Lecture 18 Flashcards
Transcription and Translation
What is Transcription?
A DNA segment into RNA.
DNA components vs RNA components?
DNA: 2-Deoxyribose Sugar and Thymine base
RNA: Ribose Sugar and Uracil base
Messenger RNA (mRNA)
500-10,000 nucleotides. Information to transport into proteins (genes). 5’ and 3’ untranslated regions carry features involved in initiating and terminating translation.
Although, Bacterial genes are 1kb long, mRNA can be longer due polycistronic.
What is Polycistronic?
The ability in of mRNA to encode several genes on the same RNA sequence.
Introns
Non-coding regions found in Eukaryotes –> size of >10kb in size. Get spliced out and removed before translation.
Transfer RNA (tRNA)
75-100 kb in size. Form secondary structures. that role is to deliver amino acids to the ribosomes. Has an anticodon which matches up with mRNA.
Ribosomal RNA (rRNA)
Structural components of ribosomes (1500-1900 (small subunits) or 2900-4700 (large subunits))
Eukarya - 80 S Ribosome: small 40S subunit + large 60S subunit
Bacteria - 70S Ribosome: small 30S subunit + large 50S subunit
Promoter
Direct RNA polymerase to initiate transcription at specific DNA positions.
Bacterial Promoters
Elements bound by sigma factors upstream of where transcription is initiated (ex. -10/-35). Direct RNA polymerase to promoter.
Alternative Sigma Factors
Direct RNA polymerase to different gene sets important in different conditions. –> co-regulated genes (ex. heat stress –> start to cool)
Eukarya Promoters
Several different elements bound to several different transcriptional factors to direct the initiation of transcription.
i.e. TATA binding protein (-20), GC box, CAAT box, Octamer box. (all upstream to where transcription begins)
Transcriptional factors (TBP, TFIIB) bind to upstream elements, one RNA pol directed to transcription site.
How many RNA polymerase does bacteria have?
One
How many RNA polymerase does eukaryotes have?
Three
What does TBP stand for?
TATA-binding protein that interacts with TATA box element in eukarya.
What is TFIIB role?
Additional transcription factor in eukarya that binds to the promoter region.
How many RNA polymerase does Archaea (similar to eukarya) have?
One
Has TBP and TFB transcriptional factors that interact with the promoter in TATA box.
How is bacteria transcription terminated?
Rho protein, makes RNA polymerase “pop-off” at specific DNA site.
OR Rho-Independent Termination where a hairpin structure forms complementary RNA stretches (G and C rich, followed by U segment)
How is eukaryotic transcription terminated?
Depends on RNA polymerase. RNA is modified after termination in eukarya: 5’ 7-methylguanosine cap added, 3’ poly A tail, Introns spliced out (exons are joined).
Translation in Bacteria
Transcription and Translation are coupled, they have spontaneously due to lack of nuclear membrane.
Charged tRNA interaction with mRNA
Assemble amino acids in a particular order. The tRNA anticodon corresponds to mRNA codon in sequence. Amino Acids delivered by tRNA build peptide bonds.
How many codons are there?
How many amino acids are there?
Start codon?
Stop codons?
64 codons. 20 amino acids.
Several codons for each amino acid, 3rd nucleotide is “wobble codon” meaning it usually leads to the same amino acid.
Start codon = AUG (Met)
Stop codons = UAA, UAG, UGA (Stop)
How are tRNA charged?
tRNA synthetase enzymes that attach amino acids to specific tRNA with matching anti-codons
Bacteria Interaction with rRNA (BOTTOM)
Interaction between Shine-Delgarno sequence (ribosome binding site) and specific site in 16S rRNA in small ribosomal subunit.
The 16S rRNA is complementary to the Shine-Delgarno sequence.
Polycistronic in Bacteria
Uses multiple shine-delgarno sequences on same mRNA to encode for multiple proteins.
What are the 3 sites? (Eukaryota Monocistronic)
A, P, and E sites
Charged tRNA’s enter A site, peptide bond formed in P site, and uncharged tRNA (lacking an amino acid) exits in E site. Ribosome moves along mRNA (only one), polypeptide released when stop codon is reached. Uses release factors (same in bacteria) for complex to fall apart at stop codon.
Chaperones
Amino acid side groups (R groups) which assist in folding proteins after leaving the ribosome. Allow correct folding.
Which group is often modified by the addition of chemical groups?
Eukaryal proteins
Protein Modification
Proteins with different chemical groups or carbohydrates can have affected folding. This can serve to activate or inhibit protein function.
What directs proteins to appropriate cellular locations?
Single Peptides (short AA sequences at N-terminus)
