DNA

• what is DNA made up of?

  nucleotides containing = deoxyribose , nitrogenous base and a phosphate group
• how are DNA strands made?

  nucleotides join via condensation reaction forming phosphodiester bonds creating the sugar-phosphate backbone
• DNA structure?

  double helix , 2 strands which are anti parallel, 4 bases guanine cytosine adenine thymine , held together by hydrogen bonds
• what is semi-conservative replication?

  DNA replication where each new DNA molecule consists of one original strand and one newly synthesized strand.
• process of DNA replication?

  1)DNA helicase breaks hydrogen bonds between bases to unwind the helix structure.

  2)each strand is used as a template , complimentary base pairing means free DNA nucleotides are attracted to exposed bases.

  3) condensation reaction joins the strands via DNA polymerase and hydrogen bonds form between bases.

  4) each new DNA contains 1 new and 1 original strand
• how is nuclear DNA coiled?

  Around histone proteins creating compact chromosomes
• what is mRNA?

  messenger RNA which carries genetic code to ribosomes , single strand
• what is tRNA?

  carries ammino acids used to make proteins , single strand folded as a clover hydrogen bonds between specific bases , anti codon and ammino acid binding site
• transcription process?

  1)hydrogen bonds broken by DNA helicase separating strands to expose some bases and one strand used as template to make mRNA

  2) RNA polymerase lines up free RNA nucleotides causing complimentary base pairing , RNA polymerase joins up their backbone

  3) double helix reforms , mRNA moves out of nucleus through nuclear pores and attaches to a ribosome
• what is splicing?

  Splicing is the process of removing introns and joining together exons in pre-mRNA to produce a mature mRNA molecule.
• translation?

  1)mRNA attaches to a ribosome tRNA carries ammino acids to it , ATP provides energy needed for ammino acids to bond to tRNA

  2) tRNA with a complimentary anticodon to the first codon attaches via specific base pairing

  3) a second tRNA does the same

  4) the 2 ammino acids are joined by a peptide bond and first tRNA leaves

  5)third tRNA binds to next codon its ammino acid joins the chain this continues till a stop codon then the polypeptide chain moves away from ribosome
• features of genetic code?

  it is degenerate , ammino acids are coded for by more than one triplet

  it is universal , same bases code for the same ammino acids in all living things

  it is non-overlapping , triplets dont share bases and are read separately
• process of meiosis?

  1)DNA unravels and replicates creating 2 copies of each chromosomes called chromatids.

  2) DNA condenses forming 2 sister chromatids joined by a centromere

  3) meiosis 1 , chromosomes arrange themselves into homologous pairs , these are later separated halving the chromosome number.

  4) meiosis 2 , sister chromatids are separated

  5) 4 haploid cells that are genetically different are produced
• what is crossing over?

  in meiosis 1 , chromatids cross over meaning each daughter cell has different alleles
• what is independent segregation?

  Independent segregation refers to the random distribution of homologous chromosomes during meiosis, resulting in the independent assortment of alleles.
• what is non-disjunction?

  Failure of homologous chromosomes or sister chromatids to separate properly during cell division, resulting in an abnormal distribution of chromosomes in daughter cells.
• what does mitosis produce?

  Two genetically identical daughter cells.
• what is mitosis used for?

  Cell division , growth and repare
• stages of cell cycle?

  g1 = cell grows , new organelles and proteins made

  synthesis = cell replicates DNA

  g2 = cell grows , proteins needed for division made
• process of mitosis?

  interphase = DNA is unravelled and doubled , organelles replicated and ATP content increased for division.

  prophase = chromosomes condense , centrioles move to opposite ends of cell forming spindle fibres and nuclear envelope breaks down

  metaphase = chromosomes line up along equator attach to spindle by centromere

  anaphase = centromeres divide separating sister chromatids pulling them to opposite poles

  telophase = chromatids reach poles and uncoil becoming chromosomes , nuclear envelope forms around each group , division of cytoplasm creates 2 daughter cells ( cytokinesis)