Biological Molecules

Question 1

Define:
Monosaccharide
Disaccharide
Polysaccharide

Answer 1

Monosaccharide - A single subunit of sugar
Disaccharide - 2 subunits of sugar
Polysaccharide - A polymer of sugar

Question 2

Name 3 monosaccharides

Answer 2

Glucose
Fructose
Galactose

Question 3

Name 3 disaccharides

Answer 3

Sucrose
Maltose
Lactose

Question 4

Name 3 polysaccharides

Answer 4

Starch
Glycogen
Cellulose

Question 5

Which monosaccharides is sucrose formed from?

Answer 5

Glucose and Fructose

Question 6

Which monosaccharide is maltose formed from?

Answer 6

α glucose

Question 7

Which monosaccharides is lactose formed from?

Answer 7

Glucose and Galactose

Question 8

Features of starch

Answer 8

Compact and insoluble storage molecule in plants - won’t affect osmosis
Made of α glucose
Amylose - chains of glucose
Amylopectin - branches
It is branched to provide free ends for condensation/hydrolysis reactions
1,4 glycosidic bonds form chains
1,6 glycosidic bonds form branches

Question 9

Features of glycogen

Answer 9

Similar to starch
Storage molecule in animals and humans
More branches (1,6 linkages) than starch
More compact than starch
Made of α glucose

Question 10

Features of cellulose

Answer 10

Found in the cell wall of plant cells
Made of β glucose (every other is flipped upside down)
This forms long straight chains
Chains held together with hydrogen bonds
Chains form microfibrils and layers for strength

Question 11

What happens when monosaccharides or disaccharides react in a condensation reaction?

Answer 11

H₂O taken from ends of reactants
Glycosidic bond(s) join the reactants together
A new disaccharide or polysaccharide is formed

Question 12

What happens when polysaccharides or disaccharides react in a hydrolysis reaction?

Answer 12

Must react with H₂O for it to work
Glycosidic bond is broken
Polysaccharide/disaccharide breaks down to form monosaccharides or disaccharides

Question 13

What is the word equation for the hydrolysis of lipids?

Answer 13

Lipids + Water –ᴸ͟ᶦ͟ᵖ͟ᵃ͟ˢ͟ᵉ͟ -> Glycerol + Fatty Acids

Question 14

Structure of fatty acids

Answer 14

R - COOH where R is a variable group

Question 15

Describe the reaction that forms a triglyceride

Answer 15

Triglycerides are formed from condensation reactions between glycerol and fatty acids. The carboxylic acid (COOH) groups of three fatty acids join to the OH groups of one glycerol. At each site one molecule of H₂O and an ester bond are formed. The products of the reaction are x triglycerides and 3x water molecules, where the reaction begins with x glyercol molcules and 3x fatty acids.

Question 16

What are the features of saturated fatty acids?

Answer 16

No carbon double bonds
Straight hydrocarbon tails
Enables tails to be tightly packed together
Tend to be solid, e.g. animal fat, lard, butter, cheese

Question 17

What are the features of unsaturated fatty acids?

Answer 17

At least one carbon double bond
Results in kinks in the hydrocarbon tail
Fatty acids cannot be tightly packed together
Fats tend to be oils, e.g. olive oil

Question 18

What is the biochemical test for lipids?

Answer 18

Method:

1) Add ethanol and shake
2) Decant top layer and add water
3) Shake

Positive result: White emulsion

Question 19

Describe the structure of phospholipids

Answer 19

Phosphate group
Only two fatty acids
Polar molecule (charged at either end)
Hydrophilic head
Hydrophobic tail

Question 20

What are polymers of amino acids known as?

Answer 20

Polypeptide chains

Question 21

Structure of an amino acid

Answer 21

H₂N – R – COOH

Question 22

What are dipeptides and how are they formed?

Answer 22

Dipeptides are molecules of two amino acids.
The H₂N group of one amino acid joins to the COOH group of another amino acid.
One molecule of H₂O is produced and a peptide bond is formed between the amino acids.
The dipeptide has been formed in a condensation reaction.
Polypeptide chains are also formed in this way.

Question 23

What are the levels of structure of a protein?

Answer 23

Primary - the specific sequence of amino acids.
Secondary - folding of the chain due to hydrogen bonds, forming α-helices and β-pleats.
Tertiary - overall folding of the chain due to disulfide bridges, ionic bonds and hydrogen bonds, to give a 3D shape.
Quaternary - when proteins are made up of more than one polypeptide chain or also have a prosthetic group (e.g. haemoglobin, antibodies).

Question 24

What is the biochemical test for proteins?

Answer 24

Add Biuret solution to the test sample

Positive result: Lilac colour

Question 25

What part of an enzyme binds to the substrate and why can it do so?

