Chromatin is the complex of negatively charged DNA coiled around positively charged histone proteins in eukaryotic cells.

It allows DNA to coil tightly to fit in the nucleus.

1. Euchromatin - loosely packed DNA that allows transcription to occur
2. Heterochromatin - tightly packed DNA that prevents transcription from occurring

Histone acetylation is the addition of acetyl groups to histone molecules, which reduces the positive charge of histones. This causes looser DNA coiling and enables gene transcription.

Phosphorylation, the addition of phosphate groups, of the histone molecules achieves the same effect.

Histone methylation increases the hydrophobicity of histones.

This causes the DNA to coil more tightly, and reduces gene transcription.

Epigenetics involves changes in gene expression without altering the underlying DNA sequence, such as through histone modifications. 

By altering the structure of chromatin, remodelling can make genes more or less accessible for transcription.

This allows cells to control which genes are active, influence cell function, and respond to environmental signals.

Transcription factors cannot bind to DNA, preventing transcription and polypeptide synthesis.

Transcription factors are proteins that bind to DNA and control gene expression in eukaryotes by decreasing or increasing the rate of transcription.

Effectively, transcription factors can switch the transcription of a gene off or on.

Transcription is initiated by transcription factors binding to specific DNA sequences.

mRNA is produced during transcription, carrying the genetic code from DNA to the ribosome.