THE GENETIC CODE & DNA REPLICATION

DNA = Code of Life

¨  DNA, which comprises an organism’s chromosomes, is considered the “code of life”

¨  It contains the code for each protein that an organism needs to survive

Types of Proteins

¨  The type of protein an organism makes is determined by the order of the nitrogenous bases

¨  Each 3 base pairs of DNA is called a “codon”

¤  Each codon “codes for” a particular amino acid n  “Code for” = blueprint for a certain amino acid n  ** Remember: amino acids = monomer of proteins

¨  A gene is a segment of DNA, made up of many codons, that codes for one particular protein. ¤  Proteins give organisms their unique traits.

Nucleotides to Codons

A Complete Set of Chromosomes

¨  Each autosome (somatic) cell in an organism contains a complete set of chromosomes. ¤ Autosomes = body cells ¤ Sex Cells = Sperm / egg cells

¨  The number of chromosomes varies depending on the organism

A Complete Set of Chromosomes

¨  Example: ¤  Humans have 23 pairs of chromosomes

n  46 TOTAL chromosomes

¤  Dogs have 39 pairs of chromosomes n  78 total chromosomes

¤  Potatoes have 24 pairs of chromosomes n  48 total chromosomes

¨  Organisms get 1 set of chromosomes from each parent ¤  Maternal Chromosomes = come from mother ¤  Paternal Chromosomes = come from father

Autosomes vs. Sex Chromosomes

¨  There are 2 types of chromosomes: 1.  Autosomes = non-sex

determining chromosomes

2.  Sex Chromosomes = chromosomes that determine the sex of the individual

Autosomes vs. Sex Chromosomes

¨  All somatic cells contain ONE PAIR of each type of chromosome ¤  1 Maternal + 1 Paternal

= 1 Homologous Pair

¨  Because one chromosome comes from the mother and one from the father, traits are passed on to offspring.

Organisms are Related

¨  Each chromosome consists of thousands of genes ¤  This is because organisms need thousands of specific

proteins to live and reproduce

¨  Organisms that are closely related may have genes that code for the same proteins, making organisms similar. ¤  Example: All maple trees have many of the same genes

¨  Organisms that are not closely related share fewer genes. ¤  Example: Red maple trees share more genes with oak

trees than with earthworms.

DNA Replication

¨  Not only does DNA function as the code of life for protein synthesis, DNA also replicates to ensure that every new cell has identical DNA

¨  DNA replication: ¤ Copying of 1 molecule of

DNA to make 2 identical molecules of DNA

DNA Replication

¨  DNA replication is carried out by a series of enzymes in the nucleus of the cell.

¨  The steps of DNA replication: 1.  Enzyme, helicase, unzips the 2 strands,

separating the base pairs 2.  Each of the separated strands serves as a

template for the attachment of complementary bases by another enzyme, DNA polymerase

DNA Replication

¨  Remember: each exposed base can only bond to its complimentary base! ¤ Adenine (A) --- Thymine (T) ¤ Guanine (G) --- Cytosine (C)

¨  The result of DNA replication is 2 identical DNA molecules ¤ Each molecules is made up of one NEW strand

and one OLD strand

Try this…

¨  Using the base pairing rules of replication, what is the complimentary strand of DNA for the following examples:

1)  A T T C G A G T T A G T 2)  T G A C C C G A T T A C

Review

¨  Give an example of 2 organisms that are likely to be closely related to one another.

¨  Give an example of 2 organisms that are NOT likely to be closely related to one another.

¨  Why is DNA called the code of life?