Edexcel GCSE Biology (1BI0) — Genetics
Every time you buy a piece of flat-pack furniture, it comes with a complete instruction manual. Your body has one too, containing all the biological information needed to build and operate you.
Most human cells contain a full copy of the genome, but there are notable cellular exceptions. Human red blood cells lack a nucleus entirely and therefore do not carry the genome, while gametes (sperm and egg cells) are haploid, meaning they only contain a half-copy of the genome (23 chromosomes).
If the genome is the entire instruction manual, a gene is a single instructional step. To describe a gene accurately, you must identify it as a specific, short section of a DNA molecule that codes for a specific protein.
These proteins carry out essential roles throughout the organism's body. Examples include structural proteins (like collagen for support), chemical messengers (like hormones), and enzymes that act as biological catalysts. The specific shape of a protein is critical to its function; for example, an enzyme must have a correctly shaped active site to fit its substrate.
Students often incorrectly define a genome as "all the genes" in an organism, but actually, it must be defined as the "entire DNA", which importantly includes all the non-coding regions as well.
When an exam question asks you to "describe a gene", examiners specifically look for the phrase "section of DNA" or "length of DNA"; saying it is just "a piece of DNA" is usually too vague for the mark.
Calculation Tip: You may be asked to calculate the number of amino acids coded for by a length of DNA. Always use the formula: . For example, 450 bases code for 150 amino acids.
Genome
The entire DNA or entire genetic material of an organism.
DNA
A polymer made of two strands coiled into a double helix that carries genetic information.
Chromosomes
Long, coiled molecules of DNA found in the nucleus that carry genetic information in the form of genes.
Gene expression
The process by which the instructions in DNA are converted into a functional product, often controlled by non-coding regions acting as switches.
Gene
A short section of a DNA molecule that codes for a specific protein by determining the sequence of amino acids.
Bases
The four chemical units (Adenine, Thymine, Cytosine, Guanine) whose sequence in a gene provides the genetic instructions.
Triplet code
The system where a sequence of three bases (a codon) in DNA codes for one specific amino acid.
Double helix
The structural shape of a DNA molecule, consisting of two intertwined polymer strands.
Amino acids
Small molecular building blocks that join together in a specific sequence to form proteins.
Enzymes
Biological catalysts made from folded proteins that possess a specifically shaped active site.
Gametes
Sex cells (sperm and eggs) that contain half the number of chromosomes of a normal body cell.
Haploid
A cell or nucleus that has a single set of unpaired chromosomes (e.g., human gametes have 23).
Polypeptide chain
A chain of many amino acids linked together by peptide bonds, which eventually folds into a functional protein.
Active site
The specific part of an enzyme where the substrate binds and the chemical reaction occurs.
Substrate
The specific molecule that fits into the active site of an enzyme to react.
Put your knowledge into practice — try past paper questions for Biology
Genome
The entire DNA or entire genetic material of an organism.
DNA
A polymer made of two strands coiled into a double helix that carries genetic information.
Chromosomes
Long, coiled molecules of DNA found in the nucleus that carry genetic information in the form of genes.
Gene expression
The process by which the instructions in DNA are converted into a functional product, often controlled by non-coding regions acting as switches.
Gene
A short section of a DNA molecule that codes for a specific protein by determining the sequence of amino acids.
Bases
The four chemical units (Adenine, Thymine, Cytosine, Guanine) whose sequence in a gene provides the genetic instructions.
Triplet code
The system where a sequence of three bases (a codon) in DNA codes for one specific amino acid.
Double helix
The structural shape of a DNA molecule, consisting of two intertwined polymer strands.
Amino acids
Small molecular building blocks that join together in a specific sequence to form proteins.
Enzymes
Biological catalysts made from folded proteins that possess a specifically shaped active site.
Gametes
Sex cells (sperm and eggs) that contain half the number of chromosomes of a normal body cell.
Haploid
A cell or nucleus that has a single set of unpaired chromosomes (e.g., human gametes have 23).
Polypeptide chain
A chain of many amino acids linked together by peptide bonds, which eventually folds into a functional protein.
Active site
The specific part of an enzyme where the substrate binds and the chemical reaction occurs.
Substrate
The specific molecule that fits into the active site of an enzyme to react.
