STRUCTURE OF CHROMATIN Lindsey Suttle, Aaron Alejandro, Christine Nam and Aruna Iyer

BUILDING BLOCKS 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 It plays a key role in its chromatin structure. 

PROTEIN SCAFFOLDING 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 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

Looped domain: the loop formed by chromatin fiber This attaches to a chromosome scaffold made of

nonhistone proteins.

2 TYPES OF INTERPAHSE CHROMATIN Heterochromatin: highly condensed state of chromatin

Visible through a light microscope Does not undergo transcription

Euchromatin: lightly compacted chromatin Undergoes transcriptions Found in both eukaryotic and prokaryotic cells

MODIFICATIONS DNA methylation: the attachment of methyl groups (-

CH3) to DNA bases (after DNA is synthesized) Methylation can turnoff genes Demethylation is when the extra methyl groups are removed

Demethylation can activate genes

Protects and stabilizes DNA

Histone acetylation: when an acetyl group (-COCH3) is attached to certain amino acids of histones. 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

http://www.youtube.com/watch?v=gbSIBhFwQ4s&feature=related

PREVIOUS VOCAB

Nucleic acids Dehydration synthesis Light microscope Proteins

R groups Mitosis/meiosis

OBJECTIVE TERMINOLOGY

Chromatin Chromosome Looped domains Heterochromatin Nucleosome “beads” Histones Proteins scaffolding DNA methylation Histone acetylation Euchromatin

REVIEW QUESTIONS What makes up Protein Scaffolding?

Histones, DNA, nucleosomes Four histones with DNA wrapped twice

around the four histones creates what is known as ______ Nucleosomes

What does DNA methylation do for the DNA? Turns off genes, protects, and stabilizes DNA

Histone Acetylation occurs to let what other process occur? Transcription, by making the fit of the DNA looser

What does the looped domain attach to? The chromosome scaffold (non histone proteins)

REVIEW QUESTIONS CONTINUED What is the main difference between

euchromatin and heterochromatin? The tightness in which they are compacted.

Heterochromatin is highly condensed form of chromatin and euchromatin is lightly compacted

In what type of cells is euchromatin found? Eukaryotic and prokaryotic cells

Which form of chromatin undergoes transcription? Euchromatin

Contrast the structure of chromatin before and after Interpahse. 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

http://www.youtube.com/watch?v=TUFsMY156fc