Lecture 3 & 4 Outline

Question 1

What are the 4 functions of the cell membrane?

Answer 1

1. Physical barrier
   - separates intracellular fluid from ECF
2. Gateway for exchange
   - controls movement of solutes: allows some to cross, prevents others from crossing (semipermeable…)
3. Communication
   - home to receptors that detect physical & chemical stimuli & starts cascade of response to stimuli
4. Cell structure
   - some membrane proteins hold cytoskeleton proteins to give cell structure
   - may also form specialized junctions

Question 2

What is the structure of cell membranes?

Answer 2

made of mostly protein & lipid
- ratio of protein & lipid is different for different cell types

early model was a “Butter sandwich”

• a clear layer of lipids sandwiched b/t 2 dark layers of protein
• implies that it is homogenous that is NOT accurate

present day model is “Fluid mosaic”
- proteins are afloat on a sea of lipid

Question 3

What are the 4 types of lipids?

Answer 3

1. Glycolipids
2. Phospholipids
3. Cholesterol
4. Sphingolipids

Question 4

Glycolipids (a lipid, & its role in cell membrane structure)

Answer 4

a carbohydrate that is covalently linked to a lipid. Glycolipids are biomolecular structures in the phospholipid bilayer of the cell membrane whose carbohydrate component extends to the outside of the cell. Glycolipids are essential in providing stability of the plasma membrane.

Question 5

Phospholipids (a lipid, & its role in cell membrane structure)

Answer 5

• mostly phospholipids
• several different varieties: (R-group, saturation)
• polar head groups toward aqueous sides, non-polar fatty acid tails inside

Question 6

Cholesterol (a lipid, & its role in cell membrane structure)

Answer 6

• flat molecule, slips b/t fatty acid tails

what it does:

1. cholesterol regulates membrane fluidity
2. slows diffusion of molecules across membrane

Question 7

Sphingolipids (a lipid, & its role in cell membrane structure)

Answer 7

have longer tails than phospholipids

tend to aggregate together = lipids raft

• rafts also have a high density of cholesterol
• some proteins associated ONLY with lipid rafts, leading to areas of SPECIALIZATION on cell membranes
• for ex: some G-protein couples receptors!

Question 8

What are the 5 components of proteins for the cell membrane structure?

Answer 8

1. Integral
2. Peripheral
3. Lipid-anchored
4. Cytoskeletal
5. Extracellular matrix

Question 9

Integral proteins (role in cell membrane structure)

Answer 9

• polytopic (=transmembrane, more than one MSR)
• bitopic (=transmembrane, one MSR)
• monotropic (=permanently associated from one side)

Question 10

Integral proteins (transmembrane)

Answer 10

permanently attached to cell membrane
- integral polytopic/bitopic = transmembrane proteins (span the lipid bilayer once or several times & approximately 20-25 hydrophobic AA’s to span the cell membrane)

Question 11

Integral proteins (monotopic)

Answer 11

permanently attached to cell membrane
- integral monotopic proteins - permanently attached to the membrane from one side

A. may have strong hydrophobic sections that allow it to tightly associate with lipid portion of bilayer
B. may be modified by the addition of a fatty acid
C. may be electrostatic or ionic interactions b/t protein & phospholipid (tightly bound)

Question 12

Peripheral proteins (role in cell membrane structure)

Answer 12

associate non-covalently with integral proteins, or polar heads of phospholipids

Question 13

Cytoskeletal/cytoskeleton (role in cell membrane structure)

Answer 13

• not a membrane protein, but often interact with membrane proteins
• flexible skeleton of fibrous proteins throughout the cytoplasm (give physical strength)

Question 14

Extracellular matrix (role in cell membrane structure)

Answer 14

• membrane proteins & secreted protein found on the extracellular side of cell membranes
• forms a “husk” around cells
• highly variable GLYCOSYLATION
• contribute to physical strength of cells

Question 15

Definition of diffusion

Answer 15

• process of moving solute molecules away from an area of high concentration towards area of low concentration (“down the concentration gradient”)
• passive (no external energy, just kinetic energy of molecules)
• process continues until equilibrium is reached

Question 16

What are the 5 factors that influence diffusion?

Answer 16

1. Fast over short distances
2. Slow over long distances
3. Rate of diffusion is faster at high temp
4. Rate of diffusion is faster for small molecules
5. Rate of diffusion is slower across a membrane

Question 17

What are the rules for diffusion across cell membranes?

