BIO topic 3

• meiosis

  is a process of cell division where the

  1. division - parent cell splits into 2 cells that have 1/2 the genetic material as the parent cell.
  2. division - then 4 non identical haploid cells are produced.
• where does meiosis occur

  females - ovaries

  men - testicles
• in the 1st cell division what happens

  the dna duplicates so that there's enough for each new cell

  chromosomes pairs line up in the center of the cell

  in the division the chromosome pairs r then split so there is a now a mixture of mum + dad chromosomes in the 2 new cells.
• what does the mixture of mum + dad chromosomes in the 2 new cells create

  genetic variation in the offspring
• what happens in the 2nd cell division of meiosis

  the CHROMATIDS line up in the center of the cell.

  as the cell divides they r split apart and now 4 haploid genetically diff cells are produced --> gametes
• what is a gamete

  the 4 haploid genetically diff cells produced in meiosis
• why are haploid cells needed for sexual reproduction?

  bc the male and female gamete fuse together to form a (full) zygote in the process of fertilisation
• asexual reproduction

  thru mitosis 2 genetically identical daughter cells r produced

  e.g bacteria
• sexual reproduction

  4 haploid genetically non identical cells (gametes) r produced
• +ive of asexual R

  • quick
  • only 1 parent is needed - don't need to find a mate - so can divide whenever they want
• -ive of asexual r

  • reduces genetic variation - so if there r selection pressures the whole species r at risk
• + ive of sexual r

  • creates genetic variation - more likely to survive selection pressures + can lead to natural selection by evolution so better adapted
• -ive of sexual r

  • takes time - human 9 months
  • need a mate
  • fewer offspring created
• sexual reproduction

  2 organisms combine to produce 2 genetically diff cells
• sexual reproduction steps

  1. meiosis produces gametes.
  2. fertilization - haploid gametes fuse together to produce a diploid zygote.
  3. diploid zygote undergoes mitosis + then develops into an embryo
  4. embryo inherits characteristics from both of its parents bc it has a mixture of chromosomes
• DNA -deoxy ribo nucleic acid 


  are stored as chromosomes and contain genes

  2 strands coiled to make a double helix structure made of nucleotides

  strands r linked by complementary bases w/ weak H+ bonds between them

  nucleotides have a sugar phosphate backbone and 1 of the 4 bases is attached to the sugar
• bases - dna

  each base on 1 strand is bonded to its complementary base on the other strand

  by weak hydrogen bonds

  G C A T

  g=c a =t
• nucleotide of dna

  is a monomer of dna

  phosphate - bonded to - sugar - bonded to base
• extracting fruit cells from dna

  1. mash up strawberrys + add detergent and salt
  2. add ice cold ethanol
• why do we mash up strawberries - extracting fruit cells from dna

  to release the dna from its cells
• why do we add detergent - extracting fruit cells from dna

  breaks down the cell membrane releasing the dna
• why do we add salt - extracting fruit cells from dna

  makes the dna stick together
• why do we add ice cold ethanol - extracting fruit cells from dna

  separates dna from other solids

  causes the dna to form as a stringy white solid which can be fished out with a glass rod
• who discovered dna

  franklin + watson
• what does transcription do

  makes mRNA from gene DNA triplet codes from an RNA polymerase in the nucleus
• steps of transcription

  1. RNA polymerase binds to a noncoding region of the DNA in front of a gene and unzips the 2 DNA strands by breaking the weak H2 bonds between the complementary bases
  2. RNA polymerase moves along the DNA template strand and attaches complementary RNA bases to the strand creating a mRNA strand
  3. triplet code of mRNA or DNA codes for 1 Amino Acid
  4. mRNA leaves the Nucleus thru N pores bc the weak H2 bonds between the mRNA and DNA strand are broken.
• triplet code

  3 of the bases

  e.g on DNA - GCA

  on mRNA - GCU
• what is the genome

  entire DNA of an organism
• gene 


  a section of DNA molecule that codes for a specific protein
• protein synthesis


  production of protein by transcription + translation
• how are specific proteins created?

  order of bases in a gene decides the order of AA + how it folds which decides the specific shape of the protein created which decides its function.

  e.g the protein - enzyme have specifically shaped active sites which allow it to catalyze only specific reactions.
• translation

  protein being made from mRNA segment at the cytoplasm in the ribosome
• translation steps

  1. mRNA binds to the ribosome
  2. the tRNA's (1) carrier molecule's anticodon joins to the mRNA's codon
  3. then the tRNA 1 passes the amino acid attached to it down to tRNA 2.
  4. tRNA 1 will leave the ribosome and the ribosome moves along the mRNA
  5. then this continues until polypeptide chain is formed which will get bigger and fold into a functioning protein.
• codon 


  is the triplet code on the mRNA
• anticodon 


  is the complementary triplet code on tRNA
• polypeptide chain

  molecule made up of AA
• mutation

  a rare random change to a DNA's base sequence that can be inherited and can be caused by intrinsic or extrinsic factors
• what happens if there's a mutation on the coding DNA of the gene

  mutation in a gene creates a genetic variant

  which can code for a diff sequence of AA causing it to fold differently creating a diff shaped protein w/ a different activity

  which can change the phenotype of an organism
• what happens if there's a mutation on the non coding DNA of the gene

  mutation in a gene creates a genetic variant

  if a mutation happened on the non-coding DNA in front of the gene the RNA polymerase (transcription) would find it harder or easier to bind do it.

  this would affect the amount of mRNA that's transcribed

  affecting the amount of protein created

  based off the p function this could affect the phenotype of an organism
• if there's a mutation in the non -coding region of DNA can it have an affect on the phenotype of the organism or is that only when a coding region is mutated ?

  Yes, it can affect phenotype. bc M in the NC R can affect the amount of mRNA transcribed and therefore the amount of protein created + depending on the function of protein the phenotype of an organism can be affected.