Gene Expression Flashcards
Genes
sequences of DNA that code for diffrent RNA’s
mRNA
codes for proteins various functional RNA’s
During embryonic development
- many diffrent cell types are developed
- they all have the same genetic material
cloning experiments
proof that adult cells contain entire set of genes needed to form the whole organism
control of Gene Expression
The amount of DNA is not correlated with the complexity of an organism
Mammalian genome
several billion nucleotides
- Enough to code 3 million proteins
- Yet only 60,000 proteins likely
- Therefore, only 1-2% of the DNA codes for essential products ( proeins and functional RNA’s)
Functions of the “extra” DNA?
- introns
- regulatory sequences
- accumulated genetic noise
in our bodies, hundreds of different cell types carry out a variety of specialized functions-
results of different genes being switched on in these cells
Cells use only some of the genes they have in the ______?
genome
Differences between cell types depend on the precise control of gene expression-
cells make and accumulate different sets of RNA and proteins.
Differences in gene expression between different cell types are illustrated by the protein______?
composition
Some proteins common to almost all cells of a organism
housekeeping proteins
housekeeping proteins
- structural proteins of chromosomes
- DNA and RNA polymerase
- DNA repair enzymes
- ribosomal proteins
- enzymes of glycolysis
- cytoskeletal proteins
Specialized proteins-
responsible for the distinctive properties of different cell types.
it is estimated that a typical differentiated human cell may express-
10,000-20,000 genes ( out of 30,000) at any time based on the number of diffrent mRNA sequences present)
From DNA to proteins
- multistep process
- all steps can be possibly controlled and regulated:
- Transcription
- RNA processing
- RNA transport
- Translation
- Protein activity
Transcription Control
- Most important from of gene regulation
- turns genes “on” and “off”
- regulates reate of transcription -expression
- mediated by DNA- binding gene regulatory proteins
In addition to the promoter genes have regulatory DNA sequences:
- used to switch genes “ on” and “off”
- 10 to 10,000 base pairs in length
- can respond to a variety of signal
- serve as binding sites for regulatory proteins
* gene activator proteins
*gene repressor proteins
_ may be lacated a great distance from the gene regulated In fact the combination of DNA sequences and its associated proteins acts as the transcription control switch
Hundreds of regulatory DNA sequences identified in cells-
each recognized by one or more gene regulatory proteins
Surfaces of gene regulatory proteins fot tightly to double helix of the regulatory ________ _______?
DNA sequences
Most often gene regulatory proteins insert into the major groove of the DNA helix and make multiple hydrogen and ionic bonds, and hydrophobic interactions with the edges of base ppairs exposed in the grooves of double helix without disrupting bonds between bases.
DNA- protein interactions
one of the strongest and most specific interactions known in biology.
Gene regulatory proteins contain very stable folding patterns (‘motifs”) that fit into the groove of DNA helix.
Common structural “ motifs”
- Homeodomain motif
- zinc finger motif
- Leucine zipper motif
in all motifs-___?
one or more alpha-helices from the protein bind to bases in the major groove of the DNA double helix.
Repressors and Activators of Transcription:
two ways to turn genes off
Negative regulation
_ binding of a repressor protein turns the gene off
- repressors- molecules that bind to a specific region of DNA to prevent transcription of an adjacent gene
Positive regulation
- Binding of an activator protein turns the gene on
- Activators - molecules that bind to the promoter and enhance
