2.5 plasma membranes

what are the features of intrinsic proteins?

• fully embedded in membrane from one side to the other

• hydrophobic amino acids on the surface of the protein which interact with hydrophobic fatty acids tails in the phospholipid bilayer

what are the two examples of intrinsic proteins?

• protein channels

• carrier proteins

how does a protein channel work?

channel running through the centre lined with hydrophobic amino acids and is filled with water molecules so allows water soluble molecules  and ions to diffuse through

how does a carrier protein work?

can change shape or position to transfer molecules/ions from one side of membrane to the other

what are the features of extrinsic proteins?

• found on one side of the membrane or the other

• sometimes attached to intrinsic proteins

• many roles eg structural or as enzymes or receptors for molecules such as hormones

what are glycoproteins? eg?

proteins that also contain a carbohydrate molecule attached

allow cells to attach to each other to form tissues such as nervous tissues or role in immune system, receptors for hormones

wat are glycolipids? eg?

carbohydrates found attached to phospholipids molecules

when cells become in contact with each other, glycolipids of one cell can be recognised by another cell, determining whether they come in contact, or as antigens

what are the features of the cell surface membrane/ plasma membrane?

• partially permeable membrane between a cell and its environment

• controls what enters and leaves the cell

• site of some chemical reactions

• site of cell communication (cell signalling) eg synapses, immune system, hormones

what does it mean for a cell to have a partially permeable membrane?

only some substances can pass through

what does compartmentalisation mean?

membranes keep the inside of organelles separate from the cytoplasm

what does cell signalling mean?

communication between cells and cell recognition. A molecule released by one cell, attaches to another and causes a response

what are features of the phospholipid bilayer?

• provides a barrier to large polar molecules

• fat, soluble substances or very small molecules can pass straight through the membrane (eg steroids,H2O, fats, cholesterol and soluble vitamins A,E,K,D)

• hydrophilic, phosphate head, polar enabling them to interact with H2O and form weak hydrogen bonds

• hydrophobic, fatty acids tails non- polar and so do not interact with water as it is repelled

what does cholesterol do?

• stabilises the membrane

• regulates the fluidity by binding to the phospholipids

• reduces permeability to charged particles

what do glycoproteins and glycolipids?

• stabilises the membrane by forming H bonds with surrounding molecules

• receptors for messenger molecules in cell signalling, drugs, hormones and antibodies

• antigen for self recognition and the immune system

what is diffusion?

net movement of atoms/molecules from an area of high concentration to an area of low concentration

passive process

what is simple diffusion?

• particles pass through directly through the phospholipid bilayer

• membrane must be permeable to the particles eg particles must be non-polar, small, lipid soluble

• eg oxygen entering RBC

what is facilitated diffusion?

• large or polar/charged molecules pass through the cell surface membrane with the aid of a protein

• proteins are specific to the molecule that they carry

• passive process

what are the two facilitated diffusion?

• protein channel

• carrier protein

what are the features of a protein channel?

• ions/ small molecules

• acts like a pore in the membrane

• often can be opened and closed to change the flow

what are the features of a carrier protein?

• transports larger molecules

• molecules are attached to the protein and it changes shape (conformational) to transfer the molecule across the membrane

what increases the rate of diffusion?

• greater concentration gradient

• increase in temperature

• increase in surface area

• thinner membrane

what are the two ways of calculating the rate of diffusion?

• distance travelled/time (not affected by changes in surface area)

• volume filled / time (varies depending on surface area)

what are the features of active transport?

• movement against a concentration gradient (low to high)

• uses a carrier protein and ATP energy

• each carrier protein is specific

e.g. mineral ions moving into a root hair cell sodium potassium pump

what is endocytosis?

• entering a cell

• large molecules entering using ATP

e.g. photosynthesis

what is exocytosis?

• exiting a cell

• large molecules exiting using ATP

e.g. digestive enzymes