Plasma Membranes Flashcards
In what 3 location are plasma membranes used?
Separating contents of cell from environment
Separate different areas within cells from their environment
Some organelles separated further by internal membranes
What is compartmentalisation?
The formation of separate membrane bound areas within the cell
State 3 factors as to why compartmentalisation is important
Allows incompatible metabolic reactions to occur simultaneously
Maintains specific concentration gradient in each part of the cell
Protects vital cell components
What is a plasma membrane?
A cell surface membrane which separates the cell from its external environment
Explain the structure of a membrane
Phospholipid bilayer- hydrophilic phosphate heads on inner and outer surface with a hydrophobic core inside the membrane
What model represents membrane structure? What does it show?
Fluid Mosaic Model-phospholipid bilayer that is free to move but embedded with proteins
What are the two types of protein in a membrane?
Intrinsic and Extrinsic
What are intrinsic proteins?
Transmembrane proteins that are embedded through both layers of a membrane
How are intrinsic proteins embedded in the membrane?
They have amino acids with a high proportion of hydrophobic R groups which interact with hydrophobic core, keeping them in place.
Give 4 examples of intrinsic proteins
Carrier Proteins
Channel Proteins
Glycoproteins
Glycolipids
What is the role of a channel protein?
A hydrophilic channel that allows for the passive movement of polar molecules and ions down a concentration gradient through membranes
What is the role of a carrier protein?
Passive and Active transport, by changing the shape of the protein
Explain the structure of a glycoprotein
Proteins embedded in cell surface membranes with attached carbohydrate chains of varying lengths and shapes.
What are the 2 major roles of glycoproteins?
Cell adhesion
Receptors for chemical signals (involved in cell signalling)
What is cell signalling?
Chemical binding to receptor, eliciting response from the cell.
Sets of a cascade of events inside the cell
Explain structure of a glycolipid
A lipid embedded in cell surface membrane with an attached carbohydrate chain
What is the role of a glycolipid?
Cell markers/ Antigen
Recognised by the immune system as self or non-self
What are extrinsic proteins?
Proteins present in one side of the bilayer
How does the structure of an extrinsic protein keep it in place?
Hydrophilic R groups that interact with polar heads of phospholipids
What is the role of cholesterol?
Regulating fluidity of the membrane
How does cholesterol carry out its function?
Has a hydrophilic end and a hydrophobic end
Hydrophilic interacts with heads
Hydrophobic interacts with core
Pulls them together
Explain the effect of increasing temperature on a membrane structure
Phospholipids have more kinetic energy, so move more
Membrane becomes more fluid and starts to lose structure
Cell will eventually break down completely
Denatures carrier and channel protein
How does increasing temperature affect function of the membrane?
Increases permeability so more particles can cross it
What do organic solvents do to plasma membranes?
Dissolve membranes, disrupting cells
Define diffusion
Diffusion is the net movement of particles from a region of higher concentration to lower concentration down a concentration gradient. Passive process.
What 2 factors affect rate of diffusion?
Temperature and concentration difference
How does temperature affect diffusion?
Higher temperatures= higher rate of diffusion
Particles have more kinetic energy and move at higher speeds
How does concentration affect diffusion?
Greater the concentration gradient the faster the movement
What is simple diffusion?
Diffusion in the absence of a barrier or membrane
Why are membranes described as partially permeable?
Hydrophobic interior repels ions so can’t pass through
Non-polar molecules can pass through
Polar molecules can pass through at slow rate
Mixture of particles that can and can’t pass through so is partially permeable
What 2 factors affect the rate that molecules diffuse across membranes?
Surface area
Thickness of membrane
How does surface area affect diffusion?
The larger the area of an exchange surface, the higher the rate of diffusion
How does thickness of membrane affect diffusion?
The thinner, the higher the rate of diffusion
What is facilitated diffusion?
Diffusion across a membrane through protein channels
What factors affect rate of facilitated diffusion?
Temperature
Concentration Gradient
Membrane surface area and thickness
Number of protein channels
Define ‘active transport’
The energy requiring(ATP) movement of molecules or ions into or out of a cell from a region of lower concentration to a higher concentration, up a concentration gradient
Explain the 6 step process of active transport
1) Molecule to be transported binds to receptors in channel of carrier protein
2) Inside cell, ATP binds to carrier protein and is hydrolysed into ADP and phosphate
3) Binding of phosphate causes change in shape of protein
4) Molecules is released inside cell
5) Phosphate molecule released and recombines to form ATP
6) Carrier protein returns to original shape
What are the 2 types of endocytosis?
Phagocytosis- solids
Pinocytosis-liquids
Explain process of endocytosis
Cell surface membrane invaginates
Membrane enfolds the material until eventually it fuses and forms a vesicle
Vesicle pinches off and travels in the cytoplasm
Explain process of exocytosis
Vesicles fuse with cell surface membrane
Contents released outside the cell
Is bulk transport an active or passive process? Why?
Active, requires ATP for movement of vesicles along cytoskeleton, changing shape of cells and fusion.
Define ‘water potential’
The pressure exerted by water molecules as they collide with a membrane or container
What is the water potential of water?
0kPa
Define osmosis
The net movement of water from a high water potential to low water potential down a concentration gradient.
Explain the process of ‘cytolysis’
Animal cell in solution with higher water potential than that of the cytoplasm
Water moves into the cell via osmosis
Increases hydrostatic pressure within cell
Cell surface membrane can’t withstand and bursts- cytolysis
Explain the process of ‘crenation’
Animal cell is placed in solution that has lower water potential than that of the cytoplasm
Water moves out of cell via osmosis
Reduction in volume of cell
Membrane puckers- crenation
Explain the process of a cell becoming ‘turgid’
Plant cell placed in a solution with higher water potential than the cell
Water enters cell via osmosis
Membrane(protoplast) is pushed up against cell wall
Turgor
Explain the process of ‘plasmolysis’
Plant cell placed in solution with lower water potential than the cell
Water leaves via osmosis
Reduction in volume in cytoplasm
Pulls cell surface membrane away from the wall
