Chapter 22 Remember cell cell signals and regulatory proteins allow developing of cells to divide move interact and differentiate 1 Game Structure and Function a sequence of mitotic and meiotic divisions process is called gametogenesis b Fertilization includes subsequent step of development cleavage gastrulation and organogenesis c sperm and egg each contribute a haploid genome containing one allele of each gene d Egg cells hundreds or thousands times larger than sperm cells 2 Sperm Structure and Function Draw a mature mammalian sperm has 4 main compartments the head neck mid piece and tail b Sperm Compartments 1 Head contains nucleus and enzyme filled structure called the acrosome these enzymes allow sperm to penetrate barriers surrounding the egg 2 Neck has a centriole that combines w centriole of egg to form centrosome centrosome req for spindle formation during mitosis 3 Mid piece packed w mitochondria produces ATP req to power movement 4 Tail consists of flagellum composed of microtubules and is surrounded by plasma membrane whips back and forth to swim 3 Egg Structure and Function a Eggs are large bec they have nutrients req for early development of embryo after about a week mamallian embryos get nutrients from placenta b 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 regulator d many eggs contain organelles called cortical granules synthesized in golgi apparatus small enzyme filled vesicles activated during fertilization e 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 pellucida 4 Fertilization a Zygote a fertilized egg b fusion limited to single sperm so egg wont have extra chromosomes c Sea urchins shed gametes into water and fertilize externally c sea urchin eggs have external jelly layer that sperm must digest through to fuse w egg digests through vitelline envelope using enzymes from acrosome d sperm nucleus mitochondria and centriole enter the egg sperm and egg nuclei fuse to form zygote nucleus 5 How Gametes from the Same Species Recognize Each Other a Protein on head of sperm called protein bindin distinct among different species even those closely related b egg cell membranes have a receptor for bindin c 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 molecules d species specific bindin molecules on sperm interact w species specific receptors on surface of the egg 6 Why Only One Sperm Enters the Egg Draw figure 22 5 a Multiple fertilization polyspermy b fertilization results in physical barrier to sperm entry barrier built when sperm causes calcium ions to exit from storage areas inside the egg c 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 sperm d 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 sperm 7 Cleavage rapid cell divisions of zygote right after fertilization a embryogenesis process by which a single celled zygote becomes a multi cellular embryo b zygote divides continuously c cytoplasm in egg divides into larger number of smaller daughter cells d cells created by cell divisions are called blastomeres mass of blastomere cells called a blastula 8 Partitioning Cytoplasmic Determinants a cytoplasmic determinants are found in specific locations within the egg cytoplasm so they end up in specific populations of blastomeres b by dividing egg cytoplasm to distribute cytoplasmic determinants to certain cells cleavage initiates process that results in cell differentiation 9 Cleavage in Mammals a In mammals cleavage occurs in the fallopian tube or oviduct structure that connects reproductive organs called the ovary and uterus b Ovary is organ in which egg matures Uterus where embryo develops c cleavage occurs as the embryo travels down the fallopian tube twd the uterus 9b Cleavage Results a cleave results in specialized type of blastula called the blastocyst exterior of blastocyst is a thin walled hollow structure called the trophoblast b 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 blood 1 Gastrulation Figure 22 8 a During Gastrulation extensive cell movements radically rearrange the embryonic cells into a structure called the gastrula b Marks the beginning of cell differentiation 2 Formation of Germ Layers a Gastrulation results int he formation of embryonic tissue layers b 3 Primary Tissue layers 1 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 adult c Cell fates determined by cell cell signals transcription factors and cytoplasmic determinants 3 Steps of gastrulation 1 Frog blastula has fluid filled interior space called the blastocoel 2 cells begin moving into blastocoel through an invagination in frogs this invagination is slit like and forms the blastophere 3 cells from periphery move to interior of the embryo through the blastopore forming a tube like structure that will become the gut or digestive tract 4 when gastrulation complete the ectoderm mesoderm and endoderm cells are arranged in 3 distinct layers 4 Roles of different germ layers a ectoderm forms the outer covering of the adult body and nervous system b mesoderm gives rise to mmuslce most internal organs and connective tissues such as bone and cartilage c endoderm produces the lining of the digestive tract or gut along w some of the associated organs 5 Definition of Body Axes a Major body axes become visible during gastrulation b In frogs the major body axes were partially determined early in development by Bicoid like
View Full Document
Unlocking...