DNA 🧬

• Adenine - Thymine

  A - T
• Guanine - Cytosine

  G - C
• DNA fits into the cell nucleus by being twisted into a double helix, then wrapped around histones to form a nucleosome. In a cell that is not dividing, the coiled DNA forms a tangled network of chromatin when a cell divides the coiled chromatin becomes even more tightly coiled.
• DNA= deoxyribonucleic acid
• The bases (A, T, C, G) are paired by hydrogen bonds along the centre of the molecule
• DNA has a double helix shape
• The DNA strands are wrapped around a group of eight special proteins called histones to form a nucleosome.
• In a cell that is not dividing, the coiled DNA forms a tangled network called chromatin.
• When a cell divides the coiled chromatin becomes even more tightly coiled.
• The first stage of DNA replication is when the two strands of the DNA molecule are separated by the enzyme helicase.
• Each strand of the separated section contains half the original information. Each strand serves as a template for the nucleotides that will form the new strand.
• Two enzymes play important roles in the synthesis of the new strands.

  • DNA polymerase adds the new nucleotides to the new strand.
  • DNA ligase joins short sections of DNA together.
• Nitrogen bases in DNA

  • Adenine
  • Thymine
  • Cytosine
  • Guanine
• Nitrogen base bonding in DNA

  • Adenine bonds with thymine
  • Cytosine bonds with guanine
  • Bonds are weak hydrogen bonds
• DNA structure


  Two strands twist into a spiral shape called a double helix
• DNA replication


  1. Strands separated by helicase

  2. Each strand serves as a template

  3. DNA polymerase adds new nucleotides

  4. DNA ligase joins short sections
• The backbone of the DNA molecule has alternating sugar and phosphate groups.
• DNA strands are antiparallel
• Most of the DNA occurs in the cell nucleus; however, each mitochondrion contains 37 genes.
• Mitochondrial genome is passed only from mother to child.
• Humans have 46 chromosomes
• 1. A ribosome binds with a START codon in mRNA. The start codon is AUG
  2. Transfer RNA (tRNA) has a complementary anticodon that attaches to a corresponding mRNA codon. tRNA carries an amino acid.
  3. As the ribosome moves along the strand of mRNA, more amino acids are added to the growing chain.
  4. At the STOP codon (UAG in this sequence), the ribosome releases the mRNA and an amino acid chain.
  5. The amino acid chain folds into a three-dimensional shape, called a protein.


  Translation
• 1. RNA polymerase attaches to the promotor region on a strand of DNA
  2. DNA strands separate, exposing nucleotides ready for copying
  3. Messenger RNA(mRNA) pairs with a DNA template strand
  4. Nucleotides are added until RNA polymerase reaches a termination sequence in the DNA and releases mRNA.
  5. mRNA moves out of the nucleus, through nuclear pores, into cytoplasm.


  Transcription
• Oncogene = gene with potential to cause cancer
• Oncogene = a gene which in certain circumstances can transform a cell into a tumour cell.
• Cancer = a disease in which abnormal cells divide uncontrollably and destroy body tissue.
• Type of cancer

  • malignant
  • Benign
• Malignant = able to spread to other parts of the body
• Benign = not able to spread to other parts of the body.
• Carcinogens can cause cancer
• Carcinogens examples

  • UV radiation
  • X-rays
• Prevention strategies:

  • Don’t use tabacco
  • Eat a healthy diet
  • be physically active
  • get vaccinated
  • be sun smart
  • regular medical care