Classes of Organic Molecules (Proteins, Lipids and Nucleic Acids)

Question 1

state 2 basic facts about lipids as a whole

Answer 1

1. lipids are bonded by a non-polar covalent bond

2. lipids have a very low solubility in water

Question 2

what percentage of organic matter in the body do lipids around for and what percentage of bodyweight is made up of lipids

Answer 2

1. lipids account for 40% organic matter in the body

2. lipids account for 15% of human body weight

Question 3

what are the 4 ways in which lipids can be organised

Answer 3

fatty acids, phospholipids, triglycerides and steroids

Question 4

what is the structure of a fatty acid

Answer 4

fatty acids are long chains made up of carbon and hydrogen atoms with an acidic carboxyl group at one end

Question 5

explain what it is meant by ‘cis unsaturated’ fats

Answer 5

most naturally occurring unsaturated fatty acids occur in the cis position with both hydrogens occurring on the same side of the double carbon to carbon bond

Question 6

explain what it is meant by ‘trans unsaturated’ fats

Answer 6

trans fatty acids can be made by modifying cis unsaturated fatty acids so both hydrogen atoms are on opposing sides of the double carbon to carbon bond

Question 7

state 2 facts about trans unsaturated fats

Answer 7

1. trans configuration adds stability to food, as well as longer storage and also alters the foods consistency
2. trans unsaturated fatty acids have been linked with a number of health conditions - for example, elevated blood cholesterol concentration

Question 8

define what it is meant by the key term ‘eicosanoids’

Answer 8

Eicosanoids are modified fatty acids - derived from the 20 carbon long fatty acid arachidonic - which regulate a number of cell functions by acting as cell signal molecules

Question 9

state 4 facts about triglycerides

Answer 9

1. the majority of lipids in the human body are triglycerides
2. formed when glycerol, a 3 carbon sugar alcohol, binds to 3 fatty acid chains
3. hydroxyl groups in glycerol bind to carboxyl groups in fatty acids via a condensation reaction forming an ester bond
4. animal fatty acids tend to be more saturated and plant fatty acids tend to be more unsaturated

Question 10

how can triglycerides be used

Answer 10

1. stored in adipose tissue
2. broken down via hydrolysis reactions
3. fatty acids transported in blood to tissue
4. cells metabolise fatty acids to re-synthesis ATP

Question 11

explain the structure of a phospholipid

Answer 11

the third hydroxyl group in the cholesterol is bonded to a phosphate group, instead of a third fatty acid chain, which has a small, polar, nitrogen attached to the phosphate group

Question 12

explain the importance of phospholipids on an general basis

Answer 12

as phospholipids are amphipathic, they form clusters in water with hydrophilic (polar) heads facing outwards and hydrophobic (non-polar) tails facing inwards

Question 13

state 2 facts about steroids

Answer 13

1. steroids are formed by interconnected rings of carbon atoms
2. a few polar hydroxyl groups may be attracted to this ring structure, but aren’t numerous enough to make a steroid water soluble

Question 14

give 4 examples of steroids

Answer 14

cholesterol, cortisol, oestrogen and testosterone

Question 15

explain two features of the structure of amino acids

Answer 15

1. each amino acid, excluding proline, has an amine group and a carboxyl group bound to the terminal carbon in the middle of the molecule
2. side chains may be polar but not ionised (7 amino acids), polar and ionised (5 amino acids) or non-polar (8 amino acids)

Question 16

how do amino acids bond together

Answer 16

condensation reactions between the carboxyl group of one amino acid and the amine group of another amino acid forms a peptide bond between two amino acids plus a water molecule

Question 17

define what it is meant by the key term ‘peptide’

Answer 17

a peptide is a functional polypeptide with 50, or fewer, amino acids in the chain and has a known biological function

Question 18

what are the two variables which determine the primary structure of a protein

Answer 18

1. the number of amino acids in the polypeptide chain

2. the type of amino acids at each point along the polypeptide chain

Question 19

what is the scientific reason between the secondary structure of a protein

Answer 19

interactions between side groups (of amino acids) leads to bonding, twisting and folding of the polypeptide chain into a more compact structure and forms something called a conformation

Question 20

explain the concept of an ‘Alpha Helix’

Answer 20

an alpha helix occurs because peptide bonds form at regular intervals along a polypeptide chain. the H-bonds between them tend to force the chain into a coiled conformation known as a double helix

Question 21

explain the concept of ‘beta pleated sheets’

Answer 21

beta pleated sheets occur because H-bonds also form between peptide bonds when extended regions of a polypeptide chain run approximately parallel to each other forming a relatively straight and extended region called a beta pleated sheet

Question 22

explain the concept of a ‘random coil conformation’

Answer 22

a random coil conformation occurs when a given region of a polypeptide chain may not assume either an alpha helix or beta pleated sheet and so are called random coil conformations

Question 23

explain the reasons for alpha helixes and beta pleated sheets

Answer 23

alpha helices and beta pleated sheets import stability to a protein to allow it to anchor onto a lipid bilayer due to the hydrophobic side chains in amino acids making them more likely to remain in lipid environments

Question 24

what enables a tertiary structure of a protein to form

Answer 24

because the secondary structure has folded the polypeptide up more, more interactions between more amino acids can take place

Question 25

what is the effect of a tertiary structure

Answer 25

a tertiary structure leads to the folding of the polypeptide into it’s final three dimensional shape making it a functional protein

Question 26

state the 2 determinants of tertiary protein structure which you must focus on learning

Answer 26

1. Van der Waals forces which are very week and transient electrical interactions with electrons in the valance shells of the atoms in close proximity of each other
2. covalent disulfide bridges linking the sulfur containing side chains to form cysteine amino acids

Question 27

what are the other 3 determinants of tertiary protein structure

Answer 27

1. H-bonds between portions of the polypeptide chain
2. ionic bonds between polar and ionised regions along the polypeptide chains
3. attraction between non-polar (hydrophobic) and polar (hydrophilic) regions along the polypeptide chain

Question 28

what is another name for quaternary proteins

Answer 28

multimenic proteins

Question 29

what are the determinants for multimenic proteins

Answer 29

multimenic proteins have the same determinants responsible for the interactions of a single polypeptide chain

Question 30

how are multimenic proteins formed

Answer 30

multimenic proteins are formed by chains being held together via the interactions between ionised, polar and non-polar side chains as well as disulfide covalent bonds between the polypeptide chains

Question 31

what percentage of bodyweight is made up of nucleic acids

Answer 31

nucleic acids only make up approximately 2% total body weight

Question 32

what are the three pyrimidine bases

Answer 32

Uracil, Thymine and Cytosine

Question 33

what are the two purine bases

Answer 33

Adenine and Guanine

Question 34

which bases pair together and how many H-bonds form between them

Answer 34

1. A + T (two H-bonds)

2. G + C (three H-bonds)