Transcript amino acid

CHAPTER 3
The Molecules of
Cells
Life’s structural and functional diversity
results from a great variety of molecules
A relatively small number of structural
patterns underlies life’s molecular diversity
Organic Compounds
Always contain
carbon
Tend to be large &
complex
A carbon atom
forms four covalent
bonds (this allows
carbon to form many
different chemical
compounds)
Carbon skeletons
vary in many ways
Carbon skeletons vary in length.
Skeletons may be unbranched or branched.
Skeletons may have double bonds, which can
vary in location
Skeletons may be arranged in rings
Cells make a huge number of
large molecules from a small set
of small molecules
• Most of the large molecules in living things
are macromolecules called polymers
– Polymers are long chains of smaller molecular
units called monomers (building blocks)
– A huge number of different polymers can be
made from a small number of monomers
– SIZE: monomer< polymer< macromolecule
Molecules of Life
• Put C, H, O, N together in different
ways to build living organisms
• What are bodies made of?
– carbohydrates
• sugars & starches
– proteins
– lipids
– nucleic acids
• DNA, RNA
Why do we eat?
• We eat to take in more of these chemicals
– Food for building materials
• to make more of us (cells)
• for growth
• for repair
– Food to make energy
• calories
• to make ATP
ATP
How do we make
these molecules?
We build them!
Building large molecules of
life
• Chain together smaller molecules
– building block molecules = monomers
• Big molecules built from little molecules
– polymers
Building large organic
molecules
• Small molecules = building blocks
• Bond them together = polymers
Building important
polymers
Carbohydrates = built from sugars
sugar – sugar – sugar – sugar – sugar – sugar
Proteins = built from amino acids
amino amino amino amino amino amino
acid – acid – acid – acid – acid – acid
Nucleic acids (DNA) = built from nucleotides
nucleotide – nucleotide – nucleotide – nucleotide
How to build large
molecules
• Dehydration Synthesis
– building bigger molecules
from smaller molecules
– building cells & bodies
• repair
• growth
• reproduction
+
ATP
Making and Breaking of
POLYMERS
• Cells link monomers to form polymers by
dehydration synthesis (building up)
Short polymer
Unlinked monomer
Removal
of
water
molecule
Longer polymer
Example of synthesis
amino acids
protein
 Proteins are synthesized by bonding amino acids
amino acids = building block
protein = polymer
Making and Breaking of
POLYMERS
• Polymers are broken down to monomers by
the reverse process, hydrolysis (hydro ~ add
water; lysis ~ to split)
Addition of
water molecule
How to take large
molecules apart
• Hydrolysis ~Digestion
– taking big molecules apart
– getting raw materials
• for synthesis & growth
– making energy (ATP)
• for synthesis, growth & everyday functions
+
ATP
Example of digestion
ATP
ATP
ATP
ATP
ATP
starch
ATP
glucose
ATP
• Starch is digested to glucose
1. CARBOHYDRATES
• They range from small sugars to large
polysaccharides
•
•
•
•
Poly~ many
Sacchar ~ sugar
Mono ~ one
Di ~ two
Monosaccharides are the
simplest carbohydrates
• Monosaccharides
are single-unit
sugars (building
blocks)
• These molecules
typically have a
formula that is a
multiple of CH2O
• Monosaccharides
are the fuels for
cellular work
Sugars = building blocks
• Names for sugars usually end in -ose
– glucose
– fructose
– sucrose
– maltose
CH2OH
H
O
H
OH
H
H
OH
HO
H
OH
glucose
C6H12O6
sucrose
fructose
maltose
Cells link single sugars to
form disaccharides
• Monosaccharides can join to form
disaccharides, such as sucrose (table
sugar) and maltose (brewing sugar)
Polysaccharides are long
chains of sugar units
• polymers of hundreds or
thousands of
monosaccharides linked by
dehydration synthesis
• Function as
– Energy storage
• Starch (plants)
• Glycogen (animals)
– Structure
• Cellulose (plants cell
walls) (fiber in diet)
• Chitin ( insects)
Digesting starch vs.
cellulose
starch
easy to
digest
cellulose
hard to
digest
enzyme
enzyme
Cellulose
• Cell walls in plants
– herbivores can digest cellulose well
– most carnivores cannot digest cellulose
• that’s why they
eat meat
to get their energy
& nutrients
• cellulose = roughage
– stays undigested
– keeps material
moving in your
intestines
Helpful bacteria
• How can cows digest cellulose so well?
– BACTERIA live in their stomachs & help digest
cellulose-rich (grass) meals
Eeeew…
Chewing
cud?
Lipids
• composed largely of
carbon and
hydrogen
– They are not true
polymers
– They are grouped
together
because they do not
mix
with water
(Nonpolar)
Lipids
• Examples
– fats
– oils
– waxes
– hormones
• sex hormones
– testosterone (male)
– estrogen (female)
2003-2004
Lipids
• Function:
– energy storage
• very concentrated
• twice the energy as carbohydrates!
