Biology
Chromosomes Structure
DNA Transcriptions and Translation
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The Triplet Code
o Gene: A sequence of nucleotide bases in a DNA molecule that codes for the
production of a specific sequence of amino acids, that in turn make up a specific
polypeptide (protein)
o Codons: Three triplets of bases that codes for a specific amino acid
 Some of the triplet codes are start and stop signals: ensures the DNA is
read correctly; tell the cell when to start or stop (met-AUG  start)
 Degenerate: 61 different triplets (minus 3 for stop signals) to minimize the
impacts of mutations
 Universal: every organism uses the same code for the same amino acid
 Non-overlapping
o Anti-codon:
 tRNA molecules that has a triplet of unpaired bases at one end
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Transcription
o Location: in the nucleus
o Process:
 DNA is unwound and the hydrogen bonds broke
 mRNA produces a complimentary copy of the DNA
 RNA polymerase bonded RNA nucleotides together to form the sugarphosphate backbone of the molecule
 After being transcribed, the double-strand reforms
 The mRNA leaves the nucleus through a pore in the nuclear envelope
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Translation:
o Location: in the cytoplasm
o Process:
 mRNA attaches to the ribosome
 tRNA carry complementary anticodon to the codon of the mRNA
 The ribosomes move along the mRNA in the 5’ to 3’ direction
 The amino acid chain is then formed
Meiosis and Mitosis
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Meiosis
o Produces 4 daughter cells that are genetically different from each other and from
the parent cell
o Sources of genetic diversity:

Independent Assortment:
 The alleles of two or more different genes get sorted into the
gametes independently
 Homologous line up in random orientations in metaphase
 Crossing over
 The process where chromatid breaks down in mitosis and rejoins
to the chromatid
o Process:
 Prophase I:
 DNA condenses and become visible as chromosomes
 DNA is being replicated and each chromosome consists of two
sister chromatids
 The homologous pair become close to each other for crossing over
between non-sister chromatids
 The centrioles migrate to the opposite pores and spindle is formed
 Nuclear envelop breaks down and the nucleolus disintegrates
 Metaphase I:
 The bivalents line up along the metaphase plate, and the spindle
fibers are attached to the centromeres
 Anaphase I:
 Chromosomes are being pulled to the opposite of the spindles
 The chromosomes are divided in half
 Telophase I:
 Chromosomes arrive at different poles
 Spindle fibers start to break down
 Nuclear envelop form around the two groups of chromosomes
 Cytokinesis:
 Cell surface membrane pinch inward to create a cleavage furrow
 The end product in two haploid cells
 Prophase II:
