Proteins, Polysaccharides and Lipids

Question 1

What are the secondary structures of proteins?

Answer 1

Alpha helix and beta pleated sheets

Question 2

Describe the alpha helix secondary structure of proteins

Answer 2

• Rod-like, right handed orientation
• Found in strong extensible proteins
• Stabilised by hydrogen bonds
• CO of each amino acid is H-bonded to NH of amino acid 4 residues ahead in sequence
• 3.6 residues per helix turn

Question 3

Give some examples of proteins with alpha helix secondary structure

Answer 3

Haemoglobin, myoglobin, keratins, fibrins, myosin

Question 4

Describe the beta pleated sheet secondary structure of proteins

Answer 4

• Zigzag chains
• Place several chains side by side, CO and NH groups align, H bonding occurs -> sheet like structure
• Parallel: chains run in same direction
• Anti-parallel: chains run in opposite direction
• Found in proteins where flexibility is needed e.g. silk fibroin

Question 5

Which is the only protein that has a triple helix structure?

Answer 5

Collagen
Very strong, water-insoluble fibres
3 chains wound round each other -> tropocollagen

Question 6

How many amino acids are there in each of the 3 chains that wind together in a triple helix structure to make up collagen?

Answer 6

~1000 amino acids

Question 7

What is the repeating structure present in each of the 3 chains that wind together in a triple helix structure to make up collagen?

Answer 7

X-Pro-Gly OR X-Hyp-Gly

Hyp = hydroxyproline

Question 8

Give examples of fibrous proteins

Answer 8

Collagen, keratin, fibrin, elastin, myosin

Question 9

What are fibrous proteins?

Answer 9

Insoluble, metabolically unreactive, principally structural proteins

Question 10

What are globular proteins?

Answer 10

• Spherical
• Backbone folds in on itself
• Water-soluble compact structures

Question 11

What is the role and structure of myoglobin?

Answer 11

• Oxygen storage in muscle
• Globular protein, associated with tertiary structure
• Single chain (153aa)
• Contains 8 helical regions
• Prosthetic haem group contained within hydrophobic pocket

Question 12

What is the role of haemoglobin?

Answer 12

Oxygen transport

Question 13

Describe the structure of haemoglobin

Answer 13

• Associated with quaternary structure
• Has 4 subunits: 2 alpha chains and 2 beta chains
• Speroidal molecule
• Contains 4 haem groups

Question 14

How many amino acids are in each alpha chain of haemoglobin?

Answer 14

141 aa

Question 15

How many amino acids are in each beta chain of haemoglobin?

Answer 15

146 aa

Question 16

What are peripheral membrane proteins?

Answer 16

Proteins that lie on the membrane surface

Question 17

What are integral membrane proteins?

Answer 17

Proteins within the lipid bilayer

Question 18

What are channel proteins?

Answer 18

• Forms a channel in membrane

- Facilitate movement of small molecules across membrane (simple diffusion)

Question 19

What are carrier proteins?

Answer 19

Proteins that bind to transported molecules (facilitated diffusion)

Question 20

What are hormones?

Answer 20

Messenger proteins that allow cells to communicate with each other

Question 21

What are some of the common modes of action of hormones?

Answer 21

1. Influence the rate of synthesis of enzymes and other proteins
2. Affect rate of enzymatic catalysis
3. Alter permeability of cell membrane

Question 22

What is the sequence of events that follows after a hormone binds with its specific membrane receptor?

Answer 22

Hormone binds to receptor -> message relayed to inside of cell -> cascade events -> cellular actions

Question 23

Give 3 examples of hormones

Answer 23

1. Insulin: sugar uptake by cells from bloodstream
2. Glucagon: sugar release by cells into bloodstream
3. Human growth hormone (HGH)

Question 24

What are enzymes?

Answer 24

• Biological catalysts
• Globular proteins
• Increase reaction rates by up to 10^20
• High specific

Question 25

Which proteins are for immune protection?

Answer 25

Antibodies, cytokines, chemokines

Question 26

Which proteins are for muscular contraction?

Answer 26

Myosin (fibrous) | Actin (globular)

Question 27

What are the building blocks of polysaccharides?

Answer 27

Monosaccharides

Question 28

What are the 2 types of monosaccharide?

Answer 28

Aldoses (contain CHO group) | Ketoses (contain CO group)

Question 29

What is a disaccharide?

Answer 29

When 2 monosaccharides come together (involves elimination of water)

Question 30

What is maltose composed of?

Answer 30

Two glucose molecules joined by alpha-1,4-glycosidic linkage

Question 31

What is sucrose composed of?

Answer 31

One glucose molecule and one fructose molecule

Question 32

What is lactose composed of?

Answer 32

One glucose molecule and one galactose molecule

Question 33

What type of sugar is glucose?

Answer 33

An aldose sugar

Question 34

Describe the structure of glucose

Answer 34

6 membered ring Exists in linear or ring form Important monosaccharide

Question 35

What are the 2 isomeric forms which glucose can exist in?

Answer 35

- Alpha configuration: hydroxyl group pointing downwards | - Beta configuration: hydroxyl group pointing upwards

Question 36

What type of reaction forms polysaccharides from monosaccharides?

Answer 36

Dehydration reactions/hydrolysis reactions form/catabolise complex carbohydrates from monosaccharides

Question 37

What is starch composed of?

Answer 37

1,4 linkages of alpha glucose

Question 38

What is cellulose compose of?

Answer 38

1,4 linkages of beta glucose

Question 39

Which polysaccharide is a food reserve in humans?

Answer 39

Starch

Question 40

Why can't humans digest cellulose?

Answer 40

Don't have the enzymes to do so (beta-glycosidase enzyme) - breaks down beta 1,4 glycosidic bonds between glucose monosaccharides

Question 41

Describe the structure of glycogen

Answer 41

- Inner region and outer region - Inner region comprised of alpha 1,4 linkages - At branch point: alpha 1,6 linkages - Tree-like structure, lots of branching

Question 42

Describe the structural differences between glycogen and starch

Answer 42

Starch = linear structure. Comprised of alpha 1,4 glycosidic linkages Glycogen = branched structure. Outer region comprised of alpha 1,4 glycosidic linkages. At branch point = alpha 1,6 glycosidic linkages

Question 43

Which polysaccharide are plant cell walls made up of?

Answer 43

Cellulose

Question 44

What are the main architectural units of plant cell walls?

Answer 44

Microfibrils composed of cellulose

Question 45

What are the monomeric units of lipids?

Answer 45

Fatty acids

Question 46

What are lipids?

Answer 46

- Fatty type molecules | - Most lipids are glycerides, based upon glycerol

Question 47

What is a phosphatidylcholine?

Answer 47

- A diaglyceride | - A major phospholipid of membranes

Question 48

what is the major phospholipid of membranes?

Answer 48

Phosphatidylcholone

Question 49

What is the function of triaglycerides?

Answer 49

Storage compounds

Question 50

What determines whether a fatty acid is solid or liquid at room temperature?

Answer 50

- Degree of saturation - Affects van Der Waal's forces - Changes the lipids physical property - Saturated fatty acids are solid at room temperature, unsaturated fatty acids are liquid at room temperature

Question 51

Give some examples of sterols

Answer 51

Cholesterol, cortisol, oestrogen, testosterone

Question 52

What are the roles of sterols?

Answer 52

- Some have essential biological activity | - Others are important constituents of biological membranes (e.g. cholesterol)