12.7 Transport across membranes Flashcards
What are phospholipids similar in structure to?
Triglycerides
What is the difference between phospholipids and triglycerides?
One of the fatty acid groups is replaced with a phosphate group
The glycerol combines with two fatty acids, instead of two
Which way do the hydrophobic fatty acid tails point?
Towards the middle, away from the water
Which way do the hydrophilic heads point?
Towards the outside of the cell, towards the water
They make contact with the cytoplasm and extracellular fluid
How would you describe the cell surface membrane?
Semi permeable
What does the cell surface contain?
Proteins, glycoproteins, phospholipids, cholesterol and carbohydrates
Why is it called a fluid structure?
The phospholipid bilayer is constantly moving
Why is it called a mosaic structure?
The protein molecules are unevenly distributed throughout the membrane
Function of phospholipids
Bilayer allows lipid soluble molecules to pass through via simple diffusion but prevents small polar molecules (ions) and larger molecules (glucose)
Function of cholesterol
Decreases permeability, increases stability of membrane
More cholesterol = less fluidity
Embedded in bilayer
Function of channel proteins
Only allow specific charged ions across the membrane via facilitated diffusion
Proteins have specific tertiary structure and can only transport molecules with complimentary shape to channel protein
Eg. Na+ ions can only pass through sodium channel protein
Function of carrier proteins
Aid the transport of ions, polar and large molecules by facilitated diffusion and active transport
Function of receptor proteins
Act as receptors to complementary molecules
Eg hormones such as insulin bin do the insulin receptor protein which increases the cells permeability to glucose
Function of enzymes
Shape of active site is complimentary to substrate, allowing them to form enzyme-substrate complexes
Embedded within cell membrane
Function of glycoproteins
Composed of carbohydrates and protein
On the outer surface of cell membrane and important in cell recognition
Produced in the Golgi body
Function of aquaporins
Special type of channel proteins specific to water
A cell with many aquaporins will be permeable to water and carry out osmosis easily
Diffusion definition
The net movement of molecules from an area of higher concentration to an area of lower concentration across a partially permeable membrane
What type of molecules move via simple diffusion?
Non polar
Small
Lipid soluble molecules
O2, CO2 and oestrogen
What is Ficks law?
Rate of diffusion = surface area x concentration gradient / diffusion distance
Factors that increase diffusion
Higher surface area
Higher concentration gradient
Higher diffusion pathway
Higher temperature
what molecules can move via facilitated diffusion?
Specific molecules to the complementary binding site as facilitated diffusion is facilitated via channel and carrier proteins
Is facilitated diffusion active or passive?
Passive
It does not require ATP
What does the curve of facilitated diffusion look like?
It plateaus when all the carrier protein binding sites are saturated
The number of carrier proteins becomes the limiting factor
Osmosis definition
The net movement of water molecules from an area of higher water potential to an area of lower water potential across a partially permeable membrane
What liquid has the highest water potential
Pure water
When does the water potential of a liquid change?
When more solute is added, the water potential becomes more negative
What does more solute mean in terms of water potential?
More solute
More negative water potential
Less free water molecules to push on membrane so water moves in
Active transport definition
Used to transport molecules across a membrane from a lower concentration to a higher concentration via carrier proteins and the use of ATP
How does active transport work?
The molecule for transport binds to the carrier protein binding site
The hydrolysis of ATP from ADP + Pi provides a small amount of energy for the carrier protein
This causes a conformational change
This change in protein shape transports the molecule across the membrane into an area of higher concentration
Two types of active transport
Endocytosis
Exocytosis
Endocytosis definition
Molecules are bulk transported into the cell via the cell surface membrane
Exocytosis defintion
Molecules are transported to the outside of the cell via the cell surface membrane
Describe the process of exo/endocytosis
The cell surface membrane is pulled inside or pushed outside to create a vesicle
Any molecules next to that part off the cell membrane are pulled into the vesicle
This process requires ATP
Describe how substances move across a cell surface membrane
- Small/non polar/lipid soluble molecules pass via the phospholipid bilayer
- via simple or facilitated diffusion from high to low concentration down the concentration gradient
- Water moves via aquaporins by osmosis from higher to lower water potential
- Active transport is movement from low to high concentration by facilitated diffusion by carrier proteins
- Active transport requires ATP
