HBS - Cell Membranes - Topic 2 Flashcards
List the components of the plasma membrane.
- Phospholipids
- Carbohydrates
- Cholestrol
- Proteins
Describe the functions of the phospholipid.
It regulates the permeability of the membrane.
- Higher concentrations of UNsaturated acids promote membrane fluidity, larger gaps
- Higher concentration of saturated fatty acids reduce cell membrane fluidity, fewer gaps
Describe the functions of Carbohydrates.
-Two main types:
Glycolipids
Glycoprotein
- Three main roles:
1) Maintain membrane stability and cell protection (glycocalyx)
2) Aid cell-cell adhesion (cell adhesion molecules)
3) Facilitate cell recognition
What is cholestrol?
- Is a lipid. Approximately 20% of membrane lipid is cholesterol.
- is amphiphilic
- Can migrate and even ‘flip’ between the membrane layers
What is the function of a protein?
Serve different functions: enzymes, carrier proteins, channel proteins, receptors, cell adhesion, recognition
What are the 2 main types of protein?
- Integral (firmly inserted into membrane)
- Peripheral (looslely attached to membrane)
Membrane fluidity is affected by:
- Extreme temperatures (hot or cold)
- Concentration of unsaturated fatty acids
- Cholesterol levels
How does low temperature affect membrane fluidity?
- Less kinetic energy
- Phospholipids pack together
- Membrane less fluid
How does high temperature affect membrane fluidity?
- More kinetic energy
- Phospholipids tend to move further away
- Membrane more fluid
How does cholestrol affect membrane fluidity?
-Maintains fluidity by preventing lipids from getting too close or too far apart from each other
Describe the differences between active and passive transport
Passive: Moves down a concentration (electrochemical) gradient
Active: against a concentration (electrochemical) gradient
Passive: Uses inherent K.E
Active: Needs external energy source
Active: Requires specific carrier protein, Has directionality
Summarise the key parts of simple diffusion.
- Small, uncharged, non polar molecules
- O2, CO2, NO, urea
- Uses kinetic energy (natural motion)
- Rate of diffusion proportional to concentration gradient
Summarise the key parts of Facilitated Diffusion.
- Small, polar molecules
- H2O, Glucose, Na+
- Uses specific integral proteins (carrier proteins)
Summarise the key parts of Osmosis.
- Net movement of water down a concentration gradient
- Water highly polar, but small amounts can ‘sneak’ through the membrane unaided
- Water moves freely and reversibly through specific protein channels called Aquaporins- fac.diffusion
Summarise the key parts of Primary Active Transport.
- Uses energy from Hydrolysis of ATP
- Movement of Na+ and K+ uses the Na+/K+ pump
- Maintaining ion concentration differences inside the cell are crucial
Summarise the key parts of Secondary Active Transport ( Co-Transport)
- 2 substances move at SAME time, a substance moves against conc gradient, and ion moves down conc gradient.
- The energy comes from the electrochemical gradient across the membrane
E.g of Secondary Active Transport?
Na+/Glucose transporter
E.g of Primary Active Transport
- Na+/K+ pump, 3 Na+ out, 2 K+ in.
- Calcium and Hydrogen pumps
What are the 2 types of secondary active transport?
Symport
Antiport
What is symport?
- Transported substances move in the same direction
- Na+/Glucose transporter
What is antiport?
- Transported substances move in opposite direction
- Na+/Ca2+ exchanger – uses the Na electrochemical gradient to transport Ca2+ out of the cell.
Define transport vesicles
- Bubble-like, membranous sacs
- Made of a phospholipid bilayer containing fluid
- Transport bubble
- Protects substances being transported
Define Endocytosis briefly.
Moves large molecules INTO the cell (ingestion / uptake)
What are the 3 types of endocytosis?
Phagocytosis
Pinocytosis
Receptor-mediated
Define Exocytosis briefly.
Moves large molecules OUT of the cell (excretion / secretion)
What are the 3 types of exocytosis.
Hormone secretion
Neurotransmitter release
Mucous secretion
Summarise Phagocytosis (endocytosis).
- cell eating
- Ingestion of large particles by specialised cells (phagocytes; in the immune system)
-Used for removing bacteria and debris
Summarise Pinocytosis (Endocytosis).
- cell-drinking’
- Process used to take in extracellular fluid with dissolved substances
-Droplet enters the cell and fuses with an endosome (sorting vesicle)
Summarise Receptor mediated endocytosis.
- Main mechanism for specific uptake of macromolecules
- Uptakes substances (hormones, cholesterol) found in small amounts
- Some viruses can hijack this route and enter our cells
Summarise Key parts of exocytosis.
- Process is stimulated by a cell-surface signal
- Transported to plasma membrane
- Fuses with membrane and ejects substance
What type of substances move out of the cell by exocytosis?
- Hormones
- Waste Products
- Neurotransmitters
