Biological molecules

Why is the RF value always less than 1?

The substance cannot move further than the solvent

How can the quantity of reducing sugar be measured?

Weigh the dried copper oxide precipitate produced from the benedicts test. This works until the copper sulfate in the benedicts reagent is no longer the limiting reactant.

Why may a colourometer be used on a qualitative colour test?

To make it quantitative

What is the -OH group called?

Hydroxyl

How is % error calculated?

(uncertainty/measurement)x100

What do phospholipids have instead of a 3rd fatty acid?

A phosphate head

What is a monomer?

Smaller units from which polymers are made

Give 2 examples of proteins with quarternary structure?

antibodies and haemoglobin

When is a quarternary structure formed?

If proteins have more than 1 polypeptide chain

Properties of hydrophobic interactions in the tertiary structure of a protein?

occur when non-polar R groups cluster away from water

Define repeatability

It can be done again with similar results

Properties of disulfide bridges in the tertiary structure of proteins?

strong covalent bonds that form between sulfur containing R groups. They are highly stable and resist heat.

Properties of ionic bonds in the tertiary structure of proteins

Form between oppositely charged R groups, they are easily broken by changes in pH.

Properties of hydrogen bonds in the tertiary structure of protein?

They form betwen Polar R groups, they are weak individually but provide strength in high amounts, they are easily broken by high temperatures

What is the 3D structure of a protein?

The specific 3D shape of a single polypeptide chain, formed by further folding and coiling.

What stabilises the Primary structure?

Peptide bonds?

How does the primary structure influence the tertiary structure?

The determination of the R group position dictates where H, ionic and disulfide bonds form in the tertiary structure

What is the secondary structure of most proetins?

alpha helix

What stabilises the secondary structure of a protein?

Hydrogen bonds

What do the hydrogen bonds cause, in the secondary structure of a protein?

An alpha helix or a beta pleated sheet

Where do hydrogen bonds form between in the secondary structure of a protein?

Between C=O and N-H groups of the backbone

What does the primary structure of a protein dictate?

The position of the R groups

What is the primary strcuture of a protein?

is the specific, linear sequence of amino acids making up its polypeptide chain

What properties make an amino acid more attracted to the mobile phase?

soluble and small

What does seperation depend on in paper chromotography?

The balance between the affinity for the mobile phase (solvent) and the stationary phase (paper).

Why do gloves need to be worn when doing paper chromotography, when identifying amino acids?

Skin proteins may ruin the test

What 2 things need to be done to the amino acid in paper chromotography?

Ninhydrin needs to be sprayed on it, and heat must be applied to it

Why does the pencil line need to be above the solvent?

So samples do not dissolve into the beaker

How to calculate RF value?

Distance moved by amino acid/ distance moved by solvent front

How is the amino acid identified in paper chromotography?

The RF value is calculated and compared with a database

What colour does ninhydrin and heat turn the amino acid in paper chromotography?

From colourless to purple

Why does ninhydrin need to be sprayed oin the amino acid and heat need to be applied to the amino acid in paper chromotography?

Amino acids are colourless

Why is pencil used to mark the solvent front?

So ink dyes dont dissolve into the paper

When does the solvent front need to be marked?

Immediately after removing the paper from the beaker

Why does the start line need to be drawn with a pencil?

So ink dyes do not seperate and interfere

Why would a singular amino acid test negative in the biochemical test for protein?

It tests for the presence of peptide bonds

Why does the solution turn purple, as a positive result, in the biochemical test for proteins?

The polypeptide chain chelates the copper ions

What is the positive result in the biochemical test for proteins?

The solution changes from blue to purple

What is benedicts reagent?

copper (II) sulfate in an alkaline solution

How much biuret reagent is added to the sample in the biochemical test for proteins?

An equal amount

How to make a solid sample into a liquid for the biochemical test for proteins?

Grind it in a pestle and mortar with distilled water, and filter the solid residue

Where does the peptide bond form between 2 amino acids?

between the amine group of one amino acid, and the hydroxyl of the other. During the condensation reaction, the hydroxyl group comes from the carboxyl group, and a hydrogen atom comes from the amine group to release water

What varies between amino acids?

The R group

What reaction joins aminio acids?

Condensation

Why are amino acids amphoteric?

can be acidic or alkaline because they have an amine (NH2) group and a carboxyl group (O=C-O-H)

Can a functional protein contain more than one polypeptide chain?

yes

What are 2 amino acids chemically bonded together called?

dipeptide

What is a polypeptide?

