Gene Expression Flashcards
Gene Expression
- Even though every cell in your body shares the same genome, each
cell does not turn on, or express itself, with the same set of genes or
at the same time. - Each cell type needs to express a different set of genes to make
different proteins to perform its’ proper function. - The process of turning on a gene to produce RNA and Proteins is
called Gene Expression.
Expression of genes is a highly regulated process
At any given time, only a subset of your genes are actually expressed
* This control mechanism saves energy
* Remember, protein synthesis requires more energy than any other metabolic
process
* The energy for protein synthesis comes from the phosphorous molecules of
the sides of the DNA molecule (from the nucleotide)
* This control mechanism saves cellular space
* Remember, cells would need to be much larger if they were to unwind all of
their DNA at the same time for replication and protein synthesis
Genes are turned off
Cells rarely use more than 5-10 percent of their
genes at any given time
* At this time, science thinks 90% of our DNA is
“junk DNA” because it does not seem to be coding
for proteins
Selective Gene Expression
Depends on:
* Type of cell
* Internal chemical conditions
* External signals
* Built-in control systems
*Regulatory Proteins-exert control over gene expression
*Master genes= genes that switch on in specific tissues at specific stages of development
*Checkpoint genes- protein that control the cell cycle when something goes wrong
during DNA replication and repair
*mutated forms often lead to cancer
Protein Synthesis in Prokaryotes (Bacteria) vs
Eukaryotes
- In Prokaryotes: Protein Synthesis occurs all at one time
(transcriptional & translational all at one time) - In Eukaryotes: Protein Synthesis occurs in steps:
- Epigenetic, Transcriptional, Post-transcriptional,
Translational, Post-translational
Different controls
Epigenetic Control – regulation of gene expression that occurs when
DNA is uncoiled and loosened from nucleosomes
* Transcriptional Control- when the RNA is transcribed
* Post-transcriptional Control – when the RNA is processed and
exported to the cytoplasm
* Post-translational Control – when the RNA is translated into a protein
Transcriptional Controls in Eukaryotes
Enhancers – region of DNA that help or increase transcription
* May be upstream, downstream, part of the gene, or thousands of nucleotides
away
* Promoters – DNA sequence that initiates “transcription”
* DNA is actually a 3-D object
* This 3-D bending allows an “enhancer” to interact with a “promoter” for
selective gene expression
* Repressors – block transcription
Post- Transcriptional Modification/ Post-Control/RNA Splicing
RNA is transcribed, it must be processed into a mature form
before it can be translated
* Results in a pre-mRNA – mRNA strand before it is spliced
is the removal of “introns” (sections of DNA that do not need to be
expressed)
* Exons remain
* Results in a mature mRNA – mRNA that has been spliced
Alternate RNA Splicing
Post-translational Control
* Gene regulation that allows different proteins to be produced from
one gene when different combinations of introns are removed.
* Many genetic diseases are a result of “alternate splicing” rather than
mutation
Chemical Modifications
Phosphorylation – provides energy for transcription/translation
* Methylation – keeps DNA tightly wound so it is not expressed
* Acetylation – unwound DNA that will be expressed
* Ubiquitination - addition of ubiquitin
* Marks a protein for degradation (kiss of death) when its lifespan is complete
* These proteins are moved to the proteosome to be degraded
Acetylation
The unwinding of a specific region of DNA
* Results in a “Transcription Bubble” or “Chromosome Puff”
* Portion of the chromosome in which the DNA has loosened up (due to
acetylation) to allow transcription
* This process takes up extra space in the cell nucleus
* Methylation – keeps the DNA tightly wound (when its not being expressed)
* Doesn’t require as much space in the nucleus
Epigenetic Controls
Human genome has over 20K genes
* Each of the 23 pairs of human chromosomes encodes thousands of
genes.
* The DNA in the nucleus is precisely wound, folded, and compacted
into chromosomes so that it will fit into the nucleus
* DNA strands are wound around a Histone (protein)
* Histones are packaged into Nucleosomes
* Histones move along the DNA strand and change the 3-D structure of the
molecule
* The “sliding nucleosome” opens up a region of DNA to be read
* Remember, when it is tightly coiled it cannot be read!, its in Chromatin form!
Cell Differenatiation
The specialization of body cells structure and function
* Master genes= genes that switch on in specific tissues
at specific stages of development to form those
tissues
* Pattern Formation- The emergence of embryonic
tissues and organs in orderly patterns
Apoptosis
Programmed cell death
* Signals the unleash of molecular weapons of self-destruction
* *Cancer cells do not commit suicide on cue
Xentransplantation
The transfer of an organ from one species into another
* Pigs are often used for this because humans don’t generally reject pig tissues
* Problem: All human pandemics have arose from an animal virus that has
adapted to be able to replicate in people (swine flu, avian flu, etc.
