Unit 19: transcription and gene expression

Outline the role of promoter DNA.

It is a region in the DNA which initiates the process of transcription. It also serves as a binding site for RNA polymerase.

State two reasons why gene expression must be regulated.

(often proteins) they use the information of the gene to make a product.

List types of epigenetic tags

- Methylation and Acetylation

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.

Define "coding sequences" and "repetitive sequences" of DNA.

-Coding Sequences are the sequences that code for a certain protein that is expressed in the organism. -Repetitive Sequences (non-protein coding) are the sequences which does not code for a protein but is repeated over and over in the genome, they're also known as "tandem repeats."

Define epigenetic and epigenome.

-Epigenetic is the study of changes in phenotype as a result of variations in gene expression levels -Epigenomic is the study of all the epigenetic modifications (chemical tags) that is involved in telling the genome what to do (epigenome).

List two major differences in gene expression between prokaryotic cells and eukaryotic cells.

1) Prokaryotic cells lacks 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. Eukaryotic cells have a cell membrane, therefore needs to make a strand of RNA first then can go to translation. 2)In Prokaryotes, cells, a single mRNA can code for multiple genes. But in Eukaryotes, due to the multisteps, the modified mRNA can only code for 1 specific type of protein to express.

Outline the process of transcription, including the role of RNA polymerase and complementary base pairing

1) The elongation process continues until a stop codon is reached. 2) The codon does not recruit another amino acid, but instead a release factor for the translation to end. 3) The polypeptide then gets released and goes through modification. The ribosome disassembly and becomes 2 independent subunits.

Outline five functions of non-coding DNA sequences found in genomes, one of which must be the telomere.

1) The telomere is at the end of the chromosomes that helps protects it. 2)Regulates where, when and how much proteins are made. 3)Provides the code to make RNA 4)Might be left-over DNA from viral infections 5) "Junk DNA"

Describe the process of alternative RNA splicing.

A gene is transcribed from the DNA. One gene can encode for a few related proteins that is derived from the same genes by different splicing ways.

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 breaks 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 it's RNA strand, the only difference would be the replacement of Thymine with Uracil.

Outline the role of enhancers, silencers and promoter-proximal elements in regulation of gene expression.

Enhancers: are DNA codes that increases gene expression. Silencers: are DNA codes that decreases gene expression. Promoter-proximal elements: are any regulatory sequence in the DNA (enhancers, silencers etc).

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. this neutralizes the charges on the histone proteins, preventing the attraction towards DNA. Therefore, this allows the DNA to be open for RNA polymerase II to come in and begin transcription.

Outline an example of alternative splicing the results in different protein products.

Let there be exons 1, 2, 3, 4 in the transcribed gene. Alternative splicing allows there to be possible arrangements such as: 1-2-3 (protein A) 1-2-4 (proteins B)

State the effect of DNA methylation on gene expression.

Methylation of histone results in a promote or inhibit transcription.

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 the next step of RNA processing.

Define transcription

The process of copying the genetic code from DNA into the form of mRNA

Describe the use of twin studies to measure the impact of environment on gene expression.

They have the same DNA sequence so scientists can see how this changes

Outline the effect of methylation of nucleosome tails on rates of gene expression.

They turn off genes which decreases gene expression.

Describe the initiation of transcription, including the role of the promoter, transcription factors, the TATA box and RNA polymerase.

Transcription initiates at the "promoter" region, which is a specific DNA sequence, such as the TATA box, that specifies to other molecules when transcription begins. Transcription factors would bind/attach itself to the promoter region, which then would trigger the the binding of the RNA polymerase.

Outline two examples of environmental influence on gene expression.

UV and smoking

Discuss the role of reprogramming and imprinting on epigenetic factors.

Usually in cell division, the methylation pattern is inherited to the daughter cell. When a sperm and an egg meet, the epigenome gets erased and goes through "reprogramming". Up to 1% of the epigenome is not erased thus yielding a result called "imprinting".

Define gene expression

the appearance in a phenotype of a characteristic or effect attributed to a particular gene.