The Cell Membrane Flashcards
State the organelles that contain membranes
- Endoplasmic reticulum
- Chloroplast
- Mitochondria
What is the purpose of the membrane in the endoplasmic reticulum
Forms a transport system
What is the function of membranes in mitochondria and chloroplast
Controls entry and exit of materials
What is the cell membrane made up of
Phospholipids
What does the phospholipid head contain, and describe its significance
The head contains phosphate and glycerol, making it polar/hydrophillic
What does the phospholipid tail contain, and describe its significance
The tail contains 2 fatty acids, which makes it non-polar/hydrophillic
Describe how bilayers form
- The cell membrane forms a barrier between the outside of the cell and the inside
- Both the outside of the cell (tissue fluid) and inside of the cell (cytoplasm) are mainly water, therefore the hydrophillic heads orient themselves outwards
- The hydrophobic tails orient themselves away from water, and therefore point inwards
Explain how the phospholipid bilayer interacts with water
- The hydrophobic polar fatty acid tails orient themselves away from water
- The hydrophilic, non-polar glycerol and phosphate heads orient themselves towards water
Why must the cell membrane be able to move
To enable transport of substances in or out the membrane
Describe the process of exocytosis
Vesicles produced within the cell can transport molecules such as proteins to the cell surface, and secrete these proteins through
Describe the process of endocytosis
Molecules enter the cell and are transported by a vesicle via endocytosis
Why are phospholipids fluid
Cells need to change shape
Describe the role of cholesterol in the cell membrane
- Cholesterol increases the rigidity and stiffness of the membrane.
- This limits the lateral (side to side) movement of the phospholipids, allowing the cell membrane to retain its shape
Why is the phospholipid bilayer selectively permeable
Due to the properties of the phospholipids
What must a molecule be in order to pass through the phospholipid bilayer
Lipid soluble
To be lipid soluble, a molecule must be…
- Non-polar
- Uncharged
State the 2 types of transport protein
- Channel protein
- Carrier proteins
Describe the properties of the 2 transport proteins, and why this makes the cell membrane selectively permeable
They’re specific, due to their specific 3D tertiary structures, so they can only transport certain molecules
What other proteins are found in the cell membrane
- Receptors
- Membrane bound enzymes
- Transport proteins
Describe the structure of receptors
Often glycoproteins, which are proteins with a carbohydrate attached.
Describe what happens when a specific molecule binds to the receptor
A response is triggered within the cell
Describe the function of membrane bound enzymes
They catalyse reactions on the cell surface
Describe the function of call identify markers
- Commonly known as antigens
- Each cell has a distinctive antigen with a different structure, allowing for identification
- These can be proteins or glycolipids (carbohydrates with a lipid attached)
Why is the phospholipid bilayer described as a fluid mosaic
The cell membrane is made up of many smaller components, with varying size and shape
What do we call proteins that span the whole phospholipid
Intrinsic proteins
- They have non polar regions to make them lipid soluble
What do we call proteins that are embedded in the membrane
Extrinsic proteins (pointing outwards)
- They are polar, so they aren’t found with the fatty acid tails
Explain how the structure of the cell membrane enables it to act as a selectively permeable barrier
- Selectively permeable means that only specific substances can pass through the membrane
- As the bilayer is made from phospholipids, only lipid soluble molecules (which are non-polar and charged) can pass directly through it
- As these proteins have a highly specific 3D tertiary structure, only particular molecules with the correct shape can be transported through them
