BIO 121 – Cell PhysiologyLecture Section II

A. Biological MembranesB. Protein Structure and FunctionC. The Cytoskeletal System and AdhesionD. Cellular MovementsE. The Endomembrane System and Intracellular Trafficking

1. Review of the Fundamental Structures and Functions of Biological Membranes

All cells have a plasmamembrane, eukaryotes have maximized use of membranes

The membranes and membrane-bound compartments of eukaryotic cells allow for the far greater complexity of structure and function in those cells

Nucleoid

Plasma membrane

Cell wallBacterialchromosome

Prokaryotes: Cytoplasm bound by plasma membrane, no organelles No nucleus, DNA in an unbound region called the nucleoid

The plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell

Smooth ERRough ER

CYTOSKELETON:

Microfilaments

Intermediatefilaments

Microtubules

MitochondrionLysosome

Golgiapparatus

Plasma membrane

Nuclearenvelope

Typicalanimal

cell

Fig. 6-9b

Nuclear envelope Rough endoplasmic reticulum

Smooth endoplasmic reticulum

Central vacuole

Microfilaments

Intermediate filamentsMicrotubules

CYTO-SKELETON

Chloroplast

PlasmodesmataWall of adjacent cell

Cell wall

Plasma membrane

Mitochondrion

Golgiapparatus

Plant and animal cells have most of the same organelles

Same for fungiand protists.....

The Eukaryotic Membrane System

• Components of the membrane system:• Plasma membrane• Nuclear envelope• Endoplasmic reticulum• Golgi apparatus• Mitochondria and Chloroplasts• Lysosomes• Peroxisomes• Vacuoles

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b. The main components of membrane structure are ......

» The Amphipathic Lipid Bilayer

» Membrane Proteins and Sugars

» The Cytosolic Submembrane Protein Meshwork

Fig. 7-2

Hydrophilichead

WATER

Hydrophobictail

WATER

The most fundamental structure of a biological membrane is a double layer of phospholipids

The Amphipathic Lipid Bilayer

Figure 10-3 Molecular Biology of the Cell (© Garland Science 2008)

There are many types of phospholipids

Figure 10-18 Molecular Biology of the Cell (© Garland Science 2008)

Glycolipids

Figure 10-5 Molecular Biology of the Cell (© Garland Science 2008)

Fig. 7-5b

Fluid

Unsaturated hydrocarbontails with kinks

Viscous

Saturated hydro-carbon tails

•Membranes must be fluid to work properly

• they are usually about as fluid as salad oil

• Membranes rich in unsaturated fatty acids are more fluid that those rich in saturated fatty acids

Fig. 7-5c

Cholesterol

•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

Figure 10-9b Molecular Biology of the Cell (© Garland Science 2008)

Membrane lipids provide hydrophobic to most molecules dissolved in water and allow a select few to diffuse across

-oxygen-carbon dioxide-urea-water

Spontaneousformation and ‘healing’

The Permeability of the Lipid Bilayer

Hydrophobic (nonpolar) molecules, such as hydrocarbons, can dissolve in the lipid bilayer and pass through the membrane rapidly

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Charged or strongly polar molecules, such as ions,sugars and proteins, do not cross the membrane easily

estradiol testosterone

glucose proteins

Fig. 7-13

Hypotonic solution

(a) Animal cell

(b) Plant cell

H2O

Lysed

H2O

Turgid (normal)

H2O

H2O

H2O

H2O

Normal

Isotonic solution

Flaccid

H2O

H2O

Shriveled

Plasmolyzed

Hypertonic solution

Figure 10-19 Molecular Biology of the Cell (© Garland Science 2008)

Transmembrane Proteins 1. single pass 2. multiple pass 3. barrel or channel

Proteins can associate with membranes in a variety of ways:

4. single sheath proteins

Anchored Proteins 5. lipid anchor 6. sugar anchor 7/8 protein anchor

Membrane proteins provide the bulk of specific membrane functions and their variation is a primary determinant of cellular identity

Protein-lipid ratio varies hugely in different membranes

protein lipid1. myelin sheath 20% 80%2. outer mitochondrial 50% 50%3. inner mitochondrial 80% 20%

Fig. 7-9ac

(a) Transport (b) Enzymatic activity (c) Signal transduction

ATP

Enzymes

Signal transduction

Signaling molecule

Receptor

Typical functions of membrane proteins

Fig. 7-9df

(d) Cell-cell recognition

Glyco-protein

(e) Intercellular joining (f) Attachment to the cytoskeleton and extracellular matrix (ECM)

Carbohydrates often play important roles on the plasma membrane. Covalently bonded to lipids (forming glycolipids) or more commonly to proteins (forming glycoproteins)

N-terminus

C-terminus

HelixCYTOPLASMICSIDE

EXTRACELLULARSIDE

Whattypesofsidechainsare on outsideofthesehelices?

