ADENINE
What makes up the backbone or sides of a DNA molecule?
A. Nitrogen bases
B. Sugar and phosphate
C. Amino acids
D. Proteins
B. Sugar and phosphate
Which scientist is known for producing Photo 51?
A. Erwin Chargaff
B. Rosalind Franklin
C. James Watson
D. Francis Crick
B. Rosalind Franklin
What are the repeating units that make up DNA called?
A. Amino acids
B. Nucleotides
C. Proteins
D. Lipids
B. Nucleotides
If a DNA molecule has 30% adenine, what percentage is thymine?
A. 10%
B. 20%
C. 30%
D. 40%
C. 30%
Which nitrogen base pairs with cytosine?
A. Adenine
B. Thymine
C. Guanine
D. Uracil
C. Guanine
Which enzyme builds the new DNA strand by adding complementary nucleotides?
A. Helicase
B. DNA polymerase
C. RNA polymerase
D. Catalase
B. DNA polymerase
Which statement is correct?
A. Purines pair with purines.
B. Pyrimidines pair with pyrimidines.
C. A purine always pairs with a pyrimidine.
D. All nitrogen bases are purines.
C. A purine always pairs with a pyrimidine
In a typical eukaryotic cell, most of the cell's DNA is found in the ________.
A. Ribosome
B. Cell membrane
C. Nucleus
D. Cytoplasm
C. Nucleus
What Does DNA Stand For?
DNA = Deoxyribonucleic acid
What is the main function of DNA?
DNA stores genetic information.
It contains instructions for making proteins.
It helps determine inherited traits.
Before DNA Replication,
The two DNA strands must separate or “unzip.”
The enzyme responsible for unzipping DNA is ______________.
Each separated strand becomes a template for a new strand.
HELICASE.
Why Is Replication Semi-Conservative?
Each new DNA molecule contains:
• 1 original (parent) strand
• 1 newly made strand
Memory trick: SEMI = HALF → half of the original DNA is kept.
Eukaryotic vs. Prokaryotic DNA
Both eukaryotic and prokaryotic cells contain DNA.
Eukaryotic cells: DNA is mainly inside the nucleus.
Prokaryotic cells: no nucleus; DNA is in the nucleoid region.
Their DNA is organized differently.
The Four Nitrogen Bases
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
Base-Pairing Rules
Adenine (A) pairs with Thymine (T).
Guanine (G) pairs with Cytosine (C).
A ↔ T
G ↔ C
Shape of DNA
DNA has a DOUBLE HELIX shape.
Think of it like a twisted ladder.
Sugar-phosphate backbones = sides
Paired nitrogen bases = rungs
What Does Antiparallel Mean?
The two DNA strands run in opposite directions.
One strand runs 5′ → 3′.
The other runs 3′ → 5′.
If A = 25%, what is T?
•T = 25%
If C = 35%, what is G?
G = 35%
Purines
A + G (2 rings)
Parts of a Nucleotide 3 PARTS
A nucleotide has 3 parts:
1. Phosphate group
2. Deoxyribose sugar
3. Nitrogenous base
Memory trick: P–S–B = Phosphate – Sugar – Base
Purines vs. Pyrimidines
PURINES: Adenine (A) and Guanine (G) → 2 rings
PYRIMIDINES: Cytosine (C) and Thymine (T) → 1 ring
Both are nitrogenous bases found in DNA.
Easy memory: A + G = Purines; C + T = Pyrimidines.
Okazaki Fragments
Okazaki fragments are short pieces of newly made DNA.
They are formed on the LAGGING strand during DNA replication.
They are later joined together.
Helicase
HELICASE = unzips/separates the DNA strands.
It breaks the hydrogen bonds between paired bases.
This allows DNA replication to begin.
Hydrogen Bonds
Hydrogen bonds connect the paired nitrogen bases.
A–T = 2 hydrogen bonds
G–C = 3 hydrogen bonds