AP Biology Discussion Notes Tuesday 10/11/2016

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

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

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)?

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

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

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

How big is a (typical) cell? Cell Size

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.

How do things get in and out of our cells?

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

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

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.

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

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

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.

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

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.

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

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.

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.

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

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

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.

(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

(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

(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

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.

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

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

Concentration Gradient Difference in concentration across an area

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

The “tonics”

Does size affect what can move across the membrane?

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

Exocytosis

Endocytosis

Questions?

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