Chapter 5 ~ Plasma Membrane Flashcards
What is the role of cell membranes?
It provides a partially permeable membrane
Cell communication/cell signalling
Site of chemical reaction
What is a cell membrane formed of?
Describe the formation of answer to q1?
It is formed of a phospholipid bilayer
It contains hydrophilic phosphate heads on the outside which attract water and hydrophobic fatty acid tails on the inside which repel water
Describe the fluid mosaic model
The phospholipids are free to move within the layers and proteins are embedded within the bilayer which vary in size and shape.
it describes the free movement of phospholipids and proteins and the random arrangement of proteins.
it is fluid as the phospholipids are constantly moving around and mosaic as they are scattered throughout the phospholipid like tiles in a mosaic.
What are the two types of proteins?
Intrinsic and extrinsic
Describe extrinsic proteins include 2 examples.
Extrinsic proteins are present on one side of the bile layer. They contain hydrophilic groups on the outer surface which interact with polar heads of phospholipids/intrinsic proteins. They provide mechanical support.
Glycolipids and glycoproteins are examples which are used in cell recognition/cell signalling
they usually function as enzymes and catalyse chemical reactions occurring inside the cell.
Describe intrinsic proteins
Present in both layers.
There are carrier proteins which have tubes filled with water which enables water soluble ions to diffuse
There are proteins which bind with other ions and large molecules and change shape to transport them
they act as channel or carrier proteins to transport water soluble molecules.
Describe the function of cholesterol
It is to regulate fluidity
What factors affect membrane structure?
Temperature and solvent
Describe how high temperature affects membrane structure
High temperature increases the kinetic energy of the phospholipid which causes them to move more. This increases fluidity and increases permeability which causes the structure to begin to break. This makes it easier for particles to cross.
Describe how solvent affect membrane permeability
Organic solvent, for example, alcohol (ethanol) dissolve within the phospholipid bile layer which causes fluidity to increase, which makes it more permeable
What is simple diffusion?
When particles move from the area of high concentration to an area of low concentration down the concentration gradient
they pass directly through the phospholipid bilayer.
what does the rate of diffusion depend on
- Concentration Gradient -
steeper gradient, faster rate - Thickness of exchange surface -
thicker, longer diffusion distance - Surface area-
larger surface area, more diffusion distance
What is facilitated diffusion?
This is diffusion across a membrane through protein channels and carrier proteins
what molecules cannot pass using simple diffusion and have to use facilitated diffusion
large polar molecules
ions
how do channel and carrier proteins work
channel proteins are gated and open and close to allow molecules to diffuse through
carrier proteins change shape to allow molecules to pass through
What is active transport?
This is the movement of molecules/ions into and out of cells from a lower concentration to a higher concentration against the concentration gradient. This uses energy in the form of ATP and carrier proteins..
It is a selective process as only certain molecules combine into the receptor site
Explain the process of active transport
1.active transport by protein
2.it is hydrolyse into ADP and PI
3. this causes protein to change, shape and open inwards inside of the membrane
4. This causes molecules to be released on other side of the membrane.
5. PI molecules release, which results in protein reverting into original shape
What type of transport is endocytosis
How many types of endocytosis is there?
Endocytosis is a type of bulk transport into the cell.
2 types of endocytosis-
There is phagocytosis, which occurs with solids and pinocytosis, which occurs with liquids
Explain the process of endocytosis
Why does it require energy
- Cell surface membrane bends inwards
- This forms a vesicle
3.vesicle pinches off and moves within the cytoplasm to transfer material
It requires energy to engulf and change shape
What is exocytosis?
Movement out of cell
Describe the process of exocytosis
Why does this process require energy?
- Vesicle moves towards cell surface membrane.
- Vesicle fuses with the membrane.
- Contents are released outside of cell.
Requires energy to move vesicle along cytoskeleton
What is osmosis?
It is water particles, moving from higher water potential to a lower water potential
What is water potential?
It is the pressure exerted by water molecules as they collide with a membrane or container it is measured in pascals
What is a water potential of water?
0 Kpa
What is isotonic solution?
Water potential is the same in solution and the cell
What is hypotonic solution?
Water potential in the solution is more positive than cell
What is hypertonic solution?
Water potential in the solution is more negative than cell
what are the components of the plasma membrane
- phospholipids
- glycoproteins
- glycolipids
- cholestrol
- intrinsic and extrinsic proteins
glycoproteins
these are proteins with a sugar molecule attached. they act as recognition sites and antigens.
glycolipids
phospholipids with a sugar molecule attached, they also act as recognition sites and antigens (similar to glycoproteins). they increase membrane stability by forming HYDROGEN bonds with water molecules.
cholesterol
regulates and maintains stability and fluidity of plasma membrane.
