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LAX5-1

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Chapter

#

STRUCTURE AND

FUNCTION OF

MACROMOLECULES

In This Chapter

5.1 Introduction

5.2 Carbohydrates

5.3 Proteins

5.4 Enzymes

5.5 Nucleic Acids

5.6 Lipids and Biological Membranes

5.1

INTRODUCTION

W

e have discussed the structure and dynamics of smaller biomolecules, which form the building blocks of the important cellular macromolecules, in earlier chapters. These biomolecules can undergo polymerization or condensation to form specific polymers of high molecular weight known as macromolecules. These macromolecules are of four distinct groups—carbohydrates, proteins, nucleic acids, and lipids. All these macromolecules are specialized for carrying out specific cellular functions, which are very closely related to their functions. So a clear understanding of their structure is required for the proper understanding of their functions in the cell metabolism.

5.2

CARBOHYDRATES

Carbohydrates, as we have discussed in the previous chapter, consist of monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Monosaccharides, or the simple sugars, are the building blocks or the monomers by which other forms are constructed. Disaccharides consist of two monosaccharide residues linked together by glycosidic bonds. This bond forms between the OH group of anomeric carbon (carbon No.1) of one sugar and with the OH group of any other carbon atom, preferably of 4th or 6th position of another sugar. The number of monomers varies

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LAX19-2

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PLANT CELL CULTURE

AND

APPLICATIONS

#&!

suspension or to intact or sliced plant tissues. For example, plant meristems or tissues capable of regeneration can be targeted directly. Unlike electroporation and microinjection, this technique does not require protoplasts or even single-cell isolations. Using biolistics, transgenic corn and soybean plants have been produced that contain heritable copies of the inserted gene.

This is also a highly mechanized or robotic mediated technique in which the speed of the micro-projectile particles is controlled by certain specific mechanisms such as high voltage electric pulse, air pressure, or gunpowder percussion.

Transgenic Analysis

The selection of transformed cells, whether plant or animal or microbial cells, is an important step in genetic-engineering procedures. Usually it is carried out by including one or more marker genes, for example, antibiotic-resistance genes along with the desired gene. The transformed cells can be selected on a special medium known as selection medium supplemented with the right type of antibiotics. The expression of the transferred gene (desired gene) can be monitored with the help of a reporter gene such as luciferase attached with the gene of interest. The gene integration and its expression can also be monitored and studied by Southern hybridization, Northern hybridization,

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LAX8-2

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CELL GROWTH

AND

DEVELOPMENT

#%

Gas Exchange in Plants

In plants gas exchange usually takes place through stomata, small openings present on the epidermis of the leaves. The stomata open into spongy parenchyma and the gas exchange takes place between the cells and the gas filled in the air space. Gas exchange is needed for both respiration and photosynthesis.

8.7

INTERNAL TRANSPORT

Living things must be capable of transporting nutrients, wastes, and gases to and from cells. Singlecelled organisms use their cell surface as a point of exchange with the outside environment.

Multicellular organisms have developed transport and circulatory systems to deliver oxygen and food to cells and remove carbon dioxide and metabolic wastes. Simple multicellular organisms such as sponges, multicellular fungi, and algae have a transport system. Sea water is the medium of transport and is propelled in and out of the sponge by ciliary action. Simple animals, such as hydra and planaria, lack specialized organs such as hearts and blood vessels, and instead use their skin as an exchange point for materials. This, however, limits the size an animal can attain. To become larger, they need specialized organs and organ systems. In lower plants such as algae and fungi, transport of material takes place through the body surface and cytoplasmic streaming movements.

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LAX14-3

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PROTEIN STRUCTURE

AND

ENGINEERING

"#!

Proteins and Enzymes Used in Analytical Applications

In addition to the use of antibodies and enzymes as therapeutic agents, they are also used in the diagnosis of diseases as the components of some confirmatory tests of certain diagnostic procedures.

Hexokinase and glucose oxidase are used in the quantification of glucose in the serum and urine.

Glucose-oxidase is used in glucose electrodes. Uricase is used for the estimation of uric acid present in urine. Alkaline phosphatase, horseradish peroxidase, and antibodies are used in ELISA (Enzyme

Linked Immunosorbent Assay).

Industrial Enzymes and Proteins

Among commercially useful proteins, industrial enzymes have the first place. Industrially useful enzymes include carbohydrate-hydrolyzing enzymes such as amylases, cellulase, invertases, etc., proteolytic enzymes such as papain, trypsin, chymotrypsin, etc., and other bacterial and fungalderived proteolytic enzymes and lipases that can hydrolyze various types of lipids and fats. All these enzymes are important in the food and beverage industries, the textile industry, paper industry, and detergent industry. Proteases have a special use in the beverage industry, meat and leather industries, cheese production, detergent industry, bread and confectionary industry, etc. Various types of lipases are used for the modifications of various types of lipids and fats, production of various organic acids including fatty acids, in detergents, production of coco butter, etc. In addition to all these, enzymes are used in chemical industries as reagents in organic synthesis for carrying out stereospecific reactions.

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LAX8-3

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CELL GROWTH

AND

DEVELOPMENT

%�

n Protoderm, which forms the surface tissues such as the epidermis. n Procambium, which forms the vascular tissues. n Ground meristem, which gives rise to ground tissues.

At this stage, the embryo takes on the shape of an axis with meristems at both ends. These meristems are the apical shoot meristem and the apical root meristem, from which structures of the shoot system and root system will ultimately develop. In addition, two bumps appear near the anterior; these are the two cotyledons, characteristic of dicot embryos. The cotyledons rapidly elongate, and the embryo is divided into regions, with respect to the cotyledons. The region above the attachment of the cotyledons is the epicotyl, which contains the apical shoot meristem. The region below the attachment of the cotyledons is the hypocotyl, which ends with the radicle, containing the apical root meristem. Typically, the embryonic axis will have to fold, to fit within the embryo sac. Endosperm may or may not be absorbed into the cotyledons. It may be consumed completely in the maturation of the embryo, or some may remain for germination. One of the main differences in the growth and development of plant systems from that of animal tissues is that in plants the growing ends or the meristems are very small but repeated many times above the ground as the terminal parts of shoot systems. These meristems are always active and never stop their embryonic nature. Because of this they continue to produce new tissues and cells throughout their life.

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