Protein Synthesis

Protein Synthesis - Key Terms

^ Nucleotide

RNA - Ribonucleic acid. The molecule is made from phosphate groups and ribose sugars linked together with one of four bases.

RNA polymerase - An enzyme that creates mRNA from DNA. Separates 2 DNA strands.

mRNA - Messenger RNA. A single strand of RNA produced in transcription.

Polypeptide - A chain of amino acids.

Codon - A set of 3 bases found in DNA and RNA. The genetic code is formed from patterns of codons.

tRNA - Transfer RNA. A molecule of RNA that carries amino acids.

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Protein Synthesis - Transcription

FIRST STAGE:

Transcription - The process by which the gentic code in one strand of DNA molecules is used to make mRNA.

Transcription Process:

  • RNA Polymerase binds to DNA and separates the strands in a non-coding region. These regions don't code for a protein.
  • The enzyme then moves along one DNA strand (template strand) adding complementary RNA nucleotides. These contain the same bases as DNA, except that Uracil (U) is used instead of Thymine (T).
  • The nucleotides link to form a strand of mRNA.
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Protein Synthesis - Translation

SECOND STAGE:

Translation - The process by which the genetic code in a molecule of mRNA is used to make a polypeptide.

Translation Process:

  • The mRNA strands travel out of the nucleus through nuclear pores.
  • In the cytoplasm, the mRNA strands attach to ribosomes.
  • A ribosome moves along the mRNA strand a codon at a time. At each codon, a molecule of tRNA with complementary bases line up, Each tRNA molecule carries a specific amino acid.
  • As the ribosome moves along it joins the amino acids from the tRNA molecules together, forming a polypeptide.

The polypeptide chain then folds up to form a protein (such as an enzyme) with a specific shape.

Some proteins contain more than 1 polypeptide chain.

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