Chapter 3, Section 4 Notes (p.97-103)
I.
The Genetic Code
a. Proteins determine traits (size, shape, color, etc.)
b. Chromosomes are made of DNA
c. DNA molecules made of four nitrogen bases
i. Adenine
ii. Thymine
iii. Guanine
iv. Cytosine
d. Genes are made up of a series of nitrogen bases
e. Order of nitrogen bases determines the protein that is produced
II.
How Cells Make Proteins
a. Protein synthesis: the production of proteins
i. Chromosomes found inside nucleus in a cell
ii. Proteins are produced in ribosomes (outside nucleus)
b. RNA – ribonucleic acid i. Made of one strand of nitrogen bases
ii. Contains uracil INSTEAD of thymine
c. Types of RNA
i. Messenger RNA – copies coded message from DNA (in nucleus)
and carries it to ribosome (in cytoplasm)
d. Transfer RNA – carries amino acids to the ribosome and adds them to a
growing protein
e. Translating the Code
i. DNA molecules “unzip” between base pairs, creates messenger
RNA to pair up with DNA strand, genetic info. is transferred from the
DNA to the messenger RNA
ii. Messenger RNA travels to cytoplasm and attaches to a ribosome
(where protein production begins); ribosome moves along the
messenger RNA strand
iii. Transfer RNA attaches to messenger RNA by matching up with
three-letter codes of bases; amino acids are added to the growing
protein chain
iv. Protein chain continues to grow until the ribosome reaches the
“stop” code; the ribosome releases the completed protein
III.
Mutations
a. Mutations: cause cells to produce an incorrect protein during synthesis.
The protein may cause an organism’s traits to change because of this
i. Only mutations occurring in a parent’s sex cells can be passed on
to the offspring.
b. Types of mutations:
i. Single nitrogen bases being substituted for other bases (can occur
during DNA replication)
ii. Chromosomes fail to separate correctly (offspring could end up
with too many or too few chromosomes)
c. Effects of Mutations
i. Mutations can be helpful, harmful, or no positive or negative effect
on the organism
ii. Mutations are harmful when they reduce the organism’s chance
for survival or reproduction
iii. Helpful mutations improve an organism’s chance for survival