Science Term 1 Notes

• Genetics


  The study of inheritance
• DNA


  Genetic makeup that carries the instructions for life (deoxyribonucleic acid)
• Nucleotides


  A subunit of DNA
• Hydrogen Bonds


  Chemical bonds that hold the two strands of DNA together
• Complementary Pairing


  Adenine always binds with thymine and guanine always binds with cytosine
• Chromosome


  A structure of tightly wound DNA
• Gene


  A length of chromosome
• Triplet


  Three DNA bases that code for an amino acid, codon for mRNA
• Genetic information/DNA is in the nucleus of cells
• DNA is a double stranded molecule that forms a double helix shape that twists like a ladder
• DNA


  A polymer as it is made up out of numerous amounts of subunits known as nucleotides
• Components of a nucleotide

  • 5 carbon sugar molecule called deoxyribose
  • Nitrogenous base – adenine (A), thymine (T), guanine (G), cytosine (C)
  • Negatively charged phosphate group
• Nucleotides bind together in the middle using hydrogen bonds to form two long strands and then twist to form a double helix
• Sugar and phosphate form the side of the ladder and are called sugar-phosphate backbone, while the nitrogenous base come towards the center and form the steps of the ladder
• Complementary pairing


  The nitrogenous bases on one strand always pairs with other strand bases: Adenine and Thymine, Guanine and Cytosine
• Guanine and adenine have double ring structures, putting them in a group of molecules called purines, thymine and cytosine have single ring structures which makes them apart of the pyrimidines. A purine is larger out of the two, so it always pairs with the smaller group to achieve a more stable molecule.
• DNA replication


  1. DNA wraps around proteins called histones to form a structure called chromosomes

  2. Each molecule of DNA forms one chromosome

  3. Along each length of chromosomes are structures called genes which are units of inheritance
• Before replication, chromosomes appear as a single structure, after replication, two chromatids (one of two molecules of DNA that make up a chromosome) join by centromeres (connects the two chromatids and is the location where fibres attach during cell division) to form X-shape known as sister chromatids
• Biomacromolecules


  • Proteins
  • Carbohydrates
  • Lipids (fats and oils)
  • Nucleic acids
• Nucleic acid


  Has two forms: DNA and RNA (ribonucleic acid)
• Purpose of DNA


  To make proteins
• Protein synthesis


  1. Transcription – DNA code for protein is 'written down' in mRNA form

  2. Translation – Convert the code written down as mRNA into a chain of amino acids
• Transcription occurs in the nucleus of cell, requires getting access to DNA code in genes, to access the code, the double strand of DNA needs to unwind so an enzyme can come in and read the code on one of the DNA strands (called DNA template strand), as it reads, it builds a copy using RNA nucleotides
• RNA uses complimentary pairing except has a uracil base, the single stranded RNA is called mRNA (messenger RNA), when it peels away from the template strand, DNA binds together and the mRNA leaves the nucleus to go to the ribosomes
• Translation


  1. mRNA is decoded and bases are put into codons

  2. tRNA then brings amino acids to ribosomes
• Sexual Reproduction


  Reproduction involving sex cells
• Gametes


  Sex cell that combine to create offspring
• Gonads


  Sex organs, testes in male and ovaries in female
• Zygote


  A fertilised egg produced by the fusion of male (sperm) and female (ovum or egg) gametes
• Embryo


  Zygote eventually turns into the embryo
• Haploid


  A cell containing only one set of chromosomes
• Diploid


  A cell containing two sets of chromosomes
• Somatic Cells


  The body cells of an organism
• Meiosis


  The process in which gonads make the haploids gametes
• Mitosis


  Process by which diploid somatic cells make identical diploid copies of themselves to grow and repair
• Reduction Division


  Cell division in which there is a reduction in the genetic material between parent and daughter cells
• Fertilization


  The fusing of egg and sperm
• Karyotype


  Pictorial representation of an organism's chromosomes
• Non-Homologous Chromosomes


  Nonmatching chromosomes
• Autosomes


  Out of 23 pairs, in humans, chromosomes pairs 1 to 22 are known as autosomes