Cell Membrane Structure Flashcards
Explain why the structure of a membrane is described as fluid-mosaic
It is simply just a phospholipid bilayer but contains things like protein for transport and cell recognition
Fluid in the model, phospholipid/proteins that can move freely + structure
mosaic in the model is the cell bilayer composed of different parts e.g proteins
Extrinsic
Intrinsic
Cholesterol presented within bilayer
Give two functions of proteins in plasma membrane
- The channel protein is able to transport ions/water by facilitated diffusion
- The carrier protein helps to transport two molecules
Give two functions of the hydrophobic tails in phospholipids in cell membrane
- Maintain different concentration gradient
- Doesn’t pass water-soluble substances through easily
Why can’t an opitcal microscope be used to see plasma membrane?
Wavelength of light is too long to define the membrane
Properties of functions:
Proteins
- Act as a hormone receptor
- Acts as an enzyme
- Involved in active transport
- Act in conjunction with glycolipid as receptors
What is channel proteins?
Transport ions/water molecules by facilitated diffusion
What is carrier proteins?
They will bind to a specific molecule causing it to change shape and release to the other side
facilitated diffusion also ATP for active transport
What does it mean that both channel and carrier proteins are passive?
NO ATP
What is liposome?
Aqueous filled cavity filled with cytoplasm
has a continous barrier of bilayer
What is the main function of cell membrane?
Control the movement of substances in and out of the organelle/cell
What is the phospholipid compromised with?
Hydrophilic heads point outwards
Hydrophobic tails point inwards
How is the membrane flexible and self-sealing?
The structure of phospholipid
- Allow lipid soluble molecules to pass through
- No water soluble molecules
Where can the proteins be located?
Integrated through the membrane - intrinsic proteins
OR
On the surface - extrinsic proteins
What are intrinsic proteins?
Include carrier proteins
Allow substances to cross the membrane
Why is cholesterol important in cell membrane?
Make membrane more rigid
Reduce laternal movement of phospholipid
Prevents leakage of water and dissolved ions from the cell - very hydrophobic
What are glycolipids made from?
Made up of a carbohydrate that is bound to lipids
Function of glycolipids
Extend from the surface of cell - acts as a cell surface receptor for certain molecules
Allow cells to ahere to one another to form tissues
What are glycoproteins?
Carbohydrates that attach to extrinsic proteins
Function of glycoproteins
Act as a cell surface receptor and neurotransmitters
Allow cells to recognize one another as well as attach to form tissues
What does it mean that the cell membrane is partially permeable?
Let some molecules through but not others
Why are receptor cells useful?
Detect chemicals released from the other cells
They signal the cell to respond in some way
Where is cholesterol presented within membrane?
Bilayer
Properties of phospholipids
- Head is hydrophilic
- Tail is hydrophobic
- Molecules automatically arrange themselves into a bilayer - heads face towards water side on either side
- Centre of bilayer is hydrophobic so membrane doesn’t allow water-soluble substance e.g ions
- It acts as a barrier for dissolves substances
Is cholesterol a type of lipid?
Yes
Is cholesterol present in all cell membrane?
Yes
expect bacterial cell membrane
Where is cholesterol held in a membrane?
Fits between phospholipids
Properties of cholesterol
- Bind to hydrophobic tails of phospholipid causing them to pack more closely together
- Restricts movement of phospholipids, making membranes less fluid and more rigid
- Maintain the shape of animal cells, important for cells who aren’t supported by other cells e.g Red blood floating free in blood
What are the different conditions that affects permeability of the cell membrane
- Temperature
- Solvent conditions
How can you investigate permeability in a more practical sense?
Beetroot cells containing coloured pigment that leaks out
Higher permeability of the membrane , more pigment leaks out the cell
Instructions of temperature affecting beetroot membrane permeability
- Use a scapel to carefully cut five pieces of beetroot in euqal sixes
- Rinse the pieces to remove pigment while cutting
- Add five pieces to five different test tubes containg 5 cm3 of water - use measuring cylinder
- Place each test tube in a water bath at different temperatures for same length of time
- Remove pieces of beetroot , leaving coloured liquid
- Coloirmeter to computer to collect data and draw a graph
What is a colorimeter?
A machine that passes light through liquid to measure how much light is absorbed
The higher the absorbance , more pigment is released - higher permeability
Why you need to be careful with colorimeter?
Need 5 minutes to stabilise before using and calibrating at zero
before taking a measurement through pure water
What happens to the cell membrane with a temperature below 0 degree Celsius?
Phospholipid don’t have much energy so can’t move much
Packed closely together and membrane is rigid
Channel and carrier proteins may deform, increasing permeability of the membrane
Ice crystals may form pierce , higher permeability
What happens to the cell membrane with temperature between 0 and 45 degree celisus?
Phospholipid can move around and aren’t packed tightly together
The membrane is partially permeable
Temperature increases, phospholipid move more as they have more energy
Increases permeability of the membrane
What happens to the cell membrane with temperatures above 45-degree celsius?
Phospholipid bilayer start to melt and the membrane becomes more permeable
Water inside the cell expands putting pressure on the membrane
Channel proteins and carrier proteins deform , control what enters or leaves
Increases permeability
Why is it important membranes allow recognition by other cells - importance to immune system
Use of glycoproteins/glycolipids - identify self cells
White blood cells don’t attack them
Allow identification of foreign cells/pathogens via their antigen
Identify two functions of the cell membrane
- Controls/maintains the two environment
- Cell communication - chemical detection via receptors
Identify two organelles and important of membrane in them
- Mitochondria - contains enzyme for respiration - increase SA for these reaction
- Nucleus - allows RNA to leave in transcription
The more unsaturated fatty acids present in the membrane the more fluid it is. Cholesterol also affects the fluidity of the membrane.
Why is it key that there isn’t too much or too little cholesterol present in the membrane for optimum cell function?
– Too much cholesterol will make the membrane too rigid/less fluid and make exchange less efficient.
-Too little cholesterol will mean that the membrane is too fluid and breaks up/doesn’t provide the necessary structure
Identify two types of molecules that can pass directly through the phospholipid bilayer.
O2,
CO2,
Uncharged,
Small
Identify two types of molecules that cannot pass directly through the membrane and give examples of each
- Large molecules e.g proteins, glucose
- Charged molecule e.g. Na+ Cl- , K
Which molecules can just diffuse straight through the cell membrane?
Small non-polar molecules
e.g oxygen and carbon dioxide
How is water transported?
Water is polar so doesn’t diffuse easily
Move into cells through aquaporins
Give one function of X.Y( glycoprotein/glycolipid)
- Surface/extrinsic protein
- Cell recognition
- Binding to hormones
- Identification
Explain three features of a plasma membrane adapt for its functions
Extrinsic proteins
Glyproteins
Glycolipid
Act as antigens
Act as receptors
