Download Chapter 11 Notes: DNA and Genes

Chapter 11 Notes: DNA and Genes
(These are not the same notes we did in class, but are pretty comprehensive)
Deoxyribonucleic Acid (DNA), is composed of monomers, called nucleotides. Each
nucleotide is made of a sugar (deoxyribose), a phosphate group, and one of 4 bases:
cytosine, guanine, thymine, and adenine. These nucleotides link together by covalent
(strong) bonds between the sugars and phosphate groups to form strands. Two of the
strands link together at the bases with hydrogen (weak) bonds.
A nucleotide
During DNA replication, an enzyme, helicase, “unzips” the DNA double helix by
breaking the weak hydrogen bonds between the bases. Another enzyme, DNA
polymerase, then moves along each strand of the molecule to rebuild each missing half
by matching up nucleotides that contain complementary bases to the original strand.
Remember the base pairing rule: C-G, and A-T.
In transcription, a single strand of mRNA is copied from DNA, by an enzyme called
RNA polymerase. In this case, however, thymine is replaced with uracil, so the “new”
base pairing rule is C-G & A-U. The mRNA is then able to move through the nuclear
membrane into the cytosol. Remember that all RNA is single stranded.
Transfer RNA (tRNA) is also single stranded, like mRNA, but it is held together in a
“hairpin” or “T” shape by hydrogen bonds. It carries a specific amino acid on one end
based on a series of three bases on the other end called an anti-codon. There are only 20
amino acids that make up all of the proteins in your body.
In order to make the proteins, tRNA must use mRNA as a template (remember, mRNA
has the “directions” from DNA). The anti-codons on tRNA match up to complimentary
codons on mRNA. Translation starts with a start codon on mRNA and ends with a
stop codon on mRNA.
The whole process of assembling proteins is accomplished by ribosomes. Ribosomes are
made up of ribosomal RNA (rRNA). The ribosomes match the tRNA anti-codons to
the mRNA codons, then link all of the amino acids together. These long links of amino
acids are called polypeptides, or proteins.