How Genes Make Proteins and Cells Flashcards
What is the central dogma of molecular biology?
It describes the process of transcription and translation.
- Genetic information is stored in DNA
- stored in genes
- mRNA copy of a gene is made using DNA as a template (transcription)
- DNA -> mRNA
- polypeptide chain is made using the mRNA as a template (translation)
- mRNA -> polypeptide chain -> protein
What is a gene and the main components of one?
- A gene is a region of DNA that provides instructions to man an RNA molecule
- All genes have the same basic structure
- Promotor: region that controls gene expression
- Transcribed region: section of the gene that is copied into mRNA
What does the transcribed region of a gene in a eukaryote contain?
The transcribed region in eukaryotic genes contains exons and introns:
- exons are the translated regions of a gene
- introns are the untranslated regions
- introns have to be spliced out of mRNA before translation
- the transcribed region in prokaryotic genes has no introns so therefore they don’t have the ability to splice mRNA
How does RNA pol use the transcribed region?
RNA polymerase is the enzyme that makes mRNA
- uses DNA as a template to make mRNA
- mRNA will have the exact sam sequence as one of the two DNA strands
- except DNA has a T (thymine) base where RNA has a U (uracil) base.
Describe the process to get from Transcription to Translation phases of replication
In eukaryotes the mRNA must be processed before it is ready to be translated
- introns removed (spliced out) so that only the protein-coding sequence remains
- some protective elements added to end of mRNA to prevent degradation before protein can be made (5’ G cap and poly-A-tail)
In eukaryotes, after transcription the mRNA is exported out of the nucleus for translation
- prokaryotes do not have a nucleus, so can transcribe and translate mRNA simultaneously
Describe the promotor region of a gene
The promotor region of a gene controls transcription
- contains transcription factor binding sites and an RNA polymerase binding site
- binding sites are short, specific, DNA sequences recognised by the transcription factor or RNA polymerase
Describe gene expression (aka. transcriptional control)
A gene is expressed or ‘turned on’ when it is transcribed
- control of gene expression is extremely important to the normal functioning of cells
RNA polymerase:
- Enzyme that makes RNA
- must be told to bind to a promotor before an mRNA can be made
Transcription factors:
- proteins that bind DA and control promotor binding of RNA polymerase
- Two kinds:
- activators: ‘turn on’ gene expression (by helping RNA pol bind)
- repressors: ‘turn off’ gene expression (by preventing RNA pol from binding)
- genes can have multiple transcription factors that control their gene expression
Describe the transcriptional factor called activators
These encourage RNA polymerase binding and creation of mRNA (transcription)
- may need more than one activator to transcribe mRNA
- They form physical connections to the RNA pol to encourage it to bind correctly
Describe the transcriptional factor called repressors
Prevent RNA polymerase from binding and prevent mRNA from being made
- can have more than one repressor - especially if it is very important for the gene to stay ‘off)
- these block the physical connection between activators and RNA pol
Why is transcriptional control important (the general idea)?
So that we are not a blob of identical cells.
- every cell has the same DNA, but there are different protein coding genes and different proteins can be made with these, depending which is activated and repressed.
Why is transcriptional control important (key reasons)?
transcription is a key control point:
- if a gene is transcribed (expressed), it can be used to make a protein
- if a gene is not transcribed, it can’t be used to make a protein
transcription factors determine if a gene is transcribed
transcription factors also determine how much a gene is transcribed
- how many mRNA copies (and so how much protein) should be made
transcriptional control is essential for making cells different to each other
- if all genes were always ‘on’, the insides of cells would be chaos
- different cells need different proteins to do their jobs
Describe how signal cascades are related to transcriptional control
Which transcription factors are present in each cell-type differs
- this determines which genes can/cannot be ‘on’ in each cell-type
Which transcription factors are present in a cell changes over time
Receptor proteins and their signal cascades can change which transcription factors are binding to genes
- encourages (or discourages) transcription based on the cell’s environment
- when a transcription factor is not in the nucleus, a signal cascade can activate it and allow it into the nucleus to activate a gene.
- Sometimes the end goal of a signal cascade is to activate a transcription factor
