Download macromolecules

145 Zoo
“Principles of Biology”
Lectures
٢٠٠٩
Prepared by
Dr. Nadia Al-Eisa
Dr. Ola Alhabit
Dr. Tahany Ayaad
Dr. Promy Virk
Dr. Intisar Alsuhaibani
١
Text Book
Biology
Seventh Edition
by
Campbell & Reece
٢
CHAPTER 5
THE STRUCTURE AND FUNCTION
OF MACROMOLECULES
Section A: Polymer principles
1. Most macromolecules are polymers
•
Cells join smaller organic molecules together to form larger
molecules.
•
These larger molecules, macromolecules, may be
composed of thousands of atoms.
•
The four major classes of macromolecules are:
carbohydrates, lipids, proteins, and nucleic acids.
٣
1. Most macromolecules are
polymers
• The macromolecules of carbohydrates, proteins,
and nucleic acids form chainlike molecules called
polymers.
– Polymers consist of many similar or identical building
blocks linked by covalent bonds.
• The repeated units are small molecules called
monomers.
٤
• The chemical mechanisms used to make and
break polymers are similar for all classes of
macromolecules.
• Monomers are connected by covalent bonds via a
dehydration reaction:
– One monomer provides
a hydroxyl group and
the other provides a
hydrogen atom to
form water.
– This process requires
energy and is aided
by enzymes.
Fig. 5.2a
٥
• The covalent bonds connecting monomers in a
polymer are disassembled by hydrolysis
(hydration) reaction.
– In hydrolysis as the covalent bond is broken a
hydrogen atom and hydroxyl group from a split water
molecule attaches where the covalent bond used to be.
– Hydrolysis reactions
dominate the
digestive process,
guided by specific
enzymes.
Fig. 5.2b
٦
(Carbohydrates, Lipids, Proteins and nucleic acids)
Mono-mer
Di-mer
Poly-mer
‫أﺣﺎدى‬
‫ﺛﻨﺎﺋﻰ‬
‫ﻋﺪﯾﺪ‬
٧
Carbohydrates - Fuel and Building Material
• Carbohydrates include both sugars and polymers.
• Monosaccharides or simple sugars are the
simplest carbohydrates.
• Disaccharides, double sugars, consist of two
monosaccharides joined by a dehydration reaction.
• Polysaccharides are polymers of many
monosaccharides.
٨
1. Sugars, the smallest carbohydrates serve
as a source of fuel and carbon sources
• Monosaccharides generally have molecular formulas
that are some multiple of CH2O.
– For example, glucose has the formula C6H12O6.
– Most names for sugars end in -ose.
• Monosaccharides have:
1. a carbonyl group (C=O) and
2. multiple hydroxyl groups (-OH).
٩
Monosaccharides are classified as following :
A- Based on the location of C=O
Aldoses: are the monosaccharides of carbonyle group (C=O)
at the end of C chain (e.g. Glucose).
Ketoses: are the monosaccharides of C=O carbonyle
group within the C chain (e.g. Fructose).
– Glucose (aldose) and fructose (a ketose), are structural
isomers.
B- Based on the number of C in the skeleton
Triose (3
3C): e.g. Glyceraldehyde.
Pentose (5
5C): e.g. Ribose.
Hexose (6
6C): e.g. Glucose, Fructose and Galactose.
Fig 5.3
١٠
Fig 5.3
١١
2- Disaccharides
Consisted of 2 monosaccharide molecules
during a dehydration reaction ‫ﺗﻔﺎﻋﻞ ﻧﺰع اﻟﻤﺎء‬.
‫ﺗﻔﺎﻋﻞ‬.
Sucrose (table sugar):
sugar): consists of Glucose + Fructose.
Fructose.
١٢
FIG. 5.5b
3. Polysaccharides, the polymers of sugars, have
storage and structural roles
• Polysaccharides are polymers of hundreds to thousands
of monosaccharides joined by glycosidic linkages.
• One function of polysaccharides is as an energy storage
macromolecule that is hydrolyzed as needed.
