Chromosomes, genes and proteins

Sex is determined by the X and Y chromosomes. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The Y chromosome carries the gene that determines maleness.

The sequence of bases in a gene determines the sequence of amino acids used to make a specific protein. This amino acid sequence dictates the protein's unique structure and function, like the enzyme amylase which breaks down starch.

Different sequences of amino acids cause a protein molecule to fold into different three-dimensional shapes. The shape of a protein is critical for its function;

DNA controls cell function by directing the production of proteins. These proteins include enzymes (catalyze reactions), membrane carriers (transport molecules), and receptors for neurotransmitters (cell communication).

The gene for a protein remains in the nucleus. Messenger RNA (mRNA), a copy of the gene, is made in the nucleus and moves to the cytoplasm. The mRNA passes through ribosomes, which assemble amino acids into protein molecules based on the mRNA sequence.

Most body cells contain the same genes, but many are not expressed. Cells only make the specific proteins they need to perform their particular function.

In a human diploid cell, there are 23 pairs of chromosomes, for a total of 46 chromosomes. These include 22 pairs of autosomes and one pair of sex chromosomes (XX or XY).