Biochemistry 1.01

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Transcribers: Aclan, J.V., Advento, V., Bolos, C.,Cabiscuelas, Y.N., Cuaderno, C., Gamboa, K.A., Javier, K., Laurilla, L.B., Rodenas, E., Roxas, F.

Cell and Cell Membrane: A Biochemical Approach

JUNE 14, 2013

Allan L. Hilario, M.D.

1.01 BIOCHEMISTRY

CELL

Outline I. Introduction  Cell Phylogeny  Classification

 Types of Cells (Comparisons): o Prokaryotes vs. Eukaryotes o Animal vs. Plant Eukaryotic

cells

 Method of Cell Organelle Identification

II. The Prokaryotic Cell  Bacteria

 Structure  Components  Biochemical Reactions

o Metabolism

o Metabolic terms, functions and locations

III. The Eukaryotic Cell  Cytoplasm o Cytosol o Organelles  Cytoskeleton  Microfilaments  Intermediate filaments  Microtubules/Tubulin  Nucleus  Mitochondria  Endoplastic Reticulum  Smooth ER  Rough ER  Golgi Apparatus  Vesicular Organelles  Lysosomes  Peroxisomes

IV. The Cell Membrane  Structure: Fluid Mosaic Model  Functions  Composition  Membrane Fluidity o Lipid movement o Self-sealing o Selective permeability  Membrane Proteins o Integral proteins o Peripheral proteins  Membrane Microdomains o Lipid raft o Caveola

 Cell Membrane Transport o Passive transport  Simple diffusion  Facilitated diffusion - Transporters:  Transporters vs. Channels  Ionotropic channels vs. Ionophores o Active transport  Primary Transport  Secondary Transport o Diseases Involving Defects in

Membranes

 Artificial Membranes (Liposomes) V. Review Questions

VI. Answer to Review Questions

INTRODUCTION

 Cell Phylogeny

Key Concept: Grouping organisms according to common properties implies

that a group of organisms evolved from a common ancestor.Based on the similarities in ribosomal RNA, living organisms are classified into 3 domains.

Three Domains of Life:

1. Archaebacteria- prokaryotes that do not contain peptidoglycan in their cell wall.

E.g.extreme halophiles, methanogens and extreme thermophiles

2. Eubacteria- prokaryotes with peptidoglycan in their cell wall E.g. purple bacteria,cyanobacteria, flavobacteria, gram positive and gram negative bacteria, and thermotoga 3. Eukaryotes- consist the animals, ciliates, fungi, plants,

flagellates and microsporidia

Fig. 1.1 Phylogenic Tree of the Three Domains of Life

 Classification According to Nutritional Patterns

Key Concept: Organisms can be classified according to their nutritional

pattern – their energy source and source of carbon. Thus, there is metabolic diversity among organisms.

Nutritional Classification of Organisms: a. Phototrophs- energy from light

Two kinds of phototrophs:

1. Autotrophs- carbon from carbon dioxide Ex. cyanobacteria, plants

2. Heterotrophs- carbon from organic compounds Ex. purple and green bacteria

b. Chemotrophs- energy from chemical compounds 1. Lithotrophs- energy from inorganic compounds

Ex. sulfur bacteria, hydrogen bacteria 2. Organotrophs- energy from organic compounds

Ex. most prokaryotes, all nonphototrophic eukaryotes

*Note: Heterotrophs can also be chemotrophs.Lithotrophs and Organotrophs are also examples of heterotrophs.

 Types of Cells

A. Comparison of Prokaryotes and Eukaryotes

Key Concept: In general, prokaryotes are structurally simpler and smaller than eukaryotes. Eukaryotes on the other hand are structurally larger and more complex than prokaryotes.

Fig1.2. Comparisons of Prokaryotes and Eukaryotes B. Comparison of Eukaryotic Animal and Plant Cells

Key Concept: There are unique features that distinguish plant cells from animal cells.

