F215 Cellular Control and variation

HideShow resource information

DNA and Protien Synthesis

  • DNA is made up of nucleotides ( deoxyribose sugar, phosphate group and nitrogenous bases)
  • Has a triplet code e.g. AUG
  • Every 3 bases codes for 1 amino acid


  1. mRNA is produced from the coding strand of DNA
  2. DNA helix unwinds and unzips by the enzyme helicase, which causes the hydrogen bonds to break
  3. RNA polymerase builds the mRNA strand which is complementary to the coding strand
  4. The mRNA leaves the nucleus through the nuclear pores


  1. mRNA strands enters the ribosome begining with AUG.
  2. complementary codons are attached by the ribosome.
  3. After every codon a peptide bond is formed between the amino acids
  4. After many amino acids this results in a polypeptide chain


  • Occur at any time during DNA replication
  • Point mutations replace one base (less of an effect on the tertiary structure)
  • Insertions and Deltions add or remove an extra base (this causes a frameshift off all codons)

Most mutations are SILENT which have no effect on the protein coding. If a change in coding occurs this may be benefical to the organism or harmful and cause diseases and conditions like Huntingtons Disease that affects mostly middle aged people( An inherited disease).


Programmed cell death (non harmful)

  1. Enzymes break down cytoskeleton
  2. Cell surface membrane shrinks and blebs form
  3. Chromatin condenses, and DNA breakes into fragments
  4. Vesicles formed containg organelles
  5. Vesicles engulfed by Phagocytosis

Lac Operon

It is a DNA Operon ( a length of DNA made up of structual genes, promoter region and operator region.

  • It dosent matter if lactose is present or not, the regulator gene always expresses the repressor protein.

If lactose is absent,

  • The repressor protein is able to bind to the promoter region.
  • This prevents RNA polymerase to bind.
  • Resulting in no structal genes synthesised

If Lactose is present,

  • The repressor protein is still produced but lactose binds to the protein.
  • This causes a change in the tertiary structure
  • The repressor protein cannot bind to the promoter region
  • RNA polymerase can bind.
  • It transcribes the mRNA to code for lactose permease and B-galactosidase

The benefit of the lac operon is that energy and resources are not wasted for coding enzymes with no specific use.


This process will produce gametes. They are haploid which combine to…


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all DNA, genetics and evolution resources »