Focus on the scientists:
Understand the contributions of Chargaff, Watson & Crick, and Franklin. Watson and Crick’s model of DNA was made possible by Franklin’s X-ray crystallography data.

Practice base pairing: Be able to identify the correct base pairs (A-T, C-G for DNA and A-U, C-G for RNA).

1. DNA and RNA Overview

DNA (Deoxyribonucleic Acid):

Structure: Double helix made of two strands coiled around each other.

Function: Stores genetic information in the cell.

Location: Primarily in the nucleus (in eukaryotes) or cytoplasm (in prokaryotes).

RNA (Ribonucleic Acid):

Structure: Single-stranded.

Function: Carries genetic information from DNA to ribosomes for protein synthesis.

Types:

mRNA (messenger RNA): Carries instructions from DNA to ribosomes.

tRNA (transfer RNA): Transfers amino acids during protein synthesis.

rRNA (ribosomal RNA): Forms part of ribosomes.

2. Nucleotides and Their Role

Nucleotides: The building blocks of DNA and RNA.

Components:

Phosphate group

Sugar (Deoxyribose in DNA, Ribose in RNA)

Nitrogenous base:

DNA: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)

RNA: Adenine (A), Uracil (U), Cytosine (C), Guanine (G)

Base Pairing Rules (Chargaff's Rule):

In DNA:

Adenine (A) pairs with Thymine (T)

Cytosine (C) pairs with Guanine (G)

In RNA:

Adenine (A) pairs with Uracil (U)

Cytosine (C) pairs with Guanine (G)

Phosphodiester Bond: Connects the sugar and phosphate of adjacent nucleotides in a strand.

3. Structure of DNA

Double Helix: The two strands of DNA wind around each other in a helical shape.

Antiparallel Strands: The two strands run in opposite directions (5’ to 3’ and 3’ to 5’).

Complementary Base Pairing: A pairs with T (in DNA) and C pairs with G.

4. Cells and DNA Replication

Prokaryotic Cells: Lack a nucleus. DNA is located in the nucleoid region.

Eukaryotic Cells: DNA is found in the nucleus.

DNA Replication: Process by which DNA makes a copy of itself.

Steps:

Unwinding: Helicase unwinds the DNA double helix.

Priming: RNA primase adds short RNA primers.

Elongation: DNA polymerase adds complementary nucleotides to the growing strand.

Termination: Replication ends when two complete DNA strands are formed.

5. Key Scientists and Their Contributions

Erwin Chargaff:

Developed Chargaff’s Rules:

The amount of adenine (A) equals the amount of thymine (T), and the amount of cytosine (C) equals the amount of guanine (G) in DNA.

James Watson & Francis Crick:

Known for discovering the double helix structure of DNA in 1953.

Used data from other scientists, including Rosalind Franklin, to build their model.

Rosalind Franklin:

Contributed to understanding the structure of DNA using X-ray crystallography.

Her famous Photo 51 was crucial in revealing the helical structure of DNA.

Her work was foundational in Watson and Crick’s discovery but was not initially credited.

6. Transcription and Translation (Central Dogma)

Transcription: The process of copying DNA into RNA.

Involves RNA polymerase, which synthesizes mRNA based on the DNA template.

Translation: The process by which mRNA is used to synthesize proteins at the ribosome.

tRNA: Carries amino acids and has anticodons that match mRNA codons.

Codons: Groups of three nucleotides in mRNA that code for specific amino acids.

7. Key Terms

Gene: A segment of DNA that codes for a protein or RNA.

Chromosome: A long, coiled DNA molecule that carries genetic information.

Allele: Different forms of a gene.

Mutation: A change in the DNA sequence that can lead to variations in traits or diseases.

8. Study Tips

Understand the relationships:

DNA is made of nucleotides, and the sequence of bases in DNA determines the genetic information.

RNA transcribes that information and uses it to make proteins during translation.

Focus on the scientists:

Understand the contributions of Chargaff, Watson & Crick, and Franklin. Watson and Crick’s model of DNA was made possible by Franklin’s X-ray crystallography data.

Practice base pairing: Be able to identify the correct base pairs (A-T, C-G for DNA and A-U, C-G for RNA).

Note