Animal Cell Plant Cell Lysosomes Cell Wall Mitochondria Glyoxysome Centrosome Plasmodesma Vacuole (smaller) Vacuole(large)

Thylakoids Chloroplast Starch Granule Plastids

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Organelle Isolation

Fig. 1.3. Isolation of cell organelles

 The large and small particles in the suspension can be separated by centrifugation at different speed

 Particles of different density can be separated by isopycnic centrifugation

THE PROKARYOTIC CELL

 The plasma membrane and the layers outside it constitute the cell envelope

 The nucleoid contains a single, circular molecule of DNA, and the cytoplasm contains one or smaller, circular segments of DNA called plasmids

Biochemical Reactions

 Metabolism – the entire set of enzyme-catalyzed transformations of organic molecules of living cells. It is the sum of anabolism and catabolism.

 Anabolism – the phase of intermediary metabolism concerned with the energy-requiring biosynthesis of cell components from smaller precursors

 Catabolism – the phase of intermediary metabolism concerned with the energy – yielding degradation of nutrient molecules

Metabolic Terms Cellular Location Glycolysis - Cytoplasm of cells Gluconeogenesis Cytoplasm of

hepatocytes, renal cells and in special condition

the intestinal cells Hexose Monophosphate Shunt Cytoplasm of all cell

Glycogenesis Cytoplasm of hepatocytes and muscles Tricarboxylic Acid Cycle or TCA or Kreb’s Cycle Mitochondria in the cytoplasm Oxidative phosphorylation and the electron transport

chain Mitochondria in the cytoplasm Lipolysis (BetaOxidation) Mitochondria Lipogenesis Cytoplasm and SER of

hepatocytes and adipocytes Alpha and BetaOxidation Peroxisomes Omegaoxidation Peroxisomes Replication Nucleus Transcription Nucleus, most rRNA in

the nucleoulus Translation Rough endoplasmic

Reticulum and cytoplasm Post-translational

modification

Smooth Endoplasmic Reticulum and Golgi

apparatus Protein

Sorting

Golgi apparatus Ketogenesis Matrix of the

mitochondia of hepatocytes, and in special condition, renal

cells Urea Cycle Mitochondria in the

cytoplasmof the hepatocytes Amino Acid Synthesis Cytoplasm of all nucleated cells Amino Acid Catabolism

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THE EUKARYOTIC CELL

 Cytoplasm

- portion of the cell enclosed by the cell membrane and outside the nucleus where the cellular organelles are found.

- Most of the biochemical reactions happens in the cytoplasm: a. Glycolysis

b. Gluconeogenesis c. Fatty acid synthesis d. Protein synthesis e. Part of urea cycle f. Purine metabolism g. Amino acid synthesis

MAJOR PARTS OF THE CYTOPLASM: o Cytosol

- fluid portion of the cytoplasm - Biochemical reactions in the cytosol: a. NADPH production (pentose phosphate

pathway; malic enzyme) b. [NADPH]/[NADP+] high c. Isoprenoid and sterol synthesis d. Fatty acid synthesis

o Organelles

- tiny structures that perform different functions in the cell.

- specialized structures within the cell that have characteristic shapes - they perform specific functions in

cellular growth, maintenance, and reproduction.

- linked together by cytoskeleton of the cell.

 Cytoskeleton

- network of protein scafolding which mainatains cell’s shape and serves as tracts for organellar movement. - assembles as polymers from protein

subunits.

- 3 types of protein filaments: a. Microfilaments (6–8 nm)

- Actin is the protein component of the microfilaments.

- 2 forms of actin:  G-actin (globular)  Monomolecular form

 asymmetrical molecule with a mass of 42 kDa, consisting of two domains.  F-actin (filamentous)

 Polymer form

b. Intermediate filaments (10 nm) - belongs to five related protein family

with cell type-specificity. These includes:

1) Cytokeratins (ectoderm) 2) Desmin (ectoderm) 3) Vimentin (mesoderm)

4) Glial fibrillary acidic protein (GFAP) (endoderm)

5) Neurofilament (endoderm) - These proteins have a rod-shape

structure at the center called super helix.

