Transcript Nerve activates contraction

Polymer Principles
Most macromolecules are polymers
Polymer = (Poly = many; mer = part); large molecule consisting of many identical or similar subunits
connected together.
Monomer = Subunit or building block molecule of a polymer
Macromolecule = (Macro = large); large organic polymer
Formation of macromolecules from smaller building block molecules represents another level
in the hierarchy of biological organization.
There are four classes of macromolecules in living organisms:
Carbohydrates
Lipids
Proteins
Nucleic acids
Polymerization reactions = Chemical reactions that link two or more small molecules to form
larger molecules with repeating structural units.
Condensation reactions = Polymerization reactions during which monomers are covalently
linked, producing net removal of a water molecule for each covalent linkage.
Figure 5.2 The synthesis and breakdown of polymers
Polymerization Reaction
Condensation or Dehydration Reaction
Requires energy, biological catalysts (enzymes)
Digestive enzymes catalyze hydrolytic reactions
Unity in life--only about 40-50 common monomers
Diversity too---new properties emerge from complex
arrangements of monomers into polymers
Figure 5.3 The structure and classification of some monosaccharides
3
5
Carbohydrates--sugars and their polymers
Sugars--smallest carbohydrates
6
Simple sugars--monomers of carbohydrates
called monosaccharides (CH2O)
Major nutrients for cells e.g. glucose
Glucose can be produced by photosynthesis
from CO2, H2O, and sunlight
Store energy--cellular respiration
Raw material for other organic molecules
Used as monomers for disaccharides and
polysaccharides--condensation reactions
Asymmetrical carbon--enantiomers
Figure 5.4 Linear and ring forms of glucose
Figure 5.5 Examples of disaccharide synthesis
Polysaccharide s = Macromolecules th at are polymers of a f ew
hundred or tho usand m onosaccharides.
Are f orme d by linking monome rs in enzyme- mediat ed condensat io n
react ions
Have tw o import ant b io logical f unct ions:
1 ) Energy stor age ( st arch and g ly cogen)
2 ) Stru ctur al suppo rt (c ellulose and chit in)
Figure 5.6 Storage polysaccharides
Cells hydrolyze storage polysaccharidesas needed for for energy
Starch--glucose polymer in plants
Amylose--unbranched polymer
Amylopectin--branched polymer
Most animals can digest starch
potato, wheat, corn, rice
Glycogen--glucose storage polysaccharide
in animals
Very highly branched
Stored in muscle and liver
Figure 5.7 Starch and cellulose structures
Figure 5.7 Starch and cellulose structures
Figure 5.7x Starch and cellulose molecular models
 Glucose
 Glucose
Cellulose
Starch
Figure 5.8 The arrangement of cellulose in plant cell walls
Cellulose reinforces plant walls
Hydrogen bonds
Cellulose cannot be digested
by most organisms--no enzyme
to break beta 1-4 linkage
Insoluble fiber, digestion
Figure 5.x1 Cellulose digestion: termite and Trichonympha
Figure 5.x2 Cellulose digestion: cow
Figure 5.10 Chitin, a structural polysaccharide: exoskeleton and surgical thread
Lipids :
Diverse Hydrophobic
Mole cule s
Lipids = Diverse group o f organic compounds th at are insoluble in w at er,
but w i ll dissolve in nonp olar solvents ( e.g., eth er chlorof orm, benzene) .
Importa nt groups are fat s, phos pholipids, and st eroids.
