12. Gene Expression Flashcards
What is a gene?
A stretch of DNA with a chromosomal locus that codes for a protein
What is mRNA?
Messenger RNA (mRNA) is a single-stranded RNA molecule that is complementary to one of the DNA strands of a gene so that it conveys genetic information from DNA to the ribosome
Which direction is mRNA made in ?
5’ to 3’
What direction is the protein made in?
From the N terminus to the C terminus
What are the 3 things needed to make a polynucleotide or polypeptide?
Enzyme
Activated substrates
Template
What are the 3 stage processes involved in Making a polynucleotide or polypeptide?
- initiation
- elongation
- termination
What are the 3 things needed in specific when making DNA during DNA replication?
enzyme : DNA polymerase
activated substrates : dNTPs - Deoxynucleoside triphosphate
template : DNA
What are the 3 things needed in specific when making RNA during transcription?
enzyme : RNA polymerase
activated substrates : NTPs
template : DNA
What are he 3 things needed when making a polypeptide during translation?
enzyme : ribosome
activated substrates : amino acids
template : mRNA
During DNA replication, describe what happens in initiation, elongation and termination.
• Initiation
- recognition origin of replication
- initiation proteins
- DNA polymerase
• Elongation
- 5’ to 3’ chain growth
• Termination
- when replication forks meet
During transcription, describe what happens in initiation, elongation and termination.
• Initiation
- promoter recognition
- transcription initiation factors
- RNA polymerase
• Elongation
- 5’ to 3’ chain growth
• Termination
- sequence dependent
What are promoters?
promoter is a region of DNA that leads to initiation of transcription of a particular gene. Promoters are located near the transcription start sites of genes, upstream on the DNA
What are transcription factors
Transcription factors are proteins that initiate and regulate the transcription of genes. Transcription factors bind to specific sequences of DNA called enhancer or promoter sequences. Some (general/basal)transcription factors bind to TATA box in a DNA promoter sequence upstream of the transcription start site and recruits RNA polymerase. Other transcription factors bind to regulatory sequences, such as enhancer sequences, and can either stimulate or repress transcription of the related gene.
Which sequence do transcription factors recognise?
TATAAAA
What does downstream mean?
Downstream is towards the 3’ end of the coding strand and 5’ end of the template strand
The direction in which mRNA is produced
What does upstream mean?
Upstream towards the 5’ end of the coding strand and 3’ end of the template strand
Opposite to the direction mRNA is made in
What is transcription?
Transcription is the process where a gene’s DNA sequence is copied (transcribed) into an RNA molecule
What is gene expression?
Gene expression is when a gene in DNA is “turned on,” that is, used to make the protein it specifies
How can the DNA affect its availability for transcription?
Is the DNA is more tightly wound around proteins into heterochromatin, it is less available so transcription factors cannot bind and the DNA cannot be transcribed.
If the DNA is loosely wound around proteins into euchromatin, it is more available so transcription factors can bind and the DNA can be transcribed
Where does RNA polymerase bind?
To the promoter region
What is the site on the DNA from which the first RNA nucleotide is transcribed called?
the +1 site, or the initiation site.
Describe how transcription factors can activate or repress transcription
Transcription factors can bind to enhancer (promoter) sequences upstream of the transcription site and where the core promoter is. This binding leads to a cascade to other proteins which may activate or repress transcription.
Some transcription factors activate transcription. For instance, they may help the general transcription factors and/or RNA polymerase bind to the promoter.
Other transcription factors repress transcription. This repression can work in a variety of ways. As one example, a repressor may get in the way of the basal transcription factors or RNA polymerase, making it so they can’t bind to the promoter or begin transcription.
What do general or basal transcription factors do?
They bind to core promoter sequences just upstream of the transcription start site and allows the binding of RNA polymerase to the promoter to start making mRNA
Summarise what happens during initiation of transcription
Transcription factors bind to the TATA box in the promoter sequence upstream of the transcription start site and causes RNA polymerase to bind to the promoter and start producing mRNA immediately.
Binding of other transcription factor to enhancer sequences, upstream of the core promoter sequence can either activate or repress transcription by affecting RNA polymerase from binding or basal transcription factors from binding
What happens during elongation of transcription?
- Dna strands seperate - Before transcription can take place, the DNA double helix must unwind near the gene that is getting transcribed. The region of opened-up DNA is called a transcription bubble.
- One strand is used as a template - the strand from 3’ to 5’
- During elongation, RNA polymerase “walks” along the template strand, in the 3’ to 5’ direction.
- For each nucleotide in the template, RNA polymerase adds a matching (complementary) RNA nucleotide to the 3’ end of the RNA strand.
- RNA polymerase always builds a new RNA strand in the 5’ to 3’ direction.
How is the coding strand different to the mRNA?
The mRNA made is nearly identical to the non-template, or coding, strand of DNA. However, RNA strands have the base uracil (U) in place of thymine (T), as well as a slightly different sugar in the nucleotide.