- The intermediate filament is produced from 8 protofilaments.

c. Microtubules (25 nm)

- Basic components: α– and β–tubulin (53 and 55 kDa).

- Thirteen protofilaments form a ring-shape and polymerize to form a long tube.

- Important during mitosis.

Plant alkaloids:

 Vinblastine- vinca alkaloid; acts in G & S phases by inhibiting microtubule formation, inhibits DNA/RNA synthesis; antineoplastic

 Vincristine- vinca alkaloid; acts in M & S phases by inhibiting microtubule formation, inhibits DNA/RNA synthesis; antineoplastic.

 Colchicine- disruption of cytoskeletal functions through inhibition of β-tubulin polymerization into microtubules which prevents activation, degranulation, and migration of neutrophils thought to mediate some gout symptoms; antigout(acute gout).

 Paclitaxel (Taxol)- natural taxane, prevents depolymerization of cellular microtubules, which results in DNA, RNA, and protein synthesis inhibition’ antineoplastic

As the ionic strength increases, G actin aggregates reversibly to form F actin, a helical homopolymer. G actincarries a firmly bound ATP molecule that is slowly hydrolyzed in F actin to form ADP. Actin therefore also has an enzyme property (ATPase activity). Myosin is the globular protein that interacts with actin in myocytes for muscle contraction.

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Transcribers: Aclan, J.V., Advento, V., Bolos, C.,Cabiscuelas, Y.N., Cuaderno, C., Gamboa, K.A., Javier, K., Laurilla, L.B., Rodenas, E., Roxas, F.  Nucleus

- largest organelle of the eukaryotic cell. - repository and cellular localization of

storage, replication and expression of genetic information.

- contains almost 99% of the cell DNA except for the 1% present in the mitochondria.

- Biochemical reactions inside the nucleus: a. Replication (replication also occurrs in the

mitochondria)

b. Synthesis of rRNA by the nucleolus (dense part of the nucleus).

c. Transcription of the tRNA, mRNA, and other types of RNA (occurs in the euchromatin part of the nucleoplasm). d. Biosynthesis of NAD+

 Mitochondria

- compose the 1% DNA of the cell

- evolved from the “Endosymbiosis Theory” Function:

- Production of energy (ATP)

- Some processes occurring within the mitochondria: - Electron transport chain and oxidative phosphorylation - Urea cycle

- Tricarboxylic acid cycle/Citric acid cycle/Kreb's cycle - ß oxidation in animal cells

- ketogenesis Endosymbiosis Theory

Key concept: The endosymbiosis theory explains the origin of mitochondria and chloroplasts and their double membranes. This concept postulates that chloroplasts and mitochondria are result of years of evolution initiated by the endocytosis of an aerobic bacteria and blue-green algae. With this theory, an accepted mechanism on how eukaryotic cells evolved from prokaryotic cells is explained.

 Endoplasmic Reticulum

- network of tubules and flattened sacs that serve a variety of functions in the cell

Rough endoplasmic reticulum (rER) -coated with ribosomes Function:

- site of protein synthesis Smooth endoplasmic reticulum (sER)

-without ribosomes Functions:

- site of carbohydrate and lipid synthesis - helps to detoxify certain compounds  Golgi Apparatus

Transport from the ER through the Golgi apparatus

-receives (on the cis-side) many of the transport vesicles produced in the rough ER

-consists of flattened membranous sacs called the cisternae -exports many substances (from trans-side) in transport vesicles rERcis-Golgi network cisternae trans-Golgi network cell exterior

Function:

- modification, sorting, and packaging of proteins and other materials

 Vesicular organelles Lysosomes

-common in animal cells but rare in plant cells Functions:

- contain hydrolytic enzymes necessary for intracellular digestion

- get rid virus and bacteria, digest food particles and other damaged organelles

Peroxisomes Functions:

- involve in the breakdown of very long chain fatty acids

- contain the enzyme catalase which decomposes the toxic hydrogen peroxide

Secretory vesicles Function:

- transport substances to the cell surface for release

THE CELL MEMBRANE

Key Concept: The central architectural feature of biological membranes is a

double layer of lipids, which acts as barrier to the passage of polar molecules and ions.

