Section 2 - Transport across cell membranes Flashcards
What is the function of glycoproteins in the cell-surface membrane?
(5 things)
- Receptors
- Antigens
- Cell signalling
- Receptor for hormone
- Cell adhesion
How can small, non polar substances move through membrane?
Pass through phospholipid bilayer
By simple diffusion
How can large substances move through membrane?
Transport
Carrier proteins
Endocytosis
How can polar substances move through membrane?
Facilitated diffusion
Channel and carrier proteins
Active transport - use of ATP
What is the role of membranes within cells?
Compartmentalisation
Reactions take place on membranes
Enzymes attached to membrane
Nuclear pore permits RNA to leave
Increases surface area of organelle
Why are phospholipids in the cell-surface orientated in a specific way?
Hydrophilic heads attracted to water
Hydrophobic tail repelled by water so they point into centre.
What does cholesterol within the cell-surface membrane do?
Add strength to the membrane
Reduce movement
Reduces fluidity
What is the process of co-transport?
- Sodium ions actively transported out of epithelial cells by sodium-potassium pump
- Low concentration of sodium ions in epithelial cell, so sodium ions diffuses down concentration gradient bringing glucose/ amino acid with it
- Glucose passes into blood plasma by facilitated diffusion
How do bacteria divide?
Binary fission
Replication of DNA
Division of cytoplasm
How does the phospholipid bilayer affect entry and exit of substances into and out of a cell?
Allows movement of lipid soluble/ non-polar molecules
Prevents movement of water soluble molecules
Large molecules do not move through
What are the functions of the cell-surface membrane?
Providing partially permeable barrier Compartmentalisation Transport of solutes Signal transduction Cell to cell recognition
What are the 2 organelles without a membrane?
Ribosome
Centriole
How many nanometres wide are membranes?
7 nm
Why is the cell-surface membrane also known as the fluid mosaic model?
Fluid: individual phospholipids and proteins can move around freely within their monolayer
Mosaic: pattern produced by scattered protein molecules when the membrane is viewed from above
What is the difference between intrinsic and extrinsic proteins in the membrane?
Intrinsic proteins: span the bilayer and form channel/ carrier proteins
Extrinsic proteins: Found on one side of bilayer, involved in cell recognition or act to stabilise membrane
Why are phospholipids important in the membrane?
Form sheets (bilayer)
Hydrophilic heads attract water
Hydrophobic tails repel water
What is the function of the phospholipid in the membrane?
Allow lipid-soluble substances to enter and leave the cell
Prevent water-soluble substances entering and leaving the cell
Make the membrane flexible and self-sealing
What is the function of proteins in the membrane?
Provide structural support
Act as a channels transporting water-soluble substances across
Allow active transport through carrier proteins
Form cell-surface receptors for identifying cells
Acts as receptors
What are the functions of cholesterol in the membrane?
Reduce lateral movement of other molecules including phospholipids
Make membrane less fluid at high temperatures
Prevent leakage of water and dissolved ions from the cell
Why is cholesterol important in the membrane?
Add strength
Limit movement of fatty acid tails by pulling them together
What is the function of glycolipids in the membrane?
Act as a recognition site
Help to maintain stability of the membrane
Help cells to attach forming tissues
What is the function of glycoproteins in the membrane?
Help cells to attach forming tissues
Allows cells to recognise one another
Acts as a recognition site
What are the glycolipids in the membrane made of?
Carbohydrate covalently bonded to a lipid
What are the glycoproteins in the membrane made of?
Carbohydrate attached to extrinsic protein
What is fluidity of the membrane controlled by?
Amount of cholesterol
Length of fatty acid
(shorter increases fluidity)
Proportion of saturated and unsaturated fatty acids
(Saturated decreases fluidity)
Why do most molecules not freely diffuse across the membrane?
Not soluble in lipids
Too large to pass through
Of same charge as protein channel
Electrically charged (polar)
What is the function of the membrane in lysosmes?
Isolated harmful substances to the cell
What is the function of the membrane in mitochondria/ chloroplast?
Controls reaction rate
Increases surface area
Controls rate substances enter
What is the function of the membrane in nucleus?
Forms separate compartment for cells
Allows RNA out in the pores
What is the function of the membrane in vesicles?
Allows substances in and out of cell
What is the function of the membrane in cell surface?
Take up fluid and form membrane-bound vesicles
What is the overall function of the cell-surface membrane?
To control the movement of substances in and out of the cell
Which end of the phospholipid lies towards the inside of the cell-surface membrane?
Hydrophobic tail
What 2 properties should a drug possess if it is to enter a cell rapidly?
Lipid soluble
Small in size
Have no electrical charge
Opposite charge of protein channel
What are the features of facilitated diffusion?
Passive process
Down concentration gradient
No energy is requires
Requires channel or carrier proteins to pass through membrane
What are channel protiens?
Form water-filled hydrophilic channels across membrane
Allow specific water-soluble ions to pass through
Channels are selective, each opening to specific ion
What are carrier proteins?
Molecule fits into proteins
Protein changes shape and molecule passes through
What is osmosis?
Net movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane.
What are 3 factors that affect the rate of diffusion?
Concentration gradient
Diffusion area
Thickness of exchange surface
Temperature
What is the difference between facilitated and simple diffusion?
Facilitated only occurs at channels on the membrane where there are specific protein carrier molecules