7.2 Transcription and gene expression (HL) Flashcards
What are promoters?
Non-coding sequence/ region of DNA responsible for initiation of transcription
How do promoters help production of polypeptides?
They act as binding sites for RNA polymerase, which is responsible for formation of covalent bonds between nucleotides that synthesize RNA/mRNA for polypeptides.
How is binding of RNA polymerase to promoter mediated?
Controlled by multiple transcription factors in eukaryotes
What are operators?
They also regulate transcription however usually through inhibition
What are repressors?
Proteins that bind to operators to prevent RNA polymerase from transcribing
In a lac operon, does the lactose need to be broken down or made and why?
When lactose is present, enzymes need to be made to break it down to provide energy for the prokaryote.
How does a lac operon work?
- Lactose binds to the repressor
- Repressor cannot bind to the operator
- RNA polymerase binds to the promoter allowing genes that produce proteins to be transcribed
- mRNA is used to make enzyme to break down lactose after which repressor is free and it will bind to the operator again
Why does transcription need to be inhibited in a lac operon?
If lactose is not present, there is no need to transcribe enzymes for it. Hence, it is more energy efficient for the prokaryote
Similarities and differences between gene expression in prokaryotes and eukaryotes
They both have promoters however eukaryotes don’t have operators. Instead they have enhancers and silencers
What is an enhancer?
Coding sequence that binds to activator proteins to increase rate of transcription
What is a silencer?
Coding sequence that can bind to repressor proteins to block or reduce rate of transcription
How can environment of an organism impact gene expression?
Exposure to pathogens, chemicals, toxic materials. Hair and skin color can be affected by sunlight and temperatures.
What is a morphogen?
Chemical that affects gene expression by regulating transcription factors
How does environment affect fur pigmentation in Himalayan rabbits?
Gene C controls pigmentation. It is active when temp is between 15-25C. At higher temp, it is inactive so fur will be white as no pigment is produced. In colder weather, the rabbit’s colder extremities (feet, nose, ears) produce a black pigment
What are specific examples of environmental impact on gene expression?
- Changing of flower color due to pH of soil
- Animals changing sex in response to social cues
What are the 3 regions of the gene
The promoter (where transcription is initiated), the coding region (region transcribed) and the terminator (where transcription ends).
How would you describe the concentration of morphogens in embryonic cells?
They contain uneven concentrations which results in activation and inhibition of different genes in different cells and hence why we are unique
What is a nucleosome made of?
- Histone H1
- DNA coils
- Octamer of histones
What part of nucleosome is exposed and what does this allow?
Tail of histone is usually exposed which allows it to be easily modified
2 chemical groups that affect transcription regulation
Acetyl and methyl group
Does methylation of histones promote or inhibit transcription?
Direct methylation usually inhibits however it can either promote or inhibit depending on location in genome
What can DNA methylation be affected by?
They can be associated with age, diet, environmental conditions or exposure to infectious agents
How are euchromatin and heterochromatin made?
- Heterochromatin is when DNA is bound more tightly to the histone to inhibit transcription making it less accessible
- Euchromatin is when DNA is loosened to make it more accessible to transcription factors
What are the types of methylation?
Hypermethylation is when genes are unable to express completely while hypomethylation is when a lot of genes are being transcribed and expressed
