Plasma Membranes Flashcards
What is the structure of a lipid?
- made of one glycerol and three fatty acids
-Ester bonds
What is a phospholipids?
When the phosphate replaces the fatty acids
What types of membranes do eukaryotes have?
- cell surface membrane
- membrane bound organelles
What types of membranes do prokaryotes have?
- cell surface membrane
- no membrane bound organelles
What are the roles of cell membranes?
- compartmentalisation
- contains reactions in separate parts of cell
- separates cell contents from environment
- keeps harmful substances separate - cell signalling and recognition
- control what enter and leaves cell
- site of chemical reactions- photosynthesis
What are the components of cell membranes?
- phospholipid
- hydrophilic head
- hydrophobic tail - phospholipid form a bilayer (basic structure of a membrane)
What is in a fluid mosaic model?
- free moving phospholipids within the layer, relative to each other - gives it flexibility
- proteins are embedded which vary in shape, size and position, like a mosaic
What are the functions of channel protein (intrinsic)?
Provides a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient through membranes
What is the function of carrier proteins (intrinsic)?
Passive transport and active transport into cells. Involves shape of protein changing
What is the function of glycoproteins (intrinsic)?
- cell adhesion and as receptors for chemical signals
- cell communication/ signalling
- cell to cell recognition
What is the function of extrinsic proteins?
To interact with heads of phospholipids or intrinsic proteins
What is an intrinsic protein?
When the protein goes through both layers of the bilayer
What is an extrinsic protein?
Proteins that only sit in one layer of the bilayer
What is the function of cholesterol?
- regulates fluidity of membrane
- adds stability without making them rigid
- prevents them becoming too solid by stopping phospholipids grouping too closely and crystallising
What is the function of glycolipids?
Contains cell markers/antigens and can be recognised by cells of immune system as self or non self
All membranes are _______________ permeable?
Partially
What is cell signalling?
A complex system of intracellular communication
What are the three mechanisms of cell signalling?
1) receptor acts as ion channel
2) receptor activates a G protein
3) receptor acts as an enzyme
Signal molecules fit into __________ molecules on the cell surface ___________?
- receptor
- membrane
What molecules could the signal molecules be?
Neurotransmitters
What structures in the membrane could the signalling molecules be?
Glycolipids, glycoproteins
What is diffusion?
Net movement of particles from an area of high to low concentration until there is an equilibrium
What type of process is diffusion?
Passive process
What is a concentration gradient?
Difference in concentration between two areas
Why does increasing temperature increase the rate of diffusion?
An increase in temperature increases the kinetic energy of the particles which increases collision rate. This increases the rate of diffusion
What factors of cells can affect the rate of diffusion?
- surface area- the larger the area if an exchange surface the higher the rate of diffusion
-thickness of membrane- thicker exchange surface the higher the rate of diffusion
What can diffuse through a phospholipid bilayer and why?
- non-polar molecules
- very small molecules
- small polar molecules e.g. water as it slowly diffuses through lipid based molecules
Why can ions now pass through the phospholipids bilayer?
The hydrophobic interior repels ions so they cannot pass through
What is facilitated diffusion?
The movement of molecules from an area of high to low concentration
What factors affect the rate of diffusion?
- temperature- higher temp=faster diffusion
- surface area- larger surface=faster diffusion
- concentration gradient- higher gradient=faster diffusion
- size of particles- smaller particles=faster diffusion
- diffusion medium- solid=slowest
- liquid=faster
- gas=fastest
What are some factors that affect the rate of facilitated diffusion?
- temperature
- concentration gradient
- surface area
- membrane thickness
-number of channel proteins present
What is meant by the term ‘model cell’?
A human-made set up that represents a cell
Describe the differences between dialysis tubing ans cell membranes with reference to transport across a membrane?
- Dialysis tubing doesn’t have proteins
- no energy in a model cell
Explain why some ions can pass through dialysis tubing by diffusion but can only pass through the cell membrane by facilitated diffusion?
- no hydrophobic interior so cannot repel ions
- permeability of viskin tubing is determined by the size of the particles
What is active transport?
The movement of molecules of ions from an area of low to high concentration (against concentration gradient)
What uses active transport?
- large and charged molecules
- anything that needs to go the opposite way
What is bulk transport?
The movement of large enzymes into or out of the cell
What are the four types of bulk transport?
- endo
- exo
- pino
- phago
What happens in endocytosis?
- bulk transport into cell
- cell surface membrane invaginates
- vesicles are formed
- vesicles pinched off into the cytoplasm
What happens in exocytosis?
- bulk transport out of cell
- vesicles move to and fuses with the cell surface membrane
- releases contents to outside of cell
Active or passive?:
1) diffusion
2) facilitated diffusion
3) active transport
4) bulk transport
1) passive
2) passive
3) active
4) active
Is ATP needed?:
1) diffusion
2) facilitated diffusion
3) active transport
4) bulk transport
1) no
2) no
3) yes
4) yes
Is protein needed?:
1) diffusion
2) facilitated diffusion
3) active transport
4) bulk transport
1) no
2) yes
3) yes
4) no
what is compartmentalisation?
the formation of separate membrane-bound areas in a cell
what types of environments do cells usually exist in?
aqueous environments
why are phospholipid bilayers suited for aqueous environments?
the outer surfaces of the hydrophobic phosphate heads can interact with water
what do intrinsic proteins contain?
amino acids with hydrophobic R-groups on their external surfaces, which interact with the hydrophobic core of the membrane, keeping them in place
what are the intrinsic proteins?
- channel proteins
- carrier proteins
- glycoproteins
what is cell signalling/ communication?
when the chemical binds to the receptor, it elicit a response from the cell. this may cause a direct response or set off a cascade of events inside a cell
What is the movement of water molecules in osmosis?
Random
- move in both directions
- if moving on one side, then the net movement is high to low water potential
Why is equilibrium needed in osmosis?
To ensure cells are normal so they can function
What liquid has the highest water potential?
Distilled water
What is water potential measured in?
Pascals (Pa) - unit of pressure
Describe the process of osmosis when a cell is in water?
Water moves by osmosis from an area of high water potential outside the cell to an area of low water potential inside the cell- this causes the cell to burst (lyses/lysis)
Describe the process of osmosis when the cell is in a solution?
Water moves by osmosis from an area of high water potential inside the cell to an area of high water potential outside the cell- causes cell to shrivel
What is the definition of osmosis?
The net movement of water molecules across a partially permeable membrane from an area of high to low concern traction as a result of random motion
What is the term for high solute concentration?
Hypertonic
What is the term for low solute concentration?
Hypotonic
What is the term for when the solute is at equilibrium with concentration.
Isotonic
What is the term for a shrivelled cell?
Plasmolyzed
What is the term for a cell with water equilibrium?
Flaccid
What is the term for a cell that’s about to burst/ has burst?
Turgid
