Triple Science Only - DNA Structure
Laura Armstrong
Teacher
Contents
Recall Questions
This topic requires prior knowledge of DNA and the genome.
Where is DNA found in a eukaryotic cell?
In the nucleus.
What name is given to the thread-like structures that are made of DNA?
Chromosomes.
What is a gene?
A small section of DNA that codes for a specific sequence of amino acids in a protein.
Topic Explainer Video
Check out this @lauradoesbiology video that explains DNA structure, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
DNA Structure
What is DNA?
- DNA stands for Deoxyribonucleic Acid.
- It is a polymer made from many repeating nucleotide units.
- Found in the nucleus of cells, DNA carries the genetic instructions for making proteins.
DNA Structure
What is a Nucleotide?
- The basic unit of DNA.
- Each nucleotide consists of:
- A phosphate group
- A sugar (deoxyribose sugar)
- One of four bases: A, T, C, or G
- DNA is formed of many nucleotides, it is a polymer.
- It consists of two strands, forming a double helix structure.
- The strands have alternating sugar and phosphate groups (the "backbone").
- The bases stick out from the sugar and pair up in the middle of the DNA double helix.
Base Pairing Rules:
- A always pairs with T (Adenine ↔ Thymine)
- C always pairs with G (Cytosine ↔ Guanine)
This is known as the complementary base pair rule.
DNA, Genes & Proteins
- A gene is a small section of DNA that codes for a sequence of amino acids in a protein.
- Three bases (a triplet code) = codes for one amino acid.
- The order of bases controls the order in which amino acids are joined together to form proteins.
Key Terms & Definitions
|
Term |
Definition |
|---|---|
|
DNA |
A polymer that carries genetic information. |
|
Nucleotide |
The repeating unit of DNA made of a sugar, phosphate, and a base. |
|
Polymer |
A large molecule made from repeating smaller units (monomers). |
|
Base |
Part of the nucleotide; four types – A, T, C, G. |
|
Triplet code |
A sequence of three DNA bases that codes for one amino acid. |
|
Protein |
A large molecule made of amino acids. |
No answer provided.
Exam Tips
You may be asked to describe the structure of DNA, label a nucleotide, or explain base pairing. Always:
- Mention that DNA is a polymer of nucleotides.
- State that each nucleotide contains a sugar, phosphate, and base.
- Use correct letters for the bases- A, T, C, G. You do not have to remember the full names.
- Include that the DNA has a double helix structure made from two strands.
- To remember the complementary base pair rule you can use the phrase AT the Golf Course. A-T and G-C.
No answer provided.
Practice Question
Describe the structure of DNA and explain how it codes for proteins. (6 marks)
Model Answer:
- DNA is a polymer made from repeating units called nucleotides.
- Each nucleotide contains a sugar, a phosphate, and one of four bases (A, T, C, or G).
- DNA has two strands, forming a double helix
- The strands are held together by complementary base pairs (A with T, C with G).
- The order of the bases in DNA determines the order of amino acids in a protein.
- Three bases (a triplet) codes for one amino acid in a protein chain.
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!