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93 Cards in this Set
- Front
- Back
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What happens in the presence of polysomes?
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mRNA translated by more than one ribosome at a time
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The study that found a link between non-gene parts of DNA with disease was performed by?
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>400 scientists from >30 labs around the world
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True or false: most mutations that affect disease are in genes.
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false
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What human diseases did researchers link the gene switches to? (5)
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multiple sclerosis lupus rheumatoid arthritis Crohn's disease celiac disease |
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What is "junk DNA" now often referred to as?
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dark matter
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What is a trait that's linked to gene switches? |
height
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True or false: protein synthesis is very energetically costly. |
true
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What is the complex that carries out protein synthesis composed of? (4) |
ribosome initiation factors mRNA charged tRNA |
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Where does the translation initiation complex assemble and disassemble? |
assembles at first mRNA codon disassembles at termination step |
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What direction is polypeptide synthesized in? |
N to C
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What are the four steps of translation? |
aminoacylation of tRNA initiation of 5' cap of mRNA elongation termination |
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binds the incoming tRNA
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aminoacyl site
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binds the tRNA with the growing peptide chain
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peptidyl site
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binds the uncharged tRNA before it leaves the ribosome
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exit site
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True or false: all ribosomes contain two subunits of unequal size. |
true
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What is an E. coli ribosome composed of? |
30S and 50S making 70S
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What is a eukaryotic ribosome composed of? |
40S and 60S making 80S
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True or false: proteins are fully synthesized before folding begins. |
false, fold as they're coming out of ribosome by chaperones present in cytoplasm
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What are the nucleotides between the 5' end of the mRNA and the first codon translated called?
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untranslated region (UTR)
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What is S-D? |
Shine-Dalgarno
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What directs protein synthesis machinery to the start site and where it is found? |
Shine-Dalgarno sequence UTR |
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True or false: S-D sequence is purine-rich. |
true
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Where is the S-D sequence located? |
10 bp upstream of the start site
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What does the S-D sequence specifically interact with and why? |
16S rRNA to correctly position the AUG codon in the A site
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What end of the 16S RNA does the S-D sequence also bind to? |
3'
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What binds mRNA to the ribosome? |
complementary base pairing between 3' end of 16S rRNA and the Shine-Dalgarno sequence
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Why does bacterial protein synthesis begin before transcription is complete? |
transcription and translation both occur in the 5' to 3' direction
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What do polyribosomes or polysomes require? |
multiple S-D sequences |
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What is bacterial protein synthesis initiated by? |
formylmethionyl tRNA
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binds only to the initiation codon
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f-Met-tRNAf
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What recognizes internal codons for methionine? |
tRNAm
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What converts methionine to formylmethionine? |
transformylase
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What site is the initiator tRNA in? |
P
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What does site A receive? |
aminoacyl-tRNAs
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What are the three steps in the elongation cycle?
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Positioning the correct aminoacyl-tRNA in site A Formation of a peptide bond Shifting mRNA by one codon |
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What catalyzes peptide bond formation? |
peptidyl transferase
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How many amino acids are added per second? |
20-40
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What helps the correct aminoacyl-tRNA insert into site A? |
elongation factor EF-Tu
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True or false: an EF-Tu-GTP complex binds to all aminoacyl-tRNA molecules.
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false, not initiator tRNA
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What ternary complex binds in the ribosomal A site? |
EF-Tu GTP aminoacyl-tRNA |
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When is the ternary complex stabilized? |
if the anticodon of the aminoacyl-tRNA correctly base pairs with the mRNA codon
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What happens if the codon and anticodon match? |
EF-Tu forms contacts with the ribosome and the peptidyl-tRNA in the P site; GTP is then converted to GDP and it and EF-Tu are released, leaving the correct aminoacyl-tRNA in the A site
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Where is peptidyl transferase activity contained? |
large ribosomal subunit
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What ribosomal proteins have substrate binding sites for peptide bond formation? |
23S rRNA and 50S
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What RNA has catalytic activity for peptide bond formation?
