Chapter 7: Membranes Flashcards
What is the function of the cellular membrane?
- Separates cells from surroundings
- Selective permeable
- Forms additional compartments in eukaryotic cells
What is the cell membrane made up of?
Lipids, proteins, some carbs
The phospholipid bi layer is crucial
What’s the phospholipid bi-layer?
It’s an amphipathic molecule; meaning it’s both hydrophilic (heads) and hydrophobic (tails)
What’s an amphipathic molecule?
Both hydrophobic and hydrophilic regions
What’s the fluid mosaic model?
Proteins are embedded in bi-layer - they’re moving, but grouped specifically by function; lipids (smaller, faster)/proteins (bigger, slower) move sideways in membrane
What’s the effect of temperature on lipid fluidity?
As temps cool, the membrane solidifies
What’s the effect of phospholipids rich in unsaturated versus saturated fatty acids?
Phospholipids rich in unsaturated fatty acids stay fluid at a lower temperature because the kinks in their tails make it so they can’t pack tightly together
Why should membranes be fluid?
It affects permeability and movement of transport proteins
How does cholesterol impact lipid fluidity?
Steroid cholesterol is wedged between phospholipids - as temps increase, it restrains phospholipid movement because steroids are rigid in membrane
As temps decrease, it hinders solidification because it prevents tight packing
How have organisms adapted to extreme conditions that impact the phospholipid bi layer?
Fishing living in extreme cold have a high number of unsaturated hydrocarbon tails; wheat has a high number of unsaturated hydrocarbon tails in the fall in preparation for winter weather
What’s the relationship between phospholipids and proteins?
Phospholipids are the main fabric of the membrane; proteins determine the function - which differs depending on type of cell
What are the two types of membrane proteins?
Integral and peripheral
What are integral proteins?
Transmembrane usually; proteins that penetrate hydrophobic core of bilayer; center is hydrophobic, top and bottom is hydrophilic; hydrophobic region consists of non polar amino acids coiled into alpha helices
What are peripheral proteins?
Bound to surface of membrane - held in place by cytoskeleton on the cytoplasmic side
What are the six major functions of membrane proteins?
Transport, enzymatic activity, signal transduction; cell-cell recognition, intercellular joining, attachment to cytoskeleton/ECM
Transport function of membrane protein?
Transport protein spanning length of membrane may have a hydrophilic channel; may also shuttle substance by changing shape (would use ATP to pump)
How does the cell membrane attach to cytoskeleton/ECM?
Microfilaments bound to membrane proteins / also coordinates extra/intra cellular changes
What is signal transduction?
A receptor protein w/ a site for an external messenger; relays messages inside cell
What is recognition?
Identifies the cell as belonging to a specific type (glycoproteins)
What’s the relationship between HIV and receptor proteins?
Protein CD4 assists HIV in infecting cells - CCR5 is a co-receptor; people immune to HIV infection have a mutation is CCR5 is absent
What is cell-to-cell recognition especially important for?
Sorting tissues/organs in embryos
Surface molecules bond to what to recognize type of cell?
1 - glycolipids (carbohydrates bonded to lipids)
2 - glycoproteins (carbohydrates bonded to proteins)
*difference in surface carbohydrate functions as cell identification
What can cross membranes?
small uncharged molecules & hydrophobic molecules (steroids)
What can’t cross membranes?
Large molecules (sugar)
Anything hydrophilic, charged; ions, Na+, K+
