Lecture 1

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Molecular biology Sabah Linjawi ١

Lecture 1

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Molecular biology Sabah Linjawi ٢

Proteins

„ Proteins are polymers of

amino acids covalently linked through peptide bonds into a chain.

„ Within and outside of cells, proteins serve a myriad of

functions, including structural roles (cytoskeleton), as

catalysts (enzymes),

transporter to ferry ions and molecules across membranes, and hormones.

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Molecular biology Sabah Linjawi ٣

Amino Acids

„ Proteins are polymers of amino acids joined together by peptide bonds.

„ There are 20 different amino acids that make up essentially all proteins on earth

„ Each of these amino acids has a fundamental design composed of a central carbon (also called the alpha carbon) bonded to:

„ a hydrogen

„ a carboxyl group

„ an amino group

„ a unique side chain or R-group

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Molecular biology Sabah Linjawi ٤

Amino Acids

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Molecular biology Sabah Linjawi ٥

Amino Acids

„ The characteristic that distinguishes one amino acid from another is its unique side chain, and it is the side chain that dictates an amino acids chemical properties .

„ The amino acids are shown with the amino and carboxyl groups ionized, as they are at physiologic pH.

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Molecular biology Sabah Linjawi ٦

Amino Acids

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Except for glycine, which has a hydrogen as its R- group, there is asymmetry about the alpha carbon in all amino acids.

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Because of this, all amino acids except glycine can exist in either of two mirror-image forms.

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The two forms - called stereoisomers - are referred to as D and L amino acids.

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With rare exceptions, all of the amino acids in

proteins are L amino acids.

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Molecular biology Sabah Linjawi ٧

Peptides and Proteins

„ Amino acids are covalently bonded together in chains by peptide bonds.

„ If the chain length is short (say less than 30 amino acids) it is called a peptide

„ longer chains are called polypeptides or proteins.

„ Peptide bonds are formed between the carboxyl group of one amino acid and the amino group of the next amino acid.

„ Peptide bond formation occurs in a condensation reaction involving loss of a molecule of water.

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Types of Proteins

„ Based upon chemical composition, proteins are divided into two major classes:

„ 1- simple proteins, which are composed of only amino acids

„ 2- conjugated proteins, which are composed of amino acids and additional organic and inorganic groupings, which are called prosthetic groups.

„ Conjugated proteins include:

„ glycoproteins, which contain carbohydrates

„ lipoproteins, which contain lipids

„ nucleoproteins, which contain nucleic acids

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Classified by biological function

„ proteins include the enzymes, which are responsible for

catalyzing the thousands of chemical reactions of the living cell

„ keratin, elastin, and collagen, which are important types of structural, or support, proteins

„ hemoglobin and other gas transport proteins; ovalbumin, casein, and other nutrient molecules

„ antibodies, which are molecules of the immune system

„ protein hormones, which regulate metabolism

„ proteins that perform mechanical work, such as actin and myosin, the contractile muscle proteins.

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Molecular biology Sabah Linjawi ١٠

Conjugated proteins

„ These proteins consist from protein and other compounds, which are called according to the group associated with it, such as:

„ 1- Nucleoproteins: protein and nucleic acid which are found in the nucleus

„ 2- Chromoproteins: Proteins and colored compounds such as hemoglobin in the blood is associated with an iron (Fe +2), as well as chlorophyll, the green protein is associated with the element magnesium (Mg +2) and may not contain an element of the group such as proteins associated with melanin in hair

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Molecular biology Sabah Linjawi ١١

Conjugated proteins

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Molecular biology Sabah Linjawi ١٢

Conjugated proteins

„ 3- Phosphoproteins: Proteins and the phosphate group such as Casein in milk and Vitellin in the egg yolk

„ 4- Glycoproteins :Protein and sugars,the carbohydrates part consists of short-chain branching, and plays an important role in the cell, such as some enzymes, hormones and antibodies

„ 5- Lipoproteins : Protein and fat which are found in cell membranes and blood plasma and egg yolk

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Molecular biology Sabah Linjawi ١٣

References

„ www.vivo.colostate.edu/hbooks/genetics/.../prostruct.html

„ en.wikipedia.org/wiki/Protein_structure

„ www.chemguide.co.uk/organicprops/.../proteinstruct.html

„ www.rothamsted.ac.uk/notebook/courses/guide/prot.htm

„ www.friedli.com/herbs/phytochem/proteins.html

„ themedicalbiochemistrypage.org/protein-structure.html

„ Molecular Biology. P.C. Turner, A.G. Mclennan, A.D. Bates &

M.R.H. White.School of Biological Sciences, University of Liverpool, Liverpool, UK. Second edition. BIOS Scientific Publishers, 2000.