7.2 (DNA Unit) Flashcards
Define gene expression.
- Gene expression is regulated by proteins that bind to specific base sequences in DNA.
- The activation of a gene that results in the formation of a protein
State two reasons why gene expression must be regulated.
- Cellular differentiation: all cells would carry all the sequences for all types of genes, but each cell type has a different function, thus some overtime is turned off.
- Insects change through a variety of body shapes during their life cycle due to the genes that get regulated throughout their life
Describe the use of twin studies to measure the impact of the environment on gene expression.
- Identical twins are born with the same DNA sequence, all throughout. They should produce the same proteins, however, their behavior can be different.
- Therefore what is affecting these changes in their gene expression would have to be due to environmental factors, how their cells are reacting to their surroundings.
Outline two examples of environmental influence on gene expression.
- UV exposure creates more melanin as it increases the expression of the melanin proteins.
- Smoking can increase the rate of DNA methylation, therefore turning off genes such as the tumor suppressor gene, increasing the risk of an uncontrolled cell division.
Outline the effect of methylation of nucleosome tails on rates of gene expression.
- They turn off genes, therefore decreasing gene expression
- The mechanism of this is still not clear.
Outline the effect of acetylation of nucleosome tails on rates of gene expression.
- Histone acetylation allows a less condensed DNA with higher levels of transcription.
- It neutralizes the charges on the histone proteins, preventing the attraction towards DNA
- This allows the DNA to be open for RNA polymerase II to come in and begin transcription.
Describe the initiation of transcription, including the role of the promoter, transcription factors, and RNA polymerase.
- Transcription initiates at the “promoter” region, which is a specific DNA sequence, that specifies to other molecules when transcription begins
- Transcription factors would bind/attach itself to the promoter region, which then would trigger the binding of the RNA polymerase
Describe elongation of transcription, including the role of nucleotide triphosphates and the direction of transcription.
- As the RNA polymerase zips down the DNA, it builds the mRNA by adding on trisphosphate nucleotides. The nucleotides would have 3 phosphate groups, which break down to provide the energy needed to create covalent bonds between the nucleotide backbones of the RNA.
- The RNA polymerase would build the mRNA in a 5’ to 3’ direction on the antisense strand in order to create a copy of the sense strand.
- The RNA polymerase would add on complementary base pairs to its RNA strand, the only difference would be the replacement of Thymine with Uracil.
Describe termination of transcription, including the role of the terminator.
- The RNA polymerase continues to unzip and transcribes the DNA codes to the RNA until it reaches the terminator, which is a sequence that ends the process.
- It releases the RNA polymerase and lodges the growing RNA strand.
- Once the RNA is made, the double helix reforms, and the RNA would move to the next step of RNA processing.
List two major differences in gene expression between prokaryotic cells and eukaryotic cells.
Prokaryotic Cells:
- Prokaryotic cells lack a cell membrane or any proteins, therefore the process of transcription and translation can occur at the same time, thus gene expression happens during transcription
- Prokaryotic cells do not contain “introns” therefore they can produce proteins right away.
- In prokaryote cells, a single mRNA can code for multiple genes.
Eukaryotic Cells:
- Eukaryotic cells have a cell membrane, therefore need to make a strand of RNA first then can go-to translation.
- Eukaryotic separation of the process allows it to modify the RNA strand before letting it leave as an mRNA.
- But in Eukaryotes, due to the multi-steps, the modified mRNA can only code for 1 specific type of protein to express.
Describe the three post-transcriptional modifications of pre-mRNA in eukaryotes.
Capping: adds a methyl group at the 5’ end of the transcribed RNA. Protects it from degradation by exonucleases. Allows it to be recognized by translation mechanism. (GTP: guanine triphosphate cap)
Polyadenylation: Addition of a poly-A-tail at the 3’ of the transcript. Stabilizes the RNA and the longer tail allows it to last longer and produce more proteins.
Splicing: The process where non-coding sequences (introns) are cut off on the RNA, leaving the coding sequences called exons to fuse together, making mRNA.
Describe the process of alternative RNA splicing.
A gene is transcribed from the DNA. One gene can encode for a few related proteins that are derived from the same genes by different splicing ways.
Outline an example of alternative splicing the results in different protein products.
In mammals, the protein tropomyosin is encoded by a gene that has eleven exons. Tropomyosin pre-mRNA is spliced differently in different tissues resulting in five different forms of the protein.
Outline the role of promoter DNA.
It is a region in the DNA that initiates the process of transcription. It also serves as a binding site for RNA polymerase
State the effect of DNA methylation on gene expression.
- Methylation of histone results in a promotes or inhibit transcription.
- Methylation of DNA, which adds a Methyl group onto the base cytosine, ends to decrease gene expression
