Term
| True or false? Each gene in eukaryotes codes for one mRNA codes for one protein. |
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Definition
| False. One gene codes for one pre-mRNA, but the pre-mRNA's can be spliced and changed to form different proteins. |
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Term
| What is a promoter? How does it relate to a transcription initiation complex? |
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Definition
| A promotor is a sequence upstream a gene, where RNA polymerase and transcription factors form a transcription initiation complex as they bind to it. |
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Term
| What does the RNA polymerase do? |
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Definition
After forming a transcription initiation complex, it separates a DNA strand and starts creating RNA. During elongation RNA poly. moves downstream and RNA lengthens. After RNA poly. passes a DNA segment, it snaps back into place and RNA pops out.
After RNA poly. has transcripted an mRNA, it passes a sequence called a transcription terminator and falls off the DNA. |
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Term
In what three ways is pre-mRNA prepped before leaving the nucleus?
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Definition
| A 5' modified GTP cap is added, a 3' poly-A tail is added, and RNA is spliced by snRNP's |
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Term
| What role do snRNP's play in transcription? |
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Definition
| snRNP's made of RNA and proteins bind to other proteins to form a spliceosome. This works to cut out "intron" sequences of RNA and splice (join together) "exon" sequences in RNA. Some exons are also removed in order to make different RNA's. |
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Term
| What do tRNA's do? How are they prepped to help with protein synthesis? |
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Definition
tRNA binds to a codon of mRNA (in the ribosome) and to an amino acid.
It is prepped by binding to an aminoacyl-tRNA synthetase, which binds it to an amino acid htrough ATP hydrolysis. It now becomes aminoacyl tRNA. |
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Term
| What is a ribosome made of? What three tRNA binding sites does it have? |
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Definition
A ribosome has a large and small subunit that combine. They are each made of rRNA.
Its three tRNA binding sites are:
A site - aminoacyl-tRNA binding site
P site - peptidyl tRNA binding site
E site - exit site
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Term
| How do ribosomes facilitate protein synthesis? What happens during initiation, elongation (and translocation) and termination? |
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Definition
Initiation: An aminoacyl tRNA binds (via its anti-codon) to an AUG (always the start codon, does for Met) sequence on an mRNA. A small ribosomal subunit binds to the mRNA from the other side.
The large ribosomal subunit then attaches, the initial tRNA is in the P site.
Elongation: An incoming aminoacyl tRNA with the correct anticodon binds to the A site. The amino acid chain from the tRNA on the P site move to the tRNA on the A site.
Translocation: The ribosome moves along the mRNA by one codon so that the tRNAs have now moved one spot over (A->P, P->E). The tRNA now in the E site leaves.
Termination: Occurs when a stop codon is reached (which codes for no amino acids). This causes a release factor to bind to the ribosome instead of a tRNA. This causes the complex to fall apart. |
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Term
| What is a polyribosome/polysome? |
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Definition
| It's when there are many ribosomes on one mRNA. Multiple units of the same protein are being made from one mRNA. |
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