bild10 week 2
TRANSCRIPT
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Embryogenesis
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inner cell
mass
All living things are made of cells.
Humans develop from a single cell -
the fertilized egg
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Sea urchin eggs divide in half about an hour after fertilization.Each cell divides again in half an hour later.
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Cleavage patterns differ between different organisms but
gastrulation is very similar in them all. Cell movements during
gastrulation generate the middle layer of cells - the mesoderm.
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A blastula (or blastocyst) is a hollow ball of hundreds of cells.
Cells move into the blastocoel through the blastopore.
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Gastrulation generates the 3 main cell layers:
ectoderm, mesoderm, and endoderm.
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Specific tissues and organs are derived from the cell layers.
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There are similarities and differences between embryos of different phylla.
Vertebrates all have a dorsal backbone along the anterior/posterior axis.
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8 weeks7 weeks
5 weeks4 weeks2 weeks 3 weeks 6 weeks
HUMAN EMBRYOGENESIS
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4 months -14 cm
9 months -35 cm
ready to be born
7 months -27 cm
may survive if born
prematurely
5 months -18 cm
mother may feel
movements (quickening)
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Subjects discussed:
1) Sperm and egg fuse at fertilization
2) Early stages: cleavage, blastula, gastrula
3) Cell layers: endoderm, mesoderm, ectoderm
Lecture 4
Embryos of all animals have much in common
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Gene Regulation
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exon 1 exon 2 exon 3intron intron
transcriptionstart
3end5 end transcriptionstop
5 end 3 end
exon 1 exon 2 exon 3
Primary transcript
Processed mRNA
Gene transcription and mRNA processing
in eukaryotes
DNA
transcriptional start transcriptional stop
RNA
polymerase
primary transcript
translation of open reading frame (ORF)on ribosomes
elongation
3 5
5
3
5
RNA
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In bacteria, regulatory proteins block binding of RNA polymerase
by covering the site in the promoter. Other proteins, such as CAP,
bind upstream and facilitate polymerase binding. Small molecules
regulate the binding affinity of regulatory proteins.
+ cAMP
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Proteins recognize specific sequences of 6-10 bases in DNA
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The lac operon encodes 3 proteins all made from the same transcript
induction
in growth media
containing lactose
no induction
in growth media
without lactose
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In eukaryotes the DNA is compacted by wrapping it around
nucleosomes which are then rolled into a selenoid. Further
compaction is necessary to get mitotic chromsomes. DNA
unrolls when it is being transcribed.
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Transcriptional activation is more complicated in eukaryotes.
Many proteins interact.
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Some complexes of regulatory proteins bind at a distance, but the DNA
can loop around to allow interaction with RNA polymerase.
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Transcription polymerizes RNA from 5' to 3' making a complementary copy
of only one strand of DNA ie. there is polarity to transcription.
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Genes are selected to make proteins.
Their mRNAs have to be translated on ribosomes.
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The code is read 5' to 3' in groups of 3 bases [triplet codons].
Translation always starts at AUG which encodes methionine.
So thephase is important.
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All proteins startwith the amino acid
methionine
The Universal Genetic Code
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Protein Folding
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Subjects discussed:
1) Initiation of transcription of DNA sequence into RNA sequence is regulated
2) mRNAs are translated into specific proteins on ribosomes using triplet code3) Most proteins fold up into their final forms by themselves
Lecture 5
To transcribe or not to transcribe
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Chapter 2: Human potential
Life as it is
Christopher Reeve Superman
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In vitro fertilization
At the 8 cell stagea cell can be removed
for analysis of the genes
Extra embryos can bestored frozen for later use.
day 5
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Establishing embryonic stem cell lines (ES cells)
from the inner cell mass of a blastocyst
mouse ES cells expressing
Pitx3:GFP in the midbrain
human ES cells proliferate
in vitro
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pancreatic insulin
producing ES cells
implanting ES cells
into a blastocystneurons from ES cells
When injected into mice, ES cells
form teratomas that include:
a. neuroepithelium
b. trabecular bone
c. cartillaged. skeletal muscle
e. primitive glomeruli
f. gut-like columnar epithelium
ES cells can be induced to differentiate
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Actor Michael J. Fox was struck with Parkinson's
disease. He is a strong advocate of support for
stem cell research.
Physicist Stephen Hawking has had ALS
(Lou Gehrig's disease) for 40 years.
He might have benefited from neural stem cells
that could replace his motor neurons.
Those with juvenile onset diabetes
might benefit from pancreatic stem cell
therapy.
The promise of stem cell therapy
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Sir John Gurdon
A nucleus from an intestinal
epithelial cell injected into
an enucleated egg gave rise
to a swimming tadpole.It did not work every time.
Nuclear transplantation in the South African Clawed Toad
Xenopus laevis first showed the totipotency of somatic nuclei
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Therapeutic cloning
Somatic cell nuclear transferThe dream
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Somatic stem cells
Intestinal stem cellsdividing in the crypt.
New hairs are continuously
produced from stem cells.
Sperm are continuouslyproduced from stem cells.
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Subjects discussed:
1) Embryonic stem cells can be grown from inner cell mass.
2) Support for stem cell research?3) Somatic nuclei have all the genes and can be transfered to ES cells.
Lecture 6
Stem cell questions