Chapter 9: Translation Flashcards by Connor Nielsen

What does DNA do?

directs the synthesis of mRNA through the process of
transcription

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What is Ribosomal RNA (rRNA)?

is made in the nucleolus
Associates with ribosomal proteins to form ribosomes

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What does transfer RNA do (tRNA)?

transports specific amino acids to the
ribosomes during protein synthesis

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What does messenger RNA do (mRNA)?

serves as the template for protein
synthesis through the process of translation

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How are transcription and translation related?

(i) Transcription
* DNA to RNA
(ii) Translation
* mRNA to protein

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Explain translation.

The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule
* Nucleotides to amino acids

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Where does mRNA attach?

The ribosome

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What are triplets of nucleotides called?

Codons

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What are codons?

The words for ribosomes to translate

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How does tRNA interact with the ribosome?

tRNA’s carry specific amino
acids and ribosomes catalyze the formation of peptide bonds

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What are the main parts of tRNA?

Amino acid attachment site:
Specific amino acid attached here
(depends on anticodon!)
Anticodon:
A sequence of 3 bases that are
complementary to a CODON on
the mRNA strand

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Is mRNA complementary and antiparallel to DNA?

yes

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What do codons do?

specify amino acids

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Do we ever write the stop codon?

NEVER

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How to translate mRNA transcript?

Split mRNA into groups of 3
Look at genetic code dictionary for each group of 3
Stop at stop codon but never write stop

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What are the steps of Translation?

Step 1: Initiation
Step 2: Elongation
Step 3: Termination

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What do all steps require?

Protein factors
Energy (GTP in this case)

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Why are there several codons for the same amino acids?

redundancy
Protects against mutations during replication

Where does translation occur?

in a ribosome which is in the cytoplasm
or the rough ER

What is the structure of the ribosome?

Formed from rRNA and ribosomal proteins
2 subunits
Small subunit
Large subunit

What is ribozyme?

rRNA which acts as an enzyme

Where does mRNA bind to the ribosome?

Small subunit

Where does tRNA bind to the ribosome?

3 sites on the large subunit

What are the 3 sites on the large subunit useful for tRNA?

(i) E-site (exit site)
* Empty tRNA
(ii) P-site (peptidyl–tRNA binding site)
* tRNA containing growing polypeptide
(iii) A-site (aminoacyl-tRNA binding site)
* tRNA carrying next amino acid

How long is tRNA?

90 nucleotides long

What happens at the 3' end of tRNA?

Specific amino acids are attached here

What are anticodons?

A sequence of 3 bases that are complementary to a CODON on the mRNA strand

What does initiation require?

initiation factors!

What are the 3 steps of initiation for translation?

i. Small ribosomal subunit binds to mRNA ii. Initiator tRNA binds to mRNA * UAC anticodon binds to AUG start codon on mRNA iii. Large ribosomal subunit binds to small subunit * Requires GTP * Initiator tRNA positioned in P-site

How does the ribosome know which reading frame is the right one?

AUG establishes the reading frame (where reading starts)

What does elongation for translation require?

Requires elongation factors (proteins)

What direction is mRNA read for elongation?

5' to 3'

What are the steps of elongation?

- codon recognition - peptide bond formation - translocation

What happens during codon recognition?

* mRNA codon at A-site forms H-bonds with anticodon of incoming tRNA * GTP is required

What happens during peptide bond formation?

* Growing polypeptide transferred from tRNA in P-site to tRNA in A-site * Peptide bond is formed * Amino terminus of new amino acid forms bond with carboxyl end of growing polypeptide

What happens during translocation?

* Growing peptide in A-site is moved to P-site * GTP is required

What happens during termination for translation?

- Stop codon reaches A-site - Release factor binds to the stop codon - Bond between tRNA (in P-site) and the polypeptide chain is hydrolyzed (broken) - Polypeptide is released - Ribosome dissociates and leaves mRNA

Do proteins have directionality?

Polypeptides will elongate from the N terminus to the C terminus. (NCC chain)

What are the two types of mutations that can occur in the sequence of bases in DNA?

- Base pair substitution (point mutation) * Replacement of one nucleotide with another - Insertions or deletions * Addition or loss of nucleotides

What are the 3 types of base pair substitutions?

(1) Silent * No change in amino acid sequence (2) Missense * Amino acid changes (3) Nonsense * New codon codes for a stop codon * Translation ends too early and polypeptide is truncated

What are the two types of base pair insertion or deletions?

- Frameshift mutations - No frameshift mutations

What are frameshift mutations?

* Alter reading frame of mRNA * Insertion or deletion is not multiple of 3 * All codons after mutation are changed

What are no frameshift mutations?

* Do not alter the reading frame of mRNA * Insertion or deletion is a multiple of 3 * Codons are either added or removed but codons before and after mutation are unchanged

How to go from template strand to amino acids?

- Compliment template strand to mRNA - Split mRNA into codons from the start codon AUG - Translate using a genetic code dictionary