Chapter 1 - The Chemical Basis of Life (3) Flashcards
Functions of proteins
enzymes = mediate chemical reactions in organisms structure = used as building material hormones = released by glands to cause an effect elsewhere in the body antibodies = produced by immune system which target pathogens for destruction transport = pump molecules against a concentration gradient recognition = identify cells to your immune system
Structure of proteins
highly organized, complex molecules
their structure is described using up to 4 different levels of scrutiny
1 has the smallest scope
4 has the largest scope
Primary structure
the order of amino acids
met, val, leu, ala, try
all amino acids have the same structure
20 different amino acids for each position in a protein allows for an almost infinite number of possible sequences
the variety leads to a diverse structural and functional importance
Alpha helix
a common, stable and strong helical arrangement
stabilized by hydrogen bonds between a carbonyl oxygen and the amide hydrogen four amino acids down the chain
R-groups project outward from helix
the ends are created due to L-proline, which makes the structure very stiff
eg. keratin
Beta-pleated sheet
different sections of a polypeptide lie side by side
stabilized by hydrogen bonds
adjacent R-groups alternately project above and below the sheet, and therefore do not get in the way of the structure
eg. silk
Tertiary structure
overall, complex structure of a polypeptide
maintained by intermolecular attractions
disulphide bridges between cysteines can link distant regions of a polypeptide
polar and charged R-groups are attracted by water and clump together in hydrophobic pockets, but are unable to associate with lipids in membranes
bulky R-groups distort secondary structures such as alpha-helices
the R-group of proline is bonded twice, the inflexibility disrupting alpha-helices
Protrusions and pockets
protrusions = allow protein to interact with complementary pocket of another protein pockets = provide attachment points for prosthetic groups and coenzymes
Quaternary structure
interaction between polypeptide and either other polypeptide(s) or prosthetic group(s)
the forces holding subunits together are the same as those that cause tertiary structure
disulphide linkages
hydrophilic and hydrophobic interactions
hydrogen bonding between subunits
Fibrous proteins
typically rod shaped
alpha-keratin
found in hair, fingernails, wool
characterized by long polypeptide chains with an uninterrupted alpha helix
beta-keratin
found in spider webs and silk
secondary structures consists of beta pleated sheets
Globular proteins
typically fold into compact spherical or oblong forms
maximizes the number of hydrogen bonds with water
hemoglobin
consists of 4 globular subunits, each with a heme prosthetic group
binds oxygen in blood cells
myoglobin
single globular polypeptide with an associated heme subgroup
binds oxygen in muscle cells
Thermodynamics
the study of energy transformations
first law = energy cannot be created or destroyed, only converted from one form to another
second law = during energy conversions, some of the energy is lost as heat, which increases the entropy of the molecules in the universe
Second law of thermodynamics
making ice cubes increases the entropy of the universe
even though water molecules are more orderly in cubes, the energy used by the freezer wasted energy
this is why there is no such thing as a perpetual motion machine
Exergonic reactions
same as exothermic, but occur at body temperature, can use enzymes
overall net release of energy
reactants have less bond energy, but more potential energy than the products
self-sustaining reactions (energy released acts as activation energy for other reactions)
eg. respiration
Endergonic reactions
same as endothermic, but occur at body temperature
require an overall input of energy
reactants have more bond energy but less potential energy than the products
not self-sustaining (requires continuous activation energy)
eg. photosynthesis
Metabolism
catabolic reaction = breaks down larger molecules to smaller ones, exergonic
anabolic reaction = builds larger molecules from smaller ones, endergonic
metabolism = total sum of the catabolic and anabolic reactions