SCIENCE QUARTER 4

• Protein


  One of the biomolecules inside cells, they compose a number of structures and perform various functions inside cells
• Protein synthesis


  The process by which cells make new proteins as required by the body
• Proteins


  • Composed of amino acids linked together by peptide bonds
• Roles and functions of proteins


  • Channels in membranes (control movement of molecules in and out of cell)
  • Structural molecules (e.g. hair, muscle)
  • Hormones (regulate cell activity)
  • Antibodies (in immune system)
  • Enzymes (act as catalysts)
• DNA (deoxyribonucleic acid)


  Stores genetic materials

  
• RNA (ribonucleic acid)


  Functions in protein synthesis, transcribing and translating the genetic code
• Differences between DNA and RNA

  • DNA is double stranded helix, RNA is single stranded
  • DNA has sugar deoxyribose, RNA has sugar ribose
  • DNA has A, T, C, G bases, RNA has A, U, C, G bases
  • DNA stores genetic materials, RNA functions in protein synthesis

  
• Transcription


  The process by which the cell uses DNA to form RNA
• 3 types of RNA


  • Messenger RNA (mRNA) - transcribes DNA to RNA
  • Ribosomal RNA (rRNA) - binds mRNA and tRNA
  • Transfer RNA (tRNA) - translates mRNA codons into amino acids
• Protein synthesis


  1. Transcription

  2. Translation
• Genetic codes


  Nucleotide bases in DNA/RNA, usually in triplets, that code for amino acids in proteins
• mRNA codons


  Determine the specific amino acids that will be brought in by tRNA during translation
• Start codon


  AUG, codes for the amino acid methionine and starts the translation stage
• Stop codons


  UAG, UGA, UAA, stop the translation stage
• Transcription


  1. DNA unzips

  2. RNA polymerase combines nucleotides to form RNA strand using DNA as template

  
• Newly synthesized mRNA


  Goes out of the nucleus to the cytoplasm where proteins are made
• Translation


  1. Ribosome sandwiches mRNA

  2. Codons in mRNA paired with anticodons in tRNA

  3. Amino acids carried by tRNA are connected by peptide bonds to form polypeptide chain

  4. Translation terminated when stop codon is read
• The polypeptide produced will be processed further before becoming a functional protein