chapter 2 chapter 2 the chemical basis f life chapter 2: the chemical basis of life dr. nezar redwan

Chapter 2Chapter 2The Chemical Basis f Life

Chapter 2: The Chemical Basis Of Life Dr. Nezar Redwan

Chapt. 3: The Chemical Basis of Lifeللحياة الكيميائية األسس

المصطلـــــح تعريف المصطلــــــــــــــح

Matter ) ويشغل ) وزن كتلة له شئ أي عن عبارة المادة

ما حيزا+Matter Is Composed Of Chemical Elements كيميائية عناصر من المادة تتكون

Elementلمواد – ) إنحاللها يمكن ال التي المادة هو العنصر

أخرى(

Essential Elements الضرورية كائن) العناصر أي في وأبدا+ دائما+ توجد

حي(

Variable Elementsالمتفاوتة تركيب) العناصر في تدخل عناصر

كائن من وجودها في تختلف ولكنها الحي الكائن) آخر إلى

Trace Elementsاألثرية الكائن) العناصر تكوين في تدخل عناصر

بعضها أو أحدها يوجد وقد جدا+ ضئيلة بنسب الحي) غيرها دون معينة كائنات في

Compound من ) اكثر أو إثنين من تتألف مادة هو المركب

) ثابتة بنسب ترتبط والتي المختلفة العناصر

Atomبخصائص تحتفظ المادة في وحدة أصغر هي الذرة

العنصرProton ) الموجبة ) الكهربية الشحنة وحيد البروتونElectron ) السالبة ) الكهربية الشحنة وحيد اإلليكترونNeutron ) ( + كهربيا متعادل النيوترون

Isotopesاإللكترونات عدد نفس لديها والتي النظائر

النيوترونات عدد في تختلف انها إال والبروتونات


One Isotope Of Carbon Has 8 Neutrons Instead Of 6 )Written 14C(

على الكربوني النظير يحتوي نيوترونات 8عندمامن 14Cيكتب 6بدال+

An Ion Is An Atom Or Molecule With An Electrical Charge Resulting From Gain Or Loss Of Electrons

تنشأ كهربائية شحنة له جزيئ أو ذرة هو األيونإليكترونات فقدان أو إكتساب من

When An Electron Is Lost, A Positive Charge Results; When One Is Gained, A Negative Charge Results

وعند اإلليكترون فقد عند موجبة شحنة تنشأسالبة شحنة تنشأ إكتسابه

Two Ions With Opposite Charges Attract Each Other

متعاكستان شحنتان لهما اللذان األيونان يجذباآلخر أحدهما

When The Attraction Holds The Ions Together, It Is Called An Ionic Bond

ببعضها متماسكة األيونات التجاذب يجعل عندمااأليونية الرابطة ذلك على يطلق فإنه البعض

A Covalent Bond Results When Atoms Share Outer-Shell Electrons

الذرات تشترك عندما التساهمية الرابطة تنشأالخارجي المدار اليكترونات في

A Molecule Is Formed When Atoms Are Held Together By Covalent Bonds

ببعضها الذرات تتماسك حينما الجزيئ يتكونتساهمية روابط بواسط البعض

Biological Molecules الحيوية الجزيئاتInorganic عضوية غيرOrganic عضوية




Hydrogen Bond الهيدروجينية الرابطةCohesion التماسك خاصيةSurface Tension السطحي التوترHydrogen Bonds Are Responsible For Surface Tension

التوتر عن المسؤلة هي الهيدروجينية الروابطالسطحي

Chemicals Other Than Water Can Contribute H+ To A Solution

) أيون ) تعطي أن الماء غير الكيماويات تستطيعللمحلول هيدروجين

They Are Called Acids + أحماضا الكيماويات هذه تسمىAn Example Is Hydrochloric Acid )Hcl( الهيدروكلوريك حامض ذلك مثالThis Is The Acid In Your Stomach That Aids In Digestion

يساعد والذي المعدة في الموجود الحامض هو هذاالهضم على

An Acidic Solution Has A Higher Concentration Of H+ Than OH–

الهيدروجين ) أيونات المحلول ( +Hتركيز فيالهيدروكسيد أيونات تركيز من أعلى الحمضي

(OH–)A Ph Scale )Ph = Potential Of Hydrogen( Is Used To Describe Whether A Solution Is Acidic Or Basic

الهيدروجيني األس مقياس الجهد ) pHيستخدمحامضي( المحلول كان إذا ما لوصف الهيدروجيني

