Amino Acids and Proteins5

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Amino Acids and Proteins

Larry Scheffler Larry Scheffler

Lincoln High School Lincoln High School

Portland OR Portland OR

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Protein

Protein adalah golongan senyawa organik

makromolekuler yang tersusun dari asam-

asam amino, dengan unsur penyusunnya

adalah C H O N , kadang- kadang

mengandung unsur S dan P.

Istilah protein berasal dari bahasa Yunani

“Proteos” berarti mempunyai peranan

penting.

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Fungsi Protein

Fungsi Protein :

1. Membangun sel baru

2. Mempertahankan sel

3. Mengganti sel yang telah Tua

Protein sangat diperlukan dalam sintesis

enzim, hormon dalam tubuh. Oksidasi 1 g

protein dapat menghasilkan 4 kalori.

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Penggolongan Protein

Berdasarkan susunan molekulnya protein dapat Berdasarkan susunan molekulnya protein dapat

digolongkan menjadi 3 golongan: digolongkan menjadi 3 golongan:

1. Protein Sederhana 1. Protein Sederhana

Adalah golongan protein yang tersusun dari asam- Adalah golongan protein yang tersusun dari asam-

asam amino saja. asam amino saja.

Contoh : albumin; globilin; glutalin; Histon.Contoh : albumin; globilin; glutalin; Histon. 2. Protein Komplek

2. Protein Komplek

Adalah golongan protein, yang tersusun dari asam- Adalah golongan protein, yang tersusun dari asam- asam amino dan senyawa lain non asam amino,

asam amino dan senyawa lain non asam amino, seperti H

seperti H₃₃POPO₄₄ dan Karbohidrat. Contoh : Nukleo dan Karbohidrat. Contoh : Nukleo protein; Chromoprotein; Lipoprotein; Glukoprotein protein; Chromoprotein; Lipoprotein; Glukoprotein

Fosfoprotein; Metallo Protein. Fosfoprotein; Metallo Protein. 3. Turunan Protein :

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Amino Acids

Amino acids have both

Amino acids have both  a carboxyl group a carboxyl group

-COOH-COOH

 an amino group an amino group

-NH_-NH₂₂

in the same molecule.. in the same molecule..

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Amino Acid Structure

The general formula of an amino acid is

shown here

The group designated by

The group designated by RR is usually a is usually a carbon chain but other

carbon chain but other

structures are also

possible

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Amino Acid Structure

Amino acids may be

Amino acids may be characterized as

characterized as __, , __ , or , or 

 amino acids depending amino acids depending

on the location of the on the location of the amino group in the amino group in the carbon chain.

carbon chain. 

 are on the carbon are on the carbon

adjacent to the carboxyl adjacent to the carboxyl group.

the carboxyl group the carboxyl group

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Amino Acids - Proteins

Amino acids are the building blocks of

proteins. Proteins are natural

polymers of successive amino acids

There are 20 different amino acids

that make up human proteins

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

amino acids

Amino acids found in

proteins are



amino acidsamino acids. .

The amino group is

always found on the

carbon adjacent to

the carboxyl group

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Amino Acid Functions

1.

1. Amino acids are the building blocks of Amino acids are the building blocks of

proteins

2.

2. Some amino acids and their derivatives Some amino acids and their derivatives

function as neurotransmitters and other

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Amino Acids and Proteins

Amino acids Amino acids

forming proteins forming proteins may be

may be

characterized as characterized as Acidic, Basic, or Acidic, Basic, or neutral

neutral

depending on depending on the character of the character of the side chain the side chain attached.

attached.

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Acidic Amino Acids

There are There are two acidic

two acidic

amino acids.

