Asam Amino

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ASAM AMINO Amino Acids

RAYMOND ARIEF N

Learning objectives • To understand

- the structural features of amino acids - the classifications of amino acids

- the properties of amino acids

Pendahuluan • Asam amino adalah penyusun protein • Terdapat 20 jenis asam amino alamiah In the following slides, we shall discuss about the structural features, classifications and properties of amino acids.

Struktur Asam Amino • Semua asam amino memiliki gugus amino (-NH3+), gugus karboksilat (-COO-) dan ikatan hydrogen dengan atom karbon (H-C) • Memiliki rantai samping (gugus-R) yang berbeda untuk setiap jenis asam amino • Gugus R bervariasi dalam struktur, ukuran, tekanan eletrik, dan perbedaan kelarutan dalam air

Structure of Amino acid

Penamaan Asam Amino  Didasarkan pada struktur D-gliseraldehid  jika gugus NH3+ di kanan  diberi awalan D,  jika NH3+ di kiri  diberi awalan L.  Semua asam amino yang ada di alam, dalam protein mempunyai konfigurasi L.  Ada beberapa asam amino penting dalam struktur protein dan metabolisme mempunyai konfigurasi D, yaitu: asam Dalanin dan D-glutamat yang merupakan komponen penyusun dinding sel bakteri tertentu.  Penulisan asam amino (20 asam amino yang umum) dapat disingkat dengan 3 huruf. Misal : Serine  Ser Glysin  Gly

RUMUS PERSPEKTIF COOH NH2

C

H H

CH3

L-ALANIN

RUMUSPROYEKSI

COOH

C

COOH

COOH

NH2

CH3

D-ALANIN

NH2

C

H

CH3

L-ALANIN

H

C CH3

D-ALANIN

Lavorotatori yakni berlawanan dengan arah jarum jam Dextrorotatory yakni searah jarum jam

NH2

Klasifikasi Asam Amino NUTRISI - Esensial - Non esensial

BERDASARKAN GUGUS R - Gugus R alifatik non polar - Gugus R polar tidak bermuatan - Gugus R aromatic - Gugus R bermuatan positif - Gugus R bermuatan negatif

Nutritional Classification of Amino acids Essential Amino Acids:

Nonessential Amino Acids:

Need to supplied in daily diet 1. Lysine 2. Leucine 3. Isoleucine 4. Metionine 5. Tryptophan 6. Phenylalanine 7. Threonine 8. Valine

Need not be supplied in daily diet • Alanine • Asparagine • Glycine • Tyrosine • Serine • Proline • Cysteine • Cystine • Histidine(essential for children) • Glutamine(conditionally essential) • Arginine(conditionally essential) • Glutamate

Glycine (Gly atau G)  Asam amino dengan struktur paling sederhana, hanya mempunyai satu atom H. Rantai samping Aliphatic berupa Alanine (Ala atau A), Valine (Val atau V), Leucine (Leu atau L), Isoleucine (Ile atau I) dan methionine (Met atau M) yang secara kimia tidak reaktif, tetapi secara alami hydrophobic. Proline (Pro atau P) juga hydrophobic, tetapi atom N berada dalam struktur cincin. Cysteine (Cys atau C) yang rantai sampingnya mengandung sulfur, juga hydrophobic dan sangat reaktif, mampu bereaksi dengan cysteine lain untuk membentuk ikatan disulfide

Rantai samping dari Asparagine (Asn atau N) dan Glutamine (Gln atau Q), masing-masing merupakan turunan Asp dan Glu tidak bermuatan tetapi dapat bertpartisipasi dalam mengikat hidrogen. Serine (Ser atau S) dan Threonine (Thr atau T) adalah asam amino polar karena gugusan hydroxyl dalam rantai samping yang reaktif, dan dapat juga berpartisipasi dalam mengikat hidrogen (seperti pada gugusan hydroxyl dari asam amino aromatic Tyr)

Phenylalanine (Phe atau F), Tyrosine (Tyr atau Y) Trypthophan (Trp atau W) yang hydrophobic karena icncin aromatic nya.

Gugusan amino pada rantai samping dari asam amino dasar bermuatan positif pada pH netral Arginin (Arg atau R) dan Lysine (Lys atau K). Rantai samping Histidine (His atau H) dapat bermuatan positif atau tidak bermuatan pada pH netral.

pada pH netral gugusan carboxyl pada rantai samping dari asam amino Aspartic Acid (Aspartate; Asp atau D) dan Glutamic Acid (Glutamate; Glu atau E) bermuatan negatif.

Structures and abbreviations of the standard amino acids

Properties of amino acids… - All the amino acids except glycine have handedness (chiral) Amino acids exist as D or L form that are nonsuperimposable mirror image of one another

– L-form naturally occurs in proteins

Structure of Amino acid (projection formula)

Horizontal bonds are assumed to project out of the plane of the paper, the vertical bond behind

Handedness of Amino Acids

Perspective formula: the wedge-shaped bonds project out of the plane of the paper and the dashed bonds behind it.

Properties of Amino Acids… •Amino acids form internal salts called zwitterions

•In the pure solid state and in aqueous solution near neutral pH, amino acids exist almost completely as zwitterions

Properties of Amino Acids… • In zwitterions of amino acids with uncharged side chain, the +ve and –ve Charges cancel one another • Amino acids in which the +ve and –ve charges are balanced is at its isoelectric point • The pH at which this balancing occurs is isoelectric pH

• An amino acids is least soluble at its isoelectric pH • Increases solubility at lower pH as well as at higher pH

Properties of Amino Acids • Amino Acids are linked to form peptide

• The condensation of the carboxylic group of one amino acid with the amino group of another amino acid releases a water molecule and forms a peptide bond or peptide link

Condensation reaction

Formation of a peptide bond

Amino acid residues

Peptide Bond

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