1,800+ MCAT terms, defined.

Mutations disable the checkpoints and growth signals that normally limit division, so cells divide unregulated, as in cancer. Oncogenes arise by gain of function (one mutant allele often suffices); tumor suppressors like p53 and Rb typic...

Pedigree analysis uses a family tree to work out how a trait is inherited (autosomal or X-linked, dominant or recessive) and to infer family members' genotypes. Most testable: two unaffected parents with an affected child usually means t...

Plasma is the liquid, cell-free part of blood, about 55% of its volume. It is mostly water with dissolved proteins, ions, nutrients, hormones, wastes and gases. Its proteins, mainly albumin, create the oncotic pressure that draws fluid b...

Synaptic transmission is the passing of a signal from a presynaptic neuron to a postsynaptic cell. At a chemical synapse, Ca²⁺ entry triggers neurotransmitter release, which binds receptors and causes an EPSP or IPSP. Electrical synapses...

Tumour suppressors are genes whose proteins restrain the cell cycle, aid DNA repair, or trigger apoptosis; p53 and Rb are the classic examples. Their loss of function usually requires both alleles to be inactivated, unlike an oncogene, w...