Biochem Lab Midterms

Complete reviewer for Biochemisty Midterms

• “hydrates of carbon”

• are compounds containing C, H, and O

• are a product of photosynthesis

Carbohydrates

Carbohydrates are compounds which are either polyhydroxyaldehydes or polyhydroxyketone or a compound which yields either or both of these upon hydrolysis.

True

building blocks / fundamental sub-units of carbohydrates

Saccharides

storage form of carbohydrate in animal tissue which is found in liver and muscle

Glycogen

storage form of carbohydrate in plant tissue

Starch

Carbohydrates are the main source of energy in the form of ATP.

True

process of breaking down into simplest forms
e.g. synthesis of fatty acids and amino acids

Metabolism

for support
e.g. cellulose (plant cell wall), chitin (insects, crustaceans, fungi)

Structural

• starch (potato, grains, rice, cereals)

• glycogen (human liver, muscles)

Energy Storage

• ribose (found in RNA)

• deoxyribose (found in DNA)

Backbone of Nucleic Acids

Classification of Carbohydrates:

Monosaccharide, Oligosaccharides, Polysaccharides

These are CHO’s that cannot be hydrolyzed to simplest forms. It has single polyhydroxy aldehyde or ketone unit with general formula C_nH_2nO_n.

Monosaccharide

presence of an aldehyde group

Aldose

presence of a ketone group

Ketose

Simplest monosaccharide not found free in nature but as products of carbohydrates metabolism (C₃H₆O₃)

Triose

4-C monosaccharide (C₄H₈O₄)

Tetroses

Glyceraldehydes

Aldose

Dihydroxyacetone

Ketose

Erythrose

Aldose

Threose

Aldose

Erythrulose

Ketose

Glycerose

Aldose

5-C monosaccharide

Pentoses

constituent of RNA

Ribose

present in cherries and seen in glycoproteins of the body

Arabinose

is seen in proteoglycans

Xylose

occurs only rarely in nature, as a component of bacterial glycolipids

Lyxose

is an intermediate in uronic acid pathway

Xylulose

• 6-C monosaccharide

• are the most important monosaccharides found in plants

• they are the first detectable sugars in plant

Hexoses

____________ occur in free state in plants, sweet fruits, honey and inverted sugar

Glucose and Fructose

most abundant monosaccharide in nature

Glucose

differ from each other only at a single carbon atom

Epimers

2nd carbon

Mannose

4th carbon

Galactose

5th carbon

Idose

7-C sugar form a vital importance in the glucose metabolism of animals and in the photosynthesis process of plants

Heptoses

8 – carbon sugar isolated from avocado pulp - D – glycerol – D – manno octulose

Octose

(C₁₂H₂₂O₁₁) considered as the most abundant oligosaccharide

Disaccharides

• those which contain a free aldehyde or ketone group

• lactose, maltose, cellobiose

Reducing disaccharides

are those whose aldehyde groups are involved in the linkage; no free aldehyde or ketone group

Non-reducing sugars

• table sugar, cane sugar, saccharose, beet sugar

• most widely distributed in nature

• obtained commercially from sugar cane and sugar beets

• connected by alpha 1-2 glycosidic linkage

Sucrose

Invert sugar is sweeter than sucrose.

True

• (C₁₈H₃₂O₁₆) raffinose

• forms in sugar beets

• made up of glucose, fructose and galactose

Trisaccharides

yield for monosaccharide molecules on hydrolysis

Tetrasaccharides

fructose + glucose + 2 molecules of galactose

Stachyose

It is a general test for monosaccharides, disaccharides, and polysaccharides, and can also react with other compounds like glycoproteins and nucleic acids.

Molisch Test

Uses a solution of alpha-naphthol and concentrated sulfuric acid to produce a ______ ring at the interface of the two layers.

violet

The reaction involves the dehydration of the carbohydrate by the acid to form an aldehyde, which then condenses with the alpha-naphthol to create the colored complex.

True

The formation of a purple ring is a negative indicator for molisch test.

False

is a chemical assay used to detect and quantify carbohydrates, including both free sugars and those bound to other molecules like lipids or proteins

Anthrone Test

The test involves heating a sample with a concentrated sulfuric acid and anthrone reagent, which causes carbohydrates to dehydrate into furfural or hydroxyl furfural. This then condenses with anthrone to form a ____________ color

blue-green

A positive test for all reducing sugars (reaction with NaOH) is a ____________ color change and the odor of burnt sugar when heated.

yellow to brown

is a weaker alkali, but it can still induce enolization. However, it can also react differently with specific sugars to form insoluble barium complexes or salts.

Ba(OH)2

Reaction with Ba(OH)2:

• Remains clear.

Glucose

Reaction with Ba(OH)2:

• Form cloudy solutions due to the precipitation of barium salts.

Fructose, Galactose, and other aldoses

is a chemical test used to detect the presence of reducing sugars and aldehydes.

Fehling’s Test

An aqueous solution of copper (II) sulfate, which is blue.

Fehling's A

An aqueous solution of an alkaline potassium sodium tartrate.

Fehling's B

In Fehling’s Test, the formation of a red or orange-red precipitate indicates the presence of a reducing sugar or an aldehyde.

True

is a chemical test used to detect the presence of reducing sugars, such as glucose and fructose, by observing a color change from blue to green, yellow, orange, or brick red after heating with Benedict's reagent.

