Cycle 7: Transcription & Translation Flashcards
What does tRNA do?
bring amino acids to the ribosome for assembly into the polypeptide chain
What is the start codon/amino acid?
AUG
Methionine (Met)
What are the stop codons?
UAA
UAG
UGA
What happens when a stop codon is reached?
polypeptide synthesis stops and the new polypeptide chain is released from the ribosome
Why is it important to remain in the correct reading frame?
insertion/deletion causes all bases to shift changing all codons –> amino acids which can change the translated protein
What are the two parts of a gene? What are their functions?
- promotor: control sequence for TRANSCRIPTION
- transcription unit: section of gene that is COPIED into an RNA molecule
What is pre-mRNA?
first transcript of a eukaryotic protein-coding gene, which is processed in the nucleus to form TRANSLATABLE mRNA
Where is mature mRNA translated?
ribosomes in cytoplasm (after leaving nucleus from processing)
What is the purpose of the 5’ cap?
- protects single stranded mRNA from degradation
-the site where ribosomes attach at the start of translation instead of SD box
When is the 5’ cap added?
soon after transcription begins
How is transcription terminated in eukaryotes?
near the 3’ end of the gene is a DNA sequences that is transcribed into the pre-mRNA called the POLYADENYLATION SIGNAL
protein bind to the signal in the RNA and cleave it just downstream
this signals RNA polymerase to stop transcription
poly(A) polymerase adds a chain of adenine nucleotides
Do the 5’ cap and poly A tail need complementary base pairing?
NO! guanine 5’ cap and poly A tail are just added
What is the poly A tail purpose?
enables mRNA to be translated efficiently and protects it from attack by RNA-digesting enzymes in the cytoplasm
What are introns?
What are exons?
intervening sequences that interrupt the protein-coding sequences and are spliced out only in eukaryotes!
introns are trasncribed into pre-mRNA but are removed from pre-mRNA
exons - AA coding sequence present in pre-mRNA translated to proceed a polypeptide
What is mRNA splicing?
remove introns and join exons in pre-mRNA in nucleus
What is a spliceosome?
a complex formed between the premRNA and small ribonucleoprotein (snRNA and protein = snRNP) particles
cleaves pre-mRNA to released intron
What does the snRNPs do?
bind to an intron pre-mRNA and form active spliceosome
How is the reading frame intact during splicing?
complementary base pairing region of snRNA and mRNA
What is alternative splicing?
mechanism that joins exons in different combinations to produce different mRNAs from a single gene which is evolved and not random
same gene -> diff mRNA -> diff protein
Why is alternative splicing beneficial?
increases variety of proteins without increasing genome size
What is translation?
assembly of amino acids into polypeptides on ribosomes
Where does translation occur in prokaryotes? eukaryotes? What does this mean?
prokaryotes: throughout cell - mRNA immediately available for translation
eukaryotes: cytoplasm (specialized genes are transcribed and translated in mitochondria or chloroplast) - must exit nucleus and is them translated
How is mRNA read? How is the polypeptide assembled?
5’ to 3’
N-terminal end to C-terminal end
How is mRNA read? How is the polypeptide assembled?
5’ to 3’
N-terminal end to C-terminal end
What does tRNA structure look like?
cloverleaf pattern with anticodon - base pairs with codon in mRNA
Where do ribosomes function in prokaryotes? eukaryotes?
prokaryotes: throughout cell
eukaryotes: only in cytoplasm - freely suspended or attached ER membranes
What are the 3 steps of translation?
- initiation - translation components assemble on the start codon of the mRNA
- elongation - assembled complex reads the string of codons in the nRMA one at a time while joining the specified AA into the polypeptide
- termination - complex disassembles after the last AA of the polypeptide is added
How is prokaryotic translation different?
rather than scanning from 5’ end of mRNA, the initiator Met-tRNA and GTP bind directly to the region of the mRNA with the AUG start codon
initiation complex is guided by ribosome binding site (instead of the start codon on mRNA) that base-pairs with a complementary sequence of rRNA in the small ribosomal unit
large ribosomal subunit then binds to the small subunit to complete the ribosome
GTP hydrolysis begins translation
How does termination occur?
release/termination factor binds to A site and causes ribosome to disassemble into its subunits
- this is a protein (not tRNA) so it can’t base pair with stop codon
What is a polysome?
multiple ribosomes attached to mRNA which increases the rate of polypeptide synthesis
Why is transcription and translation couple in prokaryotic cells? What does this mean?
no nuclear envelope
as soon as 5’ end of new mRNA emerges from RNA poly, ribosomal subunits attach to initiate translation
– much faster than eukaryotes!
