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CHAPTER 3The 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
• Small molecules = building blocks
• Bond them together = polymers
Building large organic molecules
Building important polymers
sugar – sugar – sugar – sugar – sugar – sugar
nucleotide – nucleotide – nucleotide – nucleotide
Carbohydrates = built from sugars
Proteins = built from amino acids
Nucleic acids (DNA) = built from nucleotides
aminoacid
aminoacid–
aminoacid–
aminoacid–
aminoacid–
aminoacid–
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 monomerRemoval ofwater molecule
Longer polymer
Example of synthesis
amino acids protein
amino acids = building block
protein = polymer
Proteins are synthesized by bonding amino acids
Making and Breaking of POLYMERS
• Polymers are broken down to monomers by the reverse process, hydrolysis (hydro ~ add water; lysis ~ to split)
Addition ofwater 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
starch glucose
ATP
ATP
ATP
ATP
ATP
ATPATP
• 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
– glucose– fructose– sucrose– maltose OH
OH
H
H
HO
CH2OH
HH
H
OH
O
glucoseC6H12O6
sucrose
fructose
maltose
-ose
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
starcheasy todigest
starcheasy todigest
cellulosehard todigest
cellulosehard todigest
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…Chewingcud?
Lipids• composed largely of
carbon and hydrogen– They are not true
polymers– They are grouped
together because they do not mix with water (Nonpolar)
2003-2004
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!
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
2003-2004
Saturated vs. unsaturatedsaturated unsaturated
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 biologyWaxes 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
collagen (skin)
Proteins
insulin
Examples– muscle
– skin, hair, fingernails, claws • collagen, keratin
– pepsin• digestive enzyme
in stomach
– insulin• hormone that controls blood sugar
levels
pepsin
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
Dehydrationsynthesis
Amino acid Amino acid
PEPTIDEBOND
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
DNADNA
Nucleic Acids• Function:
– genetic material• stores information
– genes– blueprint for building proteins
» DNA RNA proteins
• transfers information– blueprint for new cells– blueprint for next generation
proteinsproteins
NUCLEIC ACIDS
• The monomers of nucleic acids are nucleotides – Each nucleotide is composed of a sugar,
phosphate, and nitrogenous base
Phosphategroup
Sugar
Nitrogenousbase (A)
NUCLEIC ACIDS
• The sugar and phosphate form the backbone for the nucleic acid
Nucleotide
Sugar-phosphatebackbone
Nucleotide chains• Nucleic acids
– nucleotides chained into a polymer
• DNA– double-sided– double helix– A, C, G, T
• RNA– single-sided– A, C, G, U
phosphate
sugar N base
phosphate
sugar N base
phosphate
sugar N base
phosphate
sugar N base
strong bonds
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
Watson and Crick … and others…1953 | 1962