Answer 25

The active site binds to the substrate because it is specific and complimentary to the substrate.

Question 26

Describe the lock and key and induced fit models.

Answer 26

Lock and key
The substrate fits into the enzyme perfectly - like a key into a lock.
When the product(s) are formed, they have a different shape so are released.

Induced fit
The substrate is of a similar shape to the enzyme.
Enough of the substrate can fit so the enzyme flexes and becomes complimentary.
This puts strain on the bonds in the substrate.

Question 27

If the question says ‘describe’, what word should the answer start with?

Answer 27

As

Question 28

What is an inhibitor?

Answer 28

A inhibitor is a molecule which binds to the enzyme and decreases the rate of reaction.

Question 29

What are the differences between competitive inhibitors and non-competitive inhibitors?

Answer 29

Competitive inhibitors bind to the active site, competing with the substrate to decrease the number of enzyme-substrate complexes. They can be outcompeted by adding more substrate.

Non-competitive inhibitors bind to elsewhere on the enzyme, changing the shape of the active site so that it is no longer complimentary to the substrate. They not only decrease but limit the rate of reaction.

Question 30

What is the equation for pH?

Answer 30

pH = -log₁₀(H⁺)

Question 31

Rearrange the equation for pH for H⁺ ion concentration

Answer 31

H⁺ = 10⁻ᵖᴴ

Question 32

Structure of DNA

Answer 32

Nucleotides
    -- Monomer of DNA
    -- Phosphate group
    -- Deoxyribose sugar
    -- Nitrogenous base
    -- Join to each other in condensation reactions
    -- Phosphodiester bonds between the sugar and phosphate
    -- Forms phosphate-sugar backbone
Bases
    -- Adenine
    -- Thymine
    -- Guanine
    -- Cytasine
    -- Two hydrogen bonds form between A and T
    -- Three hydrogen bonds form between G and C
Double helix
Two strands give DNA more stability

Question 33

Structure of RNA

Answer 33

Similar to DNA
Also made of nucleotides
Ribose sugar instead of deoxyribose
Uracil instead of thymine
Single-stranded molecule

Question 34

What methods of DNA replication were theorised?

Answer 34

Conservative - entire double helix conserved, entire new copy made
Semi-conservative - each strand is conserved separately and acts as a template for the formation of a new strand
Dispersive - original double helix dispersed among the two new double helices

Question 35

Describe the process of DNA replication

Answer 35

DNA helicase breaks hydrogen bonds between bases
Strands separate
Free nucleotides are attracted to their complimentary bases
DNA polymerase adds the nucleotides to the strands
Nucleotides join with each other by undergoing condensation reactions

Question 36

Why did many scientists doubt that DNA carried the genetic code?

Answer 36

The relative simplicity of DNA led many scientists to doubt that it carried the genetic code.

Question 37

How was the structure of DNA discovered?

Answer 37

Watson and Crick worked at the University of Cambridge to theorise the structure of DNA. Using Chargaff’s rule of complimentary base pairing and Rosalind Franklin’s X - shaped image of DNA, they were able to model the structure of DNA.

Question 38

What is ATP and what is it made of?

Answer 38

ATP stands for adenosine triphosphate and is formed from ribose, adenine and three phosphate groups.
It stores energy in its high energy bonds between the phosphate groups.
It is the universal currency of energy exchange in biological systems.

Question 39

The ATP cycle

Answer 39

Start with ATP
ATP splitting releases energy used for muscle contraction, active transport and biosynthesis
Hydrolysis reaction –> ADP + P
Formation of ATP requires energy from the oxidation of glucose
Condensation reaction –> ATP

Question 40

What is ATP the source of energy/phosphate for?

Answer 40

Metabolic processes
Movement (muscle contraction)
Active transport
Secretion
Activation of molecules

Question 41

What are the important properties of water?

Answer 41

Water:
Is a metabolite in many metabolic reactions, including condensation and hydrolysis reactions
Is an important solvent in which metabolic reactions occur
Has a relatively high specific heat capacity, buffering changes in temperature
Has a relatively large latent heat of vaporisation, providing a cooling effect with little loss of water through evaporation
Has strong cohesion between water molecules; this supports columns of water in the tube-like transport cells of plants and produces surface tension where water meets air.

Question 42

Which inorganic ions are imporant and why?

Answer 42

Hydrogen ions
The more hydrogen ions the lower the pH
Affects hydrogen bonds in enzymes

Iron ions
Forms part of the haem group (prosphetic group in haemoglobin)
Attracts oxygen molecules

Sodium ions
Co-transport with glucose or amino acids in the small intestine

Phosphate ions
Provides high energy bonds in ATP
Makes up the backbone of DNA
Hydrophilic head in phospholipids