Chapter 5 - Plasma Membranes Flashcards
Define compartmentalisation
The formation of separate membrane -bound organelles
Why are phospholipids suited as membranes?
Because their hydrophilic heads can interact with water
What does the fluid-mosaic model show?
That the phospholipids are free to move within the layer relative to each other
Membrane is flexible
Because proteins embedded in the bilayer vary in shape, size and position
What are intrinsic proteins?
Transmembrane proteins that are embedded through both layers of a membrane
Have aa w hydrophobic R-groups on external surfaces which interact w the hydrophobic core of the membrane
Give 4 examples of intrinsic proteins
Channel proteins
carrier proteins
glycoproteins
glycolipids
Why do we need compartmentalisation?
Because the metabolic reactions require different conditions (e.g. chemical gradients to be maintained)
Describe the function of a channel protein?
To provide a hydrophilic channel that allows the passive movement of polar mol. and ions down a concentration gradient through membranes
How are channel proteins held together?
Through the interactions between the hydrophobic core of membrane and hydrophilic R-groups on outside
What is the role of a carrier protein?
Helps in the passive transport (down conc grad) and active transport (against conc) into cells
Where are glycoproteins found?
Embedded in the cell surface membrane w attached carbohydrate chains of varying length and shape
What role do glycoproteins have?
Cell adhesion and act as receptors for chemical signals
How do glycoproteins help with cell signals?
When the chemical binds to the receptor it creates a response from the cell
Either direct response or set of a cascade of events
Give examples of when cell signalling is used with glycoproteins
Receptors for neurotransmitters at nerve synapses
Which protein can be both intrinsic and extrinsic?
Glycolipids
What is the difference between glycolipids and glycoproteins?
Glycolipids are lipids with carbohydrate attached whereas glycoprotein is a protein
What is the function of a glycolipid?
To act as cell markers or antigens, can be recognised by immune system as self
What are extrinsic proteins?
Present in one side of the bilayer
Normally have hydrophilic R-groups on their outer surfaces and interact w polar heads of phospholipids or intrinsic proteins
What is the function of cholesterol?
To regulate the fluidity of the membrane
Positioned between hydrophobic heads and interacts
What is the effect of an increase in temperature on the phospholipid membrane?
- Increase in temp = more KE
- Each phospholipid moves more
- Membrane becomes more fluid
- Begins to lose its structure as the pplds move further away from each other
- loss of structure increases the permeability of the mem, so easier for particles to cross it
Channel and carrier proteins in mem will be denatured at high temp
What type of molecule can disrupt the bilayer?
Anything non-polar
How does alcohol affect the bilayer?
The presents of the alcohol molecule disrupts the structure of the bilayer, the individual phospholipids are further apart
More fluid and more permeable
Define diffusion
The net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient
Is diffusion active or passive?
Passive
Suggest and explain two factors affecting diffusion
- Temperature
- higher temp, particles have more KE, move at higher speed, frequency of successful collisions increases - Concentration difference
- The higher, the faster rate of diffusion bc the overall movement is larger
What molecules is the membrane permeable to? and why
non-polar molecules e.g. O2
Polar molecules will repel with the hydrophobic interior
Small polar molecules can pass (e.g. water)
What factors affect diffusion across a membrane?
Surface area
Thickness of membrane
What is facilitated diffusion?
Diffusion across a membrane through protein channels down a conc gradient
When a mem is selectively permeable the membrane has protein channels which are specific to one mol or ion (or protein channel)
What are the factors which affect facilitated diffusion?
Temperature
Conc gradient
Mem SA and thickeness
number of channel proteins present
Describe the process of active transport
- The molecule or ion to be transported binds to receptors in channel of the carrier protein on the outside of the cell
- On the inside of the cell ATP binds to the carrier protein and is hydrolysed into ADP and phosphate
- The binding of the phosphate molecule to the carrier protein causes the carrier protein to change shape (opening up to the inside of the cell)
- The molecule or ion is released to the inside of the cell
- The phosphate molecule is released from the carrier protein and recombines with ADP –> ATP
- The carrier protein returns to its OG shape
- Process is selective (only specific proteins are transported)
What is bulk transport?
A form of active transport where large molecules are moved into or out of the cell by endocytosis or exocytosis
What is endocytosis and name the two types
Bulk transport of material into cells
Phagocytosis - solids
Pinocytosis - Liquid
Describe the process of endocytosis
- Cell surface membrane invaginates when it comes into contact with the material to be transported
- Membrane enfolds the material until the membrane fuses forming a vesicle
- Vesicle pinches off and moves into the cytoplasm via the cytoskeleton
Describe the process of exocytosis
The vesicles usually formed by the Golgi Apparatus move towards and fuse w the cell surface membrane
The microtubules allow the vesicles to move
Contents released
What is necessary for endo and exocytosis?
Energy in form or ATP to move vesicles along the cytoskeleton, changing shape to engulf materials
What is water potential?
The pressure exerted by water molecules as they collide with a membrane or container
Measured in Pa
What is the water potential of pure water?
0kPa
What is the hydrostatic pressure?
The pressure created by osmosis in an enclosed system
What is cytolysis?
The bursting of an animal cell caused by increasing hydrostatic pressure as water enters by osmosis
How do animals control that not all of their water is diffused out?
Blood, an isotonic solution (cells surrounded by aqueous solutions with an equal water potential)
What is turgor?
The pressure exerted by the cell surface membrane against the cell wall in plants
What happens in plasmolysis?
The contents of the plant cell shrink because of a lower water potential outside the cell
Explain the difference between isotonic, hypertonic and hypotonic
Isotonic = no net water movement ( water potential is the same inside and out)
Hypertonic = water flow out of cell ( lower wp outside than inside)
Hypotonic = flow water into cell (higher wp outside than in)
