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| Question | Answer |
| What is a gene? | A small part of a DNA strand which determines the sequence of amino acids in a polypeptide (the primary structure of a protein) |
| How many amino acids and codes are there? | 20 different amino acids 64 different codes |
| What are the properties of a genetic code? | Degenerative (most amino acids have more than one triplet code - codons) Non-overlapping Universal |
| What are codons? | Base triplets |
| What are the 3 types of RNA? | Messenger (mRNA) Transfer (tRNA) Ribosomal (rRNA) |
| What is the structure and function of mRNA? | STRUCTURE: A single polynucleotide strand Made in the nucleus during trascription FUNCTION: Carries the genetic code from the DNA to the ribosomes in the cytoplasm where protein is made |
| What is the structure and function of tRNA? | STRUCTURE: A single polynucleotide strand folded into a clover shape Small molecules, about 80 nucleotides long Hydrogen bonds between specific base pairs hold the molecule in this shape Has a specific sequence of three bases at one end called an anticodon Has an amino acid binding site at the other end FUNCTION: Carries amino acids to the ribosomes so that the protein can be assembled |
| What is the structure and function of rRNA? | STRUCTURE: Forms the two sub-units in a ribosome, along with proteins FUNCTION: Ribosome moves along the mRNA strand during protein synthesis rRNA in a ribosome helps to catalyse the formation of peptide bonds between the amino acids |
| What are the two stages of protein synthesis? | Transcription Translation |
| Outline the process of transcription | 1. DNA unwinds (hydrogen bonds are broken between base pairs by DNA helicase) 2. One of the DNA strands acts as a template against which a matching mRNA strand can be formed (template strand). The DNA strand which is copied is called the sense/coding strand 3. The exposed bases on the template strand of DNA attract RNA nucleotides with a complimentary base 4. RNA polymerase moves along the DNA, forming bonds that add nucleotides one at a time to the RNA 5. Behind the RNA polymerase, the DNA strands join up to reform the double helix 6. When the RNA polymerase reaches a particular sequence of bases on DNA, it recognises it as a 'stop' codon and detaches |
| Outline the process of translation | 1. Translation starts with the start codon (methionine) 2. Inside the ribosome, the anticodon of the rRNA binds to the complementary codon on the mRNA 3. The tRNA molecule carrying a methionine attaches itself at the ribosome according to complementary base pairing. As ribosomes fit 2 tRNA molecules, a second one also attaches to the ribosome at the bigger sub-unit 4. A peptide bond forms between the two amino acids and the first tRNA moves out of the ribosome. The ribosome moves along the mRNA so that a third tRNA can be attached to the ribosome 5. A third tRNA comes into the ribosome and the process repeats 6. The ribosome moves along the mRNA strand, building a polypeptide chain until a stop codon occurs in the mRNA (these do NOT code for any amino acids) 7. The mRNA separates from the ribosome and the completed polypeptide chain is released to the cytoplasm |
| TRUE OR FALSE: The ribosome and mRNA can be used again | TRUE |
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