gametogenesis

-sequence of mitotic and meiotic cell divisions leading up to the production of animal sperm and egg

fertilization

-follows gametogenesis

-union of sperm/egg

-egg contributes MUCH more than chroms (100x/1000x larger than sperm)

Cycle from gametogenesis to adulthood

-gametogenesis (diploid-->haploid)

-ferilization (haploid -->diploid)

-clevage 

-gastrulation

-organogenesis

-1st trimester

-2nd trimester

-newborn

-adult

head of sperm

-contains nucleus 

&

-acrosome

acrosome

-enzyme filled structure found in head of sperm

-enzymes allow sperm to penetrate barriers surrounding the egg

Neck of sperm

-encloses a centriole

Centriole of sperm

-will combine w/centriole of egg to form

new centrosome (required for spindle formation during mitosis)

Midpiece of sperm

-mitochondria

-vacuole (some times, not present in all)

Flagellum

-in tail region of sperm

-long structure composed of microtubules

-surrounded by plasma mem that whips back and forth making swimming possible

Main difference btwn sperm and egg

eggs large (due to nutrients) and nonmotile

sperm small and very motile

placenta

-embryos obtain nutrients via this organ w/in a week or 2 after fertilization

-egg only has to supply nutrients for early development (short time)

(EXCEPT in species that lay eggs-then egg only form of nutrition)

yolk

-contain nutrients required for embryo to develop

fat and protein rich cytoplasm

-can be present on large mass or many small granules

cytoplasmic determinants

-regulatory molecules that control early events of development

(ex-bicoid mRNA-acts as a master regulator)

cortical granules

-small, enzyme filled vesicles that are activated during fertilization

-as egg matures they are synthesized in the Golgi apparatus --> transported to the cell surface, and localized just under the surface of hte plasma mem

vitelline envelope

-just outside plasma mem of eggs

-fibrous, mat like sheet of glycoproteins

sourrounds the cell

-->in humans normally thick and reffered to as-zona pellucid

zona pellucid

-vitelline envelope in humans

-usually thick

gelatinous matrix-jelly layer

-some species it surrounds vitelline envelope to further enclose the egg

zygote

-fertilized cell

fertilization in sea urchins

-externally

-head of sperm encounters jelly layer

-sperm head digests way through jelly layer and vitelline envelop using enzymes from acrosome

-once head contacts egg cell surface the plasma mem of egg and sperm fuse

-sperm mitochondria later disintergrate

-sperm and egg nuclei fuse to form zygot nucleus

protein bindin

-how gametes from samme species recognize each other

-protein on head of sea urchin sperm binds to surface of sea urchin eggs in specific manner

-binding protein from very closely related spieces are distinct-sperm bind ONLY to eggs from same species

protease

enzyme that cleaves peptide bond

Polyspermy

-mult fertilization

-result of zygote having more than 2 copies of each chromosome

How is polyspermy prevented

 -sperm entry caus influx of Ca ²⁺

-->cortical granules located inside cell's plasma mem respond to Ca 2+ signal by fusing w/the mem and releasing contents to exterior

-->whats released accumulated btwn egg's plasma emm and vitelline envelope (HIGHLY [ ] - causes H2O to flow into space btwn plasma mem and vitelline envelop by osmosis)

--->influx H2O causes envelope matrix to life away (form a fertilization envelope)

Contents found in cortical granules

-protease-digests the exterior facing fragment of hte egg cell receptor for sperm

-prevents any new sperm from binding

fertilization envelope

-due to the influx of H2O that occurs when cortical granules releases contents creating high [ ] btwn plasma mem and vitelline envelop--->resulting in osmosis of water into that same space

-this influx causes envelope matrix to lift away from cell

-prevents additional sperm from contacting egg's plasma mem

Do mammals produce fertilization evelope

NO

-instead enzymes released from contical granules destroy egg cell receptor for sperm

-they modify proteins on the egg cell surface that prevents bindin

Cleavage

-rapid cell division that takes place in zygote immediately after fertilization

-1st stemp in embryogenesis

-in most animals, it partitions the egg cytoplasm w/o additional cell growth 

-divides w/out overall cell growth

FAST

embryogenesis

-process by which single cell zygote becomes multicellular embryo

blastomeres

-cells created by cleavage division

-blastula

-when cleavage is complete

-mass of blastomere cells

cytoplasmic determinant

-molecule that exists in eggs and helps direct early developmen

(ex-bicoid mRNA)

-found in specific location w/in egg cytoplasm-end up in specific populations of blastomere

