Transcript Proteins

The Structure and Function
of Macromolecules
Part 2 Chapter 5
Emergent properties of
macromolecules from smaller subunits
• Within cells, small organic molecules are
joined together to form larger molecules.
• These large macromolecules may consist
of thousands of covalently bonded atoms
and weigh more than 100,000 daltons
In this chapter we’ll study the structure and
function of these macromolecules and
their place in living organisms.
Four major classes of
macromolecules
•
•
•
•
Carbohydrates
Lipids
Proteins
Nucleic acids
Most macromolecules are
polymers, built from monomers
• Carbohydrates, proteins, and nucleic acids are
made of polymers, repeating subunits of smaller
molecules called monomers.
• Lipids are not polymers but they are
macromolecules
• Macromolecules - very large
• Polymers - many (repeating) parts
– Monomer - one unit
Carbohydrate polymers
Monomer of
glucose
Polymers of glucose
Synthesis and digestion
•
Condensation/Dehydration reaction –
synthesis - to build
– Bonds monomers together
– Release water molecule
•
Hydrolysis/Digestion – breaks down
– hydrolysis (water breaking)
– Adds water ions to the broken ends
Condensation or dehydration
reactions
• Reaction that builds polymers from
monomers by removing one molecule of
water.
• The cell uses energy to build polymers
with the help of enzymes
Fig. 5-2a
HO
1
2
3
H
Short polymer
HO
Unlinked monomer
Dehydration removes a water
molecule, forming a new bond
HO
1
2
H
3
H2O
4
H
Longer polymer
(a) Dehydration reaction in the synthesis of a polymer
Hydrolysis/Digestion
• Reverse reaction of Condensation
• Enzymes help to speed up the reaction
• Polymers are split by addition of water
molecule
• OH (Hydroxyl) is added to one monomer
and a Hydrogen to the adjacent monomer.
• Ex. In digestion large polymers are broken
down and monomers are used to build
new polymers needed by the body.
Fig. 5-2b
HO
1
2
3
4
Hydrolysis adds a water
molecule, breaking a bond
HO
1
2
3
(b) Hydrolysis of a polymer
H
H
H2O
HO
H
Carbohydrates……Sugars
Monosaccharides have the molecular formula
in multiples of CH2O
• Glucose (C6H12O6) is the most common
monosaccharide
Monosaccharides are classified by
1. location of the carbonyl group
–
–
Aldose –carbonyl is on the last carbon in the chain
Ketose Carbonyl is located between two carbons
2. Number of carbons in the carbon skeleton
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 5-3
Trioses (C3H6O3)
Pentoses (C5H10O5)
Hexoses (C6H12O6)
Glyceraldehyde
Ribose
Glucose
Galactose
Dihydroxyacetone
Ribulose
Fructose
Examples of Disaccharides
Monosaccharide
units
Disaccharide
Sources
Maltose
Germinating grains
Used in brewing
beer
Milk, yogurt, ice
cream
glucose + glucose
Sugar cane, sugar
beets
glucose + fructose
Lactose
Sucrose
glucose + galactose
Polysaccharides
• Made of many monosaccharides joined by
glycosidic linkages
• The structure and function of a
polysaccharide is determined by the
monomers and the position of the
glycosidic linkage
Three important polysaccharides
made of repeating units of glucose
• Complex sugars - many sugar units
• Starch
– Glucose chain molecules
– Energy storage in plants
• Glycogen
– Glucose chain molecule
– Energy storage in animals
• Cellulose
– Glucose chain molecule
– Structural molecule in plant cell walls
Fig. 5-10
Chitin hard, insoluble... and yet somehow flexible
(a) The structure
of the chitin
monomer.
(b) Chitin forms the
exoskeleton of
arthropods.
(c) Chitin is used to make
a strong and flexible
surgical thread.
Chitin is polysaccharide Nacetylglucosamine (a natural derivative of glucose).
Carbohydrate structural Isomers
molecular formula C6H12O6
Lipids
• Not polymers made of Glycerol molecule
and 3 fatty acids called a triglyceride
• Hydrophobic - Water fearing
• Fats and steroids
• Fats functions
– Store twice as much energy as carbs
– Protection, Cushion and insulate internal
organs
– Fats are stored in adipose cells
– Examples include waxes, oils, fats and
steroids
Fig. 3.14
Saturated versus Unsaturated fats
• Saturated fats
– No double bonds between carbons
– All possible Hydrogens attached to carbons
– Solid at room temperature commonly
produced by animals
– Examples lard, butter, bacon grease
– Linked to cardiovascular disease
Unsaturated Fats
•
•
•
•
•
Have carbon=carbon double bonds
In place of attached Hydrogens
Liquid at room temperature
Commonly produced by plants
Examples are vegetable, corn and olive
oils
Phospholipids
• Two regions with opposite properties
• Forms plasma membrane
• Phosphate ‘head’ is polar
– Hydrophillic water loving
– Phosphate group faces out
– Towards Watery environment inside and
outside cell
• Fatty acid tails are non-polar
– Hydrophobic - water fearing
– Tails face each other
– Forms a barrier
Fig. 5-14
Hydrophilic
head
Hydrophobic
tail
WATER
WATER
Steroids
• Lipids because they are hydrophobic
• Carbon chains form 4 fused rings
• Cholesterol
– Component of cell membranes
– Forms other steroids from it
– Make into sex hormones
• Estrogen
• Testosterone
Fig. 3.15
Anabolic steroids
•
•
•
•
Mimic testosterone
First used for anemia / muscle disease
Abused by athletes
Misuse can cause
– Facial bloating/acne
– Violent mood swings
– Liver damage
– Increase cholesterol levels
– Reduce sex drive and fertility
Proteins have many structures, resulting
in a wide range of functions
• Proteins are polymers made of amino acid
monomers
• Amino acid general structure- central
carbon is bonded to a a carboxyl group,
amine group, a Hydrogen and an R group
which varies.
