7.4 translation

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7.4 translation

  1. 1. 7.4 Translation Topic 7 Nucleic Acids & Proteins
  2. 2. Translation  7.4.1 Explain that each tRNA molecule is recognized by a tRNA-activating enzyme that binds a specific amino acid to the tRNA, using ATP for energy.  Each amino acid has a specific tRNA-activating enzyme (the name aminoacyl-tRNA synthetase is not required). The shape of tRNA and CCA at the 3’ end should be included.  7.4.2 Outline the structure of ribosomes, including protein and RNA composition, large and small subunits, three tRNA binding sites and mRNA binding sites.
  3. 3. Translation  7.4.3 State that translation consists of initiation, elongation, translocation and termination.  7.4.4 State that translation occurs in a 5’→ 3’ direction.  During translation, the ribosome moves along the mRNA towards the 3’ end. The start codon is nearer to the 5’ end.  7.4.5 Draw and label a diagram showing the structure of a peptide bond between two amino acids.
  4. 4. Translation  7.4.6 Explain the process of translation, including ribosomes, polysomes, start codons and stop codons.  Use of methionine for initiation, details of the T factor and recall of actual stop codons are not required.  7.4.7 State that free ribosomes synthesize proteins for use primarily within the cell, and that bound ribosomes synthesize proteins primarily for secretion or for lysosomes.
  5. 5. The Structure of tRNA  Translation involves reading the mRNA in sets of 3 nucleotides called codons.  There are 61 codons (excluding 3 stop codons) for the 20 amino acids.  This also means there are 61 anticodons and hence 61 different types of tRNA  This is called the triplet code.  Since there are only 20 amino acids, the triplet code allows for degeneracy. (more than one tRNA per amino acid.
  6. 6. The Structure of tRNA  Transfer RNA (tRNA) has a vital role in translating the genetic code:  All tRNA molecules have:  A triplet of bases called the anticodon,in a loop of 7 nucleotides.  Two side loops.  The base sequence CCA at the 3’ terminal, which forms a site for attaching an amino acid.  Sections that become double stranded by complementary base pairing. These features allow all tRNA molecules to bind to sites on the ribosome and mRNA. Ref: Biology for the IB Diploma, Allott
  7. 7. tRNA Activating Enzymes  The variable features of each tRNA molecule give them a distinctive 3 dimensional shape.  This allows the correct amino acid to be attached to the 3’ terminal by an enzyme called the tRNA activating enzyme.  There are 20 different tRNA activating enzymes (one for each of the 20 amino acids).  Each enzyme attaches one particular amino acids to all of the tRNA molecules that have an anticodon corresponding to that amino acid.  Energy from ATP is needed for the attachment of amino acids.  The reaction of joining an amino acid to the tRNA is a condensation reaction, producing water.
  8. 8. tRNA Activating Enzymes Ref: IB Biology HL, OSC
  9. 9. Ribosome Structure  Ribosomes have a complex structure;  Proteins and ribosomal RNA molecules both form part of the structure.  There are 2 subunits, one large and one small.  There are binding sites for tRNA on the surface of the ribosome allow 2 tRNA molecules to bind at the same time.  There is a binding site for mRNA on the surface of the ribosome Ref: Biology for the IB Diploma, Allott
  10. 10. Translation  Messenger RNA carries the information needed for making polypeptides.  The information is in a code form, which is decoded during the the process of translation.  Ribosomes, tRNA molecules and tRNA activating enzymes are needed to carry out this decoding.  There are 3 main stages in Translation:  Initiation  Elongation  Termination  Like DNA replication, translation occurs in a 5’  3’ direction.
  11. 11. Translation - Initiation
  12. 12. Translation - Elongation
  13. 13. Translation -Termination
  14. 14. Polysomes  Many polypeptides are needed in large quantities  eg: enzymes, antibodies, hormones.  It would be energetically inefficient for one mRNA to synthesise a single polypeptide.  Thus as a ribosome moves along the mRNA another one can join on behind it and so on like beads on a string.  Multiple copies of the polypeptide can be synthesised rapidly.
  15. 15. Ribosomes  The distribution of ribosomes within the cell depends upon the function of the protein they make.  Some ribosomes are found bound to the endoplasmic reticulum while other float free within the cytoplasm.  Bound ribosomes produce proteins which are to be secreted out of the cell or for use in lysosomes.  Free ribosomes synthesise proteins for use primarily within the cell.
  16. 16. Translation  7.4.1 Explain that each tRNA molecule is recognized by a tRNA-activating enzyme that binds a specific amino acid to the tRNA, using ATP for energy.  Each amino acid has a specific tRNA-activating enzyme (the name aminoacyl-tRNA synthetase is not required). The shape of tRNA and CCA at the 3’ end should be included.  7.4.2 Outline the structure of ribosomes, including protein and RNA composition, large and small subunits, three tRNA binding sites and mRNA binding sites.
  17. 17. Translation  7.4.3 State that translation consists of initiation, elongation, translocation and termination.  7.4.4 State that translation occurs in a 5’→ 3’ direction.  During translation, the ribosome moves along the mRNA towards the 3’ end. The start codon is nearer to the 5’ end.  7.4.5 Draw and label a diagram showing the structure of a peptide bond between two amino acids.
  18. 18. Translation  7.4.6 Explain the process of translation, including ribosomes, polysomes, start codons and stop codons.  Use of methionine for initiation, details of the T factor and recall of actual stop codons are not required.  7.4.7 State that free ribosomes synthesize proteins for use primarily within the cell, and that bound ribosomes synthesize proteins primarily for secretion or for lysosomes.

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