Fat s st ore large amount s of energy
Fat s = Macromolecules are const ruct ed f rom:
Glycerol, a th ree-carbon alcohol
Fat t y acid ( carboxylic acid) = Composed of a carboxyl group at
one end a nd an at ta ched hydrocarbon ch ain (“ t ail” )
Figure 5.11 The synthesis and structure of a fat, or triacylglycerol
Carboxyl group has acid properties
Hydrocarbon chain, 16-18 carbons
Nonpolar C-H bonds, hydrophobic
(Condensation Reaction)
(bond between hydroxyl group and a carboxyl group)
Fats:
hydrophobic, not water soluble
variation due to fatty acid composition
fatty acids can be the same or different
fatty acids can vary in length
fatty acids can vary in the number and location
of double bonds (saturation)
A triglyceride
Figure 5.12 Examples of saturated and unsaturated fats and fatty acids
Saturated fats
no double bonds between carbons in the tail
saturated with hydrogen
solid at room temp
most animal fats, bacon grease, lard, butter
Unsaturated fats
one or more double bonds in tail
kinks the tail so cannot pack closely enough to solidify at room temp
most plant fats
Artificial hydrogenation, peanut butter, margarine
Fats have many useful functions
Energy storage 9 vs 4 Kcal/gram
more compact fuel than carbohydrates
Cushions organs e.g. kidney
Insulates against heat loss
Phospholipids
Phospholipids = Compounds with molecular building blocks of glycerol, two fatty acids, a
phosphate group, and usually, an additional small chemical group attached to the phosphate.
Differs from fat in that the third carbon of glycerol is joined to a negatively
charged phosphate group
Can have small variable molecules (usually charged or polar) attached to
phosphate
Are diverse depending upon differences in fatty acids and in phosphate
attachments
Show ambivalent behavior toward water. Hydrocarbon tails are hydrophobic and
the polar head (phosphate group with attachments) is hydrophilic.
Cluster in water as their hydrophobic portions turn away from water. One such cluster, a
micelle, assembles so the hydrophobic tails turn toward the water-free interior and the
hydrophilic phosphate heads arrange facing outward in contact with water.
Are major constituents of cell membranes. At the cell surface, phospholipids
form a bilayer held together by hydrophobic interactions among the hydrocarbon tails.
Phospholipids in water will spontaneously form such a bilayer.
Figure 5.13 The structure of a phospholipid
Phospholipids = Compounds with
molecular building blocks of glycerol, two
fatty acids, a phosphate group, and
usually, an additional small chemical
group attached to the phosphate.
Differs from fat in that the third carbon of glycerol
is joined to a negatively charged phosphate
group
Can have small variable molecules (usually
charged or polar) attached to phosphate
Are diverse depending upon differences in fatty
acids and in phosphate attachments
Show ambivalent behavior toward water.
Hydrocarbon tails are hydrophobic and the polar
head (phosphate group with attachments) is
hydrophilic.
Are major constituents of cell membranes.
Phospholipid Bilayers of Cell Membranes
Steroids
Steroids = Lipids which have four fused
carbon rings with various functional groups attached.
Cholesterol is an important steroid and is the
precursor to many other steroids including
vertebrate sex hormones and bile acids.
Is a common component of animal cell
membranes.
Can contribute to atherosclerosis.
Figure 5.15 Cholesterol, a steroid
Memebranes
Bile salts--absorption of fats
HDL and LDL---triglycerides, phospholipids, cholesterol, protein
LDL receptor deficiency--more deposition of cholesterol in arterial walls
HDL--aid in removal of cholesterol from tissues
Polypeptide chains = Polymers of amino acids that are arranged in a specific linear sequence, linked by peptide bonds
Protein = A macromolecule consisting of one or more polypeptide chains folded and coiled into specific conformations
Proteins make up 50% of the dry weight of cells
Proteins vary extensively in structure, each with a unique 3-dimensional shape (conformation)
Although they vary in structure and function, they are commonly made from only 20 amino acid monomers
Figure 5.17 The 20 amino acids of proteins: nonpolar
Amino acid = building blocks of proteins
Asymmetric carbon (alpha carbon) bonded to H, Carboxyl group, Amino group, variable R-group (side chain)
Physical and chemical properties of the side chain determine the uniqueness of each amino acid
