Which Proteins are Synthesised? (Cambridge (CIE) IGCSE Biology): Revision Note

Control of gene expression: Extended

• Expression of a gene means whether that gene is transcribed and translated (opens in a new tab) in a particular cell or not

• Most genes are not expressed in a particular cell; they are 'switched off'

• Only the genes whose proteins are vital to that cell's function are expressed ('switched on')

• In this way, DNA controls cell function by controlling the production of proteins

• The proteins may be enzymes, antibodies, or receptors for neurotransmitters

• Although all body cells in an organism contain the same genes, many genes in a particular cell are not expressed because the cell only makes the specific proteins it needs 

Haploid and diploid cells

• All humans have 23 different chromosomes in each cell

• Human body cells, not including the gametes (sex cells), contain two copies of each chromosome, leading to a total of 46 chromosomes

• Nuclei with two sets of chromosomes are known as diploid nuclei

• The gametes (egg and sperm cells) only have one copy of each chromosome, meaning they have a total of 23 chromosomes in each cell

• Nuclei with one set of unpaired chromosomes are known as haploid nuclei