Protein synthesis

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• Expression?of a gene means whether that gene is transcribed and translated in a particular cell or not
• Most genes are not expressed in a particular cell
  • They are 'switched off'
  • Because that would be a waste of energy and other resources in the cell
• Only the genes whose proteins are vital to that cell's function are expressed ('switched on')

?The triplet code of DNA (carried by mRNA) is read by the ribosome and amino acids are attached together in a specific sequence to form the protein

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• 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
• In most body cells, not including the gametes (sex cells), we have 2 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