Lecture 3

Question 1

What is the effect of high temperatures on membrane fluidity? How do cells adapt to this?

Answer 1

Membranes become more fluid because they have more kinetic energy. The gap between phospholipids increase meaning the permeability does too. Cells adapt to this by increasing the hydrocarbon tail length to increase hydrophobicity. Decrease the number of double C bonds and increase cholesterol content which increase hydrophobicity and acts as a pylon.

Question 2

What is the cell membrane made up of?

Answer 2

The cell membrane is made up of a a phospholipid bilayer

Question 3

What is cholesterol? Why is it important?

Answer 3

Cholesterol is in the cell membrane and can help control membrane fluidity by packing phospholipids closer together or forcing them farther apart

Question 4

How do low temperatures effect fluidity? How do cells adapt to this?

Answer 4

The permeability and flexibility of the membrane decreases. The space between phospholipids decreases which is the reason for lowered permeability. Cells adapt to this by increasing the double bonds of C, decreasing the length of HC tails to decrease hydrophobicity and again use cholesterol. This time it is in between the phospholipids to increase the distance. It is like a spacer.

Question 5

How are proteins associated with the bilayer?

Answer 5

There are 2 types of proteins associated with the bilayer. Integral proteins witch are imbedded in the bilayer and peripheral proteins which are in the cell and are connected to the integral proteins. The nonpolar (hydrophobic) a.a in the proteins surround the parts of the proteins that are touching the hydrophobic core of the phospholipid membrane as well as at the connection between the 2 types of protein and in the center of the protein. The polar (hydrophilic) a.a are everywhere else

Question 6

How do things transport across the membrane?

Answer 6

Small uncharged things are permeable, meaning they can diffuse through the membrane. Things that are too big or are too polar cannot diffuse across a membrane.

Question 7

What are things too big to diffuse across a membrane?

Answer 7

Ions are the least permeable, protons are too big because they have a hydration shell. Glucose is to big to pass through without active transport.

Question 8

What are things that can diffuse across a membrane?

Answer 8

Oxygen can diffuse across a membrane by passive diffusion and water can cross with osmosis. Gases are very permeable. Cholesterol is nonpolar so it can cross with passive diffusion

Question 9

What is facilitated diffusion?

Answer 9

Things that are too impermeable to diffuse across the bilayer themselves can use facilitated diffusion. This doesn’t require energy because we are moving down the concentration gradient.

Question 10

What are the 2 types of facilitated diffusion?

Answer 10

A channel protein: this is an integral membrane protein that allows transport of a solute without changing shape. Its like a tunnel. Carrier protein: Spans the bilayer and allows a specific solute to pass but does change shape. Its like a revolving door

Question 11

What is active transport? Why is it used?

Answer 11

Active transport requires energy because the solute is moving up the concentration gradient. It is used to concentrate nutrients in the cell, expel waste and to maintain a voltage or a concentration gradient

Question 12

What is an example of active transport? How does it work?

Answer 12

Sodium/Potassium pump is used in all cells all the time and is an example of cotransport. It is electrogenic meaning it generates voltage across a membrane. 3 sodium come in and 2 potassium’s come out

Question 13

What is SOPI PONI?

Answer 13

Sodium Out Potassium In Potassium Out Sodium In

Question 14

What is cotransport?

Answer 14

The transport of 2 molecules simultaneously

Question 15

What is coupled transport?

Answer 15

Using the energy generated from one gradient to establish another gradient

Question 16

What happens in a hypotonic environment?

Answer 16

The cell is too full of water and so it swells, in animal cells this could lead to bursting which is called osmotic lysis

Question 17

What happens to plant cells in a hypotonic environment?

Answer 17

The cell wall prevents the cell from bursting

Question 18

What happens in a hypertonic environment?

Answer 18

Water rushes out of the cell which can shrink the cell, shrivel it up

Question 19

What happens to plant cells in a hypertonic environment?

Answer 19

Plasmolysis: the membrane pulls away from the cell wall

Question 20

What is bulk transport?

Answer 20

When molecules are too big for transport proteins they must go through bulk transport which involves the formation of vesicles

Question 21

What is exocytosis?

Answer 21

A molecule too big for a transport membrane needs to leave the cell. A vesicle transports this molecule to the plasma membrane an then fuses with the plasma membrane. After it fuses it can just “open” the vesicle to the outside and release the molecule

Question 22

What is endocytosis?

Answer 22

A molecule too big for transport proteins needs to come into the cell. A vesicle fuses with the plasma membrane and accepts this molecule, it then goes back into the cell.

Question 23

What is RME (Receptor-mediated endocytosis)?

Answer 23

A type of endocytosis. A receptor outside the membrane tells the cell to come get a certain molecule, only this molecule come into the cell

Question 24

What is phagocytosis?

Answer 24

This is unspecific endocytosis, everything outside the cell can come into the vesicle and into the cell

Question 25

How do unsaturated fats effect membrane fluidity?

Answer 25

Unsaturated can help maintain membrane fluidity as the kinks in their tails prevent compression