2. Lecture 1 Outline (Ch. 5) I. Membrane Structure II. Permeability
III. Transport Across Membranes
A. Passive
B. Facilitated
C. Active
D. Bulk

3. Membrane structure 1915, knew membrane made of lipids and proteins
• Reasoned that membrane = bilayer
Where to place proteins?
Lipid layer 1
Proteins
Lipid layer 2

4. Membrane structure

5. Membrane structure • freeze fracture
• proteins intact, one layer or other
• two layers look different

6. Membrane structure Experiment to determine membrane fluidity:
• marked membrane proteins mixed in hybrid cell

7. Membrane structure Membrane fluidity
• phospholipid f.a. “tails”: saturation affects fluidity
• cholesterol buffers temperature changes

8. Membrane structure “fluid mosaic model” – 1970s
• fluid – phospholipids move around
• mosaic – proteins embedded in membrane

9. Membrane structure • cell membrane – amphipathic
- hydrophilic & hydrophobic
hydrophilic
hydrophobic
hydrophilic
• membrane proteins inserted, also amphipathic

10. Membrane Proteins Membrane proteins: Integral: inserted in membrane
- transmembrane – span membrane
Peripheral: next to membrane
- inside or outside

11. Membrane structure • Two transmembrane proteins: different structure
Bacteriorhodopsin: proton pump
Bacterial pore protein

12. Membrane Proteins

13. Movement of molecules
Simple Diffusion: most basic force to move molecules
• Disperse until concentration equal in all areas

14. Movement of molecules
Cell membranes only allow some molecules across w/out help:
• Small, non-polar molecules OK
ex. steroids, O2, CO2
• No charged, polar, or large molecules
ex. sugars, ions, water*

15. Transport Across Membranes
Types of transport:
Passive transport
- Simple diffusion
- Facilitated diffusion
- Osmosis
B. Active transport
C. Bulk transport
• Energy Required?
• Directionality?

16. Passive Transport - Simple Diffusion
• NO ENERGY required
- non-polar molecules (steroids, O2, CO2)
• DOWN concentration gradient
• molecules equally distribute across available area by type

17. Passive Transport – Facilitated Diffusion
• NO ENERGY required
• DOWN concentration gradient
• molecules equally distribute but cross membrane with the help of a channel (a) or carrier (b) protein.

18. Passive Transport - Osmosis
• osmosis – movement of water across cell membrane
• water crosses cell membranes via special channels called aquaporins
• moves into/out of cell until solute concentration is balanced

19. Passive Transport - Osmosis
In each situation below, does water have net movement, and which direction:
fewer solutes in solution, than in cell
equal solutes in solution as in cell
more solutes in solution, than in cell

20. Passive Transport - Osmosis
• tonicity – # solutes in solution in relation to cell
animal cell
plant cell
- hypotonic – fewer solutes in solution
- isotonic – equal solutes in solution
- hypertonic – more solutes in solution

21. Passive Transport - Osmosis
Paramecium example
• regulate water balance
• pond water hypotonic
• water into contractile vacuole
– water expelled

22. Passive Transport - Osmosis
Scenario: in movie theater, watching a long movie.
You are: drinking water
What happens to your blood?
You are: eating popcorn
What happens to your blood?

23. Active Transport • Ex. Na-K ion pump • ENERGY IS required
- Na+ ions: inside to out
• UP/AGAINST concentration gradient
- K+ ions: outside to in
• transport proteins
a. ion pumps (uniporters)
• antiporter: two molecules move opposite directions (UP gradient)
b. symporter/antiporter
c. coupled transport

24. Active Transport - uniporter
• Ex. proton (H+) pump
• ATP used pump H+ ions out
• uniporter: ONE molecule UP gradient
• against concentration and charge gradients
*gradients – used by cell for energy potential

25. Active Transport – coupled transport
• coupled transport: one molecule UP gradient & other DOWN gradient (opposite directions)
• Ex. Active glucose transporter
• Na+ diffusion used for glucose active transport
• Na+ moving DOWN concentration gradient
• Glucose moving UP concentration gradient

26. Bulk Transport • ENERGY IS required • Several or large molecules
• Molecules moved IN endocytosis
• phagocytosis – “food” in
• pinocytosis – water in

27. Bulk Transport • receptor-mediated endocytosis
– proteins bind molecules, vesicles inside
• Molecules moved OUT exocytosis

28. Self-Check Type of transport Energy required? Movement direction?
Examples:
Simple diffusion no
Down conc. gradient
O2, CO2, non-polar molecules
Osmosis
Facilitated diffusion
Active transport
Bulk transport

30. Lecture 1 Outline (Ch. 6) I. Energy and Metabolism II. Thermodynamics
A. 1st Law – conservation of energy
B. 2nd Law - entropy
Free Energy
Chemical Reactions
V. Cellular Energy - ATP
VI. Enzymes
A. Function
B. Regulation

31. The capacity to cause change
Energy
What is Energy?
The capacity to cause change
Where does energy on earth come from originally?
40 million billion calories per second!