-by dividing egg cyto to precisely distribute cytoplasmic determinants to certain cells, cleavage initiates step-by-step process (in combination w/signals receieved from other cells) results in differentiation

Fallopian tube 

(oviducts)

-structure that connects reproductive organs ovary to uteruse

-cleavage occurs here

ovary

-organ in which egg matures

uterus

-organ in which embryo develops

-fertilization occurs near ovary

-cleavage occurs in fallopian tube

clastocyt

-specialized type of blastula due to ceavage

-2 major populations of cells

-trophoblas

-inner cell mass (ICM)

trophoblast

-exterior of blastocysts

tin walled

-hallow structure

Inner Cell Mass

(ICM)

-inside trophoblast

-cluster of cells

-contain cells that undergo gastrulation and develop into the embryo

Placenta

-begins to form afte blastocysts implants into uterine wall

-derived from mixture of maternal cells and trophoblas cells

-allows nutrients and wastes to be exchanged btwn mother's blood and embryo's blood

Gastrulation

-extensive and highly organized cell movements radically rearrange the embryonic cells into a gastrula

tissue

-integrated set of cells that function as one unit

Germ Layer

-result from gastrulation

1-Ectoderm

2-Mesoderm

3-Endoderm

-give rise to organs and tissues

Ectoderm

-outside skin

-forms outer covering (skin) and nervous system

Mesoderm

-middle skin

-muscle

-most internal organs

-connective tissue (bone/cartilage)

Endoderm

-inner skin

-lining of digestive tract/gut and some associated organs

4 steps of gastrulation

1- blastula blastoceol; blastula = hollow or partially hallow

2-as gastrulation begins, cells begin moving into blastocoels through invagination (indendation); invagination eventually forms blastopore

3-cells from periphery continue to move to the interior of embryo through the blastopore, formed tube like structure that will become gut/digestive tract

4-when complete ecto/meso/endo cells arranged in 3 distinct layers

blastocoel

-fluid filled interior in blastula

invagination

(indentation)

-eventually forms a blastopore

organogenesis

-process of tissue and organ formation that begins once gastrulation is complete and the embryonic germ layers are in place

-cell proliferate ; become differentiated

-->specialized for diff jobs

-->diff cells ahve distinctive structure and function b/c they express a distinctice suit of genes

Notochord

-rod-like element

-in dorsal membrane

-runs lenght of anteripr-posterior axis of embryo

-just under dorsal surface

Chordates

-notochord is long lasting structure that fucntions as simple internal skeleton (stiffens the body; makes effiecient swimming movements possible)

IN HUMANS-notochord is transients-appears only in embryos; cells of notochord undergo apoptosis

Neural tube

-precursor of the brain and spinal cord

-notochord produces signals that direct formation of neural tube

-notochord furnishes physical support as ectodermal cells fold into their final configuration

How does ectoderm fold

-folding begins when signals from notochord trigger massive changes in cytoskeletal elements inside each of the dorsal ectodermal cells

-as cytoskeletaon reorganized, ectodermal cells extend in lenght and then constrict @ their dorsal end and expand their ventral end

somites

-mesodermal cells near neural tube become organized into blocks of tissue _______

-they form on both sides of neural tube down lenght of body

-transient structures (like notochord) but varity of structures

-break away in distinct groups that migrate to their final location and there they continue to proliferate

How is somite formation triggered?

-response to changes in cell adhesion molecules that keep mesodermal cells attached to each other

What do cells from somite build?

-vertebrae and ribs

-deeper layers of skin that cover back

-muscles of back

-body wall

-limbs

Cell determination

-as somite matures, cells become irreversibly determmined

-cell type they eventually will become has been decided based on location w/in somite

cell fate w/in cell determination

(2)

1-becomes fixed in a step-by-step process

-->guided by regulatory gene cascades

2-is a funciton of its location in the embryo

Determination

-distinct population of cells in a somite differentiate in respones to distinct local combination of cell-cell signals

How is the direction of somite cells determined?

-diff combination sof cell-cell signals direct movement of these cells when the structure breaks up and triggers the production of transcription factors required for the expression of msucle/bone/ or skin specific proteins

Myoblast

-cell derived from cells in somite

-->destined to become muscle cell but has not yet begun producing muscle-specific proteins

-->begin producing muscle determining proteins after they recieve appropriate set of cell-cell signals from nearby tissue

-reg transcription factors in myoblas that dictates them becoming muscle cell

MyoD

-myoblast determination

-protein product of the gene

-MyoD gene encodes reg transcription factor that MyoD protein bind to enhancer element located upstrea of muscle specific genes