lecture 3 - What are cells made of?

Question 1

what are some examples of macromolecules?

Answer 1

carbohydrates
lipids
proteins
nucleic acids

Question 2

what are macromolecules?

Answer 2

• components of cells are contained in many types of food, and are polymers and monomers
• knowledge of these macromolecules not only informs you about cellular structure, but can also help inform your dietary choices

Question 3

describe the synthesis of polymers

Answer 3

monomers form larger molecules called polymers through polymerisation: linking monomers together via dehydration reactions (know diagram)

Question 4

describe the breakdown of polymers

Answer 4

polymers can be shortened b removing monomers from either end using a hydrolysis reaction:
- bond between residues 4 and 5 is cleaved in the presence of water: a hydrolysis reaction

Question 5

what are carbohydrates?

Answer 5

Carbohydrates:
>serve as fuel and building material
> include both sugars and their polymers
> examples: mono-; di- and polysaccharides

Question 6

what are monosaccharides?

Answer 6

• are the simplest sugars
• can be used for fuel
• can be converted into other organic molecules
• can be combined into polymers
• may be linear OR form rings when dissolved in water

Question 7

what are Disaccharides?

Answer 7

• two monomers joined with a glycosidic bond

- maltose and cellobiose

Question 8

what are polysaccharides?

Answer 8

polymers of glucose monomers

Question 9

what is starch?

Answer 9

> starch
- a polymer of glucose monomers: major storage form of glucose in plants
- has (1-4) and a few (1-6) linkages (branching)
we can digest this, as the glucose monomers are in alpha-configuration.

Question 10

what is glycogen?

Answer 10

> glycogen

• consists of glucose monomers: the major storage form of glucose in animals
• has (1-4) and frequent (1-6) linkages (branching)
• we can break this down to release glucose monomers (alpha configuration)

Question 11

what is cellulose?

Answer 11

• is a major component of the tough walls that enclose plant cells
• note the group distribtion, linearity and packing potential
• 100 billion tonnes made annually
• mammals cannot digest this as glucose is in the beta configuration

Question 12

what is the glycemic index and how does it work?

Answer 12

• a way of measuring how quickly your blood-glucose level rises after eating carbohydrate containing foods.
• the quicker the food is digested, the faster your blood glucose level rises –> higher GI

Question 13

what is low GI?

Answer 13

• low GI foods usually contain unrefined carbs that are difficult to break down quickly
• low GI foods satisfy cravings for longer periods of time and have been linked to lowered risk of diabetes

Question 14

what are glycoproteins?

Answer 14

• combination of proteins and carbohydrates
• usually found on cell surfaces
• combinations of carbohydrate units and protein chains can often be used as a unique identifier of types of cells

Question 15

why are glycoproteins on the cell surface important?

Answer 15

• bacteria and viruses have unique cell-surface glycoproteins that are recognised by our immune system to ward off infection
• glycoproteins also present on cell surfaces of eukaryotic cells and can be used to differentiate between cell types.

Question 16

what is chitin?

Answer 16

• is found in the exoskeleton of arthropods and the cell walls of fungi
• highly resistant to enzymatic digestion
• can be used as surgical thread

Question 17

what are lipids?

Answer 17

a diverse group of hydrophobic molecules

- are found in cellular membrane structures, storage compounds etc.

Question 18

what are lipids constructed from?

Answer 18

• two types of smaller molecules, a single glycerol and usually three fatty acid chains
• vary in length and number and locations of double bonds they contain

Question 19

what are saturated fatty acids?

Answer 19

• have the maximum number of hydrogen atoms possible

- have no double bonds

Question 20

what are unsaturated fatty acids?

Answer 20

have one or more double bonds

Question 21

what are phospholipids?

Answer 21

• have only two fatty acids
• have a phosphocholine group (a phosphate derivative) instead of a third fatty acid
• consists of a hydrophilic ‘head’ and hydrophobic ‘tails’
• result in a bilayer arrangement found in cell membranes

Question 22

what are proteins?

Answer 22

• meat, dairy, nuts and seeds, are all foods that are rich in protein
• a protein consists of one or more polypeptides (polymers of amino acids)

Question 23

what are amino acids?

Answer 23

• are organic molecules possessing both carboxyl and amino groups
• differ in their properties due to differing side chains called R groups
• linked by peptide bonds. the peptide bond is very different from the glycosidic bond.

Question 24

what are two examples where protein structure affects its function?

Answer 24

Collagen
- key component of cartilage, bone and skin tissue
- durable triple helix shape allows it to form strong and flexible fibres
Glutamate receptor
- binds to the neurotransmitter glutamate to relay signals within brain cells.
- top of Y shape ‘receives’ glutamate, bottom of Y embeds into cell surface.

Question 25

what are the four levels of protein structure?

Answer 25

1) primary structure - amino acid sequence
2) secondary structure - alpha - helix
3) tertiary structure - alpha subunit
4) quaternary structure - multiple alpha subunits

Question 26

what are enzymes?

Answer 26

• enzymes are a specific type of protein
• enzymes bind to substrates very specifically to catalyse a reaction.
• this specificity is determines by protein structure

Question 27

what are the two enzyme models?

Answer 27

lock and key

induced fit

Question 28

what are the properties of enzymes?

Answer 28

• enzymes are catalysts
• are catalytically active proteins
  enzymes speed up metabolic reactions by lowering energy barriers (activation energy)

Question 29

what are two examples of enzymes?

Answer 29

Phenylalanine hydroxylase 
- converts amino acid 'phe -->tyr'
alcohol dehydrogenase
-  breaks down alcohol
found in stomach lining and liver