Interactive Resources for Schools
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Human biology
Biology
Physical education
Biology
Science (applied)
Biology
Identical twins have identical antigens on their cells. Siblings, parents and offspring have relatively similar antigens – but they are different enough for their cells to recognise each other as ‘non-self’. The cells from two organisms from the same species have more antigens in common than organisms from different species. The further apart organisms are in evolutionary terms, the more differences there will be in their cell surface antigens.
Receptor molecules
Identification of one cell by another involves specific receptor molecules in the cell surface membrane. Each cell has receptorsreceptors
Protein molecules attached to cells that only bind to specific molecules with a particular structure.
that enable it to identify matching antigens. They also have receptors which recognise foreign antigens. The cells of the immune systemimmune system
The body's natural defence mechanism against infectious diseases.
are primed with millions of receptors that enable them to recognise and ultimately destroy material that they recognise as ‘non-self’, including pathogens, cells from other organisms of the same species, abnormal body cells and toxins.
The interaction between antigenantigen
A protein, nucleic acid, or other molecule, which can stimulate a response from the immune system.
s and receptorsreceptors
Protein molecules attached to cells that only bind to specific molecules with a particular structure.
on
the surface of cell membranemembrane
A thin, flexible sheet-like structure that acts as a lining or a boundary in an organism.
s is the key to cell recognition
Communication within cells is brought about in a number of ways. It often involves the production of a signalling molecule and the presence of specific receptorsreceptors
Protein molecules attached to cells that only bind to specific molecules with a particular structure.
on the cell membranemembrane
A thin, flexible sheet-like structure that acts as a lining or a boundary in an organism.
.
Synaptic transmission between neurones
Neurotransmitter molecules made in the presynaptic knob are released into the synaptic cleft and picked up by receptors on the post-synaptic membrane. This triggers changes in membrane transport systems setting up a new action potentialaction potential
The wave of positive charge which passes along an axon in response to a stimulus.
.
Animation of a synapse:
Hormones
Hormones act by binding to specific receptor sites on the membranemembrane
A thin, flexible sheet-like structure that acts as a lining or a boundary in an organism.
of their target cells. At this point the hormone needs to affect the target cell in some way to bring about the desired change in activity. There are two main ways in which hormones can affect a cell:
Direct messengers: The hormone may pass through the membrane and act as the internal messenger itself. Inside the cell the hormone binds to a receptor and the hormone-receptor complex passes through the pores of the nuclear membranenuclear membrane
The thin, flexible structure enclosing the contents of the nucleus in a cell.
into the nucleus.
The hormone-receptor complex acts as a transcription factortranscription factor
Protein which binds to the nuclear DNA, regulating the transcription of the genetic material and sometimes changing the mRNA which is formed as a result.
, regulating gene expression and switching sections of the DNA on or off. This is the mode of action of the lipid-soluble steroid hormones such as oestrogen and testosterone.
This second messenger then activates enzymes within the cell, altering the metabolism. The most common second messenger is a substance called cyclic AMPcyclic AMP
Cyclic adenosine monophosphate (AMP). The most common second messenger molecule in cells, derived from adenosine triphosphate (ATP).
(cAMP). This in turn triggers different responses in the cell that may include increased cellular respirationcellular respiration
Breaking down glucose (food) without oxygen to provide available energy for the cells. The glucose reacts with oxygen to produce energy in the form of ATP with carbon dioxide and water as waste products.
, increased contraction of muscle cells, relaxation of smooth muscle in blood vesselsblood vessels
The tubes through which blood is carried around the body, e.g., arteries, veins and capillaries.
or other effects.
Animation showing chemical communication via a second messenger in a cell: