OCR Biology A Level- Biological Molecules

What is the charge of oxygen in a H2O molecule?

Slightly negative

Why is ice less dense than liquid water?

The hydrogen bonds between molecules in ice are slightly further apart than the average distance between liquid water molecules

What is an advantage to living organisms of ice being less dense than water?

Ice floats and forms an insulating layer on top of ponds, maintaining a constant temperature for organisms

Why is water a good solvent?

It's polar so other charged molecules are attracted to it

Why is water's high specific heat capacity useful for organisms?

It can be used as a coolant, to buffer temperature changes during chemical reactions and to provide a constant temperature for aquatic organisms

Why is water cohesive and adhesive?

Water is cohesive because the hydrogen bonds mean water molecules are attracted to one another. Water is adhesive because it can be attracted to other polar molecules.

Why is it useful to organisms that water is cohesive and adhesive?

Water acts as a good transport medium. These properties also mean that it can move upwards through narrow tubes via capillary action.

What are 3 examples of hexose monosaccharides?

Glucose, fructose, galactose

What is a hexose monosaccharide?

One with 6 carbon

What is a pentose monosaccharide?

One with 5 carbons

What are 2 examples of pentose monosaccharides?

Ribose and deoxyribose

What is the difference between alpha and beta glucose?

The OH group is below Carbon 1 on alpha, and above it on beta

Why is glucose soluble in water?

Because it contains OH groups which make it polar

What is the bond between two monosaccharides called?

Glycosidic bond

What is the disaccharide version of alpha glucose?

Maltose

What is a reaction which creates water called?

A condensation reaction

What is the addition of water to a disaccharide in order to split it into 2 monosaccharides called?

Hydrolysis

What is the test for reducing sugars called?

Benedict's test

What is Benedict's Reagant?

An alkaline solution of Copper (II) Sulfate

What colour would blue Benedict's Reagant change to if reducing sugars are present?

Red

Are all monosaccharides reducing sugars?

Yes

Are most disaccharides reducing or non-reducing sugars?

Non-reducing

Why does Benedict's Reagant turn red when reducing sugars are present?

Because the blue Cu2+ ions have an electron is added to form brick red Cu+ ions

What is the method for testing for reducing sugars?

1. Add 2cm cubed of a food sample (liquid or crushed with water)
2. Add 2cm cubed of Benedict's Reagant
3. Place the test tube in an 80°C water bath

What is the method for testing for a non-reducing sugars?

1. Confirm that the sugar is not a reducing sugar
2. Add 2cm cubed of food sample in liquid form to a test tube
3. Add 2cm cubed of hydrochloric acid
4. Place in 80°C hot water bath for 5 minutes
5. Remove and slowly add sodium hydrogencarbonate until the solution is neutral
6. Re-test the solution using the Benedict's test

How can you make the Bendict's Test quantitative?

Use a colorimeter to test the transmission of red light in the solutions. More reducing sugars= more red light

What colour does iodine change to when starch is present?

Changes to black because iodine molecules become trapped in the helix of the starch

What is the polysaccharide version of beta glucose called?

Cellulose

Which two polysaccharides make up starch?

Amylose and amylopectin

What percentage of starch is amylopectin and what percentage is amylose?

20-25% amylose
75-80% amylopectin

What type of glucose are amylose and amylopectin made up of?

Alpha glucose

What general structure are cellulose molecules?

Long, unbranched chains of beta glucose

Why are cellulose molecules straight?

The bonds between the glucose molecules are straight

What are the strong fibres formed by cellulose chains feld together by hydrogen bonds called?

Microfibrils

Why is cellulose suitable for use in cell walls?

It's microfibril structure makes it strong enough to provide structural support for cell walls

What are some properties of cellulose?

Strong, insoluble, hard to break down in fibrous form

What is alpha glucose stored as in animals and fungi?

Glycogen

Why is starch used to store glucose?

Because amylose and amylopectin are insoluble so the glucose won't interfere with osmosis

What is the general structure of amylose?

A tight, unbranched helix

What is the general structure of amylopectin?

A long, tight helix structure with branches

Why do amylopectin and amylose's structures suit their purpose?

Their tight helixes male them compact, and therefore ideal for storage

What is the general structure of Glycogen?

Similar to amylopectin except with many more side branches

Why does glycogen's structure make it suited to storage?

It is compact like amylopectin because it is coiled. It's many branches also allow energy to be released quickly, making it suited to more active animals

What are some uses of fat in organisms?

Protection around vital organs, shock absorption, buoyancy in aquatic animals, insulation, making hormones, making up cell membranes and storing energy

What are two types of lipids?

Phospholipids and triglycerides

Are phospolipids polar?

