Proteins, Polysaccharides and Lipids Flashcards
What are the characteristics of an alpha helix?
- rod-like
- Found in strong extensible proteins
- stabilised by hydrogen bonds
- CO of each AA is H-bonded to NH of AA FOUR residues ahead in the sequence
- 3.6 residues/helix turn
What are the characteristic of a beta-pleated sheet?
- Zig-zag chains
- Place several chains side by side, CO and NH groups from different chains align and H-bonding occurs –> sheet like structure
- can be parallel or anti-parallel
- Found in proteins where flexibility is needed
What are the characteristics of a triple helix?
- Collagen only
- Major component of connective tissue
- Very strong, water-insoluble fibres
- 3 chains with around 1000 AA per chain
- No H bonds in each chain but chains are held together by H bonds
- Each chain has repeating structure: X-Pro-Gly or X-Hyp-Gly
What are the characteristics of fibrous proteins?
- Insoluble, metabolically unreactive
- Principally structural proteins e.g. keratin, fibrin, elastin
What ate the characteristics of globular proteins?
- Spherical
- Tertiary or quaternary structure
- Water soluble
Characteristics of myoglobin?
- Oxygen storage in molecules
- Globular
- Single chain
- Contains 8 alpha helix regions and 0 beta-pleated sheets
- Helical segments joined by regions of random coiling where chain makes major directional change
Characteristics of haemoglobin?
- oxygen transport
- associated with quaternary structures
- two pairs of polypeptide chains
- Spheroidal molecule
- Four haem groups
- Each alpha subunit is in contact with both beta chains
- Few interactions occur between the two alpha or two beta chains
What is a peripheral membrane protein?
A protein found on the membrane surface
What is an integral membrane protein?
A protein found within the lipid bilayer
What is a membrane channel protein?
- forms a channel in membranes
- Facilitates the movement of small molecules across the membrane (simple diffusion - does not require energy)
What is a membrane carrier protein?
Binds to transport molecules (facilitated diffusion)
What is the function of hormones?
Allows cells to communicate with each other
What are the 3 modes of action of messenger proteins?
- Influence rate of synthesis of enzymes and other proteins
- Affect the rate of enzyme catalysis
- Alter permeability of cell membranes
How does a hormone work?
Hormone binds to receptor -> message relayed to inside of cell -> cascade of events -> cellular action
What are 3 examples of hormones as messenger proteins?
- Insulin: sugar uptake by cells from the bloodstream
- Glucagon: sugar release by cells into bloodstream
- Human growth hormones
