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2 gamet yang berbeda:

Sel Sperma : Berukuran Kecil Motil

Sel Telur : Berukuran Lebih besarHanya dalam spermatogenislah keempat produk miosis berkembang menjadi gamet matang.Spermatogenesis terjadi disepanjang masaSpermatogenesis menghasilkan sperma matang dari sel-sel prekursor dg urut-urutan yang tidak terputus, sementara oogenesis memiliki waktu sela yang lama.Perbedaan Spermatogenesis dan OogenesisFERTILIZATIONWhat is fertilization ??

The union or fusion of oocyte or egg (female gamete) with the sperm (male gamete) to form a zygote.Fertilization is a process, not a single even, that begins when a sperm cell first contact with the plasma membrane of the egg and ends with the intermingling of maternal and paternal chromosomes at the metaphase plate prior to the first cleavage division.

The fertilization process itself has a number of important components. This include :Initial membrane contact between egg and spermEntry of the sperm cell into the eggPrevention of polyspermy (entry of more than one sperm cell into the egg) by the egg)Metabolic activation of the eggCompletion of miosis by the eggFormation and fusion of male and female pronuclei, leading to the final cleavage division.Sea Urchin FertilizationThe chemoattraction of the sperm to the egg by soluble molecules secreted by the egg... ResactThe exocytosis of the acrosomal vesicle to release its enzymesThe binding of the sperm to the extracellular envelope (vitelline layer or zona pellucida) of the eggThe passing of the sperm through this extracellular envelopeFusion of egg and sperm cell plasma membranes

Structure of Gamet

Acrosomal Reaction

Acrosomal Process

First: Contact and RecognitionSea UrchinThe plasma membrane of the sea urchin egg is surrounded by the vitelline layer and the thicker, outer jelly coat (zona pellucida in mammals) The acrosome reaction is the release of proteolytic enzymes from the acrosome of the spermAcrosome digests a path through the external coveringsIf sea urchin gametes are of the same species, a protein called bindin on the acrosome adheres to a specific receptor on the vitelline membraneGamet fusion occurs at the tip of acrosome involves an egg microvillusSperm are attracted to the egg by chemotaxisA site of gamet fusion, the fertilized egg form.Sea Urchin Fertilization

Blocks To PolyspermyFast block to polyspermy involves egg plasma membrane action potential, prevents additional sperm from enteringThe slow block to polyspermy involves the cortical reactionCalcium ion entry causes fusion of large cortical granules with plasma membrane that release digestive enzymesThe acellular vitelline membrane (not a plasma membrane but extracellular matrix) lifts away from the plasma membrane due to the digestive activity and local increase in ionic strength from the cortical granule contentsForms a fertilization envelope that hardensIn mammals, the zona pellucida sperm receptors are modified to prevent further entry of spermSome organisms do not block polyspermy. Some amphibians degrade the supernumery sperm

Fast block polyspermae

Slow block polyspermae

The activation of all eggs appears to depend on an increase in the concentration of free calcium ions within the egg. Such an increase can occur in two ways: calcium ions can enter the egg from outside, or calcium ions can be released from the endoplasmic reticulum within the egg. Both mechanisms are used to different degrees in different species. In snails and worms, much of the calcium probably enters the egg from outside, while in fishes, frogs, sea urchins, and mammals, most of the calcium ions probably come from the endoplasmic reticulum. In both cases, a wave of calcium ions sweeps across the egg, beginning at the site of sperm-egg fusionEgg ActivationPathway of egg activation

Mammalian Fertilization

The sperm plasma membrane undergoes changes in lipid composition and other alteration that will facilitate fertilization

Reorganization the cytockeleton at the sperm tip

Removal of coating factors that mask egg binding site at the sperm surfaceCapacitationCapacitationSpermatozoa can reach uterine tube within 10 minutes of ejaculationcan not fertilize egg until undergo capacitationfemale fluids wash away cholesterol & inhibitory factorssperm membrane becomes fragile & permeable to Ca+2Sperm fertile for 48 hours after ejaculationEffects of Capacitation on SpermIncreased rate of metabolism Flagellum beats more rapidlyResult: Sperm are more motile (hyperactivated)Changes in sperm glycoproteinsAllow sperm-egg binding Pro-Acrosin (inactive) is converted to acrosin (active)Able to digest zona pellucida proteins

Fertilization The first step in development of a new individual is fertilization

The chemoattraction of the sperm to the egg by soluble molecules secreted by the eggThe exocytosis of the acrosomal vesicle to release its enzymesThe binding of the sperm to the extracellular envelope (vitelline layer or zona pellucida) of the eggThe passing of the sperm through this extracellular envelopeFusion of egg and sperm cell plasma membranes

In most common mammals, including humans, the spermatozoa are deposited in the upper vagina at insemination, but in many rodents the site of insemination is the uterus.In comparison with their size, the distance the spermatozoa must travel is great.The route may be beset with chemical hazards in the form of strong acid secretions or with mechanical obstacles, such as a crooked and compressed cervical canal or uterine tubes narrowed or occluded by disease. The Egg can be activated in the absence of a spermatozonAnother outcome of the sharp rise in Ca2+ concentration in the egg's cytosol is a substantial increase in the rates of celular respiration and protein synthesis by the egg, known as egg activation. Although egg activation is normally triggered by the binding and fusion of sperm, the unfertilized eggs of many species can be artificially activated by the injection of Ca2+ or by various mildly injurious treatments, such as temperature shock. Artificial activation switches on the metabolic responses of the egg and causes it to begin developing by parthenogenesis. It is even possible to artificially activate an egg that has had its own nucleus removed. This finding shows that proteins and mRNAs present in the cytoplasm of the unfertilized egg are sufficient for egg activation.

Once the sperm has fused with egg, a regular sequence of events leads to ultimate joining of the male and female pronuclei.With sperm entry, the block to the second meiotic division of the egg is rapidly lifted and the second polar body is released, leaving a haploid female nucleus.A new pronuclear membrane soon forms around the now decondensed nuclear material form the sperm.As the male and female pronuclei migrate toward each other, DNA syntesis occurs on the DNA of the haploid chromosomes.