biology paper 1

• Allele


  Different versions of the same gene
• Homozygous


  Having two of the same alleles for a particular gene
• Heterozygous


  Having two different alleles for a particular gene
• Dominant allele


  The allele that gets expressed when present, regardless of the other allele
• Recessive allele


  The allele that only gets expressed when two copies are present (homozygous recessive)
• Genotype


  The entire collection of alleles an organism has
• Phenotype


  The characteristics an organism displays, determined by its genotype
• Genes code for particular types of proteins
• There are often multiple forms of the same protein, each with a different genetic code (alleles)
• We have two copies of every gene, one from each parent
• If the two alleles are the same, the organism is homozygous
• If the two alleles are different, the organism is heterozygous
• When an organism is heterozygous, one allele is dominant and the other is recessive
• The dominant allele is always expressed, even in heterozygous organisms
• The only way to have a recessive trait expressed is if the organism is homozygous recessive
• Genotype refers to the genetic makeup, while phenotype refers to the expressed characteristics
• DNA


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


  1. Nucleotides

  2. Complementary base pairing

  3. How a gene codes for a protein
• Nucleotide


  Monomer that makes up DNA, consisting of a phosphate, sugar, and base
• Bases in DNA


  • Adenine
  • Thymine
  • Cytosine
  • Guanine
• DNA


  • Polymer made up of many nucleotides
  • Phosphate and sugar form a backbone
  • Bases stick out and pair up between strands
• Complementary base pairing


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


  1. Look at sequence of one strand

  2. Determine complementary bases for other strand
• Genetic code


  Sequence of DNA bases
• Gene


  Specific sequence of bases that codes for a protein
• How a gene codes for a protein

  1. DNA sequence read as triplets

  2. Triplets code for specific amino acids

  3. Amino acids combine in order to form a protein
• Proteins


  • Unique shape allows them to carry out specific functions
  • Main uses are in enzymes, hormones, and structural proteins
• Cells


  The basic building blocks of life that can replicate independently
• Multicellular organisms like animals and plants contain many cells that divide to grow or replace dead cells, not to create new organisms</b>
• Bacteria are single-celled prokaryotic organisms
• Subcellular structures common to animal and plant cells


  • Cell membrane
  • Nucleus
  • Cytoplasm
  • Mitochondria
  • Ribosomes
• Plant cells


  • Have a rigid cell wall made of cellulose
  • Contain a permanent vacuole with cell sap
  • Contain chloroplasts for photosynthesis
• Bacterial cells


  • Lack mitochondria and chloroplasts
  • Have a single circular strand of DNA instead of a nucleus
  • May have additional plasmids
  • May have flagella for movement
• Bacteria are unicellular organisms, each individual cell is a whole organism
• Photosynthesis occurs in the chloroplasts of plant cells, using chlorophyll to absorb light energy
• Mitochondria in cells break down glucose through aerobic respiration to provide energy
• Microscopy


  The use of microscopes
• Object


  The real object or sample that you're looking at
• Image


  The image that we see when we look down the microscope
• Magnification


  How many times larger the image is than the object