Учебно-методический комплекс дисциплины " Basis of biochemistry " Для специальности

An exception for mammals is the ability of nursing animals to digest lactose. Note that this ability is generaly lost at the age of weaning, at which time the animal becomes lactose intolerant. POLYSACCHARIDES

Can have both homo- and heteropolysaccharides. We will focus on homopolysaccharides as most central, but will mention some heteropolysaccharides to illustrate their functions. Homopolysaccharides have a single type of residue. Most common polysaccharides contain glucose. Used for energy (food) storage (starches and glycogen) and structure (cellulose).

Starch (energy storage in plants). Two kinds

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  Amylose: linear, alpha-1,4 glycosidic links. MW: 4,000-150,000. (Figure 8.22) [overhead 8.21 MvH] (Gives char. deep blue color with iodine due to coiled complex enclosing iodine-color is lost with heating, returns as cooled).
  
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  Amylopectin: branched every 30 or so units - linear alpha-1,4 chain of 30 glu residues then alpha-1,6 branch point. of course get branches on branches as well. MW: ->500,000. (Figure 8.23, 8.24) [overhead 10-18, V&V] Broken down by alpha-amylase (pancreas and salivary glands; random cleavage of alpha-1,4 links) to give glucose and maltose; or beta-amylase (plants; hydrolyses from reducing ends to give maltose). When either of these enzymes attack amylopectin they are blocked when they reach or are near a branch, thus end up with a "limit dextrin."
  

Glycogen: animal starch. Just like amylopectin, but more highly branched (every 8-12 residues). This allows more free ends for more rapid breakdown-important in animals.

STRUCTURAL POLYSACCHARIDES

Cellulose: beta-1,4 linkages, thus resistant to breakdown (including acid hydrolysis) as want for structure (don't want to digest self). Multiple, extended strands come together as fibrils held together with H-bonds (Figure 8.25, 8.26) [overhead 10.15, V&V], laid down in cell wall in criss-cross pattern, glued together with polyalcohols (lignin).

Chitin: Serves similar role to cellulose, but in animals (crustaceans and insects), fungi, and some algae. Homopolymer of N-acetyl-D-glucosamine. Like cellulose , it has beta-1,4 linkages, and is thus resistant to breakdown. (Figure 8.27)

Among the heteropolysaccharides are the glycans such as Hyaluronic acid, an alternating polysaccharide of D-glucuronic acid and N-acetyl-D-glucosamine; MW to 5,000,000 (Figure 8.28) which serves as a lubricant in joints and is a component of the vitreous humor. Again we see beta-1,4 linkages.

Also very important are the glycans conjugated to proteins and peptides to give proteoglycans (Figure 8.29).

Modul 7.Lipids

Biomedical value of lipids. Frame and classificationof lipids. The constitution and transport properties of cellular membranes.

LIPIDS

Recall the lipid definition: The portion of an organism which will partition into a non-polar solvent.

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  Types of Lipids: (FiFatty acids: long chain carboxylic acids. (Figure 9.2) [overhead 11.2, P; 12-3, S].Three of the most common are:
  
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    Palmitic acid: (You can view an on-line model by clicking the Palmitic acid button at this site.)
    

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  Stearic acid:
  

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  Oleic acid: C9-C10 (Delta⁹double bond; You can view an on-line model by clicking the Oleic acid button at this site.)
  

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  Triacylglycerols: Three fatty acids esterified to glycerol. (Figure 9.5) [overhead 11.6]
  
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  Glycerophospholipids: Two fatty acids and a phosphate esterified to glycerol. (Table 9.2; Figure 9.7) [overhead 11.8; Table 11.2, P; 11-4 V&V]:
  

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  Sphingolipids: (Figure 9.10) [overhead 11.16 P; 11-6, V&V]
  
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  Cholesterol: (Figure 9.15) [overhead 11-9, V&V] (You can view an on-line model by clicking the Cholesterol button at this site.)
  

Lipid Properties: An important consideration for lipids of all sorts is their fluidity. Thus membranes must be fluid enough to allow the diffusion of proteins, transport processes etc. but not so fluid as to weaken the membranes structure. For storage want fat to be fluid enough to flow to fill out body shape at normal operating temperatures. A number of strategies are used by organisms to adjust lipid fluidity:

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  Fatty acid chain length: longer chains have higher melting points (less fluid at a given temperature).
  
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  Unsaturation: double bonds introduce a "kink" in the chain, harder to stack, so less van der Waals contact and thus lower melting points (more fluid).
  
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  Branched chains (bacterial only): Again, less van der Waals contact and thus lower melting points (more fluid).
  
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  Cholesterol: Its planar shape enables it to stiffen bilayers
  

Lipid Bilayers


Detergents & Micelles: Polar heads of detergents and soaps (such as long chain fatty acids) tend to associate with polar solvents such as water, while non-polar "tails" are excluded by water and are forced to associate with themselves making globules known as micelles.

Lipid Bilayer: Figures 9.20 [overhead 11-12, V&V; 12-11]:

The lipid bilayer forms the core for the lipid bilayer membrane as seen in the Fluid Mosaic Model of biological membranes.

gure 9.1) [overhead 11.1, P]
Modul 8. Hormones

All multicellular organisms produce hormones. Plant hormones are known as phytohormones. Blood is the medium of transport of animal hormones. The term hormones is derived from Greek word homao which means to excite. It was first used by William M. Bayliss and Ernest H. Starling, both of the London University College, in the year 1904. They showed a chemical substance - secretin, secreted in the intestine can stimulate the action of a pancreatic secretion. These substances were known as 'chemical messengers'.

The tissues that produce the hormones are known as the effectors while those tissues are that are influenced by the effectors are called as targets. Hormones are of low molecular weight and they diffuse readily. The effects brought about by the hormones are not permanent as the get readily oxidized.