DNA & RNA

• genetics is the study of our genes & how characteristics are passed from parent to offspring
• heredity is the passing of features from parent to offspring by means of genes
• a gene is a section of DNA that causes the production of a protein
• gene expression is the way that genetic information is decoded in a cell & used to make a protein
• chromosomes make up protein & DNA, the protein holds the DNA in a tightly coiled structure so it fits inside a nucleus
• junk DNA is a section of DNA that doesn't code for protein
• adenine connects to thymine, cytosine connects to guanine
• DNA molecule is two strands of DNA joined together
• DNA are double-helix shaped
• bases are connected by hydrogen bonds
• genetic code is a sequence of bases in DNA that gives the instruction for a cell to form a protein
• a codon/triplet is a sequence of 3 bases that code for an amino acid
• duplication of DNA happens in the interphase of cell divisions
• DNA = deoxyribonucleic acid
• DNA replicates in order for the new cell to have the exact copy of DNA as the parent cell
• steps in replication of DNA

  • Double helix unwinds
  • enzymes break H-bonds, separating the 2 strands of DNA
  • Loose DNA bases enter nucleus from cytoplasm and attach to exposed complimentary bases
  • Each of the DNA strands act as a template for new DNA being formed
  • new strands re-winds forming double-helix
  • each new double-helix has half new + half original DNA identical to the original double-helix and to the other new double helix being formed
• genetic screening works by adding a genetic probe to a sample from the person

  • the probe will only attach to an unaltered gene
  • if the probe doesn't attach then the gene has been unaltered
• screening is done in two ways

  • adult screening
  • embryonic/foetal screening
• adult screening

  adults may be a carrier of defective gene, this means they could pass disorder to their offspring e.g. sickle cell anemia
• benefit of adult screening is people gain information on the chance of passing disease onto offspring and how it may effect the child
• embryonic/foetal screening

  cells are removed from embryo, placenta or fluid surrounding the foetus.

  these cells tell if the embryo/foetus has a genetic disorder

  e.g. sickle cell anemia, down syndrome
• ethics in genetic screening

  public knowledge- issues can arise about whether a person wishes to know about a genetic disorder that will effect them in later life.

  genetic tests may cause embarrassment to person affected

  would the knowledge of the screening allow a family to prepare for the future or be faced with a difficult decision regarding termination of the pregnancy
• DNA Profiling- method of making unique bands from a persons DNA which can be used to compare with the profile of another person
• genetic screening- testing DNA for the presence/absence of a particular gene or an altered gene
• uses of DNA profiling

  forensics

  maternity/paternity
• how genetic profiling works

  DNA is released from cells

  DNA is cut into fragments

  The fragments are separated

  The patterns are compared
• DNA is released from cells

  cells are broken down to release DNA from nucleus

  by using washing up liquid and salt mixture

  the washing up liquid dissolves the cell and nuclear membrane

  the salt mixture causes the DNA to clump together
• DNA is cut into fragments

  restriction enzymes cut DNA into fragments at specific base sequences
• The fragments are separated

  process= gel electrophoresis

  DNA fragments are placed into small maching containing sugar-based gels

  electrical current passed through gel which pulls DNA to the other end of the gel

  the smaller fragments are faster and further than the larger ones
• The patterns are compared

  only identical twins have the same DNA profile, if patterns are the same then they came from the same person
• screening is done in two ways

  Adult screening

  Embryonic/foetal screening
• Adult screening


  adults may be a carrier of a defective gene, this means they could pass a disorder to their offspring e.g. Sickle cell anemia

  Benefit= people gain information on the chance of passing a disease onto their offspring
• RNA= Ribonucleic acid
• structure of RNA

  sugar=Ribose

  Bases=A,U,G,C

  Strands=Single stranded
• Structure of DNA

  Sugar=Deoxyribose

  Bases=A,T,G,C

  Strands=Double stranded
• DNA is found in the nucleus or mitochondria
• RNA is found in the nucleus & cytoplasm
• Types of RNA

  mRNA=Messenger RNA

  tRNA=Transfer RNA

  rRNA=Ribosomal RNA
• Francis Watson, James Crick worked out the structure of DNA in 1953 with the help of Rosalind Franklin
• Nucleotides


  units of DNA=nucleotides

  3 parts=Phosphate group, sugar (5carbon), nitrogenous base