(bio) Unit 3 - Transcription an Translation Flashcards
Describe central dogma (3 steps)
- DNA replication (information and storage)
- RNA synthesis from DNA strand (information and carrier)
- Protein synthesis aka translation (Active cell machinery)
Difference between RNA and DNA
RNA - OH group on 2nd carbon (only uracil)
DNA - No OH group on 2nd carbon (only thymine)
What carbons are attached to what molecules to form nucleic acids?
Carbon 1: attached to base
Carbon 3: attached to phosphate
In what direction do nucleic acids grow? What direction does newly formed RNA travel along template strand?
- Nucleic acids grow in 5’ to 3’ direction
- Moves along 3’ to 5’ of template strand
What strand is DNA transcribed from
Template strand (non coding)
What bonds hold nucleic acids together?
Phosphodiester bonds (between phosphate groups) and hydrogen bonds (between bases)
Role of mRNA, tRNA, rRNA ?
mRNA: code for proteins
tRNA: adapters between mRNA and amino acids during protein synthesis
rRNA: involved during translation
What subunits does PROKARYOTIC RNA polymerase consist of? What are the functions of these subunits?
subunits sigma factor and core enzyme makes up the entire core enzyme aka holoenzyme.
These subunits synthesize the RNA based on template
Where does the prokaryotic RNA polymerase need to start polymerizing? What does this? Why does sigma need to bind to this?
sigma factor does this by recognizing promotor sequence (regions on non-template strand) and binds to it, located upstream of start of the gene.
Sigma needs to bind to this to properly orient the RNA polymerase holoenzyme for transcription at start site.
What are the two key regions of the prokaryotic promoters sequence.
-10 box and -35 box that will be identified by sigma
(10 and 35 bases upstream from start site)
How does sigma work during Initiation and elongation of transcription in bacteria
- sigma opens the helix
- allows ribonucleoside triphosphate (NTPs) to enter active site and begin transcription
- sigma factor is released once transcription in bacteria begins , only gets things starting correctly
How does termination of transcription in bacteria (prokaryotes) work?
- The sequence reaches a termination signal in DNA template
- The sequence will remove itself from the RNA polyermase and create a hairpin strucutre.
What makes eukaryotic DNA structure different from prokaryotic DNA
Eukaryotes DNA molecules combine with proteins to adopt higher order strucutre - chromatin which consists of DNA strand wrapped in histone proteins
What is the difference between prokaryotes and eukaryotes in terms of types of RNA Polymerases
Eukaryotes have 3 RNA polymerase (but it is focused on RNA polymerase II) - consists of a large team of accessory proteins called general transcription factors
Prokaryotes have 1 RNA polymerase and it consists of a sigma factor
What is the difference between prokaryotes and eukaryotes in terms of promoter sequences?
Eukaryotes have many promoters, an example is the TATA box within the promoter (30 bp upstream)
Prokaryotes have -10 and -35 box
Describe the initiation of transcription in eukaryotes
A TATA box is recognized by the TATA binding protein (TBP) which is a subunit of TFIID.
Binding of the TFIID distorts the helix at the transcription starting point and allows similar structures (TBP’s) to pile on to form transcription initiation complex.
Transcription factors comes off (TFIID stays) once the DNA starts transcription
What is the difference between the mRNA processing of eukaryotes and prokaryotes at the end of transcription?
Eukaryotes: mRNA undergoes a lot of processing before being shipped out of nucleus
- modifications to the transcripts carried out by sources associated with the phosphorylated tail of RNA polymermase II
- capping, splicing, poly A tail (polyadenylation)
Prokaryotes: not in the nucleus
mRNA Capping and Polyadenylation… Where are each modifcations found and their purpose
5’ cap : At the beginning of newly synthesized mRNA, consists of guanasine, 3 phosphates and a methyl group, important for translational machinery later
Poly-A tail: found on newest part or 3’ end of new mRNA , protects fron degrdation
What is splicing? When does it occur?
separating coding stretches from transcripts from non coding, separating exons and introns of Eukaryotic transcript.
Coding regions (exons - “expressed”) are kept
Non coding regions (introns) are discarded
Occurs when mRNA is still being transcribed after capping
What is the difference between primary RNA transcript and spliced (mature) transcript
Primary RNA transcript: includes exons and introns
Spliced transcript: includes only the exons
How are introns spliced and by what? What happens to introns after?
A branch point cuts the sugar phosphate backbone of the intron area. Done with spliceosomes (a RNA protein complex)
These cut ends forms covalent bonds with ribose sugar group to form a lariat strucutre
Which is eventually degraded in the nucleus
What type of mRNA can be exported from nucleus? What are those conditions?
mature mRNA
- cap and poly A tail are marked by proteins
- group of proteins binds properly to spliced mRNAs
then mRNA can transport out of nuclear pore
How is an amino acid specified?
Takes 3 bases from RNA to form a code (amino acid)
Many codons can specify for one amino acid, with the exception of methionine (Met) and tryptophan (Trp)
How is the genetic code almost universal? What are some exceptions to this?
- same codons assigned to same amino acids
- same stop and start signals
Exceptions in mitochondria from animal cells:
- stop codon is a regular amino acid on mitochondria
