cells

Question 1

3 main parts of the cell

Answer 1

1. Plasma membrane
2. cytoplasm
3. nucleus

Question 2

Plasma membrane structure

Answer 2

phospholipid bilayer

2 types of proteins: integral (transmembrane) and peripheral

Question 3

Plasma membrane lipids

Answer 3

75% phospholipids
5% glycolipids
20% cholesterol which stiffens the membrane

Question 4

Plasma membrane proteins

Answer 4

Ion channels –> integral
-have pore for specific ion
carriers/transporters –> integral
-needs substrate binding to function
receptors –> integral
-very specific response to ligands
enzymes –> integral or peripheral
-lower activation energy for chem rxns
linker –> integral or peripheral
- anchors, structures, or links cells
cell identity marker (glycoproteins)
-mark cell as “self” for immune system

Question 5

Selective permeability

Answer 5

• always permeable to small, nonpolar, uncharged molecules
• transmembrane proteins act as channels or transporters to increase permeability
• macromolecules need vesicular transport

Question 6

electrochemical gradient

Answer 6

-combination of concentration gradient and electrical gradient

Question 7

passive vs active transport

Answer 7

passive transport is from high to low concentration and doesn’t require energy

active transport is from low to high concentration and requires energy

Question 8

Simple diffusion

Answer 8

• passive
• based on random kinetic motion of molecules
• typically small, nonpolar, lipid soluble
• gasses, steroid hormones, fatty acids

Question 9

Facilitated diffusion

Answer 9

1. channel mediated
   - leakage channels = always open
   - -ligand gated channels = need ligand to open
   - voltage gated channels = open in response to transmembrane voltage change
2. carrier mediated
   - solute binds to protein which carries it to the other side of the membrane
   - rate is limited by # of carrier proteins

Question 10

Osmosis

Answer 10

• passive
• water moves from high to low concentration
• pulled by osmotic pressure

Question 11

osmolarity

Answer 11

solute concentration

Question 12

tonicity

Answer 12

iso = same
hyper = more solutes --> crenation
hypo = less solutes --> bursting/ lysing

Question 13

explain 2 ways water could pass thru membran

Answer 13

osmosis or aquaporins = single-file water channels

Question 14

what limits rate of diffusion

Answer 14

• molecule size
• steepness of concentration gradient
• temp
• surface area
• diffusion distance

Question 15

primary active transport

Answer 15

• energy from ATP changes the shape of a transporter proteins (pumps) which pump a substance against its concentration gradient
• sodium potassium pump 3 Na+ out; 2 K+ in

Question 16

secondary active transport

Answer 16

• get energy from concentration gradient built from primary active transport
• always transport more than 1 thing
• “cotransport proteins”
• e.g. sodium might drag other things along with it as it flows back into the cell

Question 17

Resting membrane potential

Answer 17

• electrical potential energy from separation of opp. charged molecules
• diff in charge = voltage
• voltage is only at membrane surface
• cells have protein anions, making them negatively charged
• concentration gradient pulls K out of cells, but electrical gradient pulls it in
• voltage is -90mV when K in = K out
• Na+ has some effect and can bring voltage to -70mV, but the membrane is less permeable for it
• Cl has no effect because its concentration and electrical gradient is balanced
• RMP is maintained by Na+K+ATPase
• neuron and muscle cells upset this by opening gated Na and K channnels

Question 18

Vesicular transport

Answer 18

1. Receptor mediated endocytosis
   - receptor on outer membrane binds to ligand
   - membrane invaginates, bringing ligand in
2. Phagocytosis
   - also uses receptor
   - membrane reaches up to surround microbe
   - forms pseudopod
3. Pinocytosis (bulk phase endocytosis)
   - no receptor
   - randomly invaginates
4. Exocytosis
   - membrane-enclosed vesicles fuse with plasma membrane and expel contents
5. Transcytosis
   - combo of endo- and exocytosis to move something from one end of the cell to the other

Question 19

Tight junctions

Answer 19

• integral proteins on adjacent cells fuse to form impermeable junction that circles cell
• prevents fluids and most molecules from getting through
• bladder and intestines

Question 20

Desmosomes

Answer 20

• mechanical, rivet-like couplings formed when linker proteins (cadherins) interlock
• cadherins are anchored to cell through plaques on inside of membrane
• keratin filaments connect plaques intercellularly
• allows give
• cardiac and skin cells

Question 21

Gap Junction

Answer 21

• Transmembrane proteins (connexons) which form tunnels
• allow cell-to-cell communication
• good for electrical signals to pass quickly b/t cells
• cardiac and smooth muscle cells

Question 22

mechanical cell-to-cell signalling

Answer 22

• 1000s of sticky cell adhesion molecules (CAMs) which are glycoproteins as part of the glycocalyx
• variety of uses

Question 23

chemical cell-to-cell signalling (primary)

Answer 23

• interaction between receptors and ligands which cause changes in cellular activity
• same ligand can have dif func.s in dif cells
• activated receptors can become enzymes, gate openers, gate closers
• ligand examples: neurotransmitters or hormones

Question 24

second messenger chemical signalling

Answer 24

• 1st messenger is ligand
• activates receptor on G protein
• G protein activates effector protein (enzyme)
• effector protein catalyzes a reaction to make the 2nd messenger chemicals (cAMP of Ca+)
• 2nd messenger activates other proteins (kinases)
• -kinases add phosphate to stuff, activating other enzymes
• ligand is usually water soluble, so cant’s get thru membrane