قاعدي أو




Sulfur And Nitrous Oxides React With Water In The Air To Form Acids

في الماء مع والكبريت النيتروز اكاسيد تتفاعلأحماض لتكون الهواء

These Fall To Earth As Acid Precipitation, Which Is Rain, Snow, Or Fog With A Ph Lower Than 5.6

حمضية كترسبات األرض إلى األحماض هذه تهبطبأس والضباب والثلوج األمطار خالل من

من أقل 5.6هيدروجيني

Greenhouse” Effect And Alters Ocean Chemistry

إلى الكربون أوكسيد ثاني من المزيد إضافةالبيت ” تأثير إنتاج في يساهم الجوي الغالف

الصوبة“ ) أو الدفيئة بتأثير أيضا+ يعرف األخضرالمحيطات( كيمياء من يغير كما الزجاجية




Topics Discussed in this chapter

1. Elements, atoms, and molecules.

2. Elements in the human body.

3. Radioactive isotopes.

4. Water properties.

5. Solutions, Acids, Bases, pH and Buffers.


Chemicals are the stuff that make up our bodies and those of other organisms.

They make up the physical environment as well.

The ordering of atoms into molecules represents the lowest level of biological organization.

Therefore, to understand life, it is important to understand the basic concepts of chemistry.

Introduction


ELEMENTS, ATOMS,

AND MOLECULES


2.1 Living organisms are composed of about 25 chemical elements

Chemicals are at the base level of biological hierarchy .

They are arranged into higher and higher levels of structural organization.

Arrangement eventually leads to formation of living organisms.


2.1 Living organisms are composed of about 25 chemical elements

Living organisms are composed of matter, which is anything that occupies space and has mass (weight)

– Matter is composed of chemical elements .

– Element—a substance that cannot be broken down to other substance.

– There are 92 elements in nature—only a few exist in a pure state.

– Life requires 25 essential elements; some are called trace elements.


Elements in the Human Body

Essential Elements

Variable Elements

Trace Elements

COHS P N CuNa Mg ClFeK IMnZn FSiSeCa

Invariably found in all living organisms

variably found in living organisms

found in trace amounts in some, but not all, organisms


2.2 CONNECTION: Trace elements are common additives to food and water

Some trace elements are required to prevent disease

– Without iron, your body cannot transport oxygen

– An iodine deficiency prevents production of thyroid hormones, resulting in goiter


Goiter in a Malaysian woman,

a symptom of iodine deficiency


2.2 CONNECTION: Trace elements are common additives to food and water

Several chemicals are added to food for a

variety of reasons

– Help preserve it

– Make it more nutritious

– Make it look better

Check out the “Nutrition Facts” label on foods and drinks you purchase


2.3 Elements can combine to form compounds

Compound—a substance consisting of two or more different elements combined in a fixed ratio.

There are many compounds that consist of only two elements.

Table salt (sodium chloride or NaCl) is an example.

Sodium is a metal, and chloride is a poisonous gas.

However, when chemically combined, an edible compound emerges.


Sodium Chloride

Chlorine Sodium

+

The emergent properties of the edible compound sodium chloride


2.4 Atoms consist of protons, neutrons, and electrons

An atom is the smallest unit of matter that still retains the properties of a element

Atoms are made of over a hundred subatomic particles, but only three are important for biological compounds

– Proton—has a single positive electrical charge

– Electron—has a single negative electrical charge

– Neutron—is electrically neutral


Electroncloud

Protons

6e–

Nucleus

Electrons

Mass number = 12Neutrons

6

6

6

Model of a carbon atomالكربون ذرة نموذج


2.4 Atoms consist of protons, neutrons, and electrons

Although all atoms of an element have the same atomic number, some differ in mass number

– The variations are isotopes, which have the same numbers of protons and electrons but different numbers of neutrons

– One isotope of carbon has 8 neutrons instead of 6 (written 14C)

– Unlike 12C, 14C is an unstable (radioactive) isotope that gives off energy


2.5 CONNECTION: Radioactive isotopes can help or harm us

Living cells cannot distinguish between isotopes of the same element.

– Therefore, when radioactive compounds are used in metabolic processes, they act as tracers.

– Radioactivity can be detected by instruments.

With instruments, the fate of radioactive tracers can be monitored in living organisms.

Radioactive tracers are frequently used in medical diagnosis.

Sophisticated imaging instruments are used to detect them.


