Bio101 B1 Lecture 3&4

Front 1

What is the fluid mosaic?

Back 1

The membrane described as a mosaic of protein molecules floating in a phosphlipid bilayer.

Front 2

The integral proteins in the plasma membrane are amphipathic, what does this mean?

Back 2

It has both hydrophobic (the middle, where the protein is in the plasma membrane) and hydrophilic parts (top and bottom of the protein that are in the intra/extracellular portion).

Front 3

How is the fluidity in the cell membrane created?

Back 3

The lateral movement of the phosphlipids causes the fluidity of the membrane.

Front 4

Compare the fluidity of saturated and unsaturated hydrocarbon tails.

Back 4

Unsaturated hydrocarbon tails create space between the tails, increasing fluidity, more fluid than saturated hydrocarbon tails.

In cold temperatures, saturated tails will solidify as they are close together while unsaturated dont as they retain fluidity.

Front 5

Why is cholesterol referred to as a fluidity buffer?

Back 5

It decreases fluidity (in moderate temperatures by pushing the phospholipids closer to each other), however at very low temperatures, the cholesterol stop the tails from interacting with each other, preventing them from solidifying, maintaining fluidity.

Front 6

What proved that membrane proteins moved?

Back 6

Fusion of human cells and mouse cells, they had mixed proteins in the end.

Front 7

What are gap junctions equivalents in plants?

Back 7

plasmodesmata, a cell junction in plant cells that connects plants cells together. They allow movements of molecules between cytoplasm of one cell to another neighbouring one.

Front 8

What is passive membrane transport?

Back 8

- Molecules move passively from high to low concentration.

- no energy required (spontaneous)

Front 9

How can molecules pass through the membrane through diffusion?

Back 9

must be small non polar (O2) or small uncharged polar (CO2) to pass through by differentiation.

Front 10

How are hydrophilic molecules passed through the membrane?

Back 10

Through facilitated diffusion. Transport proteins help hydrophilic molecules move through the plasma membrane.

Front 11

What are the two models of facilitated diffusion?

Back 11

Channel protein (molecules go down a channel)

Carrier protein (molecules carried by pac man thingy)

Front 12

Active membrane transport>

Back 12

molecules move against the concentration gradient.

requires energy from ATP

all carrier proteins

Front 13

Explain the steps of Na/K pump.

Back 13

1.Na+ comes in binding to the carrier protein.

2. ATP phosphorylates the protein causing the protein to change shape, releasing the Na+ ions to outside.

3. Protein has high affinity for K+ ions and they bind to the protein and phosphate detaches and becomes inorganic phosphate.

4. Protein changes shape releases K+ into the cell and has high affinity for Na+ again.

Front 14

How are large molecules transported accross the cell membrane.

Back 14

Exocytosis (out of the cell)''

Endocytosis - phagocytosis (cell eating)

- pinocytosis (cell drinking)

Front 15

Where are alpha helix structures often found?

Back 15

In transmembrane proteins that cross the lipid bilayer.

Front 16

What are the 5 different bonds in tertiary structure?

Back 16

disulfide bridge

hydrogen bond

hydrophobic interactions

van der waals interactions (non polar)

ionic bond

Front 17

What are chaperonins?

Back 17

Things that assist with the folding of protein, it is made of a hollow cylinder and cap.

- protects polypeptide from degradation

- polypeptides fold spontaneously into proteins.

Front 18

How do chaperonins work?

Back 18

1. polypeptide comes in the cylinder.

2. cap comes on and changes the shape, creating a hydrophilic environment for folding of the polypeptide.

3. cap comes off, folded protein released.

Front 19

What can cause the denaturation of a protein?

Back 19

Heat

PH - change ionisation patterns of R groups

Reducing agents - reduce S=S bonds to S-H

Organic solvents - disturb hydrophobic and hydrophilic interactions

Detergents - disrupt hydrophobic interactions.

Front 20

Can a denatured protein be renatured again?

Back 20

yes if the denaturing agent is removed.