Cell Membrane Flashcards
What carries the code for reactions?
DNA
How do you increase the chances of a reaction occurring?
By containing any potential reactions in a small space
What are the most important evolutionary step forward for life on earth
DNA and cell membrane
What cells have cell membranes?
>Eukaryotic cells
>Prokaryotic cells
Both
What organelles have their own cell membrane?
Nucleus + Mitochondria (+many more)
What is the structure of a cell membrane?
Thin “film” of specialised lipids held together by non-covalent bonds (van der Waals forces and hydrogen bonds).
Membranes are fluid structures, arranged as a bilayer.
What regulates nearly all the functions of the membrane
Proteins
What other molecules associate with membranes
Proteins and Sugars
Functions of Membranes
> Transporting molecules to and from the cell and organelles
Enzyme reactions
Structural links with the cells cytoskeleton
Receptors helping relay information between cells and organelles
The bilayer is largely impermeable to…
Water and water-soluble molecules
What 2 important observations do electron microscopes provide?
- The membrane is a bilayer
2.It is not uniform - there are bumps (so it’s not just a bilayer)
What are the 2 parts of a phospholipid
- A hydrophilic “polar” head region that likes water
- A hydrophobic tail that repels water
What does cholesterol do?
Makes a mebrane firm, protects it from damage and helps bind certain proteins
What is it called when the head groups bond with each other and tails bond with other tails
Amphipathic
What is a micelle
Small spheres with hydrophobic core
What is a film
Bilayer sheets
What is permeable through a phospholipid bilayer
Small hydrophobic (oxygen + carbon dioxide) and small uncharged molecules (e.g. water and ethanol)
What is impermeable through a phospholipid bilayer
- Larger polar molecules (such as glucose and amino acids)
- Ions (such as sodium, calcium and potassium)
Membrane fluidity occurs in three directions:
- Within the one of the membranes leaflets (lateral diffusion, which is very fast)
- Between the leaflets (so called “flip-flop” movement, which is very slow)
3.The molecule can twist on its own axis (spin)
What are lipid rafts
Areas of membrane that have more cholesterol, sphingolipids and saturated phospholipids than other areas
There are many proteins associated with membranes. They integrate and associate with the membrane in different ways.
Two types of association:
- Integral Proteins (embedded through the membrane), e.g the insulin receptor
- Peripheral proteins (loosely or periodically associated) e.g cytochrome C which is released from the mitochondria of dying cells
Three main mechanisms that transport molecules across a membrane (+meaning)
Simple Diffusion- molecules (e.g. carbon dioxide) move through the membrane from an area of high to low concentration
Facilitated Diffusion- involves the use of proteins to assist the movement of larger, polar, or charged molecules down their concentration gradient (e.g. glucose)
Active Transport- This moves molecules against their concentration gradient
What transport types across a membrane are passive and what are not passive (and what does this mean)
Simple diffusion and Facilitated Diffusion are both passive meaning they do not require energy.
Active Transport is not passive as it does require energy
What does it meaning ikf the net charge of all the ions is lower on the inside of the cell compared to the outside
They are polarised