Benedict’s Test

• sodium citrate, sodium carbonate, and copper(II) sulfate (CuSO₄)

• when heated, copper(II) ions are reduced to copper(I) ions (Cu+)

• the Cu+ ions then combine with the hydroxide in the solution to form a brick-red precipitate of copper(I) oxide (Cu2O)

• the intensity of the color change (from green to yellow, orange, or red) indicates the amount of reducing sugar present

Benedict’s Test Reagents

• To detect monosaccharides and differentiate them from disaccharides.

• Consists of copper(II) acetate in a dilute acetic acid solution.

• A redox reaction where monosaccharides reduce copper(II) ions in Barfoed's reagent to copper(I) oxide, forming a red precipitate.

Barfoed’s Test

Barfoed’s Test:

• React quickly, forming a reddishbrown precipitate in about 1–2 minutes.

Monosaccharides

Barfoed’s Test:

• React much more slowly, typically taking 7–8 minutes or longer to form a precipitate because they must first be hydrolyzed into monosaccharides.

Disaccharides

• The test relies on the reducing property of sugars that have a free aldehyde or ketone group, such as monosaccharides and some disaccharides.

• picric acid solution and adding sodium carbonate (Na₂CO₃)

• A color change from yellow to red or orange indicates the presence of reducing sugars.

Picric Acid Test

• is a chemical test used to detect the presence of reducing sugars, like glucose or fructose, by heating the sample with Nylander's reagent.

• When heated, the reducing sugar, it forms a black or dark brown precipitate.

Nylander’s Test

is a chemical test used to distinguish between aldehydes and ketones by producing a silver mirror on the inside of a test tube

Tollen’s Test

Aldehydes are not easily oxidized by Tollen's reagent.

False

Ketones generally do not react, so a negative result is no silver mirror, while a positive result is a shiny coating. The test is also used to distinguish between reducing and nonreducing sugar.

True

Is a colorless to amber organic compound (C4H3OCHO) used in manufacturing and food flavoring, known for its almond-like odor. It is a skin, eye, and respiratory irritant that darkens upon exposure to air and light.

Furfural

• is a chemical test used to distinguish between ketose and aldose sugars.

• A positive result for a ketose (like fructose) is a rapid formation of a cherry-red color, while an aldose (like glucose) will produce a faint pink color slowly.

Seliwanoff’s Test

• is a chemical test used to distinguish between pentose and hexose sugars, which are both monosaccharides.

• a bluish-green color indicates the presence of a pentose, while a muddy brown color indicates a hexose.

Bial’s Orcinol Test

• is a chemical test used to detect the presence of galactose or lactose in a sample by oxidizing the sugar with concentrated nitric acid.

• a positive result is indicated by the formation of insoluble white mucic acid crystals, which are visible after the mixture is boiled and cooled.

Mucic Acid Test

• Building blocks/stones of proteins

• Fundamental sub-units of proteins

Amino Acids

Amino Acids → Peptide → Proteins

True

Carboxyl Groups

Acidic Properties

Amino Group

Basic Properties

Chiral C

Asymmetric Carbon

are chains of amino acids

Peptides Bonds

dehydration from alpha carboxyl group of one amino acid and the alpha-amino group of another

Dipeptide

three amino acids can be joined by two peptide bonds

Tripeptide

four amino acids can be linked

Tetrapeptide

five amino acids

Pentapeptide

when a few amino acids are joined

Oligopeptide

when many amino acids are joined

Polypeptide

are biomolecules that contain many amide bonds, formed by joining amino acids together through peptide bonds with equal to greater than 40 amino acid residues

Proteins

• is a chemical test used to detect the presence of proteins by identifying peptide bonds

• the color changes from blue to a purple or violet hue, indicating a positive result.

Biuret Test

A deeper purple color signifies a lower protein concentration.

False

• also known as the glyoxylic acid reaction, is a chemical test used for detecting the presence of tryptophan in proteins

• concentrated sulfuric acid is slowly added to form two layers with a purple ring resulting in a positive result of tryptophan

Hopkins-Cole Test

• is a chemical test used to detect the presence of proteins containing the amino acid tyrosine.

• a positive result is indicated by the formation of a red or brick-red solution or precipitate upon heating

Millon’s Test

• is a chemical test used to detect the presence of amino acids, primary amines, and secondary amines

• A positive result is indicated by a deep blue or purple color, known as Ruhemann's purple, formed when ninhydrin reacts with the amino groups in the sample, typically after heating. Different colored reactions can signal specific compounds, such as a yellow color for proline

Ninhydrin Test

• the lead sulfide (or lead acetate) test detects sulfur-containing amino acids, primarily cysteine and cystine, in proteins

• the appearance of a brown to black color or precipitate on the lead sulfide paper (or in the test tube) indicates the presence of sulfur-containing amino acids (cysteine or cystine) in the sample

Sulfur Test/Lead Sulfide Test

• is a qualitative biochemical test used to detect the presence of aromatic amino acids like tyrosine and tryptophan in a protein sample

• is indicated by a yellow color that appears after heating the sample with concentrated nitric acid, which turns into an orange color upon adding an alkali like sodium hydroxide.

Xanthoproteic Test

• Destruction of the secondary, tertiary and quaternary structures of CHON leading to changes in its physical, chemical and biological characteristics

• Involves transformation of a well-defined folded structure of a protein formed under physiological conditions, to an unfolded state under non-physiological condition.

Denaturation of Proteins

includes heat, UV rays, high pressure

Physical Denaturating Agent

acids, bases, organic solvents, heavy metals, detergents

Chemical Denaturating Agent