4 - Cell Membranes and Transport Flashcards
Cell Membranes and Transport (28 cards)
What is the primary importance of membranes?
Create an enclosed space to separate intracellular cell environment from external environment and control exchange of materials across them
Membranes also act as interfaces for communication.
What is the structure of the phospholipid bilayer?
7nm thick, composed of two layers of phospholipid molecules with hydrophobic tails facing in and hydrophilic heads facing out
The bilayer contains proteins.
What does the fluid mosaic model explain?
How biological molecules arrange to form cell membranes and the movement between cell and surroundings
It encompasses cell interactions and signaling.
What are the components of phospholipids?
1 phosphate head (hydrophilic, polar) and 2 lipid tails (hydrophobic, non-polar)
They can form monolayers in water.
Define a micelle.
Spheres formed by shaking phospholipids with phosphate heads facing out and lipid tails facing in
Micelles are important in the formation of cellular structures.
What are intrinsic/integral proteins?
Proteins embedded in the membrane, can be transmembrane or associated with phospholipid monolayers
These proteins often function as transport proteins.
Where are extrinsic/peripheral proteins found?
On the outer or inner surfaces of the membrane
They are not embedded within the lipid bilayer.
What does the term ‘fluid’ imply in the fluid mosaic model?
Proteins and phospholipids can move about via diffusion within the membrane
This mobility contributes to membrane functionality.
List the three main types of lipids in the membrane.
- Phospholipids
- Cholesterol
- Glycolipids
What is the role of cholesterol in membranes?
Regulates fluidity, prevents close packing of phospholipids at low temperatures, increases mechanical strength
Cholesterol is only present in eukaryotic cells.
Define glycolipids.
Lipids with a hydrophobic fatty acid tail and a hydrophilic carbohydrate head, found in the outer phospholipid monolayer
They project carbohydrate chains into the extracellular space.
What are glycoproteins?
Proteins attached to carbohydrate chains, projecting into the surrounding fluid of the cell
Found in the outer phospholipid monolayer.
What is the main role of phospholipids in membranes?
Form the basic structure of the membrane and create a hydrophobic core that acts as a barrier to water-soluble molecules
They also act as signaling molecules.
How do glycolipids and glycoproteins function in cell signaling?
Carbohydrate chains act as receptor molecules that bind with substances at the cell surface
Some also function as antigens.
What are the two types of transport proteins?
- Channel proteins
- Carrier proteins
What is facilitated diffusion?
The use of proteins to help substances that can’t diffuse through membranes to pass through the phospholipid bilayer
It involves channel and carrier proteins.
Define osmosis.
The diffusion of water molecules from a region of high-water potential to a region of low-water potential across a selectively permeable membrane
It is crucial for maintaining cellular homeostasis.
What is active transport?
The movement of molecules from a region of lower concentration to a region of higher concentration using energy from respiration
It requires carrier proteins.
What are the two forms of endocytosis?
- Phagocytosis
- Pinocytosis
What happens during phagocytosis?
Bulk transport of solids into the cell, forming phagocytic vacuoles
This process is essential for immune responses.
What occurs during pinocytosis?
Bulk transport of liquids into the cell, often forming very small vacuoles
This allows cells to take in extracellular fluid.
What is plasmolysis?
When the protoplast shrinks and exerts less pressure on the cell wall, pulling away from it
It occurs in plant cells under low water potential conditions.
What is the significance of surface area to volume ratio?
As size increases, the ratio decreases, affecting the rate of diffusion
A higher ratio facilitates faster diffusion.
What happens to plant cells in pure water?
Water enters by osmosis, protoplast pushes against cell wall, cell becomes turgid
This turgidity provides structural support.
