Definition Nuclear division The process by which a nucleus divides, resulting in the separation of the genome to opposite poles of a dividing cell.
In some cases, the reverse is actually true: Changes in ion levels inside the cell can change the activity of other molecules, such as ion-binding enzymes and voltage-sensitive channels, to produce a response.
Neuronsor nerve cells, have ligand-gated channels that are bound by neurotransmitters. Diagram of a ligand-gated ion channel. When the ligand binds to a closed ion channel in the plasma membrane, the ion channel opens and ions can pass through it, moving into or out of the cell down their concentration gradient.
Image modified from " Signaling molecules and cell receptors: G protein-coupled receptors G protein-coupled receptors GPCRs are a large family of cell surface receptors that share a common structure and method of signaling. The members of the GPCR family all have seven different protein segments that cross the membrane, and they transmit signals inside the cell through a type of protein called a G protein more details below.
GPCRs are diverse and bind many different types of ligands. One particularly interesting class of GPCRs is the odorant scent receptors.
G proteins come in different types, but they all bind the nucleotide guanosine triphosphate GTPwhich they can break down hydrolyze to form GDP. Diagram of the cycle of GPCR signaling. The alpha subunit dissociates from the beta and gamma subunits and interacts with other molecules, ultimately triggering a cellular response.
The beta and gamma subunits may, in some cases, also participate in signaling. The alpha subunit comes back together with the receptor and the beta and gamma subunits. The cycle can then repeat when a new ligand-binding event takes place.
Ligand binding, however, changes the picture: The subunits can interact with other proteins, triggering a signaling pathway that leads to a response.
Cell signaling using G protein-coupled receptors is a cycle, one that can repeat over and over in response to ligand binding. G protein-coupled receptors play many different roles in the human body, and disruption of GPCR signaling can cause disease.
In cholera, for example, the water-borne bacterium Vibrio cholerae makes a toxin called choleragen, which binds to cells lining the small intestine. The toxin then enters the intestinal cells, where it modifies a G-protein that controls the opening of ion channels, locking it in a permanently active state.
Because the G-protein cannot turn itself off, the ion channels remain open much longer than they should, causing ions to pour out of the cells with water following by osmosis.
This small change in a GPCR signaling pathway causes the diarrhea, severe fluid loss, and potentially fatal dehydration seen in cholera victims.
Giving cholera patients a simple solution of salt and glucose can prevent dehydration and save lives. Learn why in the article on active transport.
Receptor tyrosine kinases Enzyme-linked receptors are cell-surface receptors with intracellular domains that are associated with an enzyme. In some cases, the intracellular domain of the receptor actually is an enzyme that can catalyze a reaction.
Receptor tyrosine kinases RTKs are a class of enzyme-linked receptors found in humans and many other species.Introduction Cambridge Advanced International Certificate of Education (AICE) Cambridge AICE is the group award of Cambridge International Advanced Supplementary Level and Advanced Level (AS Level and A Level).
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Aice Biology Nuclear Division. By admin The Best Papers 0 Comments. After DNA replication at G2 checkpoint? Spindle Checkpoints?
Detect any failure of spindle fibers? Detect improper alignment of spindle itself and block cytokinesis? Trigger apoptosis if damage is irreparable determined by volume? Volume increases faster than surface area. Interphase- the period between nuclear division in which each DNA molecule in a nucleus makes an identical copy of itself.
It consists of G1, G2, and S phases. Cambridge International Examinations (CIE) (formerly known as “University of Cambridge International Examinations”) are a provider of international qualifications, offering examinations and qualifications in more than countries.