Translation

True or False:

Protein Synthesis consumes more of a cell’s energy than any other metabolic process

True

What happens in Translation?

an mRNA message is decoded into a polypeptide product

What does each amino acid include?

Amino acid group (NH2)

Carboxyl group (COOH)

What are amino acids linked by?

peptide bonds

When are polypeptides formed?

When the amino group of one amino acid forms an amide and bonds with the carboxyl group of another amino acid

Definition of Translation

The process by which the ribosome reads mRNA codons and assembles the corresponding amino acid chain into a polypeptide

Ribosome

A complex macromolecule composed of structural and catalytic RNA.

(In eukaryotes, the nucleolus is specialized for synthesizing and assembing rRNAs)

What direction do ribosomes translate each mRNA molecule?

5’ to 3’

Transfer RNAs

Serve as adaptor molecules

True or False:

tRNAs are the molecules that actually “translate” the language of RNA into the language of proteins

True

Of 64 possible mRNA codons, how many specify termination sequences, and how many add amino acids to the polypeptide chain?

61 add amino acids

3 terminate the sequence

What is the universal start codon?

AUG

Where do Codons and Anticodons live?

Codons - on the mRNA

Anticodons - on the tRNA

Codon vs. Anticodon

Codon - The word being read

Anticodon - the complement of the codon

If a codon is AUG, what will the anticodon be?

UAC

What does it mean if a code is redundant?

Most amino acids have more than one code

What does it mean if the code is unambiguous

Each codon means exactly one thing

What are the 3 phases of mRNA synthesis?

Initiation, Elongation, Termination

Initiation

The small ribosomal subunit and mRNA assemble; the initiator tRNA finds the AUG start codon and the large subunit joins

Elongation

Charged tRNAs enter, form peptide bonds, and the ribosome moves along the mRNA three bases at a time, growing the chain

Termination

The ribosome reaches a stop codon, a release factor frees the finished portion, and the ribosome disassembles

What does protein synthesis begin with?

The formation of the initiation complex

What does the initiation complex include?

Small ribosomal subunit and the mRNA

Where is the 5’ cap located (in relation to the AUG codon), and what does it do during the initiation of Translation?

It is located upstream of the AUG codon, and it binds the small ribosomal subunit at the mRNA-binding site.

What does the binding of the small ribosomal unit ensure?

The AUG codon ends up in the P site of the large ribosomal subunit when it attaches

The initiation complex tracks along the mRNA in what direction (5’ to 3’, or 3’ to 5’)?

5’ to 3’

What does the initiation complex look for when tracking along the mRNA?

The AUG start codon

What happens after the initiation complex locates the AUG start codon?

Initiator tRNA interacts with the AUG start codon

What is formed when the initiator tRNA interacts with the AUG start codon?

Hydrogen bonds between the AUG and the tRNA anticodon UAC

(this step completes the initiation of translation in eukaryotes)

What are the 3 compartments of the ribosome’s tRNA-binding region?

A site, P site, E site

What does the A (aminoacyl) site do?

Binds incoming charged aminoacyl tRNAs

What does the P (peptidyl) site do?

Binds charged tRNA carrying amino acids that have formed peptide bonds with a growing peptide chain, but not yet dissociated from their corresponding tRNA

What does the E (exit) site do?

Releases dissociated tRNAs so they can be recharged with free amino acids

True or False:

The initial tRNA occupies P site at the start of elongation?

(Note: E site releases tRNAs so they can be recharged with amino acids)

True

During elongation, what template provides tRNA binding specifity

mRNA

How do elongation factors provide energy for each step?

Hydrolyzing GTP

What forms between the amino group of the amino acid attached to the A-site tRNA and the carboxyl group of the amino acids to the P-site tRNA

Peptide bonds

What catalyzes peptide bond information?

Peptidyl transferase

What is peptidyl transferase?

An RNA-based enzyme integrated into the 50S ribosomal subunit

What do release factors add when encountering a stop codon

water molecule to the carboxyl end of the P-site amino acid

What is a Signal sequence?

A short sequence at the amino end of a protein that directs it to a specific cellular compartment

True or False:

Many proteins fold spontaneously, but some require helper molecules

True

What are the helper molecules called? (that help proteins fold)

Chaperones

How do chaperones help the cell fold?

prevent aggregation during the complex folding process

What template is read for Translation?

mRNA codons

What is the product of Translation

Polypeptide (protein)

What is the main machine of translation

Ribosomes + tRNA

What are the building blocks for translation

amino acids

Where does translation take place

Cytoplasm / Rough ER

Missense change

Swaps one codon for another, substituting a single amino acid

Nonsense change

Creates an early stop codon (translation terminates too soon)

Frameshift change

Insertion or deletion not in multiples of 3 (every codon downstream is misread)

Altered regulation

Can change how much of a protein is translated (doesn’t change growth driver sequence at all)

What are the roles of mRNA, the ribosome, and tRNA in translation?

mRNA - carries the coded message (codons)

the ribosome - machine that binds the mRNA, holds the tRNAs, and catalyzes the peptide bonds

tRNA - carries a specific amino acid and matches its anticodon to the corresponding codon, delivering the right amino acid to the growing chain