BIO 099 Lecture #1 – Nucleic Acids
Nucleic Acids: DNA & RNA
deoxyribonucleic acid and ribonucleic acid
•nucleic acids: contain C,O,H,N, phosphorus
•structural units: nucleotides
Each nucleotide consists of 3 components (page 58)
1. nitrogen containing base
2. pentose sugar
3. phosphate group
•5 major varieties of nitrogen bases
adenine - A
thymine cytosine - C
guanine -
uracil-
•DNA & RNA both composed of nucleotides they
differ in:
1. DNA typically found in
2. DNA constitutes the
3. DNA has 2 roles:
1.) replicates itself
2.) provides instructions for
•DNA is a long double stranded polymer
(double chain of nucleotides)
bases in DNA are
and the sugar is
2 chains held together with H bonds between the bases
-the alternating sugar & phosphate molecules of each chain are called the backbone and 2 backbone
form the uprights of the ladder while the joined bases form the rungs
-bonding of bases is very specific (complementary bases):
If a sample DNA strand had the following bases:
ATCG-
RNA molecules single strands of nucleotides
-located
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-"molecular slave" of DNA
-RNA bases include
-sugar is
-3 types of RNA: mRNA, tRNA, rRNA
Transfer RNA (tRNA)
– Transfers appropriate amino acids to the ribosome for building the protein
Ribosomal RNA (rRNA)
– Helps form the ribosomes where proteins are built
Messenger RNA (mRNA)
– Carries the instructions for building a protein from the nucleus to the ribosome
DNA Replication:
•DNA replicates itself exactly so each daughter cell will have identical DNA
3 basic Steps for DNA replication:
Step 1. Enzymes termed helicases unwind the DNA helix, H bonds are broken and DNA molecule
separates into 2 strands
Step 2. Each freed nucleotide serves as a template
Step 3. The order of the nucleotides on the template strand determines the order on the new strand
being built. Requires DNA polymerase
-GTATTC on the template would bond to new nucleotides
-the comparable region on the other template strand with the sequence CATAAG bonds to new
nucleotides
4. The end result is 2 new DNA molecules that are identical to the original
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Protein Synthesis
- proteins are made up of amino acids in specific sequences
- there are 20 different amino acids which can be combined in different ways to make the hundreds of
thousands of different proteins
•DNA is the master blueprint for protein synthesis.
Located in cytoplasm
•contains genes: sequences of bases of each nucleotide
A (adenine), T (thymine), C (cytosine) & G (guanine)
•each sequence of 3 bases is called a triplet and encodes for one amino acid.
there is some overlap because there are 64 possible triplets and only 20 amino acids.
- each gene has a start and a stop code: DNA codon: TAC “universal start”
promoter is a special sequence of bases right before the gene
when a gene is activated, the promoter is turned “on” and the DNA sequence is “read” – protein
synthesis begins
Part I: Transcription: copying the code from DNA to mRNA
DNA double stranded cannot pass through nuclear pores to get to ribosomes
 involves DNA & mRNA
 mRNA enters nucleus and copies (transcribes) code from DNA
requires RNA polymerase
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 RNA polymerase binds to the promoter of the gene
 DNA two strands are termed the coding strand and template strand
coding strand has the “code” or triplets for the amino acid sequence of the protein
template strand is used as the template for mRNA
RNA polymerase then forms the mRNA strand by unwinding a small section and “reading”
DNA’s complementary strand to form the mRNA molecule via complementary base pairing.
(remember RNA bases are A,U,C and G) C  G and A  U (T)
Example:
DNA A – T –G –G –A –T –G –G –C –A –T – A – C – G – A
T – A –C –C –T –A –C –C –G –T –A – T – G – C – T
coding strand
template strand
mRNA A – U –G –G –A –U –G –G –C –A –U –A –C – G - A
mRNA molecule ends up being identical to DNA’s coding strand EXCEPT replaces T with U
each sequence of 3 bases in mRNA is termed a CODON
start codon always AUG
RNA strand is processed (edited) – nonsense regions termed introns are removed (remaining
piece is formed from exons) – provides shorter strand of mRNA
now the mRNA leaves nucleus takes code to ribosomes
Part II Translation translating the mRNA code into amino acids and placing them in the proper
sequence to make the protein.
involves mRNA, tRNA, and rRNA
•occurs at the ribosome.
•tRNA reads codons on mRNA and places the specific amino acid in the right order.
tRNA forms anticodons to mRNA’s codons.
each tRNA molecule has an anticodon on one end and the specific amino acid for that
anticodon on the other end
this continues until stop codon is reached (UAA, UGA, UAG)
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