2.3 - Transport of substances Flashcards
Structure and function of phospholipids
Hydrophilic, polar phosphate head on the outside
Hydrophobic, non-polar fatty acid tails on the inside
Form a bilayer.
● Selectively permeable - allows non-polar molecules to pass through
● Allows cell to maintain different concentrations either side
● Membranes are able to form vesicles
● Provides fluidity
Structure and function of glycoprotein
Glycoprotein - carbohydrate chain attached to protein
Important in cell recognition and cell signaling
So that the immune system can tell the difference between body cells & e.g. invading bacteria.
Glycolipid (carbohydrate chain attached to phospholipid)
For cell recognition and to provide energy (if needed for respiration it can be broken down).
Structure and function of Extrinsic protein
Receptor sites for hormones. Detect chemicals released from other cells. For cell recognition.
Structure and function of Cholesterol
Cholesterol increases fluidity/ rigidity by reducing movement of other molecules in the membrane.
Structure and function of transport protein
Can be carrier proteins or channel proteins
The channel proteins create selective hydrophilic pores (for water + water soluble compounds).
Carrier proteins are involved in facilitated diffusion and active transport.
Channel proteins are only used for facilitated diffusion.
- Why is the plasma membrane referred to as being fluid-mosaic?
● Molecules within the membrane able to move (fluid)
● Mixture of phospholipids, proteins, cholesterol, glycoproteins, glycolipids (mosaic)
- How does the bilayer formed by phospholipids affect entry and exit of substances into and out of a cell?
● allows movement of small, lipid soluble, non-polar molecules such as gases through the membrane
● prevents movement of large, water soluble, polar molecules such as ions and amino acids
● The membrane is selective and partially permeable
- Define diffusion
● It is passive NET movement of substances from an area of high concentration to an area of low concentration, down a concentration gradient.
- Where can diffusion take place?
● Diffusion can occur from one area to another or across a partially permeable membrane
- Which substances can simply diffuse across the phospholipid bilayer?
● Small, non-charged (or non-polar), lipid soluble molecules can diffuse across the phospholipid bilayer
- Explain why molecules of oxygen and carbon dioxide are able to diffuse across membranes.
● The hydrophobic fatty acid part of membrane is non-polar
● Oxygen and carbon dioxide are small non-polar molecules.
● Oxygen/carbon dioxide can diffuse through the fatty acid layer
● Down a concentration gradient
- Which factors increase the rate of diffusion and why?
● High concentration gradient
● Increase the temperature
● Increase the surface area
● Increase the pressure
● Decrease the diffusion pathway (reduce membrane width)
- Write the equation for Fick’s law:
Rate of diffusion ∝ (concentration gradient x surface area) / Diffusion pathway
- Define the process of facilitated diffusion
● The passive movement of substances from high concentration to a low concentration, down a concentration gradient, through a channel or carrier protein.
- What sorts of substances are transported using this method? Why? Examples?
● It is used for substances which are large, polar/charged or water-soluble
● The fatty acid layer of the plasma membrane is hydrophobic and non-polar, it will not allow polar substances to diffuse though
● Ions, amino acids
Compared channel and carrier proteins
Check notes
● What could limit the rate of facilitated diffusion?
● The number of transport proteins available in the membrane
● The concentration gradient
● the surface area
- Define the process of active transport
Active transport is the movement of a substance against its concentration gradient.
This requires the use of a carrier protein that uses energy released from ATP hydrolysis.
- How does active transport move substances against their concentration gradient?
● Substance binds to a carrier protein
● ATP binds to carrier protein
● ATP is hydrolysed into ADP and Pi, and this releases energy
● This causes the carrier protein’s tertiary structure to change (undergoes a conformational change)
● The substance is released on the other side of the membrane
- What could limit the rate of active transport?
● The number of carrier proteins
● The amount of oxygen available for respiration. (this affects the amount of ATP available)
● Very High temperature – if the temperature is high it could denature enzymes involved in respiration so ATP cannot be produced.
● If the temperature is moderately high increased rate of active transport as molecules have more kinetic energy increased rate of respiration more ATP ALSO more collisions between carrier proteins and substance to be transported
- Give two ways in which active transport differs from diffusion? (you can simply state the differences)
● in active transport ATP is used.
● and movement is against a concentration gradient
- Contrast the processes of facilitated diffusion and active transport. (you must write comparisons here)
● Facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins.
● Facilitated diffusion does not use ATP whereas active transport uses ATP.
● Facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient.
Summarising the different types of transport
Check notes