More than 2 amino acids chemically bonded together

What type of bond joins amino acids?

peptide

How many amino acids are common to all organisms?

20

Why does the solution turn red in the benedicts test?

copper (+2) ions are reduced to form copper (+) ions which then form copper oxide, which is a red insoluble precipitate

What is a polymer?

large molecules made many monomers that are chemically bonded together

What type of bond is formed in a condensation reaction?

Covalent

What is elimimated in a condensation reaction?

A small molecule

Are monosaccharides reducing sugars?

Yes

What is the covalent bond between 2 monosaccharides called?

Glycosidic bond

What is maltose made from?

Glucose+glucose

What is sucrose made of?

Glucose+fructose

What is lactose made from?

Glucose+galactose

Which glucose is starch made of?

alpha

Which glucose is glycogen made of?

Alpha

Which glucose is cellulose made from?

Beta

What reagent is used for the test for sugar?

Benedicts

How long does the test tube go in the 90°C water bath for, in the test for sugars?

5 minutes

What volume of benedicts and liquid sample is used in the test for sugar?

2cm³

What is the order of positive results in the test for sugar?

Blue,green,orange,red

How are the glycosidic bonds broken in the test for non-reducing sugar?

Add 2cm³ of the sample and 2cm³ HCl and heat in the 90°C water bath for 5 minutes

Why does the sample need to be neutralised after the glycosidic bonds are broken in the test for non-reducing sugar?

Benedicts reagent does not work in acidic solutions

How is the solution neutralised in the test for non-reducing sugar?

Add Sodium hydrogen Carbonate until the pH is above 7

What is the final step of the test for non-reducing sugar?

The benedicts test

Where is the OH group on alpha glucose?

Below Carbon 1

Where is the OH group on beta glucose?

Above Carbon 1

What is a hexose sugar?

A sugar with 6 carbons

Describe the stucture and function of amylose

Long unbranched chains of alpha glucose monomers chemically bonded together by 1-4 glycosidic bonds, which form helixes, making them a very dense source of energy

Describe glycogen

Highly branched chain of alpha glucose monomers due to its high ratio of 1-6 glycosidic bonds to 1-4 glycosidic bonds

What is the advantage of glycogen being highly branched?

It provides a large surface area for hydrolytic enzymes to attach allow for a rapid release of glucose

What is more branched, amylopectin or glycogen, and why?

Glycogen because it has a greater ratio of 1-6 glycosidic bonds to 1-4 glycosidic bonds

Where is glycogen stored?

muscle and liver cells

Describe cellulose

long straight chains made of beta glucose monomers which alternate in orientation, chemically bonded together by 1-4 glycosidic bonds only Many hydrogen bonds between adjacent cellulose chains creating a strong, mesh-like structure and many bonded chains form fibrils

Where is cellulose found?

Plant cell walls

What is the function of cellulose?

To make the cell wall strong and flexible which allows the cell to be turgid

What are the advantages of the hydrogen bonds in cellulose?

Provide flexibility and strength

What solution is used to test for starch?

iodine in potassium iodide

What is a positive colour change in the test for starch?

Orange to black

Why is starch insoluble, and why is this advantageous?

It is a macromolecule, this means it wont affect the cells water potential and cause osmotic bursting. Also, it means it wont leave the cell

Where is starch stored?

In amyloplasts

What are triglycerides made of?

Glycerol and 3 fatty acids

What bonds join glycerol to the 3 fatty acids?

3 ester bonds

If something is polar, is it hydrophillic or hydrophobic?

Hydrophillic

How many water molecules are eliminated when a triglyceride is made?

3

What is the main function of a triglyceride?

Energy storage

What is the benefit to the high ratio of C-H bonds in a fatty acid?

Stores alot of energy

What benefits does fatty acids being large and non-polar have?

Is insoluble so it has no effect on the cells water potential, so it wont affect osmosis and wont leave the cell.

What is the advantage of Fatty acids having many O-H bonds?

Release metabolic water when oxidised during aerobic respiration

What is a phospholipid made of?

1 glycerol, 2 fatty acids and a phosphate group

What bonds are formed when a phospholipid is formed?

2 ester bonds and a phosphoester bond

How many water molecules are elminated when a phospholipid is made?

3

What part of a phospholipid is polar?

The phosphate head

What is the main use of phospholipids?

To form membranes

Why is the phosphate head hydrophillic?

Because it's polar (-)