Section 2:Transport across membranes Flashcards
Five points
What are the main functions of the cell membrane?
- Acts as a barrier
- Acts as a site for cell recognition
- It acts as for binding hormones/transmitter chemicals via protein receptor molecules
- To allow communication between cells
- Forms impermeable barrier to water soluble substances
Describe the molecules of the cell membrane structure
Phosphollipid bilayer, proteins, cholesterol and carbohydrates
Describe the structure of a triglyceride
Glycerol binded to three fatty acid chains by an ester bond
What’s the difference between saturated and unsaturated fatty acids?
Unsaturated fatty acids have a double bond(s), this means that the carbon atoms are not bonded to all the hydrogen atoms as possible
Why is the cell membrane described as ‘fluid mosaic’?
Fluid~molecules of phospholipid and proteins have a degree of mobility within the membrane
Mosaic~proteins and phospholipids ‘fit’ together to form together patchwork of molecules
Describe the structure of a phospholipid
Hydrophillic polar charged head
Hydrophobic non-polar tail
How are phospholipids arranged in the cell surface membrane?
Bilayer~hydrophilic phosphate head facing outwards and hydrophobic fatty acid tails facing inwards
What type of proteins are found in the cell membrane?
Glycoproteins, channel proteins and carrier proteins
What are the roles of proteins in the cell membrane?
Help substances ,e.g. ions,sugars and amino acids, that cannot diffuse across the membrane but are vital to a cell’s functioning
Six points
What are the functions of the proteins?
- Carrier molecules
- Channels and pumps for ions and other substances
- Enzymes to speed up surface reactions
- Receptors for hormones
- Recognition sites for for identifying types of cells
- Adhesion sites to allow cells to stick together
What is a glycoprotein?
A protein with a carbohydrate (polysaccharide)attached to it
What is a glycolipid?
A lipid with a carbohydrate(polysaccharide) attached to it
What is the role of glycoproteins and glycolipids?
Involved in cell-cell signalling and cells recognising one another
What is the role of cholesterol in the cell membrane?
Important in keeping membranes stable at normal body temperature-without it,cells would burst without it
Define passive diffusion
The net movement of molecules or ions from an area of higher concentration to an area of low concentration
What factors that affect diffusion rate?
- Difference in concentration~faster when there is a greater difference
- Surface area~faster when larger surface area
- Thickness of cell membrane~faster when thinner
- Temperature~faster at higher temperature
What is fick’s law ?
surface area x difference in concentration/thickness of substance
Five points
How do carrier proteins work?
- The molecule to be transported to binds to the carrier protein
- Molecules must be complementary in shape to the carrier and able to bind
- As a result, binding the carrier protein changes shape
- The molecule to be transported is delivered to the other side of the membrane as a result
- The carrier returns to normal shape
Explain the difference between simple diffusion and facilitated diffusion
SD~is the movement of particles freely across the plasma membrane from a high conc to low conc
FD~when protein carriers or channels are used to facilitate diffusion.This is process is also passive,doesn’t require ATP
Define osmosis
The passage of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane
Why is water potential of a substance always less than 0 and what is measured in?
Distilled water has a water potential of 0 which is the highest possible water
Measured in kPa
What happens to water potential as solute is added?
The water potential lowers
What happens to an animal cell when placed in:
* hyponotic solution
* isotonic solution
* hypertonic solution
- Hyponotic~water enters,cells swells and may burst (lysis)
- Isotonic~no net movement of water,cell normal size
- Hypertonic~water leaves,cell shrinks and crenates
What happens when a plant cell is placed in:
* Hypotonic solution
* Isotonic solution
* Hypertonic solution
- Hypotonic~water enters,cell swells a bit and becomes turgid
- Isotonic~not net movement of water,cell normal size and incipient plasmolysis
- Hypertonic~water leaves,cytoplasm shrinks and plasmolyses