2.5 CONNECTION: Radioactive isotopes can help or harm us

In addition to benefits, there are also dangers associated with using radioactive substances

– Uncontrolled exposure can cause damage to some molecules in a living cell, especially DNA

– Chemical bonds are broken by the emitted energy,


Biological Molecules

Inorganic

Organic

Water Bases

Acids

Salts

Carbohydra

te

Nucleic acids Lipids

Proteins


2.9 Water properties

Water has atoms with different electronegativities

– Oxygen attracts the shared electrons more strongly than hydrogen

– So, the shared electrons spend more time near oxygen

– The result is a polar covalent bond

(–) (–)

O

HH

(+) (+)

A water molecule


Water is PolarWater is Polar

In each water molecule, the oxygen oxygen atom attracts moreatom attracts more than its "fair share" of electronselectrons

The oxygenoxygen end “acts” negativenegative

The hydrogenhydrogen end “acts” positivepositive

Causes the water to be POLARPOLAR

However, Water is neutralneutral (equal number of e- and p+) --- Zero Net Zero Net ChargeCharge


2.10 Hydrogen bonds are weak bonds important in the chemistry of life

Hydrogen, as part of a polar covalent bond, will share attractions with other electronegative atoms

– Examples are oxygen and nitrogen

Water molecules are electrically attracted to oppositely charged regions on neighboring molecules

– Because the positively charged region is always a hydrogen atom, the bond is called a hydrogen bond


Hydrogen bond

Hydrogen bonds between water molecules


WATER’S LIFE-SUPPORTING PROPERTIES


2.11 Hydrogen bonds make liquid water cohesive

Hydrogen bonding causes molecules to stick together, a property called cohesion

– Cohesion is much stronger for water than other liquids.

– This is useful in plants that depend upon cohesion to help transport water and nutrients up the plant.


2.11 Hydrogen bonds make liquid water cohesive

Cohesion is related to surface tension—a measure of how difficult it is to break the surface of a liquid

– Hydrogen bonds are responsible for surface tension


Surface tension allows a water strider to walk on water

Water-conductingcells

Adhesion

Cohesion

150 µm

Directionof water

Movement

Water Transport in Plants


2.13 Ice is less dense than liquid waterالسائل الماء من كثافة أقل الثلج

Water can exist as a gas, liquid, and solid

– Water is less dense as a solid, a property due to hydrogen bonding


Liquid waterHydrogen bonds

constantly break and re-form

Ice Hydrogen Bonds are stable

Hydrogen bond

2.13 Ice is less dense than liquid water

When water freezes, each molecule forms a stable hydrogen bond with four neighbors

A three-dimensional crystal results

– There is space between the water molecules

Ice is less dense than water, so it floats


Liquid waterHydrogen bonds

constantly break and re-form

Ice Hydrogen Bonds are stable

Hydrogen bond

2.14 Water is the solvent of life

Water is a versatile solvent that is fundamental to life processes

– Its versatility results from its polarity

– Table salt is an example of a solute that will go into solution in water

– Sodium and chloride ions and water are attracted to each other because of their charges


Ion in solution Salt crystal

A crystal of salt )NaCl( dissolving in water

Properties of WaterProperties of Water

CohesionCohesion--Attraction between particles of the same Attraction between particles of the same

substance.substance.

AdhesionAdhesion--Attraction between two different substances.Attraction between two different substances.

• Water will make hydrogen bonds with other surfaces such as Water will make hydrogen bonds with other surfaces such as

glass, soil, plant tissues, and cottonglass, soil, plant tissues, and cotton. .

Less Dense as a SolidLess Dense as a Solid


2.15 Acidic and basic conditions

A few water molecules can break apart into ions

– Some are hydrogen ions (H+).

– Some are hydroxide ions (OH–) .

– Both are extremely reactive.

– A balance between the two is critical for chemical processes to occur in a living organism.