• Peptide bonds link amino acids by
dehydration synthesis
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 5-UN1
General structure of an
amino acid
Amino
group
carbon
Carboxyl
group
Proteins
• Amino acids linked by peptide bonds
• The function of a protein depends on the
order and number of amino acids.
Polypeptide (protein) formation
Primary structure
– Unique sequence of amino acids
– There are 20 different amino acids
– Change in order can cause disease
• Sickle cell anemia
• One amino acid changed
Fig. 5-21a
Primary Structure
1
+H
5
3N
Amino end
10
Amino acid
subunits
15
20
25
Secondary Structure
• Secondary structure, found in most
proteins refers to one of two threedimensional shapes as a result of
Hydrogen bonding
• Alpha helix is a coiled shape
• Beta pleated sheet is an accordion shape
Fig. 5-21c
Secondary Structure
pleated sheet
Examples of
amino acid
subunits
helix
Tertiary Structure
• Tertiary structure results in a complex globular
shape due to interactions between R groups,
• Interactions include hydrogen bonds, ionic bonds,
hydrophobic interactions, and van der Waals
interactions
• Strong covalent bonds called disulfide bridges
may reinforce the protein’s structure
Animation: Tertiary Protein Structure
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 5-21e
Tertiary Structure
Quaternary Structure
Quaternary Structure
• Quaternary structure
– Interaction between two or more
polypeptide chains linked together to
form one large protein.
– Example: hemoglobin is a globular
protein with quaternary structure
composed of four chains
– Single amino acid substitution causes
sickle cell anemia
Fig. 5-21g
Polypeptide
chain
Chains
Iron
Heme
Chains
Hemoglobin
Collagen
Fig. 3.21
Fig. 5-22c
10 µm
Normal red blood
cells are full of
individual
hemoglobin
molecules, each
carrying oxygen.
10 µm
Fibers of abnormal
hemoglobin deform
red blood cell into
sickle shape.
How is structure determined?
• Order of amino acids specified by a gene recipe for a polypeptide
• Proteins include
– Structural
– Storage
– Contractile
– Transport
– Defensive
– Signal proteins
– ENZYMES!
ADD
Chaperonins
• Chaperonins are protein molecules that
assist in the proper folding of proteins
within cells.
• It provides protection against other
particles in the cytoplasm while the protein
folds.
ADD
Denaturation of Proteins
• The function of a protein is determined by
the sequence and spontaneous folding of
the polypeptide chain.
• Certain physical and chemical conditions
– pH, salt concentration, temperature
• Denaturation occurs when a protein
unfolds, loses its shape and ability to
function properly.
• Can you think of a way we denature
proteins?
• The white (albumen)
turns opaque during
cooking because
denatured proteins
solidify.
• This is why high
fevers can be fatal
• Proteins in the blood
can become
denatured from high
body temperatures
Table 5-1
Fig. 5-21d
Abdominal glands of the
spider secrete silk fibers
made of a structural protein
containing pleated sheets.
The radiating strands, made
of dry silk fibers, maintain
the shape of the web.
The spiral strands (capture
strands) are elastic, stretching
in response to wind, rain,
and the touch of insects.
Nucleic acids
•
•
•
•
DeoxyriboNucleic Acid - DNA
DNA is a recipe book for proteins
Genes direct the order of amino acids
Two types of nucleic acids
– DNA
– RNA - RiboNucleic Acid
• Chemical code
– Nucleic acid to protein language
– RNA helps with this process
Fig. 5-26-2
DNA
1 Synthesis of
mRNA in the
nucleus
mRNA
NUCLEUS
CYTOPLASM
mRNA
2 Movement of
mRNA into cytoplasm
via nuclear pore
Nucleic Acids: DNA and RNA
• DNA and RNA are polynucleotides made
up of monomers called nucleotides
• Each Nucleotide has three parts:
– Nitrogenous base (adenine, thymine, guanine,
cytosine and uracil (RNA only)
– Pentose - five carbon sugar, deoxyribose in
DNA and ribose in RNA
– Phosphate group
Fig. 5-27ab
5' end
5'C
3'C
Nucleoside
Nitrogenous
base
5'C
Phosphate
group
5'C
3'C
(b) Nucleotide
3' end
(a) Polynucleotide, or nucleic acid
3'C
Sugar
(pentose)
Nitrogenous bases
• Pyrimidines-six membered ring of carbon
and nitrogen
– Cytosine C (DNA &RNA)
– Thymine T (DNA)
– Uracil U (RNA)
• Purines-six membered ring fused to a five
membered ring of carbon and nitrogen
– Adenine A (DNA & RNA)
– Guanine G (DNA & RNA)
Fig. 3.26
Sugar –phosphate backbone
The backbone
• Adjacent nucleotides
are connected by
phosphodiester
linkages between the
OH group on the
sugar and phosphate
group of the next
nucleotide
Double helix strands run anti-parallell
The Roles of nucleic acids DNA
RNA
• DNA is the genetic material organisms
inherit from their parents
• Each chromosome contains one long DNA
molecule containing from several hundred
to more than a thousand genes.
• DNA programs all the cells activities by
producing proteins as needed
• DNA directs the synthesis of mRNA which
then directs the production of amino acids
Which of the following molecules
would contain a polar covalent
bond?
A. Cl2
B. NaCl
C. H2O
D. CH4
E. C6H12O6