Cell Membrane

Fluid Mosaic Model (Singer and Nicolson) – according to this model, the molecular arrangement of plasma membrane resembles a continually moving sea of fluid lipids that contains a mosaic of many different proteins.

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Cell Membrane Composition

The basic structural framework of the plasma membrane is the lipid bilayer.

A. Lipid bilayer

1. Phospholipids – lipids with phosphate groups

a. Phosphoglycerides – most common phospholipid; consists of glycerol backbone to which are attached two fatty acids in ester linkage and a phosphorylated alcohol (e.g. ethanolamine, choline, serine, glycerol or inositol)

b. Sphingomyelin – contains a sphingosine backbone instead of glycerol:

Ceramide = sphingosine + fatty acid

2. Glycosphingolipids (Glycolipids) – sugar containing lipids built on a backbone of ceramide

a. Cerebrosides b. Gangliosides

Note: The outer leaflet consists predominantly of

phosphatidylcholine, sphingomyelin, and glycolipids, whereas the inner leaflet contains phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol. 3. Sterols – steroidal alcohols

The most common of which is cholesterol, it intercalates among the phospholipids of the membrane, with its hydroxyl

group at the aqueous interface and the remainder of the molecule within the leaflet.

Note: Cholesterol is distributed in both leaflets of the lipid bilayer. B. Proteins 1. Integral proteins 2. Peripheral proteins C. Carbohydrates 1. Glycolipids 2. Glycoproteins Cell Membrane Functions 1. Boundary

2. Controlled metabolite transport 3. Signal reception and transmission 4. Enzymatic reactions

5. Contact with other cells 6. Anchor for cytoskeleton Cell Membrane fluidity

Membrane Fluidity refers to the viscosity of the lipid bilayer or the degree of resistance of membrane components to move. Several factors affect the fluidity of the membrane.

• Temperature (Higher temp., more fluid)

• Content of unsaturated FA (higher content, more fluid - Double bonds produce kink structures. These structures

are hard to pack, making disorganization in the membrane.

• Content of cholesterol (paradoxical- when cholesterol interacts with unsaturated/ short-chain fatty acyl PL results to less fluidity while when cholesterol interacts with

sphingolipids and long-chain fatty acyl PL tends to make it more fluid.

- Cholesterol and temperature: when amphipatic

cholesterol is placed in a very fluid membrane because of high temperature, it can penetrate deep into the membrane. low temperature makes the membrane less fluid, cholesterol can’t penetrate into the first layer of the membrane thus making it relatively more fluid.

[emphasized in the lecture]

- “Cholesterol inserts into bilayer membranes with its hydroxyl group oriented toward the aqueous phase and its hydrophobic ring system adjacent to fatty acid tails of phospholipids. The hydroxyl group of cholesterol forms hydrogen bonds with polar phospholipid head groups”.[1D trans, 2012]

- “Part of the steroid ring (the four hydrocarbon rings in between the hydroxyl group and the hydrocarbon "tail") is closely attracted to part of the fatty acid chain on the nearest phospholipid.

o This helps slightly immobilize the outer surface of the membrane and make it less soluble to very small water-soluble molecules that could otherwise pass through more easily.

o Without cholesterol, cell membranes would be too fluid, not firm enough, and too permeable to some molecules.In other words, it keeps the membranefrom turning to mush.”[1D trans 2012]

Cell Membrane Lipid Membrane Movement

Membrane Fluidity allows various components of the membrane to move in different directions. The lipid component may exhibit the following movement:

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Figure 2.1. Uncatalyzed lateral 6iffusion

Figure 2.2 Uncatalyzedtransbilayer diffusion

At physiological temperatures, transbilayer diffusion [flip-flop] of a lipid molecule from one leaflet to the other occurs very slow [figure 1x]. Lateral diffusion IN THE PLANE of the bilayer is very rapid [figure 2x].