What is alternative processing?
when ribosomes release polypeptide chains, they are inactive and new do have AA & organic groups removed and folding into final 3D shapes
removing different AA sequences increases the number of proteins encoded by a single gene
Missense mutation?
change sense codon to a sense codon for a different amino acid
Nonsense mutation?
change sense codon to a stop codon
Silent mutation?
changes sense codon to another codon for a same amino acid
Frameshift mutation?
insertion or deletion
Why can’t eukaryotic cells have transcription and translation occurring concurrently?
nuclear envelope separates the processes
eukaryotes, have pre-mRNA which then gets translated
Where can you find tRNA?
- nucleus when transcribed
- mitochondria, chloroplast
- cytoplasm
Where can you find RNA polymerase?
- synthesized in cytoplasm
- mito, chloro
- nucleus for transcription
What does the RNA transcript look like?
coding, sense, non-template strand
What is non coding RNA? coding RNA?
non coding: tRNA, rRNA, snRNA (does NOT get translated)
coding: mRNA
Which end of RNA is released first in transcription?
5’ end! (3’ to 5’ template)
Which ribosome is oldest?
closest to the 3’ end because translation occurs 5’ to 3’
What the the 5’ and 3’ UTR?
untranslated region present in DNA and mRNA that regulate translation but they are transcribed
What is the TATA box? What is -35 -10 region?
both section of promotor that are conserved
TATA box - recognized by transcription factors when determine specialization which causes RNA poly to bind
-35 -10: -10 is start sequence
What is the Open Reading Frame?
part of reading frame that has the ability to be translated containing start and stop codon
What is the SD box?
sequence in prokaryotic mRNA which rRNA is ribosome recognizes so ribosome aligns with mRNA for translation
What is the 3’ splice site sequence? What recognizes it?
N C A G G - recognized by snRNP (snRNP coupled with protein) to create spliceosome
must used comp base pair bc
Where does snRNA bind?
only to mRNA! it is the only one that does translated with introns
Where does prokaryotic transcription occur? eukaryotic?
prokaryotic: cytoplasm
eukaryotic: nucleus
What does RNA polymerase recognize in prokaryote? eukaryote?
prokaryotic: -35 and -10 regions in promotor to initiate transcription
eukaryotic: transcription factors that are bound to TATA box in the promotor to initiate transcription
How is prokaryotic transcription initiated?
RNA polymerase recognizes -35 -10 region in promotor
How does RNA polymerase recognize to begin transcription in prokaryotes? eukaryotes?
prokaryotic: recognizes sequence directly on promotor
eukaryotic: can’t recognize actual TATA sequence, only recognizes transcription factor
What are additional regulation regions in eukaryotes not in prokaryotes?
enhancer regions and promotor proximal regions
and transcription factors
How does the promotor compare in prokaryotes and eukaryotes?
not transcribed in both and recognized as DNA and not present in mRNA and premRNA
How is transcription terminated in prokaryotes?
terminator - sequence is inverted repeat that forms hairpin loop)
How does termination of transcription occur in eukaryotes?
cleavage site just after 3’UTE that is cut by site specific RNase
How care introns recognized by snRNPs?
RNA not DNA
Where is the poly A signal? How is it recognized?
within 3’ UTR
recognized by Poly A polymerase as RNA
Where does prokaryotic translation occur?
cytoplasm at the same time as transcription
Where does eukaryotic translation occur?
cytoplasm, ER, mitochondria, chloroplast
How is translation initiated in prokaryote?
ribosome recognizes SD box and its rRNA component comp base pairs with mRNA and then initiates translation at the start codon
How is translation initiated in eukaryotes?
ribosome recognizes 5’ cap and scans the 5’ UTR of the mRNA until it reaches AUG start codon
What does DNA base pair with?
self, DNA in rep, mRNA, tRNA, snRNA, rRNA (all during transcription)
What does mRNA base pair with?
self, DNA(transcription), snRNA(splicing pre-mRNA), rRNA (SD box), tRNA (translation)
What does rRNA base pair with?
DNA(transcription), rRNA, mRNA (SD box)
What does tRNA base pair with?
tRNA, DNA (transcription), mRNA (translation)
What does snRMA base pair with?
snRNA, mRNA in splicing, DNA (transcription_
What does proteins base pair with?
nothing
What is -10/-35 understood as and by?
DNA by RNA polymerase
What is TATA box understood as and by?
DNA by transcription factors
What is ATG & TAG/TGA/TAA/TGA understood as and by?
mRNA by tRNA with its anticodon and release factor
What is the terminator understood as and by?
RNA (mRNA - hairpin loop) by RNA polymerase
What is polyA signal understood as and by?
pre-mRNA polyA polymerase
What is the cleavage site understood as and by?
pre-mRNA by RNase
What is intronic splice sites understood as and by?
pre-mRNA by snRNPs
What is SD box understood as and by?
RNA (mRNA) by rRNA in ribosome – not found in tRNA or rRNA or snRNA bc no translation
What is exons understood as and by?
RNA by tRNA
What is a polyribosome?
ribosome complex with peptide chain
