Chapter 7.6 Flashcards
Why do cells regulate gene expression
- Producing proteins cost large amounts of energy (p&e)
- Each cell’s function is unique because it produces unique combinations of protein Each type of cell expresses a different subset of genes ( although each cell has a complete set of all genes it only expresses the ones needed to carryout its specific function). Not all genes in every cell is expressed some are turned off (( a hair cell would have the gene to make hemoglobin turned off and in a blood cell the genes to make hair) (Multicellular Eukaryotes)
- It gives the cell flexibility to respond to changing conditions ( e.g genes expressing enzymes to digest a meal or antibodies during an infection- when the food or infection are the the gene is shut off) (p&e)
- An intricate set of genetic instructions orchestrates the growth and the development of a multicellular organism
(Multicellular Eukaryotes)
.
In Eukaryotes, if each cell contains the same set set of genes how does it acquire it’s unique function?Why is each cell function unique
Each type of cell expresses a different subset of all the genes in each cell
Each cell’s function is unique because it produces unique combinations of protein
OPERONS
In bacteria related genes are organized as OPERONS
They are groups of bacterial related genes that share one promoter
is a group of related genes plus a PROMOTER and an OPERATOR that control the transcription of the entire group at once.
PROMOTER
Is the site to which RNA polymerase attaches to begin transcription
OPERATOR
Is a DNA sequence located between the promoter and the protein encoding regions to which gene repressor proteins bind to stop the expression of a gene.
REPRESSOR
a protein that binds to the OPERATOR in bacterial genes and prevents the transcription genes.
Is produced by a REGULATORY gene
LAC OPERON
Consists of 3 gnes that encode lactose-degrading proteins plus the promoter and an operator that control their transcription
The mechanisms for gene regulation in eukaryotic cells are
TRANSCRIPTION FACTORS
TRANSCRIPTION FACTORS
Group of proteins that bind DNA at specific sequences that regulate transcription:
without Transription factors RNA polymerase cannot bind to a promoter or initiate transcription of a gene in the absence of transcription factors
They may bind to a gene’s PROMOTER or to an ENHANCER
ENHANCER
a regulatory DNA sequence that lies outside the promoter ( they may also be located near it or within in)
List the Regulatory mechanisms in eukaryotic cells
1. Transcription factors 2, DNA Availability /Methylation 3. Rna processing/ Different combinations of intron removal 4. m Rna Exit from nucleus 5. RNA Degradation 6. Protein Processing and degradation
DNA AVAILABILITY/ Methylation
Chromosomes must be unwounded for genes to be expressed. A cell can tag an unneeded portion of DNA with a methyl group preventing gene expression and signaling the cell to fold more tightly. Transcription factors and RNA polymerase cannot access theDNA and so it is turned off
RNA PROCESSING/ Intron removal
one gene can encode multiple proteins by removing or keeping different combinations of introns
mRNA EXIT FROM NUCLEUS
A gene is silenced if it mRNA fails to leave the nucleus and attach to a ribosome
RNA DEGRADATION/ micro Dna forms a double helix
- some mRNA may not be stable and degrade before ring translated
- microRNA produced by the cell may attach to the mRNA strand making it a double helix which cannot be translated and may degrade
PROTEIN PROCESSING AND DEGRADATION
The gene is silenced when
1. if modifications to a newly synthesized polypeptide fail to occur ( folding e.g) that makes the the protein functional
- If the protein fails to go to where it is needed
- Like RNA, not all proteins are equally stable. Some degrade shortly after they are formed
. What are some reasons that cells regulate gene expression?
Protein production costs a lot of energy; the regulation of gene expression avoids t he production of unnecessary proteins and therefore saves energy.
. How do proteins determine whether a bacterial operon is expressed?
A repressor protein binds to an operator and prevents the genes in the operon from being transcribed.
. How do enhancers and transcription factors interact to regulate gene expression
Transcription factors bind to certain DNA sequences to regulate transcription, for example by preparing a promoter site to bind RNA polymerase. Transcription won’t occur without these factors. Enhancers are sequences of DNA outside of the promoter. Transcription factors can bind to the enhancers to help regulate gene expression.
What are some other ways that a cell controls which genes are expressed
Cells can keep DNA coiled or attach methyl groups to inactivate genes. During transcription different introns can be spliced out. mRNA can be contained in the nucleus or rapidly degraded. Proteins can also be degraded or modified in processing.
How is GENE EXPRESSION controlled
By regulating TRANSCRIPTION
Why is G E essential in prokaryotes
It allow the cel to take advantage of changing environment
2. Save energy
Why is G E essential in multicellular Eukaryotes
- allows genes to specialize
- direct development
- maintain homeostasis
- save energy
How is GENE EXPRESSION controlled in prokaryotes
by controlling the initiation in Transcription
( this is done by binding of proteins to regulatory sequences
How is GENE EXPRESSION controlled in Eukaryotes
Transcription control operate at distance. Transcription Factors turn genes on and off by binding to promote and enhancer ( regulatory sequences)
REGULATORY GENES
one that synthesizes REPRESSOR protein
What are involved in regulating a gene expression in a bacteria
- OPERON ( PROMOTER, OPERATOR, RELATED GENES)
2. REPRESSOR protein
How is the REPRESSOR protein involved in gene regulation in prokaryotes
- WHEN A PROTEIN IS NOT NEEDED
The REPRESSOR protein attaches to the OPERATOR preventing the transcription of its gene.
WHEN A PARTICULAR PROTEIN NEEDS TO BE EXPRESSED ( e.g lactose is present so the protein lactase is needed to break it down)
Lactase binds to the REPRESSOR protein changing its shape which forces it to release from the the OPERATOR, so that initiation can began and the protein can be expressed ( lactase.
When lactose is no longer present the REPRESSOR protein rebinds to the OPERATOR
There are 2 types of Operons
- Negatively controlling Transcription ( removing a block)
2. Positive controlling Transcription ( turn on transcription)
3 examples of a regulatory sequence
Are usually above the sequence to be expressed
1. Promotor ( in prokaryotes)
- TATA BOX in ( eukaryotes)
3 Enhancers in eukaryotes
Where does TRANSCRIPTION FACTORS bind on eukaryotes to allow ran polymerase to bind
- promoter
2. Enhancer
How does transcription factors prepare a promotor to receive RNA polymerase
- the first transcription factor to bind is attracted to a part of the promoter called the TATA BOX.
- 1st Transcription Factor attracts others including those that bind at the ENHANCER
(In all TF binds to the TATA IN THE PROMOTOR and the ENHANCERS. - This triggers the RNA polymerase to bind and titian can begin
Basically how does transcription factors turn genes off or on
by responding to stimuli