Partially- they have a polar head (The phosphate group) and a non polar tail (the fatty acids)

What is the difference between fats and oils?

Oils are liquid at room temperature, fats are solid

What is the structure of a triglyceride?

A glycerol with three fatty acids (hydrocarbon chains with a carboxyl group) joined to it by glycosidic bonds

Where are triglycerides found in the body?

Adipose tissue and in the bloodstream

Why are triglycerides insoluble in water?

Because of their non-polar tails

What is the structure of a phospholipid?

A glycerol, two fatty acids and a phosphate group

Which carbon do branches occur from in starch and glycogen?

Carbon 6

What is the main use of triglycerides and why?

Energy storage because their hydrocarbon tails contain lots of energy

What is the test for lipids in food?

The emulsion test

What result indicates the presence of lipids when using the emulsion test?

A milky emulsion forming

How would you conduct a test for lipids in a foodstuff?

1. Add 2cm cubed of ethanol to either a liquid sample, or add the ethanol to a solid sample, crush it and pipette the ethanol into a separate test tube
2. Add 2cm cubed of water to this ethanol and shake gently
3. Observe the appearance of the test tube contents

Why can ethanol form emulsions?

Because it is not polar

Why do unsaturated fats tend to be liquid rather than solid at room temperature?

Because the double bonds cause a kink in the hydrocarbon chain so the molecules can't pack together as closely

What type of alcohol is cholesterol?

A sterol

Where is cholesterol made?

Mostly the liver and intestines

What are some functions of cholesterol?

Adds stability to the cell membrane, involved in the production of steroid hormones, vitamin D and bile.

What is the structure of cholesterol?

A polar hydroxyl group and 4 carbon rings and a hydrocarbon chain tail, both of which are not polar

What is the structure of an amino acid?

An amine group, a carbon with a hydrogen and an R group (hydrocarbon chain) attached, and a carboxyl group

What is the bond between two amino acids in a dipeptide called?

A peptide bond

Which parts of amino acids bond together to form a dipeptide?

The H of one's amine group and the OH of the other's carboxyl group

What is the primary structure of a protein?

The sequence of amino acids in a chain

What is a polypeptide formed of?

Two or more amino acids

What is a protein formed of?

Two or more polypeptides

What is the secondary structure of a protein?

An alpha helix or a beta pleated sheet formed by hydrogen bonds forming between the NH and CO groups in a chain

What are some examples of bonding in a protein's tertiary structure?

Disulfide bridge, hydrogen bonds between R groups and ionic bonding between oppositely charged R groups

How are hydrophobic and hydrophilic R groups arranged in the tertiary and quaternary structure of proteins?

Hydrophobic groups on the inside, hydrophilic groups pushed to outside

What forms the quaternary structure of a protein?

Different tertiary molecules coming together and interacting.

What is a conjugated protein?

A protein which contains a non-protein group called a prosthetic group as part of its quaternary structure

What is the structure of a globular protein?

Compact and round in shape

What is a simple protein?

One without a prosthetic group

What is it called when a prosthetic group is key to a protein's function?

A cofactor

What are 3 examples of conjugated proteins

Haemoglobin (contains 4 iron haem groups), lipoproteins (contain a lipid), glycoproteins (contain a carbohydrate)

What is the general structure of a fibrous protein?

Very repetitive primary structures leading to long, strong, organised, rope-like structres which are not folded into a 3D shape

Why are fibrous proteins insoluble?

Because they have many hydrophobic R groups in their component amino acids

How can non-essential amino acids be synthesised?

By changing the R groups of essential amino acids

Solvent

A fluid into which chemicals dissolve to make a solution

Solute

A component in a solution, dissolved in the solvent.

Solution

A solute dissolved in a solvent

What is an aqueous solution?

One in which water is the solvent

Chromatography

A technique used to separate mixtures of molecules. Relies on the movement of a gas or liquid through a medium

Stationary phase

The medium (which does not move) through which the solvent moves in chromatography.

Mobile phase

The liquid/gas and solvent moving through the stationary phase

Mobile phase of paper chromatography

Any suitable liquid solvent

Why do different chemicals move at different rates in paper chromatography?

Because they have different affinities to the solvent and different properties

What is an Rf value?

The ratio of how far a chemical moved in paper chromatography compared to the maximum distance travelled by the solvent

How do we work out what a substance is using paper chromatography?

Compare it's Rf value to that of known substances

What is the qualitative test for proteins called?

The Biuret test

How do you conduct the Biuret test for proteins?

Add 2cm cubed of Biuret's reagant to a liquid food sample

What is a positive test in the Biuret Test?

The solution turning from blue to purple