Cell Surface Membrane Flashcards
How thick is the cell surface membrane
7-9Nm
Phospholipid bilayer
Arrangement of phospholipids found in cell membrane, the hydrophilic phosphate heads form both the inner and outer surface of a membrane
Hydrophilic head
Water loving, polar
Faces inwards and outwards from the cell
Hydrophobic tail
Water hating
Faces the opposite way to the heads
2 fatty acids
What does the cell surface membrane consist of
Lipids, proteins, and carbohydrates
Function of the cell surface membrane
- Partially permeable barrier between the cell and its outside environment
- controls which substances enter + leaves the cell
- membranes allow recognition by other cells
- cell signalling
- site of chemical reactions
What are intrinsic proteins
Proteins embedded within the membrane
Channel proteins, carrier proteins, glycoprotein
Another name for Extrinsic protein
Peripheral proteins
Channel protein
Provides a hydrophilic channel that allows passive movement of polar molecules down a concentration gradient.
Held in position by interactions between the hydrophobic core of the membrane and the hydrophobic R-groups on the outside of the proteins
role of Carrier protein
intrinsic protein used in both passive and active transport
Used to transport large molecules
Function on a glycolipid
lipids with attached carbohydrate chains
Act as cell markers or antigens, can be recognised by the immune system as ‘self’ or ‘non self’
Extrinsic proteins
Extrinsic proteins serve in transport of molecules and as receptors
Are found outside the cell surface membrane involved in: cell signalling, cell recognition, act as receptors for other molecules
Function of phospholipids
Controls which substances enter and leave the cell.
Site of communication with other cells
Separates cell from surroundings
Function of cholesterol
Regulates the fluidity of membranes. Adds stability to membrane without making them too rigid.
Has a hydrophilic and a hydrophobic end allowing them to pull phospholipids together
Function of receptor sites
Cape able of recognising and bonding to specific molecules
Functions of enzymes and co-enzymes
Oxidation of fatty acids. Reactions take pax’s in membranes therefore enzymes are essential
Name all the components of the cell surface membrane
Phospholipid bilayer, hydrophilic head, hydrophobic tail, intrinsic protein, extrinsic protein, channel proteins, carrier protein, receptor/glycoproteins
What effect does high temp have on membranes
Phospholipids move/ vibrate more as they have more KE
increases gaps in membrane/ between the phospholipids
Bilayer becomes more fluid and melts
Proteins/ glycoproteins denature
3 roles of membranes inside cells
Separate organelles from their outside environment
Attachment for enzymes
Creation of organelle gradients
Functions of glycoproteins
are intrinsic proteins embedded in the cell surface membrane with attached carbohydrates of varying length
act as receptors for chemical signals which may cause a cascade of reactions inside the cell
e.g. neurotransmitters such as acetylcholine
receptors for peptide hormones
Fluid mosaic model
Phospholipids are free to move within the layer relative to each other
Gives membrane flexibility
Membrane must be fluid as proteins that diffuse in vary in shape, size, and position
Effect of solvents on membranes
Water is a polar solvent, hydrophilic/hydrophobic tails and heads face away and towards forming the bilayer
Other organic solvents are less polar than water, they dissolve the membranes
Facilitated diffusion
Diffusion across a membrane through channel proteins is called facilitated diffusion.
Occurs with molecules that cannot pass through the phospholipid bilyaer e.g. large polar molecules and ions
Can also involve carrier proteins which change shape when a specific molecule binds to them
Endocytosis
Bulk transport of material into cells
Phagocytosis for solids
Pinocytosis for liquids
Exocytosis
Reverse of endocytosis
Vesicles move towards and fuse with the cell surface membrane
Contents of the vesicle are then released outside the cell
Active transport
Molecules or ions from an area of lower concentration to a area of higher concentration
Requires energy
Process of active transport
- Molecule or ion to be transported binds to receptors in the channel of the carrier protein on the outside of the cell
- On the inside, ATP binds to the carrier protein and is hydrolysed into ADP and phosphate
- protein changes shape due to the binding of the phosphate molecule to the carrier protein
- molecule or ion is released to the inside of the cell
- phosphate is released and recombines with ADP To form ATP
- Carrier protein resumes shape
Advantages of active transport
Can work against the concentration gradient
Can move large quantities
Can carry specific molecules
What are the properties of molecules that can freely diffuse through the cell membrane
Small, uncharged/non polar, lipid soluble
the roles of membranes within cells and at the surface of cells
partially permeable barriers between the cell and its environment
Barrier between organelles and the cytoplasm and within organelles
• sites of chemical reactions
• sites of cell communication (cell signalling)
What is meant by the term cell signalling
Communication between cells to cooridnate action
E.g cytokines or hormonal response
How can a glycoproteins act as a receptor
Complimentary shape of messenger molecule
Trigger a cascade of reactions inside the cell
glycolipids
antigens
lipids with attach carbohydrate sugar chain
