SCIE1106 Lecture Notes - Lecture 23: Lysine, Acetyl Group, Intellectual Disability
Introduction to Regulation of Gene Expression in
Eukaryotes
Thursday, 22 September 2016
11:30 am
The Big Picture:
Gurdon, 1962:
• Are genes lost during development or are different genes expressed?
• Xenopus eggs - DNA from undifferentiated or differentiated cells retain capacity to
produce a normal individual: no losses occur during differentiation
• Fact: All cells contain the same genes
• Genes are not gained or lost in the normal course of development
Development:
• In multicellular organisms, life begins as a single cell
• With a few exceptions somatic cells (all cells other than germ line) contain the same
genetic information as the zygote (fertilised egg)
• In development, cells commit to specific fates and differentially express subsets of
genes
• Daughter cells may differ with respect to regulatory instructions and developmental
fate, so new cells become different to their parent cell
Differentiation:
• Cells producing proteins to perform specialised tasks
• Early embryo is characterised by
o Rapid cell division
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o Followed by differentiation
• Differentiated cells produce specific proteins
• Do this by accessing specific parts of DNA
• A & D are switched on in the differentiated cell
• B is switched off
• C is a constitutively expressed gene - needed in undifferentiated and differentiated
cells
How Genotype Becomes Phenotype:
• Differentiation is a DNA-orchestrated set of cellular changes that normally occurs
without error
• Complex process - a cell changes or differentiates to carry out specialised functions
• The process is often marked by a change in cell morphology and is usually preceded by
rapid proliferation
• Differential gene expression from the same nuclear repertoire is accomplished by the
regulation of gene expression at several levels
Chromosomes and Genes:
• 25-50% of eukaryotic genes are solitary
• The remainder belong to gene families
• Proteins encoded by gene families have homologous sequences and similar (not
identical) function
• Very important in development
• Human cells contain about 2m of DNA, packaged into the nucleus that is 6um in
diameter
• Each DNA double helix is packaged into a chromosomes 10 000 times shorter than its
expected length
• Chromosomes = DNA + protein (chromatin)
• Nucleosomes - breads on DNA string, contain histone octamers
• Solenoid stabilised by another histone
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Gurdon, 1962: are genes lost during development or are different genes expressed, xenopus eggs - dna from undifferentiated or differentiated cells retain capacity to produce a normal individual: no losses occur during differentiation. Fact: all cells contain the same genes: genes are not gained or lost in the normal course of development. In multicellular organisms, life begins as a single cell: with a few exceptions somatic cells (all cells other than germ line) contain the same genetic information as the zygote (fertilised egg) In development, cells commit to specific fates and differentially express subsets of genes: daughter cells may differ with respect to regulatory instructions and developmental fate, so new cells become different to their parent cell. Scaffold spiral contains nonhistone proteins from which dna loops project (topoisomerase ii) Scaffold allows dna unwinding without tangling: chromosomes are supercoiled, chromosomes diameter ~ 700nm. Structure: condesnsed (hypo-acetylated, histone modification, extended/decondensed (acetylated) = active, changes structure = chromatin remodelling.
