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23 Cards in this Set
- Front
- Back
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What are proteins and why are they important?
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They are the workers of cells and allow them to carry out its function.
To activate cellular activities, genes of its proteins are expressed to |
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What is the difference between RNA and DNA?
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DNA:
Double stranded Backbone = deoxyribose and phosphate Thymine RNA: Single stranded Backbone = ribose and phosphate Uracil |
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What are the three steps of transcription?
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Initiation
Elongation Termination |
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What is the gene of the promoter region in the template DNA strand?
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TATA box (5'-TATAAAA-3')
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What happens during initiation of transcription?
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1. Transcription factors bind to the TATA box (promoter region).
2. Once transcription factors have binded, the RNA polymerase II can bind to transcription factors. (a transcription initiation complex) 3. It reads template strand in 3' - 5' direction and produces mRNA in 5' - 3' direction. |
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What happens during elongation of transcription?
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1. RNA polymerase II goes down the DNA template strand, unwinding it and translating to mRNA which leaves from the back and DNA helix winds back up when RNA polymerase II moves forward.
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What happens during termination of transcription?
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1. Termination begins when the RNA pol II transcribes a polyadenylation signal in DNA (sequence 5'-AAUAAA-3')
2. Somewhere along the polyadenylation signal mRNA is exised from RNA pol II |
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What happens during the maturation of mRNA?
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5' cap is added to the 5' end of the mRNA strand.
Poly-A tail is added to the 3' end of the mRNA strand. Splicing (introns removed, exons spliced together). Pre-mRNA -> mRNA which can leave outside the nucleus to the ribosome. |
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What is the importance of 5' cap and 3' cap?
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The 5' modified guanine residue cap aids stability and promotes export from the nucleus.
Poly-A tail is also for stability. Longer the A chain, the slower degradation occurs. |
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How does splicing work?
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snRNA (small nuclear RNA) and proteins form snRNPs (small ribonuclear proteins).
several snRNPs and proteins make up the spliceosome. Spliceosome cuts the introns. The snRNA is complementary to the sequence on introns, so bind to it and cut it off. Introns degrade, exons joined together. |
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What are the three sites on the ribosome?
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E - Exit site
P - Peptidyl-tRNA binding site A - Aminoacyl-tRNA binding site |
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How is the translation initiation complex formed?
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1. Small ribosomal subunit binds to the first amino acyl tRNA carrying methionine.
2. Small ribosomal subunit + tRNA bind to the 5' cap of mature mRNA. 3. Small ribosomal subunit scans down to find the translation start site in mRNA AUG. 4. Large ribosomal subunit then binds. (phosphorylation of GTP -> GDP provides energy for this). |
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What are the steps of translation elongation?
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Once the translation initiation complex forms...
1. New aminoacyl tRNA comes in the A site and binds to the complementary codon. (GTP invested to increase accuracy and effinciency). 2. Polypeptide chain breaks its peptide bond with the tRNA in P site and forms new bond with tRNA in A site. Catalysed by large ribosome subunit. 3. GTP invested shift mRNA translocating tRNAs. |
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What happens in termination of translation?
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1. Release factor binds at the A site when it reaches stop codon (UAG, UAA UGA) NOT tRNA.
2. Hydrolysis of peptide bond between polypeptide chain and tRNA. 3. Polypeptide is released. 4. INVESTMENT OF 2 GTP molecules. |
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How is a peptide bond formed?
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Dehydration
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What are the three types of side chain on a amino acid?
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non polar, polar and electrically
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What is the alpha helix structure?
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A type of secondary structure of the protein.
The primary protein coils into a spiral structure. Stabilized by hydrogens. |
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What is the B pleated structure?
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Primary amino acid chain zig-zags back and forth. Held together by hydrogen bonds.
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What kind of bonds are present in the tertiary structure of proteins?
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Hydrogen bond
Hydrophobic collapse and vander waals interactions. Disulfide bridge. Ionic bond. |
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What is the quaternary structure of proteins?
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Two or more polypeptide chains with its own tertiary structure combine to form a functional protein.
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What is a tertiary structure?
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Alpha helices and/or Beta pleated sheets fold up to form globular molecule.
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Where does polypeptide productions ALWAYS occur first?
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In the cytosol when free ribosomes begin to translate the mRNA.
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What determines if the protein produced is cytosolic or ER-bound?
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The protein itself. During translation, Signal recognition particle (SRP) bind to a signal peptide on the developing polypeptide chain, halting translation. SRP then binds to SRP receptor on ER causing it to form a pore. The SRP is then released and translation is resumed and the protein produced in the ER.
Signal peptide comes off in the end. |