There are _{There are}

two carboxyl

groups and

only one

amino group

per molecule

(asp)

(glu)

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Basic Amino Acids I

These amino These amino acids are

acids are

basic. They

have more

amino groups

than carboxyl

groups

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Basic Amino Acids II

These amino These amino acids are also

acids are also

basic. They

have more

amino groups

than carboxyl

groups

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Neutral Amino Acids I

These amino These amino Acids are

Acids are

considered

neutral. There

is one carboxyl

group per amino

group

(ala)

(gly)

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Neutral Amino Acids II

(Tyr)

(Trp)

(Cys)

(Ser)

(Val)

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Neutral Amino Acids III

(Ile)

(Asp)

(Gln)

(Thr)

(Phe)

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Amino Acids and Optical

Isomers

 Except for glycine, all amino acids have a Except for glycine, all amino acids have a

chiral carbon atom

chiral carbon atom. Therefore they can . Therefore they can have

have optical isomersoptical isomers

 The amino acids found in The amino acids found in proteins proteins are all are all

levarotatory or L forms

levarotatory or L forms..

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Amino Acids are Amphoteric

 Amino acids are _{Amino acids are}amphoteric._amphoteric. They are capable of _{They are capable of}

behaving as both an acid and a base, since they have

both a proton donor group and a proton acceptor

group.

 In neutral aqueous solutions the proton typically In neutral aqueous solutions the proton typically

migrates from the carboxyl group to the amino group,

leaving an ion with both a (

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The Zwitterion

This dipolar ion form is known as a This dipolar ion form is known as a Zwitterion.Zwitterion.

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Essential Amino Acids

 Of the 20 amino acids that make up Of the 20 amino acids that make up

proteins 10 of them can be

synthesized by the human body

 The other 10 amino acids must be The other 10 amino acids must be

acquired from food sources. These

amino acids are known as essential

amino acids

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Essential Amino Acids

Essential amino acids

 Arginine Arginine  Histidine Histidine  Isoleucine Isoleucine  Leucine Leucine  Lysine Lysine

 Methionine Methionine

 Phenylalanine Phenylalanine  Threonine Threonine

 Tryptophan Tryptophan  Valine Valine

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Non-Essential amino acids

 Alanine _Alanine_{(from pyruvic acid)}_{(from pyruvic acid)}

 Asparagine Asparagine _{(from aspartic acid)}_{(from aspartic acid)}

 Aspartic Acid Aspartic Acid _{(from oxaloacetic acid)}_{(from oxaloacetic acid)}  Cysteine _Cysteine

 Glutamic Acid Glutamic Acid _{(from oxoglutaric acid)}_{(from oxoglutaric acid)}  Glutamine (from Glutamine (from _{glutamic acid)}_{glutamic acid)}

 Glycine (_{Glycine (}_{from serine and threonine)}_{from serine and threonine)}  Proline Proline _{(from glutamic acid)}_{(from glutamic acid)}

 Serine Serine _{(from glucose)}_{(from glucose)}

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Essential Amino Acids

Complete protein Complete protein

 Contains all 10 _{Contains all 10}

essential amino acids

 Proteins derived from Proteins derived from

animal sources are

complete proteins

 Beans contain some _{Beans contain some}

complete protein as

well

23 Incomplete protein Incomplete protein

 Lack one of more of the _{Lack one of more of the}

essential amino acids

 Most vegetable proteins Most vegetable proteins

are incomplete proteins

 Beans are an exception _{Beans are an exception}

to this generalizations

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Peptide Bond

When two amino acids combine, there is When two amino acids combine, there is a formation of an amide and a loss of a

a formation of an amide and a loss of a

water molecule

+ H₂O

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Proteins- Levels of Structure

Amino acids can undergo condensation Amino acids can undergo condensation

reactions in any order, thus making it possible

to form large numbers of proteins.

Structurally, proteins can be described in four _{Structurally, proteins can be described in four}

ways.

1. Primary 2. Secondary 3. Tertiary

4. Quaternary structure.

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Primary Structure

The primary structure of a protein is defined by

the sequence of amino acids, which form the

protein. This sequence is determined by the

base pair sequence in the DNA used to create it.

