cell division ✩

• DNA

  Deoxyribonucleic acid, the chemical that all of our genetic material is made of
• DNA

  • It's a polymer made up of lots of similar units stuck together
  • It has two strands which are stuck together to form a double helix
• If you unraveled all the DNA in a single cell, the strand would be over two meters long
• Chromosome

  A really tight coil of DNA, there are 46 chromosomes in each of our cells
• There are only 23 different types of chromosomes, as we have two of each type, one from each parent
• Sex chromosomes

  The 23rd pair, consisting of an X chromosome and a Y chromosome
• Chromosomes only look like an X shape just before cell division
• Gene

  A small section of DNA that codes for a particular type of protein
• There are only 20 different types of amino acids, but they can be combined in many different sequences to form thousands of different proteins
• Genome

  The entire set of genetic material in an organism
• Scientists have now worked out the complete human genome, which allows them to identify genes linked to certain diseases
• Genomes can be used to trace the migrations of our ancestors
• Allele

  Different versions of the same gene
• Dominant

  One of the alleles that gets expressed
• Recessive

  One of the alleles that does not get expressed when the dominant allele is present
• Homozygous

  Having two of the same alleles for a gene
• Heterozygous

  Having two different alleles for a gene
• Dominant allele present

  Dominant allele gets expressed
• Recessive allele present


  Recessive allele does not get expressed
• Genotype

  The entire collection of alleles an organism has
• Phenotype

  The characteristics an organism displays, determined by its genotype
• Characteristics are often determined by multiple interacting genes, not just a single gene
• Genes code for different forms of the same protein, which are called alleles
• DNA


  Two strands wrapped around each other in a double helix
• Structure of DNA

  1. Nucleotides

  2. Complementary base pairing

  3. Gene coding for a protein
• Nucleotide

  Monomer unit of DNA, made up of a phosphate, sugar, and base
• Bases in DNA

  • Adenine
  • Thymine
  • Cytosine
  • Guanine
• DNA

  • Polymer made up of many nucleotides
  • Sugar phosphate backbone forms the outside
  • Bases in the middle hold the two strands together
• Complementary base pairing

  A always pairs with T, C always pairs with G
• Determining complementary DNA strand

  Look at original strand and pair bases accordingly
• Genetic code

  Sequence of DNA bases
• Gene

  Specific sequence of bases that codes for a protein
• Protein formation from DNA

  1. DNA read as triplet codes

  2. Amino acids coded for combined in order

  3. Chain of amino acids folds to form protein
• Proteins

  • Each type has a unique shape allowing it to carry out a particular function
  • Main uses are in enzymes, hormones, and structural proteins
• Mutation

  A change in the DNA base sequence
• Mutations happen spontaneously in our cells all the time, particularly when DNA is being duplicated before cell division like in mitosis
• Things that increase the risk of mutations

  • Carcinogens (harmful chemicals like in cigarette smoke)
  • Certain types of radiation (like x-rays or gamma rays)
• These things (carcinogens and radiation) don't always cause mutations, they just increase the risk of a mutation occurring
• Gene

  A section of DNA that codes for protein
• Triplet/Codon

  A group of 3 bases that codes for one of the 20 different amino acids