Protein Synthesis - Translation Flashcards
Protein synthesis
To make a polypeptide chain from the DNA
Describe Translation
mRNA is used to create a (functional) protein / polypeptide chain
Codon
the sequence of three consecutive nucleotides on the mRNA strand
Anti-codon
three consecutive bases on a tRNA molecule that is complementary to mRNA codon
mRNA
is a single-stranded short molecule made up of phosphate,
ribose sugar, and nitrogen bases A, U, G, and C / Made during transcription and carries the code / gene / genetic information out of the nucleus.
TRNA
carries the amino acid to the ribosome and ‘drops’ it off for polypeptide chain.
Amino acid
the building blocks of proteins / polypeptides
Polypeptide chain
is a sequence of many amino acids bonded (peptide) together
Explain TRANSLATION
mRNA forms a complex with a ribosome. The ribosome is an organelle, which ‘reads’ mRNA bases in a code of three bases at a time. This is the codon on the mRNA. tRNA brings in amino acids – there is a specific tRNA molecule for each amino acid.
Process of TRANSLATION
Three unpaired bases on the tRNA are known as an anticodon, and have a specific corresponding amino acid that attaches to it. They are complementary to a codon on the mRNA. Codon-anticodon ‘matches’ using base pairing rule, thus bringing the correct amino acid to the next part of the sequence and attaching to the polypeptide. A start codon initiates the translation. A stop codon ends translation, which causes the ribosome to stop translating and release the mRNA and the polypeptide chain. (Once the polypeptide chain is released from the ribosome, it ‘folds’ into a three- dimensional structure, becoming a functional protein).
Importance of TRANSLATION
Translation of the mRNA template converts nucleotide-based genetic
information into amino acids chains to create a polypeptide chain / actual protein. Without translation the correct order (sequence) of amino acids would not occur and the polypeptide / protein would not fold into a specific 3D SHAPE.
Why polypeptide is NOT directly translated from DNA strand
Ribosomes are used to make polypeptide chains, and are not found in the nucleus.
• Ribosomes are capable of translating only single-stranded mRNA.
• DNA is only one copy of the gene but a cell can produce many mRNA via transcription; therefore many copies of the same gene / protein in response to cell demands. If translation was to occur in the nucleus directly from the DNA template strand, it would be slow, as only one molecule of protein could be produced at a time by each cell, as there is only one copy of the needed DNA. As proteins are large molecules, these may not be able to leave the nucleus, as they would be too large to pass through the pores of the nuclear membrane.
• Maintain DNA integrity (keep it safe from damage). Blueprint, working copy of mRNA created with genetic information / DNA cannot leave the nucleus because it will get broken down / damaged / destroyed by enzymes in the cytoplasm.
