Class 01 Biological Membranes

8/3/2019 Class 01 Biological Membranes

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Bio 208 - Cell, Brain and Mind

Tues/Thur: 9:50 11:10 am, Javits 110

Course Director: Dr. Stephen Yazulla

Office 540 Life Science, 632-9877

[email protected] Lecturer: Dr. Lorne Mendell

Office 534 Life Science, 632-8632

[email protected]

Final Exam -Tuesday, December 1711:15 a.m., Room likely to be Javits 110
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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General Comments

The syllabus is posted on Blackboard, under Course

Documents. Topics of some lectures may bechanged.

Lectures will be posted in Course Documents.

There is NO text. Additional material will be postedor you will be directed to specific websites.

Questions and discussions of topics, particularlycontroversial issues, are encouraged.

Together, lets make this an interesting andexciting class.


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Please be on time!!!

I will start class promptly at 9:50.

Students who arrive late disrupt the class

and effectively steal time from theirfellow students.

Mutual consideration is the order of the day.


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Exam policy

There will be 4 hourly exams. Exam 1 Sept 24(Thur) Exam 2 Oct 22 (Tues) Exam 3 Nov 17 (Thur) Exam 4 Dec 17 (Thur) 11:15 12:35 (Finals Day)

The Final Hourly Exam has been scheduled for Thursday, December 17 from11:15 am to 1:45 pm.

No early exams will be given to accommodate Holiday travel nor willmakeups be given without documented medical or hardship excuses. If youhave a valid excuse for missing any of the first three hourly exams, youmay take a Makeup exam, which will be in an essay format and givenfollowing the 4th hourly on Finals Day. Note: that the 4th hourly will takeonly 1 hour and 20 minutes, a normal class period.

Cell phones and electronic dictionaries are not permitted duringany exam! Use of either of these devices will be considered asan act of Academic Dishonesty and treated as such.


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Course Overview;Membranes:Overcoming Barriers

Class #1

Bio 208


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Why study the Brain?

1990-2000 was decade of Brain

Defects in brain function are rarely fatal,

but have tremendous effect on quality oflife for the individual as well as family.

Neuroscience draws on virtually all other

scientific disciplines.


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Outline for today

Importance of biological membranes

Factors that control the movement of

substances across membranes Neuron Structure

Membrane potential

Re arrange with brain and neuron to setup course


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A fundamental problem in all

biology is the movement of materialacross a boundary from onecompartment to another.

The names of the substances andforces operating on them change butthe concept is the same for all cellsand organ systems.


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Homeostasis

Extracellular fluid surrounds all cellsand creates a buffer zone fromexternal world

Body actively maintains stability ofinternal environment.

Failure to maintain homeostasis resultsin pathological conditions.

Biological membranes are crucial tohomeostatsis.


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Biological Membrane


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Membrane Proteins

Structural maintain shape (cytoskeleton) and

hold cells together (cell junctions)

Enzymes catalyze reactions at cell surface

Receptors bind to chemical messengers

Transporters move chemicals acrossmembrane

Channels allow ions to pass throughmembrane

Surface recognition antibodies, self/non self


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Outline




Membrane potential


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Factors that determine the movement ofsubstances across any barrier

1.Movement from a high to a lowconcentration - does not requireenergy (Passive)

2.Movement from a low to a higherconcentration - requires energy(Active)

3.Whether it is soluble in water or fat4.Whether it is charged or neutral

5.Composition and thickness of the barrier


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Movement of substances across a plasmamembrane

Passive penetrate membrane withoutenergy input from cell, substances movedown concentration gradient (Diffusion -

lipids). Facilitated diffusion if protein carrieris involved (water soluble molecules)

Active cell provides metabolic energy from

ATP to a protein carrier to movesubstances against their concentrationgradient (Active Transport).


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Chemicalssimply movedown theirconcentrationgradients.


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Movementof a lipid-insolublemoleculefacilitated

by a carrierprotein.


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Importance ofFatversusWater solubility

Fat soluble molecules easily diffuse acrosscell membranes

Water soluble molecules do not and thusrequire protein pores or transporters.

These facts have major consequences for:

Stability of brain environment relative toblood

Protection of fetus from maternal circulation Effectiveness of drugs and anesthetics


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Two examples of disturbed

membrane proteins Cystic fibrosis defect in a transport

protein

Type 2 diabetes defect in the insulinreceptor protein needed for glucosetransport into the cell.


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Cystic fibrosisan inherited disease that affects multiple parts of the

body including the pancreas, sweat glands and lungs.


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A 3 year old receives back patting and poundingto loosen mucous so that it can be coughed up.


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People without cystic fibrosis have a small layer of salt water in thelarge airways of their lungs. This layer of salt water is under themucus layer which lines the airways and helps to clear dust andother inhaled particles from the lungs.

In people without cystic fibrosis, cystic fibrosis proteinsallow salt (chloride) to enter the air space; water then follows byosmosis. The mucus layer is dilute and not very sticky.


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In people with cystic fibrosis, the cystic fibrosis

proteins do not work; this means that no salt (chloride)enters the air space and water does not move either. Themucus layer is thus concentrated and very sticky.


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Outline




Membrane potential


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Neurons are excitable cells that:

1. generate and carry electricalsignals in response to some

stimulus.2. transmit these signals to otherneurons, muscles or gland cells bychemical transmitters.


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Neuron Communication

Neurons communicate with each otherelectrically and chemically.

We will focus on the chemical signals:

Hormones/Neurohormones -long distances via blood, alltissues are exposed to thehormone

Neurotransmitter- short distance,local action between individualneurons.


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Chemical signal

From one end of theneuron to the other

From one neuronto another

Sensory or Neural Stimulus


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Neurohormones and endocrinehormones are released directly intothe bloodstream. All tissues areexposed to the hormone BUT- Onlycells with the appropriate receptorsrespond to the hormone.

Very Important Concept!


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Presynaptic neuron

Postsynapticneurons


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Myelin Sheath


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Input Integration Output


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Outline




Membrane potential


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Neurons are little batteries How do they get that way?

There are fewer molecules with apositive charge inside the cell thanoutside.

This makes the inside of the cellnegative with respect to the outside.

The most important molecule in this

process is potassium (K+). I will briefly describe how this works.


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(substances in solution cannotcross membrane)


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El h i l E ilib i


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Electrochemical Equilibrium

When the chemical gradient driving potassiumout of the cell is exactly balanced by theelectrical gradient pulling potassium into thecell.

In a normal neuron, this occurs when theinside of the cell has a negative voltage ofabout 70 mV (or about 0.07 volts). Comparewith a AAA battery that has 1.5 volts.

All Neurons have a RESTING potential.

The resting potential of a neuron can be recorded with


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The resting potential of a neuron can be recorded withelectrodes. It is NEGATIVE on the inside, relative to areference electrode on the outside.

The reference electrode is also referred to as ground, that is, theearth as an infinite source of electrons. This is similar to sea level,in which altitude is referred to as above or below.


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For a very brief period of time (about 1/1000of a second) this equilibrium is disturbed and

the neuron goes from being very negative tovery positive inside.

This disturbance becomes the electrical signalthat allows information to go from one end ofthe neuron to the other.

It is called the ACTION POTENTIAL and wewill talk about this in the next lecture.

Class 01 Biological Membranes

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Transcript of Class 01 Biological Membranes