OCR Biology A Level- Biological Molecules

What is the charge of oxygen in a H2O molecule?

Slightly negative

Diagram of hydrogen bonding

Draw a diagram of hydrogen bonding on paper

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

Why is ice less dense than liquid water?

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

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

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

Why is water a good solvent?

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's high specific heat capacity useful for organisms?

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 water 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.

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

Glucose, fructose, galactose

What are 3 examples of hexose monosaccharides?

One with 6 carbon

What is a hexose monosaccharide?

One with 5 carbons

What is a pentose monosaccharide?

Ribose and deoxyribose

What are 2 examples of pentose monosaccharides?

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

What is the difference between alpha and beta glucose?

Because it contains OH groups which make it polar

Why is glucose soluble in water?

Glycosidic bond

What is the bond between two monosaccharides called?

Maltose

What is the disaccharide version of alpha glucose?

A condensation reaction

What is a reaction which creates water called?

Hydrolysis

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

Benedict's test

What is the test for reducing sugars called?

An alkaline solution of Copper (II) Sulfate

What is Benedict's Reagant?

Red

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

Yes

Are all monosaccharides reducing sugars?

Non-reducing

Are most disaccharides reducing or non-reducing sugars?

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

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

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 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

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

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

How can you make the Bendict's Test quantitative?

Pregnancy test, blood sugar monitor

What are 2 examples of biosensors?

The sample containing the molecule you are testing for

What is an analyte in a biosensor?

The part which interacts with the molecule you are testing for

What is the receptor in a biosensor?

Detects the change in the receptor and provides a response

What is the transducer in a biosensor?

Gives a visual representation of the change in the receptor

What does the display in a biosensor do?

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

What colour does iodine change to when starch is present?

Cellulose

What is the polysaccharide version of beta glucose called?

Amylose and amylopectin

Which two polysaccharides make up starch?

20-30% amylose

70-80% amylopectin

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

Alpha glucose

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

Long, unbranched chains of beta glucose

What general structure are cellulose molecules?

The bonds between the glucose molecules are straight

Why are cellulose molecules straight?

Microfibrils

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

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

Why is cellulose suitable for use in cell walls?

Strong, insoluble, hard to break down in fibrous form

What are some properties of cellulose?

Glycogen

What is alpha glucose stored as in animals and fungi?

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

Why is starch used to store glucose?

A tight, unbranched helix

What is the general structure of amylose?

A long, tight helix structure with branches

What is the general structure of amylopectin?

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

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

Similar to amylopectin except with many more side branches

What is the general structure of Glycogen?

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

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

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

What are some uses of fat in organisms?

Phospholipids and triglycerides

What are two types of lipids?

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

Are phospolipids polar?

Oils are liquid at room temperature, fats are solid

What is the difference between fats and oils?

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

What is the structure of a triglyceride?

Adipose tissue and in the bloodstream

Where are triglycerides found in the body?

Because of their non-polar tails

Why are triglycerides insoluble in water?

A glycerol, two fatty acids and a phosphate group

What is the structure of a phospholipid?

Carbon 6

Which carbon do branches occur from in starch and glycogen?

Energy storage because their hydrocarbon tails contain lots of energy

What is the main use of triglycerides and why?

The emulsion test

What is the test for lipids in food?

A milky emulsion forming

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

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

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

Because it is not polar

Why can ethanol form emulsions?

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

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

One double bond only

How many double bonds do monounsaturated alkenes contain?

Two or more double bonds

How many double bonds do polyunsaturated alkenes contain?

A sterol alcohol

What type of alcohol is cholesterol?

Mostly the liver and intestines

Where is cholesterol made?

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

What are some functions 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 cholesterol?

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

What is the structure of an amino acid?

A peptide bond

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

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

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

The sequence of amino acids in a chain

What is the primary structure of a protein?

Two or more amino acids

What is a polypeptide formed of?

Two or more polypeptides

What is a protein formed of?

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

What is the secondary structure of a protein?

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

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

Hydrophobic groups on the inside, hydrophilic groups pushed to outside

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

Different tertiary molecules coming together and interacting.

What forms the quaternary structure of a protein?

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

What is a conjugated protein?

Compact and round in shape

What is the structure of a globular protein?

One without a prosthetic group

What is a simple protein?

A cofactor

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

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

What are 3 examples of conjugated proteins

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

What is the general structure of a fibrous protein?

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

Why are fibrous proteins insoluble?

By changing the R groups of essential amino acids

How can non-essential amino acids be synthesised?

A fluid into which chemicals dissolve to make a solution

Solvent

A component in a solution, dissolved in the solvent.

Solute

A solute dissolved in a solvent

Solution

One in which water is the solvent

What is an aqueous solution?

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

Chromatography

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

Stationary phase

The liquid/gas and solvent moving through the stationary phase

Mobile phase

Any suitable liquid solvent

Mobile phase of paper chromatography

Because they have different affinities to the solvent and different properties

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

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

What is an Rf value?

Compare it's Rf value to that of known substances

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

The Biuret test

What is the qualitative test for proteins called?