1/27

University of Debrecen, Faculty of Medicine

• Dept. of Biophysics and Cell Biology

director: György Panyi, M.D., PhD., professor

• Biophysics Division (1st semester)

head: Péter Nagy, M.D., PhD., professor

• Biomathematics Division (1st and 2nd semester)

head: László Mátyus, M.D., PhD., professor

• Cell Biology Division (2nd semester)

head: György Vereb, M.D., PhD., professor

General Educational manager: Enikő Nizsalóczki

2/27

What is biophysics as a branch of science?

• An interdisciplinary science

• Provides a quantitative description of the physical principles of biology

and medicine

• What did biophysics give to medicine?

A. Understanding the operation of cells, tissues and organs at the

molecular level, e.g. functioning of the nervous system, role of ion

channels in action potential)

B. Understanding the pathomechanism of diseases, e.g. formation of

amyloid plaque in Alzheimer’s disease

C. Development of therapeutic approaches, e.g. photodynamic therapy,

ultrasound therapy)

D. Development of novel diagnostic tools: e.g. ECG, MRI, PET

A. C. D.

3/27

Energy and force

Attraction

Kinetic energy -

motion

Machines and

instruments

Varieties of molar

motion (pertaining to a

body of matter as a

whole, as contrasted with

molecular and atomic)

What does biophysics give a medical student?

1964

Long time ago:

• physics was taught as a part of universal

science

Now:

• Science and university education got

• specialized

• practice-oriented

• student-oriented

• Biophysics teaching follows these changes

• Aims nowadays

• way of thinking: almightiness of natural

laws

• scientific rigor: be doubtful about

pseudoscience

• explanation of physiological and

pathological processes, and diagnostic

methods

4/27

What is biophysics like? What are biophysicists like?

• Accurate, punctual (numbers have

meaning ! )

• physicist: interested in the 10th

decimal

• chemist: interested in the magnitude

• biologist: interested in whether

something increases or decreases

• Simplification, abstraction

???

5/27

What do you get from studying biophysics?

• Introduction to natural sciences

• Medical physics (e.g. physical principles of diagnostic procedures)

• Molecular biophysics (e.g. diffusion, membrane biophysics)

• Organ biophysics (e.g. vision, hearing, circulation)

• Link to other subjects

• Physiology

• Clinical physiology

• Radiology

6/27

7/27

• Make sense of what you learn

• How is it connected to previous

knowledge? How do you expect it to

be linked to future courses?

• Begin learning In time

• „I took a speed-reading course

and read War and Peace in

twenty minutes. It involves

Russia." - Woody Allen

This will be insufficient on

the exam

• You learn for yourself not for others, not to show off, not to put the

other one down, learning is your secret, it is all you have, it is the

only thing you can call your own. Nobody can take it away…

(Louise Bourgeois)

How to study at the university? How to study biophysics?

8/27

Classes

GM DENT

Biophysics lectures AOBIF05T1

• lectures: 2 h. weekly, w. 1-14

• seminar, 2 h. weekly, w. 1-14

FOBIF09D1

• lectures: 2 h. weekly, w. 1-13

• seminar, 2 h. weekly, w. 1-13

Biophysics Practical AOBIF06T1

• labs, 3 h. every 2 weeks

• total of 6 labs, weeks 1-14

FOBIF10D1

• labs, 3 h. every 2 weeks

• total of 4 labs, weeks 3-14

Seminar room F102

Biophysics lab F401

9/27

Office hours of the education manager (Dr. Enikő Nizsalóczki) from the 2nd week:

• Three times in a week, in the seminar room of the Department of Biophysics and

Cell Biology, Life Science Building, seminar room F.402

• At the same time for foreign and Hungarian students.

• Exceptions: There will be no office hours on the 1st week!

• Other exceptions and changes will be posted on the Elearning site

Monday 10:00-10:45

Thursday 15:45-16:30

Friday 14:00-14:45

Life Science Building

Ground floor

10/27

Contacting the Manager of Education

• The primary tool for contacting the Department is the e-mail:

biophysedu@med.unideb.hu

Advantages:

• If your problem (or question) can be solved by e-mail, you don’t need to go to the

office hours.

• Besides posting on the web site, we usually send “Neptun” messages about

important educational events (test writings, timetable changes, etc.). You will

receive them as an email as well, if you have a valid, working email address

registered in the “Neptun” system (and if you check it regularly…).

The only place and time we deal with students is seminar room

F.402 and during the office hours. Do not go to the 1st or 2nd

floor and disturb the teachers with your problems.

