Transcript Biology - Raleigh Charter High School

STRUCTURE OF
CHROMATIN
Lindsey Suttle, Aaron Alejandro, Christine Nam
and Aruna Iyer
BUILDING BLOCKS
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Nucleosome: The basic, beadlike unit of DNA packaging in
eukaryotes, consisting of a segment of DNA wound twice
around a protein core composed of two copies of each of four
types of histone.
Histone: A small protein with a high proportion of
positively charged amino acids that binds to the negatively
charged DNA
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It plays a key role in its chromatin structure.
PROTEIN SCAFFOLDING
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Protein Scaffolding: The H1 histone that attaches to the histones
and chromatin for support
Proteins called histones have a high proportion of positively
charged amino acids and bind to negatively charged DNA. The
DNA-histone complex is chromatin in its most basic structure.
Histones are similar in most eukaryotes. Unfolded chromosomes
look like beads on a string. Each bead and its DNA is called a
nucleosome. The nucleosome bead is DNA wound around a
protein core made of two of these histones: H2A, H2B, H3, and
H4. H1, another histone attaches to the DNA near the bead when
the chromatin undergoes the next level of packing.
CHROMATIN FIBER
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Chromatin fiber: the folded complex of DNA and histone
proteins that is roughly 30nm in thickness that are very
long and not visible with a light microscope.
The chromatin fibers coil up to form chromosomes
 Also known as 30-nm chromatin fiber or 30-nm fiber
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Looped domain: the loop formed by chromatin fiber
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This attaches to a chromosome scaffold made of nonhistone
proteins.
2 TYPES OF INTERPAHSE
CHROMATIN
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Heterochromatin: highly condensed state of chromatin
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Visible through a light microscope
Does not undergo transcription
Euchromatin: lightly compacted chromatin
Undergoes transcriptions
 Found in both eukaryotic and prokaryotic cells
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MODIFICATIONS
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DNA methylation: the attachment of methyl groups (-CH3)
to DNA bases (after DNA is synthesized)
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Methylation can turnoff genes
Demethylation is when the extra methyl groups are removed
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Demethylation can activate genes
Protects and stabilizes DNA
Histone acetylation: when an acetyl group (-COCH3) is
attached to certain amino acids of histones.
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When a histone is acetylated it changes shape making the DNA fit
less tightly allowing for other proteins to bind for transcription.
Deacetylation is the removal of acetyl groups.
YOUTUBE
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http://www.youtube.com/watch?v=gbSIBhFwQ4s
&feature=related
PREVIOUS VOCAB
Nucleic acids
 Dehydration synthesis
 Light microscope
 Proteins
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R groups
Mitosis/meiosis
OBJECTIVE TERMINOLOGY
Chromatin
 Chromosome
 Looped domains
 Heterochromatin
 Nucleosome “beads”
 Histones
 Proteins scaffolding
 DNA methylation
 Histone acetylation
 Euchromatin
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REVIEW QUESTIONS
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What makes up Protein Scaffolding?
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Four histones with DNA wrapped twice around
the four histones creates what is known as ______
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Turns off genes, protects, and stabilizes DNA
Histone Acetylation occurs to let what other
process occur?
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Nucleosomes
What does DNA methylation do for the DNA?
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Histones, DNA, nucleosomes
Transcription, by making the fit of the DNA looser
What does the looped domain attach to?
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The chromosome scaffold (non histone proteins)
REVIEW QUESTIONS CONTINUED
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What is the main difference between euchromatin
and heterochromatin?
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In what type of cells is euchromatin found?
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Eukaryotic and prokaryotic cells
Which form of chromatin undergoes transcription?
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The tightness in which they are compacted.
Heterochromatin is highly condensed form of chromatin
and euchromatin is lightly compacted
Euchromatin
Contrast the structure of chromatin before and after
Interpahse.
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Before Interpahse the chromatin is just chromatin after
Interpahse the chromatin is wound around histones and is
in the form of chromosomes
JUST FOR FUN
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http://www.youtube.com/watch?v=TUFsMY1
56fc