Cell Structure - Cell membranes Flashcards
Why is the cell membrane structure knows as fluid mosaic
- Fluid - The components can move around within the membrane
- Mosaic - Due to the pattern produced by the proteins embedded throughout the membrane
What are glycoproteins
Carbohydrate bound to a protein
What is the role of glycoproteins
The carbohydrate acts as a recognition site
What are glycolipids
Carbohydrate bound to a phospholipid
What is the role of glycolipids
The carbohydrate acts as a recognition site
What is the role of cholesterol
- Reduces the fluidity of the membrane by restricting the movement of other molecules
- Makes the membrane more rigid and less permeable
- Maintains the shape of the membrane
What is the role of phospholipids
- Forms a bilayer
- Allows lipid soluble and small, non-polar molecules to diffuse through
- Prevents the passage of charged and water soluble molecules
Define diffusion
The passive net movement of small non-polar or lipid soluble molecules from a higher concentration to a lower concentration down a concentration gradient
Define osmosis
The net movement of water molecules from a high water potential to a low water potential through a partially permeable membrane
Define facillitated diffusion
The passive net movement of water-soluble and charged molecules from a higher concentration to a lower concentration through channel proteins or carrier proteins
Define co-transport
When 2 molecules are moved across the membrane by the same protein at the same time
Define active transport
The movement of molecules across the membrane against the concentration gradient via a specific carrier protein. Requires energy from the hydrolysis of ATP
Contrast active transport and facillitated diffusion
- Active transport uses energy from the hydrolysis of ATP, whereas facilitated diffusion does not
- Active transport uses carrier proteins only, whereas facilitated diffusion uses carrier proteins and channel proteins
- In active transport, molecules are moved against a concentration gradient whereas in facilitated diffusion molecules are moved down a concentration gradient
Compare active transport and facillitated diffusion
- Both use carrier proteins
Step by step process of active transport
- The molecule binds to the carrier protein
- The carrier protein changes shape, and energy from the hydrolysis of ATP is used to transport the molecule against its concentration gradient
What is a hypotonic solution
- Higher water potential outside the cell
- Lower water potential inside the cell
What is a hypertonic solution
- Higher water potential inside the cell
- Lower water potential outside the cell
What is an isotonic solution
Water potential inside the cell = Water potential outside the cell
What happens to animal cells in a hypotonic solution
Osmotic lysis (cell bursts because of too much water)
What happens to plant cells in a hypotonic solution
- Cell becomes turgid
- Cell does not burst due to the cellulose cell wall
What happens to animal cells in a hypertonic solution
Crenation (cell shrivels)
What happens to plant cells in a hypertonic solution
- Cell becomes flaccid
- Plasmolysis occurs (cell membrane can come away from the cell wall due to large amounts of water leaving)
What happens to animal cells in an isotonic solution
No effect due to no net movement
What happens to plant cells in an isotonic solution
No effect due to no net movement
What facors can cause the rate of movement across a membrane to increase
- Higher temperature
- Greater surface area
- Higher concentration gradient
- More carrier/channel proteins
How does temperature affect the rate of movement across a membrane
- Higher temperature increases the kinetic energy of molecules
- Faster rate of diffusion
How does surface area affect the rate of movement across a membrane
- More phospholipids for diffusion
- More carrier/channel proteins for facilitated diffusion
How does concentration gradient affect the rate of movement across a membrane
As the concentration difference increases, the rate of diffusion increases
How does the number of carrier/transport proteins affect the rate of movement across a mambrane
There are more proteins for molecules to pass through
How does temperature affect membrane permeability and why
- Makes the membrane more permeable
- Higher temperatures make the phospholipids more fluid by increasing their kinetic energy
How does very high temperture affect membrane permeabilty
- Makes the membrane very permeable
- Channel/carrier proteins denature, so are non-selective, allowing any molecule through
How does alcohol affect membrane permeability and why
- Makes the membrane more permeable
- Dissolves the phospholipid bilayer
How does acid affect membrane permeability and why
- Makes the membrane more permeable
- Channel/carrier proteins denature, so they are non-selective, allowing any molecule through
Step by step process for co-transport
- Sodium ions are actively transported from the epithelial cells into the blood using a specific carrier protein and energy from the hydrolysis of ATP
- A sodium ion concentration gradient is established between the lumen and epithelial cell
- Glucose/amino acid and sodium ions are co-transported from the lumen of the small intestine into the epithelial cell via facilitated diffusion using a specific carrier protein
- The glucose/amino acid molecule moves into the blood via facilitated diffusion using a specific carrier protein
Adaptations of epithelial cells
- Microvilli for large surface area
- Many carrier proteins for active transport, facilitated diffusion and co-transport
- Many mitochondria to produce more ATP for active transport
- Epithelial lining is one squamous epithelial cell thick therefore a short diffusion pathway
