1
DNA, RNA, Protein Synthesis, and Mutations Notes
1. DNA structure
a. Nucleotide structure (3 parts)
Sugar (Deoxyribose)
Phosphate Group
Nitrogen bases (Adenine, Thymine, Cytosine, Guanine)
b. Types of bases (2 types)
Single Ring (Pyrimidine)
Thymine
Cytosine
Double Ring (Purine)
Adenine
Guanine
c. Base Pair Rule
A -- T
G -- C
T–A
C -- G
2. DNA Replication
a. Basic steps
Begins at the origins of replication, creates replication “bubbles”, part
of DNA strands open up as daughter strands grow on both sides of
each bubble, bubbles merge yielding two double stranded DNA
molecules
b. Enzymes involved and job
Helicase - responsible for unwinding the double helix
Primase - initiates the synthesis of a DNA strand
DNA polymerase – enzyme that “proofreads” new DNA strands
Ligase – “glues” the DNA strand back together
2
3. RNA
a. Differences between it and DNA
Ribose instead of Deoxyribose as the sugar
Uracil instead of Thymine as a nitrogen base
Single-stranded instead of double-stranded
4. Protein Synthesis
a. Major players and jobs:
DNA – molecule that stores heritable genetic information
mRNA – (messenger RNA) transcribed from a DNA template
1. Codon – 3-base “word that codes for one amino acid”
tRNA – (transfer RNA) translates the 3 letter codons of mRNA to the
amino acids that make proteins
2. Anticodon – complementary to a specific codon in mRNA
rRNA – (ribosomal RNA) RNA component of ribosomes
Amino Acid – building block that makes up proteins
b. Steps of Protein Synthesis (in eukaryotes)
1. Translation begins with the attachment of a ribosome and a
tRNA to a “start” codon (AUG)
2. The ribosome then moves along the mRNA transcript
3. The polypeptide (many proteins) elongates as an amino acid is
added for each codon
4. When the ribosome arrives at a “stop” codon (UAA, UAG, UGA)
the polypeptide is released
5. The proteins that are formed determine the appearance and
functioning of the cell and of the whole organism
c. Protein Synthesis Problems
Gene (triplets)
ATC GGG TTA CTA
Complementary DNA half
TAG CCC AAT GAT
mRNA (codons)
3
AUC GGG UUA CUA
tRNA (anticodons)
UAG CCC AAU GAU
Amino acids
isoleucine glysine leucine leucine
5. Mutations – Heritable changes in genetic material are
called mutations. They result from alteration in the
nucleotide sequence of DNA, and provide the
ultimate source of genetic variation for evolutionary change.