Biochemical Nature Of The Cell Membrane
Cellular Level of Organization
- Compartmentalization of chemical reactions within the specialized structures
- Regulate the materials in and out
- Genetic material is used to direct cell activity
Cytology is the study of a cellular structure
Cell Physiology is the study of cellular function
- Is made up of a lipid bilayer (proteins, carbohydrates and cholesterol)
- (Cholesterol)Unsaturated Fatty Acids make the cell membrane fluid rather than rigid
- (Protein and Carbohydrates)The outer surface communicates with hormones and neurotransmitters.
- Flexible barrier that surrounds the cytoplasm of the cell. 50% lipid and 50% protein held together by hydrogen bonds.
- 50 Lipid molecule to every 1 protein.
- Lipids are the entry and exit barrier of polar substances and proteins are gate keepers.
- Make up 75% of lipids
- Have a bilayer (2 parallel layers of molecules)
- Each molecule has both polar (hydrophilic heads) and non-polar (hydrophobic tails)areas (amphipathic). The hydrophilic heads are on the outside and the hydrophobic tails like up next to each other inside. Does my picture makes sense ?
||||||| or :==: with the hydrophobic lines inside
Glycolipids within the Cell Membrane:
- Make up 5% of lipids of the cell membrane
- Carbohydrate groups form polar (hydrophilic) heads only on the side facing the extracellular fluid.
- Glycocalyx* is a carbohydrate covering the surface of a red blood cell. It’s role is to protect the cell’s surface and to give cell recognition and blood type (BT A has A antigen, BT B has B antigen, BT AB has A and B antigen, BT O has neither antigen)
- Makes up the other 20% of the lipids. (75% phospholipid, 5% glycolipid)
- Stuck between the other lipids in bilayer
- Steroid rings and hydrocarbons are nonpolar and so like to live in the middle of the cell membrane.
- Extend across cell (if it reaches it is a transmembrane protien)
- All are amphiathic with hydrophobic tails hiding with phospholipid tails.
- Glycoproteins have sugar portion facing extracellular fluid (forms a Glycocalyx*)
- Protects cell from digestion, makes the stickiness to hold to a fluid layer (making a slippery surface)
- Attached to inner or outer surface of cell membrane
- Easily removable
Function of Membrane Protein
- Makes a channel = allows specific substances to pass through
- Transports proteins = binds a substance and changes its shape so it can move across membrane
- Receptor proteins = cellular recognition so binding can occur
- Cell Identity Marker = can be recognised by other cells
- Linker = attaches proteins to other cells in cell membrane
- Cell shape and structure allow cell moment
- Act as an Enzyme allows reactions to be sped up.
- Self sealing (will reseal when penctured)
- Membrane molecules can rotate and move freely – but it is hard for hydrophilic molecules to pass the hydrophobic core of the lipid bilayer
- The fluidity is affected by the cholesterol and the temperature, it stiffens in higher temps.
- Semipermeable (“it allows nutrients to enter the cell and waste products to leave”)
The Lipid Bilayer is Permeable to:
- nonpolar molecules
- uncharged molecules
- Water – flows through gaps that form in the hydrophobic membrane as phospholipids move around
Transmembrane Proteins Acts as a Permeable Channel to:
- Small and medium polar molecules
- Charged particles
Macromolecules that are unable to pass through the membrane use vesicular transport.
Transport Across Membrane
Concentration Gradient :
- Inside and outside the Membrane have a different concentration of substances (concentration gradient).
- The membrane can maintain the difference in charged ions inside and outside of the membrane (membrane potential). Things move down their concentration gradient towards the opposite charged area – Trying to even it out it makes them move. This is another way for transport across the plasma membrane.
Ways to cross:
- Transporter proteins assistance (mediated)
- Doesn’t use a transporter protein (non-mediated)
- ATP is used to drive the substance against their gradient (a way which doesn’t occur without energy)
- Passive Transport – where they go with the flow (follow the gradient with kinetic energy)
- Vesicular transport – moves substance across membrane in small vesicles (usinf endocytosis or exocytosis)
- Random mixture of particles as a result of particle potential energy: movement from higher concentration to lover concentration gradient
- The further it is from the current concentration gradient or surface area the faster diffusion happens
- The higher the temperature the faster it diffuses
- The further the distance, the slower diffusion happens.
- Only when it is even will equilibrium be reached.
- (Facilitated diffusion us when a substance binds to a transporter protein and only occurs during down concentration gradient, without a gradient to travel down there is no movement. In the facilitated diffusion of glucose, once glucose had binded to a protein – the transport protein changes shape then moves across the down concentration gradient)
- Movement through water through a selectively permeable membrane from a level of high water concentration to a low water concentration (like diffusion)
- Diffusion through lipid bilayer (important for absorption of nutrients and getting rid of waste)
- Only happens if the membrane is permeable to water but not o specific solids.
- Channels which the water can pass through (aquaporins a transmembrane protein) can be open all the time or gated (closed at random or by order).
ATP – Active Transport
- Movment of polar or charged substances move against their gradient, the energy used comes from the hydrolysis of ATP