BiologyChapter 13: Chromosome and DNA
DNA Structure (watson-Crick School)
DNA is a double helix.
Learning objectives
- Explain dna structure (watson-crick school) in clear biological language.
- Distinguish 1. parts from 2. complement.
- Use the key terms to answer a short Federal Board exam question.
Definition
DNA is a double helix. Backbone: sugar-phosphate. Rungs: bases. A pairs with T (two H bonds school), G with C (three). Strands antiparallel (5' to 3' opposite). Complementary: one strand dictates the other. RNA: U instead of T, usually single, ribose. Nucleotide = sugar + phosphate + base. The double helix structure explained how genetic information is stored and copied. Base pairing rules (A-T, G-C) are the foundation of replication, transcription, and genetic engineering concepts. Antiparallel means the two strands run in opposite 5-to-3 directions.
Important terms
- DNA STRUCTURE (WATSON-CRICK SCHOOL)
- DNA is a double helix.
- 1. PARTS
- Deoxyribose.
- 2. COMPLEMENT
- Template CATG -> GTAC on the other DNA strand.
Overview
Ladder, then the letters:
Parts
Deoxyribose. Phosphodiester named as the link. 5' phosphate end, 3' OH end. Chargaff: A=T, G=C in amounts. Rosalind Franklin's pattern named as evidence in the school story. Double helix: antiparallel strands, 5' to 3' direction. Purines (A, G) pair with pyrimidines (T, C). Uniform diameter because A-T and G-C pairs are equal width.
Examples Purine A G · Pyrimidine C T · U in RNA
Complement
Template CATG -> GTAC on the other DNA strand. For RNA transcript, T becomes A and A becomes U. Diameter uniform because A-T and G-C pairs fit. Template strand read 3' to 5'; new strand built 5' to 3'. mRNA uses U instead of T when copying from DNA template. One gene → one mRNA → one polypeptide (usually).
Examples A <-> T · G <-> C · A -> U in RNA
WHAT — DNA STRUCTURE (WATSON-CRICK SCHOOL)
DNA is a double helix. Backbone: sugar-phosphate. Rungs: bases. A pairs with T (two H bonds school), G with C (three). Strands antiparallel (5' to 3' opposite). Complementary: one strand dictates the other. RNA: U instead of T, usually single, ribose. Nucleotide = sugar + phosphate + base. The double helix structure explained how genetic information is stored and copied. Base pairing rules (A-T, G-C) are the foundation of replication, transcription, and genetic engineering concepts. Antiparallel means the two strands run in opposite 5-to-3 directions.
WHY — Why this topic matters
DNA STRUCTURE (WATSON-CRICK SCHOOL) is an independent FBISE learning unit because students must connect its structures and processes with their biological functions and examples.
HOW — How it works
PARTS: Deoxyribose. Phosphodiester named as the link. 5' phosphate end, 3' OH end. Chargaff: A=T, G=C in amounts. Rosalind Franklin's pattern named as evidence in the school story. Double helix: antiparallel strands, 5' to 3' direction. Purines (A, G) pair with pyrimidines (T, C). Uniform diameter because A-T and G-C pairs are equal width. Examples: Purine A G; Pyrimidine C T; U in RNA. COMPLEMENT: Template CATG -> GTAC on the other DNA strand. For RNA transcript, T becomes A and A becomes U. Diameter uniform because A-T and G-C pairs fit. Template strand read 3' to 5'; new strand built 5' to 3'. mRNA uses U instead of T when copying from DNA template. One gene → one mRNA → one polypeptide (usually). Examples: A <-> T; G <-> C; A -> U in RNA. Worked complement. Template: A G C T A DNA partner: T C G A T mRNA from template: U C G A U
Worked example
- Worked complement.
- Template: A G C T A
- DNA partner: T C G A T
- mRNA from template: U C G A U
In simple words
Structure. No synthesis-lab protocol.
Key points
- A-T, G-C
- double helix
- nucleotide three parts
- pair rules
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.DNA Structure (watson-Crick School)
Sticky Notes · Quick Revision
Core Idea
- DNA is a double helix. Backbone: sugar-phosphate. Rungs: bases. A pairs with T (two H bonds school), G with C (three). Strands antiparallel (5' to 3' opposite). Complementary: one strand dictates the other. RNA: U instead of T, usually single, ribose. Nucleotide = sugar + phosphate + base. The double helix structure explained how genetic information is stored and copied. Base pairing rules (A-T, G-C) are the foundation of replication, transcription, and genetic engineering concepts. Antiparallel means the two strands run in opposite 5-to-3 directions.
1. PARTS
- Deoxyribose. Phosphodiester named as the link. 5' phosphate end, 3' OH end. Chargaff: A=T, G=C in amounts. Rosalind Franklin's pattern named as evidence in the school story. Double helix: antiparallel strands, 5' to 3' direction. Purines (A, G) pair with pyrimidines (T, C). Uniform diameter because A-T and G-C pairs are equal width.
2. COMPLEMENT
- Template CATG -> GTAC on the other DNA strand. For RNA transcript, T becomes A and A becomes U. Diameter uniform because A-T and G-C pairs fit. Template strand read 3' to 5'; new strand built 5' to 3'. mRNA uses U instead of T when copying from DNA template. One gene → one mRNA → one polypeptide (usually).
Exam Example
- Worked complement.
- Template: A G C T A
- DNA partner: T C G A T
- mRNA from template: U C G A U
Common Misconception
- Do not treat 1. PARTS and 2. COMPLEMENT as the same idea; each explains a different part of the topic.
FBISE Exam Check
- Define dna structure (watson-crick school), explain the two key parts, and use the correct biological terms.
- Exam reminder: Worked complement.
60-second revision
- DNA is a double helix.
- 1. PARTS: Deoxyribose.
- 2. COMPLEMENT: Template CATG -> GTAC on the other DNA strand.
- Exam reminder: Worked complement.
Did you understand this topic?
Your answer is saved with your learning record. It does not mark the topic as mastered.