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BIO230H1 Chapter Notes -Lac Repressor, Lac Operon, Repressor

Course Code
Darrel Desveaux

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Lecture 1
Pages: 1-8
Heredity distinguishes life from other processes
All living cells on Earth, without exception store hereditary information in the
form of DNA composed of the same 4 nucleotides
Nucleotide: sugar (deoxyribose) + phosphate and a base
All cells replicate their DNA through a DNA template, not from a DNA in
isolation, known as template polymerization
Bonds between base pairs is weaker than the sugar-phosphate links, allowing
DNA strands to be easily pulled apart
All cells transcribe portions of their hereditary information into RNA
RNA is not always single stranded, their backbones can fold back on
themselves to form weak bonds with itself
All cells use proteins as catalysts i.e. enzymes
A gene is defined as the segment of DNA sequence corresponding to a single
Pages: 14-16
Eukaryotes keep their DNA in a membrane-enclosed compartment called the
Prokaryotes don’t have a nuclear compartment
Lecture 2: Prokaryotic Transcriptional Regulation
Pages: 411-416
Cell differentiation depends on changes in gene expression rather than on
any changes in the nucleotide sequence of the cell’s genome
The Different Cell Types of a Multicellular Organism Contain the Same DNA
The cell types in an organism become different from one another because
they synthesize and accumulate different sets of RNA and protein molecules
oThey do this without altering their sequence of DNA in MOST cases;
exceptions exist
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Different Cell Types Synthesize Different Sets of Proteins
Some proteins are abundant in the specialized cells in which they function
and can’t be detected elsewhere i.e. Haemoglobin is only found in red blood
Genes vary in their level of expression from one cell type to the next
There are many steps after transcription after which gene expression can be
regulated and proteins can be covalently modified after they’re synthesized
External Signals Can Cause a Cell to Change the Expression of Its Genes
Different cell types often respond differently to the same extracellular signal
Gene Expression Can Be Regulated at Many of the Steps in the Pathway
from DNA to RNA to Protein
A cell can control the proteins it makes by:
1. Controlling when and how often a given gene is transcribed
(transcriptional control)
2. Controlling the splicing and processing of RNA transcripts (RNA
processing control)
3. Selecting which completed mRNAs are exported from the nucleus to
the cytosol and determining where in the cytosol they are localized
(RNA transport and localization control)
4. Selecting which mRNA in the cytoplasm are translated by ribosomes
(Translational Control)
5. Selectively destabilizing certain mRNA molecules in the cytoplasm
(mRNA degradation control)
6. Selectively activating, inactivating, degrading, or locating specific
protein molecules after they have been made (protein activity
Although all of the steps involved in expressing a gene can be regulated, for
most genes, the initiation of RNA transcription is the most important point of
Gene Regulatory Proteins Were Discovered Using Bacterial Genetics
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