Figure 2.3 Three types of phospholipid translocatorsin the plasma membrane [Nelson and Cox, 2010]

Flippase catalyze translocation of the aminophospholipids [phosphatidylethanolamine and phosphatidylserine] from the extracellular to the cytosolic leaflet. Flippases consume 1 ATP per molecule of phospholipid

Keeping phosphatidylserine out of the extracellular leaflet is important: its exposure on the outer surface triggers apoptosis and engulfment by macrophages that carry phosphatidylserine receptors

Floppase move plasma membrane phospholipids from the cystolic to the extracellular leaflet.like Flippases, they are ATP-dependent. They are members of ABC transporter family which actively transport hydrophobic substrates outward across the membrane.

Scramblases are proteins that move any membrane phospholipid across the bilayer down its concentration gradient [from leaflet that has higher concentration to the leaflet with lower concentration] activity is NOT ATP-dependent.

Cell Membrane Self-sealing

The lipid bilayer of the cell membrane has the ability to reseal after a small disruption through lateral diffusion of its lipid component. Larger tear due to mechanical stress is an energy-requiring process through Ca2+- dependent process similar to exocytosis-like process.

[emphasized in the lecture]

Cell Membrane Selective Permeability

The hydrophobic hydrocarbon chains in lipid bilayer provide an impervious barrier for ionic and polar substances. Specific proteins regulate the passage of these substances in and out of the cell. Aquaporins for water. Polar substances should shed its hydration shell in order to pass the hydrophobic barrier.

Cell Membrane Asymmetry

The cell membrane has different composition of lipid and protein in its outer and inner leaflet of the lipid bilayer.

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The lipid composition of the bilayer is asymmetric, with a higher content of phosphatidylcholine and sphingomyelin in the outer leaflet and a higher content of phosphatidylserine and phosphatidylethanolamine in the inner leaflet. Phosphatidylinositol which can function in the transfer of information from hormones and neurotransmitters is also only found

in the inner leaflet. [Lieberman and Marks, 2009]

CELL MEMBRANE PROTEINS

Types of Membrane Proteins

Integral proteins Peripheral proteins Have alpha-helical structure (with

15-20 amino acids that have bulky side-chains)

Have amphiphatic alpha-helical structure

Interact intensively with the phospholipids (require the use of detergents of solubilisation)

Do not interact directly with the hydrophobic cores of the phospholipids in the bilayer Removable only by agents (e.g.

detergents, organic solvents) that interfere with hydrophobic interactions

Removed by relatively mild treatments that interfere with electrostatic interactions or break hydrogen bonds (e.g. carbonate at high pH)

Hydropathy plot- the specific number of a transmembrane segment based on its amino acid sequence.

CELL DOMAINS

These are specialized features of plasma membrane.

1. Lipid rafts – thickened portion of the bilayer involved in signal transduction and anchorage. It is where GPI-anchors and interacting peripheral proteins can be found.

2. Caveolae – invaginations of lipid rafts by the action of caveolin. Important in membrane breakage and sealing.

CELL MEMBRANE TRANSPORT

- the transfer of solutes and information across membranes

TYPES OF CELL MEMBRANE TRANSPORT

a. Cross-membrane movement of small molecules

a. Diffusion (Passive and Facilitated) b. Active Transport

b. Cross-membrane movement of large molecules

(Endocytosis and Exocytosis)

c. Signal transmission across membrane

a. Cell surface receptors

1) Signal transduction (e.g. glucagon ->cAMP) 2) Signal internalization (coupled with endocytosis eg LDL receptors, Insulin and Glut transporters)

b. Movement to intracellular receptors (steroid hormones, thyroid hormones, retinoids, Vit. D)

d. Intracellular contact of Communication

A. PASSIVE TRANSPORT

- transport that do not require energy

-movement of solute from an area of HIGH CONCENTRATION to an area of LOW CONCENTRATION

-depends on concentration gradient; creation depends on 1. chemical gradient

-difference of solute concentration or its ratio C2 /C1

2. transmembrane electrical gradient (Vm in millivolts).

