Proteins, Polysaccharides and Lipids Flashcards
What are the secondary structures of proteins?
Alpha helix and beta pleated sheets
Describe the alpha helix secondary structure of proteins
- 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
Give some examples of proteins with alpha helix secondary structure
Haemoglobin, myoglobin, keratins, fibrins, myosin
Describe the beta pleated sheet secondary structure of proteins
- 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
Which is the only protein that has a triple helix structure?
Collagen
Very strong, water-insoluble fibres
3 chains wound round each other -> tropocollagen
How many amino acids are there in each of the 3 chains that wind together in a triple helix structure to make up collagen?
~1000 amino acids
What is the repeating structure present in each of the 3 chains that wind together in a triple helix structure to make up collagen?
X-Pro-Gly OR X-Hyp-Gly
Hyp = hydroxyproline
Give examples of fibrous proteins
Collagen, keratin, fibrin, elastin, myosin
What are fibrous proteins?
Insoluble, metabolically unreactive, principally structural proteins
What are globular proteins?
- Spherical
- Backbone folds in on itself
- Water-soluble compact structures
What is the role and structure of myoglobin?
- Oxygen storage in muscle
- Globular protein, associated with tertiary structure
- Single chain (153aa)
- Contains 8 helical regions
- Prosthetic haem group contained within hydrophobic pocket
What is the role of haemoglobin?
Oxygen transport
Describe the structure of haemoglobin
- Associated with quaternary structure
- Has 4 subunits: 2 alpha chains and 2 beta chains
- Speroidal molecule
- Contains 4 haem groups
How many amino acids are in each alpha chain of haemoglobin?
141 aa
How many amino acids are in each beta chain of haemoglobin?
146 aa
What are peripheral membrane proteins?
Proteins that lie on the membrane surface
What are integral membrane proteins?
Proteins within the lipid bilayer
What are channel proteins?
- Forms a channel in membrane
- Facilitate movement of small molecules across membrane (simple diffusion)
What are carrier proteins?
Proteins that bind to transported molecules (facilitated diffusion)
What are hormones?
Messenger proteins that allow cells to communicate with each other
What are some of the common modes of action of hormones?
- Influence the rate of synthesis of enzymes and other proteins
- Affect rate of enzymatic catalysis
- Alter permeability of cell membrane
What is the sequence of events that follows after a hormone binds with its specific membrane receptor?
Hormone binds to receptor -> message relayed to inside of cell -> cascade events -> cellular actions
Give 3 examples of hormones
- Insulin: sugar uptake by cells from bloodstream
- Glucagon: sugar release by cells into bloodstream
- Human growth hormone (HGH)
What are enzymes?
- Biological catalysts
- Globular proteins
- Increase reaction rates by up to 10^20
- High specific
Which proteins are for immune protection?
Antibodies, cytokines, chemokines
Which proteins are for muscular contraction?
Myosin (fibrous)
Actin (globular)
What are the building blocks of polysaccharides?
Monosaccharides
What are the 2 types of monosaccharide?
Aldoses (contain CHO group)
Ketoses (contain CO group)
What is a disaccharide?
When 2 monosaccharides come together (involves elimination of water)
What is maltose composed of?
Two glucose molecules joined by alpha-1,4-glycosidic linkage
What is sucrose composed of?
One glucose molecule and one fructose molecule
What is lactose composed of?
One glucose molecule and one galactose molecule
What type of sugar is glucose?
An aldose sugar
Describe the structure of glucose
6 membered ring
Exists in linear or ring form
Important monosaccharide
What are the 2 isomeric forms which glucose can exist in?
- Alpha configuration: hydroxyl group pointing downwards
- Beta configuration: hydroxyl group pointing upwards
What type of reaction forms polysaccharides from monosaccharides?
Dehydration reactions/hydrolysis reactions form/catabolise complex carbohydrates from monosaccharides
What is starch composed of?
1,4 linkages of alpha glucose
What is cellulose compose of?
1,4 linkages of beta glucose
Which polysaccharide is a food reserve in humans?
Starch
Why can’t humans digest cellulose?
Don’t have the enzymes to do so (beta-glycosidase enzyme) - breaks down beta 1,4 glycosidic bonds between glucose monosaccharides
Describe the structure of glycogen
- 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
Describe the structural differences between glycogen and starch
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
Which polysaccharide are plant cell walls made up of?
Cellulose
What are the main architectural units of plant cell walls?
Microfibrils composed of cellulose
What are the monomeric units of lipids?
Fatty acids
What are lipids?
- Fatty type molecules
- Most lipids are glycerides, based upon glycerol
What is a phosphatidylcholine?
- A diaglyceride
- A major phospholipid of membranes
what is the major phospholipid of membranes?
Phosphatidylcholone
What is the function of triaglycerides?
Storage compounds
What determines whether a fatty acid is solid or liquid at room temperature?
- 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
Give some examples of sterols
Cholesterol, cortisol, oestrogen, testosterone
What are the roles of sterols?
- Some have essential biological activity
- Others are important constituents of biological membranes (e.g. cholesterol)
