Transcript Cell Chemistry

Cells and Cell Chemistry
Level of Chemical Organization of the Body
• Matter is anything that occupies space and has mass
• In the body, most chemicals are in the form of
molecules. Molecules are particles of matter that are
composed of atoms.
– Elements are pure substances.
– Compounds are substances whose molecules have
more than one element.
• Atoms: the smallest particle of an element that has the
chemical properties of the substance
– Are composed of protons, electrons, and neutrons
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The core of the atom is the nucleus.
• It consists of:
– Protons: + (positive) charge, have mass;
number of protons in the nucleus is the atom’s
atomic number.
– Neutrons: have no charge (neutral particle)
The number of protons and neutrons
combined is the atomic mass of an atom.
• Electrons: - (negative) charge, surround the
nucleus in a circle which is called an orbital.
Have no measurable mass.
• Orbitals are arranged into energy levels
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• The first energy level of an atom can hold 2 electrons
• The second level can hold up to 8 electrons
Electrons have potential energy
• Each orbital further away from the nucleus has a higher
level of energy
-- When an electron moves to an orbital closer to the
nucleus it loses energy
--When an electron moves to an orbital further away
from the nucleus, it gains energy
• In an electrically neutral atom, there is one electron for
every proton.
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• Atoms are chemically stable when the outer
occupied energy level is completely filled
– Atoms react with one another in ways to make
their outermost energy level full. To do this,
atoms can share, donate, or borrow electrons.
– The first shell can hold 2 electrons; the second can
hold 8 electrons; few atoms have a third shell
• These interactions cause the atoms to bind to
each other; this is called a “chemical bond”
• Types of chemical bonds:
– Covalent
– Ionic
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• Covalent Bond
– Formed by the sharing of electrons with
another atom (in order to fill the outermost
shell)
– Sharing of 1 pair of electrons (one electron from
each atom) is a single bond
– Sharing of 2 pairs of electrons is a double
bond
– Because atoms involved in a covalent bond
must stay close to each other, covalent bonds
are strong and normally don’t dissociate
(break apart) in water.
– Example: Hydrogen gas
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• Ionic bond- bond which is formed between an atom that
has 1-2 electrons in its outer energy shell and an atom
that needs only 1-2 electrons to fill its outer level.
– The atom with 1-2 electrons transfers its outer shell
electron(s) to the other atom.
• + charge for each electron lost
• - charge for each electron gained
– An electrically charged atom or molecule is called an
ion. Examples: Na+, Cl– The bond is of moderate strength and dissolves
easily in water (called dissociating).
– Molecules that form ions when dissolved in water are
called electrolytes.
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Compounds
• Compounds are substances whose
molecules have more than one element.
– Organic compounds are composed of
molecules that contain carbon
– Inorganic compounds do not contain carbon
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Life depends on water.
• Water is essential to life.
– It is the most abundant compound in the body
– Water is a solvent (liquid into which solutes
are dissolved)and forms aqueous solutions
in the body
– Water is involved in chemical reactions
within the body.
• Chemical reactions are interactions among
molecules in which atoms group into new
combinations.
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Acids, bases, and salts
 Are compounds that affect chemical reactions in the
body
+
 Water molecules dissociate to form equal amounts of H
(hydrogen ions) and OH– (hydroxide ions)
 Acid—substance that shifts the H+/OH– balance in
favor of H+; opposite of base
+
–
 Base—substance that shifts the H /OH balance
against H+; also known as an alkaline substance;
opposite of acid
 pH—expression of H+ concentration in a solution
 7 is neutral
 pH values above 7 are basic; pH values below 7 are
acidic
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•
•
Neutralization occurs when acids and bases
mix together
Buffers are chemical systems that absorb
excess acids or bases and thus maintain a
relatively stable pH
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Basic Structure and Function of each major
organic compound in the body
• Carbohydrates
• Lipids (fats)
• Proteins
• Nucleic acids
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Carbohydrates—sugars and complex
carbohydrates
 Contain carbon (C), hydrogen (H), oxygen (O)
 Made up of carbon subunits called:
 Monosaccharides or single sugars (e.g., glucose)
 Disaccharide—double sugar made up of two
monosaccharide units (e.g., sucrose, lactose)
--Polysaccharide—complex carbohydrate made
up of many monosaccharide units (e.g., glycogen
made up of many glucose units)
• Function of carbohydrates is to store energy for later
use
--liver and muscle cells form glycogen when there is
an excess of glucose in the blood.
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• Lipids—fats and oils
 Trigylcerides
Made up of one glycerol unit and three fatty
acids
 Store energy for use later

• Phospholipids
---Similar to triglyceride structure, except with only
two fatty acids, and with a phosphorus-containing
group attached to glycerol
---The head attracts water and the double tail does
not, thus forming stable double layers (bilayers) in
water
---Phospholipids form cell membranes
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 Cholesterol – a steroid lipid
 Molecules have a steroid structure made up of
multiple rings
 Cholesterol stabilizes the phospholipid tails in cell
membranes and is converted into steroid
hormones (estrogen, testosterone, cortisone) by
the body
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• Proteins
 Very large molecules made up of amino acids
held together in long folded chains by peptide
bonds
 Structural proteins
 Form structures of the body
 Collagen is a fibrous protein that holds many
tissues together
 Keratin forms tough waterproof fibers in the
outer layer of the skin
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 Functional proteins
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Participate in the body’s chemical processes
Examples: hormones, cell membrane channels and
receptors, enzymes
Enzymes
o
o
Are Catalysts—help chemical reactions occur but remain
unchanged
Lock-and-key—each enzyme fits a particular molecule that
it acts on as a key fits into a lock
– Proteins can combine with other organic molecules to
form glycoproteins or lipoproteins
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• Nucleic acids-DNA (deoxyribonucleic acid) and
RNA (ribonucleic acid)
– Made up of nucleotide units, each consisting of
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•
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Sugar (ribose or deoxyribose)
Phosphate
Nitrogen bases: adenine, thymine or uracil, guanine, cytosine
Nucleotides bind to one another to form strands or similar
structures
– DNA (deoxyribonucleic acid)-double helix
• Used as the cell’s “master code” for assembling proteins
• Uses deoxyribose as the sugar and Adenine, Thymine and
Guanine and Cytosine (no uracil)
• Forms a double helix
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 RNA (ribonucleic acid)
 Used as a temporary “working copy” of a gene
(portion of the DNA code)
 Uses ribose as the sugar and Adenine, Uracil,
Cytosine, and Guanine as bases (no thymine)
 By directing the formation of structural and functional
proteins, nucleic acids ultimately direct structure and
function of the entire body
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