Lecture 15: How genes make proteins/cells Flashcards
What is the “central dogma of molecular biology”?
The central dogma of molecular biology describes the process of transcription and translation. The genetic information stored in DNA is transcribed into mRNA using a DNA template strand. The mRNA is translated into a polypeptide chain, this chain folds to form proteins.
What are the key regulatory elements of a gene?
The regulatory region consists of a promotor region which controls gene expression. The promotor region contains transcription factor binding sites and an RNA polymerase binding site.
Binding sites = short, specific DNA sequences
What is the difference between a Eukaryotic and Prokaryotic gene?
Transcribed Eukaryotic genes have introns and exons whereas transcribed prokaryotic genes only have exons. Prokaryotes do not have the ability to splice mRNA.
What are the key elements of a Eukaryotic genes transcribed region?
The transcribed region contains exons (translated regions) and introns (untranslated regions). This is the DNA region that will be transcribed into mRNA by RNA polymerase II and then translated to protein.
What is a gene?
A region of DNA that provides instructions to make an RNA molecule. All genes have the same basic structure:
- Promotor and transcribed region
Briefly outline the process of transcription:
A gene is expressed or “turned on” when it is transcribed. The enzyme RNA polymerase uses DNA as a template to make mRNA, which will have the exact same sequence as one of the 2 DNA strands. (Except T -> U)
What must happen to the transcribed mRNA before translation can occur?
In Eukaryotes the introns must be spliced so that only the protein-coding sequence remains. A 5’ Gcap and a poly-A tail are added to the ends of the mRNA to prevent degradation. The mRNA is then exported out of the nucleus into the cytoplasm for translation.
Note: There is no nucleus in Prokaryotes so they can transcribe and translate mRNA simultaneously.
What is a transcription factor?
Transcription factors are proteins that bind DNA and control the promotor binding of RNA polymerase. They use physical connections to turn genes “on” (activators) or “off” (repressors). They also determine how much of a gene is transcribed.
How do activators control gene expression?
They encourage RNA polymerase binding and creation of mRNA (transcription).
Note: may need more than one activator to transcribe mRNA.
How do repressors control gene expression?
They prevent RNA polymerase from binding and prevent mRNA from being made.
They can also prevent the physical connection between activators and RNA polymerase.
Note: can have more than one repressor especially if it’s important for a gene to stay “off”
What is transcriptional control and why is it important?
Transcriptional control is how cells regulate the turning on/off of genes.
Transcriptional control is essential to making our cells different to each other - different cells needs different proteins to carry out their functions.
If every cell in the body has the same genetic code, how is it that different organs of the body are so unique?
Each cell type expresses different genes. ~10,000 are expressed in all cells and ~1000 to ~2000 are only expressed in specific cell-types. The type of transcription factor present in each cell-type differs which determines which genes are turned on/off in each cell.
Examples:
A transcription factor only made in the liver allows the gene GYS1 to be transcribed and translated into glycogen synthase
A transcription factor only made in the pancreatic beta cells allows the gene INS to be transcribed and translated into insulin
Do the transcription factors present within a cell change?
Yes, the transcription factors present in a cell change over time and receptor proteins and their signal cascades can change which transcription factors are binding to genes.
