Transcription (Eukaryotes) Flashcards
What are the three functional elements required for replication and stable inheritance of eukaryotic chromosomes?
Origins for initiation of DNA replication
Centromere
Two ends (telomeres)
What is chromatin (vs. chromosome)?
Chromatin is common state for genomic DNA, only condenses into chromosomes at cell division
What are histones?
Major protein component of chromatin
Small very basic proteins
What are the five types of histones?
H1
H2A
H2B
H3
H4
Why is H1 histone important for nucleosome?
Helps clamp the DNA onto nucleosome and participates in high-order chromatin folding
What is histone acetylation?
Reversible modification of lysines in the N-terminal of the core histones
Alters charge of histone protein
What is the result of histone acetylation?
Reduced binding to DNA
Destabilization of chromatin
True or false: Chromatin is not the protein-DNA complex
False: it IS the protein-DNA complex in which interphase chromosomes exist in nucleus
What are the two forms of chromatin?
Condensed form:
Extended form:
Difference between heterochromatin and euchromatin
Hetero: cell is less active in gene transcription, highly dense and compact
Euchromatin: more active in gene transcription, loose and less compact
What are the types of modification?
Phosphorylation of serines
Methylation of lysines
Acetylation of lysines:
What happens to chromatin when there are acetylated histones?
Histone acetylation relaxes and opens chromatin which allows access for RNA polymerase
What other thins influence chromatin unpacking?
Transcriptional activators
What are telomeres?
Repeats of sequence TTAGGG at extreme ends of chromosomes
What are the functions of telomeres?
Protection from enzymatic degradation
Allow ends of linear DNA to be replicated
What provides the end-plating function for chromosome ends?
Telomerase
What can’t polymerase synthesize? And why is that a problem?
Extreme ends of DNA molecules
Gradual shortening could lead to deletion of important info.
What does telomerase add?
Adds many copies of GTTGGG nucleotide sequence (telomere)
Where is telomerase only found?
Germ and sex cells
What happens with telomerase in cancer cells?
May lead to proliferation of tumours
How is telomerase important for cancer therapies?
Elimination of telomerase activity in somatic cells could protect from cancer
How is transcription different in eukaryotes?
3 RNA polymerases
Most mRNA transcribed by RNA pol II
Explain the RNA polymerase II transcription-initiation complex
Required general transcription factors
Proteins in this complex assemble in specific order
What regulates the assembly of transcription-initiation complexes and rate at which transcription is initiated?
Concentration and activity of activators
What is the basic principle of transcriptional activation?
Phosphorylation of RNA pol II complex
What is an example of a highly conserved promoter in eukaryotic DNA?
The TATA box
What binds to the TATA box DNA?
Conserved C-terminal domain of TBP
Describe the mRNA transcription in Eukaryotes
- Most mRNA made by RNA pol II
- Initiation requires loads of proteins
- Still works like in bacteria
- Promoter sequences are recognized (more complex)
- Basic function of RNA pol is the same
How is the activation of RNA pol regulated?
By mediators binding the polymerase general transcription factors and transcription factors
How is transcription regulated?
By signal transduction pathways
Receptors or signal transduction pathways
How do transcription factors work?
Bind directly to DNA by hydrogen bonding between amino acid side chains and bases
What can different transcription factor do?
Promote transcription - kinases
Inhibit transcription - dephosphorylases
What undergoes modification during transcription?
Protein encoding RNA to produce final mRNA that is translated
What is RNA splicing?
Primary transcripts are splice to remove non-coding region (introns) from coding regions (exons)
