Cells
The cell function
Molecular components of cells
1. 
Carbohydrates
◦  Provide short term energy storage
◦  Provide energy to cells (sugars and starches)
◦  Make important cellular structures (cellulose; fibers of cotton and
linen, main constituent of wood)
2. 
Lipids
◦  Major ingredient of cell membrane (membrane forming role is
critical in the origin of life, spontaneously form membranes in water)
◦  Long term energy storage (known as fats)
3. 
Nucleic acids
◦  Storage and transfer of information
◦  DNA – the basic hereditary material on Earth, RNA (ribonucleid
acid) helps carry out instructions contained in DNA
4. 
Proteins
◦  Basic functioning of living organisms, huge array of functions
◦  Structural elements
◦  Enzymes: important to almost all biochemical reactions, including
copying genetic material, serving as catalysts
◦  Enzymes very important: facilitate replication of DNA and the reading
of the genetic code
Metabolism – chemistry of life
Start with the cell and the biochemical processes occurring inside.
! 
Metabolism = chemical processes occurring inside cells.
◦  catabolism (destructive) breaks down molecules to obtain energy
◦  anabolism (constructive) building/synthesising new cell material
"  biosynthesis
! 
The cell is a small factory that facilitates fast chemical reactions that
otherwise would occur too slow to be useful for life
Two basic requirements for metabolism:
1. 
A source of energy to fuel the metabolism
◦  break down molecules and build new ones
2. 
A source of raw materials
◦  Molecules that provide the cell with carbon and other basic
elements needed for life (20+ elements; vitamins; minerals)
Cells can build a wide variety of molecules from a limited set of building
materials
◦  variety of enzymes, each specialized in catalyzing a specific chemical
reaction.
The instructions for enzyme creations are encoded in the DNA, and have
been evolving for billions of years
The role of “ATP”
! 
Living cells use the molecule adenosine triphosphate (ATP) to store
and release energy for biochemical processes.
diphospate
! 
External source of energy is used just to produce ATP, and not for
producing a variety of molecules within the cell.
What is ATP good for?
Powers most of the energy-consuming activities of cells, such as:
!  Most anabolic reactions
◦  Synthesis of fats
◦  Synthesis of polysaccharides like starch, glycogen, cellulose
◦  Synthesis of nucleoside triphosphates for assembly into DNA and
RNA
◦  Joining transfer RNAs to amino acids for assembly into proteins
! 
Active transport of molecules and ions
! 
Nerve impulses
Cont.
! 
Maintenance of cell volume by osmosis
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Adding phosphate groups to proteins, e.g., to alter their activity in cell
signaling.
! 
Muscle contraction
! 
Wave motion of cilia and flagella
! 
Bioluminescence
ATP provides energy for every cellular reaction
! 
ATP releases energy and a by-product - adenosine diphosphate
(ADP), that can be transformed back into ATP.
! 
All life on Earth uses ATP for energy storage => life on Earth has a
common origin!
◦  There’s no reason there could be no other molecules to serve the same
role as ATP.
Metabolic classification of life
Suffix: Carbon sources
1.  Heterotroph (hetero=others, troph=to feed): eating preexisting organic
compounds. All animals, humans and many microscopic organisms
2. 
Autotroph (self-feeding): cells that get carbon directly from the
environments, e.g., CO2 from air or dissolved in water, like trees and
most plants.
Prefix: Energy sources to make ATP
1.  Photo: sunlight – photosynthesis (plants)
2. 
Chemo: organic compounds (eat food) – chemical reactions
3. 
Chemo: inorganic chemicals from the environment that do not contain
C – chemical reactions
! 
A chemoheterotroph gets its energy from
chemical reactions and its carbon from food
◦  Humans, animals, many microorganisms
! 
A photoheterotroph gets its energy from the
Sun and its carbon from food
◦  Rare, some prokaryotes (bacteria Chloroflexus,
lakes, rivers, aquatic environments high in salts)
! 
A photoaoutotroph gets its energy from the Sun
and its carbon from the environment
◦  Plants, algae, some microorgansims
! 
A chemoautotroph gets its energy from chemical
reactions and its carbon from the environment
◦  Archaea sulfolobus in volcanic springs get energy
from chemical reactions involving sulfur
compounds
◦  Found in environments where most organisms
could not survive – most likely to be found on
other worlds with harsher conditions for life!
Metabolism – catabolism
Gibbs energy: the energy associated with a chemical reaction that can be
used to do work.
◦  A negative Gibbs energy = reaction will release energy
◦  A positive Gibbs energy = reaction will require energy
Types:
!  Aerobic respiration
◦  Glucose (C6H12O6) + 6O2 => 6CO2 + 6 H2O
◦  ∆G=-2870 kJ
◦  most effective in producing ATP => organisms grow fast
! 
Methanogenesis (anaerobic respiration)
◦  4H2 + CO2 => CH4 + 2 H2O
◦  ∆G=-131 kJ
! 
Sulfate reduction (anaerobic respiration)
◦  4H2 + SO42- + H+ => HS- + 4 H2O
◦  ∆G= -152 kJ
! 
Fermentation
◦  Low yield
◦  Breakdown of a substance by bacteria
The importance of water
! 
Life needs a liquid medium that allows carbon and energy to to come
together.
◦  Life can use a variety of different carbon and energy sources. However,
no organism on Earth can survive without liquid water!
! 
On Earth water plays 3 roles for metabolism:
1.  Allows organic chemicals to float (dissolve) and be available for
reactions
2.  Transports chemicals to, within, and out of the cells
3. 
Water molecules are necessary for reactions that store and release
ATP energy
Good properties of water
! 
Water is a very good solvent
◦  Many different types of materials can be dissolved in water
◦  Important for transport
! 
Water can be moved through cell membrane through osmosis
! 
Water takes part in many chemical reactions
◦  Reactants need to be in contact
◦  Solutions are good mediums for chemical reactions
! 
Water can act as a lubricant, i.e., to reduce friction between moving
surfaces
◦  Joints, between internal organs
Good properties of water
! 
Thermal properties are well suited for life
◦  Water has a high specific heat, 4.18 J/(g ∘C)
◦  More energy needed to increase the temperature of water compared
to other solvents
◦  Thus water can absorb or release a large amount of energy while only
adjusting its own temperature by a small amount.
◦  The body contains lots of water
"  => helps the body to cope with environmental temperature variations and
maintain the body's temperature within a safe and comfortable range.
Good properties of water
! 
Polar covalent bond: electrons distributed unevenly around the molecule
resulting in positive and negative ‘sides’
◦  Cohesion: attracts to other water molecules (forming drops)
◦  Adhesion: can attract to other materials
◦  Surface tension: molecules pull towards each other creating as small
surface area as possible
◦  Capillary action: cohesion and adhesion helps liquid to flow in narrow
spaces without external forces (sometimes against) like gravity
Exam Friday 9/25
! 
All material up through today, 9/18.
! 
Study guides (sets of questions you can work with) posted on Learn.
! 
Two parts
◦  A: Set of short answer questions
◦  B: Essay questions
! 
Test time will be extended to 3:15pm for those who’d like a bit more
time.
! 
No material allowed (no books/notes, etc.), just need something to write
with!