cell differentiation: cells are genetically programmed to be specialized and will assume unique...
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Cell Differentiation:
cells are genetically programmed to be specialized and will assume unique structural& functional attributes
Fertilized Egg = totipotential stem cellsvs.
pleuripotential stem cells
Oocyte with sperm = fertilization
Zygote=fertilized egg
Series of mitotic divisions = cleavage
2-cell stage (30 hours post fertilization)
Zygote 2-Cell Morula 16-32 Cells
8-Cell Stage…
Morula= solid ball of cells (32 cells +)
Blastocyst=hollow ball of cells, implants inuterus 6-7 days after fertilization(500-2000 cells)
Trophoblast=Chorionplacenta
Inner cell mass= embryo + amniotic sac
Embryonic disk develops from inner cell massgastrulation= endoderm
Somites mesoderm ectoderm
(2nd week) = embryonic stage
Endoderm (inner layer)=-respiratory system-Pharnyx (throat)-Pancreas-Liver-GI tract
Mesoderm (middle)=-gonads-kidneys-circulatory system-Somites = muscles, skeleton
Ectoderm (outer layer)=-skin-hair-inner ear-lens of eye-nervous system-connective tissues
Neurulation= nervous system forms(3rd week)
(2mm long)
Spina Bifida
Anencephaly
Extraembryonic Membranes
Trophoblast= placenta + chorion
Inner cell mass= embryo + amniotic sac + allantois (bladder & umbilicus) +yolk sac (nutrients & germ cells)
4th week= Organogenesis-heart begins to beat (70 bpm)
[2.5 billion beats per 70 years]-5 mm long-susceptible to teratogens
[thalidomide]
6 week embryo
2nd Month = Morphogenesis-arms, legs, tail bone form-25 mm long-major organs continue to form
7th week= sexual differentiation occurs
8th week embryo becomes a “fetus”
End of 1st trimester-most major organs are formed-placenta takes over pregnancy
2nd trimester (175 mm; 225 gm)-organs grow-nervous system continuesdevelopment
3rd trimester -baby grows rapidly!-6th month=1.3 lbs; 1 ft long
What controls growth & development?
GENES!
8 year old child withHutchinson-Gilford Syndrome(Progeria)
Homeotic Genes (Hox)=act as switchesand controlpattern formationduring development
Dermatomes
Mutations: changes made in normal genetic sequence of DNAA. Cells have DNA repair mechanisms
but… ~ 1 out of 1 billion mutations aren’t repaired
B. If change affects last nucleotide of codon = okayif 1st codon affected = bad
Why?[Overhead]
C. Mutagens: agents which cause mutations(e.g., radiation… UV-B, X-rays, sodium nitrite,
cigarettes
1. Mutations
a. Point mutations: one nitrogen base gets substituted for
another.
Ex. DNA normally read as….
…GGTCTTCTC…
UV radiation zaps and changes message to….
…GGTCATCTC
The result is Valine gets substituted for Glutamine… causing the disease….
Sickle Cell Anemia
Sickle Cell Anemia:
e.g. Sickle Cell Anemia
HbA HbS
HbA HbA/HbA HbA/HbS
HbS HbA/HbS HbS/HbS
¼ normal; ½ sickle cell trait;
¼ sickle cell anemia
Sickle Cell Anemia and Malaria
Malaria & Sickle Cell Allele Distribution
b. Frame-shift: an extra nucleotide gets slipped into message…
THE CAT RAN FAR…..
THE QCA TRA NFA R
c. Insertions: extra messages added
THE FAT CAT RAN FAR
d. Deletions: messages removed
THE RAN FAR
Mutations
A Deletion Mutation…
Mutations:
e. Trisomy: extra chromosomes are addedto our “Karyotype” = usually
lethal
Trisomy 21 and Down’s Syndrome