Protein Synthesis

• The DNA code (a series of bases) is converted into proteins (a series of amino acids)
• The process of protein synthesis has two stages:

  • Transcription - rewriting the base code of DNA into bases of RNA
  • Translation - using RNA base sequence to build amino acids into sequence in a protein
• The sequence of bases in a gene determines the sequence of amino acids that make a specific protein

  • Different sequences
• Don’t confuse sequences of bases (in DNA/RNA) with sequences of amino acids (in proteins)

  • Make sure you're clear which large molecule you're referring to and which monomers make up the larger molecule
• Protein Synthesis

  A) DNA unwinds

  B) nucleus

  C) gene

  D) gene

  E) mrna

  F) mrna

  G) out

  H) cytoplasm

  I) mrna

  J) ribosome

  K) ribosomes

  L) nuclear pore

  M) cytoplasm

  N) ribosome

  O) amino acids

  P) order

  Q) protein

  R) amino acids

  S) protein molecule

  
• Proteins are made by ribosomes with the sequence of amino acids controlled by the sequence of bases contained within DNA
• DNA cannot travel out of the nucleus to the ribosomes as it is far too big to pass through a nuclear pore so the base code of each gene is transcribed onto an RNA molecule called messenger RNA (mRNA)

  • mRNA moves out of the nucleus and attaches to a ribosome
  • The ribosome ‘reads’ the code on the mRNA in groups of three
  • each triplet of bases codes for a specific amino acid
  • the ribosome translates the sequence of bases into a sequence of amino acids that make up a protein
  • the amino acid chain assembles and it is released from the ribosome so it can fold and form the final structure of the protein
• • Triplet code of DNA

  A) peptide

  B) amino acid

  C) ribosome

  D) complementary

  E) base

  F) mrna

  
• DNA controls cell function by controlling the production of proteins

  • The proteins may be enzymes, antibodies, or receptors for neurotransmitters
• Although all body cells in an organism contain the same genes, many genes in a particular cell are not expressed because the cell only makes the specific proteins it needs
• Expression of a gene means whether that gene is transcribed and translated in a particular cell or not
• Most genes are not expressed in a particular cell

  • They are 'switched off' because that would be a waste of energy and other resources in the cell
• Only the genes whose proteins are vital to that cell's function are expressed ('switched on')
• Proteins are made from amino acids

  • there are 20 amino acids
  • amino acids have specific order based off what type of protein it is making
  • amino acids gives proteins its shape and ability
• DNA controls cell function by controlling the production of proteins such as enzymes, membrane carriers and receptors of neurotransmitters
• Bases group into 3s and the order of the bases in the group gives what amino acid is made
• MRNA - messenger RNA
• MRNA make a copy of the gene and then leaves and attaches to the ribosome which then makes a protein through reading the amino acid sequences
• Steps of protein synthesis:

  • The gene that has the coded instruction for a protein in the nucleus is transcribed into a length of RNA called messanger RNA (MRNA)
  • Many copies of this gene are made and they pass out of the pores to the ribosome
  • At the ribosome, the instructions are translated and the protein is assembled by joining together amino acids
• Detailed steps of protein synthesis:

  1. gene coding for the proteins reamin in the nucleus
  2. MRNA is a copy of a gene
  3. MRNA molecules are made in the nucleus and move to the cytoplasm
  4. MRNA passes through ribosomes
  5. Ribosomes assembles amino acids into protein molecules
  6. Specific sequence of amino acids is determined by the sequence of bases in the MRNA
• What is the process between DNA base sequence --> RNA base sequence?

  Transcription
• What is the process between RNA base sequence --> amino acid sequence?

  Translation
• What is the triplet code?

  The triplet code is a sequence of three bases in DNA or RNA that codes which amino acids is brought into the new protein molecule