9b. Cleavage Resultsa. cleave results in specialized type of blastula called the blastocyst-exterior of blastocyst is a thin-walled hollow structure called the trophoblastb. inside of trophoblast is a cluster of cells called the inner cell mass (ICM)c. Placenta is derived from a mixture of maternal cells and trophoblast cells-it allows nutrients and wastes to exchange bet. mother's blood and embryo's blood1. Gastrulation Figure 22.8a. During Gastrulation extensive cell movements radically rearrange the-embryonic cells into a structure called the gastrulab. Marks the beginning of cell differentiation2. Formation of Germ Layersa. Gastrulation results int he formation of embryonic tissue layersb. 3 Primary Tissue layers1. ectoderm (outside skin)2. Mesoderm (middle skin)3. Endoderm (inner skin) These embryonic tissues are called germ layers bec. they give rise to organs and tissues in adultc. Cell fates determined by cell-cell signals, transcription factors, and cytoplasmic determinants3. Steps of gastrulation1. Frog blastula has fluid-filled interior space called the blastocoel2. cells begin moving into blastocoel through an invagination-in frogs this invagination is slit-like and forms the blastophere3. cells from periphery move to interior of the embryo through the blastopore-forming a tube-like structure that will become the gut or digestive tract4. when gastrulation complete, the ectoderm, mesoderm-and endoderm cells are arranged in 3 distinct layers4. Roles of different germ layersa. ectoderm forms the outer covering of the adult body and nervous systemb. mesoderm gives rise to mmuslce, most internal organs-and connective tissues such as bone and cartilagec. endoderm produces the lining of the digestive tract or gut-along w. some of the associated organs5. Definition of Body Axesa. Major body axes become visible during gastrulationb. In frogs the major body axes were partially
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