Lecture 1 - Plasma Membrane I (Lipids and Proteins)

8/12/2019 Lecture 1 - Plasma Membrane I (Lipids and Proteins)

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Biology 331Summer 2014


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Dr. Lars PetersenPart II (July 23end)

Office: BI 442

Tel.: 403-

E-mail: [email protected]

Dr. T. Don NguyenPart I (startJuly 21)

Office: BI 387

Tel.: 403-220-8167

E-mail: [email protected]

E-mail to make appointments

E-mails will be replied within 24 hours (48 hours on

weekends)


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Grade components

Midterm exam (July 21) 35%

Tutorial quizzes 10%

Tutorial term project 20%

Final exam 35%

(sometime between August 15 and 18)


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Terms you are expected to be already

familiar with

You need to know the following in terms of their: composition

function

Ribosome Bacteria /ProkaryoteDNA & deoxyribonucleotides Eukaryote

RNA & ribonucleotides Archaea

Sugar (carbohydrate) Multicellular

Lipid UnicellularEnzyme Transposon

Membrane Promoter

Periodic table of elements Gene = open reading frame (ORF)

Protein & amino acids acid and base chemistry


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10 m

1 m

100 mm

(10 cm)

10 mm(1 cm)

1 mm

Human height

Length ofsome nerveand musclecells

Chickenegg

Frog egg

Paramecium

100 m

Unaide

d

eye


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Plasma Membrane

(membrane lipids and proteins)


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Eukaryote Prokaryote

10-100m

0.1-10m

The plasma membrane is an essential

feature for all cells


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Essential roles of membrane

1) Compartmentalization2) Biochemical scaffold

3) Selective permeabilitybarrier

4) Solute transport5) Signalling

6) Intercellular interaction

7) Energy transduction

8) Flexibility

CO2+RuBP

PGA

2

Acid hydrolases

1

ADP+Pi

ATP

4H+

7

H2O3

6

IP3

Ca2+

5

8


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Membranes role # 1: Compartmentalization

Membranes are barriers between sets ofmolecules such as proteins eg. Outside of cell vs. inside Inside of an organelle

vs. cytoplasm

Provides an environment specialized for thefunction / biochemical reactions that take place

within the compartment

Most prokaryotes lack internal membranes,therefore they do not have internal organelles


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Membranes role # 2: Scaffold for biochemical

activities and cytoskeleton attachment

Membranes can act as surfaces for

biochemical reactions/cellular

processes

Some reactions are more efficient in

membranes than in solution

Membranes interact with the internalcytoskeleton; connects plasma

membrane to cytoskeleton

mb

Attachment

protein


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Membranes role # 3: Selective permeability barrier


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Restricts movement of ions: different

ionic compositions on opposite sides

of the membrane.

Allows gradients to be established

Different concentrations of the same

ion on opposite sides of themembrane can form

eg. Important for nerve and muscle

function and energy

mb

H+

H+

H+H+

H+

H+

H+H+

H+

H+

H+

H+H+

H

+

H+

IN OUT

Membranes role # 3: Selective permeability barrier


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Membranes role # 4: Transporting solutes

Membranes are sites where the movement ofmolecules from one compartment to the other.

eg. Ion channels, transporters


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Signals from one side of membrane elicit a response on the

other side; (eg. response to hormones, growth factors,neurotransmitters)

Membranes role # 5: Response to external signals


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Membranes role # 6: Intercellular interactions

Sites where neighboring cells interact

adhesion, communication/signals, metabolic

interactions

Example: sperm-egg fusion produces signals during

embryo development that prevent other competing

sperm from entering the egg

cell

cellConjugation Signalling

Surface receptor

Interactions


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Fibers of

extracellularmatrix (ECM)

Enzymatic

activity

Phospholipid

Cholesterol

CYTOPLASM

CYTOPLASM

Cell-cell

recognition

Glycoprotein

Intercellular

junctions

Microfilaments

of cytoskeleton

ATPTransport

Signal

transduction

Receptor

Signaling

molecule

Attachment to the cytoskeleton

and extracellular matrix (ECM)


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Membranes role # 7: Energy transduction

