When and how ribosomes misread genetic code?
Answers
Answer:
Explanation:
Have you ever written a secret message to one of your friends? If so, you may have used a code to keep the message hidden. For instance, you may have replaced the letters of the word with numbers or symbols, following a particular set of rules. In order for your friend to understand the message, they would need to know the code and apply the same set of rules, in reverse, to decode it.
Decoding messages is also a key step in gene expression, in which information from a gene is read out to build a protein. In this article, we'll take a closer look at the genetic code, which allows DNA and RNA sequences to be "decoded" into the amino acids of a protein.
Background: Making a protein
Genes that provide instructions for proteins are expressed in a two-step process.
In transcription, the DNA sequence of a gene is "rewritten" in RNA. In eukaryotes, the RNA must go through additional processing steps to become a messenger RNA, or mRNA.
In translation, the sequence of nucleotides in the mRNA is "translated" into a sequence of amino acids in a polypeptide (protein chain).
If this is a new concept for you, you may want to learn more by watching Sal's video on transcription and translation.
Codons
Cells decode mRNAs by reading their nucleotides in groups of three, called codons. Here are some features of codons:
Most codons specify an amino acid
Three "stop" codons mark the end of a protein
One "start" codon, AUG, marks the beginning of a protein and also encodes the amino acid methionine
Codons in an mRNA are read during translation, beginning with a start codon and continuing until a stop codon is reached. mRNA codons are read from 5' to 3' , and they specify the order of amino acids in a protein from N-terminus (methionine) to C-terminus.
The mRNA sequence is:
5'-AUGAUCUCGUAA-5'
Translation involves reading the mRNA nucleotides in groups of three; each group specifies an amino acid (or provides a stop signal indicating that translation is finished).
3'-AUG AUC UCG UAA-5'
AUG $\rightarrow$ Methionine (Start)
AUC $\rightarrow$ Isoleucine
UCG $\rightarrow$ Serine
UAA $\rightarrow$ "Stop"
Polypeptide sequence: (N-terminus) Methionine-Isoleucine-Serine (C-terminus)
The mRNA sequence is:
5'-AUGAUCUCGUAA-5'
Translation involves reading the mRNA nucleotides in groups of three; each group specifies an amino acid (or provides a stop signal indicating that translation is finished).
3'-AUG AUC UCG UAA-5'
AUG \rightarrow→right arrow Methionine (Start) AUC \rightarrow→right arrow Isoleucine UCG \rightarrow→right arrow Serine UAA \rightarrow→right arrow "Stop"
Polypeptide sequence: (N-terminus) Methionine-Isoleucine-Serine (C-terminus)
What do 5' and 3' mean?
What are the N- and C-terminus?
The genetic code table
The full set of relationships between codons and amino acids (or stop signals) is called the genetic code. The genetic code is often summarized in a table.