Pathway of Protein Synthesis DNA
transcription
RNA
translation
Proteins
DNA Replication (DNA Synthesis) DNA
replication
DNA
Copy of original
backbone
Antiparallel
Strand 1
backbone Hydrogen bonds
Strand 2
Properties of DNA 4 nitrogenous bases Adenine (A) Cytosine (C)
Thymine (T) Guanine (G)
Adenine & Guanine = Purines • 2 organic rings
Thymine & Cytosine = Pyrimidines • 1 organic ring
Complementary Base Pairs Purine pairs with Pyrimidine: Adenine pairs with Thymine Guanine pairs with Cytosine
A & T = complimentary base pair G & C = complementary base pair
H-bonds stabilize complimentary base pairs
DNA is twisted into a double helix
Overview of DNA Replication • Occurs during S-phase • Original DNA strand is used as a template to synthesize a new complimentary DNA strand. • Catalyzed by DNA Polymerase – Synthesizes new DNA strand • Semi-Conservative – One strand of the replicated DNA is new, the other is the original molecule.
Original DNA strand Strand 1 sugar phosphate backbone
A C T A A T A A C G G A T G A T C
T G A T T A T T G C C T A C T A G
Strand 2
Hydrogen Bonds
Step 1. Hydrogen bonds break, and strands separate T A A C G G A T A C T A A
DNA Polymerase
G A T C
T G A T T
DNA Polymerase
A T T G C C T A Replication bubble
Step 2. DNA Polymerases attach to open strands
C T A G
Step 3. DNA Polymerase adds new bases T A A C G G A T A C T A A
A T T G C C T A
G A T C
T G A T T
T A A C G G A T
C T A G
H bonds continue to break
A T T G C C T A Replication bubble
Step 3. DNA Polymerase adds new bases A C T A A T A A C G G A T G A T C T G A T T A T T G C C T A C T A G
A C T A A T A A C G G A T T T T C T G A T T A T T G C C T A C T A G
A C T A A T A A C G G A T G A T C T G A T T A T T G C C T A C T A G
A C T A A T A A C G G A T T T T C T G A T T A T T G C C T A C T A G 2 Complete DNA molecules Each with 1 original strand & 1 new strand
The two DNA molecules separate during mitosis
End of Section 4, Chapter 4