3. Structures of Cell Membranes

Question 1

What are components (3) of cell membranes

Answer 1

1. lipids
2. proteins
3. carbohydrates

Question 2

What is the major type of lipids used to construct the two layers making up the cell membrane

Answer 2

phospholipids

Question 3

What are the components of the phospholipid?

Answer 3

• Glycerol backbone
• Two fatty acid tails
• Phosphate group + polar group head

Question 4

Draw a Micelle vs. Bilayer vs. Liposome

Answer 4

• Micelle: a ball
• Bilayer: two layers
• Liposome: a hollow ball, encloses an inner space

Question 5

Why are membranes considered to be “fluid”?

Answer 5

• Lipids can move laterally within the membrane
• Cannot flip flop

Question 6

What factors affect the fluidity of the membrane?

Answer 6

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

Question 7

What are lipid rafts?

Answer 7

• we can move things left and right but not flip flop
• lipids that move a lot in the membrane

Question 8

What are some functions of membrane proteins?

Answer 8

• 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

Question 9

What are two types of membrane proteins?

Answer 9

1. Integral: traverses the entire lipid bilayer, permanently associated with the membrane
2. Peripheral:
   - temporarily associated with lipid bilayer
   - or associated with integral proteins via covalent bonds

Question 10

How are carbohydrates able to span the membrane?

Answer 10

• it needs to attach to a protein or a lipid
  After being covalently linked, is called:
• glycoprotein
• glycolipid

Question 11

What is the fluid mosaic model?

Answer 11

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)

Question 12

What is influx vs efflux vs net flux?

Answer 12

influx: movement of substances into the cells
efflux: movement of substances out of cells
net flux: the difference

Question 13

What does it mean that the plasma membrane is selectively permeable?

Answer 13

• Some molecules are more permeable than others
• etc. gases + nonpolar molecules (etc. lipids) can move across the layer
• etc. macromolecules are too big

Question 14

What is diffusion? Does it require energy?

Answer 14

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

Question 15

What is passive transport?

Answer 15

When things are moving across a membrane by diffusion
- simple diffusion
- facilitated diffusion

Question 16

What is simple vs. facilitated diffusion?

Answer 16

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

Question 17

What are the two types of membrane transporters? Describe each one

Answer 17

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

Question 18

What is osmosis?

Answer 18

The diffusion of water tacross the semi permeable membrane

Question 19

What is the difference between:
- hypertonic
- hypotonic
- isotonic
solutions

Answer 19

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

Question 20

what is crenation?

Answer 20

what happens to animal cells when they encounter a hypertonic solution
- death by loss of water

Question 21

what is plasmolysis?

Answer 21

what happens to plant cells when they encounter a hypertonic solution
- plants cell pulls away from the surrounding cell wall

Question 22

what is hemolysis?

Answer 22

when red blood cells swells and burst
- an example of animal cells in hypotonic solutions

Question 23

what causes turgor pressure?

Answer 23

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

Question 24

What is active transport and what does it use?

Answer 24

• movement of substances against the concentration gradient
  requires
• energy
• protein carrier/active transporter

Question 25

What does primary active transport use, and what does it achieve?

Answer 25

Uses: - ATP - carrier protein Achieves: - stronger gradient, needed for secondary active transport

Question 26

Explain the order of events in the Na+/K+ATPase transport cycle - Sodium-potassium pump: Na+/K+ATPase

Answer 26

1. Na+ ions bind to the protein on the inside of the membrane 2. ATP is hydrolyzed (Phosphate group transferred to protein) 3. Conformation of Na+/K+ATPase is changed 4. Na+ ions are released to external space 5. K+ ions bind on the outside of the membrane 6. Phosphate group on the protein is removed 7. Protein snaps back into its original conformation 8. K+ ions are released inside the cell

Question 27

What are antiporters vs. symporters/cotransporters

Answer 27

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 (??)

Question 28

What is the secondary active transport and what does it use?

Answer 28

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

Question 29

Why is the difference in proton concentrations called an electrochemical gradient?

Answer 29

Chemical: there's a difference in the concentration of ions Electrical: there's a difference in charges

Question 30

On which side do Na+/K+ have higher concentrations? Where does the ATP attach?

Answer 30

Na+: high concentration outside the cell K+: high concentration within the cell ATP attaches to the carrier protein inside the cell

Question 31

What is moved in the secondary active transport of Na+? What kind of cotransporter is used?

Answer 31

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

Question 32

What are differences between animal cells and plant cells?

Answer 32

Animal cells have: - lysosomes Plant cells have: - cell walls - vacuoles - chloroplasts

Question 33

what is included in the cytoplasm?

Answer 33

everything but the nucleus

Question 34

What does the endoplasmic reticulum do and what does it look like?

Answer 34

- Where we make our proteins and lipids - Folded structure around the nucleus

Question 35

What does the golgi apparatus do and what does it look like?

Answer 35

- transports, sorts, modifies the proteins and lipids produced by the ER - Also a folded structure (consisting of cisternaes) outside the ER

Question 36

What do lysosomes do and what do they look like?

Answer 36

- contains enzymes that break down macromolecules - bean things

Question 37

What is the cytoskeleton?

Answer 37

Protein scaffolding that provides the cell structure

Question 38

What is the endomembrane system? what organelles does it include?

Answer 38

- A system of interconnected organelles, allowing for bulk transport includes: - plasma membrane + nuclear envelope - ER - Golgi apparatus - Lysosomes - Vesicles moving between the above

Question 39

What is bulk transport?

Answer 39

Moving a large amount of things between the structures relatively quickly - provided by endomembrane system

Question 40

What is endocytosis vs exocytosis?

Answer 40

Both are processes of bulk transport endocytosis: moving things inside the cell exocytosis: moving things outside the cell/specific membrane

Question 41

How does exocytosis work?

Answer 41

- vesicle bundles it cargo - vesicle the fuses with the cell membrane and delivers its contents to the extracellular space