BIOL2161 Lecture Notes - Lecture 14: Gene Expression, Consensus Sequence, Regulatory Sequence
BIOL6: Genes: Replication and
Expression
Block 3: Gene structure & regulation in eukaryotes
Eukaryotic gene regulation
• Eukaryotic "infrastructure" influences gene regulation
• Differences to prokaryotes:
o Individually positions and regulated (no operon)
o Chromatin structure
o Nuclear membrane
• Control of eukaryotic gene expression:
o
1. Transcriptional control
o
o Not all genes in the body are turned off at the same time, or in the same cells or parts of
the body
o For many genes, transcription is the key on/off point:
• If the gene is not transcribed in a cell, it can't be used to make a protein in that
cell
• If a gene does get transcribed, it is likely going to be used to make a protein, or is
expressed. Generally, the more a gene is transcribed, the more protein will be
made
find more resources at oneclass.com
find more resources at oneclass.com
o Transcription factors
• Enzyme RNA polymerase (makes new RNA molecule from DNA strand) must
attach to DNA strand
• Attaches at the promotor point
• Can only attach to promotor with the help of proteins called basal (general)
transcription factors - part of the cells core transcriptional toolkit
• Typical transcription factors bind to DNA at a certain target sequence, and it
makes it either easier or harder for RNA polymerase to bind to the promoter of a
specific gene
• Activators:
▪ Activate transcription
▪ May help general transcription factors and/or RNA polymerase bind to the
promotor
▪
▪ Bind to the regulatory promotor
• Directly upstream from promotor
• Contains different consensus sequence for different transcriptional
activators - each promoter is regulated by unique combination of
activators
•
• Repressors
▪ Repress transcription
▪ Can work in a variety of ways
find more resources at oneclass.com
find more resources at oneclass.com
▪ Example: repressor may get in the way of the basal transcription factors or
RNA polymerase, so that they can't bind to the promotor or begin
transcription
▪
▪ Bind to silencers, orientation independent and these compete with
activators
▪ May bind to sites near activator site - prevents contact of activator with BTA
- direct interference with BTA assembly
• Binding sites
▪ Binding sites for transcription factors are often close to the promotor
▪ Can also be found in other parts of the DNA, sometimes very far from
promotor, but still affect transcription of the gene
▪ Flexibility of DNA is what allows transcription factors at distant binding sites
to do their job, DNA loops like cooked spaghetti to bring far-off binding sites
and transcription factors close to general transcription factors or "mediator
proteins"
▪
• Gene expression if different body types
▪ Some genes need to be expressed in more than one area of the body/more
than one cell type, but not in the entire body
▪ Gene like this may have several enhancers or silencers
• Enhancers: Far-away clusters of binding sites for activator,
independent in position and orientation, stimulate any promotor in
the vicinity
• Insulator: boundary element, block the effect on promotors nearby,
some also limit the spread of de/condensation
• Silencers: same thing, but for repressors
• Each enhancer/silencer may activate or repress the gene in a certain
cell type or body part, binding transcription factors that are made in
that part of the body
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Block 3: gene structure & regulation in eukaryotes. Eukaryotic gene regulation: eukaryotic infrastructure influences gene regulation, differences to prokaryotes: If the gene is not transcribed in a cell, it can"t be used to make a protein in that cell. If a gene does get transcribed, it is likely going to be used to make a protein, or is expressed. Rna polymerase, so that they can"t bind to the promotor or begin transcription: bind to silencers, orientation independent and these compete with activators, may bind to sites near activator site - prevents contact of activator with bta. Insulator: boundary element, block the effect on promotors nearby, some also limit the spread of de/condensation. Single gene can be activated by several different elements - activation through different stimuli: one stimulus can activate several different genes - presence of same response element, combinational gene control.
