DNA translation

dna translation

- Also called as protein synthesis - Codons of mRNA are converted into protein - Involves decoding the language of nucleic acids and converting it into the language of proteins

codon

• language of mRNA

• group 3 nucleotides that coded for particular amino acid such as AUG, UAA

genetic code

the set of rules that determine how a nucleotide sequence is converted into the amino acid sequence of proteins

• happens in ribosomes in prokaryotes and ER for eukaryotes

AUG

is the start codon in bacteria that codes for formyl methionine rather than methionine (eukaryotes)

there are 64 codons but only 20 amino acids

type of codons

1. sense codons

2. nonsense codons

sense codons

61 including the AUG or the start codon

nonsense codons

3 stop codons (UAA, UAG, UGA) - These nonsense codons do not produce proteins, the stop the process of translation

workers in translation

1. Ribosomes (rRNA) - Is made in the cytoplasm in the prokaryotes and nucleolus in the eukaryotes A site – holds the next codon P site – holds the first codon E site – holds the deacylated tRNA before it leaves the ribosome

functions of ribosomes

- To direct the orderly binding of tRNAs to codons - To assemble the amino acid brought there into a chain producing proteins

tRNA

- each has a binding site for an amino acid - each tRNA is specific for a single amino acid, it must be able to recognize the codon on the mRNA that codes for that particular amino acid - has specific three-nucleotide sequence anticodon - example if the mRNA is UUU, its anticodon is AAA.

anticodon

- a sequence of three bases complementary to a codon - matches up with the appropriate mRNA codon like a lock and key

Overview of Translation

The building of polypeptide, 1 amino acid at time, by ribosomes using information in mRNA - ribosomes bind directly to mRNA, read codon by codon - ribosomes always start at AUG (formyl methionine rather than methionine)

- Translation also involves tRNA, each of which is attached to 1 of the 20 amino acids. - Ribosomes math the right tRNA via anticodon, with the right codon in the mRNA, then add its amino acid to the growing protein

Step by Step Process of Translation Initiation

1. Components needed to begin translation come together 2. On the assembled ribosome, a tRNA carrying the first amino acid is paired with the start codon on the mRNA. A tRNA carrying the second amino acid approaches

Elongation

3. The place on the ribosome where the first tRNA sits is called the P site. In the A site next to it, the second codon of the mRNA pairs with a tRNA carrying the second amino acid. 4. The first amino acid joins to the second by a peptide bond, and the first tRNA is released 5. The ribosome moves along the RNA until the second tRNA is in the P site, and the process, continues 6. The ribosomes continue to move along the mRNA, and new amino acids are added to the polypeptide

Termination

7. When the ribosome reaches a stop codon, the polypeptide is released. 8. Finally, the last tRNA is released and the ribosome comes apart. The release polypeptide forms a new protein.

Initiation

Ribosome assembles at specific AUG of mRNA - Ribosome binds 2 tRNA-amino acids, 2 codons at a same time; matching complementary anti-codons with mRNA codons

Elongation

- Ribosome catalyzes peptide bond formation between amino acids attached to each tRNA - Ribosome shifts 3 nucleotides (1 codon) on mRNA and repeats the process

Termination

• stop codon causes translation to end

• enables the initiation of protein synthesis by aligning the ribosome with the start codon

• generally located around 8 bases upstream of the start codon

• the rna sequence help recruit the ribosome to mRNA to initiate protein synthesis by aligning the ribosome with start codon

• once recruited tRNA may add amino acids in sequence as dictated by the codons, moving downstream from the translational start site

kozak consensus sequence

- Occurs on eukaryotic mRNA - Plays a major role in the initiation of the translation process - The sequence is recognized by the ribosome as the translation site from which protein is coded by mRNA molecule