2.6 Ribosome Protein Formation

• What is the process called when proteins are formed on ribosomes?

  Translation
• What initiates the translation process on mRNA?

  The chain-initiating codon
• How does the ribosome read the mRNA?

  Like a tape recorder reads tape
• What signals the end of a protein molecule during translation?

  The stop codon
• What are polyribosomes?

  Clusters of ribosomes on a single mRNA
• Why can a single mRNA form proteins in several ribosomes simultaneously?

  Because it can pass to successive ribosomes
• How many ribosomes can be attached to a single mRNA at the same time?

  3 to 10 ribosomes
• Is there specificity of ribosomes for given types of protein?

  No, any ribosome can form any protein
• What happens to the initial ends of forming protein molecules?

  They attach to specific receptor sites on the endoplasmic reticulum
• What gives a granular appearance to the endoplasmic reticulum?

  Attachment of ribosomes during protein formation
• What is the functional relationship between mRNA and ribosomes?

  • mRNA provides the template for protein synthesis
  • Ribosomes read the codons on mRNA
  • Ribosomes facilitate the formation of proteins
• Describe the process of ribosome attachment to the endoplasmic reticulum.

  • Ribosomes attach to specific receptor sites
  • Amino acid sequences of proteins facilitate attachment
  • Proteins penetrate the reticulum wall
  • Proteins enter the endoplasmic reticulum matrix
• What process occurs in several ribosomes at the same time in response to mRNA?

  Translation
• What do newly forming polypeptide chains pass through?

  Endoplasmic reticulum membrane
• Where are most proteins synthesized by ribosomes released?

  Into the cytosol
• What type of proteins are synthesized and released into the cytosol?

  Enzymes and internal structural proteins
• What are the chemical steps in protein synthesis?

  1. Activation of amino acids by ATP.
  2. Formation of amino acid–tRNA complex.
  3. tRNA attaches to mRNA in ribosome.
  4. Peptide bonds formed by peptidyl transferase.
  5. Energy from four high-energy phosphate bonds used.
• What is formed when ATP combines with an amino acid during activation?

  Adenosine monophosphate complex
• What is released when the activated amino acid combines with tRNA?

  Adenosine monophosphate
• What does the tRNA carry to the ribosome?

  Amino acid complex
• How does the tRNA interact with mRNA in the ribosome?

  Anticodon of tRNA attaches to codon of mRNA
• What enzyme is responsible for forming peptide bonds?

  Peptidyl transferase
• How many high-energy phosphate bonds are used for each amino acid added to the protein chain?

  Four high-energy bonds
• Why is protein synthesis considered energy-consuming?

  It requires multiple high-energy phosphate bonds