B.2.1 HL Flashcards
what is the relationship between fatty acid composition of bilayers and their fluidity?
The plasma membrane is fluid because the phospholipids at its core can rotate or drift laterally. Optimal membrane fluidity allows for molecules to diffuse through the membrane to areas of the cell where they’re needed, it facilitates interactions between proteins. It also allows membranes to fuse and ensures even distribution of membrane molecules. Temperature has an effect on membrane fluidity. Organisms adapt to their habitats temperatures so that the membrane has appropriate fluidity. Fatty acids have hydrocarbon chains and the longer the phospholipid tails, the less fluid the membrane will be. Saturated fatty acids have no double bonds and form straight chains which cause:
- Decrease in fluidity
- More density
- A lot of bonds
- Higher melting points
Unsaturated fatty acids have double bonds causing them to bend and as an effect have:
- Increased fluidity
- Less density
- Kinks create space
- Lower melting points
Adaptation to lower temperatures results in an increase of unsaturated fatty acids in membranes. High temperatures cause organisms to increase saturation of fatty acids. The saturation of membrane lipids can vary within the body of a single organism
How does cholesterol affect membrane fluidity?
In addition to phospholipids, animal cell membranes also have cholesterol. It is an amphipathic lipid which modulates membrane fluidity and permeability to certain solutes. Cholesterol is composed by:
- Hydroxyl group linked at one end -> hydrophilic and polar
- Four linked hydrocarbon rings -> hydrophobic and non polar
- A hydrocarbon tail linked to the other end -> hydrophobic and non polar.
Cholesterol inserts into the bilayer disguised as a phospholipid and the phospholipid and cholesterol heads create hydrogen bonds with each other. Cholesterol is a modulator of membrane fluidity, adjusts it. At high temperatures it restrains the movement of fatty acids, stabilizes the membrane, restrains the movement of fatty acids and causes less fluidity and less permeability to small molecules. At low temperatures, it prevents stiffening of the membrane, doesn’t allow fatty acids to pack tightly but maintains membrane fluidity.
Explain the fusion and formation of vesicles.
Phospholipids can move with the bilayer making the membrane fluid. Bulk transport refers to transport in mass for which vesicles are used. Vesicles packed with molecules to enter or leave the cell. Endocytosis is when the cell grabs a molecules from the environment allowing it to enter the cell. Exocytosis is when the cell expels a particle into the environment.
Explain gated ion channels in neurons.
They use passive diffusion, no charge is needed and the proteins open and close. They can be voltage which open and close in response to electrical potential changes which can be sodium or potassium. They can also be ligand gated channels which need to connect to open and they can stay open. They can be single pass and work through actual facial recognition (chemical messenger).
Explain acetylcholine receptors.
Acetylcholine receptors are a neurotransmitter which is essential for muscle contraction, memory, motivation, arousal, learning and attention and REM sleep. They exist between neurons and effector cells (start and end of the chain). Between the synapse the receptor undergoes conformational changes and the change in shape opens a pore in the protein allowing sodium ions to move through facilitated diffusion into the postsynaptic neuron. The cell is then depolarized and an action potential can be triggered.
Explain sodium potassium pumps as an example of exchange transport.
Sodium potassium pumps force molecules to go against their concentration gradient. Their aim is to move sodium ions out of the cell and potassium ions in. They change transporter which can cause changes in their pH (H+ is acidity). 70 mV is the resting potential and the ATP used becomes ADP after one potassium is lost. The process is:
1. Pump resets concentration
2. 3 sodium atoms bind
3. ATP binds loses a phosphate
4. The protein changes shape and opens
5. The release is made
6. 2 potassium ions bind
7. Phosphate molecule is released
8. Potassium released
Explain Sodium dependent glucose contransporters as an example of indirect active transport.
Glucose is most abundant monosaccharide and essential source to fuel cellular respiration. It can move into cells through sodium-dependent glucose cotransporters. Sodium ions move with their concentration gradient from the extracellular space into the cell. One glucose molecule moves against its concentration gradient from the extracellular space into the cell. It uses indirect active transport meaning the energy from one particle moving with its concentration to move the other against. It requires ATP, it is not passive and its indirect because the energy isn’t used directly. They have an important role in the absorption of glucose by the cells of the:
- Kidney proximal tubule: where they reabsorb glucose from the glomerular filtrate to prevent it from being lost in the urine
- Small intestine: where they absorb glucose into the body after chemical digestion in the gut ready to function at this stage
Explain adhesion of cells for the formation of tissues.
Multicellular organisms are composed of more than one cell that are adhered together. Tissues are groups of cells that stick together and can be found in multicellular organisms. The main types of tissues are connective tissue (supports and binds other tissues), epithelial tissue (provides a covering layer), muscle tissue (includes striated muscles that move the skeleton and smooth muscle) and nerve tissue (made up of neurons and used to carry electric impulses to and from parts of the body). Cell tissues form from cell junctions which provide for adhesion between neighboring cells and anchoring of a cell to the extracellular matrix. An example of this are bones or cartilage. Cell adhesion molecules (CAMs) are used by cell junctions and they are proteins embedded within the plasma membrane that bind cells with each other or the extracellular matrix. Different forms of CAMs are used for different types of cell junctions.
