2.2.1Reproduction and Inheritance
The Genome and Genes — Edexcel International GCSE Science Double Award (Modular) - Biology Unit 2 Revision Notes & Topical Questions
5 min read 6 parts Lesson 14 of 28
Part 1 of 5From genome to protein
1Genome
- Genome The genome is the complete set of DNA in an organism.
2Gene
- Gene A gene is a short section of a DNA molecule.
3Amino acid sequence
- Amino acid sequence Each gene carries a code that specifies a particular order of amino acids.
4Protein
- Protein Chains of amino acids fold to make a protein, and the proteins made decide how a cell works and what the organism is like.
Part 2 of 5Proteins controlled by genes
Genes code for proteins
Structural proteins
- Structural proteins Examples include collagen, which gives strength to skin and other tissues.
Enzymes
- Enzymes Biological catalysts that control the rate of chemical reactions in the cell.
Hormones
- Hormones Some hormones, such as insulin, are proteins and carry messages in the blood.
Part 3 of 5Chromosomes
Structure
- Structure In the nucleus, each very long DNA double helix is coiled and supercoiled into a chromosome.
- Chromosomes become visible under a microscope only when the cell is dividing.
Human number
- Human number A normal human body cell has 23 pairs of chromosomes, which is 46 in total.
- This is the diploid number, written 2n.
Pairs
- Pairs One chromosome of each pair comes from the mother and the other from the father.
- The two members of a pair are called a homologous pair.
Gene position
- Gene position Each gene occupies a particular place on a chromosome, so the same gene is found at the same position on both chromosomes of a pair.
Part 4 of 5Chromosome numbers in species
| Organism | Chromosome pairs | Total in body cell |
|---|---|---|
| Human | 23 | 46 |
| Dog | 39 | 78 |
| Rice plant | 12 | 24 |
Part 5 of 5Summary of the terms
| Term | Level of organisation |
|---|---|
| Genome | All the DNA of one organism |
| Chromosome | A structure of coiled DNA in the nucleus |
| Gene | A short length of DNA that codes for one protein |
Key terms
| Term | Meaning |
|---|---|
| Genome | The entire DNA of an organism. |
| Gene | A section of DNA that codes for a particular protein. |
| Chromosome | A coiled structure of DNA found in the nucleus. |
| Diploid | Having two sets of chromosomes, as in body cells (2n). |
| Homologous pair | Two chromosomes carrying the same genes, one from each parent. |
| Amino acid | The small molecules joined in a chain to make a protein. |
Avoid these mistakes
1
Saying that a gene codes for a whole characteristic. A gene codes for a protein, and the protein influences the characteristic.
2
Confusing the number of pairs (23) with the total number of chromosomes (46).
3
Stating that all species have 46 chromosomes. The number differs between species.
4
Writing that chromosomes are always visible. They only appear as distinct structures during cell division.
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