The Plasma Membrane (2.3) Flashcards
State what controls plasma membrane impermeability to polar molecules
The phospholipid bilayer
Describe the impact of temperature on the fluidity of the cell membrane (absence of cholesterol)
low temp - rigid, low flexibility (membrane may break)
high temp - fluid, high flexibility (membrane won’t hold shape)
Describe amphipathic
Both hydrophobic and hydrophilic regions
Provide one example of an amphipathic structure
Phospholipids
Describe lateral movement of phospholipids
Rotate to switch places horizontally
Describe transverse movement (flip-flopping) of phospholipids
Rotate to switch places vertically
Define phospholipid bilayer
Two layers of phospholipids with hydrophobic fatty acid tails projecting inwards and hydrophilic glycerol and phosphate head groups projecting outwards
Describe polar and non-polar organisation of plasma membranes
Glycerol and phosphate head group - polar
Fatty acid tails - non-polar
Describe temperature as a factor affecting the fluidity of the plasma membrane
High temp = High fluidity
Low temp = High viscosity (saturated hydrocarbon tails)
State whether a phospholipid head is hydrophilic or hydrophobic
Hydrophilic
State whether a phospholipid tail is hydrophilic or hydrophobic
Hydrophobic
State 4 functions of peripheral proteins
- Enzymes
- Receptors
- Structural attachment points
- Recognition sites
Describe 2 major functions of the plasma membrane
- Controls entry and exit of substances into and out of the cell (differentially permeable)
- Separates internal and external environment
Describe the structure of the plasma membrane
Double layer of phospholipids with proteins scattered throughout which creates a differentially permeable barrier between the intracellular and extracellular fluid
Compare and contrast membrane fluidity and viscosity (Describe phospholipid composition and structure)
Fluidity: Unsaturated hydrocarbon tails prevent packing
Viscosity: Saturated hydrocarbon tails pack together
Describe transmembrane proteins
Integral proteins that span both phospholipid layers
Describe integral proteins
Proteins that are a permanent part of the plasma membrane
Describe peripheral proteins
Proteins that are a temporary part of the plasma membrane
Describe why peripheral proteins are a temporary part of the plasma membrane
Not embedded in the phospholipid bilayer
State 2 structures which peripheral proteins attach to on the plasma membrane
- Phospholipid molecules
2. Integral proteins (either layer of the plasma membrane)
State classification of a phospholipid with a cis double bond
Unsaturated
State classification of a phospholipid without a cis double bond
Saturated
State the 6 major functions of integral proteins
- Act as transport channels
- Function as enzymes
- Involved in signal transduction
- Cell-to-cell recognition
- Attach to cytoskeleton/extracellular matrix
- Intercellular joining
Describe impact of cis double bonds on fluidity of the plasma membrane
Creates kinks in the unsaturated fatty acid chains of the plasma membrane - less easy to pack together
(increasing membrane fluidity)
Describe lipophilic
(Hydrophobic)
Not water soluble - substances easily cross membrane
Describe hydrophobic
Not water soluble - ‘water hating’
Describe hydrophilic
Water soluble - ‘water loving’
Describe why proteins group in clusters
- similar functions
- same biochemical pathways
Outline what the fluid mosaic model proposes
Phospholipids and unanchored proteins are free moving, with anchored proteins scattered throughout.
State 3 materials which are scattered throughout the plasma membrane
- Proteins
- Carbohydrates
- Cholesterol
Define phospholipid
Essential component of the plasma membrane, comprised of a hydrophilic glycerol and phosphate head group and two hydrophobic fatty acid tails
Define plasma membrane
Semi-permeable boundary that regulates the movement of substances between the extracellular to intracellular fluid, composed of a phospholipid bilayer
State the 2 forms of phospholipid tails
- Saturated
2. Unsaturated
Describe the hydrophobic and hydrophilic regions of the phospholipid bilayer
Hydrophobic interior and hydrophilic exterior
State what 2 types of regions integral proteins have
- Hydrophobic
- Hydrophilic
State 2 major carbohydrate forms found within the plasma membrane
- Glycoproteins (attached to proteins)
- Glycolipids (attached to lipids)
Describe the extracellular matrix
Collection of extracellular molecules secreted by cells that provides biochemical support to surrounding cells
State the 2 common locations of proteins within the plasma membrane
- Clustered in groups
- Distributed randomly throughout the membrane
State 3 major functions of carbohydrates within the plasma membrane
- Cell-to-cell recognition
- Cell adhesion
- Recognition of antibodies, hormones and viruses
Describe how compartmentalisation within eukaryotes optimises cellular efficiency
Groups particular enzymes and reactants for particular functions in high concentrations at optimal levels
Describe the structure of phospholipids
Composed of a hydrophilic glycerol and phosphate head group and two fatty acid tails
Phospholipids will react with the presence of water. True/False
True
State 4 major functions of the plasma membrane
- Active boundary
- Cell identity
- Receiving external signals
- Transport
Classify non-polar molecules as hydrophilic or hydrophobic
Hydrophobic
Classify polar molecules as hydrophilic or hydrophobic
Hydrophilic
Relate the characteristics of phospholipids to the arrangement of the plasma membrane
Phospholipids are amphipathic
- Fatty acid tails have a low interaction with water
- Phosphate head groups have a high interaction with water
Phospholipids aggregate by orientating hydrophobic tails towards one another
Describe the structure of glycolipids as an amphipathic protein
Sugar group (hydrophilic) and covalently bonded lipid tail (hydrophobic)
Describe the structure of cholesterol as an amphipathic protein
Hydroxyl group (-OH) (hydrophilic) and hydrocarbon chain and steroid (hydrophobic)
State in which plasma membranes cholesterol is present
Animal cells
Describe the effect of cholesterol on the plasma membrane in high temperature
Prevents increase in fluidity
Describe the effect of cholesterol on the plasma membrane at low temperatures
Prevents increase in viscosity
Describe the effect of cholesterol on the movement of phospholipids at various temperatures
Restricts phospholipid movement and acts as a buffer for changing temperatures
State 2 characteristics of membrane proteins in relation to plasma membrane structure
- Move within the bilayer
- Attach to cytoskeleton
State the 3 factors that influence the fluidity of the plasma membrane
- Phospholipid composition and structure
- Temperature
- Cholesterol
Describe what cholesterol is composed of
4 fused carbon rings
Describe phospholipid composition and structure as a factor affecting plasma membrane fluidity
Increase saturated fatty acid tails = low fluidity
Decrease saturated fatty acid tails and increase unsaturated fatty acid tails = high fluidity
Describe how compartmentalisation within eukaryotes decreases cell vulnerability to environmental changes
Separates processes inside the cell (an environmental change would affect the cell cytosol more than individual membrane bound organelles)
Describe 2 factors supporting the importance of plasma membrane fluidity
- Substance permeability
- Capacity for proteins to move across the membrane to particular cell areas
Describe vesicle
Structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer.
State whether or not carrier and channel proteins are considered permanent or temporary parts of the plasma membrane and identify the overall protein classification
Permanent
Transmembrane proteins
Provide an example of a peripheral protein in function
Proteins involved in controlling the synthesis/destruction of the cell membrane
