Transport across cell membranes Flashcards
What are the components in cell membranes?
- glycoproteins
- glycolipids
- phospholipids
- proteins
- Cholesterol
What is the role of cholesterol?
- reduces fluidity, and makes the membrane less fluid at high temperatures
- strengthens the plasma membrane
- joins fatty acid tails of phospholipid together, limiting movement
- prevents leakage of water and dissolved ions
What is the role of glycolipids?
- form tissues
-cell recognition - maintain stability
What are glycolipids?
- They are carbohydrate covalently bonded with a lipid
- They spread throughout the cell surface membrane
What are the roles of glycolipids?
- act as recognition sites
- maintain stability
- help attach cells to one another and form tissues
What is a glycoprotein?
carbohydates chains that are attached to extrinsic proteins on the cell surface membrane
What is the role of glycoprotein?
- cell recognition
- forms tissues
- allow cells to recognise each other
What is the structure of phospholipids?
- Hydrophillic head and hydrophobic tail
- the hydrophillic heads of both phospholipid layers point to the outside of the cell surface membrane and attracted to water on both sides
- the hydrophobic heads of both phospholipid layers point into the centre of the cell surface membrane, repelled by water on both sides
What is the role of phospholipids?
- Allow lipid soluble molecules to enter and leave
- prevent water soluble molecules entering and leaving
- make the membrane flexible and self-healing
Why is the cell membrane called a fluid - mosaic model?
Fluid = phospholipids allow movement and flexibility
Mosaic = All the proteins and molecules have different shapes, sizes and patterns
What is osmosis?
- the movement of water from a high water potential to a lower water potential through a partially permeable membrane
How is water potential measured?
- the greek letter psi, water potentail of solutions are always negative. The more neagtive, the lower the water potential
what happens when cells are in solutions of a higher, lower and equal water potential
Higher = enters cell, swells and bursts
Equal = no change
Lower = leaves cell, shrinks
What is diffusion?
- diffusion is the net movement of molecules from a high concentration to one of a lower concentration until molecules are evenly distributed
What molecules can be simply diffused?
- small
- non polar
- soluble
- examples are oxygen and carbon dioxide
What occurs in simple diffusion?
- molecules move directly across the phospholipid bilayer
Why does facilitated diffusion occur?
- polar and large molecules interfere with the hydrophobic nature of the phospholipid bilayer, making diffusion harder
What occurs with faciliated diffusion
proteins channels = they allow water - soluble ions to pass through, only for specific molecules
Carrier proteins = bind to molecules, this causes them to change shape and allow the molecule to diffuse
What is active transport?
The movement of molecules from a low concentration gradient to a high concentration gradient across a partially membrane and using ATP and carrier proteins
Describe the process of active transport
- molecules or ions bind to carrier proteins
- this causes a molecule of ATP to bind to protein, and ADP and a phosphate molecule is formed
- this reaction causes the shape of the carrier protein to change and transport the molecule
- the phosphate molecule then leaves, causing it to revert to its normal shape
Contrast active transport and facilitated diffusion
- Active transport is active whereas facilitated diffusion is passive
- ## active transport is agaisnt a concentration gradient and facilitated diffusion is down
Why does co transport occur?
- in the illuem, facilitated diffusion occurs and this causes diffusion from the cavity of illeum to diffuse into epithelial cells and then to the blood stream
- however as this is through facillitated diffusion, the best results are an equal concentration of glucose on either side of the epithelieum cell
What is the process of co transport?
- a sodium - potassium pump actively transports sodium out of epithelial cells
- this causes a concentration gradient as there is a low sodium concentration within epithelium cells
- this causes sodium to be transported in through a co transport protein. Along with the molecule of sodium, glucose is also transported in.
- this is indirect active transport
What is the difference between carrier proteins and protein channels?
protein channels = form water filled tubes and allow water soluble ions to diffuse across the membrane
Carrier proteins = bind to ions or molecules and have a change in shape to move the molecules across the membrane
