Week 4 - Transfer of genetic information in eukaryotic and prokaryotic cells. Flashcards
Describe gene expression in eukaryotes
Transcription % translation
is gene expression.
Read gene and translate into proteins
Define gene expression
Expressed genes include
Definition:
Information encoded in a gene translated into protein or RNA.
2 steps:
transcription and translation
Expressed genes include both
- Genes transcribed into mRNA then translated into proteins
- Genes transcribed into RNA (e.g. rRNA and tRNA) but NOT translated into protein.
Short about transcription and translation
https://www.youtube.com/watch?v=oefAI2x2CQM&t=65s
https://www.youtube.com/watch?v=oefAI2x2CQM&t=65s
Transcription: – process - making a copy of genetic information stored in DNA strand →complementary strand of mRNA, with help from RNA polymerases.
Translation: protein biosynthesis.
mRNA transports coded info → gets decoded, (prod.)→ produce specific sequences of amino acids in pp-chain.
Schematic rep. of difference in gene expression
Eukary. vs prokary.
Name the main differences in the image
Main difference is determ,ined by difference in cell structure.
We can see that since prokary. dont have membranebounded organells → all processes happen in same place.
Meaning = Both
- copy of info and synthesis of mRNA
- proteinsynthesis
takes place in cytoplasm. No spacial division of these processes and quite parallel in time (still in a sequence but happens after each other)
Eukaryoptic cell: divided in time and place.
Synthesis of mRNA in nucleua
Compare transcription in eukaryotes and prokaryotes
Combine with flashcard above?
Transcription
Intitiation
the cluster of proteins assembles on the promoter sequence at the upstream (5’) end of a gene and forms the transcription initiation complex
HOW? LOOK AT THE IMAGE BELOW
6.42 lecture 4!
During initiation of transcription RNA polymerase II forms a transcription bubble and begins
polymerization of ribonucleotides (rNTPs) at the start site, which is located within the promoter 5’ UTR region
Cellular RNA polymerases unwinds and separates approx. 14 base pairs of DNA around the transcription bubble (where one of the strands serves as a template for RNA synthesis)
- this allows the RNA polymerase to access the template strand and begin synthesizing the RNA molecule
Transcription initiation is considered completed when the RNA polymerase has succesfully added and linked the first two ribonucleotides (rNTP) via a phosphodiester bond
(a type of chemical bond that connects the sugar of one nucleotide with the phosphate group of another forming the backbone of the RNA molecule)
RNA polymerase in eukaryotes and in prokaryotes
Why do eukary. have 3 RNA polymerase
In eukaryotes exist 3 RNA polymerases:
◦ RNA polymerase II – initiate transcription in vast majority of protein coding genes. Task is to form transcriptional bubble.
◦ RNA polymerase I – initiate transcription in rRNA precursor coding gene
◦ RNA polymerase III – initiate transcription in other RNA coding genes
In prokaryotes
◦ exists 1 RNA polymerase with less complex structure
We have 3 polymerase because of regulation and process is different between protein-coding and rna-coding genes.
10.40 lect. 4
What is a transcription bubble?
8.20 lecture 4
Transcription
Elongation
- During the stage of strand elongation, RNA polymerase moves along the template DNA one base at a time, opening the double-stranded DNA in front of its direction of movement and
hybridizating the strands behind it - One ribocleotide at a time is added to the 3’ end of the growing (nascent) RNA chain during strand elongation by the protein complex polymerase
- Approximately eight nucleotides at the 3’ end of the growing RNA strand remain base-paied
to the template DNA strand in the transcription bubble
◦ Template strand: 3’-5’ (antisense strand)
◦ Coding strand: 5’-3’ (sense strand) - Synthesis of the RNA transcript proceeds in 5’ - 3’ direction, wheres the strand of the gene which is transcribed and serves a template is read in 3’ - 5’ direction
- Transcription continues trough both – exonic and intronic regions of the gene in the presence of elongation factors (stimulate elongation)
- The elongation complex, comprising RNA polymerase, template DNA and the growing (nascent) RNA strand, is very stable
- RNA synthesis occurs ate the rate ~ 1000nt/min at 37°C, the elongation complex must
remain intact for more as 24h
Transcription
Termination
(3/3)
- During transcription termination the completed RNA molecule, or primary transcript is released from the RNA polymerase and the polymerase dissociates from template DNA
- AATAAA sequence is the signal for the bound RNA polymerase to terminate transcription
(Not AAUAAA)
Sense and anti-sense strand?
Explain without looking at image which is the template strand.
Explain transcription
Complete the sentence
Primary conscripts of protein coding genes are precursor genes (pre-mRNAs) that must go several modifications termed as …. to form a ….
Primary conscripts of protein coding genes are precursor genes (pre-mRNAs) that must go several modifications termed as (RNA processing) to form a (functional mRNA)
Explain mechanism and biological role of RNA processing:
5’ capping
3’ modification
splicing
Alternatives splicing
explain the role of involved enzymes
At the 5’ end of a growing RNA chain appearing from the surface of RNA
polymerase II, it is immediately acted on by several enzymes that together synthesize the
5’ cap (7-methylguanylate). This process is called capping.
This cap protects the mRNA from enzymatic degradation, assists in export to cytoplasm and has a role in the initiation of the translation in the cytoplasm.
Processing at the 3’ end of pre-mRNA involves cleavage by an endonuclease to provide a
free 3’-OH group to which adenosines are added by an enzyme called
poly(A)-polymerase.
The final step in the processing of mRNA molecules is RNA splicing in which the internal cleavage of a transcript to remove the introns, the ligation of coding exons. Splicing is ensured by a protein complex called spliceosome.
Alternative splicing
SIMPLE
Process which inlude the exons with pre mRNA transcript differently joined or skipped → diversity when it comes to synthesis protein.
One gene can synthesize different amino acids → alternative splicing gives protein isoforms.
CANT CUT OUT first and last exon