cell differentiation: cells are genetically programmed to be specialized and will assume unique...

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