-Solutes follow the 2nd law of thermodynamics where it tends to assume spontaneously the greatest randomness and the lowest energy

1. Simple diffusion

- without membrane protein

 movement of solutes down its electrochemical gradient due torandom thermal movement or simply because the solute is

permeable through the lipid bilayer because it is small enough

and/or hydrophobic. 2. Facilitated diffusion

 movement of solutes down its electrochemical gradient through either transporters or ion channels (membrane proteins).

 Transporters allows the passage of hydrophobic solute by LOWERINGthe energy of activation of the solute

Figure1. Lowering of Activation energy with the use of transporters

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Transcribers: Aclan, J.V., Advento, V., Bolos, C.,Cabiscuelas, Y.N., Cuaderno, C., Gamboa, K.A., Javier, K., Laurilla, L.B., Rodenas, E., Roxas, F. Transporters vs. Channels

Transporters Channels

-Bind molecules and ions with high specificity, undergo conformational changes allowing the transport of molecules and ions across membranes

They show some specificity but does not act like an enzyme and only forms pores which open or close with much conformational changes

-Catalyze transport at rates well below the limits of free diffusion -saturable in the same sense as as enzymes so that futher increase in substrate conc.

-does not provide a greater transport which SLOWER THAN with channel

- does not act like an enzyme, it is not saturable with ion substrate (in contrast with saturation kinetics seen in transporters)

-transport is FASTER THANtransporter which may reach the limit of unhindered diffusion

Involve in passive (facilitated diffusion) and active transport

Mostly involve in facilitated diffusion

Types of Transport Systems based on Direction of Movement

Uniport system- moves one type of molecule bidirectionally

(egused in transporting glucose in the cell through the influence of insulin)

Co-transport system- transfer of one solute depends upon the

stoichiometric simultaneous or sequential transfer of another solute. >>2 types

 Symport- moves these solutes in the same direction (eg Glucose – sodium transport)

 Antiport-move two molecules in opposite directions

(eg, Na+ in and Ca2+ out; Chloride-bicarbonate exchanger of the RBC membrane)

Aquaporins

• water channels that only allow the passage of water molecules in the membranes of RBC and cells of the collecting ductules of the kidney.

• composed of tetramerictransmembrane proteins

• Mutation in some of these channel (AP-2) proteins may cause nephrogenic Diabetes Insipidus

Ionotropic Channels vsIonophores

Ionotropic Channels Ionophores

d e s c ri p ti o

n Receptors that are themselves acts as channels and DOES NOT NEED a secondary

messenger

Non-receptor compounds that produce channels or pores in the cell.

-If it produces pores or channels in bacteria, they serve as anti-bacterial.

-if they cause production of pores or channels on cell membranes of human cells, they cause injury or disease.

e x a m p le s *Acetylcholine- Na+ and Ca2+ *Serotonin and Glutamate- K+, Na+, Ca2+

*Glycine- Cl- Specific channels

*Valinomycin- K+channels *Monensin- Na+ channels *Gramicidin- folding creates hollow channels Bi o lo g ic a l s o u rc e s

*Dendrotoxin (mamba snake)- K+ *Tetrodotoxin (puffer fish)- Na+ *Cobrotoxin and alpha conotoxin- Acetylcholine receptor ion channel

*Diptheria toxin and activated complement- create large cellular pores causing lysis *Alpha-hemolysis (Strep.)- leak out ATP

- Type of cell membrane transport that requires energy expenditure

- Active transport is the diffusion of molecules and ions against its electrochemical gradient with the use of energy which is mostly

supplied by ATP.

o Its protein transporter has an ATPase activity hydrolyzing ATP to ADP producing the needed energy.

