Download Lecture 03 Ch2and3

Chapters 2 & 3
Biochemistry
&
The Molecules of Life
At the cellular level, are we
really what we eat?
What evidence do we have?
What do we still need to find out?
Carbohydrates, Lipids,
Proteins, and Nucleic Acids:
Larger Molecules from
Smaller Building Blocks
Macromolecules: DNA,
Carbohydrates,
Proteins
Biological Molecules
– There are four categories of large molecules in
cells:
• Carbohydrates
• Lipids
• Proteins
• Nucleic acids
Biological Molecules
– There are four categories of large molecules in
cells:
L-O-N-G
starch
molecules
• Carbohydrates
• Lipids
• Proteins
• Nucleic acids
short
sugar
molecules
short
Monosaccharides
– “mono” means “one”
– “monosaccharide” means “one sugar”
– Monosaccharides are simple sugars.
• Glucose is found in sports drinks.
• Fructose is found in fruit.
Monosaccharides
are the main fuel
that cells use to do
work.
sugar
molecules
Disaccharides
– “di” means “two”
– “disaccharide” means two sugars.
short
sugar
molecules
• It is constructed from two monosaccharides.
– The most common disaccharide
is sucrose, common table sugar.
• It consists of a glucose linked to a
fructose.
• The average American consumes
about 64 kg of sugar per year.
Polysaccharides
“poly” means “many”
“saccharide” means “sugar”
polysaccharide - means “many sugars”
L-O-N-G
starch
molecules
one sugar unit
– Complex
carbohydrates are
called
polysaccharides.
• They are long
chains of sugar
units.
Where are carbohydrates in a
In the cytosol in animals cell?
In the cell wall in plants
as glycogen
as cellulose
In amyloplasts in
plants as starch
In the cytosol of plants and animals
(organelle not shown)
as both simple and complex carbohydrates
Carbohydrate Review
• So carbohydrates are long or short
molecules that are made by joining
together different numbers of a small
subunit called a monosaccharide.
• Monosaccharide = one sugar
• Disaccharide = two sugars
• Polysaccharide = many sugars
• They are found in many cellular
structures and are a major energy
source for the cell.
So how are monosaccharides
joined together to make
polysaccharides?
– Polysaccharides are polymers.
• Polymers are made by stringing together many
smaller molecules called monomers.
• Enzymes in cells link monomers by dehydration
reactions.
(Enzyme)
Monomer - means “one unit”
(Enzyme)
Monomer - means “one unit”
Dimer - means “two units”
(Enzyme)
Monomer - means “one unit”
Dimer - means “two units”
Polymer - means “many units”
(Enzyme)
Monomer - means “one unit”
Dimer - means “two units”
Polymer - means “many units”
For carbohydrates, the “unit” is the monosaccharide!
(Enzyme)
– Organisms also have to break down
polymers.
• Enzymes in cells do this by a process called
hydrolysis.
(Enzyme)
Monomer - means “one unit”
Dimer - means “two units”
Polymer - means “many units”
(Enzyme)
Monomer - means “one unit”
Dimer - means “two units”
(Enzyme)
Monomer - means “one unit”
(Enzyme)
– Lactose is another type of disaccharide
found in milk.
• Some people lack the enzyme that hydrolyzes
lactose, and, therefore, have trouble digesting
lactose, a condition called lactose intolerance.
Dehydration and Hydrolysis
Chemical Reactions
are the exact opposites
H2O
Hydrolysis
+
Dehydration
polymer
monomers
Chemical Reactions
– Cells constantly rearrange molecules by
breaking and forming chemical bonds.
• These processes are called chemical reactions.
– Chemical reactions cannot create or destroy
matter,
• They only rearrange it.
Before we continue looking at
biological molecules let’s take
an even closer look at our
carbohydrates to review some
essential chemistry
Chemical Bonds, Molecules,
and Atoms
Here is a dehydration reaction joining
two monosaccharide molecules
to form one disaccharide molecule.
A chemical bond is formed between
the two monosaccharides keeping
these two molecules close together
to form the disaccharide.
Chemical Bonds, Molecules,
and Atoms
Abbreviated
structure
Molecules are two or
more atoms bonded
together.
Here you see the
atoms (letters) of a
glucose monosaccharide
molecule held together
by chemical bonds
(lines)
=
Check out:
http://www.chem4kids.com/files/atom_intro.html
Atoms
– Atoms are composed of subatomic
particles.
