Cell membrane Flashcards
What are all cells surrounded by?
Cell surface membrane (eukaryotic)
Plasma membrane (prokaryotic)
What are the 2 biochemical components for cell membranes?
Protein molecules
Phospholipids
How are phospholipids arranged?
As a bilayer
One sheet of phospholipid molecules opposite another
What is the actual width of the cell membrane?
7-8 nm
What happens when the phospholipids form bilayers?
Hydrophilic heads point outwards = interacts with the tissue fluid/blood plasma that surrounds the cell & cytoplasm inside the cell
Hydrophobic tails point inwards = towards the inside of the membrane
Explain why the hydrophilic heads point outwards and the hydrophobic tails point inwards when the phospholipids form bilayers
Tails repel water present in the cytoplasm and extracellular fluid
Heads are attracted to the water
How do cell membranes appear under the electron microscope?
Double line
Why is the stain used on the cell membrane water-soluble?
Associates with the hydrophilic phospholipids heads appear dark
Are all proteins in the membrane globular or fibrous?
Globular proteins
Where can globular proteins be found in the membrane?
On the surface of the bilayer
Partly embedded (extrinsic)
Extending completely across both phospholipid layers (intrinsic/transmembrane)
Describe & explain the position of the charged, or hydrophilic, parts of the protein, in relation to the phospholipids
Charged parts of the protein are attracted to the phosphate heads
Uncharged parts of the proteins associate with the non-polar fatty acid tails of the phospholipids
Where are carbohydrates found in the cell?
Pointing out of the outside of the cell
Attached to either proteins (glycoproteins)
Or attached to the phospholipids (glycolipids)
How are glycoproteins and glycolipids formed?
Through glycosylation
Collectively known as the glycocalyx
What is a glycoprotein?
Polypeptide with a side chain made of carbohydrates
What are the function of glycoproteins?
Act as receptor molecules
Act as antigens for cell recognition
Where is cholesterol present?
Between the phospholipids in animal cell membranes
Why is the model called the fluid mosaic?
Fluid : individual phospholipids molecules can move around relative to one another
Mosaic : proteins embedded in the bilayer vary in size and shape and are arranged in a random pattern
What is the main function of the cell membrane?
Aid d transport of certain substances into/out of cells
E.g. to obtain oxygen & remove carbon dioxide
What is the function of phospholipids?
Form a selective bilayer
Allows non-polar or uncharged molecules through
Prevents the passage of polar or charged molecules
What is the function of extrinsic proteins?
Associated with 1 layer only
May act as receptors for hormones
What is the function of intrinsic proteins?
Act as carriers or channels
Allow the passage of charged or polar molecules
E.g. glucose
What is the function of glycocalyx?
Act as cell-to-cell recognition
E.g. wbc in an immune response
Important in cell adhesion and acting as receptors
What is the function of cholesterol?
Controls membrane fluidity
