chapter 4.5 Flashcards
What are ways of increase the rate of diffusion across the membrane
-The epithelial cells lining the ileum posses’ microvilli, which are on the surface of the villi. These are finger-like projections of the cell-surface membrane about 0.6um in length. They are collectively termed a ‘brush border’ because, when viewing them under a light microscope they look like bristles on a brush.
The microvilli provide more surface area for the insertion of carrier proteins through which diffusion, facilitated diffusion and active transport can take place. -Another mechanism to increase transport across membranes is to increase the number of protein channels and carrier proteins in any given area of membrane.
-good blood supply to maintain a steep concentration gradient
What’s the definition if diffusion?
Diffusion is the net movement of molecules or ions from a region where they are highly concentrated to a region where their concentration is lower.
Is co-transport also used to transport molecules from where they are in high concentration to low concentration.
Yes, co transport is needed to get amino acid and glucose for example from where it is in low concentration to where it is highly concentrated (moved against the concentration gradient.
Why can’t we rely on diffusion in the gut to absoirb food in the large intestine?
Simple and facilitated diffusion because we would only get 50% of the substances diffused the lumen and into the blood stream. Therefore, it would not be good for survival rease as we would not get all they energy they we have digested and require, also if we have lots of glucose in the small intestine means we will absorb lots of water by osmosis which will lead to dirhoeia.
Why can’t we rely on active transport in the gut to absorb food into the large intestine?
We could also use active transport however if we would need two carrier proteins one of sample if this was in the gut we would need one carrier protein carried in the top of the epithial cells below the lumen and one at the bottom of the epithelia cell n the top of the blood stream. This would therefore require lots of energy in the form of ATP and in fact twice as much energy a we would need to use 2 ATP molecule
Why is good we rely on co-transport
if we were using co transport (one reason we use co-transport), as co-transport just requires one lots of active transport to be used which allows facilitated diffusion of that molecule that transported put via at which allows the passive process of the co-transported proteins as it technical gives it a free life) to take place which is a possess) Therefore we use co-transport, as this process allows 1. 100% of the molecules to diffuse across (unlike simple and facilitated diffusion would) and 2. Only used one molecule of ATP (and if we were relying on active transport this would use 2 molecules of active transport). The point of facilitated diffusion is to absorb 100% of the material’s with using minimal amount of energy.
What are the steps of co-transport for a glucose molecule:
Step 1: Sodium is actively transported out of the epithelium cells by a sodium-potassium pump into the blood. This takes place in one type of protein- carrier, a sodium-potassium pump molecule found in the cell-surface membrane of epithelial cells. This requires ATP so sodium is actively transported out of the epithelium cells and into blood. This creates a lower concentration of sodium ions inside the epithelial cell, and a higher concentration of sodium ions in the lumen of the small intestine than inside the epithelium cells. Therefore, sodium ions are moving own a concentration gradient. This uses ATP so sodium ions are actively transported out of the cell via a sodium-potassium pump (which is the type of protein used).
Step 2: The sodium ions (doesn’t have to be the same Na+ molecule will get in the co-transported that the one that got actively transported out. It can be a different one from the lumen.) being actively diffusing out of the epithelium cells creates a higher concentration gradient of sodium ions in the lumen of intestine than inside the epithelium cells. Sodium ions from the lumen of the ilium will diffuse now down this concentration radiant that was created from this sodium ion moving out by active transport (step 1)
Step 3: Therefore, sodium ions will now diffuse down their concentration gradient from the lumen and epithelium cells taking a glucose or an amino acid molecule with it. The sodium ions and glucose or amino acids will diffuse from the lumen of the small intestine so the epithelial cells transported in a co-transport protein in the cell surface membrane, as the sodium ion is moving down its concentration gradient but ATP allows this to happen (thanks to step 1) into the epithelium cells this allowing this process to be passive even though the glucose or amino acid molecule mores against its concentration gradient in
the cell.
The two molecules will be transported in a co-transport protein where it ca only work if the two molecules are both bonded in it. This will transport both the sodium and potassium into the epithelial cell. This process is passive as sodium ions are diffusion down a concentration gradient and they basically give the potassium a free lift. (therefore is passive) require any extra energy except the inbuilt motion of kinetic energy of the diffusion (therefore is passive)
Step 4: This makes a higher concentration of glucose or amino acids molecules inside the epithelial cell than in the blood stream so glucose or amino acids pass into the blood plasma diffusing out of the epithelial cell via facilitated diffusion using another type of carrier.
Which way do the glucose and sodium ions concentrations move?
Both sodium ions and glucose/amino acid molecule move into the cell but while the sodium ions move down their concentration gradient, the glucose molecules move against their concentration gradient.
What does it mean when we say that co-transport is an indirect rather than a direct form of active transport?
ATP powers the first movement the sodium molecule out of the cell which therefore creates the sodium ion concentration gradient difference which powers the movement of glucose and amino acids into the cells. This makes it an indirect rather than a direct form of active transport, as the moving of the glucose doesn’t actually require ATP however for it to not require ATP it required ATP before hand. Therefore the ATP hasn’t actually moved it into the cell but it has created the right environment allowing it to move across the plasma membrane (without using ATP), therefore as ATP is not used in the presses of the glucose or amino acid molecule moving into the membrane at that moment ATP is used indirectly.
When does ADP form back into ATP in the process of co-transport?
When the phosphate breaks away from the protein it is unbinded in the cytoplasm. When respiration occurs, it binds again with ADP to make ATP.
What is primary active transport
Primary active transport, also called direct active transport, directly uses chemical energy (such as from adenosine triphosphate or ATP in case of cell membrane) to transport all species of solutes across a membrane against their concentration gradient, ATP is used at that moment to change shape of the protein in which the molecule inside it is wanting to be moved across the membrane.
What is secondary active transport?
This is when ATP is not used directly but has been used to create the right environment for the passive transport to take place. The carrier protein uses the energy of the sodium ion gradient, that was made by using active transport. This provided a concentration gradient difference to drive the transport of glucose molecules.
