Cell membrane and movement across it

Describe the cell membrane and what it is made up off

describe of phospholipid

Has a hydrophilic phosphate head and has 2 a hydrophobic fatty acid tails. These form a bilayer when water is around so the hydrophilic phosphate heads are interacting with the water. This acts as a barrier. Different membranes contain different fatty acids. These alter the strength and flexibility of the membrane

what are the different types of protein found in the cell membrane

integral and peripheral

what is an integral protein

These go all the way through the cell membrane and contain a channel

define and explain the role of a peripheral protein on the inner membrane

These sits on the inner membrane and tend to been enzyme. These catalyse reactions and produce products

define and explain the role of a peripheral protein on the outer membrane

These sit on the outer membrane and tend to be receptors. They have a specific binding site which certain hormones or other chemicals bind to. This then triggers a specific biological event or process. This is often used in negative feedback.

what is an peripheral protein

sits on one side doesn’t go all the way through

Receptor proteins

They must be on the outside of the cell membrane and have a specific binding site where hormones and chemicals can bind to form hormone receptors complexes

enzyme proteins

catalyse reactions in the cytoplasm or outside the cell

Recognition Proteins

Proteins involved in recognition have carbohydrates attaches which form an antigen. These are glycoproteins.

Structural Protein

what is the role of structural proteins on the inside and out side

Found mainly on the inside surface membranes and are attaches to cytoskeleton. They help maintain structure and shape and motility. If on the outside then used for cell adhesion

define what simple diffusion (lipid diffusion) over a membrane is

Is the passive net movement of particles down a concentration gradients from an area of high concentration to an area of low concentration resulting in equilibrium on either side of the membrane

what is equilibrium in diffusion

This is where there is the same conc of particles on either side of a membrane. particles are still moving randomly there jus isn’t a net or overall movement.

what molecules can use simple diffusion to get across this membrane

hydrophobic molecules and very small hydrophilic molecules eg CO2 O2 H2O

Facilitated Diffusion

This the passive net movement of particles down a concentration gradients from an area of high concentration to an area of low concentration resulting in equilibrium on either side of the membrane using/ though a transport protein

name the 2 types of protein which are used in facilitated diffusion

channel and carrier proteins

what is a channel protein and how can they control the entry of sunstances

These have a channel down the middle filled with water. This allows charged substances to diffuse across membranes. Most channels can be gated (opened or closed), allowing the cell to control the entry and exit of substances eg ions. In this way cells can change their permeability to certain ions. Ions like Na+, K+, Ca2+ and Cl- diffuse across membranes through specific ion channels

Carrier proteins

These have specific binding sites meaning that they only allow certain specific solute to bind . The substance will bind on the side where it at a high concentration and be released where it is at a low concentration.

what is a cotransport

Sometimes carrier proteins have two binding sites and so carry two molecules at once. For example is the sodium/glucose cotransporter

Osmosis

what is the concentration of water in cells

concentration of water is very high (about 55mol L-1) and it never changes.

what is a hydration shell

A hydration shell is a layer of water molecules that surrounds a dissolved solute (like a salt or protein) in an aqueous solution. These water molecules interact with the solute, forming hydrogen bonds and creating a structured shell around it. 

what is active transport

The active movement of substances from a low conc to a high conc up the concentration gradient using energy

how do carrier proteins use ATP

The protein binds a molecule of the substance to be transported on one side of the membrane, changes shape using energy from ATP splitting, and releases the molecule on the other side.

what is bulk transport and what does it move

This is how cells transport macromolecules such as proteins polysaccharides and even smaller cells. which are to big for other methods of transport.

Is it passive

no its a type of active transport so it requires ATP making it not passive.

what are the 2 types of bulk transport 1. out of a cell 2. into a cell

1. out = exocytosis

2. into = endocytosis

Explain the process of exocytosis

1. proteins in the Golgi undergo modification

2. The proteins bud off in a vesicle from the Golgi and move towards the cell membrane

3. The vesicle then fuse with the cell membrane and the protein is secreted

Explain the process of endocytosis

1. The particle causes the cell membrane folds inwards into a cavity.

2. This process is called invagination.

3. The membrane completely encircles the particles to form vesicles

4. The vesicle moves into the cell

5. If the material in the vesicle is a bacteria it will digested by lysosomes. However if its another material which is useful it can be delivered to different parts of the cell where there need.

what are the 2 different types of endocytosis

Phagocytosis = This is when solid material is taken into cells

Pinocytosis = when fluid eg liquid surrounding a cell is taken in

The effects of concentration difference on simple diffusion

increase in a linearly

The effects of concentration difference on facilitated diffusion

Has a curved relationship as the number of proteins available to facilitate becomes the limiting factor

The effects of concentration difference on active transport

As it doesn’t rely on the gradient there is no difference due to concentration gradient

protein lined poor

specific channel protein which transports polar solutes which through the gap

aquaporins

Can be added or removed to change how much water enter or leaves the cell. Its not a fix set number increases when there dehydrated and when your hydrated there less.

why does leakage from cell membrane increase

1. higher temp

2. higher EK

3. more movement of phospholipid

4. more gaps when they move

5. more diffusion

6. temp continues to increase proteins end up denatured

7. this means there are large gaps where things can rush and diffuse out

define what a hypotonic solution is

A hypotonic solution is a solution that has a lower concentration of solutes and a higher concentration of water compared to another solution or tissue

define what an isotonic solution is

An isotonic solution has the same solute concentration as the cell (no net movement of water).

define what a hypertonic solution is

A hypertonic solution has a higher solute concentration (water leaves the cell).

what effects do these solutions have on cells with no cell wall eg animal cells

hypotonic= as there is more water in the solutions than the cell it moves into the cells by osmosis. This can cause the cell to burst by osmotic lysis.

isotonic= there is no movement conc of water is the same

hypertonic= there is higher conc of water inside the cell than outside in the solution . This causes the water to move out of the cell causing it to shrivel up and make the cytoplasm more concentrated.

what effects do these solutions have on cells with no cell wall eg animal cells

hypotonic= water enters the cell. The cell wall provides a compression force stopping the entry of water. This state is called turgor or turgid and is the most common in plants

isotonic = no movement no change this state is called flaccid

hypertonic= water leaves the cells. The cytoplasm shrinks making the contents more concentrated