Protein Synthesis and Cell secretion Flashcards
Protein Synthesis introduction
Proteins are composed of amino acids.
During protein synthesis, amino acids are linked together in a specific sequence to form the protein at the site of the ribosome.
A gene (section of DNA) holds the set of instructions for the sequence of amino acids in a specific protein.
Two steps to protein synthesis…
Transcription
Translation
Transcription
information of one of the DNA strands is copied to make mRNA.
It’s not an exact copy since each of the bases on the DNA strand is paired with each complementary RNA nucleotide to reproduce RNA.
Translation
In the process of translation, the nucleotide sequence in an mRNA molecule specifies the amino acid sequence of a protein.
Ribosomes in the cytoplasm carry out the translation. They have a binding site for mRNA and two sites for tRNA.
The tRNA carries the next amino acid to be added to the growing polypeptide chain.
The amino acid sequence is determined by the order of bases on the mRNA
Peptide bonds link the amino acids at a rate of 15 peptide bonds per second.
Cell secretion of proteins
Free ribosomes synthesise proteins used in the cytosol.
Ribosomes attached to the endoplasmic reticulum (ER) synthesise proteins that may be exported from the cell.
The ER transports the proteins to the Golgi complex where they are processed and packaged into secretory vesicles.
The secretory vesicles deliver the proteins to the cell membrane, where they are discharged by exocytosis into the extracellular material.