2.15 Acidic and basic conditions

Chemicals other than water can contribute H+ to a solution

– They are called acids

– An example is hydrochloric acid (HCl)

– This is the acid in your stomach that aids in digestion

An acidic solution has a higher concentration of H+ than OH–


2.15 acidic and basic conditions

A pH scale (pH = potential of hydrogen) is used to describe whether a solution is acidic or basic

– pH ranges from 0 (most acidic) to 14 (most basic)

– A solution that is neither acidic or basic is neutral (pH = 7)


The pH ScaleThe pH Scale

Indicates the concentration of Hconcentration of H++ ions ions

Ranges from 0 – 140 – 14

pH of 7 is neutral7 is neutral

pH 0 up to 7 is acid 0 up to 7 is acid … H+

pH above 7 – 14 is basicabove 7 – 14 is basic… OH-


AcidsAcids

StrongStrong Acids Acids have have a pH of a pH of 1-31-3

Produce Produce lots of lots of HH+ + ionsions


BasesBases

Strong Bases Strong Bases have a pH of 11 to 14 11 to 14

Contain lots of lots of OHOH--ions ions and fewer H+ ions


BuffersBuffers

Weak acids or bases that react with strong Weak acids or bases that react with strong acids or bases to prevent sharp, sudden acids or bases to prevent sharp, sudden changes in pH changes in pH )neutralization(.)neutralization(.

Produced naturally by the Produced naturally by the body to maintain body to maintain homeostasishomeostasis

Weak AcidWeak Acid Weak BaseWeak Base


حمضي Acidic solutionمحلول

pH scaleالهيدروجينية األس مقياس

Battery acidبطاريات حمض

0

1

2

3

4

5

Lemon juice, gastric juiceالمعدة عصارة ، ليمون عصير

Grapefruit juice, soft drink,vinegar, beer

غازي مشروب ، فروت جرب ، عصيرشعير شراب ، خل

Tomato juiceطماطم عصير

Rain water أمطار ماء

Human urine آدمي بول

Salivaلعاب

Pure water صافي ماء

6

7

Human blood,Tears

الدموع ، آآلدمي الدم

Seawater بحر ماء

8

9

10

11

12

13

Milk of magnesia المغنيسيوم حليب

Household ammoniaمنزلية أغراض أمونيا

Household bleachالمنزلية األغراض مبيض

Oven cleanerالفرن منظم

متعادل Neutral solutionمحلول

قاعدي Basic solutionمحلول

NEUTRAL[H+]=OH–]

تعادل

Incr

ea

sin

gly

AC

IDIC

(Hig

he

r c

on

cen

tra

tio

n o

f H

+)

ةضي

محا

الةاد

زي

14

Incr

ea

sin

gly

BA

SIC

(Lo

we

r c

on

cen

trat

ion

of

H+)

ةدي

عقا

الةاد

زي

The pH scale represents the relative concentration

of H+ and OH–


2.16 CONNECTION: Acid precipitation and ocean acidification threaten the environment

When we burn fossil fuels )gasoline and heating oil(, air-

polluting compounds and CO2 are released into the atmosphere

– Sulfur and nitrous oxides react with water in the air to form acids

– These fall to Earth as acid precipitation, which is rain, snow, or fog with a pH lower than 5.6.

– Additional CO2 in the atmosphere contributes to the “greenhouse” effect and alters ocean chemistry.


You should now be able to فعل على اآلن قادرا+ تكون أن ينبغييلي ما

1. Describe the importance of chemical elements to living organisms

. شرح اهمية العناصر الكيميائية للكائنات الحية1

2. Explain the formation of compounds

. شرح طريقة تكوين المركبات2

3. Describe the structure of an atom

. شرح تركيب الذرة3

4. Distinguish between ionic, hydrogen, and covalent bonds

. التفريق بين الروابط األيونية والهيدروجينية والتساهمية4

5. List and define the life-supporting properties of water

. تعديد وتعريف خصائص الماء المدعمة للحياة5

6. Explain the pH scale and the formation of acid and base solutions

. شرع معيار األس الهيدروجيني وطريقة تكون المحاليل الحمضية والقاعدية6

7. Define a chemical reaction and explain how it changes the composition of matter

. تعريف التفاعل الكيميائي وشرح كيفية تغييره لتركيب المادة7


1) All of the following are organic compound EXECPT:a) DNA b) Protein c) Waterd) Fat e) Phospholipids

2) ____________have the same numbers of protons and electrons but different numbers of neutrons.

a) Compounds b) Neutrons c) Elementsd) Electrons e) Isotopes

3) What is the atomic mass of an atom that has 6 protons, 6 neutrons, and 6 electrons?a) 6 b) 12 c) 18d) 24 e) None of the above

4) Cohesion is strongest in:a) Water b) Methyl Alcohol c) Ethyl

Alcohold) Benzene e) Ether

5) A/an _________ result from gain or loss of electrons.a) Element b) Electron c) Iond) Neutron e) Proton

Training Questions )Choose the right answer(


chapter 2 chapter 2 the chemical basis f life chapter 2: the chemical basis of life dr. nezar redwan

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