• A proton is positively charged.
• An electron is negatively charged.
• A neutron is electrically neutral.
Example:
a helium atom
Electron Arrangement and the
Chemical Properties of Atoms
– Electrons determine how an atom behaves
when it encounters other atoms.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
–Electrons orbit the nucleus of an atom in specific
electron shells.
•The number of electrons in the outermost shell
determines the chemical properties of an atom.
Chemical Bonds
– Chemical reactions enable atoms to give up or
acquire electrons in order to complete their outer
shells.
• These interactions usually result in atoms staying
close together.
• The atoms are held together by chemical bonds.
– Three main types of chemical bonds:
• Ionic bonds
• Covalent bonds
• Hydrogen bonds
Stronger bonds
Weaker bonds
Ionic Bonds
– When an atom loses or gains electrons,
it becomes electrically charged.
• Charged atoms are called ions.
• Ionic bonds are formed between oppositely
charged ions.
Covalent Bonds
– A covalent bond forms when two atoms
share one or more pairs of outer-shell
electrons.
What happens when the electrons in a
covalent bond are shared unequally?
– Water is a compound in which the
electrons in its covalent bonds are
shared unequally.
• Oxygen is greedy for electrons and keeps
their negative charge closer to itself.
• This causes it to be a polar molecule, one with
opposite charges on opposite ends.
+
-
Covalent
bonds where
electrons are
shared
unequally
Hydrogen Bonds
– The polarity of
water results in
weak electrical
attractions
between
neighboring water
molecules called
hydrogen bonds.
Covalent bond
with unequally
shared electrons
– Simple sugars and double sugars dissolve
readily in water.
• They are hydrophilic, or “water-loving.”
Slight negative
charge of oxygen in
water and sugar
molecules
are attracted to
Slight positive
charges of
hydrogen in water
and sugar
molecules.
Hydrogen bond!
Covalent bonds!
I Love
You!
Biological Molecules
– There are four categories of large molecules in
cells:
L-O-N-G Polymers
of
starch
molecules monosaccharides
• Carbohydrates
• Lipids
• Proteins
• Nucleic acids
short
sugar
molecules
held together
by covalent bonds
Monosaccharides
And
disaccharides
Biological Molecules
– There are four categories of large molecules in
cells:
–fats
• Carbohydrates
• Lipids
–steroids
• Proteins
• Nucleic acids
–Lipids are hydrophobic.
•They do not mix with water
Fats
Functions: energy storage, cushioning, insulation
Fats are formed by linking fatty acid molecule subunits
onto a glycerol molecule subunit by dehydration
reactions
– Dietary fat consists largely of the molecule
triglyceride.
Run
Away!
• Triglyceride is a combination of glycerol and
three fatty acids.
No charge! Cannot interact with water!
(hydrophobic)
– Unsaturated fats
• Have less than the maximum number of hydrogens
bonded to the carbons. (double and triple bonds)
– Saturated fats
• Have the maximum number of hydrogens bonded to
the carbons. (all single bonds)
Saturated Fatty Acids:
Too much of a good thing can be bad
– Most animal fats have a high proportion of
saturated fatty acids, which can be unhealthy.
• Example: butter
– Most plant oils tend to be low in saturated fatty
acids.
• Example: corn oil
WHY are too many saturated fats unhealthy?
– Not all fats are unhealthy.
• Some fats perform important functions in the
body and are essential to a healthy diet.
Special Lipid: Phospholipids
• Phospholipids form a two-layered
membrane, the phospholipid bilayer.
Negative charge interacts with water!
(hydrophilic)
No charge!
Cannot
interact with
water!
(hydrophobic)
Water!
Other Lipids: Steroids
– Steroids are very different from fats in structure
and function.
• The carbon skeleton is bent to form four fused rings.
– Cholesterol is the “base steroid” from which your
body produces other steroids.
• Example: sex hormones
Cholesterol is a key component
of cellular membranes…
– Synthetic anabolic steroids are
controversial.
• They are variants of testosterone.
Where are lipids in a cell?
