Unit4Lecture-3

7/27/2019 Unit4Lecture-3

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PHOTO INDUCED

EFFECTS IN BIOLOGICALSYSTEMS


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Photosynthesis

Ultraviolet Effects

Vision

Circadian Rhythmor cycle


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The synthesis of organic compounds

primarily sugars from carbon dioxide

and water (or other hydrogen(electron)

donors) using sunlight as the source of

energy and chlorophyll (or some other

closely related pigment) for trapping the light

energy.

1.PHOTOSYNTHESIS


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6CO2 + 6H2O C6H12O6 + 6O2

Carbon Dioxide Water GLUCOSE Oxygen.

Sunlight

Chlorophyll


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The Two Stages of Photosynthesis

Photosynthesis consists of two

processes

The light reactions

The Calvin cycle


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Factors affecting photosynthesis

Light irradiance and wavelength

Carbon dioxide concentration

Temperature


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2.UV Effects


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The sun radiates energy in a wide range ofwavelengths, most of which are invisible tohuman eyes.

The shorter the wavelength, the moreenergetic the radiation, and the greater thepotential for harm.

Ultraviolet (UV) radiation that reaches the

Earths surface is in wavelengths between290 and 400 nm


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Radiation at the longer UV wavelengths of

315-400 nm, called UV-A, plays a helpful

and essential role in formation of Vitamin D

by the skin, and plays a harmful role in that itcauses sunburn on human skin and

cataracts in our eyes.


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The majority of positive health effects relate

to vitaminD which has regulatory roles in

calcium metabolism (which is vital for normal

functioning of the nervous system, as well asfor bone growth and maintenance of bone

density) immunity, cell proliferation, insulin

secretion and blood pressure
http://en.wikipedia.org/wiki/Insulinhttp://en.wikipedia.org/wiki/Insulin


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The incoming radiation at shorter

wavelengths, 280-320 nm, falls within the UV-B

part of the electromagnetic spectrum.

UV-B causes damage at the molecular level tothe fundamental building block of life

deoxyribonucleic acid (DNA).


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DNA readily absorbs UV-B radiation, which

commonly changes the shape of the

molecule .

Changes in the DNA molecule often meanthat protein-building enzymes cannot read

the DNA code at that point on the molecule.

As a result, distorted proteins can be made,

or cells can die.


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3.VISION

Electromagnetic radiation all energywaves from short gamma rays to long

radio waves

Our eyes respond to a small portion of thisspectrum called thevisible spectrum

Reflected light translated into mental

image Pupil limits light, lens focuses light

Retinal rods and cones are photoreceptors


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The Retina: Photoreceptors

Rods:

Respond to dim light

Are used for peripheral vision

Cones:

Respond to bright light

Have color vision


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Excitation of Rods

The visual pigment of rods is rhodopsin(opsin + 11-cis retinal)

Light phase Rhodopsin breaks down into all-trans retinal +

opsin (bleaching of the pigment)

Dark phase

All-trans retinal converts to 11-cis form

11-cis retinal is also formed from vitamin A

11-cis retinal + opsin regenerate rhodopsin


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Excitation of Cones

Visual pigments in cones are similar to

rods

(retinal + opsins)

There are three types of cones: blue,

green, and red

Intermediate colors are perceived by

activation of more than one type of cone

Method of excitation is similar to rods


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LASER and Eyes

Laser light in the visible to near infraredspectrum (i.e., 400 - 1400 nm) can causedamage to the retina resulting in scotoma(blind spot in the fovea). This wave band isalso know as the "retinal hazard region".

Laser light in the ultraviolet (290 - 400 nm) orfar infrared (1400 - 10,600 nm) spectrum cancause damage to the cornea and/or to thelens.


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4.Circadian Rhythmor cycle

From the Latin circa (about) dies (a day), thecircadian rhythm is the twenty-four-hour cycle oflight/dark, wakefulness/sleep to which mosthuman physiologic processes are set.

At regular intervals each day, the body tends tobecome hungry, tired, active, listless, energized.

Body temperature, heart-beat, blood pressure,hormone levels, and urine flow rise and fall in

this relatively predictable, rhythmic pattern - apattern initiated and governed by exposure tosunlight and darkness.


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The biological clock can keep the time; but

in the absence of correction from the

day/light cycle provided by the sun, the

biological clock tend go out of syncaffecting our physical and mental

health(e.g.,hormonal imbalances, sleep

disorders and mood disturbances) .


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Circannual Rhythm

Circannual rhythm is the annual or yearly

cycle used by all living things.


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Circaseptan Rhythm Circaseptan rhythm is a seven-day cycle in which the

biological processes of life, including disease symptomsand development, resolve.

Many physicians believe that transplant patients tend tohave more rejection episodes seven, fourteen, twenty-one, and twenty-eight days after surgery.

They further believe that medications administered to thepatients at particular times may be more effective than at

other times. These are all related to the circaseptan rhythm.


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Chronobiology is a new science that is

concerned with identifying our cycles and

internal clocks and seeing how they

interact.

Such natural rhythms as temperature

fluctuations, weather systems, patterns of

light and dark are studied to explore how itaffects the life cycle of men and women.


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Thank You!

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Unit4Lecture-3