What effect does cholesterol have on the fluidity of the membrane? What is the d

Question

1. What effect does cholesterol have on the fluidity of the membrane?
2. What is the difference between a glycolipid and a glycoprotein?
3. Are all membranes the same? Explain.
4. Explain this statement: The plasma membrane is selectively permeable.
5. What are some of the ways (or mechanisms) different substances can get into or out of the cell? Do they all require energy? Do they all require membrane proteins?
6. What is a concentration gradient, what is an electrochemical gradient?
7. What is the difference between passive transport and active transport?
8. What is diffusion? What determines the direction of diffusion?
9. What types of molecules can pass through a membrane without the aid of a membrane protein? What types of molecules use a membrane protein in order to cross the membrane?
10. What determines the direction of movement for substances that are able to diffuse through the lipid bilayer without the aid of a membrane protein? Does this require energy?
11. What is a channel? Name 3 types of channels. What determines the direction of movement through channels? Does movement through a channel require energy?
12. What is a carrier? What is another name for a carrier? What are 3 types of carriers? What is the difference between the 3 types? Are carriers involved in facilitated diffusion, active transport, or both? Are channels involved in facilitated diffusion, active transport, or both?
13. In what direction does a substance move in active transport? In what direction does a substance move in facilitated diffusion?
14. Describe the Na+/K+-ATPase.
15. Compare and contrast primary and secondary active transport.
16. What is the difference between endocytosis and exocytosis? Do both involve vesicles? Name 3 types of endocytosis. What are some of the things that cells accomplish through endocytosis and exocytosis?
17. What is an isotonic solution, hypertonic solution, and hypotonic solution? What effect would each of these solutions have on a red blood cell and why?
18. Compare and contrast the different ways things get in and/or out of the cell, including simple diffusion, facilitated diffusion, active transport, endocytosis, exocytosis, and osmosis.
19. Can cells change the permeability of their membrane?

Explanation / Answer

1)While cholesterol adds firmness and integrity to the plasma membrane and prevents it from becoming overly fluid, it also helps maintain its fluidity.
At the high concentrations it is found in our cell's plasma membranes (close to 50 percent, molecule for molecule) cholesterol helps separate the phospholipids so that the fatty acid chains can't come together and cyrstallize.
Therefore, cholesterol helps prevent extremes-- whether too fluid, or too firm-- in the consistency of the cell membrane.
2) Glycoproteins are the proteins covalently attached to carbohydrates such as glucose, galactose, lactose, fuctose, sialic acid, N-acetylglucosamine, N-acetylgalactosamine, etc.
Glycolipids are carbohydrate-attached lipids. Their role is to provide energy and also serve as marker for cellular recognition.
Glycoproteins and glycolipids act as antennae, receiving chemical messages from other cells. They are also markers & identifiers that identify the cell to other crs for cellular recognition.
3)NO, depends on the constituent paricles and concentration. as well as they can be impermeable, semi permeable, selectively permeable or permeable. It depends on the nature of the membrane that what types of materials can pass through it.
4)PLasma membrane allows only certain things to pass through it, not all can go in and out of the membrane and hence selectively permeable,
5) Osmosis, diffusion, active and passive transport, facilitated diffusion, Active transport requires energy and osmosis requires membranes.
6)Conentration gradient meand a difference in concentration. An electrochemical gradient is a gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts, the electrical potential and a difference in the chemical concentration across a membrane.
7)Active transport is the movement of molecules across a cell membrane in the direction against their concentration gradient, i.e. moving from an area of lower concentration to an area of higher concentration. Active transport is usually associated with accumulating high concentrations of molecules that the cell needs, such as ions, glucose and amino acids. If the process uses chemical energy, such as from adenosine triphosphate (ATP), it is termed primary active transport. Secondary active transport involves the use of an electrochemical gradient. Active transport uses cellular energy, unlike passive transport, which does not use cellular energy. Active transport is a good example of a process for which cells require energy. Examples of active transport include the uptake of glucose in the intestines in humans and the uptake of mineral ions into root hair cells of plants.

Passive transport is a movement of biochemicals and other atomic or molecular substances across cell membranes. Unlike active transport, it does not require an input of chemical energy, being driven by the growth of entropy of the system. The rate of passive transport depends on the permeability of the cell membrane, which, in turn, depends on the organization and characteristics of the membrane lipids and proteins. The four main kinds of passive transport are diffusion, facilitated diffusion, filtration and osmosis.

8) Diffusion is the net movement of a substance (e.g., an atom, ion or molecule) from a region of high concentration to a region of low concentration. This is also referred to as the movement of a substance down a concentration gradient. A gradient is the change in the value of a quantity (e.g., concentration, pressure, temperature) with the change in another variable (e.g., distance). For example, a change in concentration over a distance is called a concentration gradient, a change in pressure over a distance is called a pressure gradient, and a change in temperature over a distance is a called a temperature gradient.

A change or gradient is responsible for diffusion.
9)
10)

11) and 12)

Carrier proteins and channel proteins are the two major classes of membrane transport proteins. Carrier proteins (also called carriers, permeases, or transporters) bind the specific solute to be transported and undergo a series of conformational changes to transfer the bound solute across the membrane (Figure 11-3). Channel proteins, in contrast, interact with the solute to be transported much more weakly. They form aqueous pores that extend across the lipid bilayer; when these pores are open, they allow specific solutes (usually inorganic ions of appropriate size and charge) to pass through them and thereby cross the membrane (see Figure 11-3). Not surprisingly, transport through channel proteins occurs at a much faster rate than transport mediated by carrier proteins.

13) Active transport is the movement of molecules across a cell membrane in the direction against their concentration gradient, i.e. moving from an area of lower concentration to an area of higher concentration. It requires ATP.

Facilitated diffusion (also known as facilitated transport or passive-mediated transport) is the process of spontaneous passive transport (as opposed to active transport) of molecules or ions across a biological membrane via specific transmembrane integral proteins.Being passive, facilitated transport does not directly require chemical energy from ATP hydrolysis in the transport step itself; rather, molecules and ions move down their concentration gradient reflecting its diffusive nature.

14)Na+/K+-ATPase (sodium-potassium adenosine triphosphatase, also known as Na+/K+ pump, sodium-potassium pump, or sodium pump) is an antiporter-like enzyme (an electrogenic transmembrane ATPase) located in the plasma membrane of all animal cells. The Na+/K+-ATPase enzyme pumps sodium out of cells, while pumping potassium into cells. It has antiporter-like activity but is not actually an antiporter since both molecules are moving against their concentration gradient.

15)Primary active transport utilizes energy in form of ATP to transport molecules across a membrane against their concentration gradient. Therefore, all groups of ATP-powered pumps contain one or more binding sites for ATP, which are always present on the cytosolic face of the membrane.
Based on the transport mechanism as well as genetic and structural homology, there are considered four classes of ATP-dependent ion pumps:
P-class pumps
F-class pumps
V-class pumps
ABC superfamily
The P-, F- and V-classes only transport ions, while the ABC superfamily also transports small molecules.
The energy expended by cells to maintain the concentration gradients of some ions across the plasma and intracellular membranes is considerable:
In kidney cells, up to 25 % of the ATP produced by the cell is used for ion transport;
In electrically active nerve cells, 60 -70 % of the cells

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