Transport Over Membranes Flashcards
Explain the phospholipid bilayer in the fluid mosaic model
Phospholipids form a bilayer with hydrophilic heads pointing out (attracted to the water) and hydrophobic tails point inwards (repelled by water)
What are the functions of the phospholipids in the membrane
Allow lipid soluble substances to enter/leave but prevent water soluble substances. Make the membrane flexible and self sealing
1. Form water impermeable barrier to water soluble substances/ allows non polar molecules to pass through
2. Able to fuse with other membranes/ form vesicles
Describe a phospholipid
ONE phosphate head, TWO fatty acid tails, also glycerol
Functions of proteins in the membrane
Structural support, channels to transport water soluble molecules, allow active transport through carrier proteins, form cell surface receptors, help cells adhere together
Functions of cholesterol in the membrane
Add strength to the membranes, they are hydrophobic so prevent water loss and dissolved ions leaving the cell, they pull fatty acid tails of phospholipids (limiting their movements without making membrane rigid
What makes up the mosaic model membrane
Phospholipids, cholesterol, glycolipids, glycoproteins, proteins
Why is the fluid mosaic called that
Fluid as the phospholipids can move (gives membrane flexible structure so can change shape), mosaic because proteins are imbedded in the bilayer
Diffusion definition
The net movement of molecules or ions from a region where they a more highly concentrated to one where their concentration is lower until they are evenly distributed
What kind of molecules can diffuse across a membrane
Small, non polar (like oxygen or carbon dioxide), lipid soluble
What are factors affecting diffusion
Temperature (increasing in kinetic energy makes membrane more permeable) molecular size, concentration gradient steepness
What is facilitated diffusion
Protein specific to substance, and binds to a carrier/channel protein, moves down a concentration gradient
Describe how protein channels work
They form water filled hydrophilic channels across the membrane. They allow water soluble ions to pass through. The channels are selective (control over entry and exit) the ions bind with the protein causing it to change shape (closes and opens both sides of membrane)
What are affecting factors of facilitated diffusion
Temperature, conc gradient steepness, number of channels available in membrane
Osmosis definition
Passage of water from a region where it has a higher water potential to a region where it has a lower water potential , through a selectively permeable membrane
What is a solute
A substance dissolved in a solvent
What is water potential presented by and what is it measured in
Psi and measured in kPa (kilopascals)
What water potential does pure water have
0
What will lower water potential
Addition of solute
What does a more negative value mean in terms of water potential
Lower water potential
When will osmosis continue until
Dynamic equilibrium is reached (no net movement of water)
What does isotonic mean
Water potential is the same on internal and external
The effect of solution with a higher water potential on a red blood cell
The water enters the cell through osmosis and the cell swells and bursts meaning it’s contents (haemoglobin) are released
The effect of an external solution having lower water potential than a red blood cell
Water potential of solution is lower so water leaves the cell through osmosis making it shrink
The effect of a solution with higher water potential on a plant cell
Water enters cell through osmosis , protoplast swells and the cell becomes turgid
What is the state of a plant cell in isotonic solution
Incipient plasmolysis
The effect of a solution with lower water potential on a plant cell
Water leaves cell through osmosis , protoplast shrinks and cell is plasmolysed
Active transport definition
The movement of molecules into/out of a cell from a region of lower concentration to higher concentration using ATP and carrier proteins
How does active transport differ from other transport methods
Metabolic energy in the form of atp is needed, substances are moved against a concentration gradient (low to high), carrier proteins act as pumps, selective process
Describe the active transport of a single molecule
1 Carrier proteins bind to the molecule, (molecule binds to receptor sites on proteins) 2. On inside of cell, ATP binds to protein, causing it to split into ADP + phosphate molecule Which cause protein molecule to change shape and open at opposite side of membrane and molecule released 3. Release causes protein to revert and phosphate recombined to form ATP
Differences between active transport and facilitated diffusion
Facilitated is passive, active is requires energy. Active occurs against a conc gradient but facilitated goes down conc gradient
Similarities between active transport and facilitated diffusion
Both involve carrier proteins
Which cells posses micro villi and what does it do
Epithelial cells lining the ileum, microvilli provide more surface area for insertion of carrier proteins so diffusion, facilitated diffusion and active transport can take place
What’s are methods to increase rate transport across membranes
Increase number of protein channels&carrier proteins and increase the surface are via microvilli for insertion of protein channels/carrier proteins
Describe co transport
- Na+ ions are actively transported OUT of epithelial cells via sodium potassium pump into the blood 2. This maintains a higher conc of Na+ ions in the lumen of intestine than in epithelial cells 3. Na+ diffuse into the epithelial cells via facilitated diffusion down this conc gradient through a protein carrier but as they diffuse in, they carry either an AA or glucose molecule with them, AGAINST their conc gradient
What powers the glucose into the cell during co transport
The sodium ion concentration gradient, rather than ATP, making it an indirect form of active transport
What are the functions of extrinsic proteins in the CSM
Act as cell recognition sites/ for cell recognition, binding to hormones, identification of cell
