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Lecture 3

BIOLOGY 1A03 Lecture Notes - Lecture 3: Hemoglobin, Cell Membrane, Globin


Department
Biology
Course Code
BIOLOGY 1A03
Professor
Rosa Da Silva
Lecture
3

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Theme 3 Module 3: Eukaryotic Transcriptional Regulation
Unit 1: Cellular Dierentiation
-All cells derived from a single fertilized egg, at one point as a zygote all
embryonic stem cells were identical
-Early embryonic stem cells have an almost unlimited ability to mature or
dierentiate into many dierent cell types
-Adult bodies contain around 200 distinct cell types
-Cells are able to communicate with each other, and begin to engage in
various genetic interactions that regulates continual development and
cellular dierentiation
Cells Acquire Speci#c Fates
-Development from a single fertilized zygote is dependent on molecular
communication between cells
oDepends on the signals exchanged and which genes are switched on or
o at speci!c times
Dierentiated Cells Have Distinct Functions
- Gene regulation is responsible for creating various cell types in multicellular
organisms
-Speci!c cells can be organized into groups of cells or tissue types that work
together to carry out speci!c functions
-Same genome, but gene regulation leads to altered proteomes that
contribute to distinct dierences in cellular functions

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Transcriptional Regulators Determine Cell Types
-Variation largely dependent on the
dierentiation that occurred from
common stem cells during early
the early developmental
cascade
- Transcription factors
oProteins that bind to speci!c
sequences in DNA
controlling the transcription
of DNA to RNA and
contribute to gene
regulation
oPlay essential roles in
determining the pathway a
speci!c cell will follow and determines the !nal mature or
dierentiated cell type that will form
oOften work in concert with other proteins
- Speci#c gene expression patterns triggered within dividing embryonic
stem cells and extracellular cues leads to a diverse array of specialized
cells
-Controlling which genes are active along the chromosome leads to a vast
array of cell types that are found in our bodies
oCertain proteins can be found only in speci!c cell types, or their
relative amounts can vary from cell to cell
Unit 2: Chromatin Remodeling
DNA Compaction Regulates Gene Expression
-Unlike prokaryotes, each gene is controlled by its own promoters and
enhancers and genes with similar functions are not found clustered together
-Winding of DNA in nucleosomes can aect whether DNA is transcribed or not
-Genes within tightly wound heterochromatin are not usually expressed
Nucleosome Remodelling and Accessing DNA

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- Nucleosome is made up of an octamer
of 8 histone proteins that approximately
150 DNA base pairs wrap around
-DNA is not accessible when tightly
wound into chromatin
- Chromatin Remodeling: chromatin
unravels for transcription to occur
-Begins when an activator protein or
transcription factor binds to an
accessible enhancer site
-Leads to further recruitment of other
proteins that can lead to further
chromatin remodeling
Histone Modi#cations Alter DNA Winding
-Transcriptional regulation highly
dependent on being able to reveal
the important DNA sequences that
are important for transcription
-DNA tightly wound around histone
proteins due to interactions of the
positively charged tails of histone
proteins and negatively charged
phosphates in DNA
-During chromatin remodeling,
activator proteins recruit the
coactivator enzyme histone
acetyltransferase (HAT) that
attaches acetyl groups to lysine amino acids along the positively charged
tails of nucleosome histone proteins
-When tails are acetylated, the positive charge is reduced and the interaction
between histones and DNA is weakened
-This loosening or unwinding of heterochromatin now permits transcription
factors to bind
Methylation and Acetylation of Histone Proteins
-Other chemical modi!cations include methylation of lysine and arginine and
phosphorylation of serine and threonine along the histone protein tails
-There modi!cations can also alter the charges of the tails and alter their
binding to the DNA
-End result is the modi!cation of strings of amino acids that protrude from
histone proteins
-Degree of modi!cations to the histone tails is part of a histone code that
determines whether transcription is activated or repressed
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