Lecture 9 Flashcards
Polymers
built from monomers
long molecules consisting of many similar building blocks (monomers)
Synthesis and breakdown of polymers
condensation reaction- synthesis
hydrolysis- breakdown
Condensation reaction
occurs when two monomers bond together through the loss of a small molecule (usually water)
Hydrolysis reaction
polymers are disassembled to monomers, a reaction that is essentially the reverse of condensation
Structure of amino acids
an amino group and a carboxyl group and a varying R group side chain
Amino acid side chains
non-polar side chains- hydrophobic
polar side chains- hydrophilic
electrically charged side chains- hydrophilic
Peptide bonds
each amino acid has a different side chain
amino acids are linked together by peptide bonds
the two ends of the polypeptide chains are chemically distinct
the N terminus is capped by an amino group
the C terminus by a carboxyl group
Protein structure and function
a functional protein consist of one or more polypeptides twisted, folded and coiled into a unique shape
the sequence of amino acids determines a proteins three dimensional shape
a proteins structure is determined by its function
Primary protein structure
sequence of amino acids
- determined by inherited genetic information
Secondary protein structure
the coils and folds of secondary structure due to hydrogen bonds between repeating constituents of polypeptide backbone (C-N)
alpha helixes or beta pleated sheets
Tertiary protein structure
hydrogen bonding
van der Waals interactions
ionic bonds
disulphide bonds
results from interactions between side chains
- determined by R groups
Quaternary protein structure
aggregation of two or more polypeptide chains into one functional macromolecule
Structure determining techniques
x-ray crystallography
to determine a proteins structure
bioinformatics uses computer programs to determine protein structure from amino acid sequences
many virus capsids are more or less spherical protein assemblies
Bioinformatics
uses computer programs to predict protein structure from amino acid sequences
Protein functions include
-structural support
-storage
-transport
-cellular communications
-movement
-defence against foreign molecules
Enzymatic proteins
function:
selective acceleration of chemical reactions
example:
digestive enzymes catalyse hydrolysis of food molecules
Defensive proteins
function:
protection against disease
example:
antibodies
Storage proteins
function:
storage of amino acids
example:
casein is the major source of amino acid for baby mammals (protein of milk)
Transport proteins
function:
transport of substances
examples:
haemoglobin
Hormonal proteins
function:
coordination of an organisms activities
example:
insulin
Receptor proteins
function:
response of cell to chemical stimuli
example:
receptors built into the membrane of a nerve cell detect signalling molecules released by other nerve cells
Contractile and motor proteins
function:
movement
example:
motor proteins are responsible for the undulations of cilia and flagella
structural proteins
function:
support
example:
keratin is the protein of hair, horns feathers etc
Properties of lipids
lipids are large biological molecules that do not form polymers
little or no affinity for water
hydrophobic because they consist of mostly hydrocarbons which form non polar covalent bonds
functions of lipids
the major function is energy storage
store their fat in adipose cells
adipose tissue also cushions vital organs and insulates the body
steroids are lipids characterised by a carbon skeleton consisting of four fused rings
cholesterol is used in the plasma membranes
fats and fatty acids
fats are constructed from two types of smaller molecules:
glycerol and fatty acids
Glycerol
a three carbon alcohol with a hydroxyl group attached to each carbon
general structure of phospholipids
2 hydrophobic fatty acid tails joined to a hydrophilic head containing glycerol, phosphate and a polar group such as choline
Carbohydrates
serve as fuel and building materials
include sugars and polymers of sugars
simplest carbohydrates are monosaccharides
carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks
Monosaccharides
have molecular formulas that are usually multiples of CH2O
glucose is the most common
isomers
same formula but a different arrangement
monosaccharides differ in arrangements of groups around one or two carbon atoms
these small differences make only minor changes but can be detected by enzymes and other proteins so have biological effects
formation of a disaccharide
a disaccharide is formed when a dehydration reaction joins two monosaccharides
this covalent bond is called a glycosidic linkage
Polysaccharides
polymers of sugars
they have storage and structural roles
the structure and function of a polysaccharide are determined by its sugar monomers and positions of glycosidic linkages
Starch
a storage polysaccharide of plants, consisting of entirely glucose monomers
plants store surplus starch as granules within chloroplasts
Glycogen
a storage polysaccharide in animals
humans and other animals store glycogen mainly in the liver and muscle cells
hydrolysis of glycogen releases glucose into a useable form in the body
cellulose
a major component of tough wall of plant cells
a polymer of beta glucose
- each molecule is flipped for strength and rigidity
Structure of cellulose
- polymers with beta glucose are straight (unbranched)
- unbranched cellulose molecules are held together by hydrogen bonds between OH groups on parallel strands
- parallel cellulose molecules held together this way are grouped into microfibrils
