3. Structures of Cell Membranes Flashcards
What are components (3) of cell membranes
- lipids
- proteins
- carbohydrates
What is the major type of lipids used to construct the two layers making up the cell membrane
phospholipids
What are the components of the phospholipid?
- Glycerol backbone
- Two fatty acid tails
- Phosphate group + polar group head
Draw a Micelle vs. Bilayer vs. Liposome
- Micelle: a ball
- Bilayer: two layers
- Liposome: a hollow ball, encloses an inner space
Why are membranes considered to be “fluid”?
- Lipids can move laterally within the membrane
- Cannot flip flop
What factors affect the fluidity of the membrane?
Factors affecting the fluidity of the movement:
- length of fatty acid tails
- presence of C=C bonds in fatty acid tails
- cholesterol: acts as a buffer for the membrane fluidity depending on the temperature
- if hot: makes it less fluid
- if cold: makes it more fluid
What are lipid rafts?
- we can move things left and right but not flip flop
- lipids that move a lot in the membrane
What are some functions of membrane proteins?
- Transporters that move ions + molecules
- Receptors that allow the cell to receive signals
- Enzymes that catalyze chemical reactions in the cell
- Anchors attaching to other proteins
What are two types of membrane proteins?
- Integral: traverses the entire lipid bilayer, permanently associated with the membrane
- Peripheral:
- temporarily associated with lipid bilayer
- or associated with integral proteins via covalent bonds
How are carbohydrates able to span the membrane?
- it needs to attach to a protein or a lipid
After being covalently linked, is called: - glycoprotein
- glycolipid
What is the fluid mosaic model?
Describes the lipid bilayer of the membrane
- membrane is FLUID and can allow molecules to move laterally within
- membrane is like a MOSAIC (mixture) of different types of molecules (Etc. lipids, proteins, carbohydrates)
What is influx vs efflux vs net flux?
influx: movement of substances into the cells
efflux: movement of substances out of cells
net flux: the difference
What does it mean that the plasma membrane is selectively permeable?
- Some molecules are more permeable than others
- etc. gases + nonpolar molecules (etc. lipids) can move across the layer
- etc. macromolecules are too big
What is diffusion? Does it require energy?
Movement from high to low concentration
- spontaneous; no energy
- stops when there is no concentration gradient, but will still have random movements between either side
What is passive transport?
When things are moving across a membrane by diffusion
- simple diffusion
- facilitated diffusion
What is simple vs. facilitated diffusion?
simple diffusion: just goes through the cell membrane
- small molecules
- hydrophobic molecules
facilitated diffusion: moves in the same direction as the concentration gradient through a protein transporter
- channel protein
- carrier protein
What are the two types of membrane transporters? Describe each one
These are used in facilitated diffusion, a type of passive transport
- channel protein: permeable to specific molecules
- carrier protein: protein changes shape when a molecule binds to it
What is osmosis?
The diffusion of water tacross the semi permeable membrane
What is the difference between:
- hypertonic
- hypotonic
- isotonic
solutions
hypertonic solution relative to cell:
outside solute > inside solute
- water will try to move outside the cells
hypotonic solution relative to cell:
outside solute < inside solute
- water will try to move inside the cell
isotonic:
when an equilibrium is reached
what is crenation?
what happens to animal cells when they encounter a hypertonic solution
- death by loss of water
what is plasmolysis?
what happens to plant cells when they encounter a hypertonic solution
- plants cell pulls away from the surrounding cell wall
what is hemolysis?
when red blood cells swells and burst
- an example of animal cells in hypotonic solutions
what causes turgor pressure?
plant cells in hypotonic solutions
- vacuole contains high amount of dissolved substances, which causes it to swell up
- occurs when plant cells push against the cell wall
What is active transport and what does it use?
- movement of substances against the concentration gradient
requires - energy
- protein carrier/active transporter
What does primary active transport use, and what does it achieve?
Uses:
- ATP
- carrier protein
Achieves:
- stronger gradient, needed for secondary active transport
Explain the order of events in the Na+/K+ATPase transport cycle
- Sodium-potassium pump: Na+/K+ATPase
- Na+ ions bind to the protein on the inside of the membrane
- ATP is hydrolyzed (Phosphate group transferred to protein)
- Conformation of Na+/K+ATPase is changed
- Na+ ions are released to external space
- K+ ions bind on the outside of the membrane
- Phosphate group on the protein is removed
- Protein snaps back into its original conformation
- K+ ions are released inside the cell
What are antiporters vs. symporters/cotransporters
both are used in secondary active transport:
- antiporters: moves two molecules in opposite directions
- symporters: moves two molecules in the same direction
One of the two molecules is moving with the gradient, and the other is moving against its concentration gradient, using the energy provided by the first molecule
the sodium-potassium pump is not a true antiporter because it relies on ATP + moves things both against the gradient… but for this course we will assume it is (??)
What is the secondary active transport and what does it use?
Secondary active transport (co-transport) moves two molecules at the same time
Uses:
- electrochemical gradient difference
- cotransport proteins
etc. the movement of protons along with their gradient drives the movement of other molecules against their gradient
Why is the difference in proton concentrations called an electrochemical gradient?
Chemical: there’s a difference in the concentration of ions
Electrical: there’s a difference in charges
On which side do Na+/K+ have higher concentrations? Where does the ATP attach?
Na+: high concentration outside the cell
K+: high concentration within the cell
ATP attaches to the carrier protein inside the cell
What is moved in the secondary active transport of Na+? What kind of cotransporter is used?
Symporter carrying Na+ and glucose from outside the cell into the cell
- Na+ moves along its gradient
- glucose moves against its gradient
Biologically, this is important:
- allows glucose to be transported with the cell, and later, for it to naturally diffuse in the blood stream due to concentration difference
What are differences between animal cells and plant cells?
Animal cells have:
- lysosomes
Plant cells have:
- cell walls
- vacuoles
- chloroplasts
what is included in the cytoplasm?
everything but the nucleus
What does the endoplasmic reticulum do and what does it look like?
- Where we make our proteins and lipids
- Folded structure around the nucleus
What does the golgi apparatus do and what does it look like?
- transports, sorts, modifies the proteins and lipids produced by the ER
- Also a folded structure (consisting of cisternaes) outside the ER
What do lysosomes do and what do they look like?
- contains enzymes that break down macromolecules
- bean things
What is the cytoskeleton?
Protein scaffolding that provides the cell structure
What is the endomembrane system? what organelles does it include?
- A system of interconnected organelles, allowing for bulk transport
includes: - plasma membrane + nuclear envelope
- ER
- Golgi apparatus
- Lysosomes
- Vesicles moving between the above
What is bulk transport?
Moving a large amount of things between the structures relatively quickly
- provided by endomembrane system
What is endocytosis vs exocytosis?
Both are processes of bulk transport
endocytosis: moving things inside the cell
exocytosis: moving things outside the cell/specific membrane
How does exocytosis work?
- vesicle bundles it cargo
- vesicle the fuses with the cell membrane and delivers its contents to the extracellular space
