Bio 5A- Gene Expression: Translation

Front 1

what are trnas? what do they do? How are they produced?

Back 1

They link triplet codons to amino acids. Cells use these special macromolecules, to translate the sequence of bases in mRNA into amino acids. tRNAs are themselves produced bytranscription of tRNA genes, but the primary transcript is not translated.

Front 2

What are the two functionally important parts of a trna?

Back 2

The 3' end, atwhich an amino acid is covalently attached,and the anticodon loop, a region thatundergoes RNA-RNA base pairing with thetriplet bases in mRNA.

Front 3

How many codons specify amino acids? How many tRNA genes? How can all the codons still be recognized?

Back 3

61, ~45. because some tRNAs allow the 3'-most base in the codon to tolerate a wobble base pair interaction withthe 5'-most base in the anticodon. . [Wobble pairs include G-U and A-C

Front 4

How do tRNAs become covalently attahed to amino acids- how is the correct amino acid attached?

Back 4

This is accomplished by enzymescalled aminoacyl-tRNA synthetases. These are enzymes (proteins) that can recognize the correct amino acid and the tRNA (by its three-dimensional shape, formed by RNA-RNA base pairing within the tRNA). Theycatalyze the joining of the carboxyl group of the amino acid onto one of the two –OH groups on the 3' endof the tRNA, by an overall dehydration reaction; the overall reaction requires hydrolysis of ATP as shownbelow. As proteins, aminoacyl-tRNA synthetases are gene products. Note that different aminoacyl-tRNAsynthetases are responsible for charging different tRNAs. For example, prolyl-tRNA synthetase is theenzyme that charges tRNAPro with the amino acid proline, to make prolyl-tRNAPro.

Front 5

What is involved in translation?

Back 5

(1) the mRNAwhich carries the coding region for the protein; (2)transfer RNA molecules (tRNAs) that associate thecorrect amino acid with the codon in the mRNA; and (3)the ribosome, a multi-subunit enzyme that contains bothRNA and proteins

Front 6

Draw a ribosome..

Back 6

Front 7

Describe the properties of the subunits of the ribosome

Back 7

Both subunits consist of both protein andRNA components. rRNA is transcribed in the nucleolus. About 2/3 of the mass of the ribosome isrRNA. The RNA portion is responsible for its catalytic activity.The two subunits form a functional ribosome only in the presence of an mRNA. The mRNA binds between the two subunits

Front 8

Where will tRNA interact?

Back 8

A site: Aminoacyl-tRNA binding site.
P site: Peptidyl-tRNA site, where the growing polypeptide is attached to a tRNA.
E site: Exit site, where the spent tRNA (lacking its amino acid) will leave the ribosome

Front 9

How many steps in the ribosome cycle? What are they?

Back 9

three steps that are analogous to the steps in transcription: Initiation,Elongation and Termination

Front 10

When does initiation occur in the ribosome cycle ? What happens during initiation?

Back 10

occurs when the small subunit of the ribosome recognizes sequences in the 5' end of the mRNA.The first start codon is recognized by an initiator tRNA. Multiple proteins then coordinate assembly of thefull ribosome and translation initiation complex, using the energy of GTP hydrolysis (analogous to hydrolysisof ATP)

Front 11

How many steps in elongation? what are they? When is elongation complete?

Back 11

1. Codon recognition, 2.peptide bond formation, 3.translocation.
Three steps are repeated in a cycle until a stop codon isreached.

Front 12

What happens during codon recognition? hat happens during peptide bond formation and how? What happens during translocation?

Back 12

1.During codon recognition, a new activated tRNA recognizes the next codon in the A site.2. The growing polypeptide chain is moved over from the peptidyl-tRNA in the P site to the amino acidon this incoming tRNA, leading to peptide bond formation (also called the peptidyl transferasereaction).
3. The translation complex moves, leading to movement of the new peptidyl-tRNA into the P site, andexit of the previous tRNA through the E site. The cycle can now repeat.

Front 13

Draw elongation..

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Front 14

What happens during termination in the ribosome cycle?

Back 14

Termination of translation involves the recognition of a stop codon by a release factor, a protein thatresembles a tRNA and can fit in the A site. This leads to release of the new polypeptide and disassembly ofthe translation complex.

Front 15

What are polyribosomes?

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Because the translation complex makes contact with only a small part of the mRNA at anygiven time, multiple ribosomes can translate a single mRNA molecule – such clusters are calledpolyribosomes.

Front 16

What are the differences between prokaryotes and eukaryotes?

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In bacteria, transcription and translation can occursimultaneously, with ribosomes starting to translate mRNAs just as their 5' ends have been made. This isbecause in eukaryotes, the mRNA must be exported from the nucleus before translation.
In eukaryotes, ribosomes can be bound or free depending on whether ornot the polypeptide produced will stay in the cytosol (e.g. enzymes in glycolysis) or be processed for exportthrough the endomembrane system (e.g. insulin from the pancreas). Bound ribosomes are found in therough endoplasmic reticulum (ER), while free ribosomes are in the cytosol

Front 17

What does transcription and translation look like in bacteria?

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