Cell membrane and transport Flashcards
1
Q
What are phospholipids
A
- hydrophillic polar head
- hydrophobic fatty acid tail
- phospholipids form a bi layer in water
- polar heads face outwards interacting with water outside the cell and inwards interacting with water in the cytoplasm
2
Q
What is the phospholipid bi layer
A
- phospholipids arrange into a bi lauer with proteins scattered throughout
- some proteins are extrinsic and found on surface of the bilayer act as receptors of hormones and as recognition sites
- other proteins are intrinsic and extend across both lauers accting as channel and carrier proteins for the transport of molecules
- some proteins are enzymes eg ATP synthase in cristae or digestive enzymes in eithelium of villi
3
Q
What is the fluid mosaic model
A
- singer and nicholson 1972
- phospholipids free to move
- mosaic random assortment of protein molecules
- membrane in animals cells also contain chloresterol which stabilies it
- glycoproteins act as antigens
- glycolipids act as receptor sites for molecules such as hormones
4
Q
How do molecules transport across membranes
A
- properties of molecules passing across membrane will directly affect how they cross
- non polar molecules eg vitamin A and small molecules eg oxygen can dissolve in fatty acid tail and diffuse straight across membrane
- polar molecules eg glucose have to pas via a transport protein as they cannot dissolve in fatty acid tail
5
Q
What is diffusion
A
- simple diffusion type of passive transport
- moleule move from a high to low concentration until equally distributed
- molecule constantly moving due to kinetic energy
- any factor increase energy or decrease the distance increase rate of diffusion
6
Q
What are the factors affecting rate of diffusion
A
- concentration gradient - greater difference concentration between two areas more molecules diffuse in a given time so collision with membrane more likely
- diffusion distance - takes less time for molecules to diffuse a shorter distance
- surface area of membrane - large area more molecules can diffuse in a give time
- thickness of exchange surface - take less time for molecules to diffuse a shorter distance
- increase in temprature - result in molecules possessing more kinetic energy so move faster and collide with membrane more frequently
7
Q
What is the equation for the rate of diffusion
A
- surface area x difference in concentration / length of diffusion path
8
Q
Describe faciliated diffusion
A
- polar molecules such as glucose cannot pass through cell membrane becaue they are relativley insoluble in lipids
- it i likely simple diffusion is a passive process not require ATP
- rely on kinetic energy of molecules involved
- relies on tranport proteins found within membrane assist movement of polar molecules across membrane
- affected by same factors of diffusion with on addition
- ultimatley rate will be determined by number and availbility of transport proteins
9
Q
What are transport proteins
A
- channel proteins consist of pores with hydrophollic lining allowing charged ions and polar molecules to pass through they are specific and open and close to regulate movement of particular molecules
- carrier prtoeins allow diffusion across membrane of large polar molecules such as sugars and amino acids
10
Q
What is active transport
A
- requires energy in form of ATP
- transport molecule against concentration gradient
- anything affect respiratory process affect active tranport eg cyanide respiratory inhibitor prevent aerobic respiration and production of ATP
- abcese of ATP active transport cannot occur
- utliles carrier proteins span the membrane therefore maximum rate ultimatley limited by number and availiabiity of transport protein change shape to transport molecule across membrane
11
Q
How do respiratory inhibitors affect active transport
A
- graph shows maximum rate or transport can still be reached when carrier proteins are saturated ]rate of uptake reduced wth addition of repiratory inhibitor
- active transport requires ATP
12
Q
What is Co transport
A
- transport two different molecules together
- eg sodium ions and glucose
- mechanism which glucose aborobed in ileum of mammals
- sodium ions are activley transported out of epithelium cells lining the ileum into blood creating low concentration of sodium ions within cells
- higher concentration of sodium ions in lumen of gut compared to epithelial cells causes sodium ions to diffues into epitthelial cells via co transport of proteins, As they do so they couple with glucose molecules carrying with them
- finally glucose molecule pass via failitated diffusion into blood capillaries and sodium ions by active trnasport
13
Q
Describe osmosis
A
- most cell membranes are permeable to water and certain solutes only
- higher concentration of water molecules move about freely
- solute such as glucose is dissolved there are proportionally fewer water molecules move about less freely
- adding a olute lowers potential for water molecules to move lowering the water potential making it more negative
14
Q
What is the water potential is pure water a typical cell and a strong glucose solution
A
- pure water 0 kpa
- typical cell is - 200 kpa
- strong glucose solution is around - 1000kpa
15
Q
Describe osmosis in plant cells
A
- when water enters cell by osmosis the vacuole expands pushing cytoplam against the cell wall
- cell wall can only expand a little so creates a resistance to more water entering a plant cell by osmosis known as pressure potential
- the cell is said to be turgid
- water potential = solute potential + pressure potential
- if cell placed into a solution that is hyoptonic to the cell water flows into the cell because the solution has a higher water potential
- if cell places into a hypertonic solution to the cell water flows out of the cell as solution has a lower water potential than the cell
- if it has the asame water potential as the solution internal and external are isotonic so no net movement of water in or out of the cell
