THE STRUCTURE AND FUNCTION OF

MACROMOLECULES2) Proteins :- Many Structures, Many

Functions1. A polypeptide is a polymer of amino acids connected in a specific sequence 2. A protein’s function depends on its specific conformation

Their functions include structural support, storage, transport of other substances, intercellular signaling

الخلوية بين movement, defense against microbes ,اإلشاراتand work as enzymes in the cell that regulate metabolism األيض.

Humans have tens of thousands of different proteins, each with their own structure and function.

All protein polymers are constructed from من the تتركبsame set of 20 monomers, called amino acids.

Polymers of proteins are called polypeptides ببتيدات.عديدة

A protein consists of one or more polypeptides folded and coiled into a specific conformation

2) Proteins

- The physical and chemical characteristics صفات of the R group determine تحدد the unique characteristics of a particular amino acid.

Side chain

Amino group

Carboxyl

group

General Formula of the Amino Acid: C

H

RN

H

HC

OH

O

- The side chain R links with بـ different ترتبطcompounds

*** - Monomer of amino acid includes a hydrogen atom, a carboxyl group, an amino group, and a variable متغيرة R group (or side chain), all covalently bonded to C atom.

- Differences in R groups produce the 20 different amino acids.

1. Hydrophobic: the amino acids that have hydrophobic R groups (non-polar).

Amino acids األمينية األحماض

2- Hydrophilic: the amino acids that have polar R groups, making them hydrophilic.

3- Ionized: the amino acids with functional groups that are charged (ionized) at cellular pH (7). So, some R groups are bases, others are acids.

The Peptide Bond البيبتيدية الرابطة

Peptide bond formed between the carboxyl group of one amino acid and the amino group of the other by dehydration.

OHC CH

RN

H

H

O

HCH

RNH

COH

O

Peptide bond

Polypeptide (Protein)

Dehydration الماء نزع

Amino acids Peptide

Amino acids are joined together when a dehydration reaction removes a hydroxyl group from the carboxyl end of one amino acid and a hydrogen from the amino group of another. The resulting covalent bond is called a peptide bond.

• Repeating the process over and over مرات creates a long عدةpolypeptide chain.– At one end is an amino acid with a free amino group the (the

N-terminus) and at the other is an amino acid with a free carboxyl group the (the C-terminus).

• The repeated sequence (N-C-C) is the polypeptide backbone.• Attached to the backbone are the various R groups.• Polypeptides range in size from a few monomers to thousands.

The folding إلتفاف of a protein from a chain of amino acids occurs spontaneously ذاتيا.

There are three levels of structure: primary أولى, secondary ثانوى, and tertiary ثالثى structure, are used to organize the folding within a single peptide chain.

Quaternary رباعى structure arises when two or more polypeptides (proteins) join to form another kind of protein.

Levels of Protein Structure

1. Primary structure:

It is a single peptide chain of amino acids.

Lysozyme, an enzyme that attacks bacteria, consists of a polypeptide chain of 129 amino acids.

A slight change طفيف تغييرin the primary structure can affect a protein’s conformation and ability to function.

Sickle cell disease الدم خاليا :المنجلية an abnormal hemoglobin because of a single amino

acid substitution تغيير. These abnormal hemoglobin crystallize, deforming يكسر

the red blood cells and leading to clogs إنسداد in tiny blood vessels أوعية.

2. The secondary structure: Results from hydrogen bonds at regular intervals على

متساوية .along the polypeptide backbone أبعاد

A. Coils الحلزونى (α-helix) are typical shapes

that develop from secondary structure

B. Folds (β-pleated sheets)المجعـد Composed .الشيت of several parallel α-helix coils attached by H bonds

An example for folds (β-pleated sheets) المجعد :الشيت Is the structural properties of silk الحريرbecause of the

presence of so many hydrogen bonds makes each silk fiber stronger than steel.

3. Tertiary structure: is determined by a variety of interactions among خالل

R groups and between R groups and the polypeptide backbone.

These interactions include weak bonds like hydrogen bonds among polar areas, ionic bonds between charged R groups, and hydrophobic interactions and Van der Waals interactions among hydrophobic R groups.

- Also include disulfide bridges, strong covalent bonds that form between the sulfhydryl groups (SH) of cysteine monomers, stabilize the structure.

4- The quaternary structure: Results from the aggregation تجمع of two or

more polypeptide chains.

Collagen is a fibrous protein of three polypeptides that are supercoiled, and function in connective tissues.

Hemoglobin is a globular protein withtwo copies of two kinds of polypeptides (2α and2β).

Collagen Hemoglobin

The 4 forms of protein

It is the change of protein’s conformation in response to لـ the physical and chemical إستجابةconditions.

For example, alterations تغيير in pH, salt concentration, temperature, or other factors can denature يفرد a protein. These forces break the hydrogen bonds, ionic bonds,

and disulfide bridges that maintain the protein’s complicated shape.

Some proteins can return to their original shape again after denaturation, but others cannot.

