1. AP Biology Discussion Notes
Tuesday 10/11/2016

2. Goals for the Day
Be able to describe the cell membrane composition and its components
Be able to describe what limits cell size.
Be able to list & describe how things are transported in/out of the cell

3. 10/11 Question of the Day What size are typical cells?
Why do you think that is?

4. Let’s think about cells….
What is the typical size of a cell (generally)?
Why do you think this is?
Are there exceptions (cells that are a different size)?

5. Metabolic requirements set upper limits on the size of cells
The surface area to volume ratio of a cell is critical – WANT it to be LARGE
As the surface area increases by a factor of n2, the volume increases by a factor of n3
Small cells have a greater surface area relative to volume

11. Surface area increases while total volume remains constant
Figure 6.7
Surface area increases while total volume remains constant 5 1
Total surface area [sum of the surface areas (height  width) of all box sides  number of boxes] 6
150
750
Total volume [height  width  length  number of boxes]
Figure 6.7 Geometric relationships between surface area and volume. 1
125
125
Surface-to-volume (S-to-V) ratio [surface area  volume] 6
1.2 6

12. If smaller cells are more efficient, Why aren’t cells infinitely small?

13. How big is a (typical) cell?
Cell Size

14. If smaller cells are more efficient, Why aren’t cells infinitely small?
Cell size is a balance between efficiency and function
different types of cells need different parts/numbers of parts to function and so will be different sizes to maximize efficiency and functionality.

15. How do things get in and out of our cells?

16. What is the cell membrane made of ?
Phospholipid Bilayer!
True for ALL organisms?
YES!!!

17. WATER Hydrophilic head Hydrophobic tail WATER Figure 7.2
Figure 7.2 Phospholipid bilayer (cross section). 17

18. Freeze-fracture studies of the plasma membrane supported the fluid mosaic model
Freeze-fracture is a specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer
© 2011 Pearson Education, Inc.

19. Inside of extracellular layer Inside of cytoplasmic layer
Figure 7.4
TECHNIQUE
Extracellular layer
Proteins
Knife
Plasma membrane
Cytoplasmic layer
RESULTS
Figure 7.4 Research Method: Freeze-fracture
Inside of extracellular layer
Inside of cytoplasmic layer 19

20. The Fluid Mosaic Model Figure 7.5
Fibers of extra- cellular matrix (ECM)
Glyco- protein
Carbohydrate
Glycolipid
EXTRACELLULAR SIDE OF MEMBRANE
Figure 7.5 Updated model of an animal cell’s plasma membrane (cutaway view).
Cholesterol
Microfilaments of cytoskeleton
Peripheral proteins
Integral protein
CYTOPLASMIC SIDE OF MEMBRANE 20

21. The Fluidity of Membranes
Phospholipids in the plasma membrane can move within the bilayer
Most of the lipids, and some proteins, drift laterally
Rarely does a molecule flip-flop transversely across the membrane
© 2011 Pearson Education, Inc.

22. Lateral movement occurs 107 times per second.
Figure 7.6
Lateral movement occurs 107 times per second.
Flip-flopping across the membrane is rare ( once per month).
Figure 7.6 The movement of phospholipids. 22

23. The steroid cholesterol has different effects on membrane fluidity at different temperatures
At warm temperatures (such as 37°C), cholesterol restrains movement of phospholipids
At cool temperatures, it maintains fluidity by preventing tight packing
© 2011 Pearson Education, Inc.

24. Unsaturated hydrocarbon tails Saturated hydrocarbon tails
Figure 7.8
Fluid
Viscous
Unsaturated hydrocarbon tails
Saturated hydrocarbon tails
(a) Unsaturated versus saturated hydrocarbon tails
(b) Cholesterol within the animal cell membrane
Figure 7.8 Factors that affect membrane fluidity.
Cholesterol 24

25. Membrane Proteins and Their Functions
A membrane is a collage of different proteins, often grouped together, embedded in the fluid matrix of the lipid bilayer
Proteins determine most of the membrane’s specific functions
© 2011 Pearson Education, Inc.

26. Peripheral proteins are bound to the surface of the membrane
Integral proteins penetrate the hydrophobic core – span the membrane
Aka. Transmembrane proteins
The hydrophobic regions of an integral protein consist of one or more stretches of nonpolar amino acids, often coiled into alpha helices
© 2011 Pearson Education, Inc.