Sites of energy conversion

one form ofenergy alters to another

eg. membranes of chloroplasts and mitochondria

photosynthesis and cellular respiration

eg. rhodopsin proteins in cells of the eye

Light

retina

Human eye

Light energy gives

rhodopsin thepower to transport

ions across the

membrane


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Membranes role # 8: Flexibility and deformability

Changes in plasma membrane when cells

change shape cells crawling on a substratum

Changes in membrane organization when

vesicles pinch off from plasma membrane or

internal membranes

Amoeba proteus

Membranedeformations

during cell

division


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Chemical composition of

membrane


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Plasma membrane models

2013 John Wiley & Sons, Inc. All rights reserved.

1960s 1970s to date


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Major components: lipids and proteins

Lipids and proteins arrange in a lipid bilayer:

Act as the structural backboneof the membrane

Major component that estabilishes a permeability

barrier


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Membrane proteins: specific functions A lipid:protein ratio varies greatly depending on membrane

type and cell type

Membrane proteins can vary between differentmembranes or cell types depending on the function of themembrane

Carbohydrates (sugars) Glycolipids: sugars-attached lipids

Glycoproteins: sugar-attached proteins


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Lipid composition affects

membrane properties andmembrane protein function

Three major types: phospholipids,

sphingolipids, and sterols.

Lipid composition is different in

different membranes

Membrane lipids


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Phospholipids (phosphoglycerides) are the most abundant

membrane lipid.

Esterification of glycerol to:

-Phosphate

- Two fatty acids chains

Membrane lipid type # 1: Phospholipids


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Fatty (acyl) acid chains Are hydrophobic, unbranched hydrocarbons ~1620

carbons long. (eg. C16palmytate; C18sterate)

Fatty acid tails may be: polyunsaturated (>1 double bond)

monounsaturated (1 double bond eg. C18 oleate,C=C)

saturated (no double bonds)

H3C

COOH

COOHC10C12 C6C16

H3C C8


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Phospholipids are diverse in

head group and backbone

structure.

Usual additions to phosphate:

Cholinephosphatidylcholine

Ethanolamine

phosphatidylethanolamine

Inositolphosphatidylinosinol

HydrophilicHydrophobic
http://d/pages/art_150/ch04/pages/figure%2004-06a%20part%202.htmhttp://d/pages/art_150/ch04/pages/figure%2004-06a%20part%202.htm


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Phospholipids: hydrophilic +

hydrophobic = amphipathic.

In membranes, phospholipids

are organized into lipid

bilayers with polar head

groups on each surface and

fatty acyl chains in the core

HydrophilicHydrophobic
http://d/pages/art_150/ch04/pages/figure%2004-06a%20part%202.htmhttp://d/pages/art_150/ch04/pages/figure%2004-06a%20part%202.htm


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Phospholipids arrange into

a lipid bilayers that consist

of 2 leaflets

Polar head groups faceaqueous environment

Hydrocarbon tails form

hydrophobic inner core
http://d/pages/art_150/ch04/pages/figure%2004-04%20part%201.htm


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Membrane lipid type # 2: Sphingolipids

Sphingolipids play an important role in the nervous system and

are targets for infectious disease-causing microorganisms.


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Glycolipids: substituting a carbohydrate molecule onto

a ceramide.

CH2 C C CH

OHH2N

H H

CH (CH2)n CH3

CO R

Non-polar

HO+Sugar

Ceramide


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Glycolipids

Minor components of the membrane

ABO blood group antigens are glycolipids

Gal GlcNAc Gal Glu

Fuc

Gal GlcNAc Gal Glu

Fuc

Gal GlcNAc Gal Glu

Fuc

GlcNAc

Gal

O antigen

A antigen

B antigen


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Membrane lipid type # 3:


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Membrane lipid type # 3:

Sterols and similar compounds

50% of the membrane

smaller and less amphipathic than

other membrane lipids

campesterol

(plants: phytosterols)

cholesterol

(animals: zoosterols)

ergosterol

(fungi)

sterols

diploptene(bacteria: hopanoids)


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Cholesterol inserts between phospholipids: The small hydrophilic hydroxyl group faces the membrane

surface.