The sequence for bovine insulin is shown below

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Secondary Structure

 The secondary structure describes the way that the The secondary structure describes the way that the

chain of amino acids folds itself due to intramolecular

hydrogen bonding

Two common secondary structures are the _Helix 

and the _ sheet 

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Tertiary Structure

 The tertiary structure _{The tertiary structure} maintains the three

maintains the three

dimensional shape of

the protein.

 The amino acid chain _{The amino acid chain} (in the helical, pleated

(in the helical, pleated

or random coil form)

links itself in places to

form the unique twisted

or folded shape of the

protein.

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Tertiary Structure

 There are four ways in which parts of the amino acid _{There are four ways in which parts of the amino acid}

chains interact to stabilize its tertiary shape.. They include:

I.

I.-- -- Covalent bondingCovalent bonding, for , for

example disulfide bridges

formed when two cysteine

molecules combine in which

the –SH groups are oxidized:

II.

II.-- -- Hydrogen bondingHydrogen bonding between between

polar groups on the side chain.

III.

III.-- -- Salt bridgesSalt bridges (ionic bonds) (ionic bonds)

formed between –NH

formed between –NH₂₂ and – and – COOH groups

COOH groups

IV.

IV.---- Hydrophobic Hydrophobic interactions.interactions.

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Quaternary Structure

Many proteins are not single strandsMany proteins are not single strands

The diagram below shows the quaternary structure of The diagram below shows the quaternary structure of an enzyme having four interwoven amino acid strands an enzyme having four interwoven amino acid strands

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 The natural or native structures of The natural or native structures of

proteins may be altered, and their

biological activity changed or destroyed

by treatment that does not disrupt the

primary structure.

 Following denaturation, some proteins Following denaturation, some proteins

will return to their native structures under

proper conditions; but extreme

conditions, such as strong heating,

usually cause irreversible change.

Denaturing Proteins

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 Heat Heat

 Ultraviolet Ultraviolet

Radiation

 Some Organic Some Organic

Solvents

 AgitationAgitation

Denaturing Proteins

hydrogen bonds are broken by increased translational and vibrational energy.

(coagulation of egg white albumin on frying.) Similar to heat

(sunburn)

salt formation; disruption of hydrogen bonds. (skin blisters and burns, protein precipitation.)

competition for hydrogen bonds. (precipitation of soluble proteins.)

(e.g. ethanol & acetone) change in dielectric constant and hydration of ionic groups.

(disinfectant action and precipitation of protein.)

shearing of hydrogen bonds.

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 A small change in A small change in

the sequence of the sequence of

the primary the primary

structure can have structure can have

a significant a significant

impact on protein impact on protein

structure structure

 In sickle cell In sickle cell

anemia a glutamic anemia a glutamic acid is replaced by acid is replaced by

a valine in the a valine in the

amino acid amino acid

sequence sequence

Sickle Cell Anemia

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Ninhydrin Reaction

 Triketohydrindene hydrate, commonly known as Triketohydrindene hydrate, commonly known as

ninhydrin

ninhydrin, , reacts with amino acids to form a reacts with amino acids to form a

purple colored imino derivative, This derivative

forms a useful test for amino acids, most of which

are colorless.

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Protein Tests: Biuret

 Biuret reagent is a light blue Biuret reagent is a light blue solution containing Cu

solution containing Cu2+2+ ion ion

in an alkaline solution.

Biuret turns purple when

mixed with a solution

containing protein. The

purple color is formed when

copper ions in the biuret

reagent react with the

peptide bonds of the

polypeptide chains to form a

complex.

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Xanthroprotic Test

 Concentrated Nitric acid will form a yellow Concentrated Nitric acid will form a yellow

complex with tryptophan and Tyrosine side

chains in proteins

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Disulfide Bridge Test

 Disulfide bridges will react with PbDisulfide bridges will react with Pb2+2+

ion from lead acetate in an acidfied

solution. A black precipitate indicates

the presence of disulfide-bonded

cysteine in proteins.