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 do?

• 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

what parts of the phospholipid is hydrophobic and which is hydrophilic?

• fatty acids are hydrophobic

• phosphate group is hydrophilic

what is the structure of a phospholipid?

phosphate group on the outside and fatty acid group on inside

what is function of cell-membrane function?

• barrier

• location for chemical reaction

• cell signalling 

what can pass through the phospholipid bilayer? And why?

cell-surface membrane contains hydrophobic centre, hydrophobic molecules such as steroid hormones can easily pass through the cell membrane

what can’t pass through the phospholipid bilayer? And why?

hydrophobic centre prevents hydrophilic water-soluble molecules from easily passing through. Because hydrophilic is polar so can’t easily pass through non-polar region of the membrane

what is an anomaly to the rules of whether something can pass a phospholipid bilayer?

water can pass even though it polar because its really small but happens at a slow rate

what are the two parts in cholesterol and what do they attract?

• polar hydrophilic group (OH-) at the end of this group attracts polar head of phospholipid molecules

• hydrophobic part can attract the non-polar fatty acids in phospholipids

What is point of having cholesterol in our cell surface membrane?

• increased strength

• makes cell more stable

• less likely to damage

• reduces sideways movement of phospholipids and other molecules

• controls fluidity as prevents too fluid at hot temp and too rigid at cool temp

• packs space between phospholipid, reducing movement of water soluble chemicals across the cell membrane

what are the features of intrinsic proteins?

• fully embedded in the membrane from one side to the other

• pass right through the lipid bilayer so has hydrophobic amino acids on the outside surface of the protein

• hydrophobic amino acids interact with hydrophobic fatty acid tails in phospholipid bilayer

what are two types of intrinsic proteins?

• protein channel

• carrier proteins

what are features of protein channel?

• lined with hydrophilic amino acids and filled with water molecules

• allows water soluble molecules and ions to diffuse through

what are features of carrier proteins?

• changes shape to transfer molecules or ions from one side of membrane to the other

how does active transport work?

• molecule that is going to be transported attaches to the receptor site on carrier protein, on lower concentration side

• molecule of ATP then binds to carrier protein

• ATP undergoes hydrolysis into phosphate and ADP
  phosphate attaches to the carrier protein and causes it to change shape

• shape change causes carrier protein to transport molecules onto other side of membrane where it Is released

• phosphate leaves, carrier protein returns to previous shape

• ADP and Phosphate returns to ATP during respiration

what’s osmosis?

net movement of water molecules from a more dilute solution to a more concentrated solution through a partially permeable membrane

what is water potential?

• pressure exerted by water molecules as they collide with a membrane or container 

• measured in kPa with water being 0kPa the highest

what does isotonic mean?

same concentration as cell cytoplasm

what does hypotonic mean?

lower concentration than cell cytoplasm

what does hypertonic?

higher concentration than cell cytoplasm

Explain what happens when animal cell e.g. red blood cell is in a hypertonic solution?

• water potential lower outside the cell

• water does out of the cell

• cell shrivels

• CRENATION

Explain what happens when animal cell e.g. red blood cell is in an isotonic solution?

• water potential inside and outside the cell is equal

• no net movement of water

• equilibrium

Explain what happens when animal cell e.g. red blood cell is in a hypertonic solution?

• water potential higher outside the cell

• water moves into the cell

• cell bursts

• LYSIS

Explain what happens when a plant cell e.g. palisade cells is in a hypertonic solution?

• water potential lower outside the cell

• water moves out the cell

• cell becomes PLASMOLYSED

• cytoplasm pulls away from the cell wall

Explain what happens when plant cells e.g. palisade cells in a isotonic solution?

• water potential inside and outside the cell is equal

• no net movement of water

• equilibrium

Explain what happens when plant cells e.g. palisade cells in a hypotonic solution?

• water potential is higher outside the cell

• water moves into the cell

• cell is turgid

how would you describe a plant cell e.g. palisade cell when it’s between the isotonic and hypertonic solution?

flaccid