In the smooth ER where lipids are synthesized
In all membranes as phospholipids
Triglycerides (Ex: fat in animal cells, seed oils in
plant cells) stored in cytoplasm (not shown)
Biological Molecules
– There are four categories of large molecules in
cells:
Molecules of
–fats
• Carbohydrates
• Lipids
fatty acid and
glycerol
subunits held
together by
covalent
bonds
–steroids
• Proteins
–Lipids are hydrophobic.
• Nucleic acids
•They do not mix with water
•Phospholipids are special
•They allow water and lipids to interact.
Biological Molecules
– There are four categories of large molecules in
cells:
• Carbohydrates
• Lipids
• Proteins
• Nucleic acids
Proteins
– A protein is a polymer constructed from
amino acid monomers.
– Proteins perform most of the tasks the
body needs to function.
Structural Proteins
Receptor Proteins
Storage Proteins
Enzymes
Contractile Proteins
Hormonal Proteins
Transport Proteins
Sensory Proteins
Defensive Proteins
Gene Regulatory
Proteins
Structure of an
Amino Acid
Structure of an
Amino Acid
Run
Away!
I Love
You!
The
Monomers:
Amino Acids
– All proteins are
constructed from
a common set of
20 kinds of
amino acids.
– Some fear water
(hydrophobic)
– Some love water
(hydrophilic)
Structure gives
Function!
Proteins as Polymers
– Cells link amino
acids together by
dehydration
reactions.
• The resulting
covalent bond
between them is
called a peptide
bond.
– Your body has tens of thousands of
different kinds of protein.
• The arrangement of amino acids makes each
one different.
Structure gives Function!!
Protein Shape
– Proteins have four levels of structure.
•
•
•
•
Primary
Secondary
Tertiary
Quaternary
1st level
2nd level
3rd level
4th level
– Primary structure
• The specific sequence of amino acids in a
protein
– A slight change in the primary structure of
a protein affects its ability to function.
• The substitution of one amino acid for another
in hemoglobin causes sickle-cell disease.
Protein
Shape
– Primary
structure
held together
by covalent
bonds
– Secondary
structure
held together
by hydrogen
bonds
A protein’s shape is sensitive to
the surrounding environment
– Unfavorable temperature and pH changes can cause a
protein to unravel and lose its shape.
– This happens by disrupting the hydrogen bonds that hold
together the shape of a protein.
– This is called denaturation.
– If the shape unfolds, the function is destroyed…
The Plasma Membrane:
A Fluid Mosaic of Lipids and
Proteins
– The membranes of cells are composed
mostly of:
• Lipids
• Proteins
Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings
– The lipids belong to a special category
called phospholipids.
– Phospholipids form a two-layered
membrane, the phospholipid bilayer.
– Most membranes have specific proteins
embedded in the phospholipid bilayer.
Membrane phospholipids and
proteins can drift about in the plane
of the membrane
– This behavior leads to the
description of a membrane as a
fluid mosaic:
• Molecules can move freely
within the membrane.
• A diversity of proteins exists
within the membrane.
Where are proteins in a cell?
Everywhere!! Proteins are enzymes, and structural, transport,
receptor, regulatory, contractile proteins, etc, and perform
most of the functions of a cell!
In the all membranes as integral membrane proteins
Biological Molecules
– There are four categories of large molecules in
cells:
• Carbohydrates
• Lipids
• Proteins
• Nucleic acids
Biological Molecules
– There are four categories of large molecules in
cells:
• Carbohydrates
DNA, deoxyribonucleic acid
• Lipids
• Proteins
• Nucleic acids
RNA, ribonucleic acid
Nucleic Acids
– Nucleic acids are information storage
molecules.
• They provide the directions for building
proteins.
Transcription
Translation
– Nucleic acids are polymers of nucleotides.
I Love
You!
Nucleic acids
are hydrophilic!
– Each DNA nucleotide has one of the following
bases:
– Nucleotide
monomers are
linked into long
chains.
• These chains are
called
polynucleotides, or
DNA strands.
• A sugar-phosphate
backbone joins them
together.
– Two strands of DNA
join together to form a
double helix.
– RNA, ribonucleic acid, is different from
DNA.
• Its sugar has an extra OH group.
• It has the base uracil (U) instead of thymine (T).
Where are nucleic acids in a cell?
DNA is in the nucleus, mitochondria, and chloroplasts
RNA is in the nucleus, mitochondria, chloroplasts,
cytosol, and ribosomes!