Lecture6 Flashcards

1
Q

What are membranes for prokaryotic & eukaryotic cells?

A

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

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2
Q

What is the function of cell membranes?

A

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

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3
Q

What is the structure of cell membranes?

A

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

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4
Q

Explain cell membranes.

A

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)

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5
Q

What 2 things influence the fluidity of the cell membrane?

A
  1. The type of fatty acid chains in the phospholipid

2. The presence of cholesterol.

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6
Q

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

A

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.

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7
Q

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

A

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

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8
Q

How does high temperature affect the membrane fluidity?

A

> =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.

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9
Q

How does low temperature affect the membrane fluidity?

A

<37oC

This increases the membrane fluidity by preventing clumping of phospholipids.

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10
Q

Cell membrane: What are integral membrane proteins?

A

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.

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11
Q

Cell membrane: Explain what role integral membrane proteins have.

A

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.

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12
Q

Cell membrane: What are peripheral membrane proteins?

A

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.

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13
Q

What are cell membrane carbohydrates?

A

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.

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14
Q

Cell membrane carbohydrates: what are glycolipids?

A

They’re carbohydrates that are covalently bonded to lipids.

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15
Q

Cell membrane carbohydrates: what are glycoproteins?

A

They’re carbohydrates that are covalently bonded to proteins.

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16
Q

What’s the fluid mosaic model?

A

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).

17
Q

Explain the plasma membrane.

A

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.

18
Q

What is homeostasis?

A

The active maintenance of a constant environment.

19
Q

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

A

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

20
Q

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

A

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

21
Q

Passive transport: what’s diffusion?

A

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.

22
Q

Passive transport: what’s facilitated transport?

A

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.

23
Q

Passive transport: What’s osmosis in facilitated transport?

A

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.

24
Q

What are aquaporins?

A

They are special channel proteins.

25
Q

How does diffusion work with sodium?

A

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

26
Q

Active transport: What is energy for a cell?

A

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

27
Q

Active transport: explain the energy within biological systems.

A

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

28
Q

Active transport: What’s primary active transport?

A

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.

29
Q

Active transport: What’s an electrochemical gradient?

A

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.

30
Q

What’s the most important active transport protein?

A

Na+/K+

31
Q

Active transport: What’s the secondary active transport?

A

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

32
Q

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

A
  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.
33
Q

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

A
  1. Through a membrane cotransporter protein (in this case SGLT), Na+ moves across the membrane to drive glucose against its concentration gradient into the cells.
34
Q

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

A
  1. Fructose enters the cell by facilitated diffusion.
35
Q

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

A
  1. On the GLUT2 sugar transporter, from facilitated diffusion, all 3 monosaccharides exit across the basolateral membrane.
36
Q

Expand on the theory about the cell wall.

A

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.

37
Q

What’s tugor pressure?

A

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.