11/27

Educational web site: biophys.med.unideb.hu

12/27

Teaching material (protected content) :

https://elearning.med.unideb.hu/

• access using network ID

• one must be registered for the course

(theoretically the education department takes

care of it)

• upon login one must see the courses the

student is registered to

• These four courses run by the Biophysics

dept. must bee visible:

• Med., Dent., MB Biophysics Lecture

• Med., Dent. Biophysics Practical

• Biophysical analysis and formulas

• Med., Dent. Biostatistics

13/27

2008

Compulsory at

• University of Debrecen

• Semmelweis University

• University of Pécs

Lecture course (theory)

Textbooks, resources

Practical courseonline lab manual

14/27

Study-aid for the lecture material

• Being finalized now

• A quarter-page / half-page summary

to every lecture slide of every

lecture

Legend for the lecture material:

5*

!

2

,2

1mvAEAhf kinel

important material, required for

passing the exam

material required for excellent

supplementary material

only for the daredevil

equations marked by yellow are required

15/27

Understanding biophysical equations and their application: sample

problems and exercises. Moodle e-learning module

16/27

Minimum requirement questions

• Approx. 300 questions with the correct answers

• Summary of the most basic requirements

• Available as a PDF on the elearning site

• Not your enemy, but your friend …

• Not advisable to learn it independent of the material

Also usefulBasic terms for 1st year subjects

https://aok.unideb.hu/hu/tantargyi-alapfogalmak

• Not the same as the minimum requirement questions

• We do not explicitly ask it on the exam.

• But it is worth to know it …

17/27

Self control tests:

Week 7, 21th October (Monday) 07:00 AM

Week 11, 18th November (Monday) 7:00 AM

18/27

Electromagnetic waves, dual nature of light, matter waves

Why is electromagnetic radiation necessary?

• Light is the most important type of radiation. Besides its physiological aspects light has

extensive medical applications

- vision

- optical methods (microscopic techniques, endoscopy, etc.)

- therapeutic applications (photodynamic therapy, blue light therapy, photo-

chemotherapy, etc.)

• Some components of the electromagnetic spectrum (radio waves, X-rays and gamma

radiation) are also used for diagnostic and therapeutic purposes (e.g. CT, PET, MRI, etc.)

Previous knowledge (high school physics)

• Description and characterization of waves.

• Interference and deflection of (light) waves. Huygens’ principle.

• Production and propagation of electromagnetic waves.

• Work done by the electric field. Work-energy theorem.

What do we learn today?

• Dual nature of light (particle and wave)

• de Broglie hypothesis

• Thermal radiation emitted by bodies

• Heisenberg uncertainty principle

Aim: to learn …

• the experiments that prove the dual nature of light

• the energy of electromagnetic radiation is quantized

• it is physically impossible to measure simultaneously the exact position and exact linear

momentum of a particle

19/27

The nature of light

velocity in vacuum: c = 3 108 m/s

in other materials: v = c / n, (l= c / f ) where n is the index of refraction

End of the 19th century

electromagnetic wave

transversal wave propagating with the speed of light (c), having two

components, electric and magnetic

proof for the wave nature of light: interference phenomena

Beginning of the 20th century

particle (photon)

E = hf = hc / l, where h = Planck’s constant = 6.63 10-34 Js

proof for the particle nature of light: photoelectric effect

!

20/27

0 2 4 6 8 10

-1

-0.5

0

0.5

1

x

0 2 4 6 8 10

-2

-1

0

1

2

x

Constructive interference: waves are in phase

Destructive interference: waves are out of phase

Interference: property of waves

Two-slit experiment

Alternating bright and dark bands are

observed (interference) in accordance with

the predictions of wave theory.

Intensity distribution according to the particle

theory (one bright spot in the middle.

interfering waves

resultant wave

constructive destructive

constructive: bright

destructive: dark

interference

!

21/27

2

,2

1mvAEAhf kinel

The photoelectric effect can be adequately explained only by the photon concept

electrode made of potassium,

2 eV needed to eject an electron

A=2 eV (A – work function, ionization energy)

l700 nm

no photoelectron

l550 nm

vel=2.96·105 m/s

l400 nm

vel=6.22·105 m/s

The kinetic energy of the

ejected photoelectrons is

analyzed with an electric

field.

+ _

eUmv 2

2

1

U

photon

energy

KE of

electron

stopping

potentialΔE

(eV)

2.25 eV 0.25 eV -0.25V 2 eV

3.1 eV 1.1 eV -1.1V 2 eV

potential difference

low intensity light

high intensity light

stopping potentials

550 nm

400 nm cu

rre

nt

• According to the wave theory the kinetic

energy of photoelectrons is proportional

to light intensity.

• Since this is not the case, the photon

theory has to be used for the

interpretation of the photoelectric effect.

