DNA and RNA notes

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