Monday, January 26, 2009

The rest of chapter 18

sorry I was supposed to do the blog on friday but I was busy that night and got home late and totally forgot about it but here are the notes we took on friday:
*Inducible Operon:
*An inducible operon is usually OFF but can be stimulated (induced) when a specific molecule interacts with the regulatory protein.
*Inducible operons usually function in catabolic pathways, which break down a nutrient to simpler molecules. By producing the appropriate enzymes only when the nutrient is available, the cell avoids wasting energy and precursors making proteins that are not needed.
*18.2--> Eukaryotic gene expression can be regulated at any stage
*Chromosome modification:
  • Genes in highly compacted chromatin is generally not transcribed
  • Histone acetylation seems to loosen chromatin structure, enhancing transcription
  • DNA methylation generally reduces transcription.

*Eukaryotic Chromatin Structure:

*In eukaryotic cells, DNA and proteins are packed together as chromatin. the first level of packing in chromosomes involves DNA and proteins called histones, in nearly equal amount, folded together to resemble beads on a string. Nucleasomes are the basic unit fo DNA packing- the are the complex of DNA and histones.

*In interphase, the chromosome are extended in the nucleus (and at this point are called euchromatin), but as the cell prepares for mitosis, the chromosomes become packed into a form referred to as heterochromatin.

*In histone acetylation, acetyl groups are added to amino acids of histone proteins; this makes the chromatin less tightly packed and encourages transcription.

*The Control of Gene Expression: DNA methylation

*The expression of gened can be turned off and on at any point along the pathway from gene to functional protein.

*Genes in heterochromatin (which is highly packed) usually are not transcribed; this is one form of gene control.DNA methylation (the addition of methyl groups) is one way in which the transcription of genes is controlled. Apparently methylation of DNA is responsible for the long-term inactivation of genes.

*Transcription initiation is another important control point in gene expression. At this stage, DNA control elements that bind transcription factors (needed to initiate transcription) are involved in regulation.


1. Is an inducible operon usually...

a) turned ON and could be turned OFF.

b) turned OFF and could be turned ON.

c) turned OFF and can NOT be turned ON.

d) turned ON and can NOT be turned OFF.

2. TRUE or FALSE. Histone is wrapped by chromatin.

3. When can expression genes be turned on and off along the pathway from gene to functional protein?

a) at ANY point

b) not possible

c) only at one specific point

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