At normal cellular pH both the amino and carboxyl group are ionized---pH determines which ionic state predominates
Alpha carbon, asymmetric
Amino
Side chain (R group)
Hydrophobic side chain
Carboxyl
Figure 5.17 The 20 amino acids of proteins: polar and electrically charged
Hydrophillic side chain
Figure 5.18 Making a polypeptide chain
Amino
Peptide bond = covalent bond formed by condensation reaction
Carboxyl
Backbone has a repeating sequence N-CC-N-CC-…
Figure 5.19 Conformation of a protein, the enzyme lysozyme
Protein’s function depends on its specific conformation
Protein conformation = 3-dimensional shape
Native conformation = functional conformation found under normal biological conditions
The conformation of a protein enables it to bind specifically to another molecular
e.g. hormone/receptor, enzyme/substrate, antibody/antigen
Conformation is a consequence of a specific linear sequence of amino acids
polypeptide chain coils and folds spontaneously, mostly due to hydrophobic interactions
stabilized by chemical bonds and weak interactions between neighboring regions of the folded protein
The primary structure of a protein
4 levels of protein structure
Primary
Secondary
Tertiary
Quaternary
Primary structure
sequence of amino acids
determined by genes
slight change can have large effect on function
e.g. sickle-cell hemoglobin
sequence can be determined in the lab
A single amino acid substitution in a protein causes sickle-cell disease
Sickled cells
The secondary structure of a protein
Secondary structure = regular, repeated coiling and folding
of a protein’s polypeptide backbone
Contributes to final conformation
Stabilized by H-bonds
Two major types of secondary structures
Alpha helix
helical coil stabilized by H-bonds
found in fibrous proteins e.g. keratin and collagen
and some gobular proteins e.g. lysozyme
Beta pleated sheet
a sheet of antiparallel chains folded into
accordion pleats
held together by H-bonds
found in gobular proteins e.g. lysozyme
also in fibrous proteins e.g. fibroin (silk)
Spider silk: a structural protein
Examples of interactions contributing to the tertiary structure of a protein
(Weak interaction)
Tertiary structure = 3-dimensional shape
due to bonding between and among side chains
and to interactions between side chains and the
aqueous environment
(Weak interaction)
Strong interaction (covalent bond)
(Weak interaction)
The quaternary structure of proteins
Quaternary structure = structure that results from the interactions between several polypeptide chains
Supercoiled structure gives it
strength
Review: the four levels of protein structure
Figure 5.22 Denaturation and renaturation of a protein
Proteins can be denatured by:
transfer to an organic solvent, alters hydrophobic interactions
chemical agents that disrupt hydrogen bonds, ionic bonds, disulfide bridges
excessive heat--disrupts weak interactions
Figure 5.23 A chaperonin in action
Figure 5.24 X-ray crystallography
Figure 5.25 DNA RNA  protein: a diagrammatic overview of information flow in a cell
Nucleic Acids store and transmit hereditary information
Protein conformation is determined by primary structure
Primary structure is determined by genes
Genes are hereditary units that consist of DNA, a type of
nucleic acid
Two types of nucleic acids
DNA (Deoxyribonucleic Acid)
contains coded information that programs all cell activity
contains directions for its own replication
copied and passed from one generation to the next
found primarily in the nucleus of eukaryotic cells
makes up genes that contain instructions for protein
synthesis via mRNA
RNA (Ribonucleic Acid)
functions in the actual synthesis of proteins coded for
by DNA
Sites of protein synthesis are on ribosomes
mRNA carries encoded genetic messages from
nucleus to the cytoplams
The flow of genetic info is from DNA to RNA to protein
Figure 5.26 The components of nucleic acids
Nucleic Acid = polymer of nucleotides linked together by condensation reactions
Nucleotide = building block of nucleic acid
made of: a 5 carbon sugar, phosphate group, nitrogenous base
Nucleic acid polymers (polynucleotides) are nucleotides linked together by phosphodiester linkages
Each gene contains a unique sequence of nitrogenous bases which codes for a unique sequence of amino acids in a protein
Figure 5.27 The DNA double helix and its replication
Table 5.2 Polypeptide Sequence as Evidence for Evolutionary Relationships