Biology Lab Test #2 Study Guide: Carbohydrates, Lipids, and Proteins

Comprehensive vocabulary flashcards covering carbohydrate and lipid classifications, qualitative biochemical assays, lipid properties, and protein analysis techniques from Biology Lab #5 and Lab #6.

Monosaccharides

The monomer and simplest form of carbohydrates, including glucose, galactose, fructose, ribose, and deoxyribose.

Role of carbohydrates within the cell

Used for cellular energy storage + structural support within cell

Monosaccharide Ex

• glucose

• fructose

• galactose

• ribose

• deoxyribose.

Sucrose

is not a reducing sugar or monosac

Reducing sugars

• glucose

• fructose

• galactose

• maltose

Disaccharides

Carbohydrates composed of two monosaccharides linked together by dehydration synthesis, such as maltose, sucrose, and lactose.

Disaccharide Ex

• maltose

• sucrose

• lactose

Polysaccharides

Long chains of monosaccharides bonded together by glycosidic linkages, including starch, glycogen, and cellulose.

Polysaccharide Ex

• starch

• glycogen

• cellulose.

Benedict's Reagent

A test identifying reducing sugars (monosaccharides or disaccharides); in an alkaline solution with heating, copper ions in copper (II) sulfate are reduced to copper oxide, producing a color change from blue to red.

It indicates the presence of a sugar that can transfer e- to reduce other compounds

Maltose

test positive on Benedict test because it’s glocose²

Barfoed’s Reagent

A reagent that identifies monosaccharides under acidic conditions because monosaccharides reduce copper ions much faster than disaccharides, reducing copper (II) from copper sulfate to form a red precipitate.

What is the basis for the chemical used for the Benedict’s test and Barfoed’s test?

Copper (II) sulfate, more specifically the reduction of copper ions

Iodine Test

A chemical test that identifies starch (polysaccharide); dark amber iodine solution binds to starch and turns dark blue-black.

What is necessary to determine the identity of your “unknowns”?

By performing the Benedict's, Barfoed's, Iodine, and Grease Spot tests on the unknown samples and comparing their color changes/results directly against known control standards

Triglycerides

Lipids formed by $1$ glycerol molecule joined to $3$ fatty acid hydrocarbon chains by dehydration reactions.

Phospholipids

Lipids consisting of $1$ glycerol, $2$ fatty acid chains, and $1$ phosphate-containing group.

Steroids

Lipids characterized by a molecular structure composed of $4$ fused carbon rings.

Waxes

Lipids composed of a long fatty acid hydrocarbon chain linked to a long-chain alcohol.

Properties of Lipids and Waxes

• non-polar

• hydrophobic

• possessing few oxygen atoms

• consisting largely of hydrocarbon chains.

Sudan IV

A tissue stain for lipids that stains lipid droplets red-orange in adipocytes and plant seeds.

Grease Spot Test

A test for lipids where a sample is spotted onto brown paper and dried; a translucent spot held up to light indicates lipids or oils, whereas aqueous solutions dry completely opaque.

Peptide Bond

A covalent bond formed via a dehydration synthesis reaction between the amine group ($-\text{NH}_2$) of one amino acid and the carboxylic acid group ($-\text{COOH}$) of another amino acid.

Proteins

Polymers composed of amino acid monomers linked by peptide bonds that fold into unique 3-dimensional structures (primary, secondary, tertiary, quaternary) and account for roughly half the dry biomass of most tissues.

Major groups of proteins + roles

1.  Structural fibers for hair, bones for support)

2. Antibody Proteins: Protect the body against foreign invaders like bacteria and viruses 

3. Motor Proteins: Enable movement within cells and muscle contraction 

4. intracellular machines/pumps/motors (for cellular movement and transport)

5. serum/transport proteins -  albumins, globulins)

6. Enzymes - biological catalysts

7. Receptor proteins: Receive and transmit signals on cell surfaces to control entry and exit.

Differential Solubility

The separation principle based on proteins differing in solubility depending on salt concentration and solvent composition (e.g., egg white globulins lose solubility in pure deionized water and form a solid, while albumins remain dissolved).

Electrophoresis

A technique that separates proteins based on size and charge as they migrate through a solid medium under an electric field toward positive or negative poles.

Chromatography

A laboratory method that separates molecules based on differing rates of migration across a solid medium as a solvent moves across it.

Mobile Phase

The liquid solvent that travels across the solid support medium during chromatography.

Stationary Phase

The solid chromatography paper medium across which the solvent moves.

Analyte

The substance or mixture of amino acids or proteins being separated and analyzed in chromatography.

Retention Factor ($R_f$)

A chromatographic value calculated as the distance moved by the amino acid spot divided by the distance moved by the solvent front ($=\frac{\text{distance moved by amino acid spot}}{\text{distance moved by solvent front}}$ ).

Ninhydrin Test

A qualitative test detecting peptides and amino acids where ninhydrin reacts with amine groups at the end of peptide chains, cleaving off the amine to form ammonia yielding a violet or purple precipitate as a positive result.

Pauly Test

A qualitative test used to detect the specific amino acids tyrosine and/or histidine; a yellow medium indicates a negative result where neither tyrosine nor histidine is present.

How do you differentiate between histidine and tyrosine?

Compare unknown to color of the tested sample of tyrosine and histidine

Qualitative Tests

Pauly + Ninhydrin

Quantitative Test

Biuret Test

Biuret Test

A quantitative test in which peptide bonds react with copper (II) sulfate in alkaline solutions to form a purple-blue complex proportional to the number of peptide bonds present.

Positive Result of Biuret Test

A purple-blue color

Standard Curve

A graph plotting known concentrations of a substance against their measured absorbance at $540\,\text{nm}$,

• used as a calibration tool to determine the exact concentration of an unknown sample.

What is a standard curve used for?

act as a reference or calibration tool to find the exact concentration of an unknown sample.

Determine the protein concentration of an unknow using the standard curve

Measure the unknown sample's absorbance on the spectrophotometer. Locate that absorbance value on the Y-axis, trace horizontally to intersect the standard curve, and draw a vertical line down to read the corresponding total protein amount on the X-axis

What is the relationship between absorbance and protein concentration?

A direct linear relationship (directly proportional)

Spectrophotometer

A device that measures the amount of light of a particular wavelength transmitted through a sample, used to quantify protein concentration from biuret reaction absorbance.

What was a spectrophotometer used for in this lab?

used to measure the absorbance of the purple biuret reaction product to quantify protein concentration