1. The Genetic Code and DNA Replication
B-4.3 Explain how DNA functions as the code of life and the blueprint for proteins.

2. DNA = Code of Life
DNA, which comprises an organism’s chromosomes, is considered the “code of life”
Code of life = contains the code for each protein that an organism needs to survive

3. Determining Types of Proteins to Make
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
“Codes For” = blueprint for a certain amino acid
*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

4. Nucleotides to Codons

5. A Complete Set of Chromosomes
Each autosome (somatic) cell in an organism contains a complete set of chromosomes.
Autosomes = body cells
Sex Cell = sperm/egg cells
The number of chromosomes varies depending on the organism.

6. A Complete Set of Chromosomes
Examples:
humans have 23 pairs of chromosomes
46 Total Chromosomes
dogs have 39 pairs of chromosomes
78 Total Chromosomes
potatoes have 24 pairs of chromosomes
48 Total Chromosomes
Organisms get 1 set of chromosomes from each parent
Maternal Chromosomes = come from the mother
Paternal Chromosomes = come from the father

7. Autosomes vs. Sex Chromosomes
There are 2 types of chromosomes:
Autosomes = non-sex determining chromosomes
Sex Chromosomes = chromosomes that determine the sex of the individual

8. Autosomes vs. Sex Chromosomes
All somatic cells contain ONE PAIR of each type of chromosome
1 Maternal Chromosome + 1 Paternal Chromosome = 1 Homologous Pair
Because one chromosome comes from the mother and one from the father, traits are passed on to offspring.

9. 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. This makes 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.

10. From 1 Molecule of DNA to 2 Molecules
Not only does DNA function as the code of life for protein synthesis, but 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

11. DNA Replication
DNA replication is carried out by a series of enzymes in the nucleus of the cell.
The Steps of DNA Replication:
Enzyme, helicase, unzips the 2 strands of DNA, separating the base pairs
Each of the separated strands serves as a template for the attachment of complementary bases by another enzyme, DNA polymerase

12. *Remember: each exposed base can only bond to its complimentary base*
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 molecule is made up of one NEW STRAND and one OLD STRAND

13. Try This and Reviewing…
Using the base pairing rules of replication, what is the complimentary strand of DNA for the following examples?
A T T C G A G T T A G T
T G A C C C G A T T A C
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?