The cellular membrane

Question 1

The cellular membrane

Answer 1

The cellular mambrane is composed of a phosphlipids bi-layer embeded cholosterol, proteins, and charbohydrets.
The celluar membrane is a flueid mosic.

Question 2

The rule of Cholesterol in the membrane

Answer 2

Important to stabilize the structure of the membrane itself

Question 3

The rule of Proteins in the membrane

Answer 3

There are two types of different proteins in the cellular membrane:
+ Transmembrane/integral – go all the way through the membrane.
+ Peripheral – not going all the way through the membrane.

Functions of proteins in the membrane:

• Transportation of molecules into the cell and out to the cell.
• Signals transduction (intercellular interaction).
• Intercellular joining (junctions).
• Attachments to the cytoskeleton and extracellular matrix.

Question 4

The rule of Carbohydrates in the membrane

Answer 4

Important for marking cells (like flags). They can be glycolipids (carbs attached to lipids), or glycoproteins (carbs attached to proteins).
These carbohydrates are often called oligosaccharides.

Question 5

Passive transportation:

Answer 5

In the passive transportation of a molecule, the cell does not put extra effort in order to move that specific molecule. Meaning, no extra 𝐴𝑇𝑃. 
# Diffusion - molecules moving from region of high concentration to region of low concertation. 
For instance, 𝐶𝑂2, oestrogen and ethanol  

# Facilitated diffusion – diffusion of large, polar, or charged molecules through integral protein of the membrane.  
For instance, 𝐻2𝑂(very polar) 𝑁𝐴+,𝐶𝐿−.

Question 6

Active transportation:

Answer 6

transportation of molecules against a concentration gradient, resulting in the use of 𝐴𝑇𝑃.
- Primary: this kind of transportation directly uses 𝐴𝑇𝑃. For instance, 𝑁𝑎/𝐾 𝐴𝑇𝑃𝑎𝑠𝑒. This is a
protein pump that pushes three sodium ions out of the cell, while pulling two potassium ions into
the cell. This process is done against concertation gradient and accounts for nearly 2/3 of the cell’s
𝐴𝑇𝑃 usage.

• Secondary: proteins that transfer molecules against their concertation gradient using the energy of the primary, causing the indirect use of 𝐴𝑇𝑃. For instance, 𝐴𝐺𝐿𝑇2 are proteins in the urinary
  systems that push glucose into the cell using the gradient of sodium, therefore causing the 𝑁𝑎/𝐾 𝐴𝑇𝑃𝑎𝑠𝑒 to work harder.

Question 7

Characteristics of the cell membrane:

Answer 7

*Asymmerty - the arrangements of PL across the membrane is not symmatric, significant for cellular communication and intercellular transportation.

*Liquid crystal configuration - The cell membrane is flexible as liquid but has strength resembling a solid, significant for biological flexiability
Ex. red blood cell going to the capillary.

*The fluid moasic module - The membrane is flexible containinig different glycolipids and proteins. no area looks the same and the molecules are constantly moving.

Question 8

Transport Proteins

Answer 8

There are several types of transport proteins imbedded in the cell membrane:
1. Uniporter – allows the movement of one molecule. Can be a channel (like sodium channels), or a pump (Like calcium pumps).
2. Cotransport – allows the movement of two molecules.
* Antiporter – two molecules in opposing directions,
like 𝑁𝑎/𝐾 𝐴𝑇𝑃𝑎𝑠𝑒.
* Symporter – two molecules in the same direction.
Usually couples a favourable movement
with an unfavourable movement.

Question 9

Endocytosis and Exocytosis

Answer 9

Exocytosis – a process in which the cell releases molecules by fusing membrane bond vesicles with the 
plasma membrane (the cell membrane gets bigger).    

Endocytosis – a process in which the cell takes in molecules by engulfing them with the plasma membrane
and closing it around them, creating vesicles (the cell membrane gets smaller).
Types of endocytosis:
* Pinocytosis – swallowing fluids.
* Phagocytosis – swallowing large solid or living materials like bacteria.
* Receptor mediated endocytosis – endocytosis that occurs only when there is a match between a
protein on the cell’s surface and a protein on the vesicle’s surface (receptor – ligand).

** All endocytosis/exocytosis processes require 𝐴𝑇𝑃 usage.

Question 10

Cell Junctions/Joining:

Answer 10

Multi-protein complexes of three classes and three functions:
1. Anchoring – anchoring proteins are made out of cadherin that form strong bridges keeping the
tissue intact. Desmosomes connect cells to each other, and hemi-desmosomes connect cells to
extracellular matrix. (Epithelial cells)

2. Tight junctions – complexes that seal cavities, restricting diffusion. Made out of occluding proteins.(Blood Brain Barrior)
3. Gap junctions – complexes that connect the cytoplasm of adjacent cells, increasing conductivity
   greatly. We can find them in tissues like the cardiac muscle. Made out of connexion proteins.(Heat muscles)