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23S rRNA
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When does tRNA move into E site? |
upon becoming uncharged (deacylated)
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Where are peptide bonds formed? |
P site
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new peptidyl-tRNA is moved from the A site to the P site, while the mRNA shifts by one codon |
translocation step
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What moves the ribosome by one codon? |
translocation
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What does elongation factor G do? |
hydrolyzes GTP to move mRNA by one codon
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Where is peptidyl-tRNA located?
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P site
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True or false: tRNA in the E site is disengaged from mRNA. |
true
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What does growing peptide chain extend from?
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peptidyl tRNA (Psite) through a tunnel in the 50S subunit
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When does newly synthesized polypeptide begin to fold? |
when it emerges from the tunnel
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True or false: elongation in eukaryotes is similar to E. coli. |
true
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What are the E. coli release factors? |
RF-1 RF-2 RF-3 |
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What happens at UGA, UAG, UAA? (3) |
translocation positions one of three termination codons in A site no tRNA molecules recognize these codons and protein synthesis stalls RF binds and causes hydrolysis of the peptidyl-tRNA to release the polypeptide chain |
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What are cleaved for each amino acid added to a polypeptide chain? |
four phosphoanhydride bonds
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What antibiotic changes shape of 30S portion and causes code on mRNA to be read incorrectly? |
streptomycin
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What antibiotic binds to 50S portion and prevents translocation—movement of ribosome along mRNA? |
erythromycin
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True or false: f-Met-tRNAf begins protein synthesis in eukaryotes. |
false, Met-tRNAi
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What is the initiator codon in eukaryotes? |
first AUG from the 5' end of the mRNA
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True or false: eukaryotic mRNA is circular. |
true, proteins that bind the 5' cap and poly A tail interact
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How many release factors do bacteria have? |
two
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How many release factors do eukaryotes have? |
one
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Where does eukaryotic protein synthesis occur? |
cytoplasm |
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Eukaryotic protein synthesis utilizes large complexes associated with what? |
cytoskeleton
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What do ribosomes bound to the endoplasmic reticulum manufacture?
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secretory and membrane proteins
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How are proteins inserted into the endoplasmic reticulum in the secretory pathway? |
co-translationally
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Where does protein synthesis in the secretory pathway occur? |
on ribosomes bound to the ER
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Where does the synthesis of proteins for the secretory pathway begin?
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on ribosomes that are free in the cytoplasm
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What is the signal peptide? (2) |
portion of the nascent protein that emerges from the ribosome and binds SRP 9-12 hydrophobic amino acids |
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Where is the signal peptide often located? |
N-terminal region of the primary structure
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What is SRP? |
signal-recognition particle
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What does SRP do?
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binds the signal sequence as it exits the ribosome and directs the ribosome complex to the ER
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What does SRP + ribosome do? |
bind GTP connected to translocon, GDP is then hydrolyzed and the ribosome binds with opened translocon
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What happens once the translocon is open? |
signal sequence cleaved by signal peptidase and protein is finished; ribosome released into ER lumen
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What is an iron storage protein in the cell? |
ferritin
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What is the iron response element (IRE) in the 5' UTR? |
stem-loop structure that binds the IRE binding protein (IRE-BP) when iron is absent and prevents translation
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What is IRE? |
iron binding element
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What happens when iron and 5' IRE are present? |
iron binds the IRE-BP causing it to dissociate from the IRE, allowing translation to occur
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How does 5' IRE prevent translation? |
It serves as a barrier between S-D sequence and the coding region.
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What does the transferrin receptor do?
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binds iron-rich transferrin and facilitates its entry into cells
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True or false: when iron is absent, IRE-BP binds 3' IREs allowing mRNA to be translated. |
true
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What happens without IRE-BP in the presence of IREs located in the 3' UTR? |
mRNA is degraded
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What can small RNAs do?
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regulate mRNA stability and use
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What leads to mRNA degradation induced by the presence of double-stranded RNA? |
RNA interference (RNAi)
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How long are microRNAs? |
21 nucleotides long
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What do microRNAs do?
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regulate gene expression post-transcriptionally
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How much of mammalian protein-coding genes may miRNAs regulate?
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60%
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True or false: miRNAs regulate mRNA stability and/or transcription.
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false, translation
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True or false: some miRNAs promote cleavage of specific mRNAs. |
true
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True or false: some miRNAs promote translational expression or adenylation of mRNAs. |
false, repression or deadenylation
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