– cell membrane
– cushions organs
– insulates body
• think whale blubber!
2003-2004
Lipids include fats,
• Fats are lipids whose main function is long term energy storage
• Other functions:
– Insulation in higher vertebrates
– “shock absorber” for internal organs
• A triglyceride molecule consists of one glycerol molecule
linked to three fatty acids
Fatty acid
Fatty acid
Saturated & Unsaturated fats
• fatty acids of
unsaturated fats (plant
oils) contain double
bonds
– These prevent them from
solidifying at room
temperature
• Saturated fats (lard)
lack double bonds
– They are solid at room
temperature
Saturated vs. unsaturated
saturated
unsaturated
2003-2004
Phospholipids, waxes, and
steroids are lipids
• Phospholipids are a
major component of
cell membranes
– heads are on the
outside touching water
• “like” water
– tails are on inside away
from water
• “scared” of water
– forms a barrier
between the cell
& the outside
Other lipids in biology
Waxes form
waterproof
coatings
Steroids
are often
hormones
Other lipids in biology
• Cholesterol (Steroid) (only in animal cells)
– good molecule in cell membranes
– make hormones from it
• including sex hormones
– but too much cholesterol in blood may
lead to heart disease
Connection: Anabolic steroids
• Anabolic steroids
are usually synthetic
variants of
testosterone
• Use of these
substances
can cause serious
health
problems
PROTEINS : Multipurpose molecules
• essential to the structures and
activities of life
• Make up 50% of dry weight of
cells
• Contain carbon, hydrogen, &
oxygen PLUS nitrogen and
sometimes sulfur
• Proteins are involved in
–
–
–
–
–
cellular structure
movement
defense
transport
Communication
• Monomers are called amino
acids
Proteins
Examples
– muscle
insulin
– skin, hair, fingernails, claws
• collagen, keratin
pepsin
– pepsin
• digestive enzyme
in stomach
– insulin
• hormone that controls blood sugar
levels
collagen (skin)
Proteins are made from just
20 kinds of amino acids
• Proteins are the most structurally and functionally
diverse of life’s molecules
– Their diversity is based on different arrangements of amino
acids
– R- variable group- which distinguishes each of the 20
different amino acids
Amino acids can be linked by
peptide bonds to form polymer
• Cells link amino acids together by
dehydration synthesis
• The bonds between amino acid monomers
are called peptide bonds
PEPTIDE
BOND
Dehydration
synthesis
Amino acid
Amino acid
Dipeptide
A protein’s specific shape
determines its function
• A protein consists of polypeptide chains
folded into a unique shape
– The shape determines the protein’s function
– A protein loses its specific function when its
polypeptides unravel
A protein’s specific shape
determines its function
• A protein can change in response to the physical and chemical
conditions
• Alterations in pH, salt concentration, temperature, or other
factors can unravel or denature a protein
• Some proteins can return to their functional shape after
denaturation -renature
NUCLEIC ACIDS : Information
molecules
• 1. DNA
(deoxyribonucleic
acid) contains the
instructions used to form
all of an organism’s
proteins.
•
2. RNA (ribonucleic
acid) forms a copy of
DNA for use in making
proteins.
• They ultimately control
the life of a cell
Nucleic Acids
• Function:
– genetic material
• stores information
– genes
– blueprint for building proteins
» DNA  RNA  proteins
DNA
• transfers information
– blueprint for new cells
– blueprint for next generation
proteins
NUCLEIC ACIDS
• The monomers of nucleic acids are
nucleotides
– Each nucleotide is composed of a sugar,
phosphate, and nitrogenous base
Nitrogenous
base (A)
Phosphate
group
Sugar
NUCLEIC ACIDS
• The sugar and
phosphate form the
backbone for the
nucleic acid
Nucleotide
Sugar-phosphate
backbone
Nucleotide chains
• Nucleic acids
sugar
N base
sugar
N base
phosphate
– nucleotides chained
into a polymer
• DNA
– double-sided
– double helix
– A, C, G, T
• RNA
– single-sided
– A, C, G, U
phosphate
strong bonds
sugar
N base
sugar
N base
phosphate
phosphate
RNA
DNA
• Double strand twists into a double
helix
– weak bonds between nitrogen bases join
the 2 strands
• A pairs with T
– A :: T
• C pairs with G
– C :: G
– the two strands can
separate when our
cells need to make
copies of it
– The sequence of the four kinds of
nitrogenous bases in DNA carries
genetic information
weak bonds
DNA
• Stretches of a DNA molecule called
genes program the amino acid
sequences of proteins
– DNA information is transcribed into RNA, a
single-stranded nucleic acid
– RNA is then translated into the primary
structure of proteins
1953 | 1962
Watson and Crick … and others…