Cell Membranes- Topic 2B Flashcards
What molecules can be found in a plasma membrane?
Phospholipids Proteins (carrier and channel) Cholesterol Glycolipids Glycoproteins
Name the functions of a cholesterol molecule in a membrane?
Reduces lateral movement of other molecules (phospholipids)
Makes membrane less fluid @ high temps
Prevents leakage of water and dissolved ions from the cell.
Name the functions of glycolipids
Act as recognition sites
Help maintain the stability of the membrane
Help cells to attach to one another and so form tissues.
The functions of glycoproteins in the membrane are…
Act as recognition sites
Help cells to attach to one another and so form tissues
Allows cells to recognise one another
Name the functions of proteins in the membrane
Provide structural support
Act as channels for transporting substances
Forms cell-surface receptors for identifying cells
Help cells adhere together
Act as receptors e.g hormones
Only what type of substances can be transported across the membrane?
Water-soluble substances
How does a colorimeter work?
Uses the light passed through the liquid & measures the amount of light that has been absorbed.
What two things could be your independent variable?
The concentration of solvent
The temperature of the water baths.
How can you remove any pigment released from cutting the beetroot?
Rinse the pieces after cutting them.
On a graph which axis do you plot which variables on?
The “independent variable” goes on the x axis
The “dependent variable” goes on the y axis
Define diffusion:
Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration
Why would larger molecules take a while to diffuse through the bilayer?
Because they are so big
Other than large particles, what other molecules would diffuse slowly?
Ions and polar molecules because they’re water soluble and the centre of the bilayer is HYDROPHOBIC
What is different about facilitated diffusion?
Large or charged particles diffuse through carrier proteins or channel proteins
What type of process can diffusion and facilitated diffusion be classed as?
Passive processes- they don’t use energy.
Carrier proteins move ….. ……… across membranes
Carrier proteins move large molecules across membranes
Channel proteins form pores in the membranes for ……. ……… to diffuse through.
Channel proteins form pores in the membrane for charges particles to diffuse through.
What factors does the rate of (simple) diffusion depend on?
Concentration gradient
The thickness of the exchange surface
The surface area (microvilli in epithelial cells)
What factors does facilitated diffusion depend on?
The concentration gradient
The number of channel or carrier proteins
Define Osmosis
The diffusion of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential
What is water potential?
The potential of water molecules to diffuse out of or into a solution
Pure water has the ……. water potential. This means ALL solutions have a ……. water potential than pure water.
Pure water has the highest water potential. All solutions have a lower water potential than pure water
If two solutions have the same water potential, what are they said to be?
ISOTONIC
List the factors affecting the rate of osmosis?
The water potential gradient
The thickness of the exchange surface
The surface area of exchange surface
What type of protein does active transport use?
Carrier proteins.
Co transporters are a type of ….. ……..
Carrier protein.
What are the factors affecting the rate of active transport?
The speed of the individual carrier proteins
The number of carrier proteins
The rate of respiration in the cell and the availability of ATP.
Glucose is absorbed by ……………….. in the Mammalian Ileum
Co transport
Glucose enters the ileum epithelium with …. ……..
sodium ions
Why is energy needed for active transport?
Energy is needed to transport solutes against the concentration gradient.
Describe the process by which energy is released by the cell for active transport.
energy is released by the hydrolysis of ATP into inorganic phosphate.
Why would the diffusion of chloride ions across a cell-surface membrane be extremely slow?
Because ions are water soluble and the centre of the phospholipid bilayer is hydrophobic.
What are plasmids and where are they found?
Plasmids are small loops of DNA, found in bacterial cells.
Name 5 ways that prokaryotic cells differ from eukaryotic cells
cytoplasm lacks membrane bound organelles
They are much smaller
smaller ribosomes
no nucleus
cell wall contains MUREIN. (glycoprotein)
How many microns in 1mm?
1,000
What is the difference between resolution and magnification?
Resolution=how well a microscope distinguishes between two points close together
Magnification= How much bigger the image is than the specimen
What does an optical microscope use to form an image?
Light
Why are electron microscopes better than light microscopes?
They have a higher resolution and magnification
Why are light microscopes better than electron microscopes?
Can observe living cells.
What are the two types of electron microscopes?
Transmission or Scanning
How do Transmission microscopes work?
They use electromagnets to focus a beam of electrons which is transmitted through the specimen, the denser parts of the specimen absorb more electrons making it look darker.
What is a pro and con to using a Transmission microscope?
Can only be used on thin specimens but have higher resolutions
How do Scanning microscopes work?
Scan a beam of electrons across the specimen which knocks off electrons from the specimen and are gathered in a cathode ray tube to form an image.
What is a pro and a con to using a scanning microscope?
They can be used on thick specimens BUT they have a lower resolution.
What can you use on a specimen to highlight objects in the cell?
A stain, e.g. iodine in potassium iodide solution for starch granules
Why should you avoid air bubbles in your specimen when using the cover slip ?
As they’ll obstruct your view of the specimen.
Name the 3 stages of Cell fractionation
Homogenisation- breaking up the cells
Filtration- Getting rid of the big bits
Ultracentrifugation- separating the organelles
What do channel proteins allow charged particles to do?
DIFFUSE through the membrane.
How are phospholipids always arranged?
fatty acids towards the middle due to hydrophobic (repelled by water)
the hydrophilic phosphate (attracted to water) acts as a barrier
How can we describe carrier proteins being “full”?
All working at their maximum= no further uptake
