biochem lab final

Biuret Test

A test that detects proteins by turning purple when peptide bonds are present

Positive Biuret Test

The solution turns purple

Negative Biuret Test

The solution stays blue

Glycine Biuret Test Result

Negative because glycine is only one amino acid

Casein Biuret Test Result

Positive because casein is a full protein

Xanthoproteic Test

A test that detects aromatic amino acids by turning yellow or orange

Positive Xanthoproteic Test

The solution turns yellow or orange

Negative Xanthoproteic Test

No color change

Glycine Xanthoproteic Test Result

Negative because glycine has no aromatic ring

Casein Xanthoproteic Test Result

Positive because casein contains aromatic amino acids

Protein Denaturation

When a protein loses its shape and stops working

Way to Denature Proteins

Heat

Way to Denature Proteins

Organic solvents like alcohol

Way to Denature Proteins

Heavy metal ions like silver

Heat Denatured Egg White

Turns white and solid

Organic Solvent Denatured Egg White

Turns cloudy and clumpy

Silver Ion Denatured Egg White

Forms thick white curds

Comparison of Denatured Egg White Methods

All become solid or cloudy but have slightly different textures

Carbohydrate Percentage Formula

(Carb grams ÷ total grams) × 100

Fat Percentage Formula

(Fat grams ÷ total grams) × 100

Protein Percentage Formula

(Protein grams ÷ total grams) × 100

Marshmallows Macronutrients

Mostly carbohydrates

Cashews Macronutrients

High in fat, also contain protein and carbs

Fuel Value Calculation

Multiply grams of each macronutrient by kcal value

Carb kcal Value

4 kcal per gram

Protein kcal Value

4 kcal per gram

Fat kcal Value

9 kcal per gram

Fuel Value of Marshmallows

Lower because mostly carbs

Fuel Value of Cashews

Higher because high fat content

Fuel Value Comparison

Cashews have much more energy per gram

Catalase

An enzyme that breaks down hydrogen peroxide

Where Catalase Is Found

Potatoes, liver, and many cells

Extracting Catalase

Blend potato with water and filter the juice

Catalase Activity Test

Add potato juice to hydrogen peroxide and look for bubbles

Why Bubbles Form

Oxygen gas is released

Effect of Heat on Catalase

Heat denatures the enzyme so activity decreases

Heated Catalase Outcome

Produces fewer or no bubbles

1% Solution Definition

1 gram of solute in 100 mL of solution

1% Glucose Solution

1 g glucose in 100 mL water

1% Fructose Solution

1 g fructose in 100 mL water

1% Sucrose Solution

1 g sucrose in 100 mL water

1% Starch Solution

1 g starch in 100 mL water

Benedict’s Test

A test for reducing sugars that changes color when positive

Positive Benedict’s Test

Green, yellow, orange, or red

Negative Benedict’s Test

Stays blue

Glucose Benedict’s Test

Positive

Fructose Benedict’s Test

Positive

Sucrose Benedict’s Test

Negative unless hydrolyzed

Starch Benedict’s Test

Negative

Iodine Test

A test that detects starch by turning blue-black

Positive Iodine Test

Blue-black color appears

Negative Iodine Test

Yellow-brown color stays

Glucose Iodine Test

Negative

Fructose Iodine Test

Negative

Sucrose Iodine Test

Negative

Starch Iodine Test

Positive

Hydrolysis

Breaking large carbs into smaller sugars using water

Hydrolysis of Sucrose

Makes glucose and fructose

Hydrolysis of Starch

Makes maltose and glucose

Hydrolyzed Sucrose Benedict’s Test

Positive because glucose and fructose are reducing sugars