32. Metabolism Metabolism –chemical conversions in an organism
Types of Energy:
- Kinetic Energy = energy of movement
- thermal
- Potential = stored energy
- chemical

33. Thermodynamics
Thermodynamics – study of energy transformation in a system
Potential energy can be converted to kinetic energy (& vice versa)
Potential Energy
Kinetic Energy

34. Thermodynamics
Laws of Thermodynamics: Explain the characteristics of energy
1st Law:
Energy is conserved
Energy is not created or destroyed
Energy can be converted (Chemical  Heat)
2nd Law:
During conversions, amount of useful energy decreases
No process is 100% efficient
Entropy (measure of disorder) is increased
Energy is converted from more useful to less useful forms

35. Metabolism Metabolic reactions: Chemical reactions in organism
Two Types of Metabolic Reactions:
Catabolic = breaks
down molecules
Anabolic = builds up molecules

36. Chemical Reactions Chemical Reactions:
Like home offices – tend toward disorder

37. Chemical Reactions Chemical Reactions:
Endergonic – energy required to complete reaction
Exergonic – energy given off
Exergonic
Endergonic

38. + + Chemical Reactions Chemical Reaction:
Process that makes and breaks chemical bonds +
Reactants +
Products
Two Types of Chemical Reactions:
1) Exergonic = releases energy
2) Endergonic = requires energy

39. Chemical Reactions 1. Exergonic reactions: “Energy out”
Reactants have more energy than products
Reaction releases energy
2. Endergonic reactions: “Energy in”
Products have more energy than reactants
Requires influx of energy

40. Chemical Reactions Glucose  CO2 + H20 CO2 + H20  Glucose
release free energy
intake free energy
spontaneous
non-spontaneous
• Exergonic reaction
• Endergonic reaction

41. Chemical Reactions
Activation Energy: Energy required to “jumpstart” a chemical
reaction
Must overcome repulsion of molecules due to negative
charged electrons
Nucleus
Repel
Nucleus
Repel
Activation
Energy

42. Chemical Reactions Exergonic Reaction:
“Downhill” reactions
Exergonic Reaction:
Reactants have more energy than products
But will sugar spontaneously burst into flames?
Activation energy:
Make sugar and O2 molecules collide
sugar + O2
water + CO2

43. Cellular Energy - ATP • ATP = adenosine triphosphate
• ribose, adenine, 3 phosphates
• last (terminal) phosphate - removable

44. Cellular Energy - ATP • ATP hydrolyzed to ADP
• stores 7.3 calories per mole
ATP + H2O ADP + Pi
• Energy released, coupled to another chemical reaction

45. Cellular Energy - ATP • ATP regenerated
• need 7.3 kcal/mol to build ATP
• cells power building ATP by coupling to exergonic reactions
- cellular respiration

46. Enzymes Energy of activation (EA)
• reactants – absorb energy called: EA
• Reach EA, reaction proceeds (limiting step)
Exergonic – energy given off
• EA from ambient heat usually insufficient
• This is GOOD!

47. Enzymes Enzymes • lower EA • only for specific rxns
• cell chooses which reactions go forward!
enzymes:
-do not make endergonic exergonic
-do speed up rxn would occur anyway

48. Enzymes • enzyme – specific to substrate
• active site – part of enzyme -substrate
• binding tightens fit – induced fit
• form enzyme-substrate complex
• catalytic part of enzyme: converts reactant(s) to product(s)

49. Enzymes

50. Enzymes • Enzymes lowers EA by: -template orientation -stress bonds
• substrate(s) enter
-microenvironment
• enzyme reused
• products formed
• What factors might affect enzyme activity?

51. Enzymes
• inhibitors:
• Drug – blocks HIV enzyme at the active site

52. Enzymes Feedback Inhibition: Like your furnace: Detector cold room
Furnace turns on
Room is warm
warm room

53. Lecture 1 Summary 1. Membrane composition and function (Ch. 5)
Phospholipids and cholesterol
Integral and peripheral proteins
2. How molecules cross membranes (Ch. 5)
Passive Transport
Active Transport
Bulk Transport
3. Energy (Ch. 6)
Types, conversion
4. Metabolic/chemical reactions (Ch. 6)
Catabolic/Endergonic
Anabolic/Exergonic
5. ATP (Ch. 6)
6. Enzymes (Ch. 6)
Purpose
Function
Regulation