27. Figure 7.5
Fibers of extra- cellular matrix (ECM)
Glyco- protein
Carbohydrate
Glycolipid
EXTRACELLULAR SIDE OF MEMBRANE
Figure 7.5 Updated model of an animal cell’s plasma membrane (cutaway view).
Cholesterol
Microfilaments of cytoskeleton
Peripheral proteins
Integral protein
CYTOPLASMIC SIDE OF MEMBRANE 27

28. EXTRACELLULAR SIDE N-terminus  helix C-terminus CYTOPLASMIC SIDE
Figure 7.9
EXTRACELLULAR SIDE
N-terminus
 helix
Figure 7.9 The structure of a transmembrane protein.
C-terminus
CYTOPLASMIC SIDE 28

29. Six major functions of membrane proteins
Transport
Enzymatic activity
Signal transduction
Cell-cell recognition
Intercellular joining
Attachment to the cytoskeleton and extracellular matrix (ECM)
© 2011 Pearson Education, Inc.

30. (b) Enzymatic activity (c) Signal transduction
Figure 7.10
Signaling molecule
Receptor
Enzymes
ATP
Signal transduction
(a) Transport
(b) Enzymatic activity
(c) Signal transduction
Figure 7.10 Some functions of membrane proteins.
Glyco- protein
(d) Cell-cell recognition
(e) Intercellular joining
(f) Attachment to the cytoskeleton and extracellular matrix (ECM) 30

31. (b) Enzymatic activity (c) Signal transduction
Figure 7.10a
Signaling molecule
Receptor
Enzymes
ATP
Figure 7.10 Some functions of membrane proteins.
Signal transduction
(a) Transport
(b) Enzymatic activity
(c) Signal transduction 31

32. (d) Cell-cell recognition (e) Intercellular joining
Figure 7.10b
Glyco- protein
Figure 7.10 Some functions of membrane proteins.
(d) Cell-cell recognition
(e) Intercellular joining
(f) Attachment to the cytoskeleton and extracellular matrix (ECM) 32

33. The Role of Membrane Carbohydrates in Cell-Cell Recognition
Cells recognize each other by binding to surface molecules, often containing carbohydrates, on the extracellular surface of the plasma membrane
Membrane carbohydrates may be covalently bonded to lipids (forming glycolipids) or more commonly to proteins (forming glycoproteins)
Carbohydrates on the external side of the plasma membrane vary among species, individuals, and even cell types in an individual
© 2011 Pearson Education, Inc.

34. Receptor (CD4) but no CCR5 Co-receptor (CCR5) Plasma membrane
Figure 7.11
HIV
Receptor (CD4)
Receptor (CD4) but no CCR5
Co-receptor (CCR5)
Plasma membrane
Figure 7.11 Impact: Blocking HIV Entry into Cells as a Treatment for HIV Infections
HIV can infect a cell that has CCR5 on its surface, as in most people.
HIV cannot infect a cell lacking CCR5 on its surface, as in resistant individuals. 34

35. Passive vs. Active Transport
No Energy Requirement – Passive – moves from High to Low concentration
Active Transport – Requires Energy – moves from Low – to high concentration

36. Concentration Gradient
Difference in concentration across an area

37. Passive Transport NO ATP NEEDED!!! Travels WITH the Gradient ___ to ___
Diffusion
Osmosis
--hypo, hyper, isotonic
--turgor pressure
--cytolysis
--plasmolysis
Facilitated Diffusion (channel/carrier proteins)

38. The “tonics”

40. Does size affect what can move across the membrane?

41. Active Transport ATP NEEDED!!! Travels Against the Gradient ___ to ___
Exocytosis
Endocytosis
Protein Pumps

42. Exocytosis

43. Endocytosis

44. Questions?

45. Reading & Notes Assignment
Read pages 58-66
Take notes on main ideas
Define vocab words
Draw & Describe the experiment in fig 4.2
Add functional groups pg64-65 to notes
Be able to recognize functional groups
Draw Cholesterol (pg 77), Estrodial & Testosterone (pg 63) Compare the 3 chemicals in terms of differences and similarities in structure/function *Remember cholesterol is a precursor to making steroids, including sex hormones.
536 – we essentially talked through 26.1