the genetic code & dna...
TRANSCRIPT
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?