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Transport processes

Transport processes

This animation explains active and passive transport processes occurring through cell membranes

Biology

Keywords

membrane transport, transport, cell membrane, passive transport, active transport, diffusion, channel protein, carrier molecule, symport, antiport, uniport, concentration gradient, ADP, ATP, cytology, biology

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Questions

  • What is true about the sodium-glucose transporter?
  • What is true about the sodium-potassium pump?
  • What type of transport process is not shown in the animation?
  • What type of transport process is shown in the animation?
  • What type of transporter is shown in the animation?
  • What type of transporter is NOT shown in the animation?
  • What is true about this transport system?
  • What is true about this transport system?
  • This transport system ensures...
  • This transport system ensures...
  • How is K+ transported in this transport system?
  • This transport system ensures...
  • The absorption of glucose ...

Scenes

Passive transport

  • higher concentration
  • lower concentration
  • cell membrane - Double lipid membrane with a non-polar central layer, in which non-polar substances dissolve. Small non-polar molecules (e.g. O₂, CO₂, steroids) diffuse through the lipid membrane. Small polar molecules (e.g. H₂O) pass through the temporary pores that open due to the thermal motion of lipid molecules.

Active transport

  • higher concentration
  • lower concentration
  • ATP
  • ADP
  • phosphate
  • transporter (uniporter) - In uniporter-catalysed transport only one type of molecule is transported. Active transport takes place towards the higher concentration, which requires energy, provided by ATP.

Animation

  • higher concentration
  • lower concentration
  • cell membrane - Double lipid membrane with a non-polar central layer, in which non-polar substances dissolve. Small non-polar molecules (e.g. O₂, CO₂, steroids) diffuse through the lipid membrane. Small polar molecules (e.g. H₂O) pass through the temporary pores that open due to the thermal motion of lipid molecules.
  • higher concentration
  • lower concentration
  • carrier molecule - It transports particles that otherwise cannot pass through the double lipid membrane. Such particles include polar molecules, ions and large molecules.
  • higher concentration
  • lower concentration
  • ligand - Molecules that open ion channels by binding to them. Such ligands in the nervous system are neurotransmitters. They open ion channels and thereby change the electric properties of the membrane.
  • channel protein - Polar molecules and ions not soluble in the lipid membrane pass through them. Ion channels are usually openable and closeable. The opened or closed state of certain channels depends on ligand bonds (e.g. hormones, neurotransmitters), others on the electric properties of the membrane. These are called voltage-gated ion channels, the former ones are called ligand-gated channels. Action potentials in neurons are generated by special types of voltage-gated ion channels.
  • higher concentration
  • lower concentration
  • ATP
  • ADP
  • phosphate
  • transporter (uniporter) - In uniporter-catalysed transport only one type of molecule is transported. Active transport takes place towards the higher concentration, which requires energy, provided by ATP.
  • ´A´ particle - The active transporter accumulates them on one side of the membrane. Then one passes through the symporter passively, carrying a ´B´ particle with itself. Therefore the ´B´ particle is transported against the concentration gradient.
  • ´B´ particle - One such particle is transported through the membrane passively, against the concentration gradient. For this an ´A´ particle also needs to pass through the symporter which, in turn requires the accumulation of ´A´ particles on one side of the membrane by an active transporter.
  • ATP
  • ADP
  • phosphate
  • active transporter - It creates a concentration difference of ´A´ particles. Since the particles are accumulated on one side of the membrane, the transport requires energy, which is provided by ATP.
  • symporter - It transports an ´A´ particle and a ´B´ particle in one direction simultaneously. The ´A´particles, accumulated by the active transporter, pass through the symporter down the concentration gradient, each carrying another particle with themselves, which are thus transported against the concentration gradient. Therefore this transport requires ATP only indirectly, for the active transporter to create the concentration difference.
  • ´A´ particle - The active transporter accumulates them on one side of the membrane. Then one passes through the symporter passively, carrying a ´B´ particle with itself. Therefore the ´B´ particle is transported against the concentration gradient.
  • ´B´ particle - One such particle is transported through the membrane passively, against the concentration gradient. For this an ´A´ particle also needs to pass through the symporter which, in turn requires the accumulation of ´A´ particles on one side of the membrane by an active transporter.
  • ATP
  • ADP
  • phosphate
  • active transporter - It creates a concentration difference of ´A´ particles. Since the particles are accumulated on one side of the membrane, the transport requires energy, which is provided by ATP.
  • antiporter - It simultaneously transports an ´A´ particle and a ´B´ particle in opposite directions. The ´A´ particles, accumulated by the active transporter pass through the antiporter down the concentration gradient, while another particle passes through in the opposite direction, against the concentration gradient. Therefore this transport requires ATP only indirectly, for the active transporter to create the concentration difference.

Narration

The absorption and release of certain substances takes place through cell membranes. The two basic types of these processes are passive transport and active transport, the latter requiring energy.

During passive transport, particles flow towards the lower concentration, which does not require an energy investment.
The simplest type of passive transport is simple diffusion. Particles pass through the double lipid layer of the membrane, down the concentration gradient. The central, apolar layer of the membrane dissolves apolar particles. Therefore apolar molecules, like oxygen, carbon dioxide and steroids, are capable of simple diffusion. Small polar molecules, such as water, may also pass through the membrane, through the temporary pores that open due to the thermal motion of lipid molecules.

Carrier molecules permit the transportation of particles towards the lower concentration that otherwise could not (or could not easily) pass through the double lipid membrane due to their size or hydrophobicity. These particles are polar molecules, ions and large molecules.

The membrane also contains channel proteins, which can be opened or closed. When a suitable ligand attaches, the channel opens. It transports polar molecules and ions that otherwise could not pass through the lipid layer of the membrane. Channels permit faster transport than carrier molecules, but they are less selective. Ion channels play an extremely important role in the electrical activities of neurons.

Active transport processes require energy, as particles are carried against the concentration gradient and are accumulated on one side of the membrane. The necessary energy is provided by the breakdown of ATP.

The simplest type of active transport is uniport: a uniporter transports one particle towards the higher concentration. This requires energy intake, that is, ATP. ATP breaks down into ADP and phosphate while releasing energy.

During secondary active transport, the active transporter creates a difference in the concentration of particle ´A´, using ATP. Another transporter allows the accumulated ´A´ particles to pass through the membrane. ´B´ particles are transported against the concentration gradient. The transport of ´B´ particles therefore requires ATP indirectly. Symporters transport ´A´ and ´B´ particles in one direction.

Another type of secondary active transport is called antiport. During this process the active transporter creates a difference in the concentration of particle ´A´, using ATP. The antiporter allows ´A´ particles to pass through the membrane down the concentration gradient, while it also permits a ´B´ particle through, against its concentration gradient. The transport of ´B´ particles therefore requires ATP indirectly. Antiporters transport ´A´ and ´B´ particles in opposite directions.

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