Answer 17

1. Permeability across cell membrane
   - size
   - lipid solubility: polar or non-polar or VERY non polar
2. Concentration gradient
3. Surface area
4. Temp
5. Composition of membrane
   - simple lipid bilayer vs membrane with many proteins & extracellular matrix
   - types of phospholipids & sphingolipids
   - presence of cholesterol

Question 18

What solutes can and cannot diffuse across cell membranes?

Answer 18

can:

• hydrophobic, non-polar (O2, CO2, lipids, steroids, fat soluble molecules)
• small uncharged polar molecules (urea, H20?)

cannot:

• large uncharged polar molecules (glucose, proteins, amino acids)
• charged molecules (ions K+ Cl- Na+, phosphate ions, bicarbonate, etc)

Question 19

Definition of osmosis

Answer 19

is the diffusion of water

• water can have a concentration gradient
• water will “diffuse down its concentration gradient”
• pure water has the “highest concentration of water”
• solutes lower the concentration of water
• movement of water can cause pressure

Question 20

Osmolarity describes…

Answer 20

the # of particles in a solution

Question 21

Hyposmotic

Answer 21

fewer osmoles per unit volume

Question 22

Hyperosmotic

Answer 22

more particles per unit volume, more concentrated

Question 23

Isosmotic

Answer 23

if 2 solutions contain the same amount of solute particles per unit volume

Question 24

Why is osmolarity important?

Answer 24

• changing osmolarity of the extracellular solution causes redistribution of water & some solutes in cells
• this causes cells to shrink or swell (& die)

Question 25

What is the difference b/t osmolarity & tonicity?

Answer 25

osmolarity: - describes only the # of solute molecules in a cell (units of Osm) - can compare any 2 solutions - DOES NOT ALWAYS TELL IF A CELL SWELLS OR SHRINKS tonicity: - a comparative term describes whether a cell changes volume (has no units) - compares a intracellular solution (for our purposes 290 mOsm) - SPECIFICALLY TELLS IF A CELL SWELLS OR SHRINKS

Question 26

How to predict hypotonic vs hypertonic

Answer 26

hyposmotic solutions are always hypotonic but, hyperosmotic solutions are not necessarily hypertonic

Question 26

How to predict hypotonic vs hypertonic

Answer 26

hyposmotic solutions are always hypotonic but, hyperosmotic solutions are not necessarily hypertonic

Question 27

Definition of a channel

Answer 27

a channel protein is a water filled pore | - can open to both sides

Question 28

Examples of channels

Answer 28

- water channels | - ion channels

Question 29

Carrier proteins definition

Answer 29

never form an open channel b/t the 2 sides of the membrane

Question 30

In terms of energy requirements, there are 3 categories of carrier proteins

Answer 30

1. facilitated diffusion 2. primary active transport 3. secondary active transport

Question 31

Facilitated diffusion definition

Answer 31

is defined as moving a molecule across the cell membrane via a carrier protein, & the transport does not require energy other than the concentration gradient - does not require ATP, or other solutes - also sometimes called passive transport this process alone cannot accumulate solute against a concentration gradient

Question 32

Example of facilitated diffusion

Answer 32

glucose transporter: GLUT protein

Question 33

Primary active transport definition

Answer 33

1. uses ATP 2. establishes gradients 3. sometimes called pumps

Question 34

Examples of primary active transport

Answer 34

Na+/K+/ATPase is the most widely known ex, but there are others - Ca2+ ATPase - H+ ATPase - H+/K+ ATPase

Question 35

Definition of Secondary active transport

Answer 35

does not directly utilize ATP as a source of energy | - instead, uses the concentration gradient of one molecule/ion to move another against its gradient

Question 36

Example of secondary active transport

Answer 36

Na+-glucose is a good example: SGLT-protein

Question 37

Complex ex: Transport of glucose across the kidney or gut epithelia

Answer 37

1) Na+ K+ ATPase. Establishes & maintains a Na+ gradient - primary active transport 2) Using the Na+ gradient, glucose is transported into the cell via the Na+ glucose co-transporter - secondary active transport 3) Glucose is transported across the basal membrane by the GLUT transporter - facilitated diffusion

Question 37

Complex ex: Transport of glucose across the kidney or gut epithelia

Answer 37

1) Na+ K+ ATPase. Establishes & maintains a Na+ gradient - primary active transport 2) Using the Na+ gradient, glucose is transported into the cell via the Na+ glucose co-transporter - secondary active transport 3) Glucose is transported across the basal membrane by the GLUT transporter - facilitated diffusion

Question 38

What are the 3 types of vesicular transport?

Answer 38

1. Phagocytosis 2. Endocytosis 3. Exocytosis