pro and eu 2

What are constitutively expressed genes?

Genes that code for proteins that are synthesized continuously at a fixed rate

Why is DNA organized into chromatin?

• Pack DNA into a compact form that fits inside the nucleus

• Regulate gene expression (determines accessibility for transcription)

What are the two forms of chromatin?

Heterochromatin = Highly-compacted DNA wound more tightly around histones

Euchromatin = Less-compacted DNA would less tightly around histones

What kinds of control are there at the genomic level?

• Chromatin remodeling complex → Modify chromatin structure

• DNA methylation → Add a methyl group to selected cytosine nucleotides in the CG sequences

• Histone acetylation / deacetylation → Allows chromatin to condense and decondense respectively

• Gene amplification

How do chromatin remodeling complexes alter the structure of nucleosomes temporarily?

• Results in DNA being less tightly coiled around histones → Allows RNA polymerase and GTF involved to access the promoter and initiate transcription

• Results in DNA being more tightly coiled around histones → Prevents RNA polymerase and GTF involved from accessing the promoter, blocking transcription

How does DNA methylation affect transcription?

Prevents transcription → Gene silencing (found extensively within heterochromatin)

• Blocks binding of GTF → Prevents assembly of TIC at the promoyer

• Recruits DNA-binding proteins to the methylated DNA to condense chromatin (repressors, histone deacetylases etc.)

How does histone acetylation occur?

• Addition of acetyl groups to lysine residues → Removes positive charges on histones → Decreases electrostatic interactions between negatively-charged DNA and histones → Loosens tight binding between histones and DNA → Makes the promoter region more accessible to RNA polymerase and GTF

• Works in concert with the chromatin remodeling complex

How does histone deacetylation occur?

• Removal of acetyl groups

• Restores tighter interaction between DNA and histones → Inhibits transcription

What is gene amplification?

Replication of a specific gene multiple times to create more copies of that gene

What kinds of control are there at the transcriptional level?