• Other polysaccharides serve as building materials for the
cell or whole organism.
• They are two types:
١٣
A. Storage Polysaccharides
1. Starch (in plants) is a storage polysaccharide
consisted of thousands of  glucose monomers.
–
–
–
Most monomers are joined by 1-4 linkages between the
glucose molecules.
Plants store starch within plastids, including chloroplasts.
Animals, including human, have enzymes that can
hydrolyze plant starch making glucose available for
metabolism.
١٤
Fig. 5.7b
Fig. 5.6
• There are two ring forms of glucose differ in
whether the hydroxyl group attached to the
number 1 carbon is fixed below (alpha glucose)
or above (beta glucose) the ring plane.
Fig. 5.7a
١٥
2. Glycogen (in animals):
• Animals store glucose in a polysaccharide
called as glycogen in their liver and muscles.
– Humans and other vertebrates store glycogen but
only have about a one day supply.
– Thus, it gives glucose when hydrolysed.
Fig. 5.6b
١٦
B. Structural Polysaccharides
• Structural polysaccharides form strong building
materials.
1. Cellulose (in plants):
• It is the building materials of the cell wall in plants.
• It is a polymer of thousands of β glucose molecules.
Fig. 5.7c
١٧
– Cellulose molecules are attached to each other by
hydrogen bonds forming "Microfibrils" (fig. 5.8).
– Human can not digest cellulose, as few organisms
possess enzymes that can digest  linkages of cellulose:
 Some bacteria and other microbes can digest
cellulose (e.g. that live in the cow's stomach).
١٨
Fig. 5.8
Cellulose microfibrills in plant cell wall
١٩
2. Chitin (in insects):
• It is used in the exoskeletons of arthropods
(including insects, spiders, and crustaceans).
• Chitin is is consisted of thousands of glucose molecules
with a Nitrogen atom in one end.
• It is used to manufacture the surgical threads.
Fig. 5.9
٢٠
Carbohydrates
No. of sugar molecules
Monosaccharides
Glucose & Fructose
No. of C atoms
Disaccharides
Polysaccharides
Maltose & Sucrose
Location of
C=O
Triose (3C)
Pentose (5
(5C) Hexose (6
(6C)
Glyceraldehyde
Ribose
Glucose
Aldose
C=O on top
Storage
Starch (in plants)
&
Glycogen (in animals)
Structural
Cellulose (in plants)
&
Chitin (in insects)
Ketose
C=O in chain
٢١
CHAPTER 5
THE STRUCTURE AND FUNCTION
OF MACROMOLECULES
5.3 Lipids are a diverse group of
hydrophobic molecules
٢٢
Lipids
• Lipids are macromolecules that they do not
have polymers.
• They all have little or no affinity for water.
• Lipids are different in form and function.
• They consist mostly of hydrocarbons
smaller than polymer macromolecules.
• The most important lipid families: fats,
phospholipids and steroids.
٢٣
1-
Fats
• Fats are not polymers.
• They are large molecules assembled from smaller molecules
by dehydration reactions.
Structure of Fats
• A fat molecule consists of 3 fatty acid molecules (16 – 18 C
long) joind to glycerol by an ester linkage creating a
triacylglycerol.
Ester
link
Fig. 5.11a
Dehydration
Synthesis
Fig. 5.11b
٢٤
•
Fatty acids can be classified according to
the location of double bonds:
A. Saturated fatty acids:
•
•
There are no C - C double bonds.
Every C is linked with H (it is saturated with
H).
– Most animal
saturated.
fats
are
– Saturated fat are solid at room
temperature.
– A diet rich in saturated fats may
cause
cardiovascular
disease
(atherosclerosis).
a. Saturated fats
Fig. 5.12a
٢٥
B. Unsaturated fatty acids:
– There are one or more C-C double bonds.
– These double bonds are formed by the removal
of H atoms from the carbon skeleton.
• Plant and fish fats, known as oils, are liquid are
room temperature.
