Cell Membranes Flashcards
In which type of cells eukaryotic or prokaryotic are the organelles surrounded by membranes?
Eukaryotic
What is the purpose of a cell surface membrane?
The cell surface membrane acts as a barrier between the cell and its environment , it controls what enters and leaves the cell due to the partially permeable nature of its membrane.
By which 3 processes can substances move across the cell surface membrane?
Osmosis
Diffusion
Active Transport
Why are plasma membranes that surround organelles important?
The plasma membranes that surround the organelles in eukaryotic cells are important as they help compartmentalise the cell and thus keep its organelles separate from the cytoplasm.
What types of molecules is the plasma membrane composed of?
phospholipids
proteins
carbohydrates
cholesterol
What phrase would be used to describe formation in which the molecules lie to form a plasma membrane?
A fluid mosaic model
What other word could be used as an alternative to cell membrane?
Plasma membrane
Why is the phospholipid bilayer said to be fluid?
The bilayer is said to be fluid as the phospholipids are constantly moving
Name the 3 types of protein that lie within or on the surface of a plasma membrane
Receptor proteins
Channel proteins
Carrier proteins
What do receptor proteins in the cell surface membrane do ?
Allow cell to detect chemicals released from other cells and when triggered by this they can signal the cell to respond in some way
What type of molecules do carrier proteins help cross the cell surface membrane?
Large molecules
What type of molecules do channel proteins help cross the cell surface membrane?
Charged (ions)
If a protein has a carbohydrate chain attached to it what is it referred to as?
glycoprotein
If a lipid has a carbohydrate chain attached to it what is it referred to as?
Glycolipid
Which part of a phospholipid is hydrophilic?
The phosphate head
Which part of a phospholipid is hydrophobic?
hydrocarbon tail
What do phospholipid molecules act as a barrier to?
Dissolved (water soluble)
How do phospholipids arrange themselves as they form a plasma membrane ?
the heads face out towards the water on either side of the membrane
In consequence of the middle of a phospholipid bilayer being hydrophobic which type of substances cannot pass through?
the membrane doesn’t allow water-soluble substances (like ions
and polar molecules) to diffuse through it.
What type of substances can pass through the plasma membrane?
Small, non-polar substances (e.g. carbon dioxide) and water can diffuse through the membrane
What attribute does cholesterol give to a cell membrane?
Stability
Why can water diffuse through cell membrane
Water is actually a polar molecule, but it can diffuse (by osmosis) through the cell membrane because it’s so small
Cholesterol is a type of lipid found in all cell membranes with the exception of one, which cell membrane does not contain cholesterol?
Bacterial cell membranes
Where do the molecules of cholesterol fit in relation to the phospholipids?
Between the phospholipids
What do cholesterol molecules do to make the phospholipid bilayer more stable?
Cholesterol binds to the hydrophobic tails of the phospholipids, causing them to pack more closely together. This restricts the movement of the phospholipids, making the membrane less fluid and more rigid.
In cells that don’t have a cell wall why is cholesterol particularly important?
Helps maintain the shape of animal cells that don’t have cell wall or aren’t supported by other cells eg red blood cells
Cholesterol has hydrophobic regions , hence does it add or detract from the bilayers nature as a barrier to polar substances/water?
Add
How would being in a very cold environment (0 degrees) impact the permeability of a plasma membrane?
The phospholipids don’t have much energy, so they can’t move very much. They’re packed closely together and the membrane is rigid. But channel proteins and carrier proteins in the membrane denature (lose structure and function), increasing the permeability of the membrane. Ice crystals may formand pierce the membrane, making it highly permeable when it thaws.
How do membranes change as temperature increases?
the phospholipids move more because they have more energy — this increases the permeability of the membrane.
At temperatures which exceed 45 degrees how does the phospholipid bilayer behave?
The phospholipid bilayer starts to melt (break down) and the membrane becomes more permeable. Water inside the cell expands, putting pressure on the membrane.
How does putting a plasma membrane in a solvent affect its permeability ?
Channel proteins and carrier proteins in the membrane denature so they can’t control what enters or leaves the cell — this increases the permeability of the membrane
