chapter 5 the structure and function of macromolecules · all made from 20 amino acids polypeptides...
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Chapter 5
The Structure and Function of Macromolecules
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macromolecules = smaller organic molecules that are joined together to make larger molecules
four major classes:proteinscarbohydrateslipidsnucleic acids
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Polymer principles
most macromolecules are polymerspolymers= many similar or identical building blocks linked together by covalent bonds
each unit repeated is a monomer
cells can make and break polymers by reactionscondensation/dehydration reaction = connect monomers together
requires energyaided by enzymes water is taken out
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Example of a condensation reaction
Example of a hydrolysis reaction
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Hydrolysis reaction = breaks the covalent bonds between the monomers of a polymer
water is used to break apart polymers
used greatly in the digestive system aided by enzymes
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Carbohydrates
Function fuel and building material
include sugars and polymersmonosaccharides, disaccharides, polysaccharides
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Monosaccharides = simple sugarsgeneral molecular formula = CH O
ex. glucose C H O
most sugars end in ose have a carbonyl group and many hydroxyl groups
if carbonyl gp is at end = aldoseif not = ketose
classified by number of carbons in backboneie. glucose = hexose
five carbons = pentosesthree carbons = trioses
can exist as enantiomers ie. glucose and galactose
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function of monosaccharidesa. fuel = glucose
b. for synthesis of other monomersie. amino acids
fatty acids
joined together by glycosidic linkage to form a disaccharide (dehydration reaction)
in aqueous solutions tend to form ring structures
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glucose galactose
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linear vs. ring structure of glucose
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Disaccharides
made from two monosaccharidesexamples
maltose (malt sugar) = 2 glucosessucrose (table sugar) = glucose and fructose
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Polysaccharides
= polymers of hundreds/thousands of monosaccharides (14 glycosidic linkages)
store energy broken down to release energyare building materials for cell/organism
starch= storage polysaccharidestored in plants in plastids
glycogen = stored polysaccharide of glucose in liver and muscles (1 day supply)
main monomer in polysaccharides is glucose
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cellulose =polysaccharide in plant cell wallinsoluble in humans no enzymes to break
down beta linkageshelps to stimulate mucus production in
digestive tract
cellulase digests cellulose in some organisms
chitin=polysaccharide used in exoskeletons of arthropods and cell walls of fungi
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cellulose
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use of chitin in exoskeletons of insects and suture thread
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Lipids
do not have polymersdo not like water; have non polar covalent
bondsare large molecules
Fat = made of glycerol and fatty acidsglycerol = 3C skeleton with OH group
attached to each Cfatty acids = COOH gp. attached to long C
skeleton
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ex. triacylglycerol = 3 fatty acids + glycerol joined by an ester linkage
fatty acids can be same or differentcan have double bonds in different places
Saturated fatty acid = no double bonds; maximum # of hydrogens attached
are straight chains
unsaturated fatty acid=has double bonds due to hydrogens being removed
are kinked chains where double bonds located
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Saturated fatsfound in animal fatssolid at rm. temp.can contribute to heart disease
Unsaturated fatsare plant, fish fatsaka = oilsliquid at rm. temp.can't pack tightly together due to kinks
function = energy storage = cushion organs = insulation
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Phospholipids
glycerol with two fatty acids and a phosphate gp.(neg. charge)has hydrophobic tail end (fatty acids)has hydrophilic head end (phosphate gp)
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if put in water tails point inward away from water to form a micellebilayer arrangement in cell membrane (major components)
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Steroids
= lipids with carbon skeleton (four fused carbon rings)can have different functional gps. added
cholesterol in cell membranesprecursor for all other steroidshigh levels lead to cardiovascular disease
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Proteinsfunctions=
structural support, storage, transport of substances, cell signaling, movement, defensemechanisms
structurally complex 3D shape
all made from 20 amino acids
polypeptides = polymers of proteinsprotein= one or more polypeptides folded and coiled into a specific conformation
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Amino acidfour components around a carbon
hydrogen atomcarboxyl groupamino groupR group (differences in these make the different amino acids
character of R group determine characteristics of the amino acid
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R groups can be:1. hydrophobic2. hydrophilic3. bases4. acids
amino acids are joined by a dehydration reactionto form peptide bonds
at one end of chain is a carboxyl group and the other end is a amino group
can be very long chains
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making a polypeptide
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Protein Function
depends on specific conformation
