Structure of DNA and Protein Synthesis

• DNA molecules contain a genetic code that determines which proteins are built
• DNA is made up of nucleotides

  
• DNA strands are polymers made up of lots of repeating units called nucleotides

  
• Each nucleotide consists of a sugar, a phosphate group and one 'base'

  
• The sugar and phosphate groups in the nucleotides form a 'backbone' to the DNA strands. The sugar and phosphate groups alternate. One of four different bases - A, T, C, G - joins to each sugar

  
• Each base links to a base on the opposite strand in the helix. This is called complementary base pairing

  
• It's the order of bases in a gene that decides the order of amino acids in a protein. Each amino acid is coded for by a sequence of 3 bases in the gene

  
• The amino acids are joined together to make various proteins, depending on the order of the gene's bases

  
• There are parts of DNA that don't code for proteins. Some of these non-coding parts switch genes on and off, so they control whether or not a gene is expressed (used to make a protein)

  
• mRNA carries the code to the ribosomes
• Proteins are made in the cell cytoplasm on tiny structures called ribosomes
• To make proteins, ribosomes use the code in the DNA. DNA is found in the cell nucleus and can't move out of it because it's really big. So the cell needs to get the code from the DNA to the ribosome. This is done using a molecule called mRNA - which is made by copying the code from DNA
• The mRNA acts as a messenger between the DNA and the ribosome - it carries the code between the 2
• The correct amino acids are brought to the ribosomes in the correct order by carrier molecules
• Proteins have many different functions
• 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
• Types of proteins - Enzymes

  • Act as biological catalysts to speed up chemical reactions in the body
• Types of proteins - Hormones

  • Used to carry messages around the body. E.g. insulin is a hormone released into the blood by the pancreas to regulate the blood sugar level
• Types of proteins - structural proteins

  • They're physically strong. E.g. collagen is a structural protein that strengthens connective tissues (like ligaments and cartilage)