Lecture 15 - How genes makes proteins and cells Flashcards
What is the central dogma of molecular biology?
- Genetic info is stored in DNA as genes
- mRNA copy of a gene is made using DNA as a template (transcription)
- Polypeptide chain is made using mRNA as a template (translation)
What is a gene?
a region of DNA that provides instructions to make an RNA molecule
What do all genes have?
Promoter, Transcribed region
What is the Promoter region?
Region that controls gene expression
What is the transcribed region?
Section of the gene that is copied into mRNA
What does the transcribed region of eukaryotic genes contain?
exons, introns
What are exons?
Are the translated regions of a gene
What are introns?
The untranslated regions
What happens to introns before translation?
They are spliced out of mRNA
What does the transcribed region of Prokaryotic genes lack?
Introns
What ability do Prokaryotes NOT have?
Ability to splice mRNA
What enzyme makes mRNA?
RNA polymerase
How does RNA polymerase make mRNA?
Uses DNA as a template to make mRNA, meaning the mRNA will have the exact same sequence as one of the two DNA strands except U is in place of T
How is mRNA processed before translation?
- Introns removed (spliced out) so that only the protein-coding sequence remains
- Some protective elements are added to the ends of the mRNA to prevent degradation
Where does translation occur in eukaryotes?
mRNA is exported out of the nucleus for translation
How does translation differ for prokaryotes?
since they do not have a nucleus they can transcribe and translate mRNA simultaneously
What does the promoter region contain?
transcription factor binding sites and an RNA polymerase binding site
What are binding sites?
short, specific, DNA sequences recognised by the transcription factor or RNA polymerase
What does it mean when a gene is transcribed?
the gene is expressed (turned on)
What is extremely important to the normal functioning of cells?
Control of gene expression
What are transcription factors?
Proteins that bind DNA and control promoter binding of RNA polymerase
What are the kinds of transcription factors?
- Activators (turn on gene expression)
- Repressors (turn off gene expression)
How many transcription factor control a genes expression?
Multiple
What do Activators do?
- Encourage RNA polymerase binding and creation of mRNA
- May need multiple activators to transcribe mRNA
What do repressors do?
- Prevent RNA polymerase from bind and prevent mRNA from being made
- Can have multiple repressors especially if it is very important for gene to stay ‘off’
How do transcription factors turn genes on/off?
Through the use of physical connections
How do repressors work?
Blocks the physical connection between activators and RNA polymerase
How many cells are in the human body, and into how many cell types are they split?
The human body is made up of approximately 30 trillion cells, split into around 200 cell types.
Does every cell in the human body have the same DNA?
Yes, every cell has the same DNA.
How many protein-coding genes are there in human DNA, and how many different proteins can be made from these genes?
There are about 21,000 protein-coding genes, and they can make around 85,000 different proteins.
How many genes does each cell type express?
Each cell type expresses approximately 11,000 to 17,000 genes.
How many genes are expressed in all cells, and why are they needed?
About 10,000 genes are expressed in all cells, and they are needed for basic cellular functions.
How many genes are expressed only in specific cell types?
Approximately 1,000 to 2,000 genes are expressed only in specific cell types
How are the remaining genes expressed across cell types?
The rest are expressed in some, but not all, cell types.
Why is transcription considered a key control point in gene expression?
If a gene is transcribed (expressed), it can be used to make a protein; if it is not transcribed, it cannot be used to make a protein
What determines if a gene is transcribed?
Transcription factors determine if a gene is transcribed.
What else do transcription factors determine besides whether a gene is transcribed?
Transcription factors also determine how much a gene is transcribed, including how many mRNA copies should be made and, therefore, how much protein should be produced.
Why is transcriptional control essential for cellular diversity?
Transcriptional control is essential for making cells different from each other because if all genes were always “on,” the insides of cells would be chaotic, and different cells need different proteins to do their jobs
How do transcription factors differ between cell types?
The transcription factors present in each cell type differ, determining which genes can or cannot be “on” in each cell type.
Does the presence of transcription factors in a cell remain constant over time?
No, the presence of transcription factors in a cell changes over time.
How can receptor proteins and signal cascades affect transcription factors?
Receptor proteins and their signal cascades can change which transcription factors are binding to genes, encouraging or discouraging transcription based on the cell’s environment
What role does transcriptional control play in insulin signaling for fatty acid synthesis?
In insulin signaling, transcription factors are activated to bind DNA, leading to transcription/translation of proteins necessary for fatty acid synthesis for storage
How are tuxedo cats made?
- DUring embryonic development skin/fur cells must be told to add pigments.
- Pigment genes are turned on at a specific time in development, and turned off once pigment patterning is set
- Tuxedo cats turn their pigment genes off too early leaving white patches
