DNA

• DNA


  Structure resembles a ladder
• Biomolecules


  • Carbohydrates
  • Proteins
  • Lipids
  • Nucleic acids
• Carbohydrates


  Immediate source of energy, contains sugar
• Proteins


  • Builds muscle
  • Responsible for regeneration of cells
  • Damage cells recuperate through proteins
• Amino acids


  Building blocks of proteins
• Types of amino acids

  • Essential
  • Non-essential
• Essential amino acids


  Body cannot produce, need to eat food rich in protein
• Non-essential amino acids


  Naturally produced by the body on its own
• Lipids


  • Fat and oil
  • Stored energy
  • Turned into energy if no sugar, which is why we get skinnier
• Nucleic acids


  • Responsible for expression of genes
  • Made of nucleotides - building blocks of nucleic acids
  • Responsible to create DNA and RNA
• DNA


  • Located in the nucleus
  • Looks like tightly-coiled molecule that contains gene (twisted ladder)
  • Building blocks of nucleic acids together with RNA
  • Stored (so that when we reproduce, genetic information is available and life will be possible), replicated (for reproduction purposes and regeneration), expressed (expressed by how we look) and diversified (enables us to be different from each other even if twins or siblings)
• DNA stands for Deoxyribonucleic Acid
• DNA contains genetic instructions
• DNA is made up of the sugar DEOXYRIBOSE
• DNA is made up of 2 strands
• DNA has A-T, C-G Base Pairing
• DNA is located in the nucleus
• DNA is the blueprint of biological guidelines
• RNA


  • One of the three macromolecules that are essential to life
  • Made up of the sugar RIBOSE
  • Made up of 1 strand
  • A-U, C-G Pairing
  • Located in the cytoplasm
  • Assists in carrying out DNA's blueprint guideline
• There are 3 types of RNA: messenger RNA (mRNA), ribosomal RNA (rRNA), transfer RNA (tRNA)
• mRNA


  • Located in the nucleus and cytoplasm
  • Carries information to make proteins from DNA in the form of a 3-letter code called CODON, which corresponds for a specific amino acid
• rRNA


  • Located in the cytoplasm, in the ribosomes
  • Directs translation of mRNA into proteins
  • rRNA is combined with proteins to form ribosomes
• tRNA


  • Located in the cytoplasm
  • Carries amino acids to ribosomes, where proteins are made in the process called PROTEIN SYNTHESIS
• DNA Replication


  1. Process of making two identical copies of DNA from the original DNA molecule before cell division

  2. DNA has to be copied before a cell divides

  3. DNA is copied during the S or synthesis phase of interphase

  4. New cells will need identical DNA strands
• Protein Synthesis


  1. Creation of protein

  2. Ribosomes (in the cytoplasm) create protein

  3. Proteins are made by combining 20 different amino acids in different combinations
• Transcription


  1. Copying of genetic information from DNA to RNA

  2. Part of DNA temporarily unzips and is used as a template to assemble complementary nucleotides into messenger RNA (mRNA)

  3. mRNA then goes through the pores of the nucleus with the DNA code and attaches to the ribosome
• Translation


  1. Decoding of mRNA into a protein

  2. Transfer RNA (tRNA) carries amino acids from the cytoplasm to the ribosome

  3. A series of three adjacent bases in an mRNA molecule codes for a specific amino acid—called a codon

  4. Each tRNA has 3 nucleotides that are complementary to the codon in mRNA

  5. Each tRNA codes for a different amino acid

  6. mRNA carrying the DNA instructions and tRNA carrying amino acids meet in the ribosomes

  7. Amino acids are joined together to make a protein
• Mutation


  • Change in the structure or amount of an organism's genetic material
  • Can be a tiny change in DNA structure or a large scale change in chromosome structure or number
• Types of mutation


  • Point mutations (Substitution, Inversion)
  • Frameshift mutations (Insertion, Deletion)
• Phenylketonuria (PKU)


  • Hereditary disorder caused by a genetic defect which disrupts the metabolic pathway
  • Affected person lacks the normal allele of the gene required to make the enzyme Phenylalanine Hydroxide
  • Phenylalanine is no longer converted to tyrosine, instead it undergoes alternative pathways which produces toxins that affect the metabolism of brain cells and severely limit mental development
• Cystic Fibrosis


  • Mucus is a slimy substance secreted by the inner lining of the wind pipe and intestine
  • Mucus is made of a glycoprotein which makes it thick, slimy and perfect for protection and lubrication
  • The genetic information for coding this glycoprotein is on chromosome 7
• Frequency of Mutation


  • In the absence of outside influences, gene mutations arise spontaneously and at random but occur rarely
  • Mutation rate varies from species to species, allele to allele
  • Most mutant alleles are recessive
  • A few mutant alleles are expressed by the first generation to inherit them because they are either dominant or sex linked
• Mutagenic agents


  Increases mutation rate
• Chromosomal Abnormalities


  • Chromosomes can be affected by mutations which bring about large scale changes to the genetic material
  • One type happens during meiosis in humans when unusual gametes can be formed which contain 22 or 24 chromosomes instead of the normal 23
  • This is called non-disjunction - formed when a spindle fibre fails and one of the pair of homologous chromosomes fail to become separated
• Down's Syndrome


  • Due to non-disjunction of chromosome 21
  • Abnormal egg (n=24) + normal sperm (n=23) abnormal zygote (n=47)
  • An extra copy of chromosome 21 is seen in the karyotype of someone with Down's syndrome
  • The affected individual is characterised by mental retardation and distinctive physical features
  • Egg mother cells of older women (80% due to maternal age) tend to be more prone to non-disjunction at meiosis
• Turner's Syndrome


  • If a gamete which possesses no sex chromosomes meets and fuses with a normal X gamete, the zygote formed has the following chromosome complement 44 + XO
  • Individuals are always female and short in stature
  • Their ovaries do not develop so they are infertile and fail to develop secondary sexual characteristics e.g. breast development and menstruation
  • Happens 1:2500 live births
• Klinefelter's Syndrome


  • Happens when an XX egg is fertilised by a normal Y sperm OR an normal X egg is fertilised by an XY sperm
  • Resulting with chromosome complement 44 + XXY
  • Individuals are always male and possess male sex organs
  • However they are infertile since their testes only develop to half the normal size and fail to produce sperm
  • Testes produce low levels of testosterone so facial hair, deepening of voice are only weakly expressed. Some sufferers develop small breasts
  • Occurs in 1:1000 live male births
• Cri Du Chat Syndrome

  • Missing piece of chromosome # 5 (deletion)
  • Symptoms: mental retardation, high-pitched cry that sounds like a cat
  • Incidence: avg. 1 in 40,000
  • Treatments: none
• Patau Syndrome


  • Trisomy 13
  • An extra copy of chromosome number 13
  • Severe mental retardation
  • Do not survive in infancy
  • Symptoms: Cleft lip, cleft palate, cerebral defects, anophthalmia, simian creases, polydactyly, trigger thumbs, and capillary hemangiomata
• Edward's Syndrome


  • Trisomy 18
  • Individuals with trisomy 18 often have slow growth before birth (intrauterine growth retardation) and a low birth weight