Transcript Chapter 2 – Chemical Composition of the Body

Chapter 2 – Chemical
Composition of the Body
“Because living things, including humans,
are composed only of chemicals, it is
absolutely essential for a (physiology)
student to have a basic understanding of
chemistry.”
Sylvia Mader..
• Atoms – smallest unit of an element
that can undergo a chemical change.
• Composed of subatomic particles:
Protons = (+ charge) found in the nucleus
Neutrons = (no charge) found in the
nucleus
Electrons = (e-,- charge) found orbiting the
nucleus in the electron cloud
• The number of protons determines the
atom’s identity, e.g. 6 P = carbon..
• Atomic number = sum of P
• Atomic mass = sum of P and N
• The number of N and/or e- can change.
Isotope = change the number of N
Ion = change the number of e cation = positive ion (how does it become
positive?)
 anion = negative ion
negative?)..
(how does it become
• The position of an atom’s e- is the
electron configuration. We will not study
configurations except for the outermost
level of e- = valence shell
• The e- found there are the valence e-.
• The valence e- are the ones involved in
ordinary chemical reactions..
• Bonding is accomplished by interactions
between two atom’s valence e-.
– If e- are shared between two atoms that
forms a covalent bond.
• Single bonds = one shared pair
• Double bonds = two shared pairs
• Triple bonds = three shared pairs
– If e- are transferred from one atom (ion) to
another that forms an ionic bond.
• Hydrogen bonds are special (polar)
covalent bonds that are very important
to physiology.
Covalent Animation
Ionic Animation..
• Electronegativity is the property that
describes an atom’s attraction for a
shared pair of e-.
• If two atoms with different electronegativity values share e-, i.e. form a
covalent bond, one of the atoms will have
a “larger share” of the e-.
• This produces a molecule with differently
charged ends (poles). This type of
molecule is called polar..
• Bonds formed between the hydrogen
end (+ charged) of a polar molecule
and the – end of any other polar
molecule or highly electronegative atom
(e.g. P, N, O) are called hydrogen
bonds.
• These hydrogen bonds are very
important because they alter the
physical and chemical properties of
many molecules (especially water)..
• Molecules that are formed by polar
covalent bonds have a tendency to
break apart when the electron from the
hydrogen is transferred to the more
electronegative atom. This is called
dissociation or ionization.
• Water ionizes to form equal amounts of
hydroxyl (OH-) and hydrogen (hydronium, H+) ions..
• An acid is a molecule that can release
protons (H+).
–Proton donor.
• A base is a molecule that can combine
with H+ and remove it from solution.
Bases are also defined as releasing OH-.
–Proton acceptor..
• pH = log _1__
[H+]
– [H+] = molar concentration of H+.
– pH inversely related to [H+].
• Because of logarithmic relationship, a
solution with 10 times [H+] of H20 has a
pH = 6; solution with 0.1 the [H+] has a
pH = 8.
• Hydrogen plus hydroxide molar
concentrations will always equal 10-14..
• A buffer is a system of molecules and ions
that act to prevent changes in [H+] and
stabilizes pH of a solution.
• In blood:
* H20 + C02
H2C03
H+ + HC03–Reaction can proceed in either direction
(depending upon the concentration of
molecules and ions)..
• Arterial blood pH remains remarkably
stable at 7.35 – 7.45 because of
buffering systems especially the
bicarbonate/carbonic acid system. HC03and H2C03 act as buffer pair.
• Acidosis = pH < 7.35.
• Alkalosis = pH > 7.45..
Organic Molecules
• Composed primarily of H, C, O, & N.
• Look at the common functional groups.
Carbohydrates
• Organic molecules
that contain carbon,
hydrogen and
oxygen.
– CnH2n0n.
• Monosaccharides =
simple sugars.
– Structural isomers:
• Glucose, fructose,
galactose.
• Disaccharide:
– 2 monosaccharides joined covalently.
• Sucrose (glucose and fructose), lactose (glucose and
galactose), maltose (2 glucose).
• Polysaccharide:
– Numerous monosaccharides joined covalently.
• Starch (thousands of glucose joined), glycogen
(repeating glucose joined that are highly branched)..
• Organic molecules are built by dehydration
synthesis:
C6H12O6 + C6H12O6
C12H22O11 + H2O
• Organic Molecules are broken down by
hydrolysis
C12H22O11 + H2O
C6H12O6 + C6H12O6
Lipids
• Insoluble in water because of nonpolar
molecules
– Triglycerides = 3 fatty acids + glycerol
• Saturated = joined by only single bonds
• Unsaturated = joined by at least one double bond
• Hydrolysis of triglycerides in adipose tissue
releases free fatty acids.
– Free fatty acids can be converted in the liver
to ketone bodies.
– Excess ketone bodies can lower blood pH..
– Phospholipids = phosphate + fatty acid
• phosphate end is polar = hydrophilic
• fatty acid end is nonpolar = hydrophobic
– Steroids = aromatic rings = three 6-carbon
rings joined to a 5-carbon ring
• Steroid hormones are cholesterol derivitaves..
Proteins
• Large molecules composed of long chains
of amino acids.
– 20 different amino acids can be used in
constructing a given protein.
– Each amino acid contains an amino group
(NH2) at one end and carboxyl group (COOH)
at the other end.
• Differences between amino acids are due
to differences in functional groups (“R”).
• Amino acids are joined by peptide bonds..
Protein Structure Levels
• Primary structure is the sequence of the
amino acids in the protein.
• Secondary structure is produced by
weak hydrogen bonds between
hydrogen of one amino acid and the
and oxygen of a different amino acid
nearby.
 a-helix or b-sheet..
• Tertiary structure is formed when
polypeptide chains bend and fold to
produce 3 -dimensional shape.
– Formed and stabilized by weak chemical
bonds between functional groups.
• Each type of protein has its own own
characteristic tertiary structure.
• Quaternary structure is produced when
a number of polypeptide chains
covalently linked together..
Nucleic Acids
• Include DNA and RNA.
• Nucleic acids are composed of
nucleotides to form long polynucleotide
chains.
– Each nucleotide is composed of 3 smaller
units:
• 5-carbon sugar (deoxyribose or ribose).
• Phosphate group attached to one end of sugar.
• Nitrogenous base attached to other end of
sugar..
• The “backbone” of the nucleic acid is
formed by the sugar and phosphate
pairs.
• The “rungs” are formed by paired
nitrogenous bases.
– Nitrogenous bases complementary pair
• A + T (U)
• C + G..