4.6.1.5 DNA structure

• what is a molecule of DNA?

  A polymer made from four different nucleotides
• what does each nucleotide contain?

  a common sugar and phosphate group with one of four different bases attached to the sugar
• What are the four bases in DNA?

  A (adenine), T (thiamine), C (cytosine), G (guanine)
• what does a sequence of three bases code for?

  one amino acid - called the triplet code
• what does the order of bases control?

  the order in which amino acids are assembled to produce a particular protein
• Where are proteins made?

  In the cytoplasm on structures called ribosomes
• what do ribosomes use to make proteins?

  the code in the DNA (the order of the bases)
• why can‘t the DNA move out of the nucleus?

  it is too big to pass through the nuclear pore
• how does the cell get the code from the DNA to the ribosome?

  1. the base code of the gene is transcribed onto an RNA molecule called messenger RNA (mRNA)
  2. mRNA moves out of the nucleus and attaches to the ribosome
  3. The correct sequence of amino acids are brought to the ribosome and joined together (translation)
  4. The amino acid sequence forms a protein
• what are the two base compliment pairings?

  C$\equiv$G and A$=$T
• what happens when a chain of amino acids has been assembled?

  it folds into a unique shape which allows the protein to perform the task it‘s meant to do
• what are some examples of the different types of protein formed?

  enzymes, hormones of forming structures (eg collagen)
• how often do mutations occur?

  continuously
• what is a mutation?

  a random change in an organism’s DNA
• what do most mutations not do?

  alter the protein, or only alter it slightly so its appearance or function is not changed
• what can a few mutations cause?

  the proteins shape to be altered (enzymes may not fit the substrate binding site) or different proteins to be created and so its intended function is not carried out
• what do non-coding parts of DNA do?

  switch genes on and off
• what happens when there are variations in the non-coding parts of DNA?

  may affect how genes are expressed