Biochemical structure depends on surroundings

Fig. 7-17Passive transport

Diffusion Facilitated diffusion

Active transport

ATP

Nutrient uptakeWaste eliminationpH and osmolarity maintenanceElectrical gradient maintenance

Figure 11-12 Molecular Biology of the Cell (© Garland Science 2008)

We have pumps for glucose, amino acids, calcium, and many other molecules

Figure 10-28b Molecular Biology of the Cell (© Garland Science 2008)

Sugars are found on the non-cytosolic face of membranes

Figure 10-41a Molecular Biology of the Cell (© Garland Science 2008)

Review of Membrane Structure

The third component: submembrane protein meshwork

Always on the cytosolic face

Allows membrane to communicate with the rest of the cell

Figure 10-42 Molecular Biology of the Cell (© Garland Science 2008)

A major role of the meshwork is to segregate and establish functional domains in the membrane

Some Structures that Live in the Submembrane Meshwork:

- Membrane identification proteins

- Anchor proteins for cadherins and integrins

- 2nd messengers for signaling pathways

- Ribosome docking proteins

- Chaperonin docking proteins

What are the Principle Functions of Cell Membranes?

• Compartmentilization of Cell Functions

• Defense and Integrity of Cellular or Compartmental Contents

• Selective Permeability in Two Directions

• Regulation of Internal Cellular or Compartmental Activities

• Attachment and Movement of the cell or Compartment

• Response to Signals from Outside of the Cell or Compartment

Table 12-2 Molecular Biology of the Cell (© Garland Science 2008)

Key Functions of the Nucleus and Endoplasmic Reticulum

• Store, protect and transcribe the DNA• Deliver RNAs for translation• Lipid biosynthesis and protein translation• Integration of membrane lipid and protein• Detoxification of dangerous materials• Calcium sequestration

Figure 12-8 Molecular Biology of the Cell (© Garland Science 2008)

rRNA Production

mRNA Production

Figure 12-9a Molecular Biology of the Cell (© Garland Science 2008)

Nuclear Pore Complex

Translation and Lipid Synthesis

Key Functions of the Golgi Apparatus (GA)

1. Post-translational modification of membrane lipid and protein constituents.

a. Sulfation, glycosylation, adenylation, phosphorylation, etc.

2. Membrane Targeting. Control of the cellular

destinations of prepared membrane and protein vesicles.

Figure 13-28 Molecular Biology of the Cell (© Garland Science 2008)

Functions of Mitochondria and Chloroplasts

1. Captive energy plants for the cell 2. Store, protect, express their own DNA

Figure 13-42a Molecular Biology of the Cell (© Garland Science 2008)

Key Functions of the Endosomal System

Figure 13-53 Molecular Biology of the Cell (© Garland Science 2008)

Recycling of membranecomponents

Key Functions of the Peroxisome

Key Functions of the Vacuole

Control of water and ion exchange is organisms dependent on a variable external environment

B. Protein Structure and Function

Protein biochemistry dictates their functional activities

Regulation of protein structure and function is one of the most fundamental means by which cells control their own activities

Figure 3-1 (part 2 of 2) Molecular Biology of the Cell (© Garland Science 2008)

a. Final amino acid position results from the conformation that gives the lowest free energy

most of this is driven by the polar aqueous and non-polar membrane phases

Figure 3-5 Molecular Biology of the Cell (© Garland Science 2008)

In the aqueous phase polar side chains face out, in the membrane they are hidden

Figure 3-4 Molecular Biology of the Cell (© Garland Science 2008)

Many forces help maintain the final shape

Figure 3-22 Molecular Biology of the Cell (© Garland Science 2008)

Self- and regulated- assembly of large structures

hemoglobin is made up of 2 alpha and 2 beta subunits

Figure 3-27a Molecular Biology of the Cell (© Garland Science 2008)

Collagen fibrils are made up of many collagen proteins, each of which are made of 3 collagen subunit peptides

Figure 3-12 Molecular Biology of the Cell (© Garland Science 2008)

Because of gene duplication and exon duplication modularity of structure is common: Protein families and domains

Two serine protease genes give nearly exact binding site structure

Final Structure = Final Function

Active amino acids widely distributed Folding places them into

active distribution

Fig. 7-16-1

EXTRACELLULAR FLUID [Na+] high [K+] low Na+

Na+

Na+ [Na+] low[K+] high

CYTOPLASM

Cytoplasmic Na+ binds

1

Example:The sodium-potassium pump

Binding changes protein conformation,change in conformation alters activity

Na+ binding stimulates phosphorylation by ATP.

