PHAROS UNIVERSITY FACULTY OF ALLIED MEDICAL SCIENCE

BIOCHEMISTRY 1 (MGBC-101)

Dr. Tarek El Sewedy

Department of Medical Laboratory Technology

Faculty of Allied Medical Sciences

Lecture 4Amino acids and proteins

Part 1

By the end of this lecture, students will learn:

1. Structure and function of amino acids

2. Amino Acids classification.

INTENDED LEARNING OUTCOMES

LECTURE CONTENT

• structure of Amino Acids

• Characteristics of amino acids

• Classification of amino acids

• Amino Acids and proteins nutritional facts

Structure of amino acids

• The basic structure of an amino-acid molecule consists of a carbon atom

bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen

atom, and a fourth group that differs from one amino acid to another and

often is referred to as the-R group or the side chain.

• The-R group, which can vary widely, is responsible for the differences in

chemical properties.

Amino Acids Amino acids are the building blocks of proteins.

There are 20 different amino acids that make up human proteins.

Groups of two amino acids are called di-peptides ,whereas three

amino acids together are called tri-peptides. more than 10 in a

chain, they are termed polypeptides.

A.A are linked together by Peptide bonds a special covalent bond

found in proteins.

11 out of 20 A.A can be synthesized in the body (non essential)

9 (essential) amino acids have to be obtained from food

The properties of each amino acid are determined by its

specific side chain ( R –groups ) R-groups vary in structure , Nature, electric charge

and solubility in water from one amino acid to other.

20 naturally occurring Amino acids

Amino acids names are often abbreviated as either 3 letters or single letters .

As the properties of the amino acids and their role in proteins are determined by the side chain , therefore amino acids are classified according:

1-Polarity of the side chain. -Acid -Basic -Neutral2- Structure of side chain - Aliphatic - Aromatic

Classification of Amino Acids (Depending on structure)

Neutral Amino AcidsThese amino Acids are considered neutral.

There is one carboxyl group per amino group

Acidic Amino AcidsThere are two acidic amino acids.There are two carboxyl groups and only one

amino group per molecule

Basic Amino AcidsThey have more amino groups than carboxyl

groups

Aliphatic side chain Aromatic side chain Sulphur – containing side chain Acidic side chain Basic side chain Hydroxyl side chain Imino Side Chain

CLASSIFICATION Depending on side chain structure

Amino acids may be characterized as

α, β , or γ

depending on the location of the amino

group on the carbon chain.

α are on the carbon adjacent to the

carboxyl group.

β are on the 2nd carbon

γ on the 3rd carbon from the

carboxyl group.

α, β, or γ Amino Acids

α− amino acidsAmino acids found in proteins are α− amino

acids.

The amino group is always found on the carbon adjacent to the carboxyl group

Metabolic Classification of the Amino Acids

Essential and Non-essential

Glucogenic and Ketogenic

Essential Amino AcidsOnly 11Of the 20 amino acids that make up proteins

can be synthesized by the human bodyThe other 9 amino acids must be acquiredfrom food sources. These amino acids are known as

essential amino acids

Non essential Amino Acids

Glucogenic or ketogenic Amino acids

Glucogenic amino acids are degraded to compounds that can be used as carbon skeletons for glucose synthesis via gluconeogenesis.

Ketogenic amino acids are degraded to compounds that can only be used to generate the ketone bodies.

Glucogenic Amino Acids

Ketogenic Amino AcidsMetabolized to acetyl CoA or acetoacetyl

CoA

Leucine

Lysine

Amino Acid Functions1. Amino acids are the building blocks of proteins.

2. Some amino acids and their derivatives function as neurotransmitters hormones and other regulators (Ex. L-

dopamine-Epinephrine-Thyroxine).

3. It may supply the carbohydrates pool with glucose ?????????.

Protein functions1. - Catalytic functions [enzymes]

2. - Receptor [insulin receptor]

3. - Structural function [collagen]

4. - Transport [hemoglobin]

5. - Protective functions [Antibodies]

Protein function (cont…)

6. - Hemostasis [clotting factors]

7. - Hormonal functions [insulin, glucagon, GH]

8. - Control of gene expression [transcription factors]

9. - DNA packing [histones]

10.- Act as buffers.

Protein nutritional facts

Spirulina

quinoa

soybeansAlmond

Good sources of protein

Amino Acid nutrition

Our body doesn’t use proteins in a direct way; first proteins are decomposed into amino acids and then amino acids are used for the resynthesize of muscular proteins

Students selected for assignment

عابدين محمود محمد أحمداحمد ابراهيم ساري

ASSIGNMENTS• Selected students are requested to prepare slides about one of the

following topics (To be delivered before next lecture):• Digestion of proteins • Essential amino acids.• Non essential amino acids• Physical properties of amino acids.• Chemical properties of amino acids.• Disease resulting from disturbance in amino acid metabolism.• Ketone bodies and amino acids• Translation of RNA

Study QuestionWrite three points about :

Function of amino acids1-

2-

3-

1- Tryptophan is ---------------------amino acida-Essentialb-Non essential c-Non-protein

Choose:

Correct the incorrect word:There are 30 alpha standard amino acids participate in protein synthesis.

Principles of Biochemistry, Donald J. Voet, Judith G. Voet, Charlotte W. pratt; Willey, 3rd ed.

Suggested readings: