Membranes - Module 2 Flashcards
What are the 2 physical functions of cell membranes?
- Separate contents of cells from their environment
- Separate different organelles within cell
Describe the phospholipid bilayer
Hydrophilic heads point out and the hydrophobic tails are in the centre
What is the fluid mosaic model?
The membrane as phospholipids are free to move within each other giving flexibility and proteins embedded differently in size and shape
What are intrinsic proteins?
Proteins that are embedded through both layers of membrane
What is the role of a channel protein?
A hydrophilic channel allowing passive movement of polar molecules down a concentration gradient
What is a carrier protein?
Involved in both passive and active transport into cells and the protein often has to change shape
What is a glycoprotein? And what is its role?
Intrinsic protein with attached carbohydrate chain
Play a role in cell adhesion in tissue formation and cell signalling
What are two specific cell signalling roles of glycoproteins?
- Receptors for acetylcholine at synapses
- Receptors for hormones such as insulin and glucagon
What are glycolipids? And what is their role?
Intrinsic lipids with carbohydrate group attached
Are antigens and are recognised by the immune system
What are extrinsic proteins?
Proteins present in only once size of the bilayer, some may move between layers
What is the role of cholesterol in cell membrane?
Controls the fluidity of the membrane
Why does temperature affect cell membrane? [2]
As the bilayer is always moving, increased temperature means increased kinetic energy so it will move more and become more fluid and it will eventually lose its structure and become permeable
Carrier and channel proteins will be denatured
How do solvents affect the cell membrane?
Organic solvents can dissolve membrane or cause damaged making it more permeable
What is diffusion?
Movement of particles from a region of high concentration to a region of low concentration until an equilibrium is reached (passive process)
What two factors affect the rate of diffusion? And why?
- Temperature - particles have higher kinetic energy and will move faster
- Steep concentration gradient - the greater the difference the faster the diffusion
Why is the membrane described as partially permeable?
Non polar molecules can diffuse freely
Ions cannot pass easily
Polar molecules can diffuse slowly
What affects rate of diffusion across membranes?
- Surface area
- Thickness of membrane
What is diffusion across a membrane using a protein channel called?
Facilitated diffusion
What is active transport?
Movement of molecules or ions from a region of lower concentration to a region of higher concentration
Describe the process of active transport
- Molecules to be transported binds to channel of carrier protein and protein changes shape
- ATP binds to inside of carrier protein and is hydrolysed to ADP + Pi
- Change in shape allows molecule to be released into cell
- ADP + Pi is turned back to ATP
- Carrier protein returns to normal shape
What type of transport if bulk transport? And what does it transport?
Active transport that transports molecules too big to fit through channel/carrier proteins
What is endocytosis?
Bulk transport of materials into cell
What are the two types of endocytosis?
Phagocytosis - for solids
Pinocytosis - for liquids
What is exocytosis?
Movement of contents outside of the cell
What is osmosis?
Movement of water across a partially permeable membrane from a dilute solution to a concentrated solution
If a solution is more concentrated, what will this do to its water potential?
Make it more negative
What is the water potential of pure water?
0kPa
In osmosis, which way does water move, in terms of water potential?
From a low potential to a high potential
What is cytolysis?
Bursting of cell when water moves by osmosis into cell and hydrostatic pressure is too high
What is crenation?
When water leaves a cell by osmosis and it becomes shrivelled and shrunk
What is turgor?
When water enter a plant cell increasing the hydrostatic pressure against cell wall
What does it mean if a plant cell is plasmolysed?
Cell membrane pulls away from cell wall when water is lost by osmosis
