Lecture6

Question 1

What are membranes for prokaryotic & eukaryotic cells?

Answer 1

They are one of the things prokaryotic and eukaryotic cells have in common.

Question 2

What is the function of cell membranes?

Answer 2

The plasma membrane separates the inside and the outside of the cells. They create compartments within the cell->cell membrane, organelles, vacuoles and vesicles.

Question 3

What is the structure of cell membranes?

Answer 3

Lipids, proteins & carbohydrates (glycolipids & glycoproteins). Membranes are composed of phospholipids.

Question 4

Explain cell membranes.

Answer 4

Cell membranes are fluid, which means they can move. Keeping in mind that phospholipids form cell membranes. These phospholipids turn on their axis, move laterally in any direction over the surface of the membrane. Flipping across the membrane occurs very rarely (insideout)

Question 5

What 2 things influence the fluidity of the cell membrane?

Answer 5

1. The type of fatty acid chains in the phospholipid

2. The presence of cholesterol.

Question 6

Explain how the type of fatty acid chains in the phospholipids influences the fluidity of the cell membrane.

Answer 6

If you increase the # of saturated fatty acids, the membrane fluidity will decrease. If you increase the # of unsaturated fatty acids, the membrane fluidity will increase.

Question 7

Explain how the presence of cholesterol influences the fluidity of the cell membrane.

Answer 7

Cholesterol is amphipathic. It helps maintain the integrity of membranes-> especially the plasma membrane. The effect of membrane fluidity is temperature dependent.

Question 8

How does high temperature affect the membrane fluidity?

Answer 8

> =37 oC
This decreases the membrane fluidity as the gaps between phospholipids fill and there is therefore less movement for the phospholipids as they are prevented from moving apart too much.

Question 9

How does low temperature affect the membrane fluidity?

Answer 9

<37oC

This increases the membrane fluidity by preventing clumping of phospholipids.

Question 10

Cell membrane: What are integral membrane proteins?

Answer 10

These proteins go from the outside to the inside of the membrane. They’re composed of 3 regions: 2 hydrophilic and one hydrophobic region. They’re permanently associated with the cell membrane.

Question 11

Cell membrane: Explain what role integral membrane proteins have.

Answer 11

They play an important role in moving molecules across cell membranes. The molecules that are moved are solutes and solvents. So for this process, an example would be solute transport proteins.

Question 12

Cell membrane: What are peripheral membrane proteins?

Answer 12

They’re temporarily associated with integral membrane proteins through weak non-covalent interactions (H-bonds). They’re easily separated from the membrane. They are a component of the transmission of information from external signals.

Question 13

What are cell membrane carbohydrates?

Answer 13

Carbohydrates that are membrane bound are involved in cell to cell recognition. On the extracellular surface of the plasma membrane, cells can recognize other cells by binding to molecules which usually contain carbohydrates.

Question 14

Cell membrane carbohydrates: what are glycolipids?

Answer 14

They’re carbohydrates that are covalently bonded to lipids.

Question 15

Cell membrane carbohydrates: what are glycoproteins?

Answer 15

They’re carbohydrates that are covalently bonded to proteins.

Question 16

What’s the fluid mosaic model?

Answer 16

It describes cell membranes. A plasma membrane is fluid because of phospholipids and cholesterol. They’re described as mosaic because of the proteins, glycoproteins and glycolipids embedded within the membrane (it looks like a mosaic).

Question 17

Explain the plasma membrane.

Answer 17

It separates the inside from the outside of the cell. It maintains homeostasis, and acts as a selective barrier. This is done by controlling which molecules enter and leave the cell.

Question 18

What is homeostasis?

Answer 18

The active maintenance of a constant environment.

Question 19

Movement of molecules through the membrane: What is passive transport?

Answer 19

This means that NO energy is required to move molecules. It takes advantage of diffusion and osmosis.

Question 20

Movement of molecules through the membrane: What is active transport?

Answer 20

This means that energy IS required to move molecules. It CANNOT take advantage of diffusion and osmosis.

Question 21

Passive transport: what’s diffusion?

Answer 21

This is when a solute can pass freely through a permeable membrane. Solutes move from high concentration to low concentration. Only lipids, O2 and CO2 can cross the plasma membrane with no help.

Question 22

Passive transport: what’s facilitated transport?

Answer 22

Membrane bound proteins (carrier proteins & channel proteins) help polar/large molecules, pass through the plasma membrane since they cannot pass freely through the plasma membrane, (like water, proteins, sugars & salts->ions). This is done through diffusion, therefore it does not require energy.

Question 23

Passive transport: What’s osmosis in facilitated transport?

Answer 23

It’s when solutes CANNOT pass freely through a membrane but the solvent can. The solvent is usually water. This means that the membrane is semi permeable. The H2O molecules pass through the cell membrane through aquaporins. The water molecules move from low solute concentration to high solute concentration.

Question 24

What are aquaporins?

Answer 24

They are special channel proteins.

Question 25

How does diffusion work with sodium?

Answer 25

It cannot diffuse from low to high concentration therefore it cannot diffuse into the cell without using energy.

Question 26

Active transport: What is energy for a cell?

Answer 26

It causes change, performs work, moves and changes matter in a direction/way that it would not spontaneously take.

Question 27

Active transport: explain the energy within biological systems.

Answer 27

ATP stands for Adenosine triphosphate. It's the unit (of currency) of the energy transfers in a cell.

Question 28

Active transport: What's primary active transport?

Answer 28

To move solutes from low concentration to high concentration (against the chemical gradient), energy is DIRECTLY required. Molecules that are moved can be glucose, amino acids, nucleotides and salts across the plasma membrane.

Question 29

Active transport: What's an electrochemical gradient?

Answer 29

This is created when primary active transport moves ions. Electrochemical gradient stores potential energy. This energy could be used by nerve cells to conduct a signal/muscles to contract/for secondary active transport.

Question 30

What's the most important active transport protein?

Answer 30

Na+/K+

Question 31

Active transport: What's the secondary active transport?

Answer 31

It uses the potential energy to move solutes across the concentration gradient.

Question 32

What's the first step in how food is digested in the body (nutrients)?

Answer 32

1. By creating a steep concentration gradient for Na+ entry into intestinal cells, glucose and galactose are absorbed by the energy stored in Na+/K+ pump.

Question 33

What's the second step in how food is digested in the body (nutrients)?

Answer 33

2. Through a membrane cotransporter protein (in this case SGLT), Na+ moves across the membrane to drive glucose against its concentration gradient into the cells.

Question 34

What's the third step in how food is digested in the body (nutrients)?

Answer 34

3. Fructose enters the cell by facilitated diffusion.

Question 35

What's the fourth step in how food is digested in the body (nutrients)?

Answer 35

4. On the GLUT2 sugar transporter, from facilitated diffusion, all 3 monosaccharides exit across the basolateral membrane.

Question 36

Expand on the theory about the cell wall.

Answer 36

It's located outside of the plasma membrane of prokaryotic cells, plant cells & fungi cells. It provides structural support and protection when it absorbs water, it resists expansion and allows pressure to build up in a cell, which is called tugor pressure.

Question 37

What's tugor pressure?

Answer 37

It's a force exerted by the water pressing against an object which provides structural support. This structure is made of carbohydrates and proteins that surround the plasma membrane.