Introduction to genetics
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Introduction to Genetics. -the DNA molecule -nucleotides -chromosomes vs genes -DNA replication -cell division. The DNA molecule. Composed of 2 polymers of nucleotides Polymers are oriented in antiparallel Molecule resembles a spiral staircase of complementary base pairs.

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Introduction to genetics l.jpg

Introduction to Genetics

-the DNA molecule

-nucleotides

-chromosomes vs genes

-DNA replication

-cell division


The dna molecule l.jpg
The DNA molecule

  • Composed of 2 polymers of nucleotides

  • Polymers are oriented in antiparallel

  • Molecule resembles a spiral staircase of complementary base pairs


Nucleotide structure of dna l.jpg
Nucleotide structure of DNA

  • Each nucleotide of DNA contains:

    • Deoxyribose

    • Phosphate

    • Nitrogen base (either A, G, C, T)


Nucleotide structure of rna l.jpg
Nucleotide structure of RNA

  • Each nucleotide of RNA contains:

    • Ribose

    • Phosphate

    • Nitrogen base (either A, G, C, U*)

      *contains Uracil instead of Thymine


Dna structure l.jpg
DNA structure

  • “Double helix” propsed by Watson and Crick (1953)

  • Antiparallel backbones

  • Complementary base pairing:

    • Adenine to Thymine

    • Cytosine to Guanine



Chromosomes vs genes l.jpg
Chromosomes vs Genes

  • A chromosomeconstitutes an entire DNA molecule + protein

    • Protein = histones

    • Supercoiled DNA in nucleosomes

    • Humans contain 46 such molecules (23 pairs)

      • 44 somatic chromosomes

      • 2 sex chromosomes (X +Y)


Chromosomes vs genes8 l.jpg
Chromosomes vs Genes

  • Genes constitute distinct regions on the chromosome

  • Each gene codes for a protein product

  • DNA -> RNA-> protein

  • Differences in proteins brings about differences between individuals and species


How do chromosomes become double stranded answer dna replication l.jpg
How do chromosomes become double stranded?Answer: DNA replication

  • During the life of the cell, each chromosome of DNA makes a copy of itself

  • This must occur prior to cell division to insure each daughter cell gets a complete set


Therefore prior to dividing any cell must first replicate dna l.jpg
Therefore, prior to dividing, any cell must first replicate DNA

  • Each single-stranded (SS) chromosome duplicates to become a double-stranded (DS) chromosome

  • Example:

    • A human cell is formed with 46 SS chromosomes

    • Each chromosome replicates to produce 46 DS chromosomes



Dna replication occurs during the life of a cell the cell cycle l.jpg
DNA replication occurs during the life of a cell = the DNACell Cycle

  • DNA replicates (makes a copy of itself) to produce DS chromosomes

  • During this time, the cytoplasmic contents also duplicate

  • Spindle tubules form to aid in the process of cell division

    • Mitosis in body cells

    • Meiosis in sex cells