Cell membrane, structure and transports

Question 1

How permeable is the cell membrane and what does it mean?

Answer 1

Selectively - it allows some substances to cross it more easily than others.

Question 2

What is the membrane made of?

Answer 2

Membranes are predominantly made of phospholipids and proteins held together by weak interactions that cause the membrane to be fluid.

The fluid mosaic model of cell membrane describes the membrane as fluid, with proteins embedded in or associated with the phospholipid bilayer.

Question 3

Where are the hydrophilic phosphate portions of the phospholipids?

Answer 3

They are oriented toward the aqueous inside and outside environments of the cell

Question 4

Where is the hydrophobic fatty acid?

Answer 4

They face each other in a double layer in the interior

Question 5

What do phospholipids provide?

Answer 5

In the cell membrane, they provide a hydrophobic barrier that separates the cell from ist liquid environment

Question 6

Hydrophilic molecules

Answer 6

They can not easily enter the cell

Question 7

Hydrophobic molecules

Answer 7

They can easily enter the cell

Question 8

Proteins in the cell membrane

Answer 8

Completely embedded in the membrane, including some that span the membrane completely

Pomembno vlogo imajo pri prehajanju snovi, medsebojno prepoznavanje in povezovanje celic, preopznavanje kemijskih signalov, lahko so dejavni tudi kot encimi.

Question 9

Carbohydrate in the cell membrane

Answer 9

They are crucial in cell-cell recognition and in developing organisms.

Cell surface carbohydrates vary from tissue to tissue and they are the reason that blood transfusion must be type-specific.

Question 10

Examples of nonpolar molecules

Answer 10

hydrocarbons, carbon dioxide, oxygen

Question 11

Can nonpolar molecules pass the membrane?

Answer 11

They are hydrophobic and can dissolve in the hydrophobic interior of the phospholipid biliary and cross the membrane easily.

Question 12

What does the hydrophobic core of the membrane?

Answer 12

It impedes the passage of ions and polar molecules - they are hydrophilic.

Question 13

How can hydrophilic substance avoid the lipid bilayer?

Answer 13

By passing through TRANSPORT PROTEINS than span the membrane

Question 14

Which molecule is the most important for moving across the membrane?

Answer 14

Water

Question 15

Through which transport proteins does water move in the membrane?

Answer 15

Aquaporins - greatly accelerate the speed at which water can cross membranes.

Question 16

What is passive diffusion?

Answer 16

A substance travels from where it is more concentrated to where is less concentrated.

Question 17

What is diffusing down during passive diffusion?

Answer 17

Concentration gradient

Question 18

Which substances can easily pass the membrane with passive diffusion?

Answer 18

Hydrophobic substances - carbon dioxide, hydrocarbons, oxygen

Question 19

Does passive diffusion require work?

Answer 19

No

Passive - the cell expands no energy in moving substances.

Question 20

What is osmosis?

Answer 20

The diffusion of water across a selectively permeable membrane

The cell has one of 3 relationships with the environment
Isotonic solution
Hypertonic solution
Hypotonic solution

Question 21

Isotonic solution

Answer 21

No net movement of water across the membrane.

Water crosses the membrane but at the same rate in both directions

Question 22

Hypertonic solution

Answer 22

The cell loses water to its surroundings.

The hyper - prefix refers to more solutes in the water around the cell - the movement of the water to the higher concentration of solutes.

The cell because of the loss of water to the environment will shiver and may die

Question 23

Hypotonic solution

Answer 23

Water enters the cell faster than it leaves

Hypo - prefix - the movement of water into the cell where solutes are more heavily concentrated

In this case, the cell may swell and burst

Question 24

From which to which solution does water move?

Answer 24

Hypo to hyper

Question 25

Can ions and polar molecules easily pass the membrane?

Answer 25

They can not

Question 26

What is facilitated diffusion?

Answer 26

The process by which ions and hydrophilic substances diffuse across the cell membrane whit the help of transport proteins.

Question 27

What are transport proteins?

Answer 27

They are specific for the substance they transport.

Question 28

How do transport proteins work?

Answer 28

In one of two ways:

They provide a hydrophilic channel through which the molecules in question can pass

They blin loosely to the molecules in question and carry them through the membrane

Question 29

What is active transport?

Answer 29

From the region where they are less concentrated to the region where they are more concentrated.

Question 30

Does AT require energy?

Answer 30

It requires energy, usually from ATP

Question 31

Sodium-potassium pump?

Answer 31

This transmembrane protein pumps sodium out of the cell and potassium into the cell

Question 32

Electrochemical gradient

Answer 32

A chemical force is the ions concentration gradient

A voltage gradient across the membrane, which attracts positively charged ions and repels negatively charged ions

These two things combine electrochemical gradient