Chapter 1- Cells- Membranes Flashcards
Draw structure of a phospholipid
Martha.
Draw and label the structure of membranes
Do it
(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
-what is the structure of a phospholipid? And what is this called?
Consists of a polar head (hydrophilic) made from glycerol and phosphate and 2 non-polar fatty acid tails (hydrophobic)
2) called amphipathic
(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
What does hydrophilic and hydrophobic mean?
Hydrophilic- substance is attracted to water
Hydrophobic- are not attracted to water
(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
- fatty acid ‘tails’ don’t strongly attach one another membranes what does this allow?
Fluid or flexible which allowed animal cells to have variable shapes and also allows process of endocytosis
(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
Why do phospholipids arrange in a double layer?
As when phospholipids are mixed with water the phosphate heads are attracted to the water but the tales are attracted to each other not the water
(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
What is the primary function of membranes?
To form a barrier which ions and hydrophilic molecules cannot easily pass
What does cholesterol do in phospholipids?
1) Role in determining membrane fluidity which changes the temp
2) disrupts the regular packaging of the hydrocarbon tails of phospholipid molecules so prevents them from crystallising and behaving as a solid
3) restricts fluidity of membrane
4) reduces permeability to hydrophilic particles such as sodium ions and hydrogen ions
5) due to shape can help membranes curve to become concave which helps formation of vesicles during endocytosis
What does proteins create in phospholipids?
Creates extreme diversity in membrane function
Wha role does intergralproteins have in phospholipids?
Are hydrophobic and are embedded in the hydrocarbon chains in the centre of the membrane- many are transmembrane- they extend across the membrane, with hydrophilic parts projecting through regions
What does peripheral protein remain bound to in phospholipids?
Hydrophilic so remain on surface- some have a single hydrocarbon chain attached to them which is inserted into the membrane, anchoring the protein to the membrane surface
What are the 6 functions of membrane proteins?
1) hormone binding site (hormone receptor)
2) immobilised enzymes with the active site on the outside
3) cell adhesion to form tight junctions between groups of cells in tissues and organs
4) cell to cell communication
5) channels for passive transport to allow hydrophilic particles across by facilitated diffusion
6) pumps for active transport which use ATP to move particles across the membrane
What are the 2 transport mechanisms in regard to functions of membrane proteins?
Protein channels (facilitated) and protein pumps (active)
definition of diffusion
Net movement of particles from a high region concentration to a low concentration
Definition of osmosis
Net movement of water molecules across a semi-permeable mebrane from a high region of low solute concentration to a high concentration
Definition of simple diffusion
Small, non-polar molecules can freely diffuse across the membrane - passive diffusion across semi-permeable membrane
Definition of facilitied diffusion
Larger, polar substances (ions, macromolecules) can’t freely diffuse and require assistance of transport proteins (carrier proteins/channel proteins to help their movement)
Explain the role of protein pumps and ATP in active transport across membranes:
- what is active transport?
Is the passage of materials against conc. gradients (low–>high)
(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
What does active transport require?
Requires use of protein pump which uses ATP energy to translocate the molecules against the gradient
(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
What does hydrolysis of ATP causes?
A conformational change in the protein pump takes place using the energy from ATP resulting in forced movement of substances
(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of
Protein pumps are what for given molecules? Which allows them to?
Are specific for given molecules allowing them to regulate movement
(Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain structure of cell membrane)
Draw protein channel, Carrier protein and protein pump
Lallalal
(Explain how vesicles are used to transport materials with a cell between the ER, Golgi apparatus, plasma membrane)
-how does a polypeptide get to the ER?
There designed for secretion and contain an initial target sequence which directs the ribosome to the ER
(Explain how vesicles are used to transport materials with a cell between the ER, Golgi apparatus, plasma membrane)
What happens when polypeptide reaches ER?
Continues to be synthesised by ribosomes into lumen of ER, where signal sequence is removed from Nascent chain
(Explain how vesicles are used to transport materials with a cell between the ER, Golgi apparatus, plasma membrane)
Where is polypeptide chain transferred to after ER and via what?
To the Golgi apparatus via a vesicle which forms from a budding membrane
(Explain how vesicles are used to transport materials with a cell between the ER, Golgi apparatus, plasma membrane)
Finally the polypeptide is transferred from the Golgi apparatus to what? Via what? And what happens to it?
Via a vesicle to the plasma membrane where it the protein is secreted
(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
- what is membrane principally held together by?
The relatively weak hydrophobic associations between phospholipids
(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
- what does the associations between weak Hydrogen bonds and phospholipids allow membranes to do?
Allows membranes to have fluidity/flexibility as the phospholipids can move to some extent–> allows for breaking/remaking of membranes allowing larger substances access in and out of cell
(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
What is endocytosis and what are in the vesicles?
1) Process in which large substances enter cell without travelling across the plasma membrane
2) contain water and solute a from outside the cells, or larger molecules needed by the cell which can’t pass through the plasma membrane
(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
How does it work? (Endocytosis)
1) Vesicles can be formed by pinching off a small piece of the plasma membrane of cells.
2) the vesicles is formed in the inside of the plasma membrane
3) it contains material that was outside the cell
(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
What are the main 2 types of endocytosis?
Phagocytosis and pinocytosis
(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
What is the process of phagocytosis?
Process by which solid substances (eg food particles) are ingested
(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
What is pinocytosis?
Process by which liquids/solutions (eg dissolved substances) are ingested by cell
(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
What is exocytosis?
Process in which large substances exit without passing across plasmic membrane
(Describe how the fluidity of the membrane allows it to change shape,break and reform during endocytosis or exocytosis)
How does exocytosis work
Vesicles fuse with plasma membrane expelling their contents into extracellular environment
Explain full process of endocytosis through to protein syntheses to exocytosis
1) ENDOCYTOSIS–> part of plasma membrane is pulled inwards, a droplet of fluid becomes enclosed and vesicles is pinched off, vesicles then move through the cytoplasm carrying their contents
2) proteins are synthesised by ribosomes and enter rough endoplasmic reticulum
3) vesicles bud off from the rER and carry the proteins to the Golgi apparatus
4) Golgi apparatus modifies the proteins
5) vesicles bud off from the Golgi apparatus and carry the modified proteins to the plasma membrane
6) EXOCYTOSIS –> vesicles fuse with the plasma membrane, the contents of the vesicles are expelled, the membrane flattens out again
What protein channels?
Channels are holes with a very narrow diameter. The walls of the channel consist of protein- the diameter and the chemical properties of the channel ensure that only one type of particle passes through