Denaturation of protein البروتين فرد

مفرود

Denaturation of protein البروتين *** فرد

فرد

إلى إعادةطبيعته

Amino acids

Primary

structure

Secondary

structure

Tertiary structure

Quaternary

structure1- Hydrophobic Interaction (Van

der Waals interaction);

2- H bonds;3- Ionic bonds;4- Di-

sulfide bridges;

Single chain of amino acids

e.g. LysozymeCoils &Folds

H bonds

e.g. silke.g. Collagen& Hemoglobin

two or more polypeptide

chains

Peptides

Peptide pondsDehydrati

on

Hydrophobic (non-polar R group) *** Hydrophilic (polar R group)

Ionized (charged functional groups)

Proteins

Polypeptides

Lipids; The Hydrophobic

Molecules

1.Fats store large amounts of energy2.Phospholipids are major components of cell

membranes3.Steroids include cholesterol and certain

hormones

Lipids are an exception among macromolecules because they do not have polymers.

The unifying feature المميـزة of lipids is الصفةthat they all have little or no affinity for water بالماء تـمتزج .ال This is because their structures are dominated by non-

polar covalent bonds. Lipids are the components مكونات of fats, and

are highly diverse in form and function. Although fats are not polymers, they are

large molecules assembled from من تتكونsmaller molecules by dehydration reactions.

A fat is constructed from two kinds of smaller molecules, glycerol and fatty acids

دهنية .أحماض

1) Fats:

A fat is composed of three fatty acids linked with one glycerol molecule. Fats are classified into Saturated مشبع and Un-saturated غير fats مشبع

OH

H H

C C CCCC H

HH

H H H H

H

H

O

OC

C

C

H

H

HH

OHOH

HH

Dehydration

Fatty Acid

Glycerol

Glycerol consists of a three C skeleton with an OH group attached to each C.A fatty acid consists of a carboxyl group (COOH) attached to a long carbon skeleton, often 16 to 18 carbons long.

Ester link

The many non-polar C-H bonds in the long hydrocarbon skeleton make fats hydrophobic.

In a fat, three fatty acids are joined to glycerol by an ester linkage, إستيرية = )creating a triacylglycerol رابطةtriglyceride) .

Fatty acids may vary تختلف in length (number of carbons) and in the number and locations of double bonds. If there are no carbon-carbon double bonds, then the

molecule is a saturated fatty acid مشبع (has H at every possible position).

•If there are one or more carbon-carbon double bonds, then the molecule is an unsaturated fatty acid دهنى حامض

مشبع formed by the removal of H atoms from the - غيرcarbon skeleton.

A)- Saturated Fats المشبعة الدهون

The Fatty acid components are saturated (there is no double bonds between the carbons. All C are linked with H. Thus, it is saturated with H.

Most animal fats are saturated. They are solid at room temperature.Saturated fats-rich diet results in Atherosclerosis التصلب .الشريانى

These double bonds are formed by the removal of H atoms. Most vegetable fats (oils) and fish fats are unsaturated. They are liquid at room temperature.They can be synthetically converted to saturated (solid) by adding H (Hydrogenation الهدرچـة).

B)- Un-saturated Fats مشبعة الغير الدهون

The major function of fats is energy storage. A gram of fat stores more than twice as much

energy as a gram of a polysaccharide. Humans and other mammals store fats as long-

term energy reserves المدى طويل طاقة in كمخزونadipose cells دهنية .خاليا

Phospholipids have two fatty acids attached to glycerol and a phosphate group at the third position. The phosphate group carries a negative charge.

2) Phospholipids; Are major components of cell membranes

• The interaction of phospholipids with water is complex.

• The fatty acid tails are hydrophobic, but the phosphate group and its attachments form a hydrophilic head.

When phospholipids are added to water, they self-assemble ذاتيا into تتشكلaggregates تجمعات with the hydrophobic tails pointing toward the center and the hydrophilic heads on the outside. This type of structure is

called a micelle الزهرة.• At the surface of a cell phospholipids are arranged as a bilayer مزدوجة .طبقة– Again, the hydrophilic heads

are on the outside in contact with the aqueous solution

المائى and the المحلولhydrophobic tails in the core .المركز

– The phospholipid bilayer طبقة حاجز forms a barrier مزدوجةbetween the cell and the external environment البيئة.الخارجية

• They are the major component of cell membranes.

Steroids are lipids with a carbon skeleton consisting of four fused ملتحمة carbon rings. Different steroids are created by varying functional groups

attached to the rings.

3) Steroids: Include cholesterol and certain hormones

• Cholesterol, an important steroid, is a component in animal cell membranes.

• Cholesterol is also the precursor الخام from which all المادةother steroids are synthesized. • Many of these other steroids are hormones, including the sex hormones.• While cholesterol is clearly an essential molecule, high levels of cholesterol in the blood may contribute to Atherosclerosis الشرايي نتصلب

F a t s

(Composed of Lipids)

Saturated

Unsaturated

PhospholipidsAnimal Fats Vegetable

FatsBi-layer of

cell membrane

Hydrogenation

هـدرچـــــــــة

SteroidsSex

Hormones &

Cholesterol

***

CHAPTER 5THE STRUCTURE AND

FUNCTION OF MACROMOLECULES

THE STRUCTURE AND FUNCTION OF

MACROMOLECULES

4- Nucleic Acids: The Informational Polymers

1. Nucleic acids store and transmit hereditary information الوراثية المعلومات

2. A nucleic acid strand is a polymer of nucleotides

3. Inheritance is based on replication of the DNA double helix