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A genome is the entire genetic material of an organism, and DNA is a polymer of two strands forming a double helix. Free notes and 12 questions answered.
DNA Structure and the Genome is part of Reproduction in GCSE AQA Higher Biology.
3 min
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GCSE AQA Higher
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A genome is the entire genetic material of an organism, and DNA is a polymer of two strands forming a double helix. Free notes and 12 questions answered.
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Use this lesson to stay inside Reproduction while connecting the detail back to the wider Inheritance, variation and evolution topic.
Read the core explanations from DNA Structure and the Genome before testing yourself from memory.
Every cell in your body contains a complete instruction manual - your DNA. This chemical holds the code for everything from your eye colour to how your muscles work. But DNA isn't just floating around randomly in your cells.
Think of your cell nucleus as a library. The DNA is organised into structures called chromosomes - like books on shelves. Each chromosome contains thousands of genes, which are like individual recipes in a cookbook.
Picture DNA like a twisted ladder - this is the famous double helix shape. The two strands spiral around each other, held together by chemical bonds between complementary bases.
Trap: Many students think DNA is a single strand. Actually, it's always two strands twisted together - that's what makes it stable enough to store information reliably.
Here's where it gets clever. Your DNA doesn't directly make proteins. Instead, each gene acts like a recipe that tells the cell which amino acids to join together, and in what order.
Think of it like this: Gene → Amino acid sequence → Protein → Function in your body. For example, one gene might code for insulin (a protein that controls blood sugar), while another codes for haemoglobin (the protein that carries oxygen in your blood).
Your DNA is incredibly long - if you stretched out all the DNA from one cell, it would be about 2 metres long. To fit this into a nucleus that's only a few micrometers across, the DNA is tightly coiled and packaged into chromosomes.
Humans have 46 chromosomes in most cells (23 pairs). Each chromosome contains hundreds or thousands of genes. Chromosome 1 is the largest and contains about 4,300 genes, while the Y chromosome is smallest with only about 200 genes.
Scientists have now mapped the complete human genome - all 3.2 billion DNA base pairs and approximately 20,000-25,000 genes. This massive project, completed in 2003, took 13 years and cost $2.7 billion.
Understanding our genome is revolutionary for medicine. We can now identify genes linked to diseases, develop personalised treatments, and even predict someone's risk of developing certain conditions.
Worked example: Worked Example: Applying DNA Structure and the Genome
Use this method to answer an exam-style question about the blueprint of life.
Answer: A complete response links mechanism, evidence, and conclusion for dna structure and the genome.
Exam depth extension: In dna structure and the genome, connect the blueprint of life to dna structure - the double helix using clear cause-and-effect statements. When you explain biological processes, include what changes, why it changes, and the consequence for cells, organisms, or populations. If calculations appear, show each step, include units, and end with a sentence that interprets the result in biological context.
Command word focus: 'Describe' questions want you to state what DNA looks like (double helix, two strands). 'Explain' questions want you to say WHY the genome project is important (because it helps identify disease genes, develop treatments, etc.).
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
A genome is the entire genetic material of an organism. The human genome contains all the DNA found in human chromosomes, about 3.2 billion DNA base pairs and approximately 20,000-25,000 genes.
DNA is a polymer made up of two strands forming a double helix, like a twisted ladder. The two strands spiral around each other, held together by chemical bonds between complementary bases, and DNA contains the genetic material in the nucleus of a cell.
The human genome contains approximately 20,000-25,000 genes and about 3.2 billion DNA base pairs. Scientists mapped the complete human genome in a huge project completed in 2003, which took 13 years.
The Human Genome Project was completed in 2003, after 13 years of work. It mapped all 3.2 billion DNA base pairs and approximately 20,000-25,000 genes of the human genome.
Understanding the human genome is revolutionary for medicine because scientists can identify genes linked to diseases, develop personalised treatments and predict someone's risk of developing certain conditions. The complete human genome was mapped in a project completed in 2003 that took 13 years.
A gene is a small section of DNA on a chromosome that codes for a particular sequence of amino acids, which join to make a specific protein. DNA does not make proteins directly: the gene acts like a recipe, gene → amino acid sequence → protein → function, such as insulin or haemoglobin.
DNA is the double helix polymer that carries genetic material; a chromosome is a structure of tightly coiled DNA found in the nucleus; and a gene is a small section of DNA on a chromosome that codes for a protein. Humans have 46 chromosomes (23 pairs), each containing hundreds or thousands of genes.
DNA is always two strands twisted together into a double helix, like a twisted ladder, held together by chemical bonds between complementary bases. Having two strands makes DNA stable enough to store information reliably.
The DNA from one cell would be about 2 metres long if stretched out. To fit into a nucleus only a few micrometers across, it is tightly coiled and packaged into chromosomes.
Chromosome 1 is the largest human chromosome, containing about 4,300 genes, while the Y chromosome is the smallest, with only about 200 genes. Humans have 46 chromosomes in most cells, in 23 pairs.
One example is the gene that codes for insulin, a protein that controls blood sugar, and another is the gene that codes for haemoglobin, the protein that carries oxygen in the blood. Each gene codes for a particular sequence of amino acids to make a specific protein.
Understanding the human genome helps medicine because scientists can find genes linked to diseases, personalised treatments can be developed, and a person's risk of developing certain conditions can be predicted.