Biology 1202B Lecture Notes - Lecture 12: Histone Octamer, Histone H1, Start Codon

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11 Feb 2016
Department
Kaden VanHelden
Biology 1202B: Lecture 12 – Transcription and Translation I
Transcription
Many similarities between DNA replication and transcription – keep them separate
We generally think of transcription as the first step in protein production
oFunctional products of transcription also include RNA molecules
Eukaryotic chromatin structure
The more densely packed the chromatin the less likely it is to be transcribed
Histones + charge
oDNA – charge
oHistone octamer
2x(H2A, H2B, H3, H4)
Histone tails are sites of chemical modification
oChromatin remodelling
Loosely bound DNA is more available for transcription
DNA is always in form of DNA + protein = chromatin
Histone is a protein: binds to nucleosomes and linker DNA, causing nucleosomes to
form coiled structure
Histone H1 binding
o30 nm fiber
Further packaging
oHeterochromatin
Densely packed with proteins – silent
Inactive X chromosome in females
oEuchromatin
Loosely packed – available for transcription
Beadle and Tatum
Each step in arginine synthesis controlled by a gene which codes for the required
enzyme
“one gene-one enzyme hypothesis”
Nobel prize 1958
Modified to one gene-one polypeptide
Proteins often contain more than one polypeptide
Hemoglobin molecule
oHas 4 subunits – needs all of them to function
oMain oxygen carrying component in red blood cells
What is a gene?
A region of DNA which is transcribed
The regions of DNA which are required for that transcription
oDNA binding sites for regulatory molecules
oGene transcription is a highly regulated process
Genes only turned on when necessary
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