Grade 12 Life Sciences (CAPS) Notes: DNA Replication and RNA
1. DNA Replication
Key Definitions
DNA Replication: The process by which DNA makes an identical copy of itself before cell
division.
Helicase: Enzyme that unwinds and unzips the DNA double helix.
DNA Polymerase: Enzyme that adds complementary DNA nucleotides to build a new strand.
Nucleotide: The building block of DNA (contains a sugar, phosphate, and nitrogenous base).
Semi-conservative Replication: Each new DNA molecule contains one original strand and
one newly formed strand.
Step-by-Step Process
1. DNA unwinds and unzips as hydrogen bonds break.
2. Each original DNA strand acts as a template.
3. Free DNA nucleotides pair with exposed bases:
A pairs with T
C pairs with G
4. DNA polymerase joins the nucleotides together.
5. Two identical DNA molecules are formed.
6. Each DNA molecule consists of:
One original strand
One newly made strand (semi-conservative replication)
, Importance
Ensures every new cell receives identical genetic information.
Essential for growth, repair, and reproduction.
Mnemonic
"U-T-P-J-T"
U – Unzip
T – Template
P – Pair
J – Join
T – Two identical DNA molecules
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2. RNA
Key Definitions
RNA (Ribonucleic Acid): A single-stranded nucleic acid involved in protein synthesis.
Transcription: The process of making mRNA from DNA.
Translation: The process of making proteins using mRNA.
Codon: A sequence of three bases on mRNA coding for one amino acid.
Anticodon: A sequence of three bases on tRNA complementary to an mRNA codon.
Differences Between DNA and RNA
DNA RNA
Double-stranded Single-stranded
Contains deoxyribose sugar Contains ribose sugar
1. DNA Replication
Key Definitions
DNA Replication: The process by which DNA makes an identical copy of itself before cell
division.
Helicase: Enzyme that unwinds and unzips the DNA double helix.
DNA Polymerase: Enzyme that adds complementary DNA nucleotides to build a new strand.
Nucleotide: The building block of DNA (contains a sugar, phosphate, and nitrogenous base).
Semi-conservative Replication: Each new DNA molecule contains one original strand and
one newly formed strand.
Step-by-Step Process
1. DNA unwinds and unzips as hydrogen bonds break.
2. Each original DNA strand acts as a template.
3. Free DNA nucleotides pair with exposed bases:
A pairs with T
C pairs with G
4. DNA polymerase joins the nucleotides together.
5. Two identical DNA molecules are formed.
6. Each DNA molecule consists of:
One original strand
One newly made strand (semi-conservative replication)
, Importance
Ensures every new cell receives identical genetic information.
Essential for growth, repair, and reproduction.
Mnemonic
"U-T-P-J-T"
U – Unzip
T – Template
P – Pair
J – Join
T – Two identical DNA molecules
---
2. RNA
Key Definitions
RNA (Ribonucleic Acid): A single-stranded nucleic acid involved in protein synthesis.
Transcription: The process of making mRNA from DNA.
Translation: The process of making proteins using mRNA.
Codon: A sequence of three bases on mRNA coding for one amino acid.
Anticodon: A sequence of three bases on tRNA complementary to an mRNA codon.
Differences Between DNA and RNA
DNA RNA
Double-stranded Single-stranded
Contains deoxyribose sugar Contains ribose sugar