order of amino acids determines 3D conformation(emergent property)
relys on ability to recognize and bind to another molecule
when it binds it helps a chemical reaction
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Levels of protein structure
Primary structure= the sequence of the amino acids
determined by the inherited genetic information
Lysozyme (enzyme that attacks bacteria) made of polypeptide of 129 amino acids
hard to predict the 3D structure based on amino acid sequence alone
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Primary structure of a protein
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sickle cell anemia = abnormal hemoglobindevelops due to a single amino acid change from hemoglobin
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secondary structure = results from hydrogen bonds along the polypeptide backbone
two types:1. coils (an alpha helix)
right handed coil, R groups extend outward from backbone, hydrogen of NH of one amino acid is attracted to the oxygen of C=O of another
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2. folds (a beta pleated sheets)formed from two or more polypeptide chains that are extended and lying next to each otherstabilized by hydrogen bonds between NH gps on one chain and C=O on the other
ex. silk's structural properties are due to beta pleated sheets (lots of hydrogen bonds)
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spider's silk protein
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Tertiary structure determined by interactions among and between the R groups and the polypeptide backbone
include weak interactions:hydrogen bonds among polar and/or charged areasionic bonds between charged R groupshydrophobic interactions and van der Waals interactions among hydrophobic R groups
strong covalent bonds disulfide bridges that are between sulfhydryl groups (SH) of cysteine mononers = stabilize the structure
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Tertiary structure
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Quarternary Structure happens due to two or more polypeptide subunits coming together
Ex. collagen found in connective tissue (tendons, ligaments)fibrous protein of three polypeptides supercoiled like a rope
hemoglobin globular protein with two copies of two kinds of polypeptides
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Quarternary structure
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Review of protein structure
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Physical and chemical conditions can change the conformation of the protein
pH, salt concentration, temperature and other factors can denature (change the conformation of) the protein
break the hydrogen bonds, ionic bonds, and disulfide bridges that hold the shape together
some proteins can get back their shape, others can't
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Effect on protein
temperature increases molecular movements so breaks hydrogen bonds and hydrophobic interactions
pH changes pattern of ionization of carboxyl and amino groups in R groups; disrupts ionic attractions and repulsions
high conc. of polar substances disrupts hydrogen bonds
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proteins undergo intermediate changes before they reach quarternary structure
chaperonins=proteins that shield out bad influences while the protein structure is being made (form a "cage" until folded properly)
protein is vulnerable 1. following denaturation, hydrophobic gps
on inside are exposed to outside,so can bind and form aggregates that are
insoluble2. when a protein is just being made and has not folded correctly
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How chaperonins work
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Xray crystallography tool used to look at protein structure
form crystal then hit it with xrays
pattern of diffraction by the atoms can determine the location of the atoms and a computer then builds a structure
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photo 51 Xray diffraction of sodium salt of DNA by Rosalind Franklin
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Nucleic Acids
function: store and transmit hereditary information
two types:1. RNA ribonucleic acid
used in protein synthesissingle polynucleotide chain
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2. DNA deoxyribonucleic acidused for replication of DNA directs RNA synthesishas information for all cell activities, but proteins
are responsible for implementing the instructions for the DNA
double helix (Watson and Crick 1953)Adenine pairs with thymineCytosine pairs with guanineComplementary strands
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Crick and Watson
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Rosalind Franklin
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structure of nucleic acids
are polymers of monomers of nucleotidesnucleotide = nitrogen base, a pentose sugar and a phosphate group
Nitrogen bases = rings of carbon and nitrogentwo types:
1. purines: adenine and guaninehave a sixmembered ring joined to a
five membered ring2. pyrimidines: thymine, cytosine & uracil
have a single six membered ring
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Pentose sugar:Ribose in RNADeoxyribose in DNA
a pentose sugar + a nitrogen base = nucleoside
a pentose sugar + nitrogen base + phosphate = nucleotide
polynucleotides form by phosphodiester linkages(sugar of one nucleotide attached to phosphate of other nucleotide)
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each gene has a unique sequence of nitrogen bases and can be hundred or thousands of nucleotides long
DNA and proteins can be used as markers for evolution due to the heredity of it from parents to offspring
two species that are closely related based on fossil evidence should also be alike in having similar DNA and protein sequences
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