Cell Membranes & Transport- Unit 1.3 Flashcards
What are the functions of the plasma/cell membrane? (6)
- Is the boundary separating the living cell from its non-living surroundings.
- Controls which substances diffuse in and out of cell.
- Controls uptake of nutrients.
- Allows waste products to pass out.
- Responsible for secreting substances. (enzymes & glycoproteins)
- Cell recognition.
What is the main structure of the cell membrane?
Phospholipids that form a bilayer. (and proteins)
How are membrane proteins arranged?
Randomly
What are extrinsic proteins? (3)
- Proteins that occur on the surface of the bilayer/partly embedded in it. 2.PROVIDING STRUCTURAL SUPPORT.
- Many are receptor sites which bind with proteins like hormones and neurotransmitters.
What are intrinsic proteins? (3)
- Proteins that go right through the phospholipid bilayer.
- Some act as channels/carriers to facilitate diffusion of polar molecules across the membrane.
- Others can form pumps and carry out active transport against a concentration gradient.
What is the fluid mosaic model? (Singer and Nicholson 1972)
The phospholipids are fluid as each molecule can move in relation to the other within the membrane. The proteins form a mosaic pattern within the phospholipid bilayer.
What does cholesterol do?
Found in animal cells and fits between the phospholipid molecules, increasing rigidity and stability of the membrane.
What are glycolipids? (2)
(Lipids with a carbohydrate chain)
Found in outer layer of membrane.
Involved in cell to cell recognition.
What are glycoproteins? (1)
(Proteins with carbohydrate chain)
Stick out of some membranes.
What are the factors that affect cell permeability? (4)
Increasing:
- Temperature- cell membrane becomes unstable.
- Ethanol concentration- dissolve phospholipids.
- Sodium chloride concentration- reduces mobility of phospholipids.
- Detergent concentration- reduce surface tension of phospholipids.
What is diffusion?
The net movement of molecules from a high concentration to a low concentration until equilibrium is reached (equally distributed) down a concentration gradient.
What factors affect diffusion? (6)
- Concentration
- Diffusion pathway
- Surface area
- Thickness of membrane
- Increase in temperature
- Particle size
What is the difference between simple and facilitated diffusion?
Simple- diffusion of non-polar molecules across phospholipid bilayer.
Facilitated- Polar molecules using intrinsic proteins to facilitate transport across the membrane. Is limited by available intrinsic proteins.
What are channel proteins? (3)
- Consist of pores that are hydrophilic, allowing charged ions to pass through.
- Each protein is specific for one type of ion.
- Can open/close depending on need of cell.
What are carrier proteins? (3)
- Allow facilitated diffusion of larger polar molecules.
- Molecule attaches to protein at binding site and causes protein to change shape/rotate in membrane.
- This releases the molecule on the other side of the membrane.
What is active transport?
An ATP requiring process which ions & molecules move across membranes against a concentration gradient. (up)
Ions & molecules can move in opposite direction to diffusion.
What is a pump? How does it work?
An intrinsic protein that transports a molecule. (active transport)
ATP transfers phosphate group to pump on inside of membrane, causing the pump to change shape and transport molecules across the membrane.
What are 2 processes involving active transport?
Protein synthesis & absorption of minerals.
Why is diffusion not affected by respiratory inhibitors?
Does not require ATP (respiratory inhibitors stop ATP production)
What is an example of a respiratory inhibitor that affects active transport?
Cyanide as it stops ATP production.
What is osmosis?
The passage of water molecules from high water potential to lower water potential through a partially permeable membrane.
What does 🔱cell mean?
Water potential of the cell
What does 🔱s mean?
Solute potential
What does 🔱p mean?
Pressure potential
What is the equation used to describe the relationship between the forces in a plant cell?
🔱cell= 🔱s + 🔱p
The more concentrated a solution…
more solutes dissolved
The more negative the water potential.
At high concentrations of water…
The greater the potential energy.
water molecules free to move
What is plasmolysis?
When water leaves a plant cell via osmosis, the cytoplasm & vacuole shrink, causing cell membrane to pull away from cell wall.
What does a hypotonic external medium mean? (2)
Water potential of external solution is higher than solution inside cell.
Water will move in.
What does a hypertonic external medium mean?
Has lower water potential outside than inside so water moves out of cell.
What is an isotonic external medium? (2)
The same water potential inside and outside of the cell.
No net movement by osmosis.
What happens to an animal cell when it’s external medium is hypotonic?
Cell swells and may lyse. (burst)
What happens to a plant cell when it’s external medium is hypotonic?
Cytoplasm and vacuole swell and push against cell wall, becoming turgid.
Turgid plant cells support plant tissue and structures.
What happens when an animal cell’s external medium is hypertonic?
The cell shrinks
What happens when a plant cell’s external medium is hypertonic?
Cytoplasm & vacuole shrink causing cell membrane to pull away from cell wall. (plasmolysis)
What happens when an animal cell’s external medium is isotonic?
It is optimal & normal
What happens when a plant cell’s external medium is isotonic?
(also called incipient plasmolysis)
Cells become flaccid
How do large particles enter cells?
Endocytosis.
Name the 3 steps in endocytosis.
- Plasma membrane folds inwards.
- Continues to fold, engulfing material.
- Plasma membrane fuses to enclose material.
What are the 2 types of endocytosis?
Phagocytosis (phagocytes engulfing microbes)
Pinocytosis (involves entry of liquid into the cell)
What is exocytosis? (5)
Substances leaving the cell after being transported in transport vesicles (from RER)—>
through the cytoplasm—>
to the golgi body—>
and then to the cell membrane via secretory vesicles which fuse.
Contents are secreted outside the cell.