TYPES OF ACTIVE TRANSPORT

1. Primary Active Transport - solute accumulation coupled directly to

an exergonic chemical reaction such as breakdown of ATP

2. Secondary Active transport - occurs when endergonic (uphill)

transport of one solute is coupled to an exergonic (downhill) flow of a different solute that was originally pumped uphill by a primary active transport.

Figure 4.1. Illustrative concept of the types of active transport.

Figure 4.2 A concept of how a transport ATPase works; here, the binding of Phosphate from ATP to the receptor found on the Transport ATPase would facilitate a conformational change to allow the material to go into the cell.

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Figure 4.3 Taken directly from the lecture slide; here are some types of ATP-driven Active transporters. When ATP-driven is mentioned, it means that the channel requires the use of Adenosine Triphosphate (ATP) as energy in order to establish the transport of the cellular material.

NOTE: The discussion on Nerve Impulses involving ion channels and pumps is extensively discussed in Cell and Muscle Physiology; you may refer to your Physiology trans or book for an easier concept.

Figures 4.4 & 4.5 Some diseases associated with abnormalities in the cell membrane and in ion channels. What is important to note here is the general concept that:

Genetic Mutations  genes encoding for ion channels are therefore abnormal  Ion channel mutations  abnormalities in ion transport  diseases d/t channelopathies.

ARTIFICIAL MEMBRANES & THEIR IMPORTANCE - Drug delivery where liposome being hydrophobic can easily enter the

cell, cancer cell and bacterial cells(Liposomal Doxurubicin or

ticarcillin and tobramycin).

- Gene therapy- liposome can easily penetrate the nucleus that gene insert may be easily incorporated.

• The PL may be attached to an antibody where drug delivery may be target-oriented.

LIPOSOMES

Liposome-like structures underlie such things as LDL-particles and are being used in medicine among other areas.

-

Liposomes are bilayered lipid vesicles

-

Form by sonicating lipids in aqueous solution

-

Vehicles for drug, nucleic acid, Ab delivery

-

Used in cosmetics

-

Liposomes can be filled with drugs, and used to deliver drugs for cancer and other diseases.

**** Review Questions:

1. These interactions are the main driving force for the formation of lipid bilayers.

a. Hydrophilic interactions b. Hydrophobic interactions c. Hydrogen bonding d. Ionic bonding

2. Which of the following characterstics is shared by simple and facilitated diffusion of glucose?

a. Occurs down an electrochemical gradient b. Is saturable

c. Requires metabolic energy

d. Is inhibited by the presence of galactose e. Requires a Na+ gradient

3. The following biochemical reactions occur in the cytoplasm, EXCEPT:

a. Glycolysis b. Glycogenesis c. Kreb’s cycle d. Amino acid synthesis

4. Prokaryotic cells, but not eukaryotic cells have: a. Endoplasmic reticulum

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b. Histones c. Nucleoid d. Nucleus

e. Plasma membrane

5. Mitochondria is associated with all of the following, EXCEPT: a. ATP synthesis

b. DNA synthesis c. Protein synthesis

d. Hydrolysis of various macromolecules at low pH e. Two different membranes

6. Which of the following can transport a solute against its concentration gradient?

a. Primary active transport b. Facilitated transport c. Simple diffusion d. None of the above

7. According to the fluid mosaic model of a membrane: a. Proteins are always completely embedded in the

lipid bilayer

b. Transverse movement (flip-flop) of a protein in the membrane is thermodynamically favorable c. The transmembrane domain has largely

hydrophobic amino acids

d. Proteins are distributed symmetrically in the membrane

e. Peripheral proteins are attached to the membrane only by noncovalent forces

8. The ion channel that is affected in cystic fibrosis. a. Na+

b. K+ c. Ca2+ d. Cl

-9. The most abundant type of phospholipid in cell membranes. a. Sphingomyelin

b. Phosphoglycerides c. Glycolipids d. Cholesterol

10. Which of the following will specifically increase the fluidity of the cell membrane?

a. Decrease in temperature

b. Increase the unsaturated fatty acids c. Increase the saturated fatty acids d. Removal of cholesterol Answers