E=hf=hc/ l

Ephoton=1.77 eVEphoton=2.25 eV

Ephoton=3.1 eV

!

19,

19

1V 1.6 10 1V=

=1.6 10 J 1 eV

kinetic electron electronE q C

22/27

The wave nature of matter

• electromagnetic radiation has both wave- and matter-like properties

• Davisson and Germer succeeded in generating interference with electrons classically

regarded as a particles → electrons have wave-like properties too

• certain properties of elementary particles can only be explained by the wave model

• a wavelength (called de Broglie wavelength) can be assigned to any elementary particle:

p

hl

Planck’s constant

momentum (m x v)

The de Broglie wavelength of an electron:

nmv

mvvkg

Js 729000000729.0

101.9

1063.631

34

!

23/27

400 nm

750 nm

The electromagnetic spectrum!

24/27

Thermal radiation 1

Objects emit electromagnetic radiation whose spectrum depends on their temperature only, and is

independent of the material of the object. This radiation is called thermal radiation.

Kirchhoff’s law of thermal radiation:

j

j

i

iMM

,

,

,

,

l

l

l

l

Ml,i - the intensity of radiation emitted by object ‘i’ at wavelength l

l,i – the absorption coefficient of object ‘i’ (the ratio of the absorbed

radiation to the total radiation the body is exposed to)

If the emission of an object at a given wavelength is higher, it absorbs more efficiently at that wavelength.

The object whose absorption coefficient () is 1, i.e. it absorbs all the radiation it is exposed to), is

called black-body.

black

black

black

black

i

iM

MMM,

,

,

,

,

,

1l

l

l

l

l

l

Therefore the spectrum of thermal radiation emitted by any object can be determined with the

knowledge of the spectrum of a black body radiation and the absorption coefficient.

Textbook: page 123.

!

5*

25/27

) 4TTMblack

Stefan-Boltzmann law:

Thermal radiation 2

Wien’s law:

KmconstantT 3

max 109.2l

Frequency

0 1014 2x1014 3x1014 4x1014

Inte

nsity

0

2x10-17

4x10-17

6x10-17

1000K

2000K

Frequency

0 1014 2x1014 3x1014

Inte

nsity

0

5x10-18

10-17

2x10-17

2x10-17

Planck

Rayleigh-Jeans

Explanation of the spectrum:

e-

Thermal radiation is generated by

oscillating electrons in the body.

Electrons (charged particles) oscillate

at non-zero absolute temperature.

There are two counteracting principles in action:

1. ► as the frequency increases, the number

of the states (modes) of the oscillator

increases

► each mode of oscillation has the same

(kT) amount of energy (equipartition

theorem)

Rayleigh-Jeans law:

intensity increases

with the frequency

1+2 → Planck’s law

2. ► the energy of an oscillator can only change by

integer multiples of hf

► the higher the energy of an oscillator is,

the lower its occupancy is (Boltzmann distribution)

f1

e-

f2

Textbook: page 124.

!

5*

26/27

The Heisenberg uncertainty principle

The position (x) and the impulse (px) of an elementary particle can be

determined with limited accuracy at the same time:

hpx x

A similar relation holds for the energy-time pair: the energy and lifetime of

a state cannot be determined with infinite accuracy at the same time.

htE

Error sources in the experimental determination of a parameter:

1. Heisenberg uncertainty principle

2. the measurement itself alters the examined system

3. inaccuracy of the measurement

Werner Heisenberg (1901 - 1976)

I=?A Since the current meter has non-zero resistance, the measured

current will not be identical to what existed before the

measurement.

A consequence of the Heisenberg uncertainty principle is that the quantum world does not exist in

a deterministic form, but rather as a collection of probabilities (e.g. an interference pattern can be

predicted accurately, but the exact path of photons cannot.). This so-called Copenhagen

interpretation of quantum mechanics was disputed by Einstein („I cannot believe that God would

choose to play dice with the universe”).

The Heisenberg uncertainty principle is the consequence of the wave

(quantum)-nature of particles.

Measurement error. These have

nothing to do with the

Heisenberg uncertainty principle.

ad. 2

Textbook: page 29.

5*

27/27

Take-home message

• The dual nature of light can be demonstrated experimentally.

• According to de Broglie, electrons, just like light, have a dual particle-wave nature,

thus duality is a general characteristic of matter.

• A de Broglie wavelength can be defined for particles having a mass of m and

moving at a speed of v.

• Light consists of tiny particles called photons whose energy is proportional to the

frequency of the electromagnetic wave associated with it.

• As an MD

• The medical application of light is widespread in both diagnostics and therapy

• The wave nature of an electron is used in electron microscopy to produce

high-resolution microscopic images that opens up the possibility of imaging

sub-cellular details.