Fig. 7-16-2

Na+

Na+

Na+

ATP P ADP

2

Fig. 7-16-3

Phosphorylation causes the protein to change its shape. Na+ is expelled to the outside.

Na+

P

Na+ Na+

3

Fig. 7-16-4

K+ binds on theextracellular side andtriggers release of thephosphate group.

P P

K+

K+

4

Fig. 7-16-5

Loss of the phosphaterestores the protein’s originalshape.

K+

K+

5

Fig. 7-16-6

K+ is released, and thecycle repeats.

K+

K+

6

Why do we want Na+ outside of the cell and K+ inside?

Cells can control protein activity directly by mechanisms that target the protein itself

Figure 3-58 Molecular Biology of the Cell (© Garland Science 2008)

Definition: “Allosteric”. Proteins with two or more binding sites, wherein activity away from the active site will regulate activity at the active site

Figure 3-59 Molecular Biology of the Cell (© Garland Science 2008)

Figure 3-64 Molecular Biology of the Cell (© Garland Science 2008)

1. Cells can start and stop a protein’s activity by changing its structure through the addition of a covalent subgroup

phosphorylation-dephosphorylation

Figure 12-51 Molecular Biology of the Cell (© Garland Science 2008)

glycosylation

Figure 10-20 Molecular Biology of the Cell (© Garland Science 2008)

Addition of covalently linked lipids allows a proteinto have a tight association with the membrane

Figure 3-81a Molecular Biology of the Cell (© Garland Science 2008)

Complex Covalent Regulation of the p53 Transcription Factor

Figure 3-81c Molecular Biology of the Cell (© Garland Science 2008)

Figure 3-35 Molecular Biology of the Cell (© Garland Science 2008)

2. Cells can start and stop a protein’s activity by proteolytic cleavage

Figure 18-5a Molecular Biology of the Cell (© Garland Science 2008)

The clotting cascade is the same

Figure 3-69 (part 1 of 3) Molecular Biology of the Cell (© Garland Science 2008)

3. Some regulatory mechanisms involve multiple strategies such as activation of Src protein

Figure 3-69 (part 2 of 3) Molecular Biology of the Cell (© Garland Science 2008)

Figure 3-69 (part 3 of 3) Molecular Biology of the Cell (© Garland Science 2008)

Cells can control protein activity indirectly by altering the other molecules that share its environment

Figure 15-53a Molecular Biology of the Cell (© Garland Science 2008)

1. Cells can start and stop a protein’s activity by regulating the presence of a critical binding partner

a. Ligand interaction activates receptor

Figure 11-12 Molecular Biology of the Cell (© Garland Science 2008)

2. Sequestration of effector molecules linked to controlled release

eg. Hide all of the calcium until you want to change actin-myosin activity

c. Cooperative/Coupled binding - Substrate binding in one site effects binding of substrate in second site by changing affinity

Hemoglobin binds oxygenwith greater affinity whenthere is lots of oxygen – thisensures flow of oxygen to the tissues and not away.

Figure 16-78a Molecular Biology of the Cell (© Garland Science 2008)

2. Cells can start and stop a protein’s activity by blocking its binding site

Tropomyosin blocking the myosin-binding site on actin

Figure 17-49a Molecular Biology of the Cell (© Garland Science 2008)

3. Cells can start and stop a protein’s activity by regulating the processes that make active polymers from inactive subunits

Figure 3-79 Molecular Biology of the Cell (© Garland Science 2008)

4. Cells can start and stop a protein’s activity by regulating the scaffolded interaction of the subunits of protein machines

Ubiquitinligasecomplex

Figure 19-21 Molecular Biology of the Cell (© Garland Science 2008)

Synapticscaffold

Figure 15-21a Molecular Biology of the Cell (© Garland Science 2008)

Figure 15-61 Molecular Biology of the Cell (© Garland Science 2008)

Sometimes the scaffold protein is even part of the signaling cascade!