•
Hydrogenated vegetable oils =
+H
Unsaturated fats
saturated fats (to prevent lipid liquidity)
Fig. 5.12b
b. Unsaturated fats
٢٦
2-
Phospholipids
Are major components of cell membranes
• Phospholipids have 2 fatty acids attached to glycerol and a
phosphate group at the third position.
– The phosphate group carries a
negative charge.
–
Additional smaller groups may
be attached to the phosphate
group.
• phospholipids show
ambivalent behavior toward
water:
– The fatty acid tails are
hydrophobic, but the
phosphate group and its
attachments form a
hydrophilic head.
٢٧
Fig. 5.13
• Phospholipids are major components of cell membranes:
They are arranged in a bilayer (double layer) (Fig. 5.14).
The hydrophilic heads of the molecules are on the outside of
the bilayer, in contact with the aqueous solutions on both sides
of the cell.
The hydrophobic tails point toward the interior of the
membrane, away from the water.
The phospholipid bilayer forms a barrier between the cell and
its external environment.
water
Hydrophilic
head
Hydrophobic
tails
Hydrophilic
head
water
Fig. 5.14
٢٨
Steroids
• Steroids are lipids with a carbon skeleton
consisting of 4 fused carbon rings.
Different steroids are created by varying functional
groups attached to the rings.
 Steroids include:
 Cholesterol, a component in animal cell membranes.
 sex hormones
Fig. 5.15
٢٩
Lipids
Fats
Phospholipids
Bilayer of cell
membrane
Saturated
Animal Fats
Unsaturated
Steroids
Cholesterol
&
Sex Hormones
Vegetable Fats
Hydrogenation
٣٠
CHAPTER 5
THE STRUCTURE AND FUNCTION
OF MACROMOLECULES
5.4 Proteins have many structures,
resulting in a wide range of
functions
• Proteins
account for more than 50% of the dry
weight of most cells.
• Humans have tens of thousands of different proteins,
each with a specific structure and function.
• The most important type of protein may be enzymes.
• Each type of protein has a complex three-dimensional
٣١
shape or conformation.
• protein is a polymer (polypeptide) constructed from 20
monomers (amino acids).
• A polypeptide is a polymer of many amino acids linked
by peptide bonds.
• A protein consists of one or more polypeptides folded
and coiled into a specific conformation.
Fig. 5.19
٣٢
Amino acids
• Amino acids are organic molecules consisting
of 4 components attached to a central carbon (a
carbon):
• These components include:
•
•
•
•
a hydrogen atom
a carboxyl group (–COOH)
an amino group (–NH2)
a variable R group (or side chain).
Hydrogen
atom
Carboxyl
group
Amino
group
R
Fig. The Structure of amino acid molecule
Side chain
٣٣
• Differences in R groups produce the 20 different
amino acids.
• The amino acids are grouped according to the
properties of their side chains as follows:
1. Nonpolar: the amino acids that have hydrophobic R
groups.
٣٤
Fig. 5.17
2. Polar: the amino acids that have hydrophilic R
groups.
Fig. 5.17
3. Charged: the amino acids with functional groups that
are charged (ionized) at cellular pH (7.2).
–
Fig. 5.17
Some R groups are bases, others are acids.
٣٥
Peptide bonds:
• Amino acids are joined together when a dehydration
reaction removes:
a hydrogen
a hydroxyl group (–OH)
from
the carboxyl (–COOH)
+
from
the amino group (–NH2)
of
of
one amino acid
results
the next amino acid
a peptide bond (covalent bond)
٣٦
Fig. 5.18
• Repeating the dehydration process over and over creates
a long polypeptide chain.
– Each amino acid has two ends:
– At one end there is a free amino group the (the N-terminus)
– at the other there is a free carboxyl group the (the C-terminus).
• The repeated sequence (N-C-C) is the polypeptide
backbone.
• Various R groups are
attached to the backbone.
• Polypeptides range in size
from a few monomers to
thousands.
٣٧
Amino acids
Non-polar
Polar
Charged
(Hydrophobic R group)
(Hydrophilic R group)
(Ionized functional group)
Amino
acids
Peptide bond
Polypeptide
Conformation
Protein
Dehydration
٣٨