Biological molecules

Question 1

What are the 3 basic fundamental principles of biological molecules? (3)

Answer 1

1. All reactions occur between biological molecules
2. All biological molecules are carbon-based (except for small inorganic ions).
3. Small molecules serve two purposes: Act as the building blocks for larger molecules (by polymerising) or have their own specific functions.

Question 2

What is the definition of a condensation reaction? (1)

Answer 2

The reaction that occurs when two molecules are joined together with the removal of water.

Question 3

What is the definition of a hydrolysis reaction? (2)

Answer 3

The reaction that occurs when a molecule is split apart i with the addition of water.

Question 4

What is the summary of biological molecules? (4)

Answer 4

Small molecules = 100-1000 M.W and 30 Carbon atoms

Sugars (mono) - Polysaccharides
Amino acids - proteins
Nucleotides - Nucleic acids
Fatty acids/lipids - form membranes

Question 5

3 facts about monosaccharides…. (3)

Answer 5

1. They are the most abundant biological molecule.
2. They have a general formula of CnH2nOn
3. They are good energy stores, fuels, metabolites, and structural molecules.

Question 6

Name and describe the two types of monosaccharides (2)

Answer 6

1. Ketone based - Ketose

2. Aldehyde based - Aldose

Question 7

What is the composition of a cell? (4)

Answer 7

Water - 70%
Ions - 1%
Small molecules - 3%
Polysaccharides - 26%

Question 8

Glucose (4)

Answer 8

1. Glucose is a six-carbon ring with hydroxyl groups and aldehyde groups. It can exist in straight chains or rings.
2. Glucose has 4 chiral centres, so it form entaimers. The groups bonded to these carbon atoms determine these isomers.
3. For monosaccharides, they can be grouped into the L- and D- form. L form - -OH group is found on the left of the fifth carbon and D- - -OH group is found on the right.
4. Alpha is -OH group is below plane and Beta OH group is above plane.

Question 9

Why is Glucose suited for its function? (4)

Answer 9

1. Soluble - It easily transported around the body.
2. Small - It can easily diffuse across membranes.
3. It is easily respired, oxidised to form ATP.
4. It can form maltose and glycogen.

Question 10

How are disaccharides formed? (1)

Answer 10

Disaccharides are formed when two monosaccharides are joined together in a condensation reaction, releasing a water molecule. They are joined via a glycosidic bond.

Question 11

What are the 3 features of disaccharides (3)

Answer 11

1. They are soluble in water.
2. They are insoluble in non-polar solvents.
3. They are good energy stores.

Question 12

Give the properties of starch (5)

Answer 12

1. Alpha glucose
2. 1,4 glycosidic bonds
3. It is found in dense granules
4. Amylose has a spiral structure with hydrogen bonds. The -OH are found in the centre of the molecule, so it insoluble.
5. Amylopectin has a spiral structure with emerging branches and is formed from 1,4 and 1,6 glycosidic binds

Question 13

Give the properties of glycogen

Answer 13

1. Alpha glucose.
2. 1,4 and 1,6 glycosidic bonds
3. Compact
4. Branches
5. Insoluble
6. Does not affect the water potential of cells.
7. It is easily hydrolysed and branches snipped off to produce ATP.
8. It is an aldose
9. No fibres.
10. All glucose molecules are the same orientation.

Question 14

Give the properties of cellulose (8)

Answer 14

1. Beta Glucose
2. 1,4 Glycosidic bonds
3. Hydrogen bonding
4. And forms fibril structures which are very strong
5. It cannot be digested
6. Fibers present
7. No granules
8. Adjacent glucose units in the opposite orientation (180 degrees inverted)

Question 15

Oligosaccharides (2)

Answer 15

Oligosaccharides are saccharide polymers formed from monosaccharides and lipids. They are involved in cell recognition and cell binding.

Lipids + monosaccharides = Oligosaccharides such as blood groups

Question 16

Give the properties of amino acids? (6)

Answer 16

1. Contains a chiral carbon (joined to four different groups).
2. Amino acids can occur in L- and D- forms, but only L- forms are used by cells
3. Every amino acid (except glycine) can occur in two isometric forms, because the possibility of forming two different enantiomers around the central carbon. By convention they are called L- and D- forms, analogous to left-handed and right-handed configurations. Only L- amino acids are manufactured in cells and incorporated into proteins. Some D- amino acids are found in the cell walls of bacteria, but not in bacterial proteins. E.g Alanine.
4. Glycine, the simplest amino acid, has no enantiomers because it has two hydrogen attached to the central carbon atom
5. Peptide bonds can form between amino acids to form dipeptides and tripeptides in a condensation reaction. They continue to form long protein molecules.
6. Amino acids have their own specific functions such as being precursors (a substance from which another is formed, especially in a metabolic reaction) to hormones.

Question 17

Give and describe the different protein structures (4)

Answer 17

Primary - Covalent bonds forming polymer – e.g. order of amino acid residues joined by peptide bonds

Secondary - Regular folded form, often stabilised by hydrogen bonds – e.g. helices and sheets

Tertiary - Overall 3D structure, stabilised by hydrogen bonds, hydrophobic, hydrophilic and Van der Waal’s forces

Quarternary - Organisation of macromolecules into assemblies, often stabilised by ionic bonds – e.g. several polypeptide chains can make up a protein

Question 18

Give the properties of nucleotides (8)

Answer 18

1. A nucleotide is made from 3 components: Sugar, base and phosphate.
2. The sugar will be the ribose or deoxyribose depending if its RNA or DNA. The deoxyribose has lost the oxygen on the 2-prime carbon (1 prime is the carbon attached to the base, you then count downwards/clockwise.) So, it’s either a deoxyribonucleotide or ribonucleotide. There is always a base or phosphate attached.
3. Pyrimidines are single ringed and consist of Thymine and Cytosine
4. Purines are double ringed and consist of Guanine and Adenine
5. A and T form two hydrogen bonds and C and G form three.
6. The nucleic acids are made in a 5’-3’ direction and joined through an alternating sequence of sugar-phosphate bonds. Which forms the sugar-phosphate backbone.
7. The bases are bonded by hydrogen bonds to form a double helix.
8. Nucleotides are important for ATP which has three phosphate groups. They are negatively charged so the ATP wants to be cleaved, which releases energy produced for various processes.

Question 19

Describe Fats and Lipids (4)

Answer 19

1. Acts predominantly as food reserves and are glycerol esters with fatty acids.
2. Lipid are complex molecules known as macromolecules
3. Triglycerides is made from one glycerol (alcohol) and three fatty acids (carboxylic acids)
4. Ester bonds form when esterification occurs. Esterification is when an ester bond is formed by a condensation reaction between -OH group of a carboxylic acid and the -OH group of an alcohol to produce an ester.

Question 20

Describe Cholesterol

Answer 20

1. Is a steroid
2. It can intercalate into the membrane by the OH group interacting with the polar lipid heads or its steroid scaffold interact with the fatty acids
3. Decreases fluidity and increases the flexibility of the membrane.
4. Reduces permeability for soluble molecules.

Question 21

Describe single-molecules diseases

Answer 21

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