Protein Synthesis
Biology: IB Diploma Higher Level, topic 13.2.1
Protein Synthesis
Protein synthesis is the process of making proteins in the cells.
The genome
- The genome is the complete set of genes in an individual's DNA.
- The genes in the genome encode the different proteins a cell needs.
- The proteome is the full range of proteins an individual can produce.
Base sequence
- DNA is made from a combination of four different bases (A, T, C, G).
- A specific sequence of three bases (called a codon) encodes a specific amino acid.
- The order of the bases on the DNA tells us the order for combining amino acids to create particular proteins.
Processes
- There are two processes involved in synthesising protein from a base sequence. These are:
- Transcription.
- Translation.
Types of RNA
RNA is a single-stranded nucleic acid molecule that is made from the same bases as DNA except for uracil (U) which is used instead of thymine (T). There are different types of RNA:
mRNA
- Messenger RNA (mRNA) is transcribed from DNA in the nucleus to produce a single-stranded RNA.
- The mRNA strand is complementary to the DNA base sequence.
- mRNA travels from the nucleus to the ribosomes in the cytoplasm.
- Ribosomes are proteins that translate mRNA into amino acids and synthesise the polypeptide.
tRNA
- Transfer RNA (tRNA) forms a clover-like shape and is vital for translation.
- tRNA reads the mRNA codons and brings the corresponding amino acid into the ribosomes.
Accuracy of tRNA
- It is important that the correct amino acid is brought to the ribosomes by tRNA so that the protein is assembled correctly.
- Each tRNA molecule has an anticodon which is complementary to a specific codon on mRNA.
- The amino acid that corresponds to a specific anticodon binds to a specific attachment site on the tRNA molecule.
DNA → amino acid
- There are many processes in producing an amino acid from the original DNA sequence.
- If the original DNA sequence has the codon GCC, the codon in each step is:
- DNA codon: GCC.
- mRNA complementary codon: CGG.
- tRNA anticodon: GCC.
- Amino acid: Arginine.
Test yourself on Protein Synthesis
Which of the following statements about protein synthesis are true?
Which of these is NOT a process involved in protein synthesis?
What feature of tRNA molecules ensures each tRNA binds to the correct codon?
Which of the following statements about RNA are true?
If the DNA codon is CAG, what will the mRNA complementary codon be?