The rest is embedded in the lipid bilayer.

Its flat and rigid rings interfere with movement ofphospholipid fatty acid tails

Cholesterol decreases permeabilityand increases

durabilityof the membrane.

Cholesterols stiffenthe membrane


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Membrane lipids and fluidity

Phospholipids in a bilayer:


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Phospholipids in a bilayer:1. Flex and bend

2. Rotate

3. Diffuse laterally in the plane of the membrane4. Flip-flop from leaflet of the bilayer to the other leaflet

Occurs rarely on its own

Phospholipids can be found in different amounts in each leaflet ofthe membrane, with aid of special proteins called flippases


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1. Temperature

2. Acyl chain length

3. Acyl chain saturation

4. Sterol content

Mobility of lipid bilayers is

influenced many factors


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Factor # 1: Temperature

Lipid bilayers are more fluid at higher temperature due

to "melting" of lipid-lipid interactions Temperature at which phase transition occurs is

dependent upon the lipids present in the bilayertransition temperature

Temperature

Viscosity

Transition point: meltingtemperature (Tm)


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Factor # 2: Length of fatty acid acyl side chains

Viscosity

16-carbon fatty acidacyl chains

12-carbon fatty acid

acyl chains

Temperature

Tm Tm

Factor # 3: Unsaturated bonds


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Factor # 3: Unsaturated bonds

in fatty acid acyl chains

Saturated bonds decrease fluidity.

Unsaturated bonds increase fluidity.

Organization of saturated fatty acyl chains is more

regular than that of chains with unsaturated bonds.

Unsaturated bonds introduce "kinks" into the chains.


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kink in

chain due

to double

bond


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Viscosity

Temperature

16-carbon saturated

16-carbon mono-

unsaturated

Tm Tm

F t # 4 St l


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Factor # 4: Sterols

- At low temperatures: Cholesterol ring structures keep fattyacyl chains from interacting lowersmembrane viscosity

- At high temperatures: Cholesterol ring structures are more

rigid than fatty acyl chainsincreasesmembrane viscosity


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Membrane proteins


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Membrane Proteins

Carry out various functions in the membranes

Highly variable:

The amount of protein relative to lipid changes

between cell types and between different intracellular

membranes

Proteins may not be distributed homogenously

in membranes

eg. neuromuscular synapseapical-basal

membranes of epithelial cells Three types: integral, peripheral, and lipid-

anchored.

M b t i t # 1 I t l


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Membrane protein type # 1: Integral

Integral (intrinsic) proteinspass through lipid bilayer, and

cannot be removed withoutdistruption of the bilayer(detergents)

a) Single spanning

b) Multiple spanning

Transmembrane strand

M b t i t # 2 P i h l


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Membrane protein type # 2: Peripheral

Peripheral proteins:

- Are not inserted into thebilayer;

- Are found on either side

of the membrane;

- Interacts with

phospholipids or with

integral proteins.

- Can be removed by high

salt, low/ high pH, etc.

without disrupting bilayer

Membrane protein t pe # 3 Lipid anchored


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Membrane protein type # 3: Lipid-anchored

Lipid-anchored proteins do notpass all the way through the lipid

bilayer.

- Hydrophobic amino acid

groups allow proteins to insertinto internal (cytoplasmic)

leaflet

- Glycosylphosphatidylinositol

(GPI)-anchored proteins:covalently bonded to

phosphatidylinositol by

glycosylation.

P t i di t ib t d t i ll


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Proteins are distributed asymmetrically across

cellular membranes

Most sugar groupsof glycoproteins and glycolipids on

outer sideof plasma membrane


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Proteins can be mobile in lipid bilayers

Experiments showing that proteins are mobile in

membranes will be discussed in tutorials. Cellular membranes are considered to be fluid mosaics

ie. Molecules are not homogenously distributedinmembranes and most are mobile within the plane of themembrane.

Domains of cholesterol and sphinogomyleins can aggregatetogether to form lipid rafts.

Lecture 1 - Plasma Membrane I (Lipids and Proteins)

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