Eukaryotic Gene Regulation- Part 1

In the past few posts, I covered regulation of genes in prokaryotes, using the tryptophan and lactose operons as examples. Now I'm going to talk about eukaryotic gene regulation, which will be a bit more complex as eukaryotes are more complex.

Know the meanings and importance of the key words.

(These are just my shitty definitions, not textbook definitions, so take them with a pinch of salt.)

Somatic, germ line- Germ line cells are cells that produce the gametes (eggs and sperm). Somatic cells are all of the other cells in the body.
Zygote- The cell that forms when the egg and sperm combine.
Chromatin- Complexes formed from DNA and protein. Can condense to form chromosomes.
Chromosome- Condensed chromatin. There are 46 chromosomes in a normal human cell.
Differentiation- Cells developing special features to transform from a totipotent (i.e. can become anything) stem cell to a particular mature cell in the body.
Development- The process in which cells grow and develop...? During this process, they become differentiated.
Chromatin remodelling- The modification of the chromatin in order to make the DNA more or less accessible to RNA polymerase. For example, DNA can become more or less condensed.
Histone modification- The modification of amino acids in the histones of chromatin. This may make the DNA more or less accessible.
Acetyltransferase- Enzymes that add acetyl groups to lysine residues in histones. This weakens the interaction of histones with the DNA, thereby making the DNA more accessible to RNA polymerase. This can be reversed by deacetylases.
DNA methylation- The addition of methyl groups to the DNA. Methylation of genes may cause silencing.
Morphogen- A signalling molecule that helps guide the process of differentiation.

Have a general understanding of the process of differentiation.

Differentiation, as I mentioned, is the process in which an undifferentiated cell undergoes changes to become a particular differentiated cell type. The first totipotent stem cells produced from the zygote dividing will eventually proliferate and divide to produce neurons, bone cells, blood cells etc. Remember, proliferation must proceed differentiation- you can't have one cell differentiate into 200+ types without the one cell dividing first. Differentiated cells usually have a distinct morphology (appearance) that helps us to identify them.

Differentiation is accomplished partly by gene regulation. This, in turn, may be influenced by transcription factors, which can be either general or cell/tissue specific. Contact with hormones or morphogens may also influence gene expression. Other enzymes that modify chromatin may also influence differentiation through influencing the ability of genes to be expressed.

Realise the complexity of chromosome structure & its role in gene expression.

Chromosomes are not simply long strands of DNA and protein- they are coiled a lot so that all of that information can fit inside the tiny nucleus of the cell. Some of the most prominent proteins in chromosomes are histone proteins. Eight of these fit together to form a histone octamer, around which the DNA winds. The DNA plus the histone octamer is known as a nucleosome. Nucleosomes are joined by small bits of DNA called "linker DNA." Nucleosomes, in turn, can form a spiral known as a solenoid, which is stabilised by another histone protein. Solenoids can condense even further to eventually form the banding patterns that can be seen on chromosomes. All of this coiling allows the DNA to be packed tightly without it getting so tangled up that transcription factors cannot bind.