IB Biology B2.1 Membranes and Membrane Transport HL

What is the function of cell membranes? [3]

Cell membranes...

-form a barrier between a cell and its environment

-is important because it controls what can enter or exit

-there are also membranes present inside a eukaryotic cell that divides the cytoplasm into compartments

What are all cell membranes made up of?

Phsopholipids and other amphipathic lipids which form BILAYERS

Hydrophobic hydrocarbon chains that form the core of a membrane have ___ ____ to:

LOW PERMEABILITY (nothing can go through):

1. large molecules

2. hydrophilic particles, including ions and polar molecules

What are the 4 main types of cell transport: (label passive or active)

1. Simple Diffusion PASSIVE

2. Osmosis PASSIVE

3. Facilitated Diffusion PASSIVE

4. Active Transport

Define Simple Diffusion [5]

- the spreading out of particles in liquid and gases that happens because the particles are in continuous rapid motion.

- more particles move from an area of higher CONCENTRATIONS to an area of lower concentration

-DOWN the concentration gradient

-Requires no energy, passive

-Oxygen and carbon dioxide molecules are both small and non-polar and can easily move through the membrane down the concentration gradient

Define two types of proteins found in/on cell membranes [3] [2]

Integral Proteins:

- Embedded in one or both of the lipid layer membranes

-Hydrophobic region which is embedded in the hydrocarbon chains

-Many are transmembrane proteins which extend across the membrane with hydrophilic regions on each side

Peripheral Proteins:

- Are attached to either the inside or outside surface of bilayer

-hydrophilic surface

Define Osmosis [4]

- net movement of water across a semi-permeable membrane from an area of low SOLUTE concentration to an area of high solute concentration.

-Passive process because no energy needed

-Despite water molecules being polar they can still move because they're so small

-Some cells have integral proteins called AQUAPORINS that have a channel that water can pass through

Why does Osmosis occur [3]?

1. Particles are randomly moving

and if...

2. The membrane is impermeable due to solutes

3. There is a difference in solute concentration

Define Facilitated Diffusion [4]

- movement of molecules from HIGH to LOW CONCENTRATION through CHANNEL PROTEINS

-Particles can pass in either direction, but MORE pass from high to low

-Passive process

-structure of some channel proteins make membranes selectively permeable by allowing specific ions to diffuse when open

Define Active Transport [4]

-protein pumps use adenosine triphosphate (ATP) energy to transfer specific particles across membranes

-AGAINST concentration gradient

-Pumps move in one direction, particles can move in either through channel

Pumps have 2 conformations:

1. Particle can enter pump, then pump shifts to allow particle to pass out other side

2.After particle moves out the pump shifts back to original form

Facilitated diffusion and active transport allow _____ in membranes, elaborate with simple

SELECTIVE PERMEABLILITY, simple diffusion permeability is NOT selective and depends on properties of particles

Compare and contrast 4 types of cell transport (chart)

-Along or against

-Directly through phospholipid bilayer

-Through membrane proteins

-ATP needed or not

Compare and contrast glycoproteins and glycolipids

(3)

Glycoproteins

-Carbohydrate + protein

-cell-to-cell recognition

Glycolipids

-Carbohydrate + lipid

-immune system distinguish between self and non-self cells

BOTH the protein and lipid is embedded in the hydrophobic interior of the plasma membrane and the carbohydrate projects outwards

What is glycocalyx?

Glycoproteins and glycolipids together forming a carbohydrate-rich layer on face of plasma membrane. Glycocalyx of adjacent celfls can fuse binding called cell adhesion

Drawing Skill: Draw a two-dimensional representation of a fluid mosaic model of a cell membrane

refer to notes

What is the fluid mosaic model?

Representation of cell membrane where phsopholipid molecules and proteins move laterally, proteins are embedded

What benefits do saturated fatty acids have in membranes?

Straight chains and therefore pack together tightly in the bilayers REDUCING fluidity and permeability by simple diffusion. Higher melting points and membranes are stronger at higher temperatures. WARM

What benefits do unsaturated fatty acids have in membranes?

More bends in chains so packed loosely making membranes more fluid, flexible, and permeable. LOWER melting points and flexible at temperatures experienced by cell COLD

How does a cell membrane reach ideal fluidity ratio? [2]

1. Relative amounts of saturated and unsaturated fatty acids are regulated so they have required properties FLUID but STRONG

2. Ideal ration depends on temperature that cell experiences. COLD environment animals have more unsaturated acids because they need fluidity and ability to function in the cell membrane, and a membrane with lower melting point allows that.

What is cholesterol? What properties does it have?

A type of steriod/lipid. Cholesterol has AMPHIPATHIC properties meaning its both hydrophobic and hydrophillic.

Where is cholesterol attached in the cell membrane?

Cholesterol is mostly hydrophobic, and is attached to the hydrophobic carbon tails in the center. The hydrophillic head is attracted to the phosophate heads. It aligns in the membrane between.

How does cholesterol act as a modulator?

1. Sticks to hydrocarbon tails stabilizing their shape

2. At low temps prevents stiffening and crystallization because it breaks bilayer up.

What is a vesicle? Properties?

small sac of membrane with a droplet of fluid inside. Vesicles are dynamic and are constantly being made and unmade to TRANSPORT contents in cell.

To form a vesicle....

ATP energy is needed to pinch off small regions of membrane

Define endocytosis [3] EXAMPLES [3]

When a vesicle is made from the plasma membrane by pinching INWARDS. Vesicle has material from outside of the cell and brings in materials that are TOO BIG to pass through proteins

Examples:

1. Placental proteins from blood including antibodies are absorbed

2. Unicellular organisms take in large food particles

3. White blood cells take in pathogens

Define exocytosis [3] EXAMPLES [2]

When a vesicle is made from the plasma membrane by pinching OUTWARDS. Vesicle contains material that was inside of the cell.

Examples:

1. Unicellular organisms excel excess water by loading water into a contractile vacuole

2. Polypeptides like enzymes are processed in the golgi apparatus (synthesis) for explusion

What are two types of Ion channels?

Voltage-Gated:

- sodium and potassium channels in neurons

Neurotransmitter Gated:

- syapses are gaps and acetylocholine binds to receptors

What are ion channels?

Channels that allow specific ions to pass across a membrane through FACILITATED DIFFUSION along the gradient. Open and close switch on and off

What is a sodium-potassium pump? [3]

- active transport using ATP

-three sodium ions get pumped out while two potassium ions are pumped in

-exchange transporter and transports different ions in opposite directions

SALTY BANANA

What is a sodium-glucose transporter?

Channel that transfers a sodium ion and a glucose molecule together across a plasma membrane

- Glucose works AGAINST its concentration gradient

-ATP energy needed

-Sodium ions go out of the cell while potassium ions come in SODIUM POTASSIUM PUMP

-By removing sodium the gradient is maintained and can continue

Therefore, sodium-dependent glucose cotransport is....

INDIRECT form of active transport

What are CAMs?

Cell-adhesion molecules are typicalaly proteins that are partially embedded in the plasma membrane allowing non-embedded portion to bind to CAMs on neighboring cells . (linking)

Why is cell adhesion important?

Maintains the structure of tissues and organs and is needed for functional relationships between cells DIFFERENT FORMS OF CAMS