DNA: The Code of Life - Grade 12 (CAPS)

 0.1 What Are Nucleic Acids?

Nucleic acids are large molecules that carry genetic instructions for growth, development, functioning, and reproduction.
There are two types:

1. DNA (Deoxyribonucleic Acid): The "blueprint" for an organism's characteristics.
2. RNA (Ribonucleic Acid): The "messenger" that helps make proteins based on DNA instructions.

These two nucleic acids are made of building blocks (or monomers) called nucleotides.

Why are they important?

• DNA and RNA determine how you look (e.g., eye color, hair type).
• They help cells build proteins, which are essential for everything your body does.

1.1 The Structure of DNA and RNA

DNA – The Double Helix

DNA looks like a spiral staircase or a twisted ladder.

Components:

1. Sugar: Deoxyribose (5-carbon sugar).
2. Phosphate Group: Forms the sides of the ladder.
3. Nitrogenous Bases: The steps of the ladder.

Base Pairs	Rule
Adenine (A)	Pairs with Thymine (T)
Cytosine (C)	Pairs with Guanine (G)

Remember: A-T and C-G – Always Together, Cute Guys!

RNA – The Single-Stranded Assistant

RNA is a single-stranded molecule, shorter than DNA.

Components:

1. Sugar: Ribose.
2. Phosphate Group.
3. Nitrogenous Bases:
   • Adenine (A)
   • Uracil (U) – replaces Thymine in RNA!
   • Cytosine (C)
   • Guanine (G)

1.2 Differences Between DNA and RNA

Feature	DNA	RNA
Strands	Double-stranded (double helix)	Single-stranded
Sugar	Deoxyribose	Ribose
Nitrogen Bases	A, T, C, G	A, U, C, G
Function	Stores genetic info	Helps in protein synthesis
Location	Found in the nucleus	Found in the nucleus & cytoplasm

Mnemonic to Remember Differences: D for DNA – Double, T for Thymine. R for RNA – Ribose, U for Uracil.

1.3 DNA Replication

DNA replication happens before a cell divides, ensuring each new cell gets an exact copy of the DNA.

Steps of DNA Replication

Unzipping the Helix:

• The double helix unwinds.
• Hydrogen bonds between base pairs breaks.
• Enzyme involved: Helicase (think of it as a “zipper”).

Building New Strands:

• Free nucleotides pair up with exposed bases.

• A pairs with T, C pairs with G.

• Enzyme involved: DNA Polymerase (builds new strands).

Semi-Conservative Replication:

• Each new DNA molecule has one old strand and one new strand.

Importance of DNA Replication:

• Ensures genetic information is passed to new cells accurately.

1.4 DNA Profiling

DNA profiling is a technique to identify individuals based on their unique DNA patterns.

Steps in DNA Profiling

1. Extract DNA: From a sample (blood, hair, or saliva).
2. Cut DNA into Fragments: Using restriction enzymes.
3. Separate DNA: Through a process called gel electrophoresis.
4. Analyze the Pattern: Each person has a unique DNA "barcode."

Uses of DNA Profiling

• Forensics: Identifying suspects in a crime.
• Paternity Testing: Determining biological parents.
• Medical Research: Understanding genetic diseases.

1.5 Protein Synthesis

Proteins are essential for your body’s structure and function. Protein synthesis is how your cells make these proteins.

Two Main Stages of Protein Synthesis

Transcription (In the Nucleus):

• DNA is used as a template to make mRNA (messenger RNA).
• Steps:
• DNA unzips.
• RNA nucleotides pair with the template strand of DNA.
• A pairs with U, C pairs with G.
• mRNA leaves the nucleus and travels to the ribosome.

Translation (At the Ribosome):

• mRNA is "read" and translated into a protein.
• Steps:
• Ribosome reads mRNA in triplets called codons.
• tRNA brings the correct amino acid for each codon.
• Amino acids link together to form a protein.

Mnemonic for Protein Synthesis:

T-R-A-N-S-C-R-I-P-T (write the message) → T-R-A-N-S-L-A-T-E (make the protein)!

Quick Summary: DNA vs RNA and Protein Synthesis

Concept	DNA	RNA	Protein Synthesis
Function	Stores genetic info	Transfers genetic info	Builds proteins
Location	Nucleus	Nucleus & cytoplasm	Ribosome
Processes	Replication	Transcription	Translation