Biology topic 1A-Biological Molecules

Vocabulary flashcards generated from lecture notes on mono and disaccharides, including carbohydrates formulas, isomers, and condensation reactions.

Define monosaccharides

Simple sugars that serve as the basic unit of carbohydrates.

Define Polysaccharides

Long chains of simple sugars (monosaccharides), such as cellulose and starch.

What is a Condensation Reaction

A chemical reaction in which monosaccharides combine to form polysaccharides with the release of water ($H_2O$).

Define Hydrolysis

A chemical reaction in which polysaccharides are broken down into monosaccharides by the addition of water ($H_2O$).

Give the General Formula for Carbohydrates

$(CH_2O)_n$, a general formula that all saccharides fit.

Give the Glucose Formula

$C_6H_{12}O_6$, the chemical formula for glucose.

What is Alpha Glucose?

An isomer of glucose ($\beta\text{-glucose}$ isomer sibling) where both hydroxyl ($-OH$) groups face down.

What is Beta Glucose?

An isomer of glucose where only 1 hydroxyl ($-OH$) group faces down because the position of the $-OH$ group on carbon 1 is swapped upward.

What is a Glycosidic Bond?

A covalent bond formed between two monosaccharide molecules during a condensation reaction.

What does the condensation reaction, alpha glucose + alpha glucose form? What type of substance is this?

A disaccharide called maltose

Alpha Glucose Structure

Diagram depicting the chemical structure of $\text{alpha glucose}$ showing numbered carbon atoms $C_1$ to $C_6$ and hydroxyl ($-OH$) groups.

Beta Glucose Structure

Diagram depicting the ring structure of $\text{beta glucose}$, illustrating the swapped position of the $-OH$ group on carbon 1.

What is hydrogen bonding?

A strong intermolecular attraction between a δ⁺ hydrogen atom bonded to N, O or F and a lone pair of electrons on N, O or F in another molecule.

Why does hydrogen become δ⁺?

N, O and F are highly electronegative and attract the bonding pair of electrons towards themselves.

What must hydrogen be bonded to for hydrogen bonding to occur?

N, O or F

What attracts the δ⁺ hydrogen?

A lone pair of electrons on an N, O or F atom of another molecule.

Is hydrogen bonding an intermolecular or intramolecular force?

Intermolecular

How do hydrogen bonds affect boiling point & melting point?

Stronger intermolecular forces require more energy to overcome, so the boiling point annd melting point increases.

What happens to intermolecular hydrogen bonds when water boils?

They are overcome; the covalent O–H bonds are not broken.

What are monomers?

Small, basic, molecular units of life that can form a polymer

What are polymers?

Large, complex molecules composed of long chains of monomers joined together

How are most biological polymers formed?

Condensation reactions

What is a condensation reaction?

A chemical bond between monomers, releasing a H2O (water) molecule

How are polymers often broken down into monomers?

Hydrolysis

What is a hydrolysis reaction?

The breaking of chemical bonds between monomers, using a water molecule. (The H2O bonds to the single oxygen to form 2x OH).

What elements do all carbohydrates contain and what are the monomers called which make up carbohydrates?

C, H and O

Carbohydrates monomers are monosaccharides

What type of sugar is glucose? What does this mean?

A hexose sugar- six carbon atoms in each molecule

What are the 2 isomers of glucose?

Alpha and Beta

Describe the structure of alpha glucose

Both OH face down

Describe the structure of beta glucose

1 OH up, 1 OH down

What is a disaccharide and how is it formed?

Two monosaccharides joined together

Through condensation reaction

What type of bond forms between the two monosaccharides when a disaccharide is formed?

Glycosidic bond, and H2O is released

How is sucrose formed?

Condensation reaction between 1 glucose molecule and 1 fructose molecule (forming a disaccharide)

How is lactose formed?

Condensation between a glucose and galactose molecule

How is maltose formed?

Two alpha glucose

What are the two classifications of sugars? How can they be tested for?

Reducing and non-reducing

Benedict’s test

What do reducing sugars include?

ALL monosaccharides and some disaccharides (maltose and lactose)

Describe the Benedict’s test for reducing sugars

Add blue Benedict’s reagent to a sample and heat in a hot water bath brought to the boil. A positive test will form a coloured precipitate

What is the positive versus negative result for the Benedict’s test for reducing sugars

Positive- sample forms green- yellow- orange- brick red precipitate (REDUCING sugars present)

Negative- sample stays blue (no REDUCING sugars present)

How is a higher concentration of reducing sugars indicated?

By how far the colour change goes (e.g. green= low conc. / brick-red= high conc.)

What is a more accurate way to measure the concentration of reducing sugars after Benedict’s test?

1) Filter the solution and weigh the precipitate

2) Remove the precipitate and use a colorimeter to measure the absorbance of the remaining Benedict’s reagent.

If the result of the Benedict’s test is firstly negative, what could this still mean?

A non-reducing sugar could still be present.

What must you first do when testing for a non-reducing sugar, like sucrose?

Break them down into monosaccharides

How do you carry out the test for non-reducing sugars?

Gather a new sample of the test solution, and add dilute HCl. Then carefully heat at boiling point in hot water bath and neutralise using sodium hydrogencarbonate. Then carry out same Benedict’s test.

What are polysaccharides?

Carbohydrates made from large numbers of monosaccharides bonding in condensation reactions.

How are polysaccharides broken back down into monosaccharides?

By hydrolysis reactions, breaking the glycosidic bond using a H2O molecule.

What 3 polysaccharides must you know the structure and function of?

Starch

Glycogen

Cellulose

What is starch?

How plants store excess glucose to be broken back down when energy is required

What two polysaccharides is starch a mixture of?

Two polysaccharides of alpha-glucose

Amylose and Amylopectin

What is Amylose? How does its structure support its function?

A long, unbranched chain of alpha glucose.

The angles of the glycosidic bonds give it a coiled structure, making it compact so that it is good for storage (can fit more into a small space)

What is Amylopectin? How does its structure support its function?

A long, branched chain of alpha glucose

Side branches allow the enzymes that break down the molecule to access the glycosidic bonds easily, meaning the glucose can be released quickly

Why is starch good for storage as well?

It is insoluble in water and doesn’t affect water potential, so doesn’t cause water to enter cells by osmosis (which would make them swell).

What is glycogen used for?

Storing glucose in animal cells (and bacteria)

What is the structure of glycogen?

Polysaccharide of alpha glucose, very similar to amylopectin, but has loads more sides branches

How does glycogens many branched structure relate to its function?

Stored glucose can be quickly released by hydrolysis (by enzymes), for quick energy release in animals

Also very compact, so is able to store a lot of glucose in a small space

What is cellulose made of? Describe its structure in a chain

Long, unbranched chain of beta-glucose, bonded by condensation to form glycosidic bonds. Each beta glucose molecule in the chain has an alternating orientation

How are cellulose chains linked together? Why is this useful?

Many hydrogen bonds, forming strong fibres called microfibrils.

This high tensile strength provides structural support for cells- e.g. stops plant cell wall from bursting

Describe the test for starch

Iodine test

Add iodine dissolved in potassium iodide to the test sample

Browny-orange= starch present

Dark blue-black=NO starch present

What are lipids made from? What do they all contain?

Proteins and carbohydrates

ALL contain hydrocarbons

What are the 2 types of lipids?

Triglycerides and Phospholipids

Describe the structure of Triglycerides

One molecule of glycerol with 3 fatty acids attached to it