Physiology 3140A Lecture Notes - Lecture 7: Antiporter, Symporter, Not Like That
2 May 2018
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Physiology 3140 Lecture 7
Transport Across Epithelium 2
September 22 2017
Symporters and Antiporters
- Movement of ions and/or macromolecules across a membrane with the aid of the concentration
gradient of another molecule
o Piggy back something that is moving up concentration gradient with something that is trying
to move down its concentration gradient
- Form of Secondary Active Transport
o No ATP necessary
- Are symporters only involved in glucose uptake?
o NO
Amino Acid Transporters
Amino Acid/ Na+ Symporters
- Large family of transporters (> 10 families identified)
- At least 10 members within each family
o Examples:
▪ Lysine exporter family (basic amino acids)
▪ Alanine/Glycine symporter (Ala or Gly)
▪ Branched chain amino acid symporter (2-3 amino acid chains)
o Intestine (absorption) and Kidney (reabsorption)
▪ Body wants to keep as much macronutrients inside, and NOT excrete
- Over 100 symporters
o Have a lot of transporters for amino acids
- Intestine (form of absorption) or kidney (form of reabsorption) uses Na+ to drag amino acids across
their concentration gradients
- Use sodium going down its concentration gradient, also take amino acids (one or branched)
Antiporters
Ca+2/Na+ Antiporter
- Low cytosolic concentrations of calcium is required for maintaining the ability to allow cardiac
muscles to contract in response to internal calcium release (more sensitive to change)
- A perceived rise in calcium will trigger a contraction in your muscles
o Why you have to keep the calcium concentrations in the cytosol very low (kept in ER, SR, or
outside cell)
o Need to pump out the calcium (Calcium is going outside of the cell, Na going the other way)
- Antiport of 3:1 Na+/Ca+2 is required
o Antiport 3 Na+ for one Ca++
- When this antiporter is activated, the strength of the contraction is reduced!
o Getting rid of the calcium inside the cell
Membrane Transport of Iron
- Iron is an essential component in the cells of our body
o Daily requirement: 10-20mg
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- Essential to the function of hemoglobin, myoglobin, cytochromes, peroxidase, catalase, etc.
o A lot of enzymes require iron
- Most of the iron that we normally contained within our bodies is in:
o Hemoglobin (~65%)
o Liver parenchymal cells (15-30%), mostly as ferritin (stores it)
- When levels of iron drop, liver releases ferritin stores and iron is transported in the plasma (bound
to a carrier protein)
- Unlike glucose, goes into our blood stream and transported to other cells and taken up that is not
toxic
o IRON IS NOT LIKE THAT; once you take up iron from the diet, it needs to bind something
(protein) in order to be transported somewhere else
- Free iron is bad in the blood! As soon as iron is taken in, it has to bind to another protein
Iron Transport in the Body
- Iron comes in Ferric (3+) or Ferrous (2+) states
- Ferric iron is ingested by the diet and converted at the cell surface in order to get absorbed as ferrous
iron
- Ferrous iron absorbed by active transport in the intestine
- Cells convert the iron into ferric, and it makes its way to the plasma
- Transferrin (binds to iron and moves it around in the bloodstream) in our plasma will make its way
to the bone marrow
o Iron incorporated to heme incorporated to hemoglobin necessary for RBC synthesis
- RBC live 120 days in the blood, until they get destroyed by spleen
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Form of secondary active transport: no atp necessary. Are symporters only involved in glucose uptake: no. Large family of transporters (> 10 families identified) At least 10 members within each family: examples, lysine exporter family (basic amino acids, alanine/glycine symporter (ala or gly, branched chain amino acid symporter (2-3 amino acid chains) Intestine (absorption) and kidney (reabsorption: body wants to keep as much macronutrients inside, and not excrete. Over 100 symporters: have a lot of transporters for amino acids. Intestine (form of absorption) or kidney (form of reabsorption) uses na+ to drag amino acids across their concentration gradients. Use sodium going down its concentration gradient, also take amino acids (one or branched) Low cytosolic concentrations of calcium is required for maintaining the ability to allow cardiac muscles to contract in response to internal calcium release (more sensitive to change) Antiport of 3:1 na+/ca+2 is required: antiport 3 na+ for one ca++
