基础生物实验 4 - 实验二理论简介：Macromolecules

2021-01-30 21:53 作者:追寻花火の久妹Riku 0人读过 | 我要投稿

本期内容是生物高分子实验的基础理论部分，实验手册请看下期、实验模拟请看下下期。本部分内容来自 University of California, Berkeley - UC Berkeley Extension, 虚拟实验的内容来自 Labster. 本部分内容均不会标记为为原创，但由于是UP主购买的课程，因此不接受非授权的转载，谢谢您的理解。

每一个生物基础实验均会分为三部分：第一部分为实验的生物理论；第二部分为实验的指导手册；第三部分为 Labster 的虚拟实验模拟。第一部分的基本信息由 Ying Liu, Ph.D. 提供，第二部分的实验手册来自 Labster, 第三部分的实验模拟过程由UP主操作。

Lab 2 - Macromolecules: Basic Information:

Molecules of Life:

Biological macromolecules are large molecules made up of repeating units of sMaller molecules;

These are also called organic molecules because they contain carbon and hydrogen;

The four classes of biological macromolecules are: Carbohydrates, Proteins, Lipids, Nucleic Acids.

Four Classes of Biological Macromolecules & Building Blocks

Dehydration and Hydrolysis Reactions

Macromolecules are polymers, made of repeating units of building blocks called monomers;

The synthesis of the polymers uses reaction called dehydration reaction, because the removal of water allows subunits (monomers) to link together into larger molecules;

The breakdown of the polymers uses hydrolysis reaction because the addition of water breaks larger molecules into their subunits.

[1] Carbohydrates

- Carbohydrates are made of C, H, and O, usually at the ratio of 1:2:1 (glucose: C6H12O6);

- Function as short- and long-term energy storage;

- Name generally end in ‘-ose’;

- One monomer unit is called a monosaccharide;

Glucose: the most common monosaccharide:

- End product of photosynthesis in plants;

- Metabolized by cells (cellular respiration) to produce ATP (a source of energy).

A disaccharide is formed when two monosaccharides are covalently bonded together (sucrose, lactose, etc.);

Glycosidic linkage: the covalent bond formed;

Polysaccharides (complex carbohydrates) are made of many carbon rings;

Starch is the storage form in plants (less branched);

Glycogen is the storage form in animals (highly branched);

Cellulose (fiber) is found in plant cell wall (structural support);

Chemical bonds in cellulose are different from those in starch, and we don’t have the enzymes to break it down;

Fiber passes through our body undigested.

Assays for Carbohydrates

- I2KI test for starch: Starch (colorless) + I2KI (amber): turns blue-black when together;

- Benedict’s test for reducing sugar: Benedict’s reagent (blue) turns green or orange / red if glucose is present.

Iodine Assay for Starch

- Amylose in starch combines with iodine to give a blue-black color;

- Iodine+iodide slide into helical structure of amylose;

- Glucose does not have helix, no change in color with iodine;

- Add several drops of Lugol’s until visibly yellow-amber.

Benedict’s Reagent Assay

- Aldehyde or ketone group of simple sugar reduces blue Cu++ to Cu+ which precipitates as red copper oxide;

- Color change to green/yellow/orange/red indicates reducing sugar;

- Starch has few groups (only the glucose at the end of a chain of starch will have an exposed aldehyde functional group to react with Benedict's reagent), so no reaction;

- Sucrose gives negative result.

[2] Proteins

- Proteins are made of subunits called amino acids;

- There are 20 amino acids in our cells;

- Peptide bonds link the carboxyl group (COOH) of one amino acid to the amino group (NH2) of another amino acid;

- Important for diverse functions in the body including hormones, enzymes, antibodies and transport.

- The chains of amino acids linked by peptide bonds are called polypeptides, ranging from a few amino acids to hundreds of amino acids long;

- Proteins fold into 3D structures (native state), which is essential for their function;

- Loss of the 3D structure (denaturation) leads to loss of function.

Protein Structures:

Protein Functions:

- Support: structural proteins such as keratin in our hair and nails, collagen in our skin, cytoskeleton;

- Enzymes: molecules that catalyze reactions all over the body.

- Transport channels: facilitate the movement of chemicals into and out of our cells;

- Hormones: insulin and glucagon both regulate blood glucose level;

- Antibodies: molecules important in the immune system;

Assay for Proteins

- Biuret test: presence of proteins:

- Dye reacts with the peptide bonds;

- Copper (II) is reduced to copper (I), which forms a complex with the nitrogens and carbons of the peptide bonds in an alkaline solution.

[3] Lipids

- Lipids consist mostly of carbon and hydrogen, and do not dissolve in water;

- Major functions of lipids include: Energy storage (Triglycerides), Cell membrane (Phospholipids), Hormones (steroids), etc.;

- Their low water solubility is an absence of hydrophilic polar groups;

- Building blocks: fatty acids.

Triglycerides: Fats and Oils

- Triglyceride is composed of one molecule of glycerol and three molecules of fatty acids (16-18 carbon long);

- Saturated fat has single bonds and is solid at room temperature;

- Unsaturated fat contains double bond(s) and is liquid at room temperature.

Fats (saturated) usually come from animals;

- Function for long-term energy storage, insulation from heat loss, and cushion for organs;

Oils (unsaturated) usually come from plants.

Artificial trans fats are created in an industrial process to make them more solid (extend shelf life) - Doughnuts, baked